Greg KeeffeHead of DesignManchester School of Architecture, Manchester UKg.keeffe@mmu.ac.uk

The Passive House: Issues of Cooling: Form, shading,ventilation.

Living (bioclimatic) architecture

Climate derives form

Uruguay Climate: Hot Humid

Uruguay Climate: Hot Humid

Passive Design

Building and equipment is system to provideoccupant comfort

Key issuesForm OrientationMass (inside and out)Façade design – fenestration / shading in particularFabric Solar GainVentilation controlIncidental and ambient gainsBuilding and equipment a single system

Resource/Material loop

Passive Design

Form - The Passive zone.

It is crucial all rooms are within the passive zone

The passive zone is typically 7metres from the building edge

Sometimes this can be extended

Passive Design

Form - Surface area to volume ratio

Compact versus rambling

Passive Design

Form - Self shading

Passive Design

Form - the Courtyard

Offers self shading with microclimate

Fathy Houses Tunis

Alberto Campo Baeza, Caspar House

Passive Design

Form - Minimise West façade

The West façade is the most difficult to shade

Passive Design

Form - Layering

Passive Design

Orientation

Re sun and wind

Glenn Murcutt

Passive Design

Issues of thermal Mass

Heavy or light??

Tropical light, arid heavy.

Bedouin tent - Alhrambra

Passive Design

Façade design

Nouvel

Corderch

Passive Design

Fabric design

Mass, Insulation, fenestration

Passive Design

Ventilation Control

Passive Design

Incidental and ambient gain

Passive Design

Building and equipment as single system

Rogers MVRDV Future Systems

IN WARM WEATHER

1. MINIMIZE HEAT GAINS.

2. AVOID OVERHEATING.

3. OPTIMISE COOL AIR VENTILATION AND OTHERNATURAL COOLING METHODS.

Shigeru Ban

Givoni’s bioclimatic chart

THE NEED FOR COOLING

1. SOLAR CONTROL

• To prevent the sun’s rays from reaching andentering the building.

COOLING STRATEGIES

2. EXTERNAL GAINS

• To prevent increases in heat due toconduction through the building skin or by theinfiltration of external hot air.

COOLING STRATEGIES

3. INTERNAL GAINS

• To prevent unwanted heat from occupantsand equipment raising internal temperatures.

COOLING STRATEGIES

4. VENTILATION

• Unwanted hot air may be expelled andreplaced by fresh external air at a suitabletemperature.

COOLING STRATEGIES

5. NATURAL COOLING

• To transfer excess heat from the building toambient heat sinks.

COOLING STRATEGIES

SOLAR CONTROL

• External essential.

• examples are overhangs, awnings, movableblinds/louvres and planted screens.

COOLING STRATEGIES

SOLAR CONTROL (SHADING)

• The degree and type of shade necessary dependson the position of the sun and the position andgeometry of the part of the building being shaded.

COOLING STRATEGIES

Solar Geometry and shading

Orientation

• Long axis East-West

• Shading of North fenestration simple• East and West facing windows, are more difficult

to shade

COOLING STRATEGIES

COOLING STRATEGIES

Hostel for Youth Education Institute, Windberg, Thomas Herzog

SOLAR CONTROL (FIXED SHADING)

• South facing windows can be shaded by anfixed overhang above the glazed element.

• The depth of the overhang should take intoaccount not only its distance above thewindow but also the aperture height.

• The length of the overhang is determined bythe window width.

COOLING STRATEGIES

SOLAR CONTROL (ADJUSTABLE SHADING)

• The effectiveness of fixed screens varies according tothe seasonal changes in the position of the sun.

COOLING STRATEGIES

Discarded music cassettes, Pavilion of Christ, Volkenroda.Transparent Insulation Material (extruded honeycomb).

House, Amsterdam, Heren 5

Administration Building, Wiesbaden, Herzog + Partners

Curved sunscreen and light-deflecting elements in south facingIntelligent façade allow differentiated natural lighting on overcast andclear days.

Overcast day Clear sky

Foliage used as solar filter at Tokyo-Nara tower,Japan, Exhibition Tower, Ken Yeang

Bioclimatic Skyscraper proposed forKuala Lumpur, Malaysia

Learning Resource Centre, Jubilee campus, Nottingham, Hopkins Architects

Audi Mobile Museum, Ingolstadt, Munich, Germany,Design-Agency KMS

Heliotropic solar shading, Siemens Pavilion, Expo’92 Seville, by Siemens Architecture Dept.

Albert Camus School, Frejus, FranceFoster+Partners

Single family House,Wohnhaus, Vaise, FranceJourda & Perraudin

SOLAR CONTROL (ADJUSTABLE SHADING)

• Outside the building envelope

• Daylighting important too

COOLING STRATEGIES

SOLAR CONTROL (Double Skins)

• Consists of outer single glazing - shading - doubleglazing

• Interstitial space acts as solar chimney to increaseventilation.

