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Primary energy performance and perceived indoor environment quality in Finnish low-energy and conventional houses
Building and Environment 87 (2015) 92e101
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Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Primary energy performance and perceived indoor environment quality in Finnish low-energy and conventional houses €hko € nen a, Pertti Pasanen b, Kari Reijula a, c Rauno Holopainen a, *, Kari Salmi a, Erkki Ka a
Finnish Institute of Occupational Health, Arinatie 3 A, FI-00370 Helsinki, Finland University of Eastern Finland, PO Box 1627, FI-70211 Kuopio, Finland c Hjelt Institute, PO Box 41, FI-00014 University of Helsinki, Finland b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 December 2014 Received in revised form 23 January 2015 Accepted 23 January 2015 Available online 4 February 2015
The primary energy demand of five recently built low-energy houses (built 2009e2012) and five older conventional houses (1974e2011) was calculated in accordance with the Finnish law regarding the building energy performance certificate of 2013. The purchased energy and water use data for the year 2013 was collected from the house owners. We interviewed the occupants and evaluated their perceived environment quality with a questionnaire survey. The average calculated primary energy demand was 120 kWh/m2 a (85e136 kWh/m2 a) in the low-energy houses and 323 kWh/m2 a (203e577 kWh/m2 a) in the conventional houses. The average purchased primary energy use was 125 kWh/m2 a (88e177 kWh/ m2 a) in the low energy houses and 220 kWh/m2 a (155e277 kWh/m2 a) in the conventional houses. The occupants in the low-energy houses perceived indoor environment quality as slightly better than the occupants in the conventional houses. Too high and varying room temperature were the most unsatisfactory indoor environment factors reported in both the low-energy and conventional houses in the winter and summer. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Low-energy house Conventional house Energy performance certificate Calculated primary energy demand Purchased primary energy use Perceived indoor environment quality
1. Introduction Buildings use 30e40% of total worldwide primary energy [1]. In Europe, the largest cost-effective saving potential is in the residential and commercial buildings sector, where the full potential is estimated to be 27% and 30% of energy use, respectively [2]. This presents a major possibility for climate change mitigation targets. To reduce greenhouse gas emissions, the European Parliament and Council has adopted a new energy performance directive for buildings [3]. The Directive requires Member States to lay down the necessary measures for establishing an energy performance certification system for buildings. The Finnish Ministry of the Environment has issued new energy efficiency regulations for new and renovated buildings [4]. The purpose of these regulations is to promote energy efficiency and the use of renewable energy in buildings, as well as to reduce buildings' energy consumption and carbon dioxide (CO2) emission. Current regulations in Finland have not set a minimum requirement for renewable energy use in buildings.
* Corresponding author. Tel.: þ358 43825914; fax: þ358 9506 1087. E-mail address: rauno.holopainen@ttl.fi (R. Holopainen). http://dx.doi.org/10.1016/j.buildenv.2015.01.024 0360-1323/© 2015 Elsevier Ltd. All rights reserved.
The law regarding a building energy performance certificate was first passed in Finland in 2007 [5] and revised later in 2013 [6,7]. The new law demands an energy performance certificate for new constructions and also for existing buildings when they are sold or rented. The calculated primary energy demand [kWh/m2 a] and the corresponding building energy performance class (AeG) have to be presented on the energy performance certificate. The calculation procedure is described in the National building code of Finland in parts D3 and D5 [8,9] as well as in Standard SFS-EN ISO 13790 [10]. The energy performance of energy efficient buildings has been studied particularly during the last decade in Europe, for example in the CEPHEUS project [11,12]. Energy efficient construction has been found to have a positive impact on both buildings' energy use [11e16] and indoor air quality [11,12,14]. However, in some cases, occupants have not been satisfied with thermal conditions in wellinsulated passive houses [17]. The first aim of the study was to compare the calculated primary energy demand (need) and the purchased primary energy use (consumption) in five Finnish low-energy houses and five conventional houses. We calculated the primary energy demand according to the energy performance certificate, which came into force in Finland in 2013. The second aim was to determine how the
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
air tightness, air flow rates and room temperature of the houses corresponded to the given input values for the calculation, and how they fulfilled the given guideline values. The measurements were carried out during 2012e2013. The third aim was to determine how occupants perceived indoor environment quality in the studied low-energy and conventional houses. The questionnaire survey was carried out in the winter and autumn of 2013.
2. Materials and methods 2.1. Low-energy and conventional houses studied We selected five low-energy houses and five conventional houses for the study. The low-energy houses were built in 2009e2012, and the conventional houses in 1974e2011. The houses were located between Southern Finland and the Oulu region. The selected houses presented typical, recently built, one- or twostoried low-energy houses; and older one-storied, conventionally built houses in Finland. Typical low-energy and conventional houses are presented in Fig. 1. The average living area of the low-energy houses was 192 m2, and the average air volume 594 m3. The outer wall and loadbearing structure of the houses were concrete or wood. The average thermal conductance (thermal transmittance surface area) of the houses' envelopes, including roof, floor, doors and windows, was 0.18 W/K. The ratio of the wall to windows surface area was on average 0.15. The largest windows in the houses were located in the southeast, southern or southwest facade. All windows were equipped with curtains, blinds and external solar shading or sun protection film. The low-energy houses were equipped with a mechanical supply and exhaust ventilation system with cooling and heat recovery units. The heat recovery units were cross flow, counter flow or regenerative heat exchangers. Floor and ventilation heating were the main heating system in the lowenergy houses. The hot water tanks' capacity was on average 0.7 m3 in the houses. Heat pumps were installed in four of the lowenergy houses.
93
The average living area of the conventional houses was 121 m2 and air volume 307 m3. The outer wall and load-bearing structure of the houses were brick, concrete or wood. The average thermal conductance of the houses' envelopes was 0.43 W/K. The ratio of the wall to windows surface area was on average 0.21. All windows in the houses were equipped with curtains and blinds. The houses had natural ventilation or mechanical supply and exhaust ventilation systems with cross flow heat exchangers. Electric, floor and ventilation heating were the main heating systems in the conventional houses. The average capacity of the houses' hot water tanks was 0.9 m3. A heat pump was installed in one conventional house. According to the occupants, no energy conservation renovations had been carried out in the houses. All the houses studied had fireplaces. More detailed information on the low-energy houses is given in Table 1 and on the conventional houses in Table 2. 2.2. Calculation details The houses' primary energy demand was calculated using the commercial MX6 Energy programme, version 6.4.0 [18], which calculates the house's energy demand using a monthly method [10]. The designed thermal transmittance of the houses' walls, roofs, floors, doors, and windows, as well as the measured air tightness of the house envelope were used in the calculation. The calculation used the following input values [7,8,19]: supply and exhaust air flow rates of 1.44 m3/hm2, space heating limited to below 21 C, specific hot water energy of 4200 kWh/a (35 kWh/ m2 a), house occupancy rate of 0.6, electricity for lighting at 8 W/m2 and for appliances 3 W/m2, and occupants' heating load of 2 W/m2. In addition, the renewable energy of the fireplace was limited to 2000 kWh/a, and the outdoor air to air heat pump energy to 1000e6000 kWh/a, depending on the year in which the house building permit was issued. The heat transfer efficiency of the fireplace was assumed to be 0.6 [9]. Annual heat recovery efficiency (ha) was determined on the basis of the heat exchanger type according to Refs. [8,9]. The seasonal performance factor (SPF) of the heat pumps that were used in the calculation was taken from
Fig. 1. (a) Location of the low-energy houses (white circle) and conventional houses (grey circle) in Finland. (b) A typical low-energy house and (c) a conventional house.
Location House (year of construction)
Number of stories, shape of house and roof
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Table 1 Detailed information on low-energy houses. Living Air Ratio of window Thermal area volume and wall surface conductance of 2 3 [m ] [m ] house envelope area [e] [W/K]
Heating energy form: space Ventilation systema heating system
Renewable energy systemb
Number of occupants (age) 4e6 (adults 30e45 and children 5e10) 4e5 (adults 30e35 and children 5e15) 2 (adults 30e40)
Two stories with Helsinki Metropolitan cellar, union of two blocks, pitched roof area
337
1030
0.21
0.21
Electricity: ventilation heating
Mechanical supply and exhaust ventilation with counter flow heat exchanger (ha ¼ 58%)
Fireplace and ground source heat pump (SPF ¼ 2.3e3.4)
Low H2 (2011)
Uusimaa regional council
One storey block, double-pitched roof
125
425
0.10
0.14
Electricity: ventilation heating and electric floor heating in wet rooms
Mechanical supply and exhaust ventilation with regenerator heat exchanger (ha ¼ 61%)
Fireplace and outdoor air to air heat pump (SPF ¼ 1.8e2.8)
Low H3 (2011)
The regional council of Satakunta The regional council of Satakunta
Two stories block with 190 porch, double-pitched roof One storey with cellar, 152 union of two blocks, pitched roof
628
0.16
0.16
0.19
0.19
Mechanical supply and exhaust ventilation with cross flow heat exchanger (ha ¼ 49%) Mechanical supply and exhaust ventilation with counter flow heat exchanger (ha ¼ 58%)
Fireplace and exhaust air to water heat pump (SPF ¼ 2.0)
475
Electricity: ventilation heating and electric floor heating in wet rooms Electricity: floor heating
Oulu region
Two stories, union of two blocks, doublepitched roof
410
0.11
0.18
Wood: floor heating
Mechanical supply and exhaust ventilation with regenerator heat exchanger (ha ¼ 61%)
Low H4 (2012)
Low H5 (2010) a b
157
Fireplace and ground source heat pump (SPF ¼ 2.3e3.4), supply air was pre-heated by geothermal heating circuit Fireplace, connected to hot water boiler, supply air pre-heated by geothermal heating circuit
3 (adults 30e35 and children 5) 2 (adults 60e65)
Annual heat recovery efficiency ha [9]. Seasonal performance factor SPF [9].
