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Passive homesGUIDELINES FOR THE DESIGN AND CONSTRUCTION OF PASSIVE HOUSE DWELLINGS IN IRELAND

Sustainable Energy Ireland (SEI)

Sustainable Energy Ireland was established as Ireland’s national energy agency under the Sustainable Energy Act 2002. SEI’smission is to promote and assist the development of sustainable energy. This encompasses environmentally andeconomically sustainable production, supply and use of energy, in support of Government policy, across all sectors of theeconomy including public bodies, the business sector, local communities and individual consumers. Its remit relates mainlyto improving energy efficiency, advancing the development and competitive deployment of renewable sources of energyand combined heat and power, and reducing the environmental impact of energy production and use, particularly inrespect of greenhouse gas emissions.

SEI is charged with implementing significant aspects of government policy on sustainable energy and the climate changeabatement, including:

• Assisting deployment of superior energy technologies in each sector as required;

• Raising awareness and providing information, advice and publicity on best practice;

• Stimulating research, development and demonstration;

• Stimulating preparation of necessary standards and codes;

• Publishing statistics and projections on sustainable energy and achievement of targets.

It is funded by the Government through the National Development Plan with programmes part financed by the EuropeanUnion.

© Sustainable Energy Ireland, 2007. All rights reserved.

No part of this material may be reproduced, in whole or in part, in any form or by any means, without permission. The material contained in thispublication is presented in good faith, but its application must be considered in the light of individual projects. Sustainable Energy Ireland can not be held

responsible for any effect, loss or expense resulting from the use of material presented in this publication.

Prepared by MosArt Architecture and UCD Energy Research Groupwith contribution from Sharon McManus as part of MEngSc thesis.

Table of Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

SECTION ONE

The‘Passive House’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Passive House and the Passivhaus Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Definition of the Passivhaus Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.2 Technical Definition of the Passivhaus Standard for Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Application of the Passivhaus Standard in the EU and Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 Evolution of the Passivhaus Standard in Europe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.2 Application of the Passivhaus Standard in Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

SECTION TWO

How to Design and Specify a Passive House in Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.1 Building Design Process for a Passive House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 General Principles: Heat Energy Losses & Heat Energy Gains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.1 Passive House Building Envelope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.2 Passive House Building Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.3 Energy Balance Calculations and Passive House Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.3.1 PHPP Software and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.3.2 Passive House Certifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

SECTION THREE

Passive House Prototype for Application in Ireland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.1 Design and Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.1.1 Combining Aesthetic and Energy Performance in House Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.1.2 Decision Support using Passive House Planning Package (PHPP) Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3.1.3 Prototype Passive House External Wall Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.1.4 Prototype Passive House Design including Mechanical and Electrical Services . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.2 Cost Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

i

PrefaceBy Dr Wolfgang Feist, Founder of the Passive House Institute, Germany

Energy Efficient Passive Houses – Reducing the Impact of Global Warming

The February 2007 report of the Inter-Governmental Panel on Climate Change(IPCC) has shown that climate change is already a very serious global issue. Thenegative effects it will have on the ecosystem, the world economy and on livingconditions are anticipated to be on a massive scale.

Climate change is caused largely by human behaviour due mainly to the use offossil fuels as our main source of energy generation. The magnitude of futureclimate changes is closely linked to worldwide CO2 emissions into the earth’satmosphere. The worst effects of global warming, such as a thawing of the entireland-borne ice in Greenland and Antarctica, can still be prevented. However, thisrequires a substantial reduction in worldwide CO2 emissions far below thecurrent level.

There is hardly any doubt that an energy system ready for the future will have tobe sustainable. Sustainable development is economic development that can becontinued in the future without causing significant problems for other people,the environment and future generations.

Passive Housing can play a major role in reducing the impact of global warming.The energy requirement of a passive house is so low that a family will never againneed to worry about energy price hikes. Passive Houses are virtually independentof fossil sources of energy and can be fully supplied with renewable energy if acompact heat pump unit is used in combination with an ecological electricitysupplier. Due to the low energy requirement of passive houses the regionallyavailable renewable energy sources are sufficient to provide a constant supply ofenergy for everyone.

Ireland’s mild climate puts it in a favourable position to introduce Passive Housesto mainstream construction compared to the more severe climates prevalent incentral Europe.

ii

Foreword

Sustainable Energy Ireland is Ireland’s national energy agency, set up to support Irish government energy

policy objectives. Following the introduction of new legislation, most notably the European Community

Directive on the Energy Performance of Buildings and the recent announcement of the intent to regulate

and require the use of renewable energy systems in new buildings, we are seeing the emergence of

extraordinary standards of energy performance for building construction in Ireland, as well as a rapid

increase in the uptake of renewable energy technologies for building services.

Ireland is facing a number of serious challenges includingrising energy costs and meeting our emissions obligationsunder the Kyoto protocol. These and other factors havegiven rise to a fundamental rethink in the way we design,construct and operate buildings. As we move forward, it isbecoming clear that building ‘green’ has evolved and is fastbecoming the preferred choice, providing high quality, highefficiency, dynamic and cost effective solutions forconsumers and businesses. The passive house is theultimate low energy building. The passive house standard isrecognised in Europe as the most advanced in terms ofenergy performance of buildings and going forward theEuropean Commission is set on implementing the passivehouse standard and also on setting more stringentrequirements for the refurbishment of existing buildings.

Today, the passive house offers one of the most desirabletechnological and economical solutions for comfortableliving and working. It can be applied to new and existingbuildings in the commercial, industrial, public andresidential sectors. With close to 10,000 passive houses builtin Europe, this well proven and tested innovative standard isnow attracting significant interest in Ireland with pioneerslike MosArt and Scandinavian Homes leading an emergingmovement in the construction industry.

In response to the need to educate professionals and theirclients on how to design, specify and construct passive

houses and facilitate the further development of thisstandard here in Ireland SEI commissioned ‘Guidelines forthe Design and Construction of Passive House Dwellings inIreland‘. These detailed guidelines for self-builders andarchitects focus on new build houses and cover bothconventional block construction and timber frameconstruction methods. They will ultimately become part ofa suite of guidelines to cover, for example, multipledwellings, non-residential buildings, extensions,renovations etc.

The guidelines cover the rationale and definition of thepassive house standard, how to design and specify a passivehouse along with, construction options, associated services,cost considerations and lifestyle issues. SEI hopes they willbe useful in increasing awareness and understanding of thekey principles and techniques in designing, constructingand operating the ultimate low energy building – thepassive house.

David TaylorCEO Sustainable Energy Ireland

iii

SECTION ONE

The ‘Passive House’

1.1 Passive House and thePassivhaus Standard

A passive house1 is an energy-efficientbuilding with year-round comfort andgood indoor environmental conditionswithout the use of active space heatingor cooling systems. The space heatrequirement is reduced by means ofpassive measures to the point at whichthere is no longer any need for aconventional heating system; the airsupply system essentially suffices todistribute the remaining heatrequirement. A passive house providesvery high level of thermal comfort andprovision of whole-house eventemperature. The concept is based onminimising heat losses and maximisingheat gains, thus enabling the use ofsimple building services. Theappearance of a passive house does notneed to differ from a conventional houseand living in it does not require anylifestyle changes. Passive houses arelight and bright due to large glazedareas designed to optimise solar gains,as well as healthy buildings in which tolive and work due to fresh air supplythrough the ventilation system.

The Passivhaus Standard is aconstruction standard developed by thePassivhaus Institut in Germany(http://www.passiv.de). The Standard canbe met using a variety of designstrategies, construction methods andtechnologies and is applicable to anybuilding type.

This publication outlines therequirements in applying that standardin Ireland and in all cases when referringto a passive house is describing a housebuilt to the requirements of thePassivhaus Standard.

1.1.1 Definition of the PassivhausStandard

The Passivhaus Standard is a specificconstruction standard for buildings withgood comfort conditions during winterand summer, without traditional spaceheating systems and without activecooling. Typically this includesoptimised insulation levels with minimalthermal bridges, very low air-leakagethrough the building, utilisation ofpassive solar and internal gains andgood indoor air quality maintained by amechanical ventilation system withhighly efficient heat recovery.Renewable energy sources are used asmuch as possible to meet the resultingenergy demand (PEP, 2006), includingthat required for the provision ofdomestic hot water (DHW). It should benoted that the primary focus in buildingto the Passivhaus Standard is directedtowards creating a thermally efficientenvelope which makes the optimum useof free heat gains in order to minimisespace heating requirement. While thereare also limitations on the amount ofprimary energy that can be used by adwelling for such uses as DHW, lightingand household appliances, this will notbe the primary focus of these guidelines.That is not intended to imply that suchenergy uses are insignificant, however.In fact, a passive house will have thesame DHW requirements as any typicalhouse in Ireland and given the lowenergy required for space heating theenergy demand for DHW will represent arelatively high proportion of the overallconsumption. In order to address this,some guidance is provided on strategiesto ensure that renewable energies areemployed as much as possible forproduction of DHW.

1

The ‘Passive House’

Passive house in Ghent, Belgium (2004).Source: Passiefhuis Platform vzw.

Passive house in Oberosterreich, Austria (2000).Source: IG Passivhaus Osterreich Innovative Passivhausprojekte.

Interior of passive house in Oberosterreich, Austria(2000). Source: IG Passivhaus Osterreich InnovativePassivhaus projekte.

Structural air-tightness (reduction of airinfiltration) and minimal thermalbridging are essential. A whole-housemechanical heat recovery ventilationsystem (MHRV) is used to supplycontrolled amounts of fresh air to thehouse. The incoming fresh air is pre-heated via a heat exchanger, by theoutgoing warm stale air. If additionalheat is required, a small efficient back-upsystem (using a renewable energysource, for example) can be used toboost the temperature of the fresh airsupplied to the house.

The energy requirement of a house builtto the Passivhaus Standard is:

• Space heating requirement (deliver-ed energy) of 15kWh/(m2year)

treated floor area (TFA), and

• The upper limit for total primaryenergy demand for space and waterheating, ventilation, electricity forfans and pumps, householdappliances, and lighting notexceeding 120kWh/(m2year), regard-less of energy source.

Additionally, the air-leakage test resultsmust not exceed 0.6 air changes perhour using 50Pa overpressurisation andunder-pressurisation testing.

In order to maintain high comfort levelsin any building, heat losses must bereplaced by heat gains. Heat losses occurthrough the building fabric due totransmission through poorly insulatedwalls, floor, ceiling and glazing as well as

2

Air-leakage (or infiltration) is theuncontrolled penetration of outsideair into a building. It takes placethrough openings, primarily throughinadequate and imperfect sealingbetween window frames and walls,between the opening sections of thewindow and along the joints of thebuilding envelope.

Thermal bridging refers to a material,or assembly of materials, in abuilding envelope through whichheat is transferred at a substantiallyhigher rate (due to higher thermalconductivity) than through thesurrounding materials. Junctionsbetween window or door and wall,wall and floor, and wall and roofshould be designed carefully to avoidthermal bridging. A thermal bridgeincreases heat loss through thestructure, and in some extreme casesmay cause surface condensation orinterstitial condensation into theconstruction. Surface mould growthor wood rot may be the consequencesof a thermal bridge.

Measure/Solution Passivhaus Standard for the Prototype House in the Irish Climate

1. Super Insulation Insulation Walls U < 0.175 W/m2K Insulation Roof U < 0.15 W/m2K Insulation Floor U < 0.15 W/m2K Window Frames, Doors U < 0.8 W/m2K Window Glazing U < 0.8 W/m2K Thermal Bridges Linear heat Coefficient Ψ < 0.01 W/mK Structural Air Tightness n50 < 0.6/ air changes per hour 2. Heat Recovery/ Air Quality Ventilation counter flow air to air heat exchanger

Heat Recovery Efficiency > 75%

Minimal Space Heating Post heating ventilation air/ Low temperature heating

Efficient small capacity heating system Biomass, compact unit, gas etc. Air quality through ventilation rate Min 0.4 ac/hr or 30m3/pers/hr Ventilation Supply Ducts Insulated Applicable 3. Domestic Hot Water Biomass, compact unit, gas, heat pump, etc. DHW cylinder and pipes well insulated Applicable Solar thermal system Recommended 4. Passive Solar Gain Window Glazing Solar energy transmittance g > 50% DHW solar heating Area to be dictated by house size and

occupancy Solar Orientation Minimal glazing to north Thermal Mass within Envelope Recommended 5. Electric Efficiency Energy labelled Household appliances A rated appliances Hot water connection to washing machines/ dishwashers

Recommended

Compact Fluorescent Lighting Recommended Regular maintenance ventilation filters Recommended Energy Efficient fans Recommended 6. On-site Renewables Solar thermal system Recommended Biomass system Recommended Photovoltaics Application in a case by case basis Wind Turbine Application in a case by case basis Other including geothermal Application in a case by case basis

Table 1. Technical Definition of the Passivhaus Standard for Ireland.

Passive house in Hannover, Germany (2004).Source: IG Passivhaus Deutschland InnovativePassivhaus projekte.

from uncontrolled cold air infiltrationthrough leaky construction and poorlyfitted windows and doors. In a typicaldwelling, such heat losses have to bebalanced by heat gains mostlycontributed by a space heating system.The internal heat gains from occupantsand other sources such as householdappliances as well as passive solar gainscontribute a relatively small proportionof the total overall need in aconventional dwelling. In a passivehouse, the heat losses are reduced sodramatically (through better insulationand airtight detailing) such that thesame internal gains and passive solargain now contribute a relatively highproportion of the total need. As a resultof this, a smaller space heating system istherefore required compared to that

needed in a conventional dwelling.

