Energy renovation saving potentials of typical Finnish buildings

Transcription

1 Energy renovation saving potentials of typical Finnish buildings R. Holopainen, Research scientist, Technical Research Centre of Finland VTT; M. Hekkanen, Lecturer, Oulu University of Applied Sciences KEYWORDS: energy use, costs, renovation, Finland. SUMMARY: VTT s Energy renovation technologies-project (26) studied the profitability of energy renovation measures for buildings. Different energy renovation technologies for structural improvements (retrofit insulation, air tightening), heat supply systems, ventilation systems, lighting, electrical appliances, solar shading and cooling were evaluated. The effects of different energy renovation measures to reduce heating or cooling energy were simulated for two single-family houses, three apartment houses and one office building. The energy consumption of the example buildings was simulated before and after the renovation, and payback times of the renovation procedures were calculated. The total energy renovations reduced the annual heating and ventilation electricity consumption of the electrically heated single-family house by 67 % and the annual heating energy consumption of the oil-heated single-family house by 65 %. The specific heat consumptions of the studied apartment houses were reduced between 46 % - 56 %. The annual cooling energy use of the office building was reduced between 44 % - 71 %. With current energy prices, the calculated payback times of these energy renovations were in most cases too long for repairing the building only to reduce its energy use. 1. Introduction The heating energy and electrical energy use of Finnish residential and public buildings is responsible for about 3 % of the Finnish CO 2 emissions. Energy renovations, such as supplementary insulation and heat recovery from outlet air, can be performed to reduce the buildings energy use and CO 2 emissions. Following energy saving potential calculations for single-family houses are made with WinEtana, a building energy use calculation tool developed at VTT. The calculations for the apartment houses are made with VTTenergiaseniori, also developed at VTT. The dynamical simulations for the office building are made with IDAIce. In payback time calculations the oil price is.6 /dm 3 (.6 /kwh), electricity price.11 /kwh and district heating price.5 /kwh. 2. Single-family houses The studied house is a typic al in 196 built one-storey single-family house. It is inhabited by a four-person family, 2 adults and 2 children. The building volume is 466 m 3, the floor area is 147 m 2, the brutto area is 163 m 2 and the room height is 2.5 m. The original U-values of the envelope are based on the 1969 building regulations: outer walls.81 W/m 2 K, roof and base floor.47 W/m 2 K and windows 3.14 W/m 2 K. The energy calculations are made for Helsinki (South Finland) and Jyväskylä (Central Finland). The original space heating demand of the brutto area is 252 kwh/m 2 in Helsinki and 275 kwh/m 2 in Jyväskylä. Two similar houses with different heating systems are studied: 1) direct electrical heating and 2) water central heating with an oil-fired boiler. Common energy renovation technologies for the both houses are:

2 supplementary insulation to fulfil the present heat insulation regulations, U-values: outer walls.25 W/m 2 K, roof.16 W/m 2 K, base floor.2 W/m 2 K; new windows, U-value 1,1 W/m 2 K; air tightening the envelope and thus reducing the air leakage rate (n 5 ) from 7 1/h to 3 1/h; changing the existing mechanical exhaust ventilation system to a mechanical supply and exhaust ventilation system with heat recovery. The energy efficiency of the new fan is 1.6 kw/(m 3 /s) (energy class A), air inlet temperature 2 C, annual heat recovery efficiency 6 %. The increase of the electricity use of the ventilation system is 28 kwh/a. The calculated annual heating and ventilation electricity use of the single-family house with a direct electrical heating is 46 5 kwh in Helsinki and 5 3 kwh in Jyväskylä, and the respective annual costs are 5 12 and Besides the common energy renovations, the effect of an outdoor air heat pump is evaluated. The outdoor heat pump is assumed to produce 17 % of the space heating energy use. After the energy renovations the space heating demand of the brutto area is 76 kwh/m 2 in Helsinki and 84 kwh/m 2 in Jyväskylä. The total electricity consumption for heating and ventilation is 15 5 kwh/a in Helsinki and 16 9 kwh/a in Jyväskylä, the costs respectively 1 7 /a and 1 86 /a. Figure 2 shows the gradual decrease of the annual electricity use for heating and ventilation. Electricity use, kwh/a Single-house, direct electrical heating: heating and ventilation electricity use Before renovation Retrofit insulation New windows Mechanical ventilation with heat recovery Helsinki Jyväskylä Outdoor air heat pump FIG. 1: Single-house with direct electrical heating: decrease of the annual electricity use (space heating, domestic hot water and ventilation) by energy renovation procedures. The estimated total renovation costs are with states funding as 15 % of the investment price of the heat pump. The construction costs are not included. The payback times of the total energy renovation are 13 years in Helsinki and 12 years in Jyväskylä with the state funding as 15 % from the cost of the outdoor heat pump included. The energy escalation (yearly price increase) is 1.5 % and interest rate 5 %. The annual savings and payback times are also calculated for separate energy renovation procedures (Table 1).

