- Email: [email protected]
Primary energy implications of ventilation heat recovery in residential buildings
Energy and Buildings 43 (2011) 1566–1572
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Primary energy implications of ventilation heat recovery in residential buildings Ambrose Dodoo a,∗ , Leif Gustavsson a,b , Roger Sathre a a b
Mid Sweden University, 83125 Östersund, Sweden Linnaeus University, 35195 Växjö, Sweden
a r t i c l e
i n f o
Article history: Received 26 October 2010 Received in revised form 27 January 2011 Accepted 28 February 2011 Keywords: Mechanical ventilation Heat recovery Heat supply systems Electric resistance heating Heat pump District heating CHP plant Primary energy
a b s t r a c t In this study, we analyze the impact of ventilation heat recovery (VHR) on the operation primary energy use in residential buildings. We calculate the operation primary energy use of a case-study apartment building built to conventional and passive house standard, both with and without VHR, and using different end-use heating systems including electric resistance heating, bedrock heat pump and district heating based on combined heat and power (CHP) production. VHR increases the electrical energy used for ventilation and reduces the heat energy used for space heating. Significantly greater primary energy savings is achieved when VHR is used in resistance heated buildings than in district heated buildings. For district heated buildings the primary energy savings are small. VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the amount of electricity used for VHR and the airtightness of buildings. This study shows the importance of considering the interactions between heat supply systems and VHR systems to reduce primary energy use in buildings. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Building energy use is a major concern in the European Union, where the building sector accounts for the 40% of total primary energy use [1]. Member States of the European Union are required to implement energy efficiency measures for buildings under the Energy Performance of Building Directive [2]. The Swedish government target of reducing the final energy use per heated building area is 20% and 50% below 1995 levels by 2020 and 2050, respectively [3]. Heat recovery from exhaust ventilation air in existing apartment buildings is considered an important means to reach this target [4]. Ventilation has a significant impact on the energy performance of buildings, accounting for 30–60% of the energy use in buildings [5–7]. Energy is used to cover the heat losses due to the ventilation air and to move the ventilation air for mechanical ventilation. The ventilation system also influences the air infiltration through the building envelope. Recent building standards require high energy efficiency of buildings, and therefore considerable efforts have been made to improve airtightness and insulation of buildings. In such buildings infiltration is low and mechanical ventilation systems are often used to achieve the required airflow. Mechanical ventilation systems can include ventilation heat recovery (VHR) systems to recover heat from exhaust air to reduce ventilation heat losses.
∗ Corresponding author. Tel.: +46 63 165383; fax: +46 63 165500. E-mail address: [email protected] (A. Dodoo). 0378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2011.02.019
VHR systems transfer the heat from the exhaust air to the supply air via a heat exchanger. Ventilation heat losses can be typically 35–40 kWh/m2 -year in residential buildings, and up to 90% of this can be recovered with VHR depending on airtightness and insulation of buildings [8]. In very low energy buildings, such as passive house buildings, VHR systems can be equipped with additional air heaters to cover the space heating demand. VHR is therefore gaining increasing interest in low energy and retrofitted buildings [9]. Various studies have analyzed the impacts of VHR on energy use of buildings. For example, Hekmat et al. [10] compared different residential ventilation strategies including VHR systems in different US climatic conditions. They found that the total energy for space and tap water heating was reduced by 9–21% by using VHR. The European TIP-Vent [11] explored the impacts of VHR systems on the energy performance of different types of buildings in several European countries including Sweden. They found that VHR systems reduced the total energy for space heating by 20–50%, depending on building type and airtightness. Jokisalo et al. [12] simulated the performance of VHR systems in a typical Finnish apartment building using centralized or decentralized ventilation units. They found that energy performance of decentralized ventilation units is not significantly improved when VHR is installed. Sherman and Walker [13] analyzed the energy impact of different ventilation norms in typical US buildings. They found that VHR generally increased net energy use as the energy used by the blower offset the energy savings from space conditioning. The above studies, however, analyzed only final energy use and not primary energy use.
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
1567
Table 1 Thermal properties of the building components. U-value (W/m2 K)
Building
Conventional Passive
Air leakage (l/s m2 ) at 50 Pa
Ground floor
External walls
Windows
Doors
Roof
0.23 0.23
0.20 0.10
1.90 0.85
1.19 0.80
0.13 0.08
Fewer studies (e.g. [14–16]) have analyzed the impacts of VHR on primary energy use of residential buildings. The concept of primary energy is used to denote the total energy needed in order to generate the final energy service, including inputs and losses along the entire supply chains. Primary energy use, in contrast to final energy use, determines the natural resource use and the environmental impact of supplying the energy services. The various processes along the energy supply chain, from the extraction of raw material to refining, transport, conversion to heat and electricity, and distribution to the user can be performed with different energy efficiencies. All the energy input from these processes need to be included for a full description of a particular energy system. Nyman and Simonson [14] and Zmeureanu and Wu [16] found VHR to reduce net primary energy use, and Nyman and Simonson [15] concluded that VHR is an environmentally favourable solution for a cold climate region. However, these studies analyzed the impacts of VHR in buildings heated with electric-based heaters or gas-fired boilers. The heat demand of a building can be provided by different end-use heating systems and energy supply technologies which can result in significantly different primary energy use [17–19]. A comprehensive analysis of the impacts of VHR on the primary energy use of buildings with different end-use heating and energy supply systems is lacking. In this study we analyze the primary energy implications of VHR in residential buildings heated with electric resistance heating, bedrock heat pump, or district heating based on combined heat and power (CHP) production. We consider cases where energy supply is based on steam turbine technology or integrated gasification combine cycle technology, all using biomass-based fuels. Our analysis considers the entire energy chains, and the trade-off between electricity use by the ventilation system and the reduction in space heat.
2. Methodology Our analysis is based on simulation modeling of a case-study apartment building with mechanical ventilation. We model the primary energy use for the original and improved level of energy efficiency of the building, both with and without VHR. Next we compare the primary energy use of the buildings and calculate
0.8 0.3
the net primary energy savings achieved by the VHR, taking into account the changed electricity use due to VHR, as well as the changed heat demand due to VHR and changed air infiltration. 2.1. Building descriptions Our case-study building is a 4-storey wood-frame building with 16 apartments and a total heated floor area of 1190 m2 . The outer walls of the building consist of three layers, including plastercompatible mineral wool panels, timber studs with mineral wool between the studs, and a wiring and plumbing installation layer consisting of timber studs and mineral wool. Two-thirds of the outer fac¸ade is plastered with stucco, with the remainder covered with wood paneling. The ground floor consists of oak boarding laid on a concrete slab, expanded polystyrene and crushed stones, and the upper floors are made of light timber joists. Persson [20] describes the construction and thermal characteristics of the building in detail. The ground floor plan and photograph of the building are shown in Fig. 1. To compare the impacts of VHR in buildings of different envelope characteristics and airtightness, a second building is modeled with thermal envelope properties of passive house but otherwise identical to the existing building. Table 1 shows the thermal characteristics of the conventional building and the passive building. In addition to lower U-values, the passive building is assumed to have much better airtightness than the conventional building. For both the conventional and passive buildings, we analyze the energy performance with and without VHR. For the buildings without VHR, exhaust air is extracted from the kitchens, bathrooms and closets with fan and duct system, and fresh air is supplied through slot openings under windows in the bedrooms and living rooms. For the buildings with VHR, the ventilation system provides the same airflow as in the buildings without VHR. For the conventional building the existing ventilation system is complemented with ventilation ducts for incoming air and a heat recovery unit [21]. 2.2. Calculation of final energy We calculate the annual final energy use of the buildings, both with and without VHR, using the ENORM software ([22,23]). The
Fig. 1. Ground floor plan (left) and photograph (right) of the case-study wood-frame building. The ground floor plan is adapted from Persson [20].