A new built semi-detached, two-storeyIrish house built to comply with therequirements of Building RegulationsTechnical Guidance Document (TGD)Part L 2005, Conservation of Fuel andEnergy), uses approx. 75kWh/m2

delivered energy for space heating and159kWh/m2 primary energy. ThePassivhaus Standard requirement forspace heating is 15kWh/(m2year)delivered energy. When compared, thereduction in space heating demandrepresents 80%.

1.1.2 Technical Definition of thePassivhaus Standard for Ireland

In Table 1, a range of U-values arespecified in order to meet the Passivhaus

Standard of space heating requirement(delivered energy) of 15kWh/(m2year) forthe Irish climate. Specifying U-values isdependent upon many variables andcan only be verified through testing theperformance of the dwelling design inthe PHPP software. The U-valuesincluded in Table 1 have been tested forthe prototype passive house presentedlater in Section 3. This prototype house isa semi-detached two storey house ofvery compact form. A detachedbungalow house of sprawling formwould require much lower U-values tomeet the Passivhaus Standard. Due tothe mild Irish climate, it is possible to useU-values for walls in the prototypehouse that are higher than thosetypically recommended by thePassivhaus Institute for colder centralEuropean climates.

A sensitivity analysis was undertakenusing different U-values for theprototype house in order to see, forexample, whether it would be possibleto relax the building fabric requirementse.g. double glazing, in Ireland and stillachieve the Passivhaus Standard. Theresults of this analysis are included inSection 2.

1.2 Applications of thePassivhaus Standard inthe EU and Ireland

1.2.1 Evolution of the PassivhausStandard in Europe

The Passivhaus Standard originated in1988 by Professor Bo Adamson of theUniversity of Lund, Sweden and Dr.Wolfgang Feist of the Institute forHousing and the Environment. Theconcept was developed through anumber of research projects and firsttested on a row of terraced houses by Dr.Wolfgang Feist in 1991 in Darmstadt,Germany. The Passivhaus Institut(http://www.passiv.de) was founded inDarmstadt, Germany in 1996 by Dr.Wolfgang Feist as an independentresearch institution. Since then, it hasbeen at the forefront of the PassiveHouse movement in Germany and hasbeen instrumental in disseminating thestandard throughout Europe andoverseas (more details in Section 2).

3

Comparison of delivered energy in conventional house and in house built to Passivhaus Standard.Source: Passivhaus Institut. http://www.passiv.de.

0

10

20

30

40

50

60

70

80

21

kWh/

m y

Building Regulations 2005(TGD) Part L

Passive House

80% Reduction2

Delivered space heating energy comparison, Building Regulations (TGD) Part L and Passivhaus Standard.Source: UCD Energy Research Group.

Dwellings built to the PassivhausStandard have been constructed all overEurope in recent years but mostespecially in Germany and Austria wherethe Passivhaus Standard was firstapplied.2 Over 10,000 dwellings havebeen built to the standard throughoutEurope, including 4,000 in Germany andAustria, Norway, Sweden, Denmark andBelgium and this number is continuingto grow. CEPHEUS3 (Cost Efficient PassiveHouses as European Standards) was aresearch project (1998–2001) thatassessed and validated the PassivhausStandard on a wider European scale. Theproject was sponsored by the EuropeanUnion as part of the THERMIEProgramme of the EuropeanCommission, Directorate-General ofTransport and Energy. Under CEPHEUS,14 housing developments were built,resulting in a total of 221 homesconstructed to the Passivhaus Standardin five European countries. Anotherproject supported by the EuropeanCommission, Dictorate General forEnergy and Transport is PEP, whichstands for ‘Promotion of EuropeanPassive Houses’ (http://www.europeanpassivehouses.org). PEP is a consortiumof European partners aiming to spreadthe knowledge and experience on thepassive house concept throughout theprofessional building community,beyond the select group of specialists.

1.2.2 Application of PassivhausStandard in Ireland

The Kyoto Protocol came into force in2005 and the proposed targets ofreducing CO2 emissions by 8%compared to 1990 levels by the period2008–2012 became legally binding forEU Member States (UNFCCC, 1997).Ireland’s target under the Kyoto Protocolto limit green house gas emissions to13% above 1990 levels by that periodwas reached in 1997, and it is likely thatthe target will be overshot by up to 37%(74Mt CO2) by 2010 (O’Leary et al, 2006).The EC Green Paper on Energy Efficiency(EC, 2005), states that it is possible forthe EU-25 Member States to achieveenergy savings of 20% by 2010, and seesthe greatest proportion of these savings(32%) coming from the built environ-ment.

In Ireland the residential sector accountsfor 26% of primary energy consumption

and 27% of energy related CO2

emissions (11,376 kt CO2), the secondlargest sector after transport at 32%. Theaverage dwelling emits approximately8.2 tonnes of CO2 emissions, 5 tonnesfrom direct fuel use and 3.2 tonnes fromelectricity use (O’Leary et al, 2006) andIrish dwellings have a higherconsumption of energy, electricity andenergy related CO2 emissions perdwelling compared to the average of theEU-15 (EC, 2005).

The Government White Paper ‘Deliveringa Sustainable Energy Future for Ireland’(DCMNR, 2007) highlighted thatamendment to the Building Regulationsin 2008 would bring a further 40%energy reduction and related CO2

emissions in new build construction. Therecent Programme for Government hasbrought forward that amendment to2007 and committed to a furtheramendment in 2010 to 60% belowcurrent standards.

It is clear that the performance of bothnew build and existing housing stockmust be addressed if we are to achievethe objectives set out both at Europeanand national level. The energyrequirement of a house built toPassivhaus Standard goes beyond theproposed 40% energy reduction andrelated CO2 emissions in new buildconstruction.

A study completed by UCD EnergyResearch Group quantified the potentialreduction for space heating energy andCO2 emissions when the PassivhausStandard for space heating of15kWh/m2year is applied to the Irish newbuild residential construction market(Brophy et al. 2006). Five scenarios ofvarying levels of application wereinvestigated. The tool used in this studywas a computer based model,developed as part of the “Homes for the21st Century” study (Brophy et al. 1999),which profiled the existing nationaldwelling stock by dwelling form,insulation characteristics and heatingsystem types. The model was used topredict the energy consumption andCO2 emissions of dwellings with a typicalfloor area of 100m2, constructed to 2002building regulation standard. Thisprovided national common practiceenergy consumption and CO2 emissionsfigures. It was found that a typical Irish

4

Passive house in Guenzburg, Germany (2006).Source: UCD Energy Research Group.

Passivhaus Eusenstadt, Austria. Source: Construct Ireland Issue 2, Vol 3.

Multy family dwelling, ‘Hohe Strasse’, Hannover,Germany. Source: UCD Energy Research Group.

Kronsberg Passivhaus Complex Hannover, Germany.Source: UCD Energy Research Group.

dwelling consumes 9,722 kWh/year ofdelivered energy on space heating andas a result releases 2,855 kgCO2/yearinto the atmosphere. The space heatingrequirements for the same size ofdwelling built to Passivhaus Standardswas found to be only 1,500 kWh/year ofdelivered energy which equates to 176kgCO2/year. (It was assumed 50:50 splitbetween the use of gas and woodpellets for space heating energy sourceas typically used in passive houses). Thedifference in delivered energyconsumption and carbon dioxideemissions between the two constructiontypes for a single building over one yearwas therefore 8,222 kWh/year and 2,680kgCO2/year. Applying potential energyand CO2 emissions saving rates to the 20year average new build dwellingconstruction rate of 40,000 homes peryear the following results werecalculated. The results showed thatsubstantial savings are achievablethrough the application of thePassivhaus Standard in Ireland (Table 2).

The Passivhaus Standard was firstintroduced in Ireland by the Swedisharchitect Hans Eek at the ‘See the Light’conference organised by SustainableEnergy Ireland (SEI) in June 2002. TomásO’Leary of MosArt Architects, a delegateat the conference, was so enthused byMr Eek’s presentation that he decided onthe spot to sell his townhouse, buy a sitein the countryside in Co. Wicklow andbuild a passive house. The O’Leary familyhas been living in the “Out of the Blue”house since Spring 2005. This house isthe first Irish passive house to becertified by the Passivhaus Institute inGermany, and has been the focus of aresearch, demonstration and energymonitoring project funded bySustainable Energy Ireland. MosArtArchitects, the Passivhaus Institute of DrWolfgang Feist and the UCD EnergyResearch Group are partners in theproject. The project is instrumental inestablishing the basis for thedeployment of the Passivhaus Standardin Ireland in different ways:

• it has provided a learning experiencefor professionals involved in thedesign, specification, constructionand servicing stages

• it will provide a scientific basis forperformance assessment through

5

Percentage (and number) of new dwellings built to Passivhaus

Standard

Potential energy and CO2 emissions savings per

year

Potential energy and CO2

emissions savings in

3.29 GWh 0.691 TWh 1% (400)

1.07 ktCO2 5.02 MtCO2

16.44 GWh 3.453 TWh 5% (2,000)

5.36 ktCO2 25.10 MtCO2

65.78 GWh 13.813 TWh 20% (8,000)

21.44 ktCO2 100.41 MtCO2

164.44 GWh 34.533 TWh 50% (20,000)

53.59 ktCO2 251.03 MtCO2

20 years

Table 2: Potential for space heating energy and carbon dioxide savings.

Building Energy Rating Label. Source: Sustainable Energy Ireland.

The EU Energy Performance of Buildings Directive (EPBD) was transposed into Irishlaw on 4th January 2006. This states that when a building is constructed, rented orsold a Building Energy Rating (BER) certificate and label must be made available toprospective buyers or tenants. The BER is expressed in terms of kWh of primaryenergy/m2/year. A passive house would achieve an A2 rating (UCD Energy ResearchGroup).

monitoring and evaluation

• it is an excellent demonstration tooland has been the focus of manyvisits, presentations and journalarticles.

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References

Brophy, V., Clinch, J.P., Convery, F.J.,Healy, J.D., King, C. and Lewis, J.O., 1999“Homes for the 21st Century - The Costs& Benefits of Comfortable Housing forIreland”. Dublin. Report prepared forEnergy Action Ltd.

Brophy, V., Kondratenko, I., Hernandez,P., Burke, K., 2006 “Potential for Energyand CO2 Emission Savings throughapplication of the Passive houseStandard in Ireland”. Published in thePassive House Conference 2006 pp. 119-124. Hanover, Germany.

European Commission (EC), 2005.“Green Paper on Energy Efficiency”.[Internet] EC. Available at:http://ec.europa.eu/energy/efficiency/index_en.html

European Commission (EC), 2006.

“Promotion of European Passive Houses(PEP)". [Internet] PEP. Available at: http://www.europeanpassivehouses.org/html

Government of Ireland, Department ofCommunications, Energy and NaturalResources (DCMNR), 2007. Government"White Paper Delivering a SustainableEnergy Future for Ireland". [Internet]DCERN. Available at:http://w w w.dcmnr.gov.ie/Energy/Energy+Planning+Division/Energy+White+Paper.html

O’Leary, F., Howley, M., and O’Gallagher,B., 2006. “Energy in Ireland 1990-2004,Trends, issues, forecast and indicators”.Dublin. Sustainable Energy Ireland.

United Nations Framework Conventionon Climate Change (UNFCCC), 1997.The Kyoto Protocal. [Internet]. UNFCCC.Available at: http://unfccc.int/resource/docs/convkp/kpeng.html

1 A passive house is a building, for whichthermal comfort (ISO7730) can beachieved solely by post-heating or post-cooling of the fresh airmass, which isrequired to fulfill sufficient indoor airquality conditions (DIN 1946) - without aneed for recirculated air. Source:http://w w w.passivhaustagung.de/P a s s i v e _ H o u s e _ E / p a s s i v e h o u s e _definition.html

2 See http://www.passiv-on.org/

3 See http://www.passiv.de/07_eng/ news/CEPHEUS_final_short.pdf

Ireland’s first Passive House, Wicklow.Source: MosArt Architecture.

The O’Leary’s embark on their passive house project.Source: MosArt Architecture.

SECTION TWO

How to Design & Specify a Passive House in Ireland

This section introduces the passivehouse building design process as well asexplaining the balance between energylosses and gains. It also provides anoverview of the various building systemsand technologies typically employed ina passive house and presents the PHPPsoftware used for energy balancecalculations. The design andspecification of the example prototypepassive house in the Irish climatedeveloped as part of these guidelineswill be covered in greater detail inSection 3.

2.1 Building Design Processfor a Passive House

Client’s BriefThe design of a passive house willtypically commence with developing abrief with the Client, whether this is afamily wishing to build a single ruraldwelling, a Local Authority progressing ahousing scheme or a commercialdeveloper proposing a mixed residentialproject. The brief would typically outlinethe Client’s practical requirements interms of space functions and densityand also their preferred image orconcept for the building(s). Clientsinterested in building a passive housewill often have carried out aconsiderable amount of research on thesubject and so will already be relativelywell informed regarding the benefits ofliving in a passive house.

Site VisitA site visit is important to (thus reducingthe potential for achieving a glazedsouth facing façade) identify thepresence of structures, landform orevergreen trees which might castshadows on the house during the shortwinter days when the sun is low in the

sky. It may happen that the best viewsfrom the site are to the north suggestingthe placement of large glazing areas onthe northern façade in order to optimisethe best view. All orientation optionsmust be considered by the designer atthis stage - the house must not onlyfunction well in terms of energyefficiency but also in terms of optimisingthe potential of the site and itssurroundings.

