Available online at www.sciencedirect.com ScienceDirect Energy Procedia 78 (2015 ) 907 912 6th International Building Physics Conference, IBPC 2015 Potential for finance and energy savings of detached houses in Estonia Üllar Alev a, *, Ats Allikmaa a, Targo Kalamees a a Tallinn University of Technology, Ehitajate tee 5, Tallinn, 19086, Estonia Abstract In the current study potential for finance and energy savings of detached houses in Estonia is calculated by combining five real average example buildings, five bundles of original building envelopes, six types of heat source, and three ventilation systems to represent the building tradition from five time periods. Measures analyzed are additional insulation of the building envelope and change of heat source for space heating, ventilation, and domestic hot water. The influence of renovation measures on the energy saving was calculated with the multi-zone indoor climate and energy simulation program IDA Indoor Climate and Energy, with the standard use of the building. The economic effect of the renovation measures was assessed through a balance of investment cost and energy savings. It was found that the installation of the mechanical ventilation system with 60% or 80% heat recovery is the most cost effective measure. In newer houses, the replacement of an ineffective heating system was found to lower the global cost of the house. 2015 The The Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the CENTRO CONGRESSI INTERNAZIONALE SRL. Peer-review under responsibility of the CENTRO CONGRESSI INTERNAZIONALE SRL Keywords: Energy saving measures; Low energy renovation; Cost effectiveness; Detached house, Renovation 1. Introduction Improvement of energy performance of existing buildings plays an important role in the national energy efficiency and greenhouse gas emissions targets, because the annual replacement of existing stock is only 1 2%. In their review, * Corresponding author. Tel.: +372 620 2402. E-mail address: ullar.alev@ttu.ee 1876-6102 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the CENTRO CONGRESSI INTERNAZIONALE SRL doi:10.1016/j.egypro.2015.11.017
908 Üllar Alev et al. / Energy Procedia 78 ( 2015 ) 907 912 Saidur et al. [1] showed that the worldwide residential sector consumes about 16 50% of the total energy. According to Ballarini et al. [2], due to poor energy quality of existing buildings, the energy savings for the standard refurbishment expressed in terms of annual primary energy need for space heating and domestic hot water range from 41% (Czech Republic) to 75% (Italy, Middle Climatic Zone), while the energy savings for the advanced refurbishment vary from 49% (Denmark) to 86% (Greece). In Norway the total building envelope upgrade using passive house components and a lower on-site renewable energy production have resulted in a 50 85% reduction of the heating requirement depending on the renewable energy production [3]. As a detached house is the second largest dwelling type in many countries, energy renovation of houses could decrease also the national energy use and greenhouse emissions. In the renovation of houses, different aspects should be taken into account. The survey of houses in Estonia, Finland and Sweden showed different structural, building physical and indoor climate as well as energy performance and building service related aspects that need to be considered in the renovation process [4]. By combining the renovation process with the improvement of energy performance and indoor climate of a building it is possible to find cost effective solutions. In their study of energy and investment intensity of integrated renovation of Estonian buildings, Kurnitski et al. [5] analyzed also detached houses. Nevertheless, the main purpose of their study was a large scale analysis and cost optimal savings by 2030. Their analysis uses only two example houses. In this study potential for finance and energy savings of detached houses in Estonia is calculated by combining five real average example buildings, five bundles of original building envelopes, six types of energy source for room heating, and three ventilation systems to represent the building tradition from five time periods. 2. Methods 2.1. Calculations The influence of renovation measures on energy saving was calculated with the multi-zone indoor climate and energy simulation program IDA Indoor Climate and Energy 4.5.1 (IDA ICE) [8,9]. Based on the measurements of indoor climate, building envelope, performance of service systems, the energy use simulation models were calibrated for the houses from the first [4] and the fifth time periods [7]. The knowledge obtained in these calibrations was utilized in building up other models. After calibration of the simulation model, the energy usage before and after renovation was calculated with the standard use of the building [10]. According to Kurnitski et al. [5] and Alev et al. [11], old detached houses could have low ventilation rate and lower temperature than the standard [12] recommendation. Nevertheless, indoor climate and energy calculations were done with the standard use of the building because the aim of the study is to analyze energy usage of a building type and occupant behavior related energy usage, which is variable and unrelated to the building type and usage. The economic effect of renovation measures was assessed through a balance of the investment cost and the energy savings. Global cost (the net present value (NPV), considering the investment cost over a 20 year period) was used to assess the economic effect of the renovation measures according to the principles set in the Commission s cost optimality methodology [13] developed for the assessment of cost optimal energy performance levels. The