Cost optimal and nZEB energy performance levels for buildings...Jarek Kurnitski Sitra, the Finnish...

Technical report:

Cost optimal and nZEB energy performance

levels for buildings

May 30, 2011

Jarek Kurnitski

Sitra, the Finnish Innovation Fund

Arto Saari

Aalto University

Mika Vuolle

Equa Simulation Finland Oy

Finland

KENA cost optimal and nZEB def 2

Contents

1 Introduction ............................................................................................................................................................................ 3

2 Methods ................................................................................................................................................................................... 3

3 Technical definition for net zero energy buildings ................................................................................................. 4

4 Results ....................................................................................................................................................................................... 9

4.1 Net present value calculation ................................................................................................................................. 9

4.2 Results for detached houses ................................................................................................................................ 10

4.3 Results for apartment building ........................................................................................................................... 19

4.4 Results for office building ..................................................................................................................................... 23

5 Conclusions .......................................................................................................................................................................... 29


1 Introduction

Energy performance of buildings is regulated in Estonia with the government act on minimum

requirements for energy performance. This act includes primary energy requirements for all common

building types, mandatory input data for energy calculation (standard use of the buildings) as well as

calculation rules and guidelines, and requirements for calculation tools. The framework and procedure

is one of the most generic and flexible in EU and can be used as is for net zero energy building energy

performance calculations. Energy certificate values for new buildings are also calculated with this act.

EPBD recast launched cost optimal principle of the minimum requirements and the roadmap to nearly

zero energy buildings in 2019-2021. Demanding construction clients need already today a common

definition for low energy and nearly zero energy buildings that would be more ambitious than existing

minimum requirements. These new top categories are to be implemented into energy performance

certificate in the future revision.

This report proposes definitions for cost optimal low-energy buildings and nearly zero-energy

buildings of selected building types. The cost optimal principle of EPBD recast with net present value

calculation is used to derive the low energy performance level. Nearly zero energy performance level is

derived as the lowest possible primary energy use technically reasonable achievable.

2 Methods

The definitions for low energy and nearly zero energy buildings were prepared for the following

building types:

• detached house

• apartment building

• nursing home

• day-care centre

• school building

• office building

Cost optimal primary energy use was calculated for each building type based on solutions leading to

minimum net present value with 30 years period. The net present value calculation included both

investment and operation cost discounted with common real interest rate of 3%. To show the

sensitivity to the interest rate, the escalation of the energy price was varied between 1 and 4%. For

initial energy prices the current price data was used.

The calculation procedure was started with selection of reference buildings. Energy and cost

simulations were conducted for two most feasible, currently known low energy concepts for each

building type. For each low energy concept a series of energy simulations were conducted with several

building envelope thermal insulation, heat recovery and other parameter values. After that, the net

present value calculation showed cost optimal levels for each building type. Energy simulations were

carried out for all building types studied (6), but economical calculations only for every second

building type due to similarity of technical solutions in non-residential buildings.


All low energy building concepts studied were equipped with effective heat recovery. For detached

houses, the main concepts with ground source heat pump, air to water heat pump and passive house

with electrical heating and solar collector were studied. All other building types were calculated with

district heating as a main heat source. Two alternative construction concepts were formulated mainly

through daylight control and demand controlled ventilation options.

Energy simulations were conducted with input data and calculation rules of the Estonian act of

minimum requirements for energy performance. These include indoor climate, Estonian TRY and

standard use of the building (occupancy and other internal gains and DHW data). This calculation

procedure provides delivered energy use from which primary energy rating ET-value was calculated

with energy carrier factors.

Derived nearly zero energy and low energy performance levels are proposed to be implemented in the

energy performance certificate scale, so that category A will correspond to nearly zero energy and

category B or C to cost optimal low energy building energy performance level, depending on the

difference between the nearly zero and cost optimal, Figure 1.

Figure 1. A proposal for the implementation of nearly zero energy and cost optimal low

energy buildings energy performance levels into the energy performance certificate scale.

3 Technical definition for net zero energy buildings

The following general definition format proposed by REHVA Task Force “Nearly Zero Energy Buildings”

(REHVA Journal 3/2011) was used as a framework for nearly zero energy building energy performance

calculations. EPBD recast requires nearly nZEB buildings, but since it does not give minimum or

maximum harmonized requirements as well as details of energy performance calculation framework, it

will be up to the Member States to define what these for them exactly constitute.

Nearly net zero energy building definition shall be based on delivered and exported energy according

to EPBD recast and EN 15603:2008. The net delivered energy, which is delivered minus exported

energy per energy carrier, is shown in Figure 2 and described with detailed system boundary definition

in Figure 3. This system boundary definition is a general form modified from the one of EN

15603:2008. Suggesting the inclusion of energy use of appliances (households and outlets), the system

boundary proposes that all energy used in buildings will be accounted in net delivered energy as well

as in nearly net zero energy building definition, in accordance with Estonian act on minimum

Type of buildingEnergy performance value, kWh/(m2·a)

ANearly-

zero

BLow-

energy

C DNew

buildings

EReconst-ruction

F G

Detached house

Nursing home

Day-care centre

Apartment building

Office building

Schools


requirements for energy performance. This means that energy use in the buildings includes inter alia,

energy used for heating, cooling, ventilation, hot water, lighting and appliances.

