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There are two main concepts in the research on thermal comfort. On the one hand, there is the position originating from the work of Fanger, which is based on experiments in climate chambers and equations based on the thermal heat balance. This approach led to two important indices commonly used these days for the assessment of the thermal conditions – the predicted mean vote (PMV), which predicts the mean vote of a large group of people according to the ASHRAE thermal sensation scale from -3 cold to +3 hot, and the predicted percentage dissatisfied (PPD), which is a quantitative measure of the thermal comfort of a group of people at a particular thermal environment (Fanger, 1970).
On the other hand, there is the adaptive comfort model based on the analysis of field studies. In contrast to the previous described models, the adaptive model sets the temperature perceived as comfortabel in relation to the thermal background by including a weighted running mean of outdoor temperature (Humphreys and Nicol, 1998; deDear and Brager, 1998).
A third position, which started to be recognized as useful by only a handful of scientists so far, is the one developed by Shukuya (2009a,b). He set up the equations to calculate the Human-Body Exergy1-Consumption (HBx-) rate on the basis both of the first and second laws of thermodynamics.
All of these approaches, except the adaptive one, are concerned with the relationship between the prevailing conditions at the time of evaluation within the occupied space and the perceived thermal comfort. Only the adaptive approach includes past conditions by means of a weighted running mean of outdoor temperature.
In the same manner, the adaptive comfort model shows the influence of past conditions on the perceived level of comfort, a unique study by Schweiker and Shukuya (2009) concludes that also the decision to sleep with the air-conditioning unit switched on or off is partly based on the thermal conditions in the foregoing nights. In addition, a pilot study presented by the same authors found a relationship between the decision to sleep with an open or closed window and the HBx-Rate (Schweiker and Shukuya, 2007). Based on their findings, one can postulate that not only the prevailing conditions but also past conditions influence on our perceived thermal comfort.
Up to 90% of the total operating costs of an office building are spent for labour costs, while less than 10% are commonly used to provide comfortable working conditions (Olesen, 2005). However, according to recent studies there is a strong relationship between comfortable working conditions and productivity as well as between the former and well-being (Wyon, 2004). This can lead to conflicts during design and operation of such buildings between the expected productivity on the one hand and the amount of energy used on the other hand.
Therefore, the necessity was found to develop a singular model together with related equations for building simulation programs showing the relationship between thermal comfort and related behaviours, as well as the thermal background of the individual being. Therefore, this research project aimed at the development of a new holistic model of thermal comfort in the office environment by implementing the thermal background and behavioural actions of an individual human being. The expected results are a theoretical model together with equations to be used for prediction purposes.
Within this project in total five experimental series were conducted in so-called field laboratories. These special buildings in Wuppertal and Karlsruhe, Germany, allow the control of indoor conditions while enabling the subjects not only to have a real view to the outdoor environment, but also to interact with the windows, shades and other devices of the room. During these studies, psychological reactions (e.g. thermal sensation votes), physiological reactions (e.g. skin temperature and heart rate), and behavioural reactions (e.g. window usage) were recorded.
In addition field studies were conducted in several office buildings in Karlsruhe, Germany. During these studies, psychological, physiological and behavioural reactions were recorded in a minimized manner.
The data analyses of these experimental and field campaign data were augmented by several interdisciplinary and international discussion rounds together with a deep literature review.
The result is a framework for an adaptive heat balance model. This model does include as behavioural actions the adaptive clothing behaviours of office workers and their thermal background. It offers therefore an opportunity to be applicable to a wide range of thermal environments. The model is based on existing thermal comfort models and is therefore easily implemented with few adjustments into existing simulation programs.
This detailed understanding and the ability to predict the expected thermal comfort of an office worker together with the energy used for an existing or projected building must be crucial for a higher quality of life for the office worker, reduced costs for the entrepreneur and a reduced energy demand and CO2-emissions from the building sector. In addition, this will lead to further technological and conceptual advancements within the construction industry and the architectural design field as well as the interior design field. Therefore, these results offer the potential to achieve a higher satisfaction of EU office workers, an increased productivity of EU based companies, while achieving the set goals for CO2-emission reduction more easily in the long term.