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Occupant behaviour and the related reference levels for heating and cooling – Analysis of the factors causing individual differences together with the evaluation of their effect on the exergy consumption within the residential built environment

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One solution commonly heard to face the decline of fossil energy resources is the reduction of demand through greater efficiency of the building systems. This is an issue even in the residential building sector even though its demand depends strongly on the occupant behaviour. The research on occupant behaviour often focuses on the analysis of general behaviour patterns and not on the factors leading to individual differences in the behaviour. However, such differences are the reason for many variations in the energy used for heating and cooling. The objectives of this research are (1) the identification of those factors having a major influence on the occupant behaviour and its reference levels, (2) the analysis of the potential to influence the reference level towards a change of occupant behaviour and (3) the evaluation of the exergy consumption for cooling and heating in relation to the differences in occupant behaviour. The analyses presented in this dissertation are based on (1) a comprehensive literature review within the fields of built environmental research, neurology, psychology, control theory and behavioural ecology; (2) a field measurement conducted in an international student dormitory (39 students in summer and 34 in winter) together with their answers to a survey and interviews; and (3) an Internet‐based survey leading to a qualitative database of comfort votes, recent behaviours and personal background of 434 participants for summer and 845 for winter. Overall, this dissertation highlights the importance of researching the individual’s behaviour in order to understand the differences in certain types of energy usage. Besides being limited to the cases of heating and cooling with an AC‐unit for most of the analyses, the methodology presented can also be applied to other types of behaviours. This dissertation shows another possible solution of how to change the current paradigms of energy usage towards the one that permits well‐being with less exergy.
The whole dissertation consists of four parts. In the first chapter of part 1 (chapters 2–4), the development of a theoretical occupant‐behaviour model is described based on the comprehensive literature review. In this context, the reference level is introduced as the entity to which all input values deriving from the body’s sensory systems are compared. Therefore, the reference level has a special place in the model, because the decision whether to perform or not to perform a certain type of behaviour is based on the outcome of this comparison. Second, the nature of the reference level was analysed by looking at the success, the purpose and the ranking of occupant behaviour based on the data from the Internet‐based survey. It was found that there must be a separate reference level for different input values such as thermal comfort and noise, which are independent of each other. Third, a first trial analysis on the human body exergy consumption (HBx) rate as reference level shows that the decision to sleep with an open or closed window could be partly explained with the current HBx rate in comparison to the HBx rate range during childhood.
In part 2 (chapters 5–7), the factors influencing on the reference levels for thermal comfort were elaborated and a method to quantify the relative importance of those factors were established. The first analysis of the data obtained from the measurement in the student dormitory showed the significance of individual factors in relation to differences in the behaviour. Examples for such individual factors are a preference for air-conditioned spaces and thermal background, which refers to the climate a person spent the majority of their first 10 years of life. In the next step, the influence of external factors such as temperature and humidity as well as various individual factors were evaluated according to their significance in describing the observed behaviour by the mean of multivariate logistic regression analyses. As a result, statistical models of occupant‐behaviour prediction including an exponentially weighted running mean of the outdoor temperature during the night and 17 individual factors such as above mentioned preference and thermal background were presented. The factors included in these models were then judged by introducing an importance factor. It was found that, on the one hand, the running mean of the temperature has a similar impact to the individual factors in summer, while, on the other hand, the latter have a much higher influence in winter than in summer.
Part 3 (chapters 8–9) analyses whether and to what degree long‐term or short‐term experiences can influence the set‐up or a change of the reference levels. Firstly, the effects of long‐term experiences such as cultural influences are shown by comparing the stated behaviour with respect to sleeping conditions of those participating in the Internet‐based survey. This revealed, on the one hand that the behaviour is influenced by the type of building as well as the surrounding, and on the other hand, it was shown by means of a detailed analysis of Germans living in Japan compared to those living in Germany that behaviour can be influenced by such external factors. Second, the influences of knowledge transfer methods on the reference levels, which can be regarded as short‐term experiences, were evaluated. It was shown that the knowledge transfer methods can motivate the recipients to try out strategies not practised before, but there is a huge discrepancy between the stated intention immediately after the knowledge transfer and the actions performed in reality. With respect to the usage of AC‐unit, the effect of knowledge transfer processes such as workshops or information papers could be quantified to lead to a reduction of up to 16% in the case of the workshop, but no significant change was detected in response to the information paper.
Part 4 (chapter 10) describes the effect of differences in the reference levels compared to building envelope improvements on the exergy consumption for heating and cooling. Based on a steady‐state exergy  calculation, the influence of the occupant behaviour was highly significant (more than 90% decrease of exergy consumption) when the difference between indoor and outdoor air temperature is small, which is the case for long periods in those regions with moderate temperatures during summer and/or winter. On the other hand, the building envelope improvements have a much higher influence wherever the difference in temperature
between indoors and outdoors are larger. Nevertheless, both measures combined lead to a reduction of up to 95% and should be the final goal.