1568
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572 Table 3 Configurations of end-use heating and energy supply systems modeled.
Table 2 Major ventilation input values. Description
Value
End-use heating
Supply system
Air change rate (l/s m2 ) Heat recovery efficiency (%) Ventilated volume (m3 ) Supply air flow rate (m3 /h)
0.35 85 2861 1540
Electric resistance heating
BST stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder BIGCC stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder
Bedrock heat pump
BST stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder BIGCC stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder
District heating
CHP-BST plant cover 50% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 50% of the district heat production and light-oil fired boilers cover the remainder CHP-BST plant cover 90% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 90% of the district heat production and light-oil fired boilers cover the remainder CHP-BST plant cover 80% of the district heat production and light-oil fired boilers cover remainder CHP-BST plant cover 83% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 76% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 78% of the district heat production and light-oil fired boilers cover the remainder
software is commonly used by contractors, consultants and engineers in Sweden [24]. It calculates the space heating, ventilation, domestic hot water, and household and facility management electricity use of a building, and is also adapted to verify if a building meets the energy standard of the Swedish regulations. The software calculates the energy and power demand for a 12-month period, on a 24-h basis based on the building’s physical characteristics, internal and solar heat gains, occupancy pattern, outdoor climate, indoor temperature, heating and ventilation systems, etc. We use climate data for the city of Växjö in southern Sweden, and assume an indoor temperature of 22 ◦ C. We design the ventilation systems to give the airflow rates and specific fan power required by the Swedish regulation [25,26]. Table 2 shows principal values used to calculate the electricity use for ventilation. Other values including fan efficiency and operation mode of the ventilation systems are based on the assumptions of the ENORM software. 2.3. Supply systems We analyze cases where space heat is delivered by electric resistance heating, heat pump or district heating. For the electric resistance heating and heat pump, 95% of the electricity is assumed to be supplied from stand-alone biomass steam turbine (BST) plants and the remaining from light-oil gas turbine plants. We assume that the district heat is supplied from a CHP plant using biomass steam turbines (CHP-BST). Joelsson [27] observed that the dimensioning of a CHP plant in district heating systems influences primary energy use. To explore this, we consider scenarios where the CHP plant accounts for either 50% or 90% of the district heat production, with oil boilers accounting for the remainder. To show the potential impact of energy supply technology currently being developed, we also analyze a case where biomass integrated gasification combined cycle (BIGCC) technology is used instead of the BST technology for both CHP and stand-alone power production. Furthermore, Gustavsson et al. [28] explored the structure of district heat production under different environmental taxation regimes. They found that the CHP production should be 80–83% of the total district-heat production when using BST technology and 76–78% when using BIGCC technology. The difference in share of district-heat production between the technologies varies because the BIGCC technology is more efficient and capital intensive than the BST technology. To explore the implications of this for VHR, we calculate the primary energy savings when district heating is based on such CHP production systems. Table 3 summarizes the configurations of the end-use heating and energy supply systems modeled. The electricity use for ventilation and for household and facility management is assumed to be produced in a stand-alone power plant with the same technology and fuel as the heat. The capacities and the efficiencies of the power plants, cogeneration plants and end-use heating systems are given in Table 4. 2.4. Calculation of primary energy We use the ENSYST software [29] to quantify the primary energy needed to provide the final energy use in the different cases. The software calculates primary energy use considering the entire energy chain from natural resource extraction to final energy
supply, taking into account the fuel inputs at each stage in the energy system chain and the energy efficiency of each process. We follow Gustavsson and Karlsson’s [30] assumptions about the production and transport of fuels for electricity and heat when using the ENSYST software. For biomass-based heat and electricity productions, wood chips are assumed to be the fuel used. The crude oil for the production of petrol, diesel and light fuel oil is assumed to be imported from Norway. We assume distribution losses of 7% to the building for both electricity and district heat. The CHP plant cogenerates heat and electricity and therefore an allocation issue may arise. Different methods have been suggested to address allocation in co-product systems [31–33]. A method that avoids allocation is preferred, as allocation can be subjective [34,35]. Gustavsson and Karlsson [36] explored the multi-functional and the subtraction methods of system expansion Table 4 Capacity and efficiency of the power plants, cogeneration plants and end-use heating technologies. Technology
Capacity
Efficiency
Stand-alone power plants BST BIG/CC Light-oil gas turbines Cogeneration plants CHP-BST CHP-BIG/CC End-use heating District heating Heat pump Resistance heating
(MWelec ) 200 100 120 (MWelec /MWheat ) 36/72 60/60 (kWheat ) 10.5 7 10.5
(elec ) 0.40 0.47 0.27 (elec /heat ) 0.3/0.60 0.43/0.43 (heat ) 0.95 3 0.97
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
1569
Table 5 Annual final operation energy use. Final energy use (kWh/m2 year)
Building
Conventional building Conventional building with VHR Passive building Passive building with VHR
Space heating
Ventilation electricity
Tap water heating
Household and facility electricity
Total
70 50 43 13
4 8 4 8
40 40 40 40
52 52 52 52
166 150 143 113
Table 6 Annual operation primary energy use for the building with different end-use heating systems with energy supply based on BST technology. Primary energy use (kWh/m2 year)
Description
Resistance heating Conventional building Conventional building with VHR Passive building Passive building with VHR Heat pump Conventional building Conventional building with VHR Passive building Passive building with VHR District heating, 50% CHP Conventional building Conventional building with VHR Passive building Passive building with VHR District heating, 90% CHP Conventional building Conventional building with VHR Passive building Passive building with VHR
Space heating
Ventilation electricity
Tap water heating
Household and facility electricity
Total
209 149 128 39
12 24 12 24
119 119 119 119
155 155 155 155
495 447 414 337
78 55 48 14
12 24 12 24
45 45 45 45
155 155 155 155
290 279 260 238
66 47 41 12
12 24 12 24
38 38 38 38
155 155 155 155
271 264 246 229
42 30 26 8
12 24 12 24
24 24 24 24
155 155 155 155
233 233 217 211
to avoid allocation when comparing cogeneration and separate heat and electricity production systems. In this study we use the subtraction method to calculate the primary energy use for heat. The cogenerated electricity replace electricity that otherwise had been produced in a stand-alone plant using the same fuel and technology as the CHP plant. The primary energy used for the replaced electricity in the stand-alone plant is subtracted from the CHP plant to obtain the primary energy for the heat. 3. Results Table 5 shows the annual final energy use of the conventional and the passive buildings with and without VHR. The annual total final energy use of the passive building with VHR is about 21% lower than for the passive building without VHR. The corresponding reduction for the conventional building is 10%. VHR decreases the final heat use for ventilation losses heating, but increases the electricity used to operate the ventilation system and the air infiltration. Overall, VHR reduces the final energy for space heating and ventilation by 55% and 22% for the passive and the conventional building, respectively, relative to the alternatives without VHR. Table 6 shows the annual operation primary energy use for the conventional and the passive buildings with different end-use
heating systems. The energy supply is based on BST technology. Ventilation accounts for 2–11% of the operation primary energy use. The primary energy for heating for the district heated buildings is low due to the high overall efficiency of district heating systems with CHP plants. Table 7 compares the percentage primary energy savings of VHR in relation to the primary energy for space heating and ventilation. The VHR primary energy savings for space heating and ventilation ranges from 0 to 55%. The change in annual primary energy use for space heating and ventilation electricity when using VHR with different end-use heating system with BST or BIGCC energy supply are shown in Fig. 2. The net savings are shown in Fig. 3. The primary energy savings due to VHR are significantly greater when using resistance heating, followed by heat pump and district heating with 50% CHP. However, much smaller or no primary energy savings are achieved when using district heating with 90% CHP. The savings due to VHR are larger for the passive building than for the conventional building due to the better air-tightness of the passive building. The BIGCC technology gives similar results as the BST technology, but the net primary energy savings are lower compared to the BST technology. In cold climatic regions frost may occur on the heat recovery unit during winters. VHR systems may be fitted with additional
Table 7 Percentage primary energy savings of VHR, in relation to the primary energy used for space heating and ventilation for the different end-use heating systems with BST energy supply technology. Building
Conventional Passive
Relative primary energy savings Resistance heating
Heat pump
District heating, 50% CHP
District heating, 90% CHP
22% 55%
12% 37%
9% 32%
0 16%
1570
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
Fig. 2. Change in annual primary energy use for space heating and ventilation electricity when using VHR with BST or BIGCC energy supply.
preheating devices to overcome this problem, increasing the electricity use for VHR [37]. Our base calculations are based on electricity use of 4 kWh/m2 for the VHR [22,38], and do not include electricity to defrost the system. Tommerup and Svendsen [8] reported that electricity use in VHR system of 80–90% efficiency is typically 7 kWh/m2 under Danish conditions, and suggested this might be reduced to 3 kWh/m2 with more efficient units. In Fig. 3 the error bars show the change in net primary energy savings for VHR, when the electricity use for VHR is 7 kWh/m2 . The higher electricity use for operating VHR reduces the net primary energy
savings in particular for the district heated buildings. In fact, a ventilation electricity use of 7 kWh/m2 increases the net primary energy use for the buildings with district heating based on 90% CHP. Hence, a low electricity use for VHR is important. For the conventional building with lower airtightness together with district heating based on a large share of CHP production, VHR may even be counterproductive. In our base case calculations, the CHP production accounts for 50 and 90% of the total district heat production [39]. In this section, we show the net primary energy savings for VHR when more
Fig. 3. Net annual primary energy savings for VHR when using BST or BIGCC energy supply. The error bars show the savings when electricity use by the VHR is 7 kWh/m2 .
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
1571
Fig. 4. Net annual primary energy savings for VHR when more optimal designed CHP production systems are used.
optimally designed CHP production systems are used. Fig. 4 shows the net primary energy savings for VHR when district heating is based on the lower and upper optimal CHP productions according to Gustavsson et al. [28]. VHR always increases net primary energy use when the electricity use for VHR is 7 kWh/m2 . The net savings is also very low for the conventional buildings with electric efficient VHR systems. 4. Discussion and conclusions Primary energy use strongly influences natural resources efficiency and the environmental impacts of energy supply activities. In this study we explore the primary energy implications of VHR in residential buildings. Our results show that primary energy savings of VHR can be very significant, depending on the type of heat supply system, the airtightness of buildings, and the increased use of electricity to operate the VHR system. The biggest savings is achieved when VHR is installed in a resistance heated building. However, small primary energy savings are achieved when the VHR is installed in CHP-based district heated buildings. VHR gives much smaller primary energy savings for the district heating with 90% CHP than with 50% CHP, supporting the findings of Dodoo et al. [39]. For district heating systems mainly based on CHP, the reduced heat demand reduces the potential to cogenerate electricity and is more significant if BIGCC technology is used instead of BST technology. The primary energy savings of VHR depend on the electricity use to operate the VHR system. Therefore the amount of electricity required to operate VHR systems should be minimized. Regulations and guidelines for VHR in buildings may set limits and recommendations for specific fan power for fans used in VHR systems. Specific fan power takes into account the total electric power use of all fans in the ventilation system of a building, and can play an important role in reducing the electricity use for VHR. However, proper design and installation are critical to achieve the designed specific fan power in practice [40]. The primary energy savings of VHR were greater for the passive building than for the conventional building, confirming that VHR systems perform better with improved airtightness [8,10]. Hence, the air-tightness of buildings should be in the range as
for new constructed passive houses to minimize primary energy use when using VHR systems. Experience from new passive house construction in Sweden shows that airtightness of up to 0.1 l/m2 s is achievable with careful planning and efficient construction and workmanship techniques [41]. In addition to effective planning and detailed specifications, a range of measures including placing plastic foil in building elements and using double sided adhesive tapes and fillers to seal drilled holes and gaps in building elements can be employed to improve the airtightness of building envelopes. VHR is often used in passive houses [42]. Our results show that VHR can give low primary energy savings in such buildings when combined with energy-efficient heat supply systems. In some cases, the passive building with VHR may even use more primary energy than the same building without VHR, depending on the use of ventilation electricity. However, constructing houses with energy characteristics comparable to that of passive houses, with low electricity ventilation use and heated with CHP-plants, gives very low primary energy use for space heating and ventilation. In Sweden, increased attention is being placed on VHR in existing apartment buildings [4]. There is a technology procurement project to develop and promote VHR systems which can be adapted for existing Swedish apartment buildings [21]. However, district heating based on CHP production is well established in Sweden, and 82% of the total heated area in multi-storey apartment buildings are district heated [43]. This study indicates that VHR could increase instead of decrease net primary energy use for a district heated building heated mainly with a CHP plant. Gustavsson et al. [28] analyzed the effects on district heating systems of reduced heat demand from various end-use energy efficiency measures, including VHR. They found VHR to be less primary energy efficient compared to measures such as energy-efficient windows, doors and water taps, improved attic and wall insulation. In summary, VHR may not be suitable for less airtight buildings with CHP-based district heating, in particular for CHP plants with a high ratio between electricity and heat production, to minimize primary energy use of such buildings. Our study is based on detailed analysis of the interactions between heat supply systems and VHR systems and our conclusion may also be generally valid for regions and countries with similar
1572
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
characteristics as analyzed here. Nevertheless, specific analysis would be needed to determine the precise impact of VHR systems on primary energy use in buildings for a particular case, as energy supply and building design may vary between regions and countries. The analytical approach used in this study could be used for such analysis. This study shows that VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the electricity used for VHR and the airtightness of buildings. A system-wide primary energy analysis is necessary to evaluate the energy benefits of VHR in residential buildings. Hence, when deciding on installing VHR, attention should be given to the interaction between the electricity use for VHR, airtightness of the building and the type of heat supply system, in particular district heating with a large share of CHP production, as suggested by Dodoo et al. [39] and Gustavsson and Joelsson [19]. Acknowledgements We gratefully acknowledge funding support from the European Union, the Swedish Energy Agency, and the Jämtland County Council, as well as comments from the anonymous reviewers. References [1] European Commission, 2020 Vision: Saving Our Energy, 2007, web accessed at http://www.energy.eu/publications/2007 eeap en.pdf on June 9 2010. [2] Directive, 2002/91/EC of the European Parliament and of the Council of 16 December 2002 on the Energy Performance of Buildings, Official Journal L (001), 04.01.2003, 0065–0071. [3] Swedish Government Bill, 2005/06:145. A National Programme for Energy Efficiency and Energy Smart Construction, 2009, web accessed at http://www.regeringen.se on April 20, 2009. [4] Swedish Energy Agency, Teknikupphandling av värmeåtervinningssystem i befintliga flerbostadshus (Technology Procurement of Heat Recovery Systems in Existing Apartment Buildings), 2010, web accessed at http://www.energimyndigheten on October 1, 2010. [5] M.W. Liddament, M. Orme, Energy and ventilation, Applied Thermal Engineering 18 (1998) 1101–1109. [6] H.B. Awbi, Chapter 7 – ventilation, Renewable and Sustainable Energy Reviews 2 (1–2) (1998) 157–188. [7] M. Orme, Estimates of the energy impact of ventilation and associated financial expenditures, Energy and Buildings 33 (3) (2001) 199–205. [8] H. Tommerup, S. Svendsen, Energy savings in Danish residential building stock, Energy and Buildings 38 (6) (2006) 618–626. [9] H. Manz, H. Huber, A. Schälin, A. Weber, M. Ferrazzini, M. Studer, Performance of single room ventilation units with recuperative or regenerative heat recovery, Energy and Buildings 31 (1) (2000) 37–47. [10] D. Hekmat, H.E. Feustel, M.P. Modera, Impacts of ventilation strategies on energy consumption and indoor air quality in single-family residences, Energy and Buildings 9 (3) (1986) 239–251. [11] TIP-Vent, Towards Improved Performances of Mechanical Ventilation Systems, 2001, web accessed at http://www.inive.org/Documents/TipVent Source Book.pdf on March 1, 2010. [12] J. Jokisolao, J. Kurnitska, M. Vuolle, A. Torkki, Performance of balanced ventilation with heat recovery in residential buildings in a cold climate, International Journal of Ventilation 2 (3) (2003) 223–235. [13] M.H. Sherman, I.S. Walker, Energy Impact of Residential Ventilation Norms in the United States. LBNL Paper LBNL-62341, Lawrence Berkeley National Laboratory, Berkeley, CA, 2007. [14] M. Nyman, C.J. Simonson, Life cycle assessment (LCA) of air handling units with and without air-to-air energy exchangers, ASHRAE Transactions 110 (1) (2004) 399–409. [15] M. Nyman, C.J. Simonson, Life cycle assessment of residential ventilation units in a cold climate, Building and Environment 40 (1) (2005) 15–27.
[16] R. Zmeureanu, X.Y. Wu, Energy and exergy performance of residential heating systems with separate mechanical ventilation, Energy 32 (3) (2007) 187–195. [17] L. Gustavsson, A. Joelsson, Energy conservation and conversion of electrical heating systems in detached houses, Energy and Buildings 39 (6) (2007) 716–726. [18] A. Joelsson, L. Gustavsson, Perspectives on implementing energy efficiency in existing Swedish detached houses, Energy Policy 36 (1) (2008) 84–96. [19] L. Gustavsson, A. Joelsson, Life cycle primary energy analysis of residential buildings, Energy and Buildings 42 (2) (2010) 210–220. [20] S. Persson, Wälludden trähus i fem våningar: Erfarenheter och lärdomar (Wälludden Wooden Building with Five Stories: Experiences and Knowledge Acquired). Report TVBK-3032, Lund Institute of Technology, Lund, 1998. [21] Å. Wahlström, Å. Blomsterberg, D. Olsson, Värmeåtervinningssystem för befintliga flerbostadshus. Förstudie inför teknikupphandling (Ventilation Heat Recovery System for the Existing Multi-residential Buildings. Feasibility Study for Technology Procurement), BeBo, Gothenburg, 2009. [22] EQUA, ENORM Version 1000, EQUA Simulation AB, Stockholm, 2004. [23] K. Adalberth, Energy use during the life cycle of buildings: a method, Building and Environment 32 (4) (1997) 317–320. [24] A. Joelsson, L. Gustavsson, District heating and energy conservation in detached houses of differing size and construction, Applied Energy 86 (2) (2009) 126–134. [25] Boverkets Byggregler, Boverkets Författningssamling (The Swedish Building Regulations), The National Board of Housing, Building and Planning, Karlskrona, 1994. [26] Boverkets Byggregler, Boverkets Författningssamling (The Swedish Building Regulations), The National Board of Housing, Building and Planning, Karlskrona, 2009. [27] A. Joelsson, Primary energy efficiency and CO2 mitigation in Swedish residential buildings, PhD Dissertation, Mid Sweden University, 2008. [28] L. Gustavsson, A. Dodoo, N.L. Truong, I. Danielski, Primary energy implications of end-use energy efficiency measures in district heated buildings, Energy and Buildings 43 (2011) 38–48. [29] Å. Karlsson, ENSYST Version 1.2, Lund University, Lund, 2003. [30] L. Gustavsson, Å. Karlsson, A system perspective on the heating of detached houses, Energy Policy 30 (2002) 553–574. [31] T. Ekvall, G. Finnveden, Allocation in ISO 14041—a critical review, Journal of Cleaner Production 9 (3) (2001) 197–208. [32] A. Azapagic, R. Clift, Allocation of environmental burdens in multiple-function systems, Journal of Cleaner Production 7 (2) (1999) 101–119. [33] G. Finnveden, T. Ekvall, Life-cycle assessment as a decision-support tool—the case of recycling versus incineration of paper, Resources, Conservation and Recycling 24 (3–4) (1998) 235–256. [34] ISO 14041, European Committee for Standardization, Brussels, 1997. [35] B. Schlamadinger, M. Apps, F. Bohlin, L. Gustavsson, G. Jungmeier, G. Marland, K. Pingoud, I. Savolainen, Towards a standard methodology for greenhouse gas balances of bioenergy systems in comparison with fossil fuel energy systems, Biomass and Bioenergy 13 (6) (1997) 359–375. [36] L. Gustavsson, Å. Karlsson, CO2 mitigation: on methods and parameters for comparison of fossil-fuel and biofuel systems, Mitigation and Adaptation Strategies for Global Change 11 (5-6) (2006) 935–959. [37] J. Kragh, J. Rose, T.R. Nielsen, S. Svendsen, New counter flow heat exchanger designed for ventilation systems in cold climates, Energy and Buildings 39 (11) (2007) 1151–1158. [38] K. Adalberth, Energy use and environmental impact of new residential buildings, PhD Dissertation, Department of Building Physics, Lund University, Sweden, 2000. [39] A. Dodoo, L. Gustavsson, R. Sathre, Life cycle primary energy implication of retrofitting a Swedish apartment building to passive house standard, Resources, Conservation and Recycling 54 (12) (2010) 1152–1160. [40] J. Railio, P. Mäkinen, Specific fan power—a tool for better performance of air handling systems Proceedings of Clima 2007 Well Being Indoors, Helsinki, Finland, 10–14 June, 2007. [41] U. Janson, Passive Houses in Sweden—Experiences from Design and Construction Phase. Report EBD-T-08/9, Department of Architecture and Built Environment, Lund University, Sweden, 2008. [42] W. Feist, J. Schnieders, V. Dorer, A. Haas, Re-inventing air heating: convenient and comfortable within the frame of the passive house concept, Energy and Building 37 (11) (2005) 1186–1203. [43] Swedish Energy Agency, Energistatistik för flerbostadshus 2008 (Energy Statistics for Multi-dwelling Buildings in 2008). Report ES 2009:08, Swedish Energy Agency, Eskilstuna, 2009.