Table 2 Detailed information on conventional houses. House (year of Location construction)
Ratio of window Number of stories, shape Living Air volume and wall surface of house and roof area 2 3 [m ] area [e] [m ]
Thermal conductance of house envelope [W/K]
Heating energy form: space heating system
Ref H1 (1974)
One story block, hipped roof
Ref H2 (1985)
Ref H3 (2011)
Ref H4 (1986)
Ref H5 (1994)
a b
Helsinki Metropolitan area Helsinki Metropolitan area Helsinki Metropolitan area Kuopio region Oulu region
Ventilation systema
Renewable energy systemb
Number of occupants (age)
108
268
0.34
0.78
Electricity: electric Natural ventilation (ha ¼ 0%) radiator
Fireplace
2 (adults 55e60)
One storey block with bay 136 window, double-pitched roof One storey, union of two 130 blocks, double pitched roof One storey block, double- 104 pitched roof
337
0.16
0.33
Fireplace
3 (adults 55e60 and children 20)
350
0.16
0.26
260
0.22
0.39
321
0.15
0.39
Electricity: Mechanical supply and exhaust ventilation heating ventilation with cross flow heat exchanger (ha ¼ 49%) Electricity: electric Mechanical supply and exhaust floor heating ventilation with cross flow heat exchanger (ha ¼ 49%) Electricity: radiant Mechanical supply and exhaust ceiling heating ventilation with cross flow heat exchanger (ha ¼ 49%) Wood: floor Mechanical supply and exhaust heating ventilation with cross flow heat exchanger (ha ¼ 49%)
One storey block with porch and attic, doublepitched roof
Annual heat recovery efficiency ha [9]. Seasonal performance factor SPF [9].
125
Fireplace and outdoor air 4 (adults 25e30 and children 5e8) to air heat pump (SPF ¼ 1.8e2.8) Fireplace 1 (adult 50)
Fireplace and wood boiler 1e2 (adults 30e40)
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Low H1 (2009)
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Table 3 Calculated energy demand, CO2 emission and energy performance class in low-energy houses. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Energy performance class (AeG)
Low Low Low Low Low
47 72 67 71 48
12 34 12 28 27
10 27 18 22 89
85 136 123 132 126
10.5 16.1 14.9 15.8 10.7
B B B C C
H1 H2 H3 H4 H5
Ref. [9]. The houses' cooling energy demand was not taken into account because the energy performance certificate did not require its calculation in single-family houses. The calculation used the HelsinkieVantaa climate zone data given in Ref. [8]. The average heat value of wood fuel was assumed to be 1700 kWh/m3 (stack m3) for birch and 1300 kWh/m3 for mixed wood [7]. The primary energy factors used were 1.7 for electricity and 0.5 for renewable energy [7,8]. The CO2 emission factors used were 223 kg CO2/MWh for electricity and 0 kg CO2/MWh for wood fuel [19]. 2.3. Purchased energy use in the houses
Finnish Institute of Occupational Health [23]. It is based on the Swedish standardized MM-40 questionnaire [24], and elicits environmental problems (draught, dry, stuffy air, etc.) from the past three months. Environmental problems that occurred every week or occasionally were also elicited and collected. The survey was carried out during the cooling and heating season of the winter of 2013 and the autumn of 2013, respectively.
3. Results 3.1. Calculated energy demand
The purchased energy and water use data for 2013, concerning wood burned in the fireplaces as fuel, was collected from the house owners. They were asked to take the purchased energy and water use data from their electricity and water bills. Purchased space heating energy use in the houses located outside the HelsinkieVantaa climate zone was normalized to that of HelsinkieVantaa [20,21], assuming that electricity energy for lighting and appliances was part of the space heating energy. 2.4. Measurements in the houses The air tightness of the houses' envelopes was measured using Minneapolis Blower Door Systems. Air leakage gaps were visualized by using tracer smoke and the FLIR B200 thermal camera. The supply and exhaust air flow rates were measured from the air terminal units using the SwemaFlow 125 air flow hood. The air change rate of the house equipped with natural ventilation systems was determined using a tracer gas method (CO2). The air change rate was measured in the winter in the unoccupied house, the windows and doors of which were closed. Room temperature and relative humidity were measured in the houses' living and bedrooms with TinyTag View 2 sensors. Data loggers saved the measured values in 15 min. Outdoor air temperature data was collected from the weather station of the Finnish Meteorological Institute [22]. Room temperature and relative humidity measurements were carried out during July 2012 and October 2013. Only mean room temperature values are presented in the Results. 2.5. Interview and questionnaire survey We interviewed the occupants and assessed perceived indoor environment quality using a questionnaire survey developed by the
Tables 3 and 4 present the calculated electricity, hot water, renewable and primary energy demands, and CO2 emission per living area per year in the low-energy and conventional houses. The average primary energy demand was 120 kWh/m2 a (85e136 kWh/ m2 a) in the low-energy houses and 323 kWh/m2 a (203e577 kWh/ m2 a) in the conventional houses. Average CO2 emission was 13.6 kg CO2/m2 a (10.5e16.1 kg CO2/m2 a) in the low-energy houses and 37.7 kg CO2/m2 a (10.9e73.6 kg CO2/m2 a) in the conventional houses. Electricity energy for lighting and appliances was 23 kWh/ m2 a in all the houses [7,8]. Primary energy demand corresponded to energy performance classes BeC in the low-energy houses and classes DeG in the conventional houses. It should be noted that the energy performance class of single-family houses depends on living area [7].
3.2. Purchased energy use in 2013 The average purchased primary energy use was 125 kWh/m2 a (88e177 kWh/m2 a) in the low energy houses, and 220 kWh/m2 a (155e277 kWh/m2 a) in the conventional houses. The corresponding average CO2 emission of purchased energy use was 15.5 kg CO2/m2 a (9.6e23.2 kg CO2/m2 a) in the low-energy houses, and 25.1 kg CO2/m2 a (10.7e34.1 kg CO2/m2 a) in the conventional houses. The purchased electricity, hot water, renewable and primary energy use, as well CO2 emission per living area per year in the low-energy and conventional houses in 2013 are presented in Tables 5 and 6. Table 7 presents the ratio of calculated and purchased electricity, water, renewable and primary energy, as well as CO2 emission per living area in 2013. Renewable energy consists of space heating energy, i.e. wood fuel in fireplaces.
Table 4 Calculated energy demand, CO2 emission and energy performance class in conventional houses. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Energy performance class (AeG)
Ref Ref Ref Ref Ref
330 170 123 174 49
35 31 32 35 34
31 25 26 32 239
577 301 222 312 203
73.6 37.9 27.4 38.8 10.9
G E D E D
H1 H2 H3 H4 H5
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Table 5 Purchased energy use and CO2 emission in low-energy houses in 2013. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Low Low Low Low Low
53 104 45 77 86
18 16 18 20 10
4 0 31 21 19
93 177 88a 136a 133a
12.7 23.2 9.6a 16.5a 16.3a
a
H1 H2 H3 H4 H5
Space heating energy is normalized to correspond to HelsinkieVantaa climate zone [20,21].
Table 6 Purchased energy use and CO2 emission in conventional houses in 2013. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Ref Ref Ref Ref Ref
138 153 128 108 55
12 26 10 9 11
31 35 20 63 177
250 277 227 193a 155a
30.8 34.1 28.5 21.7a 10.7a
a
H1 H2 H3 H4 H5
Space heating energy is normalized to correspond to HelsinkieVantaa climate zone [20,21].
3.3. Measured air tightness, air change rate and room temperature
4. Discussion
The average air tightness of the houses' envelopes was 0.4 1/h (0.2e0.6 1/h) in the low-energy houses and 4.2 1/h (1.2e11.3 1/h) in the conventional houses. The average air change rate in the lowenergy houses was 0.3 1/h (0.2e0.5 1/h) and in the conventional houses 0.4 1/h (0.2e0.7 1/h). During the winter season (Dec 2012 and Feb 2013), the mean room temperature was 21.9 C (20.8e22.5 C) in the low-energy houses and 20.7 C (18.1e22.0 C) in the conventional houses. During the summer season (June and Aug 2013), the mean room temperature in the low-energy houses was 22.6 C (21.9e23.8 C), and in the conventional houses 23.1 C (21.4e24.0 C). The results are shown in Tables 8 and 9.
