Low-energy residential housing

ENE G't AND

BUILDINGS ELSEVIER

Energy and Buildings 21 (1994) 187-197

Low-energy residential housing Jyri Nieminen Technical Research Centre of Finland (VTT), Building Technology P.O. Box 18011 FIN-02044 ~

Espoo, Finland

Abstract Designs for houses with heating energy consumption 75%, 50%, 25% and less of the consumption of a standard small house that fulfils the current building regulations in Finland were developed. Over thirty concepts of heating energy consumption and energy-saving costs were analysed. The results of the theoretical studies have been applied to various experimental building projects. One of the most important projects is the Finnish demonstration house for IEA Task 13 "Advanced solar low-energy houses". The total yearly consumption of purchased electricity is estimated at about 20 kWh/m2 which is below 10% of the current average level in small houses in Finland. Keywords: Low-energyhousing; Heating energy consumption; Solar house; IEA solar programme

1. Introduction The consumption of energy in the production and use of buildings accounts for a fairly large (30-40%) proportion of total energy use in Finland, and a large percentage of that energy use has to be produced using imported fuels or electrical energy. T h e potential of saving energy in buildings is significant. The objective of the low-energy residential housing project has been to create low-energy concepts featuring lower energy consumption than is the case with small houses of the present day. Designs for houses with different heating energy consumption levels were developed. The heating energy consumption and costs of energy conservation of concepts with different technologies and building structures were analysed. The results of the theoretical study were then applied to various demonstration building projects. The main emphasis in these projects has been on finding economically sustainable concepts for reducing the heating energy consumption of buildings. The l E A Task 13 "Advanced Solar Low-Energy Houses" of the International Energy Agency's Solar Heating and Cooling Programme was established to promote international cooperation in the design, testing and use of buildings and components that make use of solar energy. The objective is to minimize the amount of purchased energy and at the same time to achieve a good indoor climate. Eleven countries in Europe, the E u r o p e a n Community as well as USA, Canada and Japan are participating

0378-7788/94/$07.00 © 1994 Elsevier Science S.A. All rights reserved SSDI 0378-7788(94)00897-S

in the study. The objective of the participating countries is to design and build at least one building that utilizes solar energy. The Finnish l E A Task 13 demonstration house, IEA5 Solar House, has been designed within the framework of the international collaboration. The objective of the IEA5 Solar House is to examine what is possible using present technology or new technology based on recognized construction principles in Finnish climatic conditions. The house was a showpiece at Pietarsaari housing fair and open for public viewing in July-August, 1994.

2. Heating energy consumption and energy-saving measures The means of saving heating energy can be divided into those that reduce heat losses and those that make use of free sources of energy. The selection of the means depends essentially on the objectives pursued in realizing the savings. Table 1 compiles the different solutions in the various low-energy house concepts to reach the target levels of heating energy consumption. A house of 120 m 2 of heated space that fulfils the current building regulations was used as a reference. This house consumes about 160 kWh of heating energy per m 2 of heated space a year in the climate of Jyv~iskyl~i in central Finland (heating degree-days 5050, base 17 °C) [1,21.

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J. Nieminen / Energy and Buildings 21 (1994) 187-197

The heating energy consumption of the standard house can be halved by reducing heat losses. Such measures include improving the thermal insulation of the building envelope, better windows and installation of heat recovery equipment in the ventilation system. When seeking an even lower level of consumption, free sources of energy must be considered. Fig. 1 presents the share of the total heat losses represented by the different consumption components of the energy used to heat the standard house and a house that consumes about 25% of the consumption. The Figure shows that the proportion of the different consumption components does not change significantly when different measures are applied in a balanced manner [3]. The profitability of various energy-saving concepts shown in Table 1 was examined in terms of the building's annual costs compared to the reference house, Table 2. According to the results, the most economically viable means of saving energy are those that reduce heat losses at current energy prices in Finland. In general, Finnish small houses are built better than the building regulations require, Table 3. An average small house in southern Filand would need about 120 kWh of heating energy per heated m 2 a year [4].

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E n e r g y price of e c o n o m i c concept

100

75/1 75/2 75/5 75/6 75/7 75/8 75/9 75/10 75/11 75/12

18000 12000 77000 106000 106000 114000 159000 318000 71000 71000

1100 840 5800 8100 8400 8800 11800 24000 5400 5400

470 340 5300 7800 7600 8100 11300 23400 4900 4500

-750 - 680 4300 7300 7500 6800 10400 22300 3900 3100

-3300 - 2700 2400 6200 6500 4200 8500 20200 2000 400

35 35 160 360 250 250 375 750 150 120

50/1 50/2 50/5 50/7 50/8 50/9

43000 85000 73000 35000 35000 85000

1900 5700 4300 1500 1700 6040

600 4800 3000 140 520 4920

- 2100 2900 600 - 2600 - 1900 2700

- 7300 - 900 - 3600 - 8200 - 6700 - 1800

30 90 60 25 30 80

25/1 25/6 25/7 25/8

148000 124000 78000 81000

9800 8200 3800 4200

7900 6300 1900 2200

4100 2500 - 1900 - 1000

-2700 -5100 - 5700 - 8900

80 65 40 40

IEA 1 IEA 2 IEA 3

100000 145000 110000

4000 8200 4000

2000 6100 2700

- 2200 2000 - 1400

-- 10400 - 6200 - 9600

35 60 40

3.1. Design

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Cost effects (FIM)

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Table 2 Cost effects ( e x t r a costs), a n n u a l costs a n d e n e r g y p r i c e s o f e c o n o m i c concepts. Level of b u i l d i n g costs M a y 1990, i n t e r e s t r a t e 5%, b u i l d i n g v o l u m e 500 m 3 a n d service life 45 years. C u r r e n t a v e r a g e p r i c e of electrical e n e r g y is b e t w e e n 30 a n d 35 F i n n i s h p e n n i e s (0.3-0.35 FIM)

3. Low-energy demonstration houses

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Tables 4 and 5 and Figs. 2-5 show the key features of three Finnish low-energy houses. All the houses are wood-framed one-family houses insulated with rock wool insulation. Two of them are built on site (Lappeenranta and Rovaniemi) and one of prefabricated large units (Espoo). A fireplace is a very typical component in the Finnish small houses. Modem fireplaces can be considered as an energy-saving measure (domestic fuel, very often free) if they are operated efficiently. Fireplaces can be used to reduce the peak power demand of houses which is a very important feature of saving energy. Especially in the Rovaniemi house, the fireplace will be utilized in the heating of the house. Table 5 compiles the energy-saving measures and estimated heating energy consumption in the houses. In each of the houses the main emphasis has been on reducing the consumption-purchased energy for heating the house. The strategy of saving energy has been to

190

J. Nieminen / Energy and Buildings 21 (1994) 187-197

Table 3 Typical Finnish small houses. The standard house corresponds to the National Building Code requirements, with mineral wool insulation Building type

Component

Insulation thickness

U-value (W/m2K)

(mm) Standard house

Wall Floor • Roof Window Door Ventilation

Existing houses

Wall Roof Floor" Window Door Infiltration Ventilation

Air change

Heat recovery

(lrn)

(%)

0.28 0.36 0.22 2.1 0.7 0.5 150-250 200-350 100

0.28-0.17 0.22-0.13 0.24 1.8 0.7 0.2-0.3 0.5

(60)

"Slab on ground. Insulation beneath the slab. Table 4 T h r e e low-energy demonstration houses. The heating degree-days (base 17 °C) of each location is given in parenthesis Building

Component

Insulation thickness

U-value (W/m 2 K)

(ram) Lappeenranta (4734) Year built 1993 H e a t e d area 140 m 2

Wall Floor (crawl space) Roof Window Door Ventilation

250 350 400

0.17 0.13 0.11 1.8 0.7

Espoo (4366) Year built 1991 H e a t e d area 164 m 2

Wall Floor (slab on ground) Roof Door Window Infiltration Ventilation

300 150 500

0.14 0.19 0.09 0.7 1.2

Wall Floor (slab on ground) Roof Window Door Ventilation

280 200 500

Rovaniemi (6434) Year built 1993 H e a t e d area 125 m 2

Air change (I/h)

Heat recovery (%)

0.5

0.1 0.6

80

0.5

60"

0.17 0.15 0.09 0.9 0.7

"Efficiency of the heat exchanger. Effect of circulation air not included.

minimize the heat losses using the latest existing technology available on the market.

3.2. Energy consumption Measured data is available only from the Espoo house where the two-year monitoring period finished in July 1993. The results show that the measured heating energy consumption was only 35% of the estimated consumption of a standard house and 47% of the measured average consumption of ten normal houses located in the same area (Figs. 6 and 7) [5-7].

The consumption of household electricity in the Espoo house and reference houses is shown in Fig. 8. The breakdown of different consumption components is also shown in Fig. 9. The total energy consumption was 151 kWh/m 2 a year in 1992 which is about 60% of the average consumption in the reference houses. This can be explained by the user habits and the number of occupants in the houses (five in the low-energy house and an average of 3.9 in the reference houses). Especially the gross energy consumption by the hot water heater has been fairly high in 1992 (6240 kWh or 1250 kWh/ person or 38 kWh/m 2 compared to 4330 kWh or 1110

J. Nieminen / Energy and Buildings 21 (1994) 187-197

191

Table 5 Energy-saving measures and target levels of heating energy consumption in the three demonstration houses House

Energy-saving measures

Energy consumption (kWh/m2)

Lappeenranta

Improved thermal insulation Airtight building envelope 1000 litre water tank charged using nighttime electricity Fireplace

lO0

Espoo

Super insulation Airtight building envelope Good windows (U= 1.2 W/m2K) Ventilation heat recovery (thermal efficiency 80%)

60

Rovaniemi

Super insulation Airtight building envelope Superwindows (U= 1.0 W/m2K) Ventilation heat recovery exploiting circulation air from above the fireplace

50

Fig. 2. Low-energy house in Lappeenranta. The house is built of pre-cut timber with rock wool insulation.

Fig. 3. Low-energy house in Espoo. The house is built of large prefabricated wall units. The wooden frame of the house consists of two 50 mm×50 mm studs with insulation between the studs.

Fig. 4. Low-energy house in Espoo.

Fig. 5. Low-energy-house in Rovaniemi. The site-built wooden frame of the house is covered on the outside with a gypsum board and an additional layer of rigid rock wool with a windproofing plasticfibre fabric surface.

3.3. Airtightness kWh/person or 28 kWh/m2). The total water usage in the Espoo house was as high as 106 litres per day per person.

In a cold climate, ventilation is the largest single component causing heat losses. In order for the balanced

J. Nieminen / Energy and Buildings 21 (1994) 187-197

192 20. []

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Fig. 6. The heating energy consumption by the Espoo house and average consumption by reference houses [5-7].

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11/1991 - 6/1993

Fig. 7. Measured monthly heating energy consumption by the Espoo house from November 1991 to June 1993 [7].

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Fig. 8. Consumption of household electricity in the Espoo house and the minimum, average and maximum consumptions in the reference houses [6].

HVAC

SAUNA

Fig. 9. The breakdown of different energy consumption components in the Espoo house [7].

ventilation system to work properly, it is of the utmost importance that the building's envelope is tightly sealed. There is a rough rule of thumb that the infiltration rate (air leakages) in an unoccupied small house with no mechanical ventilation system may be 3-11)% of the building envelope's air leakage rate measured at 50 Pa pressure difference. To reduce the building's heating energy demand, uncontrolled ventilation (air leakages) should be minimized. If the objective is to reduce the building's heating energy consumption to less than half of the consumption of a normal house, 0.1 1/h can be considered the recommended maximum value for the air leakage rate. This gives a requirement of 1.0-1.5 1/h for the airtightness of the building envelope. The airtightness of normal Finnish wooden small houses at 50 Pa pressure difference is typically between 3 and 4 1/h. In the demonstration houses the air leakage rates are between 1 and 2 1/h which is slightly above the acceptable level (with the exception of the IEA5 house where the air leakage rate was 0.8 1/h at 50 Pa). More attention should have been paid on the sealing of the envelope structures. In the Espoo house it was clearly seen that the present typical installation and sealing techniques for a timber house built from prefabricated units should be improved when a thermal insulation layer is to be made thicker. Many of the present sealing techniques are not suitable for superinsulated wooden structures where the building frame is thermally broken as each structural jointing. In general, airtightness of the envelope comes from simple structural solutions. Fig. 10 shows an example of how to built an airtight construction for an external wall-upper floor connection in a two-storey small house. In the Rovaniemi case the vapour barrier goes continuously from the lower floor level to the top of the wall. Supports for the upper floor are fixed on top of the vapour barrier. In the Lappeenranta house the upper-floor supports are forced into the load-bearing