Sketch DesignThe next phase of the design process isto develop a sketch design for the house.The basic principles of passive housedesign will greatly inform thedevelopment of the initial design. Anideal approach would be to have thelongest façade of the house facingsouth, a bias of glazing towards thesouthern elevation with reduced glazingarea on the northern elevation and acompact form in order to minimisesurface to volume ratio. Shading devicesmay be required in order to protectagainst the risk of overheating insummer and the aesthetic integration ofthese are essential. In terms of internallayout, it is preferable to organise, wherepossible, family rooms and bedrooms onthe southern elevation with utility roomand circulation spaces on the northernelevation where availability of sunlight isnot so critical.

Initial Evaluation of Energy PerformanceOnce the sketch design has beenapproved by the client, it is important totest the energy balance of the housedesign using the Passive House PlanningPackage (PHPP). The essential elementsof the design are entered into thespreadsheet U-values of walls, floors,roof and glazing as well as orientation,

volume, and size of the house. This willprovide an early indication of whetherthe Passivhaus Standard is beingachieved. If the space heat requirementis significantly above the threshold of15kWh/(m2year) then the building willhave to be modified whether in terms ofimproved U-values, reorganisation ofglazing or adjustment of form. Thedesigner should intuitively know howimprovements can best be achievedwhile broadly remaining true to theagreed sketch design. If the space heatrequirement is significantly less than thethreshold level, then it might be possibleto increase the U-values and thereforesave on insulation costs. Care should betaken to note other performanceindicators calculated by the software,such as frequency of overheating, forexample.

Detailed Design and SpecificationThe design of the house is nextdeveloped to the level of detail requiredto apply for planning permission.Typically this would not require allconstruction details but it is wise toconsider the various technologies at thisstage in order to avoid difficulties lateron. The type of construction will need tobe considered, whether timber frame,concrete, externally insulated masonry,insulated concrete formwork, straw bale,etc as well as the space required forservices such as solar panels, largedomestic hot water tank, mechanicalventilation equipment with supply andexhaust ducting. The specification ofsuch services might be outside theexpertise of the house designer and itmay be required to commission theservices of a Mechanical and ElectricalEngineer. It is also critically important toplan ahead in terms of airtightness and

9

How to Design & Specify a Passive House in Ireland

cold bridging detailing as these oftenrepresent the most challenging aspectsof passive house design. The detaileddesign should be re-tested in the PHPPsoftware to ensure that the PassivhausStandard is achieved. At this stage all therequired data fields have to becompleted as accurately as possible(details of the PHPP tool datasheets isoutlined in section 2.3.1). This mightrequire some minor redesign of theinitial house design. The Client shouldbe kept informed at all times of thedecisions being made by the designteam and have the opportunity tosuggest alterations should the needarise.

Tender Documents and DrawingsOnce planning permission has beengranted, a more detailed set of technicaldrawings will be required in order toenable the construction of the house. Ashighlighted above, the emphasis will beon detailing of junctions betweendifferent elements of the building,practical requirements for minimisingheat loss through cold bridging,planning for airtightness and thelocation and routing of services. Thesizing of the ventilation equipment,back-up space heating, solar domestichot water system, as well as details ofcontrols for space and water heating andventilation, will have to be specified atthis stage. The detailed drawings andspecification can then be issued fortender to competent contractors.

Site OperationsThe detailed design of the passive housemust now be realised on-site and qualitycontrol is paramount to achieving thestandard envisaged in the PHPPsoftware. The most challenging aspectwill typically be achieving the required

level of airtightness, as this is greatlyaffected by the quality of craftsmanshipon site. The challenge becomes all themore difficult if the building contractorhas no prior experience of building tothe Passivhaus Standard. Morechallenging again is the commonpractice of the house built by ‘directlabour’ and without an experiencedsupervisor with overall responsibility toachieve the high standards set.

It will usually be necessary to engagespecialist Sub-Contractors to supply andinstall such elements as the ventilationequipment, solar system, back-upheating systems and controls.

Post Construction TestingThis is the final stage to determinewhether the constructed dwellingactually meets the air-tightnessrequirements of the PassivhausStandard. The air-leakage must notexceed 0.6 air changes per hour using50Pa overpressurisation andunderpressurisation testing. Anindependent inspection and testingbody should conduct the testingactivities. It is important to undertakethis test as soon as the airtight layer iscomplete so that any leaks can berectified. When the house does not meetthe requirements further testing may berequired.

2.2 General Principles: HeatEnergy Losses & HeatEnergy Gains

2.2.1 Passive House BuildingEnvelope

The building envelope consists of allelements of the construction whichseparate the indoor climate from theoutdoor climate. The aim of the passive

10

Roof Loss 30%-35%Flue Loss

Ventilation Loss 25%

Window Loss 15%

Floor Loss 7%-10%

Loss through Walls

25%-30%

Areas of Heat Loss in Homes

Comparison typical building fabric heat loss patternsin a detached dwelling, excluding ventilation andinfiltration. Source: SEI.

Figure depicting 2005 Building Regulation standard required for insulation and required insulation to meet thePassivhaus Standard in Ireland. Source: UCD Energy Research Group.

Thermographic image illustrating difference in heatloss through building envelope in a conventional andpassive house building.Source: UCD Energy Research Group.

0

0.05

0.1

0.15

0.2

0.25

0.3

321

U-v

alue

W/m

K

TGD Part L

Passive House

Walls RoofFloor

2

Thermal transmittance (U-value)relates to a building component orstructure, and is a measure of the rateat which heat passes through thatcomponent or structure when unittemperature difference is maintainedbetween the ambient air temper-atures on each side. It is expressed inunits of Watts per square metre perdegree of air temperature difference(W/m2K).

Source: Building Regulations TechnicalGuidance Document, Part L Conserv-ation of Fuel and Energy 2005.

house is to construct a buildingenvelope that will significantly minimiseheat loss and optimise solar and internalheat gain to reduce the space heatingrequirement to 15KWh/(m2year).

The following building envelopeparameters are fundamental in thisprocess:

1. Well insulated building envelope2. High energy performing windows

and doors3. Minimised heat loss through thermal

bridging 4. Significantly reduced structural air

infiltration 5. Optimal use of passive solar and

internal heat gains

Building Envelope InsulationMany building methods can be used inthe construction of a passive house,including masonry, lightweight frames(timber and steel), prefabricatedelements, insulated concrete formwork,straw bale and combinations of theabove. The prototype house presentedin this publication (details in Section 2and 3) illustrates both masonry andtimber frame construction asrepresentative of most typically usedbuilding methods for dwellings inIreland.

Continuous insulation of the entirethermal envelope of a building is themost effective measure to reduce heatlosses in order to meet the PassivhausStandard.

A thermographic image is used toillustrate the difference between thewell and poorly insulation levels in ahouse. Heat loss through the buildingenvelope is highlighted by the green,yellow and red colouring. The amount ofradiation emitted increases with

temperature, therefore warm objectsstand out well against coolerbackgrounds. In the passive house someheat is lost through windows but heatlost through the external wall is very low.In the conventional building, on theother hand, there is heat loss from theentire building envelope, especiallythrough windows.

Insulation of the building envelope canbe divided into four distinct areas:external wall, floor, roof and windows.Existing passive houses in Central andNorthern European countries have beenachieved with U-values for walls, floorsand roofs ranging from 0.09 to 0.15W/(m2K) and average U-value forwindows (including glazing and windowframes) in the region of 0.60 to 0.80W/(m2K). These U-values far exceedthose currently required under the IrishBuilding Regulations, with the mostmarked difference pertaining towindows, wall and floor.

A sensitivity analysis using the PassiveHouse Planning Package (PHPP), v2004,software was undertaken using a rangeof U-values for the timber frame andmasonry constructions of the prototypehouse using climate data for Dublin. Inall options tested the same data wasinput into PHPP for air-tightness0.6ac/h@50Pa, ventilation andminimised thermal bridging. Variousparameters were tested in order todetermine, for example, the requiredlevel of U-values for the buildingenvelope in the Irish climate, and toascertain whether it would be possibleto use double glazing and still achievethe Passivhaus Standard in Ireland. Theresults are: Option 1 being the mostenergy efficient house and Option 8being the least energy efficient. Anoutline description of each of the eight

11

Irish Building Regulations, ElementalHeat Loss Method (BuildingRegulations Technical GuidanceDocument Part L, Conservation ofFuel and Energy 2005).

Maximum average elemental U-valueW/(m2K)

• Pitched roof, insulation horizontalat ceiling level 0.16

• Pitched roof, insulation on slope0.20

• Flat roof 0.22• Walls 0.27 • Ground Floors 0.25 • Other Exposed Floors 0.25 • Windows and roof lights 2.20

*Regulations due to be updated in 2008

Light filled room in a passive house.Source: MosArt Architecture.

Light, bright and airy.Source: MosArt Architecture.

Windows on the northern elevation should ideally besmall. Source: MosArt Architecture.

Comparison of the interior surface temperature depending on the type of glazing.Source: Internorm, fenster–Lichtund Leben catalogue 2007/2008, pp.91.

options analysed is provided. Only thefirst four achieve the PassivhausStandard set for space heating(delivered energy) of 15 kWh/(m2year)treated floor area:

• Option 1 - U-value 0.10 W(m2K) for allbuilding elements combined withtriple gazed windows with averageU-value (including glazing andwindow frames) of 0.80 W(m2K)results in space heating requirementsignificantly below the standardrequired of 15 kWh/(m2 year).

• Option 2 - (This is the option that hasbeen used in the design of theprototype passive house in Ireland aspart of these Guidelines), with U-value 0.15 W(m2K) for all buildingenvelope elements combined withtriple glazing. The results show spaceheating requirement below thePassivhaus Standard.

• Option 3 - All building envelopeelements with U-value of 0.10W(m2K) combined with an efficientdouble glazed unit with low U-value1.1 W/(m2K) achieves the PassivhausStandard.

• Option 4 - U-value 0.175 W(m2K) forexternal walls and U-value 0.15

W(m2K) for all other buildingenvelope elements, coupled withtriple glazed windows. The result isexactly at the threshold of thePassivhaus Standard but was notused for the prototype house as thereis no margin in site operations.

• Option 5 - U-values for walls, roofand floor employed in the IrishBuilding Regulations, Elemental HeatLoss Method (Building RegulationsTGD Part L, Conservation of Fuel andEnergy 2005) combined with tripleglazed windows, failing to achievethe required standard.

• Option 6 - also a failure is thecombination of U-value 0.10W(m2K)for building fabric in combinationwith standard double glazed units.

• Option 7 - U-values 0.15 W(m2K) forwalls, roof and floor as the prototypehouse but with standard doubleglazing U-value 2.20 W(m2K) whichcomes way above the PassivhausStandard.

• Option 8 - U-values for walls, roofand floor employed in the IrishBuilding Regulations, Elemental HeatLoss Method (Building RegulationsTDG Part L, Conservation of Fuel andEnergy 2005) and standard doubleglazed units underachieving thePassivhaus Standard.

Thermal ConductivityThermal conductivity ( -value) relates toa material or substance, and is a measureof the rate at which heat passes througha uniform slab of unit thickness of thatmaterial or substance, when unittemperature difference is maintainedbetween its faces. It is expressed in unitsof Watts per metre per degree (W/mK),(Building Regulations TechnicalGuidance Document Part L,Conservation of Fuel and Energy 2005).Insulation materials for walls, roofs andfloors vary in terms of thermalconductivity. Typical conductivities fordifferent insulation materials areincluded below as well as theapproximate thickness required in orderto achieve a U-value of 0.15 W(m2K) and0.10W(m2K). (Table 4)

Typical insulation materials used inIreland include mineral wool,polystyrene, polyurethane, polyiso-cyanurate, sheep wool and hemp.Different insulation materials suitdifferent types of construction

12

Note: Advantages and disadvantagesof using triple glazed windows arediscussed in detail in section ‘Windows& Doors’)

Note: Results presented here areindicative only and should be used asstarting point for specification of apassive house dwelling in Ireland.Meeting the Passivhaus Standard mustbe tested and verified with the PHPPsoftware for the specific dwellingdesign.

Option

U-Values of ext. wall

U-Values of roof

U-Values of

floor

AverageU-Value of

windows and doors

Space heating requirement

1 0.10 W(m2K) 0.10 W(m2K) 0.10 W(m2K) 0.80 W(m2K) 8 kWh/( m2a)








Table 3: Sensitivity analysis of the passive house prototype house in Ireland outline test results for eight options. Source: MosArt Architecture.

application and it is important to use thematerial best suited for the situation. Forexample, cellulose insulation is suitablefor use in an open attic space where itwill fill completely between ceiling joistsin comparison with rigid insulationwhere there is a high risk of thermalbridging unless cut perfectly to fitsnuggly between the joists. Conversely,a high density rigid insulation is bettersuited under a floor slab compared withinsulation that easily compress or areaffected by moisture.

The U-value of the construction isdetermined by the conductivity ofmaterials and components used fromthe internal surface to the externalsurface of the thermal envelope.Examples of typical constructionmethods and materials used for theprototype passive house in Ireland areillustrated later in Section 3.

Windows & DoorsThe recommended approach to thedesign of a passive house is to haveavoid excessive area of north facingglazing and place relatively largewindows facing south or due south. Thisis in order to minimise heat lossesthrough the north facing elevation,which receives no direct sunlight, whilemaximising ‘free’ solar heat gains on thesouth. An advantage of large windows isan increase in interior day light levelswhich in turn reduces the need for use ofelectricity for artificial lighting and alsoensures a more pleasant natural light-filled living environment.