Figure 2. System boundary for nearly net zero energy building definition, connecting a

building to energy networks. Net delivered energy is delivered Edel,i minus exported energy

Eexp,i accounted separately for each energy carrier i. Primary energy E is calculated with

primary energy factors fi. (Adopted from REHVA Task Force “Nearly Zero Energy

Buildings”)

Net zero energy requirement has exact performance level of 0 kWh/(m2 a) primary energy. The

performance level of “nearly” net zero energy use is a subject of national decision taking into account:

• cost optimal and technically reasonably achievable level of primary energy use

• how many % of the primary energy is covered by renewable sources

• ambition level of the definition

The following definitions, proposed by REHVA Task Force “Nearly Zero Energy Buildings” (REHVA

Journal 3/2011) were used:

net zero energy building (nZEB)

energy use of 0 kWh/(m2 a) primary energy

NOTE 1 A nZEB is typically a grid connected building with very high energy performance. nZEB

balances its primary energy use so that the primary energy feed-in to the grid or other energy network

equals to the primary energy delivered to nZEB from energy networks. Annual balance of 0 kWh/(m2

a) primary energy use typically leads to the situation where significant amount of the on-site energy

generation will be exchanged with the grid. Therefore a nZEB produces energy when conditions are

suitable, and uses delivered energy during rest of the time.

nearly net zero energy building (nnZEB)

national cost optimal energy use of > 0 kWh/(m2 a) primary energy

DELIVERED ENERGY

EXPORTED ENERGY( )∑ −=

i

iiidel fEEE exp,,


NOTE 1 The Commission shall establish by 30 June 2011 a comparative methodology framework for

calculation of cost-optimal levels (EPBD recast).

NOTE 2 Not all renewable energy technologies needed for nearly zero energy building have to be

cost-effective, if appropriate financial incentives are not available.

For the detailed energy boundary specification, the guidance is provided in EN 15603:2008. Inside the

boundary the system losses are to be taken into account explicitly, outside they are taken into account

in the conversion factor (=primary energy factor). Technical building systems located partly outside of

the building envelope are considered to be inside the system boundary. It is also clearly stated that the

assessment can be made for a group of buildings serviced by the same technical systems.

EN 15603:2008 states that for active solar and wind systems only the energy delivered by the

generation devices and auxiliary energy are taken into account in the energy balance (i.e. kinetic

energy of wind is not).

The detailed energy boundary is modified from EN 15603:2008 and as stated in EPBD recast,

renewable energy produced on site is not considered as part of delivered energy, i.e. the positive

influence of it is taken into account, Figure 3.

Figure 3. Energy boundary of net delivered energy and how it forms from energy need,

energy use of technical building systems, on site renewable energy production, delivered

energy and exported energy. The box of “Energy need” refers to rooms in a building and

both system boundary lines may be interpreted as the building site boundary. (Adopted from

REHVA Task Force “Nearly Zero Energy Buildings”)

Energy need represents energy need in a building for heating, cooling, ventilation, domestic hot water,

lighting and appliances (if appliances are included in the system boundary as proposed). Energy need

for heating is caused by heat losses and is reduced by solar and internal heat gains. Net energy need is

ENERGY NEED

HeatingCoolingVentilation

DHWLighting

Appliances

System boundary of net delivered energy

Net

deli

vere

d e

nerg

y

(ele

ctr

icity,

dis

tric

t h

ea

t, d

istr

ict

co

olin

g, f

ue

ls)

System boundary of delivered energy

heating energy

cooling energy

electricity for lighting

fuels

BUILDING

TECHNICAL SYSTEMS

Energy use and production

System losses and conversions

electricity

cooling energy

On site renewable

energy w/o fuels

district heat

district cooling

electricity

heating energy

Solar and internal

heat gains/loads

Heat exchange

through the building envelope

NET ENERGY

NEED

DELIVERED

ENERGY

EXPORTED ENERGY

(renewable and non-renewable)

electricity for

appliances


the energy need minus heat gains, i.e. thermal energy without any system losses needed to maintain

indoor climate conditions. For the lighting and appliances electrical energy is needed.

Building technical systems supply the amount of net energy needs of heating, cooling and electrical

energy. To supply these net energy needs, building technical systems use energy and have typically

some system losses and energy conversion in some systems (i.e. heat pumps, fuel cells). The energy

used by the building technical systems is from delivered energy to the building or from on site

renewable energy (without fuels).

Delivered energy to the building is grid electricity, district heat and cooling, renewable and non-

renewable fuels. On site renewable energy without fuels is energy produced from active solar and wind

(and from hydro if available). Renewable fuels are not included in this term, because they are treated

as delivered energy to the building, i.e. off-site renewables. Energy from heat sources of heat pumps

(air, ground, water) is also renewable energy, but this information is not needed for heat pump system

and delivered energy calculations which are based on COP data of heat pumps. (However, energy

taken from heat sources of heat pumps is needed for calculation of the share of renewable energy,

which is additional information).

On site renewable energy production systems may supply other technical building systems, thus

reducing the need for the delivered energy to building, or may be directly exported to energy

networks. This is taken into account in the net delivered energy balance. Net delivered energy is

delivered minus exported energy, both expressed per energy carrier.

Primary energy use is calculated from net delivered energy, per energy carrier, as product of primary

energy factor and net delivered energy of that energy carrier.