In all the low-energy houses and in four of the conventional houses, the occupants were the original occupants of the houses. They worked in construction, HVAC, research, the indoor environment field, or the business sector. The number of occupants was 2e6 in the low-energy houses and 1e4 in the conventional houses. The average age of the adults in the low-energy houses was 40, and in the conventional houses 45. Three low-energy houses and three conventional houses also had children as occupants. The occupants did not observe indoor air problems in the houses. Electricity was the main heating form in four of the low-energy and four of the conventional houses. The average living area per person was 61 m2 in the low-energy houses and 60 m2 in the conventional houses. The air change rate was on average slightly lower in the low-energy houses than in the conventional houses. However, the air volume of the low-energy houses was almost twice that of the conventional houses. The air change rate in the studied low-energy and conventional houses was of the same magnitude as that measured in the passive houses in the CEPHEUS project (0.25e0.4 1/h) [12]. The designed value of the thermal conductance of the lowenergy houses' envelopes was almost half that of the conventional houses. In addition, the air tightness of the low-energy houses' envelopes was about ten times better than that of the conventional houses' envelopes. The ratio of the wall to windows surfaces area was on average slightly lower in the low-energy houses than that in the conventional houses. The average annual heat recovery efficiency of the ventilation systems was estimated to be 57% and 39% in the low-energy and conventional houses, respectively. Thus, the heat loss of the low-energy houses per floor surface area has to be lower than in the conventional houses under the same conditions. An energy performance certificate was given to all the lowenergy houses during their design process. The energy performance of the low-energy houses was classified as class A according to the old law [5]. High annual heat recovery efficiencies of ventilation systems were used in the calculation. Ice formation in heat exchangers reduces heat recovery efficiency in cold climates such as those in Nordic countries [27], and this must be taken into account in the calculation. In this study, the calculation used a ventilation heat exchanger efficiency of 49e61% in the low-energy
3.4. Perceived indoor air quality Occupants perceived indoor environment quality as slightly better in the low-energy houses than in the conventional houses. The occupants of the conventional houses more often complained about draught, high or varying room temperature, stuffy and dry air, insufficient ventilation, unpleasant odours, or dim light in the winter than the occupants of the low-energy houses. In the summer, the occupants more often reported high room temperatures, insufficient ventilation, noise, and dim light than the occupants of the low-energy houses. The perceived indoor environment quality in the low-energy and conventional houses is presented in Figs. 2 and 3 (also Tables 8 and 9) during the winter and summer of 2013, respectively. Table 7 The ratio of calculated and purchased electricity, water, renewable and primary energy, and CO2 emission in low-energy and conventional houses (purchased energy use in 2013). Calculated energy demand/purchased energy use mean value (minemax) [e]
Electricity energy Hot water energy Renewable energya Primary energy CO2 emission a
Low-energy houses
Conventional houses
0.91 1.51 1.69 1.00 0.95
1.39 2.84 0.98 1.46 1.46
(0.56e1.50) (0.66e2.67) (0.00e4.57) (0.77e1.40) (0.66e1.55)
Space heating energy: wood fuel in fireplace.
(0.89e2.39) (1.21e3.90) (0.51e1.35) (0.98e2.30) (0.96e2.39)
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Table 8 Low-energy houses: air tightness, air change rate, mean room temperature (minemax) in winter 2012e2013 and summer 2013, as well as ratio of calculated primary energy demand and purchased primary energy use. Occupants' reported insufficient ventilation (I), or high (H), varying (V) or low (L) room temperature are marked in parenthesis. House
Low Low Low Low Low
H1 H2 H3 H4 H5
Air tightnessa [1/h]
0.2 0.4 0.6 0.4 0.5
Air change rateb [1/h] 0.3 0.5 0.2 0.4 0.3
Room temperaturec Winterd [ C]
Summere [ C]
21.2 22.4 20.8 22.5 22.4
22.3 22.6 21.9 23.8 22.2
(19.7e22.3) (20.4e23.3) (H/V/L) (16.3e23.6) (H/V/L) (21.0e24.7) (18.9e24.0)
Primary energy demand/usef [e]
(20.9e23.9) (20.3e25.3) (H/V/L) (19.4e24.4) (H/V/L) (22.0e26.4) (19.1e25.1)
0.91 0.77 1.40 0.97 0.95
a
Air tightness n50 value for passive house must be equal to or below 0.6 1/h [25]. Air change rate must be equal to or higher than 0.5 1/h [26]. A tolerable level of room temperature is 18 C and a good level 21 C. In addition, room temperature should not exceed 23e24 C during the heating season. Room temperature may exceed 26 C only if this caused by outdoor conditions [26]. d Measurements carried out during December 2012 and February 2013. e Measurements carried out during June and October 2013. f Purchased primary energy use in 2013. b c
houses, and 0e49% in the conventional houses. The calculated primary energy demand corresponded to energy performance classes BeC in the low-energy houses. However, energy performance class B would have been achieved in all low-energy houses if we had used annual ventilation heat recovery efficiency that was higher than 70%. It should also be noted that the energy performance classes given in Refs. [5,6] cannot be directly compared with each other. The space heating energy demand is estimated to be 15e25 kWh/m2 a in high performance houses in the climate of Stockholm, Oslo and Helsinki [28]. This estimation is based on simulation, which was carried out using a heat exchanger efficiency of 80%. According to this study, the energy demand, without electricity for lighting and appliances and hot water energy, was on average 49 kWh/m2 a (22e87 kWh/m2 a) in the low-energy houses, and 183 kWh/m2 a (94e303 kWh/m2 a) in the conventional houses. Only low-energy house Low H1 achieved the target value presented above. The air tightness of the houses' envelopes was measured in the winter of 2012e2013. The air tightness in the low-energy houses varied roughly within a similar range to that measured in the passive houses (0.3e0.6 1/h) [12]. We used measured values as the input value in the calculation. In general, air leakage gaps were found in doors, windows and the structure joints of the houses' envelope. During the air tightness test, we used a thermal camera to visualize envelope heat loss, and this revealed that the heat loss of the low energy houses' envelopes was less than that of the conventional houses. Air tightness fulfilled the given guideline values [8,25] in all houses except in conventional house Ref H1, as we found a large air leakage in its roof structure.
The average measured supply and exhaust air flow rate was 1.03 m3/hm2 (0.55e1.76 m3/hm2) in the low-energy houses and 0.82 m3/hm2 (0.38e1.88 m3/hm2) in the conventional houses. These were both on average lower than the given input value of 1.44 m3/hm2 for the energy performance certificate calculation. As the calculation had to be carried out with an air flow rate of 1.44 m3/hm2 also in the house that was equipped with a natural ventilation system [7,8], it may overestimate the heat loss from ventilation, especially in conventional house Ref H1. The mean room temperature fulfilled the given minimum (tolerable level of 18 C) and maximum values (26 C) in all the houses studied. Roughly similar room temperatures, on average 22e23 C, were measured in the Danish energy efficient houses in the winter [16]. Room temperature was exceptionally low in conventional house Ref H1, on average 18.1 C, in the winter of 2012e2013. The occupants of this house had to keep room temperatures low for energy-saving reasons. The low room temperature considerably decreased the house space heating energy use, and thus, also primary energy use and CO2 emission (Figs. 4 and 5). The purchased primary energy use was lower than the calculated primary energy demand in all the houses studied, the average room temperature of which was below 21 C in the winter (Tables 8 and 9). The houses were not equipped with a separate electricity energy meter for lighting and appliances. The occupants estimated electricity use for these to be 20e30 kWh/m2 a in the low-energy houses, and 20e65 kWh/m2 a in the conventional houses. The occupants' estimations were based on the electric power of lighting and appliances as well as their estimated operating time in 2013. The purchased electricity energy use in conventional house Ref H5
Table 9 Conventional houses: air tightness, air change rate, mean room temperature (minemax) in winter 2012e2013 and summer 2013, as well as ratio of calculated primary energy demand and purchased primary energy use. Occupants' reported insufficient ventilation (I), or high (H), varying (V) or low (L) room temperature are marked in parenthesis. House
Ref Ref Ref Ref Ref a
H1 H2 H3 H4 H5
Air tightnessa [1/h]
11.3 2.0 1.2 2.1 4.0
Air change rateb [1/h] 0.2 (I) 0.3 0.7 0.3 0.2
Room temperaturec Winterd [ C] 18.1 22.0 22.0 20.5 22.0
(10.1e21.8) (20.2e29.2) (19.6e24.1) (13.3e24.8) (17.3e23.7)
Primary energy demand/usef [e]
Summere [ C] (H/V/L) (H/V) (H/V/L) (H/V)
21.4 23.6 23.7 22.6 24.0
(18.2e24.9) (19.1e27.7) (21.0e26.5) (13.5e27.2) (20.2e28.5)
(V/L) (H) (H/V) (H) (H)
2.30 1.09 0.98 1.61 1.31
Air tightness q50 value for conventional house must be equal to or below 4.0 m3/hm2 [8], which corresponds roughly to an n50 value of 4.0 1/h. b Air change rate must be equal to or higher than 0.5 1/h [26]. c A tolerable level of room temperature is 18 C and a good level 21 C. In addition, room temperature should not exceed 23e24 C during the heating season. Furthermore, room temperature may exceed 26 C only if this is caused by outdoor conditions [26]. d Measurements carried out during December 2012 and February 2013. e Measurements carried out during June and October 2013. f Purchased primary energy use in 2013.
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Questionnaire: low-energy and conventional houses (n=5) Have any of following factors disturbed you in the past three months? (winter time) dim light/glare
noise
draught 100 80
room temperature too high
60
varying room temperature
40 20
passive smoking
room temperature too low
0
other unpleasant odours
stuffy "bad" air
odour of mould or underground dry air cellar insufficient ventilation
Conventional houses
Low-energy houses
Fig. 2. Perceived indoor environment quality in low-energy and conventional houses in winter 2013.