COOLING STRATEGIES

Business Promotion Centre, Duisberg, Germany,Foster & Partners

SOLAR CONTROL The roof

Extending the eaves offers shading potential

COOLING STRATEGIES

SOLAR CONTROL (SPECIAL GLAZING)

For windows which are difficult to shade,• Absorbing glass• Reflecting glass

COOLING STRATEGIES

Reflecting glass & clear glass Absorbing glass & clear glass

SOLAR CONTROL (SPECIAL GLAZING)

• Photochromic, thermochromic, and electrochromicglasses modify the incoming rays of the sun so thatthe optical properties of the glass change i.e. the glassdarkens.

COOLING STRATEGIES

Schematic diagram of a five-layer electrochromic coating system.A reversible low voltage charge forces ions to migrate between anactive electrochromic layer and a passive counterelectrode layercausing the active layer to darken. When the voltage is reversed andthe ions are removed, the electrochromic layer returns to its clear state.

High-transmission State (Clear) Low-transmission State (Coloured)

SOLAR CONTROL (PLANTING )

• Shading can also be provided by vegetation.

• If deciduous, the branches are bare in winter allowingsolar penetration, from spring onwards as the leavesgrow shade increases.

COOLING STRATEGIES

Minimise EXTERNAL GAINS

• Walls and roofs heated by the sun and by thewarm outside air produce uncomfortableconditions inside.

• INSULATION• THERMAL INERTIA• REFLECTION.

COOLING STRATEGIES

EXTERNAL GAINS (INSULATION)

Can be used to prevent overheating byconduction in summer.

COOLING STRATEGIES

EXTERNAL GAINS (THERMAL INERTIA)there is a time delay due to the thermal inertia ofthe walls and roof, etc., in the flow of heatthrough the building envelope which can beexploited in a heavyweight building for coolingpurposes.

COOLING STRATEGIES

COOLING STRATEGIES

EXTERNAL GAINS (THERMAL INERTIA)

Turf roofs offer transpiration coolingAnd insulation

EXTERNAL GAINS (THERMAL INERTIA)

• When solar radiation strikes an opaque surfacesuch as a wall or a roof the exterior surfaceabsorbs part of the radiation and converts it toheat.

• Part of the heat is directly re-emitted to theoutside.

• The remainder is conducted through the wall orroof at a rate which depends on the thermalproperties of the material.

COOLING STRATEGIES

Concrete has a delay of 20mins per 10mm

STORAGE OF COLD (REMOTE MASS)

• Rock beds located away from the occupied spacecan be used to increase the amount of heat andcold that can be effectively stored.

COOLING STRATEGIES

Princeton Professional Park, Princeton, New Jersey, Harrison Fraker

Summer Cooling strategy Day/Night

EXTERNAL GAINS (REFLECTION)

• Light colours

• In an air-filled cavity wall or roof space radiation iskey thermal transport, so add foil.

COOLING STRATEGIES

Minimise INTERNAL GAINS

Artificial lighting, appliances andthe tasks of occupants all lead tointernal heat gains.

This can be reduced by naturaldaylighting and by:

• Accurate control.• Choosing efficient appliances.• Expelling the heat generated.

COOLING STRATEGIES

VENTILATION

• Usually buildings are warmer inside than out.

• Thus increasing ventilation using cooler fresh airgives relief

COOLING STRATEGIES

Stack effect

Solar chimneys use the sun to warm-up the internal surface ofthe chimney. Buoyancy forces due to temperature differencehelp induce an upward flow along the plate.

Osuna Housing SevilleSotomayer, Dominguez Lopez

VENTILATION (STACK EFFECT)

• The same effect can be used to create cross ventilation.

COOLING STRATEGIES

Summer operation – Ventilation and air circulation

Am Lindenwaldle, Freiburg, GermanyDominic Michaelis Associates

La Salut, Barcelona, SpainC. Parant

Cooling mode:

Cool air is drawn up from thenorth face of the house to beexhausted through the skylights.

Office Building, Dresden, LOG ID

1. Cavity between concrete and steel roof promotes cooling of concrete.2. Stale air exits the classrooms at the highest point, preventing the formation of a

warm static air layer.3. Cross ventilation through classrooms.4. Entry of fresh air at a low height enhances air circulation in the classrooms.5. Perforated steel louvres shade from direct sunlight.6. Stale, warm air exits through the open louvres.7. Ventilation enhanced by Stack/chimney effect.

VENTILATION (WIND PRESSURE EFFECT)

• When wind strikes a building a high pressure on theexposed side and a low pressure on the opposite,sheltered face results.