An example of energy flow calculation (adopted from REHVA Task Force “Nearly Zero Energy

Buildings”)

Consider an nnZEB office building located in Paris with following annual net energy needs (all values

are specific values in kWh/(m2 a)):

• 3.8 kWh/(m2 a) net energy need for heating (including ventilation and DHW)

• 11.9 kWh/(m2 a) net energy need for cooling

• 21.5 kWh/(m2 a) electricity for appliances

• 10.0 kWh/(m2 a) electricity for lighting

Breakdown of the net energy need is shown in Figure 4.

The building has a gas boiler for heating with seasonal efficiency of 90%. For the cooling, free cooling

from boreholes (about 1/3 of the need) is used and the rest is covered with mechanical cooling. For

borehole cooling, seasonal energy efficiency ratio of 10 is used and for mechanical cooling 3.5.

Ventilation system with specific fan power of 1.2 kW/(m3/s) will use 5.6 kWh/(m2 a) fan energy. There

is installed a solar PV system providing 15.0 kWh/(m2 a), from which 6.0 is utilized in the building and

9.0 is exported to the grid.

Energy calculation results are shown in Figure 4, in the building technical systems box. Gas boiler with

90% efficiency results in 4.2 kWh/(m2 a) fuel energy. Electricity use of the cooling system is calculated

with seasonal energy efficiency ratios 10 and 3.5 respectively. Electricity use of free cooling, mechanical

cooling, ventilation, lighting and appliances is 39.8 kWh/(m2 a). Solar electricity of 15.0 kWh/(m

2 a)

reduces the net delivered electricity to 24.8 kWh/(m2 a). Net delivered fuel energy (caloric value of


delivered natural gas) is 4.2 kWh/(m2 a). From these two net delivered energy flows, primary energy is

calculated with the result of 66 kWh/(m2 a).

Figure 4. Calculation example of the energy flows in nnZEB office building. (Adopted from

REHVA Task Force “Nearly Zero Energy Buildings”)

System boundary of delivered energy

3.8 heating

11.9 cooling

10.0 lighting

BUILDING TECHNICAL

SYSTEMS

15.0 PV electricity,from which 6.0 used

in the building and

9.0 exported

Fuel 4.2

Electricity 33.8

Solar and internal

heat gains/loads

Heat exchange

through the

building envelope

NET ENERGY NEED

(47.2 kWh/(m2 a))

DELIVERED ENERGYBoiler

3.8/0.9 = 4.2

Free cooling

4.0/10 = 0.4 Compressor cooling

7.9/3.5 = 2.3

Lighting 10.0

Ventilation 5.6

Appliances 21.5

Primary energy:

4.2*1.0 + (33.8-9.0)*2.5 = 66 kWh/(m2 a)

EXPORTED ENERGY

System boundary of net delivered energy

Ne

t d

eli

ve

red

en

erg

y

Electricity 9.0

21.5 appliances

(Sum of electricity 39.8)

21,5

10

3,2

0,61,1

10,8

NET ENERGY NEED (47.2 kWh/(m2 a))

Appliances

(users')

Lighting

Space

heating

Heating of

air in AHU

Cooling in

room units

Cooling of

air in AHU


4 Results

4.1 Net present value calculation

Economic calculations included construction cost calculations and discounted energy cost calculation

for 30 years. Construction cost was calculated not as a total construction costs, but only construction

works and components related to energy performance were included in the cost (energy performance

related construction cost). Such construction works and components were:

• thermal insulation

• windows

• air handling units (without ductwork)

• heat supply solutions (boilers, heat pumps etc.)

In all calculated cases an under floor heating system and a hot water boiler was considered, but these

were not included in the energy performance related construction cost.

Labour costs, material costs, overheads, the share of project management and design costs, and VAT

were included in the energy performance related construction cost.

Global energy performance related cost was calculated as a sum of the energy performance related

construction cost and discounted energy costs for 30 years, including all electrical and heating energy

use.

For the energy prices, the current price levels were used as follows:

• Electricity 0.0983 €/kWh + VAT (20%)

• Natural gas 0.0395 €/kWh + VAT (20%) (consumption over 750 m3/year)

• Pellet 0.033 €/kWh + VAT (20%)

• Heating oil 0.0717 €/kWh + VAT (20%)

• District heating 0.0569 €/kWh + VAT (20%) (Tallinn, natural gas boiler)

Connection fees for electricity and heating were taken into account as follows:

• Electricity 111.85 € + VAT (20%) per 1 A

• Gas 2046 € + VAT (20%)

• District heating 2500 € VAT (20%)

For electricity connection, 20 A was considered in most of cases. In two less insulated electrically

heated cases, DH 0.76 and DH 0.96, 25 A was used.

Global energy performance related costs were calculated in the basic case with discounting interest

rate of 1% which corresponds to real interest rate of 3% and escalation of energy prices of 2%,

according to the Commission’s draft cost optimal document. This discounting interest rate, that was

used in the discounting of energy cost, is the difference between the real interest rate and the

escalation of the energy price. For example, discounting interest rate of 1.5% may correspond to real

interest rate of 3% and escalation of 1.5%, or real interest rate of 2% and escalation of 0.5%.

In order to include some safety margin into the discounting interest rate (making sure that the cost

optimal building will not underinvested in the construction phase), discounting interest rate of 0 %

corresponding to real interest rate of 3% and escalation of 3% was calculated. To show the sensitivity

to the escalation rate, discounting interest rate of 2% was used (corresponding to escalation of 1%

with the real interest rate of 3%).