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Primary energy implications of ventilation heat recovery in residential buildings Ambrose Dodoo a,∗ , Leif Gustavsson a,b , Roger Sathre a a b
Mid Sweden University, 83125 Östersund, Sweden Linnaeus University, 35195 Växjö, Sweden
a r t i c l e
i n f o
Article history: Received 26 October 2010 Received in revised form 27 January 2011 Accepted 28 February 2011 Keywords: Mechanical ventilation Heat recovery Heat supply systems Electric resistance heating Heat pump District heating CHP plant Primary energy
a b s t r a c t In this study, we analyze the impact of ventilation heat recovery (VHR) on the operation primary energy use in residential buildings. We calculate the operation primary energy use of a case-study apartment building built to conventional and passive house standard, both with and without VHR, and using different end-use heating systems including electric resistance heating, bedrock heat pump and district heating based on combined heat and power (CHP) production. VHR increases the electrical energy used for ventilation and reduces the heat energy used for space heating. Significantly greater primary energy savings is achieved when VHR is used in resistance heated buildings than in district heated buildings. For district heated buildings the primary energy savings are small. VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the amount of electricity used for VHR and the airtightness of buildings. This study shows the importance of considering the interactions between heat supply systems and VHR systems to reduce primary energy use in buildings. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Building energy use is a major concern in the European Union, where the building sector accounts for the 40% of total primary energy use [1]. Member States of the European Union are required to implement energy efficiency measures for buildings under the Energy Performance of Building Directive [2]. The Swedish government target of reducing the final energy use per heated building area is 20% and 50% below 1995 levels by 2020 and 2050, respectively [3]. Heat recovery from exhaust ventilation air in existing apartment buildings is considered an important means to reach this target [4]. Ventilation has a significant impact on the energy performance of buildings, accounting for 30–60% of the energy use in buildings [5–7]. Energy is used to cover the heat losses due to the ventilation air and to move the ventilation air for mechanical ventilation. The ventilation system also influences the air infiltration through the building envelope. Recent building standards require high energy efficiency of buildings, and therefore considerable efforts have been made to improve airtightness and insulation of buildings. In such buildings infiltration is low and mechanical ventilation systems are often used to achieve the required airflow. Mechanical ventilation systems can include ventilation heat recovery (VHR) systems to recover heat from exhaust air to reduce ventilation heat losses.
∗ Corresponding author. Tel.: +46 63 165383; fax: +46 63 165500. E-mail address: [email protected] (A. Dodoo). 0378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2011.02.019
VHR systems transfer the heat from the exhaust air to the supply air via a heat exchanger. Ventilation heat losses can be typically 35–40 kWh/m2 -year in residential buildings, and up to 90% of this can be recovered with VHR depending on airtightness and insulation of buildings [8]. In very low energy buildings, such as passive house buildings, VHR systems can be equipped with additional air heaters to cover the space heating demand. VHR is therefore gaining increasing interest in low energy and retrofitted buildings [9]. Various studies have analyzed the impacts of VHR on energy use of buildings. For example, Hekmat et al. [10] compared different residential ventilation strategies including VHR systems in different US climatic conditions. They found that the total energy for space and tap water heating was reduced by 9–21% by using VHR. The European TIP-Vent [11] explored the impacts of VHR systems on the energy performance of different types of buildings in several European countries including Sweden. They found that VHR systems reduced the total energy for space heating by 20–50%, depending on building type and airtightness. Jokisalo et al. [12] simulated the performance of VHR systems in a typical Finnish apartment building using centralized or decentralized ventilation units. They found that energy performance of decentralized ventilation units is not significantly improved when VHR is installed. Sherman and Walker [13] analyzed the energy impact of different ventilation norms in typical US buildings. They found that VHR generally increased net energy use as the energy used by the blower offset the energy savings from space conditioning. The above studies, however, analyzed only final energy use and not primary energy use.
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
1567
Table 1 Thermal properties of the building components. U-value (W/m2 K)
Building
Conventional Passive
Air leakage (l/s m2 ) at 50 Pa
Ground floor
External walls
Windows
Doors
Roof
0.23 0.23
0.20 0.10
1.90 0.85
1.19 0.80
0.13 0.08
Fewer studies (e.g. [14–16]) have analyzed the impacts of VHR on primary energy use of residential buildings. The concept of primary energy is used to denote the total energy needed in order to generate the final energy service, including inputs and losses along the entire supply chains. Primary energy use, in contrast to final energy use, determines the natural resource use and the environmental impact of supplying the energy services. The various processes along the energy supply chain, from the extraction of raw material to refining, transport, conversion to heat and electricity, and distribution to the user can be performed with different energy efficiencies. All the energy input from these processes need to be included for a full description of a particular energy system. Nyman and Simonson [14] and Zmeureanu and Wu [16] found VHR to reduce net primary energy use, and Nyman and Simonson [15] concluded that VHR is an environmentally favourable solution for a cold climate region. However, these studies analyzed the impacts of VHR in buildings heated with electric-based heaters or gas-fired boilers. The heat demand of a building can be provided by different end-use heating systems and energy supply technologies which can result in significantly different primary energy use [17–19]. A comprehensive analysis of the impacts of VHR on the primary energy use of buildings with different end-use heating and energy supply systems is lacking. In this study we analyze the primary energy implications of VHR in residential buildings heated with electric resistance heating, bedrock heat pump, or district heating based on combined heat and power (CHP) production. We consider cases where energy supply is based on steam turbine technology or integrated gasification combine cycle technology, all using biomass-based fuels. Our analysis considers the entire energy chains, and the trade-off between electricity use by the ventilation system and the reduction in space heat.
2. Methodology Our analysis is based on simulation modeling of a case-study apartment building with mechanical ventilation. We model the primary energy use for the original and improved level of energy efficiency of the building, both with and without VHR. Next we compare the primary energy use of the buildings and calculate
0.8 0.3
the net primary energy savings achieved by the VHR, taking into account the changed electricity use due to VHR, as well as the changed heat demand due to VHR and changed air infiltration. 2.1. Building descriptions Our case-study building is a 4-storey wood-frame building with 16 apartments and a total heated floor area of 1190 m2 . The outer walls of the building consist of three layers, including plastercompatible mineral wool panels, timber studs with mineral wool between the studs, and a wiring and plumbing installation layer consisting of timber studs and mineral wool. Two-thirds of the outer fac¸ade is plastered with stucco, with the remainder covered with wood paneling. The ground floor consists of oak boarding laid on a concrete slab, expanded polystyrene and crushed stones, and the upper floors are made of light timber joists. Persson [20] describes the construction and thermal characteristics of the building in detail. The ground floor plan and photograph of the building are shown in Fig. 1. To compare the impacts of VHR in buildings of different envelope characteristics and airtightness, a second building is modeled with thermal envelope properties of passive house but otherwise identical to the existing building. Table 1 shows the thermal characteristics of the conventional building and the passive building. In addition to lower U-values, the passive building is assumed to have much better airtightness than the conventional building. For both the conventional and passive buildings, we analyze the energy performance with and without VHR. For the buildings without VHR, exhaust air is extracted from the kitchens, bathrooms and closets with fan and duct system, and fresh air is supplied through slot openings under windows in the bedrooms and living rooms. For the buildings with VHR, the ventilation system provides the same airflow as in the buildings without VHR. For the conventional building the existing ventilation system is complemented with ventilation ducts for incoming air and a heat recovery unit [21]. 2.2. Calculation of final energy We calculate the annual final energy use of the buildings, both with and without VHR, using the ENORM software ([22,23]). The
Fig. 1. Ground floor plan (left) and photograph (right) of the case-study wood-frame building. The ground floor plan is adapted from Persson [20].
