Usability of residential thermostats: Preliminary investigations

Residential thermostats control 9% of the total energy use in the United States and similar amounts in most developed countries; however, the details of how people use them have been largely ignored. Five parallel investigations related to the usability of residential thermostats were undertaken. No single investigation was representative of the whole population, but each gave insights into different groups or usage patterns. Personal interviews revealed widespread misunderstanding of thermostat operation. The on-line surveys found that most thermostats were selected by previous residents, landlords, or other agents. The majority of occupants operated thermostats manually, rather than relying on their programmable features and almost 90% of respondents reported that they rarely or never adjusted the thermostat to set a weekend or weekday program. Photographs of thermostats were collected in one on-line survey, which revealed that about 20% of the thermostats displayed the wrong time and that about 50% of the respondents set their programmable thermostats on “long term hold” (or its equivalent). Low-income families were visited and their thermostats photographed. Even though 85% of the respondents declared that they use programming features to automatically raise or lower the temperature, the photos indicated that 45% were in hold. Laboratory tests were undertaken to measure usability of thermostats. A measurement protocol was developed and a metric was created that could quantitatively distinguish usability among five thermostats. This metric could be used to establish minimum levels of usability in programmable thermostats and other energy-using devices with complex controls.