As such, the global energy performance related cost has a little meaning, because the basic

construction cost is not included. The difference in the global energy performance related cost can be

used for ranking of calculation cases. The case with the lowest global energy performance related cost

represents the cost optimal for 30 year period studied. The cost difference can be calculated also

relative to business as usual (BAU) construction, if BAU is well established. If so, a global additional

energy performance related cost can be either negative if BAU is not cost optimal, or positive if the

case studied leads to higher global cost than BAU.

4.2 Results for detached houses

The results are calculated for the reference detached house with heated net floor area of 178.6 m2,

Figure 5 and 6. The garage is considered as not heated and it is not included in the heated net floor

area. The reference house has 3 bedrooms and is intended for 4 persons.

Figure 5. Plans of 2-storey reference detached house with heated net floor area of 178.6 m2.


Figure 6. IDA-ICE building simulation model of the reference detached house.

Analyses were conducted for four construction concepts, where the building envelope and ventilation

system energy performance levels were varied as shown in Table 1. These construction concepts are

marked with the specific heat loss value, i.e. DH 0.42 means the reference detached house with the

specific heat loss of 0.42 W/(m2 K). The specific heat loss includes transmission losses through the

building envelope and infiltration losses, and is calculated per heated net floor area. DH 0.42

construction concept represents the best available technology which may be associated with nearly

zero energy buildings. DH 0.96 represents business as usual construction.


Table 1. Construction concepts for the reference detached house of 178.6 m2.

DH 0.42

“Nearly zero”

DH 0.58

“Low”

DH 0.76

DH 0.96

“BAU”

Specific heat

loss coefficient

H/A, W/m2K

0.42 0.58 0.76 0.96

External wall

170 m2

20cm LECA block, plaster

+ 35cm EPS-insulation

U 0.1 W/m2K



U 0.14 W/m2K



U 0.17 W/m2K



U 0.23 W/m2K

Roof

93 m2

Wooden beams, metal

sheet, 80cm min.wool

insulation, concrete slab

U 0.06 W/m2K

Wooden beams, metal



U 0.09 W/m2K

Wooden beams, metal



U 0.14 W/m2K

Wooden beams, metal



U 0.18 W/m2K

Ground floor

93 m2

Concrete slab on ground,

70cm EPS insulation

U 0.06 W/m2K


45cm EPS insulation

U 0.09 W/m2K


25cm EPS insulation

U 0.14 W/m2K


18cm EPS insulation

U 0.18 W/m2K

q50, m3/(hm

2) 0.6 1.0 1.5 3.0

Windows

48 m2

glazing/frame/total

4mm-16mmAr-SN4mm-

16mmAr-SN4mm

Insulated frame

0.6/0.7 W/m2K

0.7 W/m2K

4mm-16mmAr-4mm-

16mmAr-SN4mm

Insulated frame

0.8/0.8 W/m2K

0.8 W/m2K

4mm-16mm-4mm-

16mmAr-SN4mm

1.0/1.3 W/m2K

1.1 W/m2K

4mm-16mmAr-

SN4mm

Common frame

1,1/1,4 W/m2K

1,2 W/m2K

g-value 0.46 0.5 0.55 0.63

Ext. door, 6 m2 U 0.7 W/m

2K U 0.7 W/m

2K U 0.7 W/m

2K U 0.7 W/m

2K

Ventilation l/s, SFP, AHU HR

80 l/s, SFP 1.5

kW/(m3/s), AHU HR

85%

80 l/s, SFP 2.0

kW/(m3/s), AHU HR

80%

80 l/s, SFP 2.0

kW/(m3/s), AHU HR

80%

70 l/s, SFP 2.0

kW/(m3/s), AHU HR

80%

Heating

capacity, kW 5 6 8 9

Cooling

capacity, kW 5 5 5 8

Net energy need kWh/(m2 a)

Space heating 21.3 35.3 52.8 68.5

Ventilation

heating 3.9 5.5 5.5 5.5

Domestic hot

water 28.1 28.1 28.1 28.1

Cooling 13 10.6 8.8 14.4

Fans and

pumps 7.6 8.4 9.6 9.6

Lighting 7 7 7 7

Appliances 18 18 18 18

Total net

energy need 98.9 112.9 129.8 151.1

Table 1 shows also simulated net energy needs. Depending on heating and cooling systems, delivered

and primary energy use can be calculated. For each construction concept, the following heating

systems were considered:

• ground source heat pump


• air to water heat pump

• district heating

• electrical heating

• gas boiler

• oil boiler

• pellet boiler

Delivered energy use was calculated for these heating systems, by dividing net energy needs with

relevant system efficiency. System efficiency values (combined efficiency of the generation and

distribution) are shown in Table 2. To calculate the combined efficiency, floor heating distribution is

considered according to Estonian method with average distribution efficiency of 0.9, which is included

in the combined efficiency values in Table 2.

Table 2. System efficiencies for delivered energy calculation.

Heat source (under floor heating)

Generation and distribution combined efficiency, -

Space heating/cooling Domestic hot water Gas/oil condensing boiler 0.86 0.83

Pellet boiler 0.77 0.77

Air to water heat pump 1.98 1.62

Electrical heating 0.90 0.90

Ground source heat pump 3.15 2.43

District heating 0.90 0.90

Cooling (electricity) 3.0

Highly insulated DH 0.42 and 0.58 cases are calculated with solar collectors with the size of 6 m2,

providing an half of domestic hot water. Other cases are calculated without solar collectors. Primary

energy values (ET-values), calculated with Estonian primary energy factors for all construction concepts

and heating systems, are shown in Figure 7.

