Human comfort and self-estimated performance in relation to indoor environmental parameters and building features

Abstract

The main objective of the Ph.D. study was to examine occupants’ perception of comfort and self-estimated job performance in non-industrial buildings (homes and offices), in particular how building occupants understand comfort and which parameters, not necessarily related to indoor environments, influence the perception of comfort. To meet the objective, the following actions were taken: (1) a literature survey exploring which indoor environmental parameters (thermal, acoustic, visual environment and air quality) predominantly determine overall comfort and whether other factors unrelated to the indoor environment influence the perception of comfort; the literature survey summarized 42 peer-reviewed and conference articles and 1 book covering the period from 1970 to 2009; (2) preparation, distribution and analysis of a questionnaire survey sent to 2499 addresses representing the most common types of residential buildings in Denmark and filled out by 645 persons (response rate of 26%); and (3) analysis of the post-occupancy satisfaction survey conducted by the Center for the Built Environment (CBE) at the University of California Berkeley in 351 mainly U.S. office buildings and filled out by 52,980 building occupants. The results of the literature survey showed that thermal, acoustic and visual environments and air quality all influenced evaluation of the overall indoor environment and that thermal comfort was ranked in the majority of cases to be of slightly greater importance for overall comfort than acoustic and visual comfort and satisfaction with air quality. The data from the Danish residential buildings showed actually slightly different results, indicating that when the acceptability of thermal, acoustic, visual conditions and air quality are of a similar magnitude, corresponding to low levels of dissatisfaction, then the acceptability of the overall indoor environment can be approximated by averaging acceptability of these individual parameters. The literature survey suggested also that there are other factors unrelated to indoor environment such as personal characteristics of building occupants, building-related factors (type of building and control over the indoor environment) and the outdoor climate (including seasonal changes), that can influence the perception of comfort. Providing people with the possibility to control the indoor environment had a beneficial effect on the perception of comfort, indicating that control over the indoor environment should be delegated to building occupants. When the systems for controlling thermal environment are designed, the building type (naturally ventilated or air-conditioned) and local climate conditions should be taken into account. This has been further confirmed by the results from the Danish residential buildings showing that not only indoor environmental parameters contributed to occupants’ comfort but also a peaceful atmosphere, contact with nature and the view through a window. In office buildings, overall satisfaction with personal workspace was influenced by satisfaction with not only indoor environmental parameters but also satisfaction with workspace and building features. The highest increase in overall satisfaction with personal workspace would be achieved when increasing satisfaction with the amount of space for work and storage, noise level and visual privacy. However, if job performance is considered, then satisfaction with the main indoor environmental parameters should be addressed first as they affected self-estimated job performance to the highest extent. The present study showed that overall satisfaction with personal workspace affected significantly the self-estimated job performance. Increasing overall satisfaction with the personal workspace by about 15% would correspond to an increase of self-estimated job performance by 3.7%. Among indoor environmental parameters and building features, satisfaction with temperature was the most important parameter for self-estimated job performance, followed by satisfaction with noise level and air quality. It is obvious that there is a discrepancy between ranking of indoor environmental parameters and building features regarding their importance for overall workspace satisfaction and self-estimated job performance. Thus, the investments in improving conditions in indoor environments should be made according to whether improvement of satisfaction or self-estimated job performance is the aim. The study in Danish residential buildings indicated that manual control of the indoor environment was highly preferred, and only in the case of temperature did respondents accept both manual and automatic control. The majority of respondents who reported having at least one problem related to the indoor environment, did not try to find information on how to solve the problem. This may suggest that there is a need for increasing people’s awareness regarding the consequences of a poor indoor environment on their health and for improving people’s knowledge on how to ensure a good indoor climate. The present results, although comprehensive, need further validation.