Z Nieminen / Energy and Buildings 21 (1994) 187-197

193

centration in the basement was caused by bad ventilation. The ventilation rate was increased after the measurements.

3.5. Energy-saving costs The payback time of extra building costs of the Espoo house compared to existing buildings (Table 3) is shown in Fig. 11. At the current price of energy, the payback time is less than six years which can be regarded as very acceptable.

4. Solar house IEA5: the Finnish IEA Task 13 demonstration house

4.1. Energy-saving principles in the building

Fig. 10. Structural solution for the external wail-upper floor connection in the (a) Rovaniemi and (b) Lappeenranta houses.

frame construction and the vapour barrier has to be sealed around each supporting beam.

3.4. Indoor air quality The quality of the indoor air has been monitored in the Espoo house (Table 6). The quality was found to be good. According to the occupants, the indoor climate is draught-free and comfortable. The high radon con-

The savings in heating energy in the building are based on minimizing heat losses through the building envelope with the use of effective thermal insulation, as well as exploiting free energy. The thickness of thermal insulation in the structures are clearly greater than normal. The building has super windows with a total U-value three times better than for conventional windows used in Finland. Free solar energy will be exploited directly in the house's PV-system (solar electricity) as well as through solar collectors, which will be used for heat production. Moreover, solar energy will be exploited with a groundsource heat pump.

Table 6 Indoor air quality measurements in the Espoo house Indoor air quality characteristic

Measuring period

Measured value

Recommended values

Temperature" Relative humidity Total air change rate CO2 Formaldehyde content ¢ Total fibre content a'~ Mineral wool fibre content a Radon content Bedroom 1 Bedroom 2 Living room Basement

11/91-4/92 11/91-4/92 4/92 4/92 4/92 4/92 4/92 3/92-4/92

19.7-22.3 °C 25-55% 0.8 lPa 350-1330 ppm =0 0.03 fibre/cm3 =0

19-21 °C b

70 110 150 760

0.5 1/h max. 2500 ppm 0.15 mg/m3 f r 200 Bq/m3g

Bq/m3 Bq/m3 Bq/m 3 Bq/m3

aVariation of monthly averages at 10 measuring points bRecommended value depends on use of the room CAccuracy of measurement 0.02 mg/m3 ~Scanning electron microscope, accuracy 0.01 fibre/cm3 of sample eBuilding materials contain no asbestos fNo recommended value for artificial fibres in Finland, recommended value for asbestos fibre in indoor air max. 0.05 fibre/cm3 STarget design value for new buildings.

194

J. 9

Nieminen / Energy and Buildings 21 (1994) 187-197 Table 7 Thermal insulation of the external envelope of the IEA5 Solar House

INTERESTRATE:5% J

ISERv'OE L'FE: [

I- BUILDINGENVELOPE:45 YEARS

Component

Thermal insulation (mm rock wool)

U-value (W/m 2 K)

Exterior wall Roof Floor Window Greenhouse

310 500 500

0.12 0.09 0.11 0.7 1.8

I WINDOWS:20 YEARS I _~ I-vL) 5 < tn

~

~ ~

~

UNIT: 15 YEARS

I" DUCTS:30 YEARS I

CURRENTAVERAGE:

NIG,,2

o.e

1

o.~s O'.a O.gS 0'.4

--"

O.:~B O:S O.gS O'.S O.SS

ENERGY PRICE [FIM] Fig. 11. Espoo house: the payback time of extra building costs compared to average Finnish small houses [6].