There is, however, a balance to beachieved between heat losses throughthe glazing and solar heat gains throughthe south/east/west facing windows.When designing a passive house, PHPPsoftware should be used to calculate theheat losses and heat gains taking intoaccount building orientation, areas ofglazing and specific types of glazing so

the optimum balance of glazing for eachpassive house design can be reached.

It has been illustrated above that the useof windows and doors with average U-values of 0.8 W/(m²K) can be combinedwith U-values for opaque elements of0.15 W/(m²K) to comfortably achieve thePassivhaus Standard in Ireland. There area number of advantages in usingwindows with average U-values of 0.8W/(m²K) as well as highly insulateddoors, principally the assurance of acomfortable indoor climate due to thelower cold radiation heat transfer at thesurface of the glass. One will not sense adrop in temperature standingimmediately adjacent to this standard ofwindow, unlike the experience ofstanding next to a conventional doubleglazed unit with U-value, for example of2.2 W/(m2K). An added benefit of usinghighly energy efficient windows anddoors includes significant draughtreduction due to the fact that they havetypically two seals or gaskets (comparedwith conventional double glazed unitswhich often have only one) as well asexcellent sound insulation. Finally,natural convection which is driven bytemperature difference between theinside face of the glass and the roominterior is much reduced with which inturn will reduce cold air flows andthermal discomfort.

The sensitivity analysis for a passivehouse dwelling in Ireland (showed inOption 3), achieves the PassivhausStandard yearly space heatingrequirement with extremely efficientdouble glazed windows with a U-valueno greater than 1.1 W/(m²K). When usedin a passive house, however, they mustbe used in conjunction with very low U-values for all other elements of thebuilding envelope. This may negate anyfinancial saving in not using moreefficient glazing as well as compromise

the thermal comfort level in the house.

Typically triple glazed window units areused in passive houses in Central andNorthern Europe. The Passivhaus Instituthas certified a range of glazing and doorunits suitable for use in passive housebuildings. Although it is not aprerequisite to use certified passivehouse products (http://www.passiv.de) ina passive house, choosing approvedproducts means the validity of technicaldata has been tested and verified by anindependent certifier. The principlecharacteristics and advantages of usingtriple glazed windows in a passive houseare listed below, for both windowglazing and frames:

Glazing• Three panes of glass separated by

special low-conductivity spacerseliminates the risk of condensation atthe bottom of the glass in coldweather (which may lead to rottingof timber frames over time).

• High solar energy transmittance (g50) which allows solar radiation to

penetrate the glass and contributetowards heating of the dwelling.

• A low emissivity (low-e) coating onthe inside of the outer two paneswhich reduces solar re-radiation backout through the glass. It should benoted that a ‘soft coat’ has slightlybetter U-value but a ‘hard coat’glazing has higher solar trans-mittances.

• Insulating gases between the glasspanes, typically argon or krypton,which help to reduce heat escapingthrough the glass.

Frame• The frame must be well insulated and

also be thermally broken. Even woodconducts heat and a thermallybroken timber window frame willresult in much lower heat losses thana solid one.

• There will typically be two weathergaskets on triple glazed windowsused in a passive house dwelling, theprimary function of the outer onebeing for weathering with the innerone serving to improve airtightness.The majority of these types ofwindows open outwards which iscommon place in Continental Europe

13

Insulation Material Type

Thermal conductivity W/mK

Thickness for U-Value of 0.15

W(m2K)

Thickness for U-Value of 0.10

W(m2K)

Polyisocyuranate or polyurethane 0.023 145mm 220mm

Polystyrene, sheep wool 0.035 220mm 340mm

Cellulose, Hemp and Rockwool

0.04 250mm 400mm

Wood 0.13 825mm 1,250mm

Table 4: Conductivity of insulation materials and approximate thickness to achieve specific U-value for externalwalls. Source: MosArt Architecture.

however, there are models of inwardopening windows being developedwhich will soon be available in theIrish market. One advantage ofoutward opening windows is thatthey don’t intrude in the room spacewhich may be important in morecompact dwellings.

• Triple glazing window frames aretypically much wider and strongerconstruction than their conventionaldouble glazing counterparts.

• Triple glazed windows with low-emissivity coating and insulatedwindow frames will have improvedU-values compared to double glazedwindows, resulting in less heat loss.However with triple glazing the solarenergy transmittance (gs), that is, theamount of solar energy enteringthrough that glazing, is somewhatreduced compared to double glazingdue to the effect of the additionallayer of glass. The requirements ofthe Passivhaus Standard is to useglazing with minimum solartransmittance of 50% or higher.

The use of larger areas of glazing on thesouth elevation is helpful in maximisingthe amount of sunlight available in theshort days of winter. It must beremembered, however, that highlyenergy efficient windows allow lessdaylight (visible light transmittance) intoa building than a normal double glazedwindows without e-coating. Lighttransmittance is an optical property thatindicates the amount of visible lightbeing transmitted through the glazing.It varies between 0 and 1 (0 to 100%light transmitted) with the higher thelight transmittance value the more lightis transmitted. A double glazed windowwith low-e coating will transmit 72% ofvisible light. A triple glazed energyefficient window will transmit 65% ofvisible transmittance (these areindicative values only - actual valuesdepend on the manufacturer’s specific-ation).

In a conventionally constructed house inIreland radiators are typically positionedunder windows in order to heat the coldair entering through the single ordouble glazing. In a passive houselocating radiators beneath windows issimply not required as the heat load is

transferred throughout the house viathe mechanical ventilation system. Thishas the added benefit of enablingunobstructed use for placing furnitureagainst all external walls.

Thermal BridgingThermal bridging (i.e. un-insulated jointsbetween walls, floors/walls, ceilings/adjacent walls, windows/walls etc) areweak points of the building envelopeand cause unwanted losses of energywhich should be eliminated orsignificantly reduced to a degree thatthe associated heat losses becomenegligible.

A thermal bridge increases heat lossthrough the structure, and in someextreme cases this may cause surfacecondensation or interstitial conden-sation in the structure. Surface mouldgrowth or wood rot may be theconsequences of a thermal bridge.Typical effects of thermal bridges are:

• Significantly increased heat losses.

• Decreased interior surface temper-ature which may result in highhumidity in parts of the construction.

• Mould growth cause by warminternal air condensing on coldsurfaces.

All of the above situations can beavoided in houses built to thePassivhaus Standard. The PassivhausStandard for linear thermal trans-mittance (ψ) should not exceed 0.01W/(mK). This requires the buildingdesigner to identify and locate allpotential thermal bridging in theconstruction, careful specification anddetailing of those elements providingwhere possible a continous layer ofinsulation, as well as care being taken toexecute those elements on site as perdesign details.

Designing and building a passive housein Ireland requires the development ofconstruction details that go far beyondguidance provided (to avoid excessiveheat losses and local condensation) inBuilding Regulations Technical GuidanceDocument Part L, Conservation of Fueland Energy 2005. Building practitionerscould refer to the accredited con-struction details specifically developedfor passive house building published inGermany “Thermal Bridge-Free Con-struction” (PHPP 2007, pp.96). Thermal

14

Cross section though a triple glazed insulated windowand frame. Source: MosArt Architecture.

The risk of internal condensation is dramaticallyreduced. Source: MosArt Architecture.

The quantity which describes the heatloss associated with a thermal bridge isits’ linear thermal transmittance (ψ).This is a property of a thermal bridgeand is the rate of heat flow per degreeper unit length of bridge that is notaccounted for in the U-values of theplane building elements containingthe thermal bridge.

Source: SEI, Dwelling Energy Assess-ment Procedure (DEAP) 2005 edition,version 2, pp.55

bridging can be tested and verified inthe PHPP software as the design of thepassive house building is beingdeveloped.

Structural Air-Tightness and Draught-Proofing Building an airtight or leak-free structureis imperative to achieving the PassivhausStandard. If there are gaps in thebuilding structure then uncontrolledamounts of cold external air caninfiltrate the building. Achieving a highlevel of air-tightness eliminates colddraughts and associated comfort losses.It also prevents condensation of indoormoist, warm air penetrating thestructure, and possible structuraldamages due to decay, corrosion andfrost.

Air-tightness is achieved by carefulapplication of appropriate membranesand tapes or wet plastering in concreteconstruction within the buildingenvelope. A great deal of attention mustbe paid to detailing and workmanship inorder to ensure that the airtight layer iscontinuous all round the building,especially around junctions betweenwalls and floors, roof, windows, doors,etc. Penetrations of the airtight layer bymechanical and electrical services mustbe properly sealed.

The air-tightness of a building can beaccurately measured by carrying out ablower-door test. The test involvesplacing a powerful fan suspended in acanvas sheet within a door opening andoperating the fan at very high speedsthereby creating either negative orpositive pressure within the house. Bysucking air out of the house, forexample, a negative pressure is createdwith the result that external air will besucked in through any gaps or cracks inthe building envelope. The pressureused for such tests is 50 Pascal which canbe accurately set by the blower doorequipment.

When undertaking the test it is usuallyquite easy to identify major leaks due tothe presence of a strong draught whichcan be felt by the hand or, for smallerleaks, can be detected by athermographic camera. The cause ofthese draughts can then be sealed withappropriate materials as the test is beingundertaken. It may also happen that the

leaks in the envelope are very minor andtherefore difficult to locate. In thesesituations it is typical to reverse thedirection of the fan and suck air into thehouse putting it under positive pressure.Odorless smoke can then be releasedinto the building and leaks can beobserved from the outside where thesmoke appears through the envelope. Itis important to notify the fire service ifyou are carrying out such a test in case itis mistakenly reported as a house fire bypassers by.

The Passivhaus Standard is reachedwhen there are less than or equal to 0.6air changes per hour @50Pa pressure.

The most critical issue regarding testingfor airtightness is timing during thebuilding process. It is important thatremedial measures can be carried out inorder to remedy any leaks or cracks. Thetest should be carried out before secondfix carpentry, for example, when thereare no skirting boards or window boardsfitted and where the junctions coveredby such materials are still accessible andcan be sealed. The test should also becarried out after all mechanical andelectrical services, that need topenetrate the building envelope, havebeen installed. Otherwise, installingsuch services after the test couldseverely compromise the airtightness ofthe building.

In a typical Irish house built inaccordance with building regulationsTGD Part F 2002 the method in whichhabitable rooms are ventilated is usuallyvia a hole in the wall or ventilator in thewindows of 6,500mm2 fitted with acontrollable grille. Such means ofventilation can result in large amounts ofcool external air infiltrating the buildingdepending on wind speed and pressure.In a passive house, on the other hand,the supply of fresh air is provided by awhole house mechanical ventilationsystem with heat recovery whichnegates the necessity for openings inthe wall or windows. Thereby draughtsare eliminated and structural air-tightness is not compromised.

In developing the building design it isvery important to anticipate differentialmovement and decay of adhesives andchemical bonds by detailing junctionswhich will assist in maintaining an

15

Infrared image of the interior of a passive housewindow. All surfaces (wall structure, window frame,and the glazing) are pleasantly warm (over 17°C). Evenat the glass edge, the temperature does not fall below15°C (light green area).Source: Passivhaus Institut, http://www.passiv.de fromthe passive house Kranichstein).

For comparison, a typical older double glazed windowis shown. The centre of glass surface temperature isbelow 14°C. In addition, there are large thermalbridges, particularly where the window meets theexternal wall. The consequences are significant radianttemperature asymmetry, drafts, and pooling of cold airin the room. IR-photography: Passivhaus Institut.Source: Passivhaus Institut, http://www.passiv.de fromthe passive house Kranichstein).

Timber Frame I-Beam construction reducing thermalbridging. Source: Passivhaus Institut, Germany.

airtight layer for the life of the building.Many excellent details, for example, canbe found at the website of the ScottishEcological Design Association(www.seda2.org/dfa/index.htm). It is alsoimportant to use membranes andplasters that are both airtight but alsovapour diffusing which allow moisturewithin the structure to escape to theoutside thereby reducing the risk ofinterstitial moisture and the threat of rotand decay over time.

Passive Heat GainsPassive heat gains in a passive house area result of the combination of solar gainsand internal gains.

Solar Heat GainsPassive solar gain is optimised byproviding an east-west alignment to thebuilding, if possible on the site, resultingin the longest façade facing south, andby placing the majority of the glazingtowards the south. Very high qualitywindows (average U-value 0.8W/m2K)facing south will have a positive thermalbalance - it will have more heat gainthan heat loss throughout the year.Results of a recent parametric study by J.Schnieders of the Passivhaus Institut“Climate Data for Determination ofPassive House Heat Loads in NorthwestEurope” illustrates the relationshipbetween the area of south facing glazingand the space heat demand for a passivehouse dwelling located in Ireland(measured climate data for Birr used).The parametric study uses the firstpassive house built by Dr. Wolfgang Feistof the Passivhaus Institut as a case studybuilding, shown below. It can be seenthat the space heating demand initiallydecreases quite steeply with increasingsouth facing glazing. There arediminishing returns from increasing thearea of south facing glass, however, andthere eventually comes a point wherethere is little or no benefit in providingmore south facing glass as the net heatloss is greater than the heat gains overthe year.

There is no optimal ratio of glazing tofloor area that can be used as a rule ofthumb in deciding what proportion of agiven façade should be glazed. The areaof glass has to be determined as part ofthe design verification procedure usingthe PHPP software.

Internal Heat GainsA passive house is very efficient atutilising ‘free’ internal heat gains fromdomestic household appliances, kitchenand utility equipment, electronicequipment, artificial lighting, andoccupants. Heat losses from stoves orboilers also contribute towards theoverall space heating requirement aslong as they are positioned within thebuilding envelope. Occupants of thebuilding also contribute to the heat load- a human continuously emits 100W ofheat when stationary. A family of fivepersons, therefore, can emit 0.5KW ofheat. This may seem like a small amountbut it equates to approximately onethird of the total space heat load for theprototype passive house presented inSection 3.