3 TABLE. 1: Payback times for separate energy renovation procedures in Helsinki and Jyväskylä Retrofit insulation Total investment cost, Annual saving in Helsinki, Payback time in Helsinki, a Annual saving in Jyväskylä, Payback time in Jyväskylä, a New windows Mechanical ventilation with heat recovery Outdoor air heat pump The heating system of the oil-heated single-family house is a water central floor heating with an oil-fired boiler. The annual heating oil use is 5 75 dm 3 in Helsinki and 6 16 dm 3 in Jyväskylä, with respective costs as 3 45 and 3 7. Besides the common energy renovation procedures, the effect of installing a new oil-heating system equipped with a solar heating system is studied. The new oil heating system has a yearly efficiency of 93 % (87 % for the old system), and the solar-heating equipment is assumed to heat up 5 % of the domestic hot water in annual level. After the energy renovations the annual oil use is 2 3 dm 3 in Helsinki and 2 18 dm 3 in Jyväskylä, with respective costs as 1 22 and Property electricity use has increased 3 kwh/a (33 /a). Figure 2 shows the gradual decrease of the annual oil use. Energy use, kwh/a Before renovation New oil heating equipment and solar heating system Single-house, oil-heating: total heating energy use Helsinki Jyväskylä Retrofit insulation New windows Mechanical ventilation with heat recovery FIG. 2: Oil-heated single-house: decrease of the annual heating energy use by energy renovation procedures.. The total renovation cost with the state funding included (15 % of the investment costs of a new oil-heating system equipped with a solar heating system) is The payback time of the total renovation is 31 years in Helsinki and 27 years in Jyväskylä with the energy escalation 1.5 % and interest rate 5 %. The payback times for separate renovation procedures are presented in Table 2.

4 TABLE. 2: Payback times for separate energy renovation procedures, oil-heated single-house in Helsinki and Jyväskylä. New oil-heating system Retrofit insulation Total investment cost, (State funding included) Annual net saving in Helsinki, Payback time in Helsinki, a Annual net saving in Jyväskylä, Payback time in Jyväskylä, a New windows Mechanical ventilation with heat recovery The total energy renovations reduce the annual heating and ventilation electricity consumption of the electrically heated house by 67 % and the annual heating energy consumption of the oil-heated house by 65 %. The payback times for the total energy renovations for the both single-houses as a function of the energy escalation rate are presented in Figure 3. Single-houses, total energy renovation 35 3 single-house with oil-heating single-house with direct electrical heating Payback time, a % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % 1 % Energy escalation FIG. 3: Single-houses: payback times as a function of the annual energy price increase rate (Location: Jyväskylä)

5 3. Apartment houses The three simulated houses represent typical Finnish apartment houses built in years 195, 196 or 197. The apartment areas are 1613 m 2 (195), 339 m 2 (196) and 3863 m 2 (197). The houses are heated by district heating and the original annual specific heat consumptions are 255 kwh/m 2 (195), 213 kwh/m 2 (196) and 188 kwh/m 2 (197). The apartment houses are renovated with exterior retrofit insulation and new surface structure for the outside walls. The windows, balcony doors and front doors are renewed. The district heating centre and the heat supply system are modernized. Mechanical supply and exhaust ventilation systems with heat recovery (annual efficiency 3 %) are installed in all apartments. After the renovation the specific heat consumptions are 138 kwh/m 2 (195), 116 kwh/m 2 (196) and 82 kwh/m 2 (197). The specific heat consumption was thus reduced between 46 % -56 %. Energy renovation procedures for apartment buildings are nearly always done in connection with other renovations; an energy renovation also increases the indoor air quality and the energy efficiency of the house. For these reasons, in following payback time calculations (Figure 4) the interest rate is % and the investment costs are taken as the price difference between a traditional repair method and an energy saving repair method, e.g. installing windows with lower U-values instead of standard windows. Apartment houses, total energy renovation and 197 Payback time, a % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % 1 % Energy escalation FIG. 4: Apartment houses: payback times as a function of the annual energy price increase rate (Location: Jyväskylä)

6 4. Office building The simulated office building is built in 198, the brutto area is 916 brm 2, and the annual cooling energy demand is 31.5 MWh. The cooling energy reduction potential of the office building is calculated by dynamic simulation. The power level of the lighting is reduced from 17.5 W/m 2 to 1 W/m 2 by means of energy-efficient lamps. The effects of four different solar shading technologies are studied: two different solar control glass windows (total transmittance factor g =.21 or.44), blinds and awning (between April and September). Combined with the reduction of the lighting power level, the annual cooling energy use is reduced from 44 % to 69 % with solar control glass windows, 56 % with blinds and 71 % with awning. Office building, solar shading technologies Payback time, a Awnings Solar control glass window, g =.21 Solar control glass window, g =.44 Blinds 1 % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % 1 % Energy escalation FIG. 5: Office building: payback times of different solar shading technologies (combined with the reduction of lighting power level) as a function of the annual energy price increase rate (Location: Helsinki) 5. Conclusions The theoretical energy saving potential of the existing building stock is large. The energy renovations procedures calculated in this study reduced the annual heating and ventilation electricity consumption of the electrically heated single-family house by 67 % and the annual heating energy consumption of the oil-heated single-family house by 65 %. The specific heat consumptions of the studied apartment houses were reduced between 46 % - 56 %. The annual cooling energy use of the office building was reduced between 44 % - 71 %. With current energy prices, the payback times of energy renovations are often too long for repairing the building only to reduce its energy use. Energy renovation actions can be cost-effectively carried out in connection with another renovation procedures (e.g. building façade renovation, renovation of the ventilation system). Renewable energy sources should be utilized, when possible.

7 The technological solutions of energy renovations are already available; the essential development need lies in the implementation process. Thermal comfort issues should be emphasized in marketing: controlled mechanical ventilation improves the indoor air quality, and with increased insulation levels the inner surface temperatures are higher, which decreases the draught experienced by the radiation of cold surfaces. New business service models are needed to offer attractive and cost-effective energy renovations for customers. References WinEtana simulation program is developed at VTT for estimating building energy consumption. The program is described in following publications: 1) R. Kosonen, J. Shemeikka, The use of simple simulation tool for energy analysis, in: Proceedings of Building Simulation 97, 5th International IBPSA Conference, Prague, September 8 1, 1997, pp and 2) J. Shemeikka, WinEtana 1. LT Building Energy Calculation Program Manual, Technical Research Centre of Finland, Espoo, 1997, p. 29 (in Finnish). VTTenergiaseniori calculation tool for estimating building energy consumption is developed at VTT. The program is described in: Hekkanen, Martti, Hienonen, Markku, Ilmarinen, Juhani, Kilpeläinen, Mikko, Klemettilä, Tapio, Mäkikyrö, Tapani, Riippa, Tommi, Seppälä, Pekka & Tulla, Kauko. Pientalon ekomittarit [Key methods for energy efficiency and ecological impacts in private housing]. Espoo 26. VTT Tiedotteita. Research Notes p. + app. 9 p. (in Finnish) IDA ICE, A tool for simulation of thermal comfort, indoor air quality and energy consumption in buildings Suomalaisten rakennusten energiakorjausmenetelmät ja säästöpotentiaalit [Energy renovation technologies and saving potentials of Finnish buildings]. Holopainen, Riikka; Hekkanen, Martti; Hemmilä, Kari; Norvasuo, Markku. 27. VTT, Espoo. 14 s. + liitt. 2 s. VTT Tiedotteita - Research Notes : (in Finnish)