1568
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572 Table 3 Configurations of end-use heating and energy supply systems modeled.
Table 2 Major ventilation input values. Description
Value
End-use heating
Supply system
Air change rate (l/s m2 ) Heat recovery efficiency (%) Ventilated volume (m3 ) Supply air flow rate (m3 /h)
0.35 85 2861 1540
Electric resistance heating
BST stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder BIGCC stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder
Bedrock heat pump
BST stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder BIGCC stand-alone condensing plant cover 95% of the electricity production and light-oil fired gas turbines cover the remainder
District heating
CHP-BST plant cover 50% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 50% of the district heat production and light-oil fired boilers cover the remainder CHP-BST plant cover 90% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 90% of the district heat production and light-oil fired boilers cover the remainder CHP-BST plant cover 80% of the district heat production and light-oil fired boilers cover remainder CHP-BST plant cover 83% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 76% of the district heat production and light-oil fired boilers cover the remainder CHP-BIGCC plant cover 78% of the district heat production and light-oil fired boilers cover the remainder
software is commonly used by contractors, consultants and engineers in Sweden [24]. It calculates the space heating, ventilation, domestic hot water, and household and facility management electricity use of a building, and is also adapted to verify if a building meets the energy standard of the Swedish regulations. The software calculates the energy and power demand for a 12-month period, on a 24-h basis based on the building’s physical characteristics, internal and solar heat gains, occupancy pattern, outdoor climate, indoor temperature, heating and ventilation systems, etc. We use climate data for the city of Växjö in southern Sweden, and assume an indoor temperature of 22 ◦ C. We design the ventilation systems to give the airflow rates and specific fan power required by the Swedish regulation [25,26]. Table 2 shows principal values used to calculate the electricity use for ventilation. Other values including fan efficiency and operation mode of the ventilation systems are based on the assumptions of the ENORM software. 2.3. Supply systems We analyze cases where space heat is delivered by electric resistance heating, heat pump or district heating. For the electric resistance heating and heat pump, 95% of the electricity is assumed to be supplied from stand-alone biomass steam turbine (BST) plants and the remaining from light-oil gas turbine plants. We assume that the district heat is supplied from a CHP plant using biomass steam turbines (CHP-BST). Joelsson [27] observed that the dimensioning of a CHP plant in district heating systems influences primary energy use. To explore this, we consider scenarios where the CHP plant accounts for either 50% or 90% of the district heat production, with oil boilers accounting for the remainder. To show the potential impact of energy supply technology currently being developed, we also analyze a case where biomass integrated gasification combined cycle (BIGCC) technology is used instead of the BST technology for both CHP and stand-alone power production. Furthermore, Gustavsson et al. [28] explored the structure of district heat production under different environmental taxation regimes. They found that the CHP production should be 80–83% of the total district-heat production when using BST technology and 76–78% when using BIGCC technology. The difference in share of district-heat production between the technologies varies because the BIGCC technology is more efficient and capital intensive than the BST technology. To explore the implications of this for VHR, we calculate the primary energy savings when district heating is based on such CHP production systems. Table 3 summarizes the configurations of the end-use heating and energy supply systems modeled. The electricity use for ventilation and for household and facility management is assumed to be produced in a stand-alone power plant with the same technology and fuel as the heat. The capacities and the efficiencies of the power plants, cogeneration plants and end-use heating systems are given in Table 4. 2.4. Calculation of primary energy We use the ENSYST software [29] to quantify the primary energy needed to provide the final energy use in the different cases. The software calculates primary energy use considering the entire energy chain from natural resource extraction to final energy
supply, taking into account the fuel inputs at each stage in the energy system chain and the energy efficiency of each process. We follow Gustavsson and Karlsson’s [30] assumptions about the production and transport of fuels for electricity and heat when using the ENSYST software. For biomass-based heat and electricity productions, wood chips are assumed to be the fuel used. The crude oil for the production of petrol, diesel and light fuel oil is assumed to be imported from Norway. We assume distribution losses of 7% to the building for both electricity and district heat. The CHP plant cogenerates heat and electricity and therefore an allocation issue may arise. Different methods have been suggested to address allocation in co-product systems [31–33]. A method that avoids allocation is preferred, as allocation can be subjective [34,35]. Gustavsson and Karlsson [36] explored the multi-functional and the subtraction methods of system expansion Table 4 Capacity and efficiency of the power plants, cogeneration plants and end-use heating technologies. Technology
Capacity
Efficiency
Stand-alone power plants BST BIG/CC Light-oil gas turbines Cogeneration plants CHP-BST CHP-BIG/CC End-use heating District heating Heat pump Resistance heating
(MWelec ) 200 100 120 (MWelec /MWheat ) 36/72 60/60 (kWheat ) 10.5 7 10.5
(elec ) 0.40 0.47 0.27 (elec /heat ) 0.3/0.60 0.43/0.43 (heat ) 0.95 3 0.97
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
1569
Table 5 Annual final operation energy use. Final energy use (kWh/m2 year)
Building
Conventional building Conventional building with VHR Passive building Passive building with VHR
Space heating
Ventilation electricity
Tap water heating
Household and facility electricity
Total
70 50 43 13
4 8 4 8
40 40 40 40
52 52 52 52
166 150 143 113
Table 6 Annual operation primary energy use for the building with different end-use heating systems with energy supply based on BST technology. Primary energy use (kWh/m2 year)
Description
Resistance heating Conventional building Conventional building with VHR Passive building Passive building with VHR Heat pump Conventional building Conventional building with VHR Passive building Passive building with VHR District heating, 50% CHP Conventional building Conventional building with VHR Passive building Passive building with VHR District heating, 90% CHP Conventional building Conventional building with VHR Passive building Passive building with VHR
Space heating
Ventilation electricity
Tap water heating
Household and facility electricity
Total
209 149 128 39
12 24 12 24
119 119 119 119
155 155 155 155
495 447 414 337
78 55 48 14
12 24 12 24
45 45 45 45
155 155 155 155
290 279 260 238
66 47 41 12
12 24 12 24
38 38 38 38
155 155 155 155
271 264 246 229
42 30 26 8
12 24 12 24
24 24 24 24
155 155 155 155
233 233 217 211
to avoid allocation when comparing cogeneration and separate heat and electricity production systems. In this study we use the subtraction method to calculate the primary energy use for heat. The cogenerated electricity replace electricity that otherwise had been produced in a stand-alone plant using the same fuel and technology as the CHP plant. The primary energy used for the replaced electricity in the stand-alone plant is subtracted from the CHP plant to obtain the primary energy for the heat. 3. Results Table 5 shows the annual final energy use of the conventional and the passive buildings with and without VHR. The annual total final energy use of the passive building with VHR is about 21% lower than for the passive building without VHR. The corresponding reduction for the conventional building is 10%. VHR decreases the final heat use for ventilation losses heating, but increases the electricity used to operate the ventilation system and the air infiltration. Overall, VHR reduces the final energy for space heating and ventilation by 55% and 22% for the passive and the conventional building, respectively, relative to the alternatives without VHR. Table 6 shows the annual operation primary energy use for the conventional and the passive buildings with different end-use
heating systems. The energy supply is based on BST technology. Ventilation accounts for 2–11% of the operation primary energy use. The primary energy for heating for the district heated buildings is low due to the high overall efficiency of district heating systems with CHP plants. Table 7 compares the percentage primary energy savings of VHR in relation to the primary energy for space heating and ventilation. The VHR primary energy savings for space heating and ventilation ranges from 0 to 55%. The change in annual primary energy use for space heating and ventilation electricity when using VHR with different end-use heating system with BST or BIGCC energy supply are shown in Fig. 2. The net savings are shown in Fig. 3. The primary energy savings due to VHR are significantly greater when using resistance heating, followed by heat pump and district heating with 50% CHP. However, much smaller or no primary energy savings are achieved when using district heating with 90% CHP. The savings due to VHR are larger for the passive building than for the conventional building due to the better air-tightness of the passive building. The BIGCC technology gives similar results as the BST technology, but the net primary energy savings are lower compared to the BST technology. In cold climatic regions frost may occur on the heat recovery unit during winters. VHR systems may be fitted with additional
Table 7 Percentage primary energy savings of VHR, in relation to the primary energy used for space heating and ventilation for the different end-use heating systems with BST energy supply technology. Building
Conventional Passive
Relative primary energy savings Resistance heating
Heat pump
District heating, 50% CHP
District heating, 90% CHP
22% 55%
12% 37%
9% 32%
0 16%
1570
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
Fig. 2. Change in annual primary energy use for space heating and ventilation electricity when using VHR with BST or BIGCC energy supply.
preheating devices to overcome this problem, increasing the electricity use for VHR [37]. Our base calculations are based on electricity use of 4 kWh/m2 for the VHR [22,38], and do not include electricity to defrost the system. Tommerup and Svendsen [8] reported that electricity use in VHR system of 80–90% efficiency is typically 7 kWh/m2 under Danish conditions, and suggested this might be reduced to 3 kWh/m2 with more efficient units. In Fig. 3 the error bars show the change in net primary energy savings for VHR, when the electricity use for VHR is 7 kWh/m2 . The higher electricity use for operating VHR reduces the net primary energy
savings in particular for the district heated buildings. In fact, a ventilation electricity use of 7 kWh/m2 increases the net primary energy use for the buildings with district heating based on 90% CHP. Hence, a low electricity use for VHR is important. For the conventional building with lower airtightness together with district heating based on a large share of CHP production, VHR may even be counterproductive. In our base case calculations, the CHP production accounts for 50 and 90% of the total district heat production [39]. In this section, we show the net primary energy savings for VHR when more
Fig. 3. Net annual primary energy savings for VHR when using BST or BIGCC energy supply. The error bars show the savings when electricity use by the VHR is 7 kWh/m2 .
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
1571
Fig. 4. Net annual primary energy savings for VHR when more optimal designed CHP production systems are used.
optimally designed CHP production systems are used. Fig. 4 shows the net primary energy savings for VHR when district heating is based on the lower and upper optimal CHP productions according to Gustavsson et al. [28]. VHR always increases net primary energy use when the electricity use for VHR is 7 kWh/m2 . The net savings is also very low for the conventional buildings with electric efficient VHR systems. 4. Discussion and conclusions Primary energy use strongly influences natural resources efficiency and the environmental impacts of energy supply activities. In this study we explore the primary energy implications of VHR in residential buildings. Our results show that primary energy savings of VHR can be very significant, depending on the type of heat supply system, the airtightness of buildings, and the increased use of electricity to operate the VHR system. The biggest savings is achieved when VHR is installed in a resistance heated building. However, small primary energy savings are achieved when the VHR is installed in CHP-based district heated buildings. VHR gives much smaller primary energy savings for the district heating with 90% CHP than with 50% CHP, supporting the findings of Dodoo et al. [39]. For district heating systems mainly based on CHP, the reduced heat demand reduces the potential to cogenerate electricity and is more significant if BIGCC technology is used instead of BST technology. The primary energy savings of VHR depend on the electricity use to operate the VHR system. Therefore the amount of electricity required to operate VHR systems should be minimized. Regulations and guidelines for VHR in buildings may set limits and recommendations for specific fan power for fans used in VHR systems. Specific fan power takes into account the total electric power use of all fans in the ventilation system of a building, and can play an important role in reducing the electricity use for VHR. However, proper design and installation are critical to achieve the designed specific fan power in practice [40]. The primary energy savings of VHR were greater for the passive building than for the conventional building, confirming that VHR systems perform better with improved airtightness [8,10]. Hence, the air-tightness of buildings should be in the range as
for new constructed passive houses to minimize primary energy use when using VHR systems. Experience from new passive house construction in Sweden shows that airtightness of up to 0.1 l/m2 s is achievable with careful planning and efficient construction and workmanship techniques [41]. In addition to effective planning and detailed specifications, a range of measures including placing plastic foil in building elements and using double sided adhesive tapes and fillers to seal drilled holes and gaps in building elements can be employed to improve the airtightness of building envelopes. VHR is often used in passive houses [42]. Our results show that VHR can give low primary energy savings in such buildings when combined with energy-efficient heat supply systems. In some cases, the passive building with VHR may even use more primary energy than the same building without VHR, depending on the use of ventilation electricity. However, constructing houses with energy characteristics comparable to that of passive houses, with low electricity ventilation use and heated with CHP-plants, gives very low primary energy use for space heating and ventilation. In Sweden, increased attention is being placed on VHR in existing apartment buildings [4]. There is a technology procurement project to develop and promote VHR systems which can be adapted for existing Swedish apartment buildings [21]. However, district heating based on CHP production is well established in Sweden, and 82% of the total heated area in multi-storey apartment buildings are district heated [43]. This study indicates that VHR could increase instead of decrease net primary energy use for a district heated building heated mainly with a CHP plant. Gustavsson et al. [28] analyzed the effects on district heating systems of reduced heat demand from various end-use energy efficiency measures, including VHR. They found VHR to be less primary energy efficient compared to measures such as energy-efficient windows, doors and water taps, improved attic and wall insulation. In summary, VHR may not be suitable for less airtight buildings with CHP-based district heating, in particular for CHP plants with a high ratio between electricity and heat production, to minimize primary energy use of such buildings. Our study is based on detailed analysis of the interactions between heat supply systems and VHR systems and our conclusion may also be generally valid for regions and countries with similar
1572
A. Dodoo et al. / Energy and Buildings 43 (2011) 1566–1572
characteristics as analyzed here. Nevertheless, specific analysis would be needed to determine the precise impact of VHR systems on primary energy use in buildings for a particular case, as energy supply and building design may vary between regions and countries. The analytical approach used in this study could be used for such analysis. This study shows that VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the electricity used for VHR and the airtightness of buildings. A system-wide primary energy analysis is necessary to evaluate the energy benefits of VHR in residential buildings. Hence, when deciding on installing VHR, attention should be given to the interaction between the electricity use for VHR, airtightness of the building and the type of heat supply system, in particular district heating with a large share of CHP production, as suggested by Dodoo et al. [39] and Gustavsson and Joelsson [19]. Acknowledgements We gratefully acknowledge funding support from the European Union, the Swedish Energy Agency, and the Jämtland County Council, as well as comments from the anonymous reviewers. References [1] European Commission, 2020 Vision: Saving Our Energy, 2007, web accessed at http://www.energy.eu/publications/2007 eeap en.pdf on June 9 2010. [2] Directive, 2002/91/EC of the European Parliament and of the Council of 16 December 2002 on the Energy Performance of Buildings, Official Journal L (001), 04.01.2003, 0065–0071. [3] Swedish Government Bill, 2005/06:145. A National Programme for Energy Efficiency and Energy Smart Construction, 2009, web accessed at http://www.regeringen.se on April 20, 2009. [4] Swedish Energy Agency, Teknikupphandling av värmeåtervinningssystem i befintliga flerbostadshus (Technology Procurement of Heat Recovery Systems in Existing Apartment Buildings), 2010, web accessed at http://www.energimyndigheten on October 1, 2010. [5] M.W. Liddament, M. Orme, Energy and ventilation, Applied Thermal Engineering 18 (1998) 1101–1109. [6] H.B. Awbi, Chapter 7 – ventilation, Renewable and Sustainable Energy Reviews 2 (1–2) (1998) 157–188. [7] M. Orme, Estimates of the energy impact of ventilation and associated financial expenditures, Energy and Buildings 33 (3) (2001) 199–205. [8] H. Tommerup, S. Svendsen, Energy savings in Danish residential building stock, Energy and Buildings 38 (6) (2006) 618–626. [9] H. Manz, H. Huber, A. Schälin, A. Weber, M. Ferrazzini, M. Studer, Performance of single room ventilation units with recuperative or regenerative heat recovery, Energy and Buildings 31 (1) (2000) 37–47. [10] D. Hekmat, H.E. Feustel, M.P. Modera, Impacts of ventilation strategies on energy consumption and indoor air quality in single-family residences, Energy and Buildings 9 (3) (1986) 239–251. [11] TIP-Vent, Towards Improved Performances of Mechanical Ventilation Systems, 2001, web accessed at http://www.inive.org/Documents/TipVent Source Book.pdf on March 1, 2010. [12] J. Jokisolao, J. Kurnitska, M. Vuolle, A. Torkki, Performance of balanced ventilation with heat recovery in residential buildings in a cold climate, International Journal of Ventilation 2 (3) (2003) 223–235. [13] M.H. Sherman, I.S. Walker, Energy Impact of Residential Ventilation Norms in the United States. LBNL Paper LBNL-62341, Lawrence Berkeley National Laboratory, Berkeley, CA, 2007. [14] M. Nyman, C.J. Simonson, Life cycle assessment (LCA) of air handling units with and without air-to-air energy exchangers, ASHRAE Transactions 110 (1) (2004) 399–409. [15] M. Nyman, C.J. Simonson, Life cycle assessment of residential ventilation units in a cold climate, Building and Environment 40 (1) (2005) 15–27.
[16] R. Zmeureanu, X.Y. Wu, Energy and exergy performance of residential heating systems with separate mechanical ventilation, Energy 32 (3) (2007) 187–195. [17] L. Gustavsson, A. Joelsson, Energy conservation and conversion of electrical heating systems in detached houses, Energy and Buildings 39 (6) (2007) 716–726. [18] A. Joelsson, L. Gustavsson, Perspectives on implementing energy efficiency in existing Swedish detached houses, Energy Policy 36 (1) (2008) 84–96. [19] L. Gustavsson, A. Joelsson, Life cycle primary energy analysis of residential buildings, Energy and Buildings 42 (2) (2010) 210–220. [20] S. Persson, Wälludden trähus i fem våningar: Erfarenheter och lärdomar (Wälludden Wooden Building with Five Stories: Experiences and Knowledge Acquired). Report TVBK-3032, Lund Institute of Technology, Lund, 1998. [21] Å. Wahlström, Å. Blomsterberg, D. Olsson, Värmeåtervinningssystem för befintliga flerbostadshus. Förstudie inför teknikupphandling (Ventilation Heat Recovery System for the Existing Multi-residential Buildings. Feasibility Study for Technology Procurement), BeBo, Gothenburg, 2009. [22] EQUA, ENORM Version 1000, EQUA Simulation AB, Stockholm, 2004. [23] K. Adalberth, Energy use during the life cycle of buildings: a method, Building and Environment 32 (4) (1997) 317–320. [24] A. Joelsson, L. Gustavsson, District heating and energy conservation in detached houses of differing size and construction, Applied Energy 86 (2) (2009) 126–134. [25] Boverkets Byggregler, Boverkets Författningssamling (The Swedish Building Regulations), The National Board of Housing, Building and Planning, Karlskrona, 1994. [26] Boverkets Byggregler, Boverkets Författningssamling (The Swedish Building Regulations), The National Board of Housing, Building and Planning, Karlskrona, 2009. [27] A. Joelsson, Primary energy efficiency and CO2 mitigation in Swedish residential buildings, PhD Dissertation, Mid Sweden University, 2008. [28] L. Gustavsson, A. Dodoo, N.L. Truong, I. Danielski, Primary energy implications of end-use energy efficiency measures in district heated buildings, Energy and Buildings 43 (2011) 38–48. [29] Å. Karlsson, ENSYST Version 1.2, Lund University, Lund, 2003. [30] L. Gustavsson, Å. Karlsson, A system perspective on the heating of detached houses, Energy Policy 30 (2002) 553–574. [31] T. Ekvall, G. Finnveden, Allocation in ISO 14041—a critical review, Journal of Cleaner Production 9 (3) (2001) 197–208. [32] A. Azapagic, R. Clift, Allocation of environmental burdens in multiple-function systems, Journal of Cleaner Production 7 (2) (1999) 101–119. [33] G. Finnveden, T. Ekvall, Life-cycle assessment as a decision-support tool—the case of recycling versus incineration of paper, Resources, Conservation and Recycling 24 (3–4) (1998) 235–256. [34] ISO 14041, European Committee for Standardization, Brussels, 1997. [35] B. Schlamadinger, M. Apps, F. Bohlin, L. Gustavsson, G. Jungmeier, G. Marland, K. Pingoud, I. Savolainen, Towards a standard methodology for greenhouse gas balances of bioenergy systems in comparison with fossil fuel energy systems, Biomass and Bioenergy 13 (6) (1997) 359–375. [36] L. Gustavsson, Å. Karlsson, CO2 mitigation: on methods and parameters for comparison of fossil-fuel and biofuel systems, Mitigation and Adaptation Strategies for Global Change 11 (5-6) (2006) 935–959. [37] J. Kragh, J. Rose, T.R. Nielsen, S. Svendsen, New counter flow heat exchanger designed for ventilation systems in cold climates, Energy and Buildings 39 (11) (2007) 1151–1158. [38] K. Adalberth, Energy use and environmental impact of new residential buildings, PhD Dissertation, Department of Building Physics, Lund University, Sweden, 2000. [39] A. Dodoo, L. Gustavsson, R. Sathre, Life cycle primary energy implication of retrofitting a Swedish apartment building to passive house standard, Resources, Conservation and Recycling 54 (12) (2010) 1152–1160. [40] J. Railio, P. Mäkinen, Specific fan power—a tool for better performance of air handling systems Proceedings of Clima 2007 Well Being Indoors, Helsinki, Finland, 10–14 June, 2007. [41] U. Janson, Passive Houses in Sweden—Experiences from Design and Construction Phase. Report EBD-T-08/9, Department of Architecture and Built Environment, Lund University, Sweden, 2008. [42] W. Feist, J. Schnieders, V. Dorer, A. Haas, Re-inventing air heating: convenient and comfortable within the frame of the passive house concept, Energy and Building 37 (11) (2005) 1186–1203. [43] Swedish Energy Agency, Energistatistik för flerbostadshus 2008 (Energy Statistics for Multi-dwelling Buildings in 2008). Report ES 2009:08, Swedish Energy Agency, Eskilstuna, 2009.