Risk of OverheatingPlacing extensive areas of glass on thesouth facing façade in a well insulatedand air-tight dwelling may lead tooverheating in warm sunny days. ThePHPP software will alert the designer toany risk of overheating by calculatingthe frequency of overheating expressingthis as a percentage of the year in whichthe internal temperature in the houserises above 25oC. If frequency oftemperatures over the comfort limit of25oC exceeds 10% of the year, additionalmeasures for reducing overheatingshould be included in the dwelling. Toprevent uncomfortable indoortemperature in a passive house dwellingit is recommended to specify shadingdevices (blinds, overhangs or awnings,etc.) which allow low sun to enter thehome in winter but prevent the high sunentering in summer.

In the first Irish passive house in Wicklowshading was not in place on the southfacing glazing during the first summerand the house did overheat. A balconywas installed ahead of the secondsummer, which significantly reduced thefrequency of overheating. In mid-summer when the daylight hours arelong the sun only enters the buildinglater in the day while during winterwhen the daylight hours are short thelow sun completely illuminates theentire interior of the building.

In the temperate climate in Irelandwhere external temperature rarelyexceeds 25oC, the risk of overheating

16

Correctly insulated house avoiding thermal brid.Source: Passivhaus Institut, Germany.

Timber frame house pre-cladding fitted airtightmembrane. Source: Passivhaus Institut, Germany.

Continuous Airtight Membrane. Source: IG Passivhaus Osterreich Innovative Passivhausprojekte.

There are two measurements used todefine airtightness, namely cubicmetres of air per square metre ofexternal envelope per hour (m3/m2h) orair changes per hour (ac/h). While themeasured result for the former isgenerally 20% greater than that of thelatter, the difference is practice greatlydepends on the building form.

should be avoided by carefulconsideration of shading devices,provision of openings for naturalventilation in combination with thermalmass inside the dwelling (exposedconcrete floor; masonry wall, etc.). Insome cases the mechanical ventilationsystem could be used to distribute freshair throughout the building by switchingto a ‘summer bypass’ setting. Thishowever should be avoided wherepossible as the ventilation system willconsume electricity resulting inincreased primary energy. The dwellingdesigner should employ ‘passive’ coolingstrategies to minimise overheating.

2.2.2 Passive House BuildingSystems

As explained earlier a passive housedoes not need a conventional spaceheating system of radiators orunderfloor heating to maintain acomfortable indoor climate. Instead,typically, the following building servicesare required in a passive house:

• Mechanical ventilation system withheat recovery which provides most ofthe space heat requirement.

• Back-up system capable of heatingthe air passing through the dwellingvia mechanical ventilation. Typicalfuel sources for the back-up systeminclude biomass, gas, and in someinstances electricity (for example‘green electricity’ from renewablesources). Since the demand for spaceheating in a passive house dwelling isvery low, the back-up system is usedto provide hot water, either

throughout the year or during winterif a solar water heating system is usedduring summer.

Each of these items is dealt withseparately in greater detail below.

Given the lengths to which the designerand builder go to in terms of ensuring ahighly insulated building envelope,excellent air-tightness and minimalthermal bridging, it is important that thebuilding services in a passive house areas energy efficient as possible. This isespecially critical in the case of themechanical ventilation heat recoverysystem. Therefore, the requiredefficiency of the mechanical ventilationsystem with heat recovery for a passivehouse dwelling is 75%. It is also veryimportant to consider comfort, healthand safety issues in the design of thebuilding services for a passive house,ensuring for example that the back-upheating system is adequately sized todeal with extreme weather conditions;that filters in the ventilation equipmentare replaced regularly and that there is afresh air supply for any combustiondevices such as a boiler. These and otherissues are dealt with in greater detailbelow.

Mechanical Heat Recovery Ventilation(MHRV)An airtight house requires a well-designed mechanical ventilation systemto provide good indoor air quality. Apassive house is ventilated using amechanical system which incorporatesair to air heat recovery (mechanicalventilation heat recovery, or MVHR).

17

Climate Data for the Determination of Passive House Heat Loads in Northwest Europe.Source: J. Schnieders, Passivhaus Institut.

No more than 0.6 air changes/hour at 50 Pascalpressure should be observed in accordance with thePassivhaus Standard. This should be checked forcompliance with a blowerdoor test which willimmediately highlight leaky areas. Air-tightness can beachieved through the use of membranes, roofing feltsand plasters combined with sealants and vapourdiffusing resistant materials.Source: UCD Energy Research Group.

Location of overhang and balcony. Source: MosArt Architecture.

Lighting contributes towards internal heat gains.Source: MosArt Architecture.

02468

1012141618202224

0 10 20 30 40 50 60

Area South Facing Windows [m2]

Spac

e H

eat D

eman

d / H

eat L

oad

Space Heat Demand [kWh/(m2a)]

Heat Load [W/m2]

Ireland - Birr

U-Value Wall = 0.175 W/(m2K)U-Value Window = 0.85 W/(m2K)

Deep roof overhang shadesupstairs windows

Balcony shades downstairs windows

Exhaust air is extracted from rooms thattypically produce heat, moisture andunwanted smells such as kitchens andbathrooms. Before this air is expelled tothe outside it passes through a heatexchanger where the heat is transferredto the incoming fresh air, therebyeliminating the need to completely heatthe fresh air as it enters the building. It isimportant to highlight that the staleexhaust air and clean fresh air do not mixin the heat exchanger and thereforethere is no risk whatsoever of whatmight be referred to as ‘sick buildingsyndrome’. Rather, the stale air and cleanair is channelled through closely spacedbut separate narrow sleeves in the coreof the heat exchanger.

The benefits of having a whole-housemechanical heat recovery ventilationsystem (MHRV) are many, including:

• Constant supply of the correctamount of fresh air to all habitablerooms thereby reducing CO2 levelsand removing the cause of stuffinessand tiredness.

• Simultaneous extraction of moisture-laden air from bathrooms, utilityrooms and kitchens as well asventilating noxious gases andunwanted smells if present.

• A lowering in humidity levelsreducing mould and fungus that mayappear over time and decreasingdust mite levels.

System EfficiencyThe efficiency of the heat exchanger inthe MHRV determines the amount ofheat that can be recovered from theexhaust air and, therefore, has a verysignificant influence on the additional

space heating that may be required in apassive house. The aim is to use thewarm exhaust air to raise the temper-ature of the cool fresh air to provide forthermal comfort all around the house.On a night where outside temperaturesare below freezing, the fresh air shouldbe raised to, for example, 18oC, havingpassed through the MVHR. Theefficiency of sensible heat recoveryshould exceed 75% for the nominalrange of flow rates specified for the unitwhen measured in terms of the supply-air side temperature ratio as described inEN 13141-7:2004.1 Specifiers anddesigners should be wary of productsclaiming extraordinary efficiency rates of95% or higher. The safest route is toinstall equipment that has beenindependently tested and verified bysuch bodies as the Passivhaus Institute.

The graph above is based on actualtesting of the first Irish passive house inWicklow. It illustrates, for example, howmechanical ventilation ensures goodindoor air quality by removing the highconcentrations of a tracer gas that wasdeliberately released into the house aspart of the test procedure. In less than1.5 hours the air quality in the house hadreturned to normal.

Recommended Ventilation RateAccording to the Passivhaus Institut, theappropriate air change rate for dwellingsis between 0.3 and 0.4 times the volumeof the building per hour, with a generalrecommendation of leaning toward thelower rate. This maintains high indoor airquality while ensuring a comfortablelevel of humidity and maximizingenergy savings.

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Photo depicting how the low winter sun enters theroom below the overhang/awning/balcony. Source: MosArt Architecture.

Schematic of the supply air ducts, the extract air ductsand the heat exchanger within mechanicallyventilated house. Source: Passivhaus Institut.

The sommer-bypass can be used for cooling in thesummer if needed. Source: MosArt Architecture.

Photo depicting how the house is shaded from the highsummer sun by the overhang/awning/balcony.Source: MosArt Architecture.

Graph depicting how mechanical ventilation ensures a good indoor air quality by removing the high concentrationsof tracer gas that were inserted into the house under test conditions. Source: UCD Energy Research Group.

IR C

once

ntra

tion

Hours

The PHPP software suggests that 30m3

per person per hour should be providedto dwellings to ensure good air quality.These two measurements can be used tochoose an appropriately sized machinefor different dwelling designs. Taking theprototype house presented later inSection 3 as an example, an occupancyof 5 persons would require 150m3 offresh air delivered to the house per hour.In terms of extract, the PHPP softwareuses the following rates for differentroom types as default values, kitchen =60m3h, bathroom = 40m3h, shower =20m3h and WC = 20m3h. In the prototypehouse these total 140 m3h which is closeto the supply volume which will ensurethat the whole house system will bebalanced. The supply and extractvolumes can be accurately set by using adigital anemometer and adjusting thevalves on the vents in each room asrequired.

Adjustment of Fan Speed and ExchangeRateMost MVHR machines have differentsettings for different circumstances.These are often referred to as a ‘party’setting, where there are a lot of peoplein the house and where additional freshair is required, and ‘holiday’ setting,where the house is being left vacant andthe flow of air is reduced. The former ofthese settings will use more energy andalso decrease the level of humiditywhereas the latter will use less energyand perhaps lead to an increase inhumidity.

It is not advisable to constantly run theequipment on the lower setting just tosave energy when the house isoccupied. MHRV machines usessurprisingly little energy given theimportant role that they play in thepassive house. The PHPP software usesstandard value 0.45Wh for every m3

transported air software in thecalculation of electricity due to MHRV.When designing a passive house inIreland the specific fan power should becarefully considered as the electricityconsumed for fans has direct impact interms of primary energy performanceand energy labelling, the BuildingEnergy Rating (BER), recently introducedto Ireland. Therefore, specific fan powerfor fans should be less than 1w/l/s.

Winter and Summer ModeThere are generally two ventilationmodes in a passive house: SummerMode and Winter Mode. In winter, theMHRV uses the heat in the exhausted airto warm the incoming fresh air. Insummer, a bypass in the equipment canbe set to open automatically (controlledby thermostats) such that the incomingfresh air is not heated. Alternatively insummer natural cross ventilation may beused and the MHRV system can beswitched off.

Insulation and Positioning of Duct Workand VentsIit is very important to adequatelyinsulate the supply air ducting so thatthere is minimal loss of temperature indelivering warm air around the house.The thickness of insulation generallyused in passive houses is between 6cmand 10cm for ductwork. It is alsopreferable to locate the ducting withinthe thermal envelope and to keep piperuns as short as possible by ideallypositioning the MVHR unit in the centreof the house. This requires carefulplanning at a very early stage of buildingdesign.

Vents are normally placed in the ceilingbut can also be placed in the wall ifnecessary. The air inlets are typicallydesigned to spread the air horizontallyacross the ceiling, minimizing down-ward drafts. There should be a gap eitherunder or over the door of each room toenable the easy movement of air fromone room to the next. If doors are fittedtight without such a gap, rooms withexhaust vents would be under negativepressure and rooms with supply airunder positive pressure.

Noise Fan and valve noises can be almostcompletely eliminated by sound controlmeasures (e.g. vibration isolationmounts, low air speed and acousticlining in ducts). The grilles on ventsgenerally guide incoming air along theceiling from where it uniformly diffusesthroughout the room at velocities thatare barely perceptible. If the ventilationequipment is operating on a highsetting (‘Party Mode’) the noise of theequipment and the air flow may be morenoticeable. MVHR machines aregenerally housed in a well insulated

19

A pellet stove is at the hearth of an Irish passive house.Source: MosArt Architecture.

The ventilation system can be used in a sealed closet todry clothes. Source: MosArt Architecture.

Supply air ducts should be well insulated.Source: MosArt Architecture.

Ceiling air supply vent. Source: MosArt Architecture.

casing and noise should not be a criticalissue.

Maintaining Good Air QualityIt is important that attention is paid toregular replacement of air-filters for bothincoming and exhaust air. Filters areused not only to provide clean air for theoccupants but also to ensure that theheat exchanger is not clogged with dustand other matter. If the filters are notregularly replaced (for example every sixto twelve months) and they themselvesbecome clogged with dirt the MHRV willhave to work harder to provide the samevolume of air to the house, therebyincreasing the speeds of the fans and,ultimately, using more energy. Incountries where this system is relativelynew, occupants may not be aware of thismaintenance need and indoor air qualitymay suffer as a consequence. Equipmentdiffers with respect to the types of filtersused, some have to be replaced whileothers can be washed and reused.

Sometimes the extractor hood in thekitchen is connected to the MHRVequipment to extract kitchen smells andto use the waste heat from cooking towarm the incoming fresh air. In suchinstances, it is very important that thehood is fitted with a high quality filterthat can easily be cleaned or replaced inorder to prevent the built up of grease inthe ducting system which could be a firehazard.

What happens in the event of a powerfailure?If there is a loss of electricity (and thedwelling has no back-up generator) theventilation system will stop working andthe supply of fresh air will be cut off. Ifpower is lost for a short while (forexample a few hours), then there is likelyto be no noticeable difference in indoorair quality. If the loss of power isprolonged, the simple solution is toopen the windows and to create naturalcross flow ventilation through thebuilding.