Figure 7. Primary energy values (ET-values)in the reference detached house for all

combination of construction concepts and heating systems.

0

50

100

150

200

250

Gas/oil Pellet AWHP GSHP Electricity Distr. h.

Pri

ma

ry e

ne

rgy

, E

T-v

alu

e,

kW

h/

(m2

a)

DH 0.42

DH 0.58

DH 0.76

DH 0.96

min. req. 180


Global energy performance related costs (explained in Ch. 4.1) are shown in Figure 8 and 9 for

discounted interest rate of 1 % that corresponds to real interest rate of 3% and escalation of 2%. The

global cost is presented as an additional cost compared to the business as usual construction concept

DH 0.96 with gas boiler, just complying the minimum requirement of 180 kWh/(m2 a) primary energy.

According to the results, the cheaper energy sources, district heating and gas achieve the lowest NPV

of the global additional cost with relatively high primary energy use. The lowest NPV defines the cost

optimal performance level which is achieved for district heating DH 0.76 construction concept with

primary energy of about 140 kWh/(m2 a). The global cost is marginally higher for gas heating which

achieves the lowest NPV value for DH 0.76 and DH 0.96 cases with primary energy of about 160–180

kWh/(m2 a).

If district heating or gas supply are not available, the cost optimal primary energy use will significantly

dropped down in both heat pump and oil heating cases. Therefore, for building sites without district

heat or gas supply, the cost optimal is achieved with ground source heat pump DH 0.96 construction

concept with primary energy of about 120 kWh/(m2 a). At that primary energy level the cost curve of

ground source heat pump is lower than that of gas heating, but still 18 €/m2 NPV higher compared to

district heating.

Figure 8. Global energy performance related costs in the reference detached house calculated

with discounting interest rate of 1% (the real interest rate of 3% and the escalation 2%) and

30 years time period. (AWHP – air to water heat pump, GSHP – ground source heat pump,

DH – district heating.) For each heating system, from left to right DH 0.42, 0.58, 0.76 and

0.96 cases are shown. Two last points of the electrical heating are out of the range of the

chart, being (200 kWh/(m2 a);153 €/m

2) and (226 kWh/(m

2 a);188 €/m

2).

-50

0

50

100

150

50 100 150 200

Glo

ba

l ad

dit

ion

al e

ne

rgy

pe

rfo

rma

nce

co

st (

NP

V),

€/m

2

Primary energy, ET-value, kWh/(m2 a)

Gas

Pellet

AWHP

GSHP

Electric

Oil

DH


The results show that for cheaper energy sources the cost optimal of 140 and 160 kWh/(m2 a) was

achieved without solar collectors, (as well as without solar PV which is not cost efficient without feed in

tariff or investment support) and in relatively low thermal insulation level. Thus, this cost optimal

energy performance is still quite far from nearly zero energy performance level. Improved thermal

insulation level and solar collectors became cost effective for air to water heat pump, oil heating and

electrical heating.

It is important to notice that the additional global cost is less than additional investment cost, because

of reduced cost of energy use. The breakdown of global cost components is shown in Figure 9. It can

be seen that an additional investment cost of improved thermal insulation is about 13 000 € and air

handling unit 2 000 € from DH 0.96 to DH 0.42 construction concept. This 15 000 € investment drops

primary energy to about 75 kWh/(m2 a) in the ground source heat pump case and corresponds to

7 100 increase in NPV. For nearly zero energy building, this has to be supported with relevant solar PV

installation. If 5 kW solar PV installation with about 25 000 € investment cost is considered, this will

result in about 4500 kWh/a electricity generation (about 25 kWh/(m2 a)) corresponding to 1.5*25=37,5

kWh/(m2 a) primary energy reduction, leading to the performance level of nearly zero energy building

of about 40 kWh/(m2 a) primary energy and extra investment cost of about 40 000 € (224 €/m

2).

The results are sensitive to the interest rate. Figure 10 shows the effect of higher energy cost escalation

– discounting interest rate of 0% (real interest rate of 3% and escalation 3%). This interest rate will shift

the cost optimal to the left to the lower primary energy use. Negative NPV values compared to BAU

mean that the better construction standard can save some global cost. The cost optimal curves have

become more flat especially for gas, district heating and ground source heat pump. For gas and district

heating, the global cost is within 5 €/m2 for the primary energy range of 120–160 kWh/(m

2 a). Thus this

interest rate would allow to suggest 120 kWh/(m2 a) primary energy as cost optimal performance level.

For discounting interest rate of 2% (the real interest rate of 3% and the escalation 1%), the cost

optimal is generally shifted to the right, i.e. the cases with lower investment cost and higher primary

energy use became cost optimal, Figure 11.


Figure 9. Breakdown of the global energy performance related costs for three heating system.

Interest rate of 1 % (the real interest rate of 3% and escalation2%) and 30 years time period.

First four categories from left are construction cost components and two last categories NPV

of energy cost.