Fig. 12. The IEA5 Solar House during construction in November 1993. The house is built of prefabricated large wooden units.

l

;~!~r

1[I',[iI-',[FI]

S~_ " ~l~I

)

Fig. 13. The facades of the IEA5 Solar House.

4.2. Structural design Fig. 12 shows the house during construction in November 1993 and Fig. 13 the architect's drawings of the facades. The house is built of prefabricated wooden units. The envelope structures are shown in Table 7.

The cross-section of the external wall is shown in Figs. 14 and 15. In the wall units, 240 mm of rock wool is between two layers of gypsum board. On top of the outer gypsum board, rigid rock wool coated with a plastic fibre windproofing fabric is installed using point-type fasteners. The idea of the additional insulation is to improve the U-value of the structure and on the other hand to increase the temperature of the gypsum board to decrease the possibility of temperaturebased natural convection inside the insulation cavity of the wall units. The extra rock wool layer goes continuously from the concrete footings to the top of the wall forming an unbreakable air barrier for the wall. The insulation surface which is exposed to outdoor climate is rendered with thin rendering of about 5 mm. The roof of the house is insulated with 500 mm of rock wool. Roof insulation was installed at the site. The house has steel column concrete footings because of the bad load-bearing properties of the ground. The crawl-space foundation has a 500 mm airspace ventilated with outdoor air. The floor is also built of prefabricated units with 300 mm rock wool insulation. The total insulation thickness of the floor is 500 mm since 200 mm of rigid rock wool is fixed underneath the floor on site, Fig. 16. The extra insulation is made of two layers of rock wool with a plastic fibre windproofing fabric underneath each layer. The floor construction is a specially designed lightweight structure for a floor heating system. The water pipes are embedded in a construction consisting of three layers of gypsum boards. The windows are prototype super windows with thermally broken wooden frame and sash. The window has two low-emissivity plastic films in the middle of a sealed glazing unit with krypton gas filling and an extra pane outside the sealed unit. The calculated total U-value of the window is 0.7 W/m2 K. Special attention has been paid to the airtightness of the building envelope. Each joint between building elements was sealed during the installation. The airtightness was tested immediately after the envelope was finished. The air leakage rate at 50 Pa pressure difference is about 0.8 1/h which is well below the requirement of 1.0 1/h set for the house.

J. Nierninen / Energy and Buildings 21 (1994) 187-197

195

SPACE

WOOD STUDS 45 * 7 0 A N D 45 * 45 MM - - -

RIGID ROCK W o o L 70 MM WITH PLASTIC FIBRE FABRIC SURFACE

GYPSUM BOARD 9 MM

PLASTIC F I L M BARRIER 0.2 MI

GYPSUM BOJ

RENDERING 5 MM

PLASTIC FIBRE FABRIC

RIGID ROCK WOOL 100 + 100 MM W

RIGID ROCK W o o L 100 MM

PLASTIC FIBRE FABRIC SURFACE Fig. 14. The cross-section of an external wall.

Fig. 15. T h e IEA5 Solar House is built of prefabricated large units. An additional layer of rigid rock wool insulation and external wooden cladding was installed on top of the outside gypsum board seen in the photo.

4.3. Heating and ventilation system The building's heating system is a low-temperature water-circulation floor heating system, incorporating a 3000 litre water tank for heat storage. The floor heating

Fig. 16. The IEA5 Solar House. Installation of prefabricated floor units and additional layers of insulation.

system can be regulated on an individual room basis. The heating system is shown in Fig. 17. In winter the tank will mainly be charged with the heat pump (COP 3.3), at other times with the solar collectors (10 m2). If the tank is overheated in summer, the ground piping loops of the heat pump can be used

J. Nieminen I Energy and Buildings 21 (1994) 187-197

196 PV-PANEL

SOLAR C O L L E C F O ~

EXPANSION TANK

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TYPE CHZ-30 ETHANOL/WATER LIQUID

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i,

UNOm =-. ~ . ~ , , - - , ~

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Fig. 17. Heating system in the IEA5 Solar House.

for cooling of the collectors and tank. Also, the floor heating system may be used for cooling if the water in the floor pipe is circulated through the ground loops. Domestic hot water is heated in the upper section of the tank to the temperature for use, and if necessary by an auxiliary heater in a 60 litre tank. The building's ventilation is wholly mechanical. The system involves separate heat exchanger for normal air exchange and kitchen fan. The thermal efficiency of the heat exchangers are 80% and 60%. A control system will keep the total air exchange constant or increased if overheating occurs.