Back-up Heating SystemAs previously highlighted in theseguidelines, space heating requirementin a passive house is so low that there isno need for a traditional space heatingsystem. The optimal way to transfer thesmall amount of required heat through-out the house is through the mechanical

ventilation system. This section of theguidelines will provide an overview ofthe typical back-up heating systemsused in passive houses to providethermal comfort .

Space heating demand in a passivehouse is typically met through passivesolar gains (40–60%), internal heat gains(20–30%) and the remainder (10–40%)needs to be provided from buildingsystems.

The PHPP software will accuratelypredict the following two measure-ments for each passive house design:

• Annual Space Heat Requirement -this measures the amount of energythat is needed to maintain acomfortable indoor temperature,specified in kilowatt hours per squaremetre of treated floor area per year,or kWh/(m2year).

• Heat Load - this measures thecapacity of the space heating systemrequired to maintain comfortableindoor temperatures at any one time,specified in Watts per square metre oftreated floor area, or W/m2.

For the prototype house the annualspace heat requirement is15kWh/(m2year) equating to approx-imately 1,650 KWh over an entire year(the house measures 110m2 in treatedfloor area). This would equate to 155litres/year of oil, 160m3/year of mains gasor 350kg/year of wood pellets (in bags)at a cost of approximately €92/yearwhen using oil, €55/year when using gas(without standing charges for gas or€345/year with standing charges) or€97/year when using wood pellets. Unitprice: heating oil 5.62c/kWh; mains gas3.39c/kWh standing charges €256/year;wood pellets - in bags 5.92c/kWh.Source: SEI, Dwelling Energy AssessmentProcedure (DEAP) 2005 edition, version2, Manual pp. 84.

The heat load, on the other hand, isapproximately 1,800 W, or just 1.8 kW.This amount of energy could beprovided by a very small stove / heater /boiler compared to what might betypically required in a family home.

The most common method of 'heating'in a passive house is by post-heating thefresh air after it has already beenwarmed by the exhaust air in the MVHR.

20

Used air filter. Source: MosArt Architecture.

What a clean filter looks like. Source: MosArt Architecture.

Water to air heat exchanger unit. Source: MosArt Architecture.

Compact unit including ventilation heat recovery andair to water heat pump. Source: Drexel und Weiss.

There are a number of ways in which thetemperature of the air can be boosted,including those listed below:

• Water to air heat exchanger.

• Compact unit with electrical heatpump.

• Compact unit with natural gas.

The first two of these is explored inoutline below. The compact unit withnatural gas, while used in Central Europeis virtually unheard of in Ireland andwould have to be approved for use bythe appropriate authorities.

Water to Air Heat ExchangerThis method involves using a heatingdevice placed immediately on the freshair supply outlet of the MVHR. There is asmall radiator inside this device and it isheated by hot water connected to thedomestic hot water tank. If the houseneeds additional heat (which isdetermined by a thermostat) then hotwater is circulated through the device,hence the appropriate title of ‘water toair heat exchanger’. Once the house hasreached the programmed temperature,the hot water stops circulating and theair is no longer heated. The water in thedomestic hot water (DHW) tank isheated, in turn, by using a number ofenergy sources including a stove orboiler (for a larger house) in combinationwith solar hot water panels. Theprinciple advantage of this system overthe compact unit system describedbelow is that when fueled by acombination of firewood and sunshine itis carbon neutral.

Compact Unit with Electrical Heat PumpThis system is so-named as itincorporates all of the technologyrequired for a passive house in arelatively small unit, namely the MVHR,the DHW and the heating power for thehome, in this case powered by anelectrically powered heat pump. It istherefore very suited to smaller homeswhere space might be limited for largetanks, stoves and storage for wood.Compact units are becoming morewidespread in use in passive housesbuilt in Central and Northern Europe.

Integrated controls for heating in aPassive HouseHeating systems in Ireland havetraditionally been very simple, perhaps

the most common boiler based systemsusing a timer and a cylinder thermostat,sometimes even room thermostats beenabsent. New building regulations Part L(2005) recommend minimum levels ofcontrol, installing equipment to achievethe following:

• Automatic control of space heatingon the basis of room temperature;

• Automatic control of heat input tostored hot water on basis of storedwater temperature;

• Separate and independent auto-matic time control of space heatingand hot water;

• Shut down of boiler or other heatsource when there is no demand foreither space or water heating fromthat source.

Additional control features can beincorporated to a heating system so theoverall system performance improves.One example is the ‘weather com-pensation’ feature, which is the ability to

21

Schematic of mechanical system that can be used for back-up heating in a passive house.Source: Passivhaus Institut, Germany (http://www.passiv.de).

Sunlight amounts for Ireland. Source: Green Design, Sustainable Building for Ireland, pp. 28.

adjust the output of the system basedon the measured external temperature.The main advantage of using weathercompensation is that the heating systemclosely monitors external temperaturetrends and adjusts the outputaccordingly. If, for example, the externaltemperature starts to drop rapidly, thesystem can ‘anticipate’ that the dwellingmay come under pressure to maintain itscurrent internal temperature and canverify whether there is sufficient powerto generate the back-up heat that mightbe required.

The preferred internal temperature canbe set using an internal thermostat. Ifthe internal temperature goes below thethermostat setting, the system willautomatically start to heat the fresh airpassing through the ventilationequipment. The principle function of theheating control system is to ensure thatthere is always sufficient heat in thebuffer tank to deliver the heat loadrequired to maintain the comfort levelsset by the occupants. In the case of theOut of the Blue house, if there isinsufficient heat in the buffer tank, andthe solar input can not provide the heatdemand at that particular time, thepellet stove can be ignited automaticallyto provide the back-up required. Thepellet stove will then cut out when thereis sufficient energy available. A similarcontrol system is found in the CompactUnits, except that a heat pump is usedinstead of a pellet stove.

The amount of heat delivered to thefresh air by the heat exchanger isregulated by the internal and externaltemperatures. The control system isusually set up to deliver a relatively highheat load if the temperature outside isvery cold, or alternatively a low heat loadif it is not too cold.

It would also be possible to use an‘instantaneous’ system eliminating theneed for a large buffer tank. Suchsystems do not typically suit the use of apellet boiler, however, as the boilerwould have to switch on and off forshort periods of time to maintain aneven temperature in the house.

Individual Room Temperature Control Different rooms may have differenttemperatures due to solar gains,occupation and internal heat loads.

Room based temperature controls fortemperature differentiation betweendifferent rooms may be necessary ifindividual comfort requirements are setfor different rooms. In a centralisedventilation heating system, however, thesupply air temperature is constant forthe whole house and this would betypical for most houses built to thePassivhaus Standard.

Domestic Hot Water Production As in any type of dwelling, the passivehouse requires a system that providesdomestic hot water (DHW). As withspace heating, it is important that thesystem is energy efficient, wellcontrolled and has an adequate capacityto meet demand. Generally the DHWsystem in a passive house is combinedwith a heat source such as a wood stove,solar thermal collector, compact unit orheat pump for space heating. Mostpassive house examples encounteredhave utilised solar thermal collectors asthey reduce the use of primary energyand CO2 emissions. It is important tonote, however, that the PassivhausStandard is achievable without solarbased water heating. The introduction ofBuilding Energy Rating system as anindication of the energy performance ofdwellings in Ireland is likely to increasethe installation of solar technology as itinfluences the energy rating of a home,and in particular CO2 emissions.

Domestic Water Heating - Solar InputIt is reasonable to expect that anoptimized solar based system (flat plateof 5–7m2 area or evacuated tubes) willproduce up to 60% of total annual hotwater demand the Irish climate and theyhave a relatively shorter pay back periodwhen taking into account availablegrants, in comparison to other re-newable energy technologies such aswind turbines or photo voltaic panels. InIreland the amount of solar irradiationreceived each year is approximately900–1,150 KWh/m². This is the equival-ent of close to 100 litres of oil. Manypeople would be surprised to learn thatDublin receives the same amount ofirradiation as Paris.

In terms of specifying a solar collectorsystem, the following outline guidanceshould be considered:

• The optimal orientation is directlydue south and deviation from this

will reduce the contribution of thecollectors to DHW production. Inplaces where there is no south facingroof, additional panels over the m2

area which might otherwise beneeded can be fitted to east or westfacing roofs.

• The optimal tilt of the solar panels tomeet approximately 50% of theannual heating demand for DHW isapproximately 45 degrees (at a pitchgreater than 45 degrees the potentialannual output is compromisedsomewhat).

• There are two types of solarcollectors typically used in Ireland,flat plate panels and evacuatedtubes. A comparison of theperformance of these types, basedon 5m2 collector area, along withconsideration of orientation andangle of incidence is provided here.The calculation was developed forthe prototype passive house usingthe calculation methodology forsolar water heating in DwellingEnergy Assessment Procedure DEAP2005, version 2.

Three different inclinations of solarpanels (30o, 45o, 60o) and three differentorientations were calculated, with thefollowing specification: standardnumber of 3.6 occupants according toDEAP assumption; water storage tank300 lit., with 150 lit. dedicated to solar,and 50mm factory insulation; withthermostat control.

• As a general rule of thumb, the areaof solar panels is roughly 1 to 2m2 ofcollector area per person. The systemshould be capable of providing up to50 litres of DHW per person per dayin season.

• In terms of sizing a solar tank, aminimum of 80 and preferably 100litres storage per m2 of collectorshould be provided. In a typical Irishhome this could mean installing atank of between 300 and 500 litrescapacity. It is important to use aproper solar water tank which is verywell insulated. Insulation of hot waterpipes is also important for energyconservation, using at least 1 timeand preferably 1.3 times the pipediameter.

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The 40% or more of DHW needs that arenot provided by solar energy can be metby several means including biomassboilers or stoves, immersion heaters ornatural gas. An outline of the first ofthese is provided below. It must beremembered that space heating in apassive house is often provided by usinghot water to heat the air passingthrough the ventilation system. In suchcases, hot water production is essentialin the heating season when solar panelson the roof will not be sufficient to meetthe demand for heating the hot water.Accordingly, many passive houses willhave a biomass stove burning eithernatural logs or wood chip or pellets. Theadvantage of the latter two of these isthat they are more easily automated sothat they fire up and switch off in thesame way as a conventional gas or oilburner.

The following issues should beremembered when consideringinstalling a wood stove or boiler:

• The equipment must be sized

appropriately to the heat load of thehouse. This will be defined by the‘Verification page’ in the PHPPsoftware. Taking the prototype housepresented in these guidelines, a stoveof 3kW output would be sufficient forall space heating and DHW needs.

• A combustion air supply must beprovided to any stove or boiler in apassive house bearing in mind thelevel of airtightness that has to beachieved. The provisions of an airsupply and flue for stoves or boilerswill generally not adversely impacton airtightness or the balancing ofventilation flows due to the 'closed'nature of their construction. Airrequired for combustion is drawn inthrough a relatively small diameterduct and expelled through the flue.

• A stove or boiler that directs most ofthe heat output to the DHW tank isessential if the hot water is to be usedto heat the ventilation air. A modelthat simply radiates all the heat intothe space in which it is located

cannot generally be used for wholehouse heating.

• Wood (whether logs, chipped or inpellets) is bulky and a considerablevolume is required for storageespecially if it is purchased in bulk tokeep costs to a minimum.

• Most wood stoves are highly efficient(up to 90%) and when burningpellets there is very little ashremaining following combustion. Aflue will be required to take exhaustgas emissions safely away from thehouse, as with any typical stove.

Electricity Consumption in a PassiveHouseThe Passivhaus Standard primary energyrequirement has a limit of 120 kWh/(m2

year), regardless of energy source for allspace and water heating, ventilation,electricity for fans and pumps,household appliances, and lightingenergy requirements of the house. Thislimit means that in a passive house theefficiency of household appliances and

23

5 square meters of FLAT PLATE collectors (ηη0=0.75 and a1=6) No obstructions:

Solar Input kWh/year

Tilt of collector South SE/SW E/W

30O 1264.9 1246.3 1191.2

45O 1264.2 1240.4 1167.9

60O 1248.5 1221.3 1137.0

Solar input to demand ratio Tilt of collector

South SE/SW E/W

30O 49% 48% 46%

45O 49% 48% 45%

60O 48% 47% 44%

5 square meters of EVACUATED TUBE collectors (η0=0.6 and a1=3)

No obstructions: Solar Input kWh/year

Tilt of collector South SE/SW E/W

30O 1324.3 1300.7 1231.5

45O 1323.4 1293.2 1202.5

60O 1303.4 1269.1 1164.4

Solar input to demand ratio Tilt of collector

South SE/SW E/W

30O 51% 50% 48%

45O 51% 50% 47%

60O 50% 49% 45%

Domestic solar water heating - solar input (flat plate collectors and evacuated tube) for the prototype passive house(described in Section 3), calculated with the Dwelling Energy Assessment Procedure DEAP 2005 version 2. Source: UCD Energy Research Group.

Primary energy, in kWh/year: Thisincludes delivered energy, plus anallowance for the energy “overhead”incurred in extracting, processing andtransporting a fuel or other energycarrier to the dwelling. For example, inthe case of electricity it takes accountof generation efficiency at powerstations.

Source: SEI, Dwelling Energy Assess-ment Procedure (DEAP), 2005 version2, pp. 28.

Delivered energy, in kWh/year: Thiscorresponds to the energy con-sumption that would normally appearon the energy bills of the dwelling forthe assumed standardised occupancyand end-uses considered.

Source: SEI, Dwelling Energy Assess-ment Procedure (DEAP), 2005 version2, pp. 28.

all electrical systems is crucial to meetthis challenging requirement. This isemphasised with the fact that theprimary energy factor for electricitytaken in the PHPP software (as well as inthe DEAP, Dwelling Energy AssessmentProcedure) is 2.7. Therefore 1kWhelectricity used in a passive houseaccounts for 2.7kWh of the primaryenergy.