30602

26245

21167

17611

5474

3445

3445

3445

9373

9373

9373

9373

4479

4479

0

0

8766

12205

19273

22735

20920

20920

21260

21260

0 20000 40000 60000 80000 100000

DH 0.42

DH 0.58

DH 0.76

DH 0.96

NPV, €

Gas

Building envelope

Ventilation units

Gas boiler

Solar collectors 6m2

Energy cost for heating

Energy cost for electricity

30602

26245

21167

17611

5474

3445

3445

3445

15542

15542

15542

15542

4479

4479

0

0

7806

10612

17033

19857

20920

20920

21260

21260

0 20000 40000 60000 80000 100000

DH 0.42

DH 0.58

DH 0.76

DH 0.96

NPV, €

Ground source heat pump

Building envelope

Ventilation units

Ground source heat pump




30602

26245

21167

17611

5474

3445

3445

3445

7215

7215

7215

7215

4479

4479

0

0

8688

12141

19124

22599

20920

20920

21260

21260

0 20000 40000 60000 80000 100000

DH 0.42

DH 0.58

DH 0.76

DH 0.96

NPV, €

District heat

Building envelope

Ventilation units

District heating substation





Figure 10. The same results as in Figure 8, but with the interest rate of 0% (the real interest

rate of 3% and escalation of 3%).

Figure 11. The same results as in Figure 8, but with the interest rate of 2% (the real interest

rate of 3% and escalation of 1%).

-50

0

50

100

150

50 100 150 200

Glo

ba

l ad

dit

ion

al e

ne

rgy

pe

rfo

rma

nce

co

st (

NP

V),

€/m

2


Gas

Pellet

AWHP

GSHP

Electric

Oil

DH

-50

0

50

100

150

50 100 150 200

Glo

ba

l ad

dit

ion

al e

ne

rgy

pe

rfo

rma

nce

co

st (

NP

V),

€/m

2


Gas

Pellet

AWHP

GSHP

Electric

Oil

DH


As a conclusion, primary energy ET= 120 kWh/(m2 a) can be proposed for the cost optimal energy

performance level for the reference detached house, if a small safety marginal of 5 €/m2 global cost

and escalation of 3% are used (Figure 10). ET= 120 kWh/(m2 a) is achievable with any heating system

studied. Compared to business as usual construction according to minimum requirement of ET= 180

kWh/(m2 a), this will lead to marginal 2.5 €/m

2 global cost increase.

Because of still far from zero energy, these cost optimal levels may be proposed most likely for low

energy building category C. Nearly zero energy performance level is not cost optimal with current

prices and may be defined through technically reasonable achievable level with current best practices

and renewable on site energy production. The lowest ET value, achieved with DH 0.42 with ground

source heat pump was about ET=75 kWh/(m2 a), which can be reduced with PV electricity production.

Therefore ET=40 kWh/(m2 a) was achievable for the reference detached house. The distance from

cost optimal to nearly zero energy performance level was about 224 €/m2 upfront investment cost

that corresponded to about 20% extra construction cost.

Given values (120 and 40) apply for the reference detached house and do not include any building size

and architecture related (compactness, No of floors, glazing size, etc.) safety margin which has to be

included in the final values. A factor of 1.15 may be proposed for final values.


4.3 Results for apartment building

The results are calculated for the reference apartment building with heated net floor area of 1796 m2,

Figure 12–14. The building consists of 22 apartments intended for 62 persons.

Figure 12. Plans of the reference apartment building for ground floor and 4th

floor.

Figure 13. Plans of the reference apartment building for 2nd

floor and 3rd

floor.


Figure 14. IDA-ICE building simulation model of the reference apartment building.



marked with the specific heat loss value, i.e. AB 0.23 means the reference apartment building with the

specific heat loss of 0.42 W/(m2K), including transmission losses through building envelope and

infiltration and calculated per heated net floor area. AB 0.23 construction concept represents the best

available technology which may be associated with nearly zero energy buildings. AB 0.96 represents

business as usual construction.


Table 3. Construction concepts for the reference apartment building of 1796 m2.

AB 0.23

“Nearly zero”

AB 0.32

“Low”

AB 0.43

AB 0.52

“BAU“

Specific heat

loss coefficient

H/A, W/m2K

0.231 0.315 0.431 0.521

External wall

591 m2



U 0.1 W/m2K



U 0.14 W/m2K



U 0.17 W/m2K



U 0.23 W/m2K

Roof

449 m2

Wooden beams, metal



U 0.06 W/m2K

Wooden beams, metal



U 0.09 W/m2K

Wooden beams, metal



U 0.14 W/m2K

Wooden beams, metal



U 0.18 W/m2K

Floor

449 m2


70cm EPS insulation

U 0.06 W/m2K


45cm EPS insulation

U 0.09 W/m2K


25cm EPS insulation

U 0.14 W/m2K


18cm EPS insulation

U 0.18 W/m2K

q50, m3/(hm

2) 0.6 1.0 2.0 3.0

Windows

433 m2

glazing/frame/total

U, W/m2K

4mm-16mmAr-SN4mm-

16mmAr-SN4mm

Insulated frame

0.6/0.7 W/m2K

0.7 W/m2K

4mm-16mmAr-4mm-

16mmAr-SN4mm

Insulated frame

0.8/0.8 W/m2K

0.8 W/m2K

4mm-16mm-4mm-

16mmAr-SN4mm

1.0/1.3 W/m2K

1.1 W/m2K

4mm-16mmAr-

SN4mm

Common frame

1,1/1,4 W/m2K

1,2 W/m2K

g-value 0.46 0.5 0.55 0.63

Ventilation l/s, SFP, AHU HR

1114 l/s*1), SFP 1.5

kW/(m3/s), AHU HR

85%

1114 l/s*1), SFP 1.7

kW/(m3/s), AHU HR

80%

1114 l/s*1), SFP 2.0

kW/(m3/s), AHU HR

80%

1114 l/s*1), SFP 2.0

kW/(m3/s), AHU HR

70%

Heating capa-

city, kW (te -21oC)