(55 kWh/m2 a) included mainly electricity for lighting and appliances, because space heating and hot water were produced by a wood fuel boiler. The value of 23 kWh/m2 a, which is given as an input value for the calculation, does not include energy use outside the houses, for example, outdoor lighting and car heating [7,8]. Total water use was on average 40 m3/a (17e72 m3/a) per person in the low-energy houses and 32 m3/a (15e50 m3/a) per person in the conventional houses. The amount of hot water was assumed to be 40% of total water use [29]. Thus, the average purchased hot water energy use in low-energy houses was 2945 kWh/a (16 kWh/ m2 a), and in the conventional houses 1685 kWh/a (14 kWh/m2 a), which are both much lower that the given value of 4200 kWh/a (35 kWh/m2 a) for the calculation. The occupants interviewed said that the use of fireplace wood fuel varied yearly, depending on space heating demand, the
availability of wood, and the price of electricity. According to the occupants of low-energy house Low H2, they could not burn wood in the fireplace even in the winter, because it overheated the house. The amount of renewable energy for the calculation was limited to 2000 kWh/a in a normal fireplace [7,8]. Heat pumps had been installed in four of the low-energy houses and in one conventional house. The pumps were used for space heating and cooling in the houses. However, the energy performance certificate did not require calculation of the cooling energy demand in the single-family houses. According to Ref. [30], using outdoor air to air heat pump can produce more space heating energy in the Finnish cold climate, depending on heating demand, than the given limited value of 1000 kWh/a for new houses. The largest windows in the studied low-energy houses were located to the southern facade. According to Ref. [13], the size of
Questionnaire: low-energy and conventional houses (n=5) Have any of following factors disturbed you in the past three months? (summer time) dim light/glare noise
draught 100
80
room temperature too high
60
varying room temperature
40 20
passive smoking
room temperature too low
0
other unpleasant odours
stuffy "bad" air
odour of mould or underground dry air cellar insufficient ventilation
Conventional houses
Low-energy houses
Fig. 3. Perceived indoor environment quality in low-energy and conventional houses in summer 2013.
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
99
Low H1 Calculated primary energy demand Purchased primary energy use
Low H2 Low H3 Low H4 Low H5 Ref H1 Ref H2 Ref H3 Ref H4 Ref H5 0
100
200
300 400 Primary energy [kWh/m2a]
500
600
Fig. 4. Calculated primary energy demand and purchased primary energy use in low-energy and conventional houses (purchased energy use in 2013).
energy-efficient windows has only a minor influence on the space heating demand in the winter, but a major influence on the cooling demand in the summer. Thus, it is possible to also use larger windows on the northern facade to obtain better daylight conditions in the low-energy houses. The lowest calculated primary energy demand was in more complicatedly-shaped, two-storied, low-energy house Low H1, the living area and air volume of which were much higher than in the other low-energy houses. The lowest primary purchased energy use was in compact-shaped, two-storied, low-energy house Low H3, which was occupied by a childless couple. Both the highest calculated primary energy demand and the highest purchased primary energy use were in compact-shaped, one-storied, lowenergy house Low H2, the living area and air volume of which were the smallest of the low-energy houses. Both the lowest calculated primary energy demand and the lowest purchased primary energy use were in conventional house Ref H5, which was occupied by a childless couple and the space
heating and hot water energy of which were produced by a wood boiler. The highest calculated primary energy demand was in old electricity-heated conventional house Ref H1, which was equipped with a natural ventilation system. The highest purchased primary energy use was in ventilation-heated conventional house Ref H2, the living area and air volume of which were the highest of the conventional houses. In this study, the calculation estimated a slightly lower average primary energy demand in the low-energy houses and a considerably higher one in the conventional houses than purchased primary energy use. However, variation was great, especially in the conventional houses. The year 2013 was exceptionally warm compared to the long-term average in Finland [31]. Thus, the purchased space heating energy use in 2013 may have been lower than the average for a year. Fig. 4 presents the calculated and purchased primary energy in low-energy and conventional houses. The primary energy factors had a significant effect on the calculated primary energy demand and the purchased primary
Low H1 Calculated energy demand CO2 emission Purchased energy use CO2 emission
Low H2 Low H3 Low H4 Low H5 Ref H1 Ref H2 Ref H3 Ref H4 Ref H5 0
10
20
30 40 50 CO2 emission [kg CO2/m2a]
60
70
80
Fig. 5. Calculated and purchased energy of CO2 emission in low-energy and conventional houses (purchased energy use in 2013).
100
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
energy use in the low-energy and conventional houses studied. The primary energy factor for electricity was particularly high, and therefore affected the houses' energy performance classes. Primary energy factors can be used as a tool for selecting energy forms in order to achieve a low primary energy demand in the house. The variation of CO2 emission in electricity-heated houses was similar to that of primary energy demand and energy use. The same order of magnitude of CO2 emission is reported in Swedish residential houses [32] as that in this study. Fig. 5 presents the calculated and purchased energy of CO2 emission in the low-energy and conventional houses. The perceived indoor environment quality was slightly better in the low-energy houses than in the conventional houses. In particular, the occupants perceived less high room temperature, insufficient ventilation and dim light in the low-energy houses than the occupants in the conventional houses in the winter and summer. However, too high and varying room temperature were the most commonly reported unsatisfactory indoor environment factors in both the low-energy and conventional houses in the winter and summer. Therefore, correct room temperature was an important factor for primary energy use and perceived indoor environment quality in the houses. The measured air change rate did not fulfil the given minimum value in four of the low-energy houses and four of the conventional houses. Despite this, only the occupants of one conventional house (Ref H1), which was equipped with a natural ventilation system, complained of insufficient ventilation in the winter and summer. In a recently published Swedish study [17], occupants complained more often of cold floors and varying room temperatures in passive houses than in conventional houses. In addition, a high number of the occupants' complaints was related to excessively high room temperatures in the summer. The passive houses' windows had not been equipped with external shading, which may have contributed to this. In our study, the g-value (so called solar factor) of the low-energy houses' windows varied between 0.44 and 0.56. The houses' ventilation systems also had a cooling unit to ensure comfortable room temperature in the houses during the summer. The number of houses we studied was small, and therefore, the results may present a rather narrow scope of information regarding primary energy performance in Finnish houses. In addition, the conventional houses studied were on average 21 years older than the low-energy houses. Furthermore, the occupants evaluated the indoor environment quality of their own house, which may also have affected the results of the questionnaire survey. However, the results still reveal differences between the calculated primary energy demand and purchased primary energy use in recently built low-energy and older conventional houses. In addition, they provide information on how occupants perceived the environment quality in these houses, and how the measured air tightness, air change rate and room temperature of the houses met the given Finnish guideline values. 5. Conclusions We calculated the primary energy demand of five recently built low-energy houses and five older conventional houses in accordance with the 2013 building energy certificate of Finland. The calculated primary energy demand corresponded to energy performance classes BeC in the low-energy houses and classes DeG in the conventional houses. The primary energy demand was on average 2.7 times higher in the conventional houses than in the low-energy houses. Purchased primary energy use in 2013 was on average 1.7 times higher in the conventional houses than in the low-energy houses. Measured air flow rates and purchased hot
water use were on average lower than the given input values for the calculation in both the low-energy and conventional houses. According to the interview and questionnaire survey, occupants suffered less from high room temperature, insufficient ventilation and dim light in the recently built low-energy houses than the occupants in the older conventional houses. The factors that caused the most dissatisfaction in the low-energy and conventional houses were excessively high and varying room temperatures. The differences between the perceived environment quality of the lowenergy and conventional houses were higher in the winter than in the summer.
Acknowledgements The study was the part of RYM Indoor Environment programme. The authors warmly thank Tekes e the Finnish Funding Agency for Innovation, and the companies that supported the studies. This study would not have been possible without field measurements in real houses, and thus the authors wish to kindly thank the occupants of the low-energy and conventional houses for their smooth, €inen, fruitful co-operation. In addition, the advice of Leevi Myyryla €inen, CEO, on the use of Senior Engineer (HVAC) and Antti Myyryla the MX6 Energy programme is gratefully acknowledged.
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R. Holopainen et al. / Building and Environment 87 (2015) 92e101 [17] Rohdin P, Molin A, Moshfegh B. Experiences from nine passive houses in Sweden e indoor thermal environment and energy use. Build Environ 2014;71:176e85. [18] MX6-Energy Program. MX6 Teknologiat Oy. http://www.kolumbus.fi/ mx6teknologiat/Tuotteet/tuotteet_energia.htm [accessed 21.11.14] [in Finnish]. [19] Calculation instruction for CO2 emission of a single building and the used CO2 emission factors. Motiva; 2012. http://www.motiva.fi/files/8886/CO2laskentaohje_Yksittainen_kohde.pdf. 2/12 [accessed 21.11.14] [in Finnish]. [20] Heating degree days. Finnish Meteorological Institute. http://en. ilmatieteenlaitos.fi/heating-degree-days [accessed 21.11.14]. [21] Formulas: heating energy consumption. Motiva. http://www.motiva.fi/ julkinen_sektori/energiankayton_tehostaminen/kiinteistojen_ energianhallinta/kulutuksen_normitus/laskukaavat_ lammitysenergiankulutus [accessed 21.11.14] [in Finnish]. [22] Finnish Meteorological Institute's open data. Finnish Meteorological Institute. https://en.ilmatieteenlaitos.fi/open-data [accessed 21.11.14]. [23] Reijula K, Sundman-Digert C. Assessment of indoor air problems at work with a questionnaire. Occup Environ Med 2004;61:33e8. [24] Andersson K. Epidemiological approach to indoor problems. Indoor Air 1998;8(S4):32e9. [25] Passive house guidelines. International Passive House Association. iPHA. http://www.passivehouse-international.org/index.php?page_id¼80 [accessed 21.11.14].