When designing a passive house, thePHPP software is used to calculate theelectricity balance. The first step is tocalculate the electricity requirement inthe house including all householdappliances and lighting. In order toachieve the Passivhaus Standard it isnecessary to specify refrigerators,freezers, cookers, artificial lighting,washing machines, dryers, etc. with thehighest energy efficiency available onthe market (i.e. category ‘A’ energy ratedhousehold appliances). The second stepis calculating the auxiliary electricityrequirement, in which electricityconsumption is specified for mechanicalventilation system fans and controls,DHW circulation pumps, and any otherpresent in the dwelling. Calculationresults are presented in primary energykWh/(m2year) and included in the PHPP‘Verification page’.

2.3 Energy BalanceCalculations and PassiveHouse Specification

2.3.1 PHPP Software andApplications

An introduction to the PassivhausPlanning Package (PHPP) was providedat the beginning of this chapter within adiscussion of the building designprocess for passive houses. PHPP is asoftware package based on a series ofelaborate and interlinked Excel datasheets which collectively allow buildingdesigns to be verified against thePassivhaus Standard. The latest versionof the PHPP software can be purchasedfor a nominal fee from SEI RenewableEnergy Information Office. Theverification requires the input of veryspecific and detailed data about thedesign, materials and components intothe PHPP spreadsheets and is thenrelated to the climate data for the regionin which the house would be built. Thevalidity of the result from this process is

of course highly dependent upon thevalidity of the data entered.

Some of the principle datasheetsincluded in the software are listedbelow, along with their main functions:

• Climate data - it is possible to choosethe climate which the passive houseis being designed for which has asignificant impact on the U-valuesrequired to achieve the thresholdannual heat requirement.

• Verification - this sheet collates theresults of the overall evaluation of thebuilding including the Space HeatingRequirement, Specific PrimaryEnergy Requirement, Heat Load andFrequency of Overheating. The usercan see at a glance on this sheetwhether or not the building can becertified as a Passive House.

• U-value - this sheet enables theassessor to specify the constructionof all the opaque (i.e. does notinclude windows) elements of thebuilding envelope for the purposesof calculating the U-value of thoseelements. The sheet requires theinput of the lambda value of thebuilding materials proposed as wellas their thicknesses and theproportion of insulation occupied bystructural elements.

• Windows - the orientation and size ofall windows is entered into this sheet,along with the U-values of the glassand frames as well as other technicalspecifications which have discussedearlier in this chapter.

• Annual Heat Requirement - this valueis calculated by subtracting the heatlosses through transmission andventilation from the total solar andinternal heat gains. The Annual HeatRequirement must be less than15kWh/(m2year).

• Heat Load - the building's heat load isbased on energy balance calculationsestimated by subtracting theminimum solar gains and internalheat sources from the maximumtransmission and ventilation heatlosses.

The PHPP software is very com-prehensive and detailed and therefore

requires some training prior toembarking on practical application to areal project. However, the software isalso quite user friendly and theVerification page enables the user tocheck whether or not such thresholdssuch as Space Heating Requirement aremet. In the event that the key PassivhausStandard criteria are not met, forexample, the assessor will firstly have tocheck to see if there are any funda-mental errors in terms of data entry. Ifthis is not the cause of the problem, thenthe building will likely have to bemodified in order to achieve therequired standards. This will typicallyinvolve improving the U-values of thebuilding envelope, or altering theproportion and orientation of glazing.

Extracts from the PHPP software areincluded later in Section 3 pertaining tothe prototype passive houses.

2.3.2 Passive House Certification

At the time of writing these Guidelines, apassive house in Ireland can be certifiedby the Passivhaus Institut in Darmstad,Germany (http://www.passiv.de) orcertifying body approved by thePassivhaus Institut. For further infor-mation on certification of passivehouses in Ireland contact the SEIRenewable Energy Information Office orthe Passivhaus Institut directly. Theevaluation criteria for the certification(Source: PHPP 2007, pp.23) is:

- Specific Space Heat Demand max. 15kWh/(m2year)

- Pressurisation Test Result n50 max. 0.6ac/h

- Entire Specific Primary EnergyDemand max. 120kWh/(m2year)including domestic electricity.

The above criteria have to be verifiedwith the Passive House PlanningPackage 2007 and the required list ofdocumentation for the passive housequality approval certificate, constructiondrawings and technical specificationwith product data sheets, must besubmitted to the certifying party(including PHPP calculations). Also,verification of the airtight buildingenvelope according to DIN EN 13829, arecord of adjustment of the ventilationsystem, declaration of the constructionsupervisor and photographs of the

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complete building must also besubmitted. Upon examination ofreceived documentation the applicantreceives the results of the examinationfrom the certifying party.

A wider European passive housecertification scheme has beendeveloped within the Intelligent EnergyEurope project (2005–2007) “Promotionof European Passive Houses, PEP”(http://www.europeanpassivehouses.org). This certification scheme isapplicable to ‘an emerging marketscenario’ (i.e. countries with a smallnumber of passive house buildings),aims to ensure that the design of aparticular passive house can deliver thespecific energy requirements inaccordance with the Passive HousePlanning Package (PHPP) and confirmthe air-tightness of the completedbuilding. This certification schemeinvolves the verification of the ‘as built’design (i.e. that reflects the actualconstruction, incorporating anymodifications made during con-struction) in accordance with the PassiveHouse Planning Package (PHPP) andconfirmation of the air-tightness of thecompleted building by a fanpressurization test performed inaccordance with EN 13829.

Since the above assessment criteriaapply to the ‘as built’ design details andthe completed building, there is asignificant risk that any non compliancesdue to fundamental errors will bedifficult to correct when the building iscomplete. It is therefore recommendedthat the design is checked against thePHPP before construction is started toconfirm that the criteria for the specificheating and primary energy require-ments are met; the construction on siteshould be checked to ensure that thedwelling design has been realised; airpermeability measurements arerecorded during the constructionprocess so that air leakage problems canbe identified and remedied while accessto the air-tightness membranes etc isstill available.

Since the actual performance of thebuilding is very dependent on thecorrect operation and maintenance bythe occupant, it is recommended thatadequate written information andinstructions are provided to the

occupants. Also, an approach tocertification of products and tech-nologies used in passive house designshas been developed. (Source: PEPPromotion of European Passive Houses,passive house building certification,http://www.europeanpassive houses.org).

Lifestyle IssuesIt is a very common misconception thatwindows cannot be opened in a passivehouse. They can indeed be opened butthey don’t have to be opened. In apassive house the ventilation systemensures that a constant controlledamount of fresh air is circulated aroundthe house so a stuffy or uncomfortableatmosphere is avoided. If the occupantswould prefer to have the windows openat night or provide natural crossventilation during a hot summer’s daythen it is entirely possible to openwhatever windows or doors onechooses. The MVHR should be switchedoff if there are a lot of windows or doorsbeing left open as it would be anunnecessary waste of electrical energy.

Living in a passive house encourages agreater interest in and awareness ofweather patterns and the impact theyhave (or don’t have) on indoor climate.The passing of cloud cover brings with itinstant brightness and rising tem-peratures on the display panel for thesolar collectors. A very hard frost willsometimes leave a veil of ice crystals onthe outside pane of the glazing whichrapidly melts in the morning sunshine.Extremely cold clear weather usuallymeans that the back-up heating is notrequired during the day due to the highlevels of solar irradiation available. Dullmuggy days, on the other hand, whilenot especially cold, may well require theuse of the pellet stove due to the lack ofsunlight. Windows may have to be flungopen to cool the house on New Years Evenight depending on how many friendsand neighbours you manage to attractto join the celebrations!

As an illustration of the indoortemperature comfort,2 monitoringresults of the room temperatures in thepassive house in Wicklow and sitemeasured temperature is shown onpage 26. The graph represents measuredaverage indoor and outdoor tem-peratures from January 2006 toNovember 2007.

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Passivhaus Institut Certificate example, QualityApproved Passive House. Source: Passivhaus Institut, Germany.

The above diagram illustratestemperature variation in different partsof the house and cooler averagetemperatures in the first heating season(early 2006) compared to the secondand third heating seasons (late 2006/early 2007 and late 2007 respectively).The reasons for these variations areinteresting and warrant someelaboration, below:

• The three coolest rooms (‘office’,‘garage’ and ‘bathroom down’) areeach on the north side of thebuilding, receive no direct sunlightduring the winter months and arevery infrequently used compared tothe remainder of the house. The firsttwo of these spaces have threeexternal walls and so are more proneto heat losses compared with the restof the house.

• The three warmest rooms (‘kitchen’,‘main bedroom’ and ‘stairs’) all openout to the south of the house and soreceive the maximum amount ofsolar gain in winter. Furthermore,they are occupied for significantparts of the day and / or night.

• In the first few months of 2006, theonly back-up heat source in thehouse was a pellet boiler in thesitting room. This alone wasinsufficient to heat the entire houseas its direct output into the room is

just 2kW. As a result, those rooms onthe northern side of the house werebelow thermal comfort levels for thefirst few months of 2006. This wentlargely unnoticed by the family dueto the fact that the rooms in questionare not used.

• In the autumn of 2006, a water-to-airheat exchanger was fitted to theMVHR equipment which enabledheating the fresh air as it passesthroughout the house. This wasactively used for the first time inDecember 2006 which resulted inraising the temperatures in all rooms(even those three on the north side)to well within the normal comfortlevel. In late 2007 the temperatureshave improved yet again.

• There is still in evidence atemperature gradient (increasing intemperature) from north to southand from first floor to ground floor.

The specification of materials and veryhigh quality build creates a strong senseof living in a well-built house that willlast the test of time. The heavy doors andwindows close with a reassuringly solid‘clunk’ and keep out draughts andreduce external noise. The walls are thickand substantial and are packed full ofinsulation to keep out the cold and theheat in. There is no condensation on theinternal glazing early on a cold morning.

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2006 2007

Januray 2006 - November 2007 OUT OF THE BLUE TEMPERATURES

0

5

10

15

20

25

30

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Deg

ree

Cels

ius

Bathroom DownKitchenMain bedroomStairsGarageLiving roomOfficeExternal Temperature

Average daily temperatures, January 2006 – November 2007, monitoring results for the first passive house in Wicklow. Source: UCD Energy Research Group.

You can open windows and doors in passive houses! Source: MosArt Architecture.

Comfort levels all year round in a passive house. Source: MosArt Architecture.

The health aspects of living in amechanically ventilated house are alsoreadily apparent, with no lingeringodours, little or no condensation inwashrooms after showering and anoverall sense of high indoor air qualitythroughout. Changing the filters on theventilation system is always an eyeopener - seeing what dust and dirt istaken out of the incoming air and what isextracted from the indoor air.

Living in a house that has a low carbonfootprint can bring about other changesin lifestyle that are positive for theenvironment, including growing yourown food and reducing the impact oftravel whether by car or by plane.Raising children in a passive house willalso bring about positive change for thenext generation who will expect toimprove even further on what theirparents achieved.

Perhaps the overall lifestyle benefit ofliving in a passive house is that itprovides very high levels of overallcomfort without compromising theenvironment and at a fraction of the costof living in a so-called ‘normal’ house.

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Passive houses provide a stable environment for houseplants. Source: MosArt Architecture.

References

Passive House Planning Package 2007,“Protokolband 16: Waermedruecken-freis Konstruiren (Thermal Bridge-FreeConstruction)”, pp.96. PHPP 2007Technical Information PHI-2007/1(E),Passive House Institute, Dr. WolfgangFeist.

Passive House Planning Package 2007,“Certification of Passive Houses”, pp.28.PHPP 2007 Technical Information PHI-2007/1(E), Passive House Institute, Dr.Wolfgang Feist.

European Commission (EC), 2006.“Promotion of European Passive Houses(PEP)”. [Internet] PEP. Available at:http://www.europeanpassivehouses.org/html

Schnieders J. 2006, “Climate Data forDetermination of Passive House HeatLoads in Northwest Europe”. Darmstadt,Germany, Passivhaus Institut.

1 EN 13141-7:2004, Ventilation forbuildings/ performance testing ofcomponents/products for residentialventilation. Performance testing of amechanical supply and exhaustventilation units (including heatrecovery) for mechanical ventilationsystems intended for single familydwellings.

2 Thermal comfort is defined in BritishStandard BS EN ISO 7730 as: ‘thatcondition of mind which expressessatisfaction with the thermal environ-ment.’ It is affected by the key environ-mental factors as air temperature,radiant temperature, air velocity andhumidity.

SECTION THREE

Passive House Prototype for Application in Ireland

This section of the guidelinesdemonstrates the practical applicationof Passivhaus Standard to a prototypehouse designed especially for thisproject and suitable for the masshousing in Ireland. The house typedemonstrated is a semi-detached twostorey house with a floor area ofapproximately 110m2. The house isdepicted in plan and elevation below.The house is typical in most aspects of itsdesign, comprising three bedroomsupstairs (including one ensuite andfamily bathroom) and a living room,dining room, kitchen/utility andwheelchair accessible WC down-stairs.There are also some non-conventionalelements included, including a double-height sun room, solar panels, pelletboiler and shading pergola. These are alldescribed in greater detail below.

The final part of this section examinesthe capital construction costs associatedwith the passive house.