46 52 59 65

Cooling capacity,

kW 48 50 51 70


Space heating 7.1 13.0 21.9 28.4

Ventilation

heating 4.7 6.6 6.9 7.0

Domestic hot

water 35.6 35.6 35.6 35.6

Cooling 11.3 9.9 8.6 14.5

Fans and

pumps 8.9 9.9 11.6 11.6

Lighting 7.0 7.0 7.0 7.0

Appliances 22.3 22.3 22.3 22.3

Total net

energy need 96.9 104.3 113.9 126.4


and primary energy use can be calculated. For each construction concept, the following heating



• gas boiler


• oil boiler

• pellet boiler






distribution) are shown in Table 4. To calculate the combined efficiency, radiator distribution is

considered according to Estonian method with average distribution efficiency of 0.97, which is

included in the combined efficiency values in Table 4.


Heat source (radiator heating)


Space heating/cooling Domestic hot water District heat 0.97 0.97

Gas/oil condensing boiler 0.92 0.89







4.4 Results for office building

The results are calculated for the reference four storey office building with modeled heated net floor

area of 2750 m2, Figure 15–17.

Figure 15. Plans of the reference office building for 2nd

floor.

Figure 16. Plans of the reference office building for 4th

floor.


Figure 17. IDA-ICE building simulation model of the reference office building.



marked with the specific heat loss value, i.e. AB 0.23 means the reference apartment building with the

specific heat loss of 0.42 W/(m2K), including transmission losses through building envelope and

infiltration and calculated per heated net floor area. AB 0.23 construction concept represents the best

available technology which may be associated with nearly zero energy buildings. AB 0.96 represents

business as usual construction.


Table 5. Construction concepts for the reference office building of 2750 m2.

OB 0.25

“Nearly zero”

OB 0.33

“Low”

OB 0.45

OB 0.55

“BAU“

Specific heat

loss coefficient

H/A, W/m2K

0.245 0.334 0.454 0.548

External wall

1098 m2



U 0.1 W/m2K



U 0.14 W/m2K



U 0.17 W/m2K



U 0.23 W/m2K

Roof

621 m2

Wooden beams, metal



U 0.06 W/m2K

Wooden beams, metal



U 0.09 W/m2K

Wooden beams, metal



U 0.14 W/m2K

Wooden beams, metal



U 0.18 W/m2K

Floor

606 m2


70cm EPS insulation

U 0.06 W/m2K


45cm EPS insulation

U 0.09 W/m2K


25cm EPS insulation

U 0.14 W/m2K


18cm EPS insulation

U 0.18 W/m2K

q50, m3/(h m

2) 0.6 1.0 2.0 3.0

Windows

715 m2

glazing/frame/total

U, W/m2K

4mm-16mmAr-SN4mm-

16mmAr-SN4mm

Insulated frame

0.6/0.7 W/m2K

0.7 W/m2K

4mm-16mmAr-4mm-

16mmAr-SN4mm

Insulated frame

0.8/0.8 W/m2K

0.8 W/m2K

4mm-16mm-4mm-

16mmAr-SN4mm

1.0/1.3 W/m2K

1.1 W/m2K

4mm-16mmAr-

SN4mm

Common frame

1,1/1,4 W/m2K

1,2 W/m2K

g-value 0.46 0.5 0.55 0.63

Ventilation m

3/s, SFP, AHU HR

4.6 m3/s, SFP 1.5

kW/(m3/s), AHU HR

80%

4.6 m3/s, SFP 1.7

kW/(m3/s), AHU HR

75%

4.6 m3/s, SFP 2.0

kW/(m3/s), AHU HR

75%

4.6 m3/s, SFP 2.0

kW/(m3/s), AHU HR

75%

Heating capa-

city, kW (te -21oC)

151 160 172 181

Cooling capacity,

kW 155 156 160 193


Space heating 5.8 11.4 21.9 29.0

Ventilation

heating 2.8 4.1 6.2 6.4

Domestic hot

water 7.4 7.4 7.4 7.4

Cooling 32.9 30.9 28.9 37.8

Fans and

pumps 7.3 7.9 10.9 10.9

Lighting 18.9 18.9 18.9 18.9

Appliances 23.7 23.7 23.7 23.7

Total net

energy need 98.8 104.3 117.9 134.1


and primary energy use can be calculated. For each construction concept, the following technical




• gas boiler

• oil boiler

• pellet boiler






distribution) are shown in Table 6. To calculate the combined efficiency, radiator distribution is

considered according to Estonian method with average distribution efficiency of 0.97, which is

included in the combined efficiency values in Table 6.