4.4. PV-system The PV-system consists of approximately 2 kW of thin film amorphous silicon photovoltaic modules. The output is converted to AC with an inverter and is fed to a local AC grid. Each PV-module has a stable peak power rating of 11 W. They are especially designed for large systems.

4.5. Energy consumption The estimated total energy consumption in the IEA5 Solar House is around 34 kWh per heated m 2 a year,

Fig. 18. The PV-system will produce about 14 kWh/ m 2 and the need for purchased energy will be 20 kWh/ m 2 which is less than 10% of the average need of a typical small house in Finland.

2015~"

10.

z

o_ S-1 a 0

0-

',~ -5" Z 0 ~ -10+ -1 ~

0 0

-15-

-20 I

I

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Fig. 18. Yearly energy consumption and production in the IEA5 Solar House.

J. Nieminen / Energy and Buildings 21 (1994) 187-197

4. 6. Building costs

The building costs of the IEA5 Solar House are estimated roughly at 280 000 US$. This includes also manufacturing of components (e.g., windows) that are still prototypes. The extra investment compared to an average house with corresponding architecture is around 90 000 US$ leaving 210 000 US$ for the price of the house. A minor part of the building costs, some 20 000 US$, comes from the very high quality surface finishings in the house. Nevertheless, the extra costs cannot be gained by reduced energy consumption. The price of electrical energy is very low in Finland, which makes only simple energy-saving measures economically sustainable. Economical aspects were not an issue in the IEA5 project.

5. Conclusions

The heating energy consumption of a present-day Finnish small house can be easily halved by using existing building technology. This can be done without greatly increasing the annual costs of the building, which makes the energy-saving measures profitable. The emphasis in the low-energy demonstrations has mainly been to reduce the heating energy consumption in the houses. In the future, total energy should also be an issue. Otherwise the household energy consumption will be larger than heating energy consumption, which is exactly the opposite of today's situation. The solar house IEA5 demonstrates what gains are possible using new innovative technology for reducing total energy consumption of a small house. At the moment, the price of energy in Finland remains at a very low level which makes solar technologies quite

197

unprofitable compared to conventional energy-saving technologies. The requirements set for the house of the future will include minimal energy consumption, good indoor climate, easily convertible spaces, versatility of usage and convertibility of the building according to user's needs. Even though the mid-winter climate of Finland is not very advantageous for solar energy utilization, solar energy will be an important feature of building design in the future. However, there are many traditions within building construction that restrain the design. Because of them, new solutions and applications can become quite complicated. It will be a task for future research to find technically and architecturally stable solutions and designs for solar houses that fullfil the house builder's needs and can compete with the traditional way of building. References [1] I. Kouhia et al., Low-energy residential housing, Energy Efficient Buildings and Building Components Research Programme, ETRR Rep. 5, 1990. [2] I. Kouhia et al., Low-energy residential housing, Part II, Energy Efficient Buildings and Building Components Research Programme, ETRR Rep. 12, 1990. [31 I. Kouhia et al., Low-energy residential housing, Part III, Energy Efficient Buildings and Building Components Research Programme, ETRR Rep. 31, 1993. [4] M. Virtanen, Energy consumption of single-family houses: Direct electric heating, Res. Notes 1246, VTT, Espoo, 1991 (in Finnish). [5] J. Nieminen et al., Low-energy small house 50%: Experimental house research, Energy Efficient Buildings and Building Components Research Programme ETRR Rep. 18, 1992 (in Finnish). [6] J. Nieminen, Low-energy residential housing: A case study, Proc. Int. Syrup. Energy Efficient BulTdt'ngs, Stuttgart, 1993, CIB Proc. Publ. 152. [7] J. Nieminen et al., Energy consumption and profitability of energy-saving measures in a low-energy small house, Res. Notes 1589, VTI', Espoo, 1994 (in Finnish).