3.1 Design and Specification

The two most common residentialconstruction methods in Ireland wereused in the design and specification ofthe prototype passive house, namelytimber frame1,2 and masonry. It isdemonstrated below that the PassivhausStandard can be easily achieved inIreland using both of these constructionmethods and that there are no majoradvantages of one method over anotherin terms of thermal performance. Bothpassive house construction types can bebuilt using mostly conventionalelements as can be seen from thedetailed wall sections provided inSection 3.1.4.

3.1.1 Combining Aesthetic andEnergy Performance in HouseDesign

The design of a passive house is stronglyinfluenced by the need to minimise heatloss through the building fabric, tomaximise solar gains and to cater for thevarious building services. Form andfunction played equal roles in the designof the prototype passive house. Theoverriding principle used in the designof the prototype house was that itshould be broadly similar in character tocontemporary housing, thus maximisingease of acceptance to the currenthousing market in Ireland.

As has been described in some detail inthe preceding sections, much of the‘free’ energy required to heat a passivehouse comes directly from the wintersun through south facing windows. It istherefore typical (though not essential)to have a bias in terms of placement ofglazing on the southern elevation.Combined with such glazing is the needto prevent overheating in summer andthis is easily ensured through the use ofshading, in this case with a balcony andpergola. The walls of a passive house aretypically thicker than those ofconventional construction due to theneed for additional insulation and thismust be borne in mind in the earlystages of design development. The otherkey issue to consider when developingthe design of a passive house is the needto minimise thermal bridges includingthat created between the foundationand internal walls, for example. Bearingin mind the above principles of glazingorientation, wall thickness andminimised thermal bridging, thedesigners commenced the development

of the prototype passive house.

3.1.2 Decision Support using PassiveHouse Planning Package (PHPP)Software

The Passive House Planning Package(PHPP v2004) has been introducedalready in these guidelines. It is an Excel-based software that can be used to ‘test’the energy performance of a building asit is being designed. It includes Irishclimatic data which is very useful inensuring that buildings are not over-specified in terms of thermal per-formance. Key aspects of the emergingprototype passive house were enteredinto the software with a view to ensuringthat the design achieved the minimumrequirements of (a) yearly space heatingdelivered energy demand of 15 kWh/m2

treated floor area (TFA3), and (b) upperlimit for total primary energy demandfor space and water heating, ventilation,electricity for fans and pumps, house-hold appliances, and artificial lightingnot exceeding 120kWh/(m2year), regard-less of energy source.

The thickness of insulation required inthe walls, floor and roof is stronglyguided by the PHPP software, as is thespecification and positioning of thewindows, the sizing of the back-upspace heating system, the considerationof thermal bridges and many otheraspects of the design. The design is thusan iterative process. Different insulationtypes can be tested in the software, withhigher performance materials (in termsof lower Lambda values) requiringthinner walls than other less efficientmaterials.

Two extracts from the PHPP software areincluded below in order to give an

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Passive House Prototype for Application in Ireland

insight into how the software can beused to assist the designer. PassiveHouse Verification Sheet deals withannual heat requirement based on abalance of heat losses (transmission andventilation) pitched against heat gains(solar and internal) in order tosummarise the Annual Heat Require-ment. The annual space heat require-ment of 15kWh/m2 is achieved.

The second illustration provides aninsight into how the U-values of majorbuilding elements are calculated. Thefirst table provides details on how a U-value of 0.15W/(m2K) is achieved for aconcrete cavity wall, the second table

details a timber frame wall with aninsulated service cavity and the thirdtable illustrates the depth of insulationrequired in the roof. The partial thermalbridge caused by the timber studs istaken into account in the software bycalculating the proportion of theinsulated wall occupied by timber (inthis case 10%).

3.1.3 Prototype Passive HouseExternal Wall Sections

The wall sections for both constructiontypes are illustrated also. It should benoted that no dimensions are includedon the sections below as they are

intended to be diagram only. Theyshould not be used as a basis fordetailed construction drawings.

The following key issues can be notedfrom the detailed wall sections:

• Thicker than normal wall sections aredesigned in order to accommodatethe required depth of insulation. There is also substantial insulation inboth the roof and under the floor.

• The insulation at the junction of roofand wall, as well as wall and floor,overlap in order to minimise thermal bridging at these critical locations.The window frame is also partly

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Passive House Verification for the prototype passive house, concrete block construction.Source: MosArt Architecture.

bedded in insulation in order toreduce heat loss.

• Membranes and specialist tapes areused to create an airtight envelope.This is especially critical at junctionsbetween different elements, such asaround windows, and also where thefirst floor penetrates the external wallfaçade.

• A service cavity is proposed, internalto the airtight layer in the timberframe wall, in order to accommodatemechanical and electrical fittings. Asimilar cavity is proposed in theunderside of the ceiling at first floorlevel for both house types.

• Blockwork with a low thermalconductivity is used in the risingwalls to reduce thermal bridgingbetween foundations and walls.

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Passive House Verification for the prototype passive house, timber frame construction.Source: MosArt Architecture.

IFC, Insulated Concrete Forms. Source: UCD Energy Research Group.

Externally insulated concrete block wall. Source: MosArt Architecture.

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U-value of building elements for the prototype passive house, concrete block construction. Source: MosArt Architecture.

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U-value of building elements for the prototype passive house, timber frame construction. Source: MosArt Architecture.

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Cross section, prototype passive house. Concrete block construction. Source: MosArt Architecture.

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Cross section, prototype passive house. Timber frame construction. Source: MosArt Architecture.

3.1.4 Prototype Passive HouseDesign including Mechanicaland Electrical Services

The final design of the prototype passivehouse is presented below in plan,elevation, section and, finally, a 3Dmodel. A number of mechanical andelectrical features are highlighted whichhave been included specifically in thedevelopment of the passive houseprototype:

• In terms of mechanical ventilation, anaverage air flow rate ofapproximately 115m3/h would berequired providing an approximatelyair change of 0.4 per hour. A fresh airoutlet is provided to the living room,dining room, double height sunroom (at ground floor level) andbedrooms whereas an extract vent isprovided in WC’s and bathrooms aswell as the kitchen, the utility roomand the upper part of the sun room.The mechanical ventilation with heatrecovery unit is located in the utilityroom and will recover the majority ofthe heat from the extracted air towarm the incoming fresh air. Anairing cupboard is located on the firstfloor along with the washingmachine. This space is connected tothe ventilation system and canfunction as drying cabinet for dryingclothes in the winter. Soundattenuators should be used in orderto minimise noise travelling alongducts and air filters should bechanged as required in order not tocompromise indoor airflows and / orair quality.

• A pellet stove is proposed for theback-up space and water heatingsystem.4 For the prototype house theannual space heat requirement is15kWh/(m2year) equating to approx-imately 1,650 KWh over an entire year(the house measures 110m2 intreated floor area). This would equateto 155 litres/year of oil, 160 m3/year ofmains gas or 350kg/year of woodpellets (in bags) at a cost ofapproximately €92/year when usingoil, €55/year when using gas (withoutstanding charges for gas or€345/year with standing charges) or€97/year when using wood pellets.Unit price: heating oil 5.62c/kWh;mains gas 3.39c/kWh standing

charges €256/year; wood pellets - inbags 5.92c/kWh. Source: SEI, DwellingEnergy Assessment Procedure (DEAP)2005 edition, version 2, Manual pp. 84.

The heat load, on the other hand, isapproximately 1,800 W, or just 1.8 kW.This amount of energy could beprovided by a very small stove/heater/boiler compared to whatmight be typically required in afamily home (there are several such‘small’ boilers on the market whichrange in output from 2.4 to 8kW, withapproximate efficiency of 90%). Thepellet stove in the prototype househas been positioned in the sittingroom, but space has also been left inthe utility room as this might bepreferable for users. The pellet stovecan be filled manually as the needarises, or could be automatically fedusing an underground pellet storage‘bunker’ located underground to thepublic road side of the house for easeof delivery. While a house of this sizecould probably manage without anautomatic feed from a bunker (givenan average use of approximately15kg of pellets per week), theadvantage of such a system is in thespace saved from having to storepellets in the house or garden shed.In positioning the pellet stove in thesitting room, there is an aestheticbenefit to be gained from visibility ofthe flames coupled with the deliveryof some heat directly into the sittingroom. Care must be taken to use astove that delivers most of the heatoutput to the hot water tank and notdirectly into the room in which it islocated. It is also critically importantthat the pellet stove has its own freshair supply, given the airtight nature ofthe construction, and that anappropriate flue for venting ofexhaust gases is provided. Suchsystems are common place in passivehouses and will not adversely affectthe balanced ventilation system.

• The domestic hot water tank (550litre)5 is located adjacent to themechanical ventilation unit, in theutility room. The back-up heatingsystem, in this case, is provided byheating the fresh air circulatingaround the house by the hot water inthe ‘buffer’ tank using a water to air

heat exchanger. In this regard, allsupply air ducts should be insulatedin order to minimise heat losses, evenif they are located within the thermalenvelope.

• Solar panels (measuring 7.5m2) arepositioned on the south facing roofwhich is pitched at the optimal angleof 45 degrees. These have been sizedin accordance with the needs of sucha house and could include either flatplate collectors or evacuated tubes.

Other aspects of the design which arenot related to the mechanical orelectrical services are listed below:

• All windows in the prototype houseare triple glazed with low emissivitycoating, thermally broken frames andgaskets especially designed tominimise air infiltration. A passivehouse triple glazed window istypically four times more energyefficient than a standard doubleglazed unit and, if south facing, willtake in more energy in a year than itlets out. The use of such glazingensures high thermal comfort in coldweather through minimal temper-ature difference between internalglass pane surface and room temper-ature.

• A balcony is provided at first floorlevel, the primary function of which isto shade the extensive area of glasson the south elevation. This balconycan be accessed via the gallery whichoverlooks the double-height sunroom. A wooden pergola is providedoverhead the balcony to shade theupper story windows. A possiblealternative to this pergola could be adeep roof overhang but the steep-ness of the pitch in the prototypehouse would mean that this lattersolution would restrict high levelviews from the upper storey.

• The internal party walls can beconstructed as per a conventionalhouse as long as it is within theboundaries of the building envelope.

• The hatch to the attic should be verywell insulated and completelyairtight to minimise cold airinfiltration.

• Ceiling insulation is placedhorizontally on the attic floor in the

38

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prototype passive house. It wouldalso be possible to place thisinsulation between the rafters, albeitwith design and constructionimplications.

• The timber frame option depicted inthese guidelines is ventilated with anexternal cavity.

• Energy efficient light fittings shouldbe used which use less primaryenergy (they will also reduce internalheat gains). It is also preferable to useenergy efficient appliances.

Various building methods can be used inthe construction of a passive house,including, insulated concrete formworkand externally insulated concrete blockwall. The prototype house presented inthis publication illustrates masonry andtimber frame construction asrepresentative of most typically usedbuilding methods for dwellings inIreland.

3.2 Cost Considerations

An analysis of additional costsassociated with construction of theprototype house to the PassivhausStandard was carried out by Gardinerand Theobald Cost Consultants. Theadditional cost of the key itemsincluding enhanced insulation, glazing,airtightness and thermal bridging wasestimated, along with the cost of suchtechnologies as MVHR, solar panels forDHW, a pellet stove as well as energy

efficient light bulbs and householdappliances. Included in their analysiswas an allowance for the foregone costsassociated with ‘conventional’ housefeatures such as a fireplace and boilerwith radiators. Gardiner and Theobaldundertook their analysis for both timberframe and the concrete blockconstruction methods.

The additional ‘extra over’ costassociated with building the prototypehouse to the Passivhaus Standard wasestimated at approximately €25,000 forboth construction methods, includingVAT and design fees. Approximately 60%of this cost can be attributed towardsimprovement of the building shell(enhanced insulation, higher gradewindows, improved airtightness andreduced thermal bridging) with theremaining 40% covering buildingsystems including MVHR, solar thermalsystem, low energy lighting and woodpellet boiler.

Gardiner and Theobald next sought toexpress the additional passive housecosts as a proportion of conventionalconstruction costs. The cost of aconventional house varies considerablyaccording to the quality of finishesrequired. An average cost of €196,000was proposed as representing a mid-grade finish, including VAT and designfees. The additional cost of €25,000 thusrepresents approximately 12.5% ofcurrent conventional costs.

References

Passive House Planning Package, PHPP2004, Technical Information PHI-2004/1(E). Darmstadt, Germany.Passive House Institute, Dr. WolfgangFeist.

1 Approximately 17% of houses built inIreland are semi-detached.

2 According to the Irish Timber FrameManufacturers’ Association (ITFMA) thenumber of timber frame housecompletions has grown from a marketshare of 15% in 1999 to a market shareof 30% in 2006.

3 The TFA is the living area within thethermal envelope. Any rooms or areasbeyond the boundaries of the thermalenvelope are not considered.

4 Other sources of heat such as gas or heatpumps can also be used.

5 Estimated heating requirement for hotwater (incl 50% SWH) + space heating =3200 kWh = c.650 kg pellets/year =10–15 kg/week.

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Prototype passive house, floor plans (not to scale). Source: MosArt Architecture

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Prototype passive house, floor plans (not to scale). Source: MosArt Architecture

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Prototype passive house, cross section (not to scale). Source: MosArt Architecture

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Prototype passive house, front, back and side elevations (not to scale). Source: MosArt Architecture

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Prototype passive house, 3D model (not to scale). Source: MosArt Architecture

Sustainable Energy IrelandRenewable Energy Information OfficeShinagh HouseBandonCo. CorkIreland

T. +353 23 42193F. +353 23 54165

[email protected]

SEI is funded by the Irish Government under theNational Development Plan 2007 - 2013 with programmes part financed by the European Union.

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