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[26] Housing Health Code. Housing and other facilities the physical, chemical and microbiological factors. Ministry of Social Affairs and Health; 2003. http:// www.finlex.fi/pdf/normit/14951-asumisterveysohje_pdf.pdf [accessed 21.11.14] [in Finnish]. [27] Kragh J, Rose J, Nielsen TR, Svendsen S. New counter flow heat exchanger design for ventilation systems in cold climates. Energy Build 2007;39:1151e8. [28] Smeds J, Wall M. Enhanced energy conversation in houses through high performance design. Energy Build 2007;39:273e8. [29] Formulas: domestic hot water. Motiva. http://www.motiva.fi/julkinen_ sektori/energiankayton_tehostaminen/kiinteistojen_energianhallinta/ kulutuksen_normitus/laskukaavat_lammin_kayttovesi [accessed 21.11.14] [in Finnish]. [30] Laitinen A, Tuominen P, Holopainen R, Tuomaala P, Jokisalo J, Eskola J, et al. Renewable energy production of Finnish heat pumps. Final report of the SPFproject. VTT Technology; 2014., http://www.vtt.fi/inf/pdf/technology/2014/ T164.pdf. 164 [accessed 23.11.14]. [31] The weather in 2013. Finnish Meteorological Institute. http:// ilmatieteenlaitos.fi/vuosi-2013 [accessed 21.11.14] [in Finnish]. [32] Joelsson A. Primary energy efficiency and CO2 mitigation in residential buildings [Mid Sweden University Doctoral Thesis 58]. Ecotechnology and Environmental Science Department of Engineering and Sustainable Development; 2008., http://www.diva-portal.org/smash/get/diva2:132717/ FULLTEXT01.pdf [accessed 24.11.14].
Contents lists available at ScienceDirect
Building and Environment journal homepage: www.elsevier.com/locate/buildenv
Primary energy performance and perceived indoor environment quality in Finnish low-energy and conventional houses €hko € nen a, Pertti Pasanen b, Kari Reijula a, c Rauno Holopainen a, *, Kari Salmi a, Erkki Ka a
Finnish Institute of Occupational Health, Arinatie 3 A, FI-00370 Helsinki, Finland University of Eastern Finland, PO Box 1627, FI-70211 Kuopio, Finland c Hjelt Institute, PO Box 41, FI-00014 University of Helsinki, Finland b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 December 2014 Received in revised form 23 January 2015 Accepted 23 January 2015 Available online 4 February 2015
The primary energy demand of five recently built low-energy houses (built 2009e2012) and five older conventional houses (1974e2011) was calculated in accordance with the Finnish law regarding the building energy performance certificate of 2013. The purchased energy and water use data for the year 2013 was collected from the house owners. We interviewed the occupants and evaluated their perceived environment quality with a questionnaire survey. The average calculated primary energy demand was 120 kWh/m2 a (85e136 kWh/m2 a) in the low-energy houses and 323 kWh/m2 a (203e577 kWh/m2 a) in the conventional houses. The average purchased primary energy use was 125 kWh/m2 a (88e177 kWh/ m2 a) in the low energy houses and 220 kWh/m2 a (155e277 kWh/m2 a) in the conventional houses. The occupants in the low-energy houses perceived indoor environment quality as slightly better than the occupants in the conventional houses. Too high and varying room temperature were the most unsatisfactory indoor environment factors reported in both the low-energy and conventional houses in the winter and summer. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Low-energy house Conventional house Energy performance certificate Calculated primary energy demand Purchased primary energy use Perceived indoor environment quality
1. Introduction Buildings use 30e40% of total worldwide primary energy [1]. In Europe, the largest cost-effective saving potential is in the residential and commercial buildings sector, where the full potential is estimated to be 27% and 30% of energy use, respectively [2]. This presents a major possibility for climate change mitigation targets. To reduce greenhouse gas emissions, the European Parliament and Council has adopted a new energy performance directive for buildings [3]. The Directive requires Member States to lay down the necessary measures for establishing an energy performance certification system for buildings. The Finnish Ministry of the Environment has issued new energy efficiency regulations for new and renovated buildings [4]. The purpose of these regulations is to promote energy efficiency and the use of renewable energy in buildings, as well as to reduce buildings' energy consumption and carbon dioxide (CO2) emission. Current regulations in Finland have not set a minimum requirement for renewable energy use in buildings.
* Corresponding author. Tel.: þ358 43825914; fax: þ358 9506 1087. E-mail address: rauno.holopainen@ttl.fi (R. Holopainen). http://dx.doi.org/10.1016/j.buildenv.2015.01.024 0360-1323/© 2015 Elsevier Ltd. All rights reserved.
The law regarding a building energy performance certificate was first passed in Finland in 2007 [5] and revised later in 2013 [6,7]. The new law demands an energy performance certificate for new constructions and also for existing buildings when they are sold or rented. The calculated primary energy demand [kWh/m2 a] and the corresponding building energy performance class (AeG) have to be presented on the energy performance certificate. The calculation procedure is described in the National building code of Finland in parts D3 and D5 [8,9] as well as in Standard SFS-EN ISO 13790 [10]. The energy performance of energy efficient buildings has been studied particularly during the last decade in Europe, for example in the CEPHEUS project [11,12]. Energy efficient construction has been found to have a positive impact on both buildings' energy use [11e16] and indoor air quality [11,12,14]. However, in some cases, occupants have not been satisfied with thermal conditions in wellinsulated passive houses [17]. The first aim of the study was to compare the calculated primary energy demand (need) and the purchased primary energy use (consumption) in five Finnish low-energy houses and five conventional houses. We calculated the primary energy demand according to the energy performance certificate, which came into force in Finland in 2013. The second aim was to determine how the
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
air tightness, air flow rates and room temperature of the houses corresponded to the given input values for the calculation, and how they fulfilled the given guideline values. The measurements were carried out during 2012e2013. The third aim was to determine how occupants perceived indoor environment quality in the studied low-energy and conventional houses. The questionnaire survey was carried out in the winter and autumn of 2013.
2. Materials and methods 2.1. Low-energy and conventional houses studied We selected five low-energy houses and five conventional houses for the study. The low-energy houses were built in 2009e2012, and the conventional houses in 1974e2011. The houses were located between Southern Finland and the Oulu region. The selected houses presented typical, recently built, one- or twostoried low-energy houses; and older one-storied, conventionally built houses in Finland. Typical low-energy and conventional houses are presented in Fig. 1. The average living area of the low-energy houses was 192 m2, and the average air volume 594 m3. The outer wall and loadbearing structure of the houses were concrete or wood. The average thermal conductance (thermal transmittance surface area) of the houses' envelopes, including roof, floor, doors and windows, was 0.18 W/K. The ratio of the wall to windows surface area was on average 0.15. The largest windows in the houses were located in the southeast, southern or southwest facade. All windows were equipped with curtains, blinds and external solar shading or sun protection film. The low-energy houses were equipped with a mechanical supply and exhaust ventilation system with cooling and heat recovery units. The heat recovery units were cross flow, counter flow or regenerative heat exchangers. Floor and ventilation heating were the main heating system in the lowenergy houses. The hot water tanks' capacity was on average 0.7 m3 in the houses. Heat pumps were installed in four of the lowenergy houses.
93
The average living area of the conventional houses was 121 m2 and air volume 307 m3. The outer wall and load-bearing structure of the houses were brick, concrete or wood. The average thermal conductance of the houses' envelopes was 0.43 W/K. The ratio of the wall to windows surface area was on average 0.21. All windows in the houses were equipped with curtains and blinds. The houses had natural ventilation or mechanical supply and exhaust ventilation systems with cross flow heat exchangers. Electric, floor and ventilation heating were the main heating systems in the conventional houses. The average capacity of the houses' hot water tanks was 0.9 m3. A heat pump was installed in one conventional house. According to the occupants, no energy conservation renovations had been carried out in the houses. All the houses studied had fireplaces. More detailed information on the low-energy houses is given in Table 1 and on the conventional houses in Table 2. 2.2. Calculation details The houses' primary energy demand was calculated using the commercial MX6 Energy programme, version 6.4.0 [18], which calculates the house's energy demand using a monthly method [10]. The designed thermal transmittance of the houses' walls, roofs, floors, doors, and windows, as well as the measured air tightness of the house envelope were used in the calculation. The calculation used the following input values [7,8,19]: supply and exhaust air flow rates of 1.44 m3/hm2, space heating limited to below 21 C, specific hot water energy of 4200 kWh/a (35 kWh/ m2 a), house occupancy rate of 0.6, electricity for lighting at 8 W/m2 and for appliances 3 W/m2, and occupants' heating load of 2 W/m2. In addition, the renewable energy of the fireplace was limited to 2000 kWh/a, and the outdoor air to air heat pump energy to 1000e6000 kWh/a, depending on the year in which the house building permit was issued. The heat transfer efficiency of the fireplace was assumed to be 0.6 [9]. Annual heat recovery efficiency (ha) was determined on the basis of the heat exchanger type according to Refs. [8,9]. The seasonal performance factor (SPF) of the heat pumps that were used in the calculation was taken from
Fig. 1. (a) Location of the low-energy houses (white circle) and conventional houses (grey circle) in Finland. (b) A typical low-energy house and (c) a conventional house.
