Facilitating energy savings through enhanced usability of thermostats

Panel: 6. Innovations in buildings and appliances

This is a peer-reviewed paper.

Authors:
Alan Meier, Lawrence Berkeley National Laboratory, USA
Cecilia Aragon, Lawrence Berkeley National Laboratory, USA
Marco Pritoni, Lawrence Berkeley National Laboratory, USA
Daniel Perry, Lawrence Berkeley National Laboratory, USA
Therese Peffer, California Institute for Energy and Environment
University of California, Berkeley, USA

Abstract

Thermostats are a key element in controlling centrally heated and cooled homes. However, today’s modern programmable thermostats have interfaces that are complicated and difficult for users to understand, leading to errors in operation and wasted energy. Studies in the UK, Finland, and the United States have all demonstrated that typical users are unable to effectively operate thermostats. One obstacle to improving the usability of thermostats is the lack of quantitative procedures to measure usability of the interface. We developed a methodology to measure usability. The first step is to list the key tasks to be performed by the thermostat (such as to enter the time, switch off heating, view status, etc.). A panel of subjects is asked to perform those tasks. The time to accomplish the tasks (or their inability to accomplish them) is recorded. An overall usability score was calculated based on the subjects’ ability to accomplish the group of tasks. The methodology was tested with five thermostats (including one web-based interface) and over 50 subjects. We observed a wide range in the subjects’ ability to accomplish tasks that was clearly linked to the design of the interfaces. The thermostats could be quantifiably ranked by their usability score. Moreover, a third-party testing organisation used the same methodology and obtained the same results. The Energy Star program will require minimum levels of usability in its next specification for programmable