COOLING STRATEGIES

VENTILATION (WIND PRESSURE EFFECT)

• The movement of air across a site is from highpressure zones to low pressure zones, throughopenings in the building envelope.

• The best distribution of fresh air throughout thebuilding is achieved when the openings arediagonally opposite each other and air flow is nothindered excessively by partitions and furniture,etc.

COOLING STRATEGIES

VENTILATION (WIND PRESSURE EFFECT)

• Maximum ventilation should be provided duringthe day in occupied areas of the building athead height.

• In addition, there should always be a good flowof fresh air along the building’s most massiveelements so that as much heat as possible isdissipated from them.

COOLING STRATEGIES

VENTILATION (THE VENTURI EFFECT)

• Used to induce circulation of air in a particulardirection.

• The air is encouraged to flow through a constrictedpart of the building. At this position, its speedincreases and the pressure decreases accordingly.

• The reduced pressure creates an air flow which canbe used to drive hot air from the building and thuscause ventilation.

COOLING STRATEGIES

The Venturi tube illustrates the ‘Bernoulli effect’: as theVelocity of air increases its static pressure decreases.

A Venturi tube used as a roof ventilator

Kanak Centre, New Calendonia, Renzo Piano

Passive ventilation: light breezes Strong Winds

Cyclone Reverse Winds

Kanak Centre, New Calendonia, Renzo Piano

Night cooling using (CROSSVENTILATION)

It is a necessary complement to heatstorage.

NIGHT-TIME VENTILATION air ispreferentially circulated pasthigh thermal inertia masses toremove the heat they haveaccumulated during the day.

COOLING STRATEGIES

COOLING STRATEGIES - Night purging

NIGHT-TIME VENTILATION AIR

COOLING STRATEGIES

Room temperaturesdependant on outsidetemperature (Summer day)

Operation of Night Cooling:06:00 to 19:00hrs.

VENTILATION (WIND TOWERS)

• Wind towers draw upon the force of the wind togenerate air movement within the building.

• The inlet of a Wind Scoop are oriented toward thewindward side to capture the wind and drive airdown a chimney.

• Alternatively, a chimney cap is designed to create alow pressure region at the top of the tower, and theresultant drop in air pressure causes air to flow upthe chimney.

COOLING STRATEGIES

SCOOP

Ventilation using Wind Towers

CAP

Windcatchers - vernacular

Iran Hydrabad

WIND TOWERS - modern• Both these principles may be combined in a

single tower providing both admittance andexhaust of air.

• A self-contained system is thus created.

COOLING STRATEGIES

View of wind cowl, Jubilee Campus, Nottingham University, Michael Hopkins

NATURAL COOLING

• EVAPORATION.

• GROUND COOLING.

• RADIATIVE HEAT LOSS tothe sky and by CROSSVENTILATION.

COOLING STRATEGIES

COOLING OF INFILTRATION AIR(EVAPORATIVE COOLING)

• To change its state from liquid to vapour, waterrequires a certain amount of heat known as the LATENTHEAT OF VAPORIZATION.

• When this heat is supplied by hot air there is a drop inair temperature.

COOLING STRATEGIES

Passively cooled house, Arizona

Stanford University CA, Ecology CentreEsherick Homsey Dodge & Davis

GROUND COOLING3 methods

Ground couplingAir systemsWater systems

COOLING STRATEGIES Future Systems

Hope House, Bill Dunster

RADIATIVE HEAT LOSS TO THE SKY

• Radiative transfer of heat always occurs between twoadjacent masses at different temperatures.

• clear night skies are (even in the warm season) cold soexposed surfaces cool appreciatively

COOLING STRATEGIES

Indirect direct direct

Skytherm House 1973

In roof ponds the heat accumulated in a building during the dayis trapped and stored in the roof pond, which is protected on the outside by movable insulation.

•At night, the insulation is removed to allow •the stored heat to be radiated to the sky.

REFERENCES

Brown, G.Z. and Dekay, M. Sun, Wind and Light: Architectural DesignStrategies (John Wiley & Sons Inc. 2000).

Santamouris, M. Advances in Passive Cooling (Buildings, Energy and SolarTechnology) (EarthScan books 2007).

Herzog, Thomas. Solar energy in architecture and urban planning (Munich:Prestel 1996).

Givoni, Baruch The Passive Cooling of Buildings (Architecture) (Wiley 1994).

Goulding, J.R., Lewis, J.O., and Steemers, T.C. Energy in Architecture: TheEuropean Passive Solar Handbook (Batsford Ltd. 1993).

Goulding, J.R., Lewis, J.O., and Steemers, T.C. (eds.) Energy ConsciousDesign: A Primer for Architects.

Melet, Ed. Sustainable Architecture: Towards A Diverse Built Environment(Rotterdam: NAI Publishers 1999).