Location House (year of construction)
Number of stories, shape of house and roof
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Table 1 Detailed information on low-energy houses. Living Air Ratio of window Thermal area volume and wall surface conductance of 2 3 [m ] [m ] house envelope area [e] [W/K]
Heating energy form: space Ventilation systema heating system
Renewable energy systemb
Number of occupants (age) 4e6 (adults 30e45 and children 5e10) 4e5 (adults 30e35 and children 5e15) 2 (adults 30e40)
Two stories with Helsinki Metropolitan cellar, union of two blocks, pitched roof area
337
1030
0.21
0.21
Electricity: ventilation heating
Mechanical supply and exhaust ventilation with counter flow heat exchanger (ha ¼ 58%)
Fireplace and ground source heat pump (SPF ¼ 2.3e3.4)
Low H2 (2011)
Uusimaa regional council
One storey block, double-pitched roof
125
425
0.10
0.14
Electricity: ventilation heating and electric floor heating in wet rooms
Mechanical supply and exhaust ventilation with regenerator heat exchanger (ha ¼ 61%)
Fireplace and outdoor air to air heat pump (SPF ¼ 1.8e2.8)
Low H3 (2011)
The regional council of Satakunta The regional council of Satakunta
Two stories block with 190 porch, double-pitched roof One storey with cellar, 152 union of two blocks, pitched roof
628
0.16
0.16
0.19
0.19
Mechanical supply and exhaust ventilation with cross flow heat exchanger (ha ¼ 49%) Mechanical supply and exhaust ventilation with counter flow heat exchanger (ha ¼ 58%)
Fireplace and exhaust air to water heat pump (SPF ¼ 2.0)
475
Electricity: ventilation heating and electric floor heating in wet rooms Electricity: floor heating
Oulu region
Two stories, union of two blocks, doublepitched roof
410
0.11
0.18
Wood: floor heating
Mechanical supply and exhaust ventilation with regenerator heat exchanger (ha ¼ 61%)
Low H4 (2012)
Low H5 (2010) a b
157
Fireplace and ground source heat pump (SPF ¼ 2.3e3.4), supply air was pre-heated by geothermal heating circuit Fireplace, connected to hot water boiler, supply air pre-heated by geothermal heating circuit
3 (adults 30e35 and children 5) 2 (adults 60e65)
Annual heat recovery efficiency ha [9]. Seasonal performance factor SPF [9].
Table 2 Detailed information on conventional houses. House (year of Location construction)
Ratio of window Number of stories, shape Living Air volume and wall surface of house and roof area 2 3 [m ] area [e] [m ]
Thermal conductance of house envelope [W/K]
Heating energy form: space heating system
Ref H1 (1974)
One story block, hipped roof
Ref H2 (1985)
Ref H3 (2011)
Ref H4 (1986)
Ref H5 (1994)
a b
Helsinki Metropolitan area Helsinki Metropolitan area Helsinki Metropolitan area Kuopio region Oulu region
Ventilation systema
Renewable energy systemb
Number of occupants (age)
108
268
0.34
0.78
Electricity: electric Natural ventilation (ha ¼ 0%) radiator
Fireplace
2 (adults 55e60)
One storey block with bay 136 window, double-pitched roof One storey, union of two 130 blocks, double pitched roof One storey block, double- 104 pitched roof
337
0.16
0.33
Fireplace
3 (adults 55e60 and children 20)
350
0.16
0.26
260
0.22
0.39
321
0.15
0.39
Electricity: Mechanical supply and exhaust ventilation heating ventilation with cross flow heat exchanger (ha ¼ 49%) Electricity: electric Mechanical supply and exhaust floor heating ventilation with cross flow heat exchanger (ha ¼ 49%) Electricity: radiant Mechanical supply and exhaust ceiling heating ventilation with cross flow heat exchanger (ha ¼ 49%) Wood: floor Mechanical supply and exhaust heating ventilation with cross flow heat exchanger (ha ¼ 49%)
One storey block with porch and attic, doublepitched roof
Annual heat recovery efficiency ha [9]. Seasonal performance factor SPF [9].
125
Fireplace and outdoor air 4 (adults 25e30 and children 5e8) to air heat pump (SPF ¼ 1.8e2.8) Fireplace 1 (adult 50)
Fireplace and wood boiler 1e2 (adults 30e40)
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
Low H1 (2009)
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
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Table 3 Calculated energy demand, CO2 emission and energy performance class in low-energy houses. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Energy performance class (AeG)
Low Low Low Low Low
47 72 67 71 48
12 34 12 28 27
10 27 18 22 89
85 136 123 132 126
10.5 16.1 14.9 15.8 10.7
B B B C C
H1 H2 H3 H4 H5
Ref. [9]. The houses' cooling energy demand was not taken into account because the energy performance certificate did not require its calculation in single-family houses. The calculation used the HelsinkieVantaa climate zone data given in Ref. [8]. The average heat value of wood fuel was assumed to be 1700 kWh/m3 (stack m3) for birch and 1300 kWh/m3 for mixed wood [7]. The primary energy factors used were 1.7 for electricity and 0.5 for renewable energy [7,8]. The CO2 emission factors used were 223 kg CO2/MWh for electricity and 0 kg CO2/MWh for wood fuel [19]. 2.3. Purchased energy use in the houses
Finnish Institute of Occupational Health [23]. It is based on the Swedish standardized MM-40 questionnaire [24], and elicits environmental problems (draught, dry, stuffy air, etc.) from the past three months. Environmental problems that occurred every week or occasionally were also elicited and collected. The survey was carried out during the cooling and heating season of the winter of 2013 and the autumn of 2013, respectively.
3. Results 3.1. Calculated energy demand
The purchased energy and water use data for 2013, concerning wood burned in the fireplaces as fuel, was collected from the house owners. They were asked to take the purchased energy and water use data from their electricity and water bills. Purchased space heating energy use in the houses located outside the HelsinkieVantaa climate zone was normalized to that of HelsinkieVantaa [20,21], assuming that electricity energy for lighting and appliances was part of the space heating energy. 2.4. Measurements in the houses The air tightness of the houses' envelopes was measured using Minneapolis Blower Door Systems. Air leakage gaps were visualized by using tracer smoke and the FLIR B200 thermal camera. The supply and exhaust air flow rates were measured from the air terminal units using the SwemaFlow 125 air flow hood. The air change rate of the house equipped with natural ventilation systems was determined using a tracer gas method (CO2). The air change rate was measured in the winter in the unoccupied house, the windows and doors of which were closed. Room temperature and relative humidity were measured in the houses' living and bedrooms with TinyTag View 2 sensors. Data loggers saved the measured values in 15 min. Outdoor air temperature data was collected from the weather station of the Finnish Meteorological Institute [22]. Room temperature and relative humidity measurements were carried out during July 2012 and October 2013. Only mean room temperature values are presented in the Results. 2.5. Interview and questionnaire survey We interviewed the occupants and assessed perceived indoor environment quality using a questionnaire survey developed by the
Tables 3 and 4 present the calculated electricity, hot water, renewable and primary energy demands, and CO2 emission per living area per year in the low-energy and conventional houses. The average primary energy demand was 120 kWh/m2 a (85e136 kWh/ m2 a) in the low-energy houses and 323 kWh/m2 a (203e577 kWh/ m2 a) in the conventional houses. Average CO2 emission was 13.6 kg CO2/m2 a (10.5e16.1 kg CO2/m2 a) in the low-energy houses and 37.7 kg CO2/m2 a (10.9e73.6 kg CO2/m2 a) in the conventional houses. Electricity energy for lighting and appliances was 23 kWh/ m2 a in all the houses [7,8]. Primary energy demand corresponded to energy performance classes BeC in the low-energy houses and classes DeG in the conventional houses. It should be noted that the energy performance class of single-family houses depends on living area [7].
3.2. Purchased energy use in 2013 The average purchased primary energy use was 125 kWh/m2 a (88e177 kWh/m2 a) in the low energy houses, and 220 kWh/m2 a (155e277 kWh/m2 a) in the conventional houses. The corresponding average CO2 emission of purchased energy use was 15.5 kg CO2/m2 a (9.6e23.2 kg CO2/m2 a) in the low-energy houses, and 25.1 kg CO2/m2 a (10.7e34.1 kg CO2/m2 a) in the conventional houses. The purchased electricity, hot water, renewable and primary energy use, as well CO2 emission per living area per year in the low-energy and conventional houses in 2013 are presented in Tables 5 and 6. Table 7 presents the ratio of calculated and purchased electricity, water, renewable and primary energy, as well as CO2 emission per living area in 2013. Renewable energy consists of space heating energy, i.e. wood fuel in fireplaces.
Table 4 Calculated energy demand, CO2 emission and energy performance class in conventional houses. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Energy performance class (AeG)
Ref Ref Ref Ref Ref
330 170 123 174 49
35 31 32 35 34
31 25 26 32 239
577 301 222 312 203
73.6 37.9 27.4 38.8 10.9
G E D E D
H1 H2 H3 H4 H5
96
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Table 5 Purchased energy use and CO2 emission in low-energy houses in 2013. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Low Low Low Low Low
53 104 45 77 86
18 16 18 20 10
4 0 31 21 19
93 177 88a 136a 133a
12.7 23.2 9.6a 16.5a 16.3a
a
H1 H2 H3 H4 H5
Space heating energy is normalized to correspond to HelsinkieVantaa climate zone [20,21].
Table 6 Purchased energy use and CO2 emission in conventional houses in 2013. House
Electricity energy [kWh/m2 a]
Hot water energy [kWh/m2 a]
Renewable energy in fireplace [kWh/m2 a]
Primary energy [kWh/m2 a]
CO2 emission [kg CO2/m2 a]
Ref Ref Ref Ref Ref
138 153 128 108 55
12 26 10 9 11
31 35 20 63 177
250 277 227 193a 155a
30.8 34.1 28.5 21.7a 10.7a
a
H1 H2 H3 H4 H5
Space heating energy is normalized to correspond to HelsinkieVantaa climate zone [20,21].