Heat source (radiator heating)


Space heating/cooling Domestic hot water District heat 0.97 0.97

Gas/oil condensing boiler 0.92 0.89






Primary energy values (ET-values), calculated with Estonian primary energy factors for all construction

concepts and heating systems, are shown in Figure 18. All values are much lower compared to the

minimum requirement of 220 kWh/(m2 a) showing that business as usual construction with reasonable

massing and glazing leads to significantly improved energy performance.

Figure 18. Primary energy values (ET-values)in the reference office building for all

combination of construction concepts and technical systems.

0

20

40

60

80

100

120

140

160

180

200

220

Gas/oil Pellet AWHP GSHP Electricity Distr. h.

Pri

ma

ry e

ne

rgy

, E

T-v

alu

e,

kW

h/

(m2

a)

OB 0.25

OB 0.33

OB 0.45

OB 0.55

min. req. 220


Cost optimal results shown in Figure 19 for discounting interest rate of 1% (real interest rate of 3% and

escalation of 2%) suggest that business as usual thermal insulation of building envelope leads to cost

optimal with district heating at around 140 kWh/(m2 a) primary energy. Global cost differences are

generally smaller between the most of cases compared to residential buildings. The breakdown of

global cost components is shown in Figure 20.

Figure 19. Global energy performance related costs in the reference office building

calculated with discounting interest rate of 1% (the real interest rate of 3% and the escalation

2%) and 30 years time period. (AWHP – air to water heat pump, GSHP – ground source heat

pump, DH – district heating.) For each technical system, from left to right OB 0.25, 0.33, 0.45

and 0.55 cases are shown.

-30

0

30

60

90

90 110 130 150 170

Glo

ba

l ad

dit

ion

al e

ne

rgy

pe

rfo

rma

nce

co

st (

NP

V),

€/m

2


Gas

Pellet

AWHP

GSHP

Electric

Oil

DH


Figure 20. Breakdown of the global energy performance related costs for most typical technical

systems. Interest rate of 1 % (the real interest rate of 3% and escalation2%) and 30 years time period.

First four categories from left are construction cost components and two last categories NPV of energy

cost.

For nZEB performance level, on site renewable energy production has to be added for cases with

highest energy performance. Results calculated with solar PV show that primary energy of about 105

kWh/(m2 a) is achievable with most technical solutions studied. As solar PV can produce in office

buildings at least 15 kWh/(m2 a) primary energy, nZEB performance level of about 90 kWh/(m

2 a)

primary energy can be proposed.

333195

289806

259851

222201

52152

52152

52152

52152

50318

50318

59722

59722

43138

43138

0

0

34622

49323

76170

91723

356422

356032

369695

387067

0 200000 400000 600000 800000 1000000

OB 0.25

OB 0.33

OB 0.45

OB 0.55

NPV, €

Gas

Building envelope

Ventilation units

Gas boiler




333195

289806

259851

222201

52152

52152

52152

52152

19000

19000

19000

19000

43138

43138

0

0

33970

48620

75372

90871

356422

356032

369695

387067

0 200000 400000 600000 800000 1000000

OB 0.25

OB 0.33

OB 0.45

OB 0.55

NPV, €

District heat

Building envelope

Ventilation units

District heating substation





5 Conclusions

Global cost calculations for construction concepts from business as usual construction to passive

house building envelope level combined with all possible technical systems showed that cost optimal

in the reference detached house was between ET= 120-140 kWh/(m2 a) primary energy and in

reference office buildings about ET= 140 kWh/(m2 a) primary energy.

In the reference detached house, ET= 120 kWh/(m2 a) was possible to select for the cost optimal

energy performance level, when accepting a small increase of 5 €/m2 in global cost and escalation of

3% (Figure 10). ET= 120 kWh/(m2 a) was achievable with any heating system studied. Compared to

business as usual construction according to minimum requirement of ET= 180 kWh/(m2 a), this led to

marginal 2.5 €/m2 global cost increase. When compared with passive house standard, the cost optimal

value is exactly the same that is required for passive houses (120 kWh/(m2 a) primary energy) in

Central European climate, but was achieved with water based heating systems with most cost

efficiently.

In residential buildings, the cost optimal performance level is reasonably lower that the current

minimum requirement of 180, but in the office buildings the current requirement of 220 is much

higher compared to cost optimal value. Because of still far from zero energy, the cost optimal levels

may be proposed for low energy building category B or C in the energy performance certificate scale

Nearly zero energy performance level is not yet cost optimal with current prices and is suggested to be

defined through technically reasonable achievable level with current best practices and renewable on

site energy production. With reasonable amount of PV electricity production ET=40 and ET=90

kWh/(m2 a) were achieved for the reference detached house and office buildings respectively. In the

detached house, the distance from cost optimal to nearly zero energy performance level was about

224 €/m2 upfront investment cost that corresponded to about 20% extra construction cost. In offices,

the extra construction cost was smaller, estimated to be about 10%.

To determine the final cost optimal and nZEB performance levels a safety margin taking into account

the building compactness and other architecture and energy supply related factors has to be used.

With a safety margin factor of 1.15 the values shown in Table 7 may be proposed.

Table 7. Proposed cost optimal and nZEB energy performance levels.

nZEB Cost optimal Current req.

kWh/(m2 a) kWh/(m

2 a) kWh/(m

2 a)

primary energy primary energy primary energy

Detached house 50 140 180

Apartment building 70 130 150

Nursing home 130 200 300

Day care centre 140 200 300

School building 80 120 300

Office buildings 100 150 220

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