net present value was calculated as the global cost consisting of the construction cost and the discounted energy costs according to [14]. Renovation measures were assessed based on the difference of NPV ( NPV) of the reference case and the renovated case. Prices for the different parts of the construction works were obtained from the construction companies. The construction costs included labor costs, material costs, overhead, the share of project management and value added tax (VAT, 20%). Discounted energy cost included all annual costs related to heating and electricity energy consumption. The prices for the energy carriers were obtained from information of the suppliers: wood billet 0.031, pellets 0.054, gas 0.055, oil 0.088, and electricity 0.14 /kwh (VAT included); 2.2. Example houses and energy renovation measures The study concentrates on the detached houses that represent 42% of the area of dwellings with usual residence in Estonia [6]. Example houses were selected based on the statistical analysis of [7] age, size, number of storeys,
Üllar Alev et al. / Energy Procedia 78 ( 2015 ) 907 912 909 construction of external walls and heat source. The detached houses were divided into five time periods on the basis of decades, Table 1. There are two main building materials used in the detached houses: wood (49 %) and brick/block (31 %). For real average buildings, syntactical average building envelopes were used by combining two or three types of the building envelope. In houses with usual residences the dominant heating system is a wooden stove (71%) while local central heating (boiler or heat pump) is in 23% and electrical heating in 4 % of the detached houses. As the electrical heating is used often as background heating for wooden stoves, in this study the proportion of direct electricity for room heating was selected to be 10%. Table 1 Matrix of simulated houses and structures. Characteristics Reference houses based on the time period DH 1: 1920 DH 2: 1921-1940 DH 3: 1941-1970 DH 4: 1971-1990 DH 5: 1991 Percentage of area (completed houses) 12% 22% 22% 18% 26% Heated area, m 2 76 165 205 174 183 Properties of building envelope: U, thermal transmittance, q 50, air leakage rate U external wall = 0.63W/(m 2 K) 90% U windows = 2.80W/(m 2 K) BE1 U attic floor = 0.34W/(m 2 K) q 50 = 15 m 3 /(h m 2 ) BE2 U attic floor = 0.48W/(m 2 K) Percentage of building envelope in specific type of detached houses. Description of service systems: WS: wooden stove; EL: electricity, WB: wooden boiler; OB: oil boiler; GB: gas boiler; HP: heat pump. NV: natural passive stack ventilation, window airing; EV: mechanical exhaust ventilation without heat recovery; BV: mechanical supply-exhaust, with heat recovery. U external wall = 0.54W/(m 2 K) 90% U windows = 2.80W/(m 2 K) q 50 = 15 m 3 /(h m 2 ) 20% U basement wall = 0.77W/(m 2 K) 70% U external wall = 0.52W/(m 2 K) BE3 U windows = 2.80W/(m 2 K) U attic floor = 0.43W/(m 2 K) q 50 = 9 m 3 /(h m 2 ) U basement wall = 1.06W/(m 2 K) 10% U external wall = 0.99W/(m 2 K) BE4 U windows = 2.80W/(m 2 K) U attic floor = 0.32W/(m 2 K) q 50 = 9 m 3 /(h m 2 ) 10% EL DHW: WB, EL EL DHW: WB, EL 10% EL DHW: WB, EL 50% EL, OB Ventilation: EV DHW: WB, EL, OB 40% EL, OB Ventilation: EV DHW: WB, EL, OB 10% EL, OB Ventilation: EV DHW: WB, EL, OB U external wall = 0.25W/(m 2 K) 80% U windows = 1.80W/(m 2 K) BE5 U attic floor = 0.16W/(m 2 K) q 50 = 6 m 3 /(h m 2 ) 20% Heating: WB, EL, Ventilation: BV DHW: WB, EL, Heating: WB, EL, Ventilation: BV DHW: WB, EL,
910 Üllar Alev et al. / Energy Procedia 78 ( 2015 ) 907 912 Energy renovation measures were applied to the building envelope (facade, attic floor, roof, windows-doors, and basement floor) and to the service systems (heating, ventilation, heat source). The thickness of additional insulation for the façade and floor ( =0.04 W/(m K)) was 100, 200, 300 mm, for the roof the change of original 175 mm insulation and additional insulation of 50, 150, 250 mm. Three renovation measures for windows were considered from the renovation of original windows (U 1.5 W/(m 2 K)) up to the installation of new windows (U 1.1 and 0.7 W/(m 2 K)). Two different new door options were considered (U 1.5 and 1.0 W/(m 2 K)). The reference case is a building with its original structure and service systems that provide indoor climate according to category class III (an acceptable, moderate level of expectation). Along with improved energy efficiency, also indoor climate was upgraded to correspond to ICC II (normal level of expectation) requirements. Mechanical supply and exhaust ventilation with two types of ventilation heat recovery efficiency was considered: 60% and 80%. 3. Results Results in Fig. 1 are weighted averages of different envelope systems for all five houses. Older log houses DH1 and DH2 presented together in Fig. 1 (top left) are similar. The highest decrease of primary energy consumption can be achieved by replacing the existing heating system with either the air-water heat pump, the wooden boiler or the ground source heat pump (Fig. 1). Replacing the heating system is cost-effective only in DH5. Adding additional insulation to the external wall can decrease the energy usage by 100 kwh/(m 2 y), but this also increases the NPV of the house, especially in newer DH5, Fig. 1. Installing a new ventilation system with heat recovery is cost-effective in every studied house. Adding insulation to the ceiling can also be cost-effective in a few houses. Other single energy renovation measures reduce the primary energy usage, but also increase the net present value of the house. Fig. 1. Change of net present value and decrease of primary energy use in houses DH1 and DH2 (avg. top left), DH3 (top right), DH4 (bottom left) and DH5 (bottom right).
Üllar Alev et al. / Energy Procedia 78 ( 2015 ) 907 912 911 In a newer house, the renovation should be concentrated on the technical systems, because replacing/installing a new ventilation system and replacing an ineffective heating source are the only cost-effective renovation measures. Fig. 2 presents all the combinations of previously described renovation measures. Using the ground source heat pump lowers the primary energy usage most (Fig. 2 bottom right). The optimum energy renovation level of DH1 (lowest point of cost optimal curve) is distinctively higher than other levels. Maximum achievable renovation level is 133 (123 134) kwh/(m 2 y) for all houses with different envelope solutions. The renovation of the newer house DH5 is the least economical. When the envelope has higher thermal transmittance (DH4), then its renovation is not more cost effective than in other cases. Most cost-effective renovation combinations: DH1: R250; AWHP + EW200 + R250 + V0.8; WB + EW200 + R250; GSHP + R250; DH2: V0.8; AWHP + EW200 + R150 + D1.0 + V0.8; WB + EW200 + V0.8; GSHP + V0.8; DH3: V0.8; AWHP + EW200 + F200 + D1.0 + V0.8; WB + V0.8; GSHP + V0.8; DH4: V0.8; AWHP + EW300 + F100; WB + EW200 + V0.8; GSHP + EW200 + V0.8; DH5: R150 + V0.8; AWHP + R150 + V0.8; WB + V0.8; GSHP + V0.8. Fig. 2. Change of net present value and primary energy use in all houses with original envelope heating system (top left), air-water heat pump (top right), wooden boiler (bottom left), and ground source heat pump (bottom right). 4. Discussion As the thermal transmittance of log or wooden walls is lower than that in brick or massive stone houses like in Sweden [4], it is not cost effective for detached houses. Adding additional insulation to the floor or the external wall is not economical when considering the investment cost over a period of 20 years (positive NPV), but when calculating
912 Üllar Alev et al. / Energy Procedia 78 ( 2015 ) 907 912 over a longer period like 30 years, then the NPV becomes negative. Therefore, some renovation measures can be considered cost-effective over a period longer than 20 years. Additional insulation of the external wall may become cost effective when the repair or replacement cost of the wooden cladding is considered as a periodic cost to preserve the visual appearance of the house and not as a part of energy renovation measure. If we consider that the indoor climate needs improvement anyway and therefore a high quality ventilation system with heat recovery is installed, then there is no need to calculate only the energy saving from the improvement. As the prices for wood billet are so low compared to electricity and the weighting factor for wood is also almost third of that of electricity, it is not economical to replace wooden stoves with the ground source heat pump or the airwater heat pump. Even the replacement with the pellet boiler is not economical considering the investment and the higher cost of pellets compared to wood billets. The main reason to replace wooden stoves or wooden billet boilers to electric heating sources may be their less labor-intensive operation. To lower the national energy use in the residential sector, the government should provide supporting mechanisms to encourage the homeowners to make their houses more energy efficient. Current cost-effective primary energy use level of the studied detached houses is around 250 kwh/(m 2 y), which is still relatively high and the target level can and should be lower. Acknowledgements The study has been conducted as part of the IUT1-15 project Nearly-zero energy solutions and their implementation on deep renovation of buildings. 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