3.3. Measured air tightness, air change rate and room temperature
4. Discussion
The average air tightness of the houses' envelopes was 0.4 1/h (0.2e0.6 1/h) in the low-energy houses and 4.2 1/h (1.2e11.3 1/h) in the conventional houses. The average air change rate in the lowenergy houses was 0.3 1/h (0.2e0.5 1/h) and in the conventional houses 0.4 1/h (0.2e0.7 1/h). During the winter season (Dec 2012 and Feb 2013), the mean room temperature was 21.9 C (20.8e22.5 C) in the low-energy houses and 20.7 C (18.1e22.0 C) in the conventional houses. During the summer season (June and Aug 2013), the mean room temperature in the low-energy houses was 22.6 C (21.9e23.8 C), and in the conventional houses 23.1 C (21.4e24.0 C). The results are shown in Tables 8 and 9.
In all the low-energy houses and in four of the conventional houses, the occupants were the original occupants of the houses. They worked in construction, HVAC, research, the indoor environment field, or the business sector. The number of occupants was 2e6 in the low-energy houses and 1e4 in the conventional houses. The average age of the adults in the low-energy houses was 40, and in the conventional houses 45. Three low-energy houses and three conventional houses also had children as occupants. The occupants did not observe indoor air problems in the houses. Electricity was the main heating form in four of the low-energy and four of the conventional houses. The average living area per person was 61 m2 in the low-energy houses and 60 m2 in the conventional houses. The air change rate was on average slightly lower in the low-energy houses than in the conventional houses. However, the air volume of the low-energy houses was almost twice that of the conventional houses. The air change rate in the studied low-energy and conventional houses was of the same magnitude as that measured in the passive houses in the CEPHEUS project (0.25e0.4 1/h) [12]. The designed value of the thermal conductance of the lowenergy houses' envelopes was almost half that of the conventional houses. In addition, the air tightness of the low-energy houses' envelopes was about ten times better than that of the conventional houses' envelopes. The ratio of the wall to windows surfaces area was on average slightly lower in the low-energy houses than that in the conventional houses. The average annual heat recovery efficiency of the ventilation systems was estimated to be 57% and 39% in the low-energy and conventional houses, respectively. Thus, the heat loss of the low-energy houses per floor surface area has to be lower than in the conventional houses under the same conditions. An energy performance certificate was given to all the lowenergy houses during their design process. The energy performance of the low-energy houses was classified as class A according to the old law [5]. High annual heat recovery efficiencies of ventilation systems were used in the calculation. Ice formation in heat exchangers reduces heat recovery efficiency in cold climates such as those in Nordic countries [27], and this must be taken into account in the calculation. In this study, the calculation used a ventilation heat exchanger efficiency of 49e61% in the low-energy
3.4. Perceived indoor air quality Occupants perceived indoor environment quality as slightly better in the low-energy houses than in the conventional houses. The occupants of the conventional houses more often complained about draught, high or varying room temperature, stuffy and dry air, insufficient ventilation, unpleasant odours, or dim light in the winter than the occupants of the low-energy houses. In the summer, the occupants more often reported high room temperatures, insufficient ventilation, noise, and dim light than the occupants of the low-energy houses. The perceived indoor environment quality in the low-energy and conventional houses is presented in Figs. 2 and 3 (also Tables 8 and 9) during the winter and summer of 2013, respectively. Table 7 The ratio of calculated and purchased electricity, water, renewable and primary energy, and CO2 emission in low-energy and conventional houses (purchased energy use in 2013). Calculated energy demand/purchased energy use mean value (minemax) [e]
Electricity energy Hot water energy Renewable energya Primary energy CO2 emission a
Low-energy houses
Conventional houses
0.91 1.51 1.69 1.00 0.95
1.39 2.84 0.98 1.46 1.46
(0.56e1.50) (0.66e2.67) (0.00e4.57) (0.77e1.40) (0.66e1.55)
Space heating energy: wood fuel in fireplace.
(0.89e2.39) (1.21e3.90) (0.51e1.35) (0.98e2.30) (0.96e2.39)
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Table 8 Low-energy houses: air tightness, air change rate, mean room temperature (minemax) in winter 2012e2013 and summer 2013, as well as ratio of calculated primary energy demand and purchased primary energy use. Occupants' reported insufficient ventilation (I), or high (H), varying (V) or low (L) room temperature are marked in parenthesis. House
Low Low Low Low Low
H1 H2 H3 H4 H5
Air tightnessa [1/h]
0.2 0.4 0.6 0.4 0.5
Air change rateb [1/h] 0.3 0.5 0.2 0.4 0.3
Room temperaturec Winterd [ C]
Summere [ C]
21.2 22.4 20.8 22.5 22.4
22.3 22.6 21.9 23.8 22.2
(19.7e22.3) (20.4e23.3) (H/V/L) (16.3e23.6) (H/V/L) (21.0e24.7) (18.9e24.0)
Primary energy demand/usef [e]
(20.9e23.9) (20.3e25.3) (H/V/L) (19.4e24.4) (H/V/L) (22.0e26.4) (19.1e25.1)
0.91 0.77 1.40 0.97 0.95
a
Air tightness n50 value for passive house must be equal to or below 0.6 1/h [25]. Air change rate must be equal to or higher than 0.5 1/h [26]. A tolerable level of room temperature is 18 C and a good level 21 C. In addition, room temperature should not exceed 23e24 C during the heating season. Room temperature may exceed 26 C only if this caused by outdoor conditions [26]. d Measurements carried out during December 2012 and February 2013. e Measurements carried out during June and October 2013. f Purchased primary energy use in 2013. b c
houses, and 0e49% in the conventional houses. The calculated primary energy demand corresponded to energy performance classes BeC in the low-energy houses. However, energy performance class B would have been achieved in all low-energy houses if we had used annual ventilation heat recovery efficiency that was higher than 70%. It should also be noted that the energy performance classes given in Refs. [5,6] cannot be directly compared with each other. The space heating energy demand is estimated to be 15e25 kWh/m2 a in high performance houses in the climate of Stockholm, Oslo and Helsinki [28]. This estimation is based on simulation, which was carried out using a heat exchanger efficiency of 80%. According to this study, the energy demand, without electricity for lighting and appliances and hot water energy, was on average 49 kWh/m2 a (22e87 kWh/m2 a) in the low-energy houses, and 183 kWh/m2 a (94e303 kWh/m2 a) in the conventional houses. Only low-energy house Low H1 achieved the target value presented above. The air tightness of the houses' envelopes was measured in the winter of 2012e2013. The air tightness in the low-energy houses varied roughly within a similar range to that measured in the passive houses (0.3e0.6 1/h) [12]. We used measured values as the input value in the calculation. In general, air leakage gaps were found in doors, windows and the structure joints of the houses' envelope. During the air tightness test, we used a thermal camera to visualize envelope heat loss, and this revealed that the heat loss of the low energy houses' envelopes was less than that of the conventional houses. Air tightness fulfilled the given guideline values [8,25] in all houses except in conventional house Ref H1, as we found a large air leakage in its roof structure.
The average measured supply and exhaust air flow rate was 1.03 m3/hm2 (0.55e1.76 m3/hm2) in the low-energy houses and 0.82 m3/hm2 (0.38e1.88 m3/hm2) in the conventional houses. These were both on average lower than the given input value of 1.44 m3/hm2 for the energy performance certificate calculation. As the calculation had to be carried out with an air flow rate of 1.44 m3/hm2 also in the house that was equipped with a natural ventilation system [7,8], it may overestimate the heat loss from ventilation, especially in conventional house Ref H1. The mean room temperature fulfilled the given minimum (tolerable level of 18 C) and maximum values (26 C) in all the houses studied. Roughly similar room temperatures, on average 22e23 C, were measured in the Danish energy efficient houses in the winter [16]. Room temperature was exceptionally low in conventional house Ref H1, on average 18.1 C, in the winter of 2012e2013. The occupants of this house had to keep room temperatures low for energy-saving reasons. The low room temperature considerably decreased the house space heating energy use, and thus, also primary energy use and CO2 emission (Figs. 4 and 5). The purchased primary energy use was lower than the calculated primary energy demand in all the houses studied, the average room temperature of which was below 21 C in the winter (Tables 8 and 9). The houses were not equipped with a separate electricity energy meter for lighting and appliances. The occupants estimated electricity use for these to be 20e30 kWh/m2 a in the low-energy houses, and 20e65 kWh/m2 a in the conventional houses. The occupants' estimations were based on the electric power of lighting and appliances as well as their estimated operating time in 2013. The purchased electricity energy use in conventional house Ref H5
Table 9 Conventional houses: air tightness, air change rate, mean room temperature (minemax) in winter 2012e2013 and summer 2013, as well as ratio of calculated primary energy demand and purchased primary energy use. Occupants' reported insufficient ventilation (I), or high (H), varying (V) or low (L) room temperature are marked in parenthesis. House
Ref Ref Ref Ref Ref a
H1 H2 H3 H4 H5
Air tightnessa [1/h]
11.3 2.0 1.2 2.1 4.0
Air change rateb [1/h] 0.2 (I) 0.3 0.7 0.3 0.2
Room temperaturec Winterd [ C] 18.1 22.0 22.0 20.5 22.0
(10.1e21.8) (20.2e29.2) (19.6e24.1) (13.3e24.8) (17.3e23.7)
Primary energy demand/usef [e]
Summere [ C] (H/V/L) (H/V) (H/V/L) (H/V)
21.4 23.6 23.7 22.6 24.0
(18.2e24.9) (19.1e27.7) (21.0e26.5) (13.5e27.2) (20.2e28.5)
(V/L) (H) (H/V) (H) (H)
2.30 1.09 0.98 1.61 1.31
Air tightness q50 value for conventional house must be equal to or below 4.0 m3/hm2 [8], which corresponds roughly to an n50 value of 4.0 1/h. b Air change rate must be equal to or higher than 0.5 1/h [26]. c A tolerable level of room temperature is 18 C and a good level 21 C. In addition, room temperature should not exceed 23e24 C during the heating season. Furthermore, room temperature may exceed 26 C only if this is caused by outdoor conditions [26]. d Measurements carried out during December 2012 and February 2013. e Measurements carried out during June and October 2013. f Purchased primary energy use in 2013.
