The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

The Characteristics of Usable Room Temperature Control

Sami Karjalainen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium T2 at Helsinki University of Technology (Espoo, Finland) on the 15th of February, 2008, at 12 noon.

Overview in PDF format (ISBN 978-951-38-7060-7)   [1508 KB]
VTT Publications 662, ISSN 1455-0849

Dissertation is also available in print (ISBN 978-951-38-7059-1)
Copyright © 2008 VTT Technical Research Centre of Finland
VTT Publications 662, ISSN 1235-0621


Individual thermal control is important for handling individual differences in thermal preference. Several studies have shown that comfort, health and productivity in offices can be improved by individual thermal control. Local controls for temperature are commonly available in modern office buildings. However, office occupants are often still dissatisfied with thermal environments and control options.

The overall aim of the work is to improve office occupants' control over room temperature by improving the usability of interfaces of heating and cooling systems. Both qualitative and quantitative methods were employed to study office occupants as users of room temperature controls. The work started with qualitative interviews taken in actual context, in the offices of the participants. Twenty-seven office occupants were asked to show and tell us how they use the controls in offices. The problems with thermostats were found to be diverse and fundamental. Office occupants do not always even know they have a possibility to individually control the room temperature, because the device is not recognised at all, or the purpose of the device remains unclear. Although the room thermostats in offices are simple, symbols in the user interface are often not understood correctly, and it is not always known whether the temperature control is operating or not. In general, users are not satisfied with the feedback they get from the systems. The main reason for many of the problems is that the systems are planned and constructed without a realistic view of their users, i.e. users are supposed to have knowledge they do not have.

Next, in a quantitative interview survey, users were studied with a large and nationally representative sample: 1 000 Finnish office occupants answered questions concerning the office environment. Additionally, to simulate the real use of thermostats, controlled experiments were taken. The quantitative interview survey and the controlled experiments revealed statistically significant differences between the genders: females tend to be more critical of their thermal environments and are more sensitive to both cold and hot room temperatures. It was also found in the quantitative interview survey that most of occupants have a false idea of the absolute Celsius values of comfortable room temperatures in the summer season, i.e. they think that in the summer season room temperatures should be lower than in the winter season.

Based on the results of the preceding user studies, user interface prototypes for room temperature control were next developed with a user-centred approach. Usability tests were conducted several times during the development process. The results show that novice users are able to use the user interface prototypes with high effectiveness, high efficiency and high satisfaction, and all the 42 participants in the usability tests would like to have that kind of user interface for their own use.

As the definitive result of the work, usability guidelines for room temperature controls were developed. The usability guidelines are based on the user research performed in this work and the experiences gained from the user interface development. The usability guidelines are: (1) keep occupants in the loop, (2) visibility, identification and reachability of temperature controls, (3) shared temperature controls with heating and cooling systems, (4) acceptable default settings, (5) simplicity of interface, (6) clear way to adjust room temperature, (7) advice on comfortable room temperatures, (8) clear and sufficient feedback after adjustment, (9) fast effect on room temperature, (10) adequate effect on room temperature, (11) informative help, (12) aesthetic design and (13) females as test users in real-life situations. The usability guidelines help designers to create user interfaces that enable office occupants to adjust the room temperature of their own office with high effectiveness, high efficiency and high satisfaction.

This thesis consists of an overview and of the following 5 publications:

  1. Karjalainen, S. and Koistinen, O. 2007, User problems with individual temperature control in offices, Building and Environment, Vol. 42, No. 8, pp. 2880-2887.
  2. Karjalainen, S. 2007, Why it is difficult to use a simple device: an analysis of a room thermostat, in Human-Computer Interaction. Interaction Design and Usability, ed. J. Jacko, Proceedings of the 12th International Conference on Human-Computer Interaction (HCII 2007), Part I, Peking, China, 22-27 July 2007, Springer-Verlag Berlin, Heidelberg, Lecture Notes in Computer Science, Vol. 4550, pp. 544-548.
  3. Karjalainen, S. 2007, Gender differences in thermal comfort and use of thermostats in everyday thermal environments, Building and Environment, Vol. 42, No. 4, pp. 1594-1603.
  4. Karjalainen, S. and Vastamäki, R. 2007, Occupants have a false idea of comfortable summer season temperatures, in Proceedings of the 9th REHVA World Congress Clima 2007 WellBeing Indoors, eds. O. Seppänen and J. Säteri, Helsinki, Finland, 10-14 June 2007, abstract book p. 496, full paper on CD-ROM (A11B1073.pdf).
  5. Karjalainen, S., Siivola, M., Johnson, M. and Nieminen, M. 2007, User requirements and user interface solutions for individual control of temperature in offices, Helsinki University of Technology, Software Business and Engineering Institute, Preprints 14 (HUT-SoberIT-B14), Espoo, Finland, pp. 1-22.

Keywords: room temperature, thermal comfort, user interface, usability, usability guidelines

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© 2008 Helsinki University of Technology

Last update 2011-05-26