Case study on residential building renovation and its impact on the energy use and thermal comfort

Transcription

1 Case study on residential building renovation and its impact on the energy use and thermal comfort Hanne Kauko, Maria Justo Alonso, Ole Stavset and Ingrid Camilla Claussen SINTEF Energy Research

2 Motivation and background Energy consumption by different sectors Fishing, agriculture, forestry etc. Services Households Industry Transport Source: European Environment Agency In EU In Norway 2

3 Motivation and background Norwegian building stock Age distribution of the Norwegian building stock in total and for the biggest building types. Enovas Byggestatistikk

4 Motivation and background Effect of the new standards and regulations Change in the demand for energy use per m 2 for different building types based on thedifferent regulations and standards. Enovas Potensial- og barrierestudie 1/3, 2/3 og 3/3, 2012 (Enova Resultatrapport 2013). 4

5 Introduction The present study Hypothetical study of renovating an apartment building in Trondheim from 1988 with an oil-based heating system to a near-zero energy building. Building with three floors, three 80m 2 apartments in each floor Study performed using simulations from the IDA Indoor Climate and Energy (IDA ICE) software. Two alternative heating systems considered: i. Solar collectors alone ii. Solar collectors combined with borehole thermal storage and a ground-source heat pump (GHP) Energy consumption, thermal comfort and indoor climate were studied. 5

6 Introduction Solar collectors and ground-source heat pump good together Solar alone requires supplementary (electric) heating and/or thermal storage. Continuous use of a GHP for heating only may lead to thermal depletion (reduction in the ground temperature). Reduction in the system performance Excess solar heat in the summer time, and lower temperatures from the collectors in the spring and winter can be exploited to recharge the boreholes. Increased brine temperature will increase the heat pump efficiency. Beneficial especially if boreholes are too short, or thermally influencing each other. Can help to reduce the required borehole length, and hence the system costs. Reduced demand for compressor power. V. Trillat-Berdal, B. Souyri, G. Achard, Applied Thermal Engineering 27 (10) (2007) E. Kjellsson, G. Hellström, B. Perers, Energy 35 (6) (2010)

7 Simulations The building envelope Component External wall Roof Floor (towards an unheated basement) Windows Specifications (original/upgraded) Concrete covered with bricks, 110/280mm mineral wool, timber frame, 50mm thermal bridge break Roof tiles, 170/380mm mineral wool, concrete slab Concrete slab, 120/300mm mineral wool Double glass, one coated, air filled/ Triple glass, two coated, argon filled U-value (W/m 2 K) SHGH (g-value) Original Upgraded Original Upgraded Original: Building customs and regulations for apartment buildings built in (Enova, Potensial- og barrierestudie 1/3: Energieektivisering av norske boliger (2012)). Upgraded: Requirements of the Norwegian research centre on Zero Emission Buildings (ZEB) (T. H. Dokka, T. Kristjansdottir, B. Time, S. Mellegård, M. Haase, J. Tønnesen, A zero emission concept analysis of an office building (2013)). 7

8 Simulations Ventilation and hydronic system Parameter Original Upgraded Ventilation Exhaust ventilation, air flow rate 0.5 l/sm 2 Air tightness, n h h -1 Radiator max heating capacity (per apartment) Radiator inlet/outlet temperature 8 kw 2 kw 90 o C/70 o C 55 o C/35 o C DHW use (daily average) 60 l/person 36 l/person CAV with heat recovery efficiency 0.8, air flow rate 0.6 l/sm 2 8

9 Simulations Heating system Original: Central oil boiler with an efficiency of 0.88 Common, stratified storage tank of 2 m 3 for DHW and heating Alternative heating systems i. 50m 2 planar solar collectors ii. Combined system i. 36m 2 planar solar collectors, 6x200m boreholes (BHE) and a heat pump ii. 50m 2 planar solar collectors, 6x200m BHE and a heat pump iii. 36m 2 planar solar collectors, 8x200m BHE and a heat pump iv. 50m 2 planar solar collectors, 8x200m BHE and a heat pump 9

10 Results Heat load: original vs. upgraded Original Upgraded Total heat load reduced to one third of the original As a result of increased insulation, reduced use in DHW as well as the heat recovery in the air handling unit. The share of DHW of the total heat load was 47% for the original building and 85% for the upgraded building. 10

11 Results Heat load and production: The alternative heating systems Solar only, 50m 2 collectors Solar collectors 36m 2 with borehole thermal storage and a HP High demand for electric top heating in the solar only system: 24.6 kwh/m 2 /year Partially due to high losses in the storage tank, resulting from high temperature variations In the combined system, demand for electric top heating low. Compressor power reduced by 20% as compared to a GHP only system (not shown) 11

12 Results Heat load and production: The alternative heating systems Solar collectors 50m 2 6x200m BHE Solar collectors 36m 2 8x200m BHE Solar collectors 50m 2 8x200m BHE Top heating demand negligible for each case Partially due to heat stored in the tank? Increased number of boreholes leads in increased demand for compressor power Additionally, increased costs due to drilling Cost-optimal dimensions? 12

13 Results Heat load and production: Mismatch The portion of the head load covered by the alternative heating sources. Period Solar only Combined (36m 2 SC, 8x200m BHE) Annually Monthly Daily

14 Results Thermal comfort The warmest summer day in the warmest zone The coldest winter day in the coldest zone Longer periods with elevated temperatures in the upgraded building. T > 27 o C on 29 days (18 for the original building) Note! Windows were assumed to be kept closed all the time! Difference small on a cold winter day, but maintaining the temperature in the upgraded building requires high radiator temperatures. Reduced air quality due to dust burned. 14

15 Results Air quality Somewhat lower CO 2 levels in the upgraded building as a result of increased ventilation (from 0.5 to 0.6 l/sm 2 ) CO 2 levels acceptable already in the old building Is the increase in ventilation necessary? Other contaminants were not considered in the simulations CO2 levels for the hottest summer day in warmest zone and the coldest winter day in the coldest zone for the original and upgraded building. 15

16 Conclusions Renovation of the building envelope Renovation resulted in a reduction in the total annual heat load to one third of the original. Renewable heat production With solar collectors combined with borehole thermal storage and a GHP, the total annual heat load could be covered almost completely. Thermal comfort and air quality In the upgraded building, longer periods with elevated temperatures were observed. No significant reduction in the CO 2 levels from the original to the upgrade building. 16

17 Thank you for your attention. Acknowledgements This work has been supported by the Research Council of Norway and several partners through the SINTEF/NTNU The Research Centre on Zero Emissions Buildings (ZEB). 17