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Questionnaire: low-energy and conventional houses (n=5) Have any of following factors disturbed you in the past three months? (winter time) dim light/glare
noise
draught 100 80
room temperature too high
60
varying room temperature
40 20
passive smoking
room temperature too low
0
other unpleasant odours
stuffy "bad" air
odour of mould or underground dry air cellar insufficient ventilation
Conventional houses
Low-energy houses
Fig. 2. Perceived indoor environment quality in low-energy and conventional houses in winter 2013.
(55 kWh/m2 a) included mainly electricity for lighting and appliances, because space heating and hot water were produced by a wood fuel boiler. The value of 23 kWh/m2 a, which is given as an input value for the calculation, does not include energy use outside the houses, for example, outdoor lighting and car heating [7,8]. Total water use was on average 40 m3/a (17e72 m3/a) per person in the low-energy houses and 32 m3/a (15e50 m3/a) per person in the conventional houses. The amount of hot water was assumed to be 40% of total water use [29]. Thus, the average purchased hot water energy use in low-energy houses was 2945 kWh/a (16 kWh/ m2 a), and in the conventional houses 1685 kWh/a (14 kWh/m2 a), which are both much lower that the given value of 4200 kWh/a (35 kWh/m2 a) for the calculation. The occupants interviewed said that the use of fireplace wood fuel varied yearly, depending on space heating demand, the
availability of wood, and the price of electricity. According to the occupants of low-energy house Low H2, they could not burn wood in the fireplace even in the winter, because it overheated the house. The amount of renewable energy for the calculation was limited to 2000 kWh/a in a normal fireplace [7,8]. Heat pumps had been installed in four of the low-energy houses and in one conventional house. The pumps were used for space heating and cooling in the houses. However, the energy performance certificate did not require calculation of the cooling energy demand in the single-family houses. According to Ref. [30], using outdoor air to air heat pump can produce more space heating energy in the Finnish cold climate, depending on heating demand, than the given limited value of 1000 kWh/a for new houses. The largest windows in the studied low-energy houses were located to the southern facade. According to Ref. [13], the size of
Questionnaire: low-energy and conventional houses (n=5) Have any of following factors disturbed you in the past three months? (summer time) dim light/glare noise
draught 100
80
room temperature too high
60
varying room temperature
40 20
passive smoking
room temperature too low
0
other unpleasant odours
stuffy "bad" air
odour of mould or underground dry air cellar insufficient ventilation
Conventional houses
Low-energy houses
Fig. 3. Perceived indoor environment quality in low-energy and conventional houses in summer 2013.
R. Holopainen et al. / Building and Environment 87 (2015) 92e101
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Low H1 Calculated primary energy demand Purchased primary energy use
Low H2 Low H3 Low H4 Low H5 Ref H1 Ref H2 Ref H3 Ref H4 Ref H5 0
100
200
300 400 Primary energy [kWh/m2a]
500
600
Fig. 4. Calculated primary energy demand and purchased primary energy use in low-energy and conventional houses (purchased energy use in 2013).
energy-efficient windows has only a minor influence on the space heating demand in the winter, but a major influence on the cooling demand in the summer. Thus, it is possible to also use larger windows on the northern facade to obtain better daylight conditions in the low-energy houses. The lowest calculated primary energy demand was in more complicatedly-shaped, two-storied, low-energy house Low H1, the living area and air volume of which were much higher than in the other low-energy houses. The lowest primary purchased energy use was in compact-shaped, two-storied, low-energy house Low H3, which was occupied by a childless couple. Both the highest calculated primary energy demand and the highest purchased primary energy use were in compact-shaped, one-storied, lowenergy house Low H2, the living area and air volume of which were the smallest of the low-energy houses. Both the lowest calculated primary energy demand and the lowest purchased primary energy use were in conventional house Ref H5, which was occupied by a childless couple and the space
heating and hot water energy of which were produced by a wood boiler. The highest calculated primary energy demand was in old electricity-heated conventional house Ref H1, which was equipped with a natural ventilation system. The highest purchased primary energy use was in ventilation-heated conventional house Ref H2, the living area and air volume of which were the highest of the conventional houses. In this study, the calculation estimated a slightly lower average primary energy demand in the low-energy houses and a considerably higher one in the conventional houses than purchased primary energy use. However, variation was great, especially in the conventional houses. The year 2013 was exceptionally warm compared to the long-term average in Finland [31]. Thus, the purchased space heating energy use in 2013 may have been lower than the average for a year. Fig. 4 presents the calculated and purchased primary energy in low-energy and conventional houses. The primary energy factors had a significant effect on the calculated primary energy demand and the purchased primary
Low H1 Calculated energy demand CO2 emission Purchased energy use CO2 emission
Low H2 Low H3 Low H4 Low H5 Ref H1 Ref H2 Ref H3 Ref H4 Ref H5 0
10
20
30 40 50 CO2 emission [kg CO2/m2a]
60
70
80
Fig. 5. Calculated and purchased energy of CO2 emission in low-energy and conventional houses (purchased energy use in 2013).
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R. Holopainen et al. / Building and Environment 87 (2015) 92e101
energy use in the low-energy and conventional houses studied. The primary energy factor for electricity was particularly high, and therefore affected the houses' energy performance classes. Primary energy factors can be used as a tool for selecting energy forms in order to achieve a low primary energy demand in the house. The variation of CO2 emission in electricity-heated houses was similar to that of primary energy demand and energy use. The same order of magnitude of CO2 emission is reported in Swedish residential houses [32] as that in this study. Fig. 5 presents the calculated and purchased energy of CO2 emission in the low-energy and conventional houses. The perceived indoor environment quality was slightly better in the low-energy houses than in the conventional houses. In particular, the occupants perceived less high room temperature, insufficient ventilation and dim light in the low-energy houses than the occupants in the conventional houses in the winter and summer. However, too high and varying room temperature were the most commonly reported unsatisfactory indoor environment factors in both the low-energy and conventional houses in the winter and summer. Therefore, correct room temperature was an important factor for primary energy use and perceived indoor environment quality in the houses. The measured air change rate did not fulfil the given minimum value in four of the low-energy houses and four of the conventional houses. Despite this, only the occupants of one conventional house (Ref H1), which was equipped with a natural ventilation system, complained of insufficient ventilation in the winter and summer. In a recently published Swedish study [17], occupants complained more often of cold floors and varying room temperatures in passive houses than in conventional houses. In addition, a high number of the occupants' complaints was related to excessively high room temperatures in the summer. The passive houses' windows had not been equipped with external shading, which may have contributed to this. In our study, the g-value (so called solar factor) of the low-energy houses' windows varied between 0.44 and 0.56. The houses' ventilation systems also had a cooling unit to ensure comfortable room temperature in the houses during the summer. The number of houses we studied was small, and therefore, the results may present a rather narrow scope of information regarding primary energy performance in Finnish houses. In addition, the conventional houses studied were on average 21 years older than the low-energy houses. Furthermore, the occupants evaluated the indoor environment quality of their own house, which may also have affected the results of the questionnaire survey. However, the results still reveal differences between the calculated primary energy demand and purchased primary energy use in recently built low-energy and older conventional houses. In addition, they provide information on how occupants perceived the environment quality in these houses, and how the measured air tightness, air change rate and room temperature of the houses met the given Finnish guideline values. 5. Conclusions We calculated the primary energy demand of five recently built low-energy houses and five older conventional houses in accordance with the 2013 building energy certificate of Finland. The calculated primary energy demand corresponded to energy performance classes BeC in the low-energy houses and classes DeG in the conventional houses. The primary energy demand was on average 2.7 times higher in the conventional houses than in the low-energy houses. Purchased primary energy use in 2013 was on average 1.7 times higher in the conventional houses than in the low-energy houses. Measured air flow rates and purchased hot
water use were on average lower than the given input values for the calculation in both the low-energy and conventional houses. According to the interview and questionnaire survey, occupants suffered less from high room temperature, insufficient ventilation and dim light in the recently built low-energy houses than the occupants in the older conventional houses. The factors that caused the most dissatisfaction in the low-energy and conventional houses were excessively high and varying room temperatures. The differences between the perceived environment quality of the lowenergy and conventional houses were higher in the winter than in the summer.
Acknowledgements The study was the part of RYM Indoor Environment programme. The authors warmly thank Tekes e the Finnish Funding Agency for Innovation, and the companies that supported the studies. This study would not have been possible without field measurements in real houses, and thus the authors wish to kindly thank the occupants of the low-energy and conventional houses for their smooth, €inen, fruitful co-operation. In addition, the advice of Leevi Myyryla €inen, CEO, on the use of Senior Engineer (HVAC) and Antti Myyryla the MX6 Energy programme is gratefully acknowledged.
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