The impact of consumers behaviour on the difference between practical and theoretical domestic energy consumption for space heating

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1 The impact of consumers behaviour on the difference between practical and theoretical domestic energy consumption for space heating AMARYLLIS AUDENAERT Department of Industrial Sciences Artesis Hogeschool Antwerpen Paardenmarkt 92, BE-2000 Antwerp BELGIUM & University of Antwerp Prinsstraat 13, BE-2000 Antwerp BELGIUM KATLEEN BRIFFAERTS Vlaams Energieagentschap Elfjulistraat 39, BE-9000 Gent BELGIUM Abstract: Methods to calculate the theoretical energy consumption consider the number of degree days per year that needs to be compensated by heating, the characteristics of the dwelling and the characteristics of the installation for space heating and sanitary hot water. [1,2] However, these methods do not take into account the consumer behaviour that may affect the actual consumption [3]. Also socio-economic characteristics of households (household size, social position, income, etc.) are suitable to explain household's behaviour concerning space heating given technical building characteristics. [4]. The software is based on assumptions and uses standardized parameters. To demonstrate the difference between the actual and the theoretical energy consumption, the residents behaviour with regard to energy consumption will be analyzed by means of a literature study and a practical research. On behalf of this these, an EAP audit was executed in five dwellings, as well as a survey regarding the energy consumption and the consciousness of the households. [8] There was chosen to use a standardized model dwelling so that a comparison between the dwellings was made possible. It concerns five detached dwellings with each four residents, a working family with two children. The dwellings have a similar geometry and are all heated by gas. The theoretically calculated consumption is compared with the actual billed energy consumption of the families. The difference between those values is then explained by their behaviour. By comparing average actual indoor temperatures with the default value in EAP, a part of the difference can be explained. For example, EAP assumes that the dwelling is constantly en fully heated, while the inquiry shows that this is not always the case, leading to differences in average indoor temperatures. Also atmospheric heating such as a fireplace is not included in the theoretical calculation, but can sometimes in reality create a reduction in energy consumption. Estimations of ventilation losses and heat gains are often highly simplified by EAP, but tend to be difficult to prove in reality. The maintenance of the heating system influences the actual energy consumption, if it s not properly maintained, the efficiency is lower than expected. These results can contribute to an optimization of the calculation methods, but human behaviour will always ISBN:

2 remain unpredictable, so it s not always possible to draw up average values for the calculation of the theoretical consumption. Key-Words: practical energy consumption, theoretical energy consumption, consumer behaviour 1 Introduction Various methods are used to make an assessment of the domestic energy consumption for space heating, among which EAP. When the theoretical energy consumption is being compared to the actual energy consumption, it appears that there is a difference between the two [3]. This difference is influenced by many factors. The actual energy consumption is determined by the exterior climate, the characteristics of the dwelling, the characteristics of the installation for space heating and its maintenance and the consumer behaviour [5]. This last factor varies between different dwellings. Also, EAP is based on a number of assumptions. For example, it assumes that the dwelling is constantly en fully heated at a constant temperature. However, in practice, the consumer behaviour is different. How is the actual consumption affected by the residents behaviour? A literature study shows that the behaviour can influence the energy consumption in a very large extent. There are different ways to save energy, but an energy saving does not always have the desired effect. The consumer behaviour affects these savings, because an improved energy situation leads to an increased demand for comfort [6]. This effect is known as the rebound effect. To declare the already proven difference between practical and theoretical energy consumption, the consumer behaviour is researched. By using an EAP audit in selected dwellings, the theoretical consumption can be calculated. This result is then compared with the actual billed energy consumption. By a survey of the families, the behaviour regarding energy consumption can be defined. This behaviour can then explain the difference between the practical and the theoretical consumption. The results can explain the already concluded differences, as well as contribute to an optimization of the EAP method. In chapter 2 of this paper the methodology is described, chapter 3 shows the results, followed by the conclusions in chapter 4. 2 Methodology The purpose of this research is to explain the difference between actual and theoretical energy consumptions by using EAP and an inquiry regarding consumer behaviour. There was chosen to use a standardized model dwelling to ensure that the dwellings can be compared. Five dwellings were chosen, with the following characteristics: The dwelling is detached. There are four inhabitants. The dwellings are heated by gas, since the amount of gas consumed was only used for space heating and hot water. When there is heated by electricity, it is very difficult to estimate what portion of the consumed electricity was used for space heating. There must be a good overview on the annual energy consumption. To calculate the theoretical energy consumptions, EAP software was used. This procedure is intended for existing dwellings and determines the quality of the houses. The procedure gives an energy label to the building characteristic and to the installation for space heating and hot water. In EAP there are five steps to follow: The collection of data in the field. The launch of the software. Entering the collected data in the software. Performing the calculations. Generating the EAP-evaluation and the energy advice. [7] When these five steps are followed, a theoretical consumption is given by EAP. To calculate this theoretical consumption, the procedure is based on a number of assumptions. For example, EAP assumes that the dwelling is constantly and fully heated to a ISBN:

3 temperature of 18 degrees, or 17 degrees when temperature reduction during the night is applied. Also, EAP does not take into account additional heating systems like fire places and ventilation losses. EAP also calculates the actual consumption, based on the billed consumption, corrected with degree days. When all of these steps are followed, the theoretical and the actual consumption, in MJ, given by EAP, can be compared. In order to define the consumer behaviour, a survey was conducted, during the visit when the data for EAP was collected. The following questions were asked: Question 1: Are you aware of your energy consumption? Question 2: At what times is the dwelling heated? Question 3: What areas are heated? Question 4: Is there a thermostat in the room? Question 5: Is there an outdoor sensor? Question 6: What is the heating temperature during daytime? Question 7: What is the reduced temperature during the night? Question 8: Do the radiators have thermostatic cranes? All the radiators? Question 9: Is the heating turned off during long absences? Question 10: Is the system properly maintained? Question 11: Do you use an additional heating system (for example a fire place)? Question 12: Is there a ventilation system? If so, what type of system? Question 13: How long and how often do you open the windows during the day? Question 14: Do you use environmentally friendly energy? Question 15: Is there a bath and/or a shower present? Question 16: What is the number of baths taken in one week? Question 17: What is the number of showers taken in one week? Question 18: Does the shower have an energysaving shower nozzle? Question 19: Does the shower have a thermostatic or a mixing tap? 3 Results 3. 1 Results of EAP Table1 contains for the five dwellings: The heat losses to the external environment. The heat losses to the soil. The heat losses to unheated spaces. The total heat loss. The total area where the heat losses occur. The average U-value. The energy label. Heat losses by transmission find their source in the temperature difference between the inside and the outside environment. Transmission of heat trough the walls occurs. Table 1. Results of the building characteristics HL EE (W/K) HL S (W/K) HL US (W/K) Total HL (W/K) Total area (m²) U m (W/m²K) dwelling 1 311,3 72,8 0,0 384,2 584,01 0,66 dwelling 2 328,0 36,9 103,2 468,1 442,76 1,06 dwelling 3 226,1 88,0 7,1 321,2 383,85 0,84 dwelling 4 450,5 84,4 0,0 516,9 483,70 1,11 dwelling 5 289,1 0,0 46,5 335,6 620,43 0,54 Energy label ISBN:

4 Table 2. Results of the building characteristics Installation efficiency Actual Theoretical dwelling 1 0,745 0,739 dwelling 2 0,893 0,909 dwelling 3 ground floor 0,630 0,655 dwelling 3 bathroom 0,361 0,361 dwelling 4 0,950 0,950 dwelling 5 0,745 0,751 Energy label Table 3. Energy consumption for space heating Energy consumption for space Difference heating Actual Theoretical Dwelling MJ MJ 9% Dwelling MJ MJ 49% Dwelling MJ MJ 25% Dwelling MJ MJ 39% Dwelling MJ MJ 13% Figure 1. Energy consumption for space heating ISBN:

5 The size of the heat losses depends on the degree of isolation and on the size of the total area where the heat losses occur. Based on the U-value of the different building components, such as walls, roofs, floors, windows and doors, an average U-value is being calculated. The U-value is the heat transmission coefficient of a building component. It specifies the amount of heat that is being transferred trough a wall per time unit, per area unit and per unit of temperature difference (W/m²K). [7] Table 2 shows the results of EAP for the actual and the theoretical installation efficiency of the heating system. The installation efficiency of a heating system is calculated as the product of the production efficiency, the distribution efficiency, the adjustment efficiency and the delivery efficiency. [7] The values of the actual efficiency is calculated based on the billing data and (optionally) a maintenance certificate. In order to find the value of the theoretical efficiency the net energy need is first calculated, after which the theoretical consumption is calculated using default values. Remark: in dwelling 3, there are two energy sectors. The ground floor is heated with central heating, while the bathroom is heated with electric heating. Figure 1 shows a clear representation of the difference between the actual and the theoretical consumption. It proves that there is indeed a difference between them. The expectations do not match the reality, due to the consumers behaviour. By means of the survey this difference can be partially explained Results of survey The survey of the families released the answers that can be found in table 5. Table 5 shows that each household has another way to deal with energy consumption. This means that when different families would live in a similar dwelling, the consumption would be different. By using the survey table 4 can be defined. Table 4: Results survey Average temperature during the day Average temperature during the night # hours per day that the dwelling is heated (week) # hours per day that the dwelling is heated (weekend) Woning 1 Woning 2 Woning 3 Woning 4 Woning 5 21 C 18,75 C 20 C 21 C 19,5 C 16 C 15 C 14 C 16 C 17 C , ISBN:

6 Table 5: Survey regarding consumers behaviour. Dwelling 1 Dwelling 2 Dwelling 3 Dwelling 4 Dwelling 5 Q1 Yes Yes( only the Yes No Yes parents) Q2 W: 06h30-10h30, 16h30 22h30 W: in the morning and in the evening W: 06h00 08h00, 17h00 23h00 W: 06h00 08h00, 17h00 22h00 W: 06h00 08h00, 18h00 22h30 Q3 All, except the bedrooms and the garage All, except the garage Ground floor (- garage): central heating, bathroom: electric heating All All, except the attic Q4 Yes Yes Yes Yes Yes Q5 Yes Yes No No No Q6 21 C 18 à 19,5 C 19 à 21 C 20 à 22 C 20 C, weekend 18 C Q7 16 C 15 C 14 C 16 C 17 C Q8 Floor heating Yes, First Floor No Yes Yes and hal Q9 Yes Yes Yes Yes Yes Q10 Too little Yes Yes Yes Maintenancefree Q11 Fire place, rarely Q12 No No No Yes, ventilation grids in windows Q13 5 à 10 min, bedrooms constantly Fire place, often Fire place No Yes, gas stove Bedrooms 1 à 2 hours per day During winter: rarely Grids + bedrooms constantly Nee Slaapkamers ½ uur per dag Q14 No No No No No Q15 Both Both Both Both Both Q per month Q Q18 Yes No No No Yes Q19 Yes No Yes Yes Yes ISBN:

7 Table 1: Average actual indoor temperature Average actual indoor temperature Number of hours per week the dwelling is heated Average indoor temperature Dwelling ,4 C Dwelling ,7 C Dwelling ,5 C Dwelling C Dwelling 5 62,5 18 C 4 Discussion and Conclusion EAP assumes a constant indoor temperature of 18 C or 17 C when the temperature is reduced at night, what occurs in all five dwellings. Therefore a constant temperature of 17 C is expected in all spaces of the dwellings. However, this occurs in none of the dwellings, with exception of dwelling 4. In table 6 is the average actual indoor temperature calculated, taking into account the hours the dwelling is heated during the week and weekends, as well as the indoor temperature during the day and night in the dwelling. There is a ratio between the temperature during the day and night, as well as a ratio between week and weekend days. This table shows that the behaviour regarding indoor temperatures can influence the actual energy consumptions. In reality a fire place is often used, while EAP does not take account of fire places. When a fire place is used, the central heating is turned off, what can lead to an increase of the actual energy consumption. In dwelling 4, we find that the actual energy consumption is very high. This is due to the swimming pool heating which also consumes gas. Large ventilation losses can contribute to a higher actual energy consumption. When a lot of heat is lost by ventilation, there will be a larger energy consumption because of the higher demand for heat. Literature [8] shows that the ventilation rate is overestimated in theoretical calculations, so a higher energy consumption is expected. This overestimation may lead to a difference between the actual and the theoretical energy consumption. The survey of the families reveals that the residents ventilate their homes rarely. During the winter, little fresh air is admitted to the dwelling, resulting in fewer ventilation losses than predicted by EAP. Previous research shows that not only the consumer behaviour is a reason for the difference between the actual and the theoretical consumption. [5] The theoretical characteristics of the building can differ from the actual characteristics. There is a possibility that, for example, the insulation is not perfect, resulting in thermal bridges. It can also occur that the air permeability is not as good as expected. The actual and the theoretical characteristics will in practice never be the same, resulting in a difference between the actual and the theoretical consumption. This study focused on the consumer behaviour, influencing the actual energy consumption. In order to take into account the consumer behaviour, EAP must be customized. When there is a possibility to enter more variables in EAP, referring to the behaviour, a better estimation of the energy consumption is made possible. Human behaviour is unpredictable, as a result of which there should be more data entered in EAP. Default values should be avoided, since no family shows the same behaviour. This study proves that dwellings are not constantly and fully heated at a constant temperature, that a fire place is often used and that ventilation rates are overestimated. References: ISBN:

8 [1] Audenaert Amaryllis, de Cleyn Sven, Vankerckhove B..- Economic analysis of passive houses and low-energy houses compared with standard houses Energy policy - ISSN :1(2008), p [2] Audenaert Amaryllis, de Boeck Liesje, Roelants Kristof.- Economic analysis of the profitability of energy-saving architectural measures for the achievement of the EPB-standard Energy - ISSN (2010), p [3] Françoise Bartiaux, Guy Vekemans, Kirsten Gram-Hanssen, Dries Maes, Madeleine Cantaert,Benoît Spies Johan Desmedt (2006). Sociotechnical factor influencing residential energyconsumption (SEREC). (report), 223 p. [4] Andreas Schuler, Christoph Weber, Ulrich Fahl (2000) Energy consumption for space heating of West-German households: empirical evidence, scenario projections and policy implications. Energy Policy, 28:12( 2000), p [5] Dirk Van Orshoven, Lore Stevens (2003). Een inschatting van de energiebesparing ingevolge REG maatregelen in nieuwbouwwoningen. (report WTCB), 12 p. [6] Reinhard Haas, Hans Auer, Peter Biermayr (1998). The impact of consumer behavior onresidential energy demand for space heating. Energy and Buildings, 27, [7] Guide to EAP CSTC-WTCB VITO ICEDD [8] Vina Kukadia, Martin White (2006). Monitoring ventilation in homes built before 1995: A pilot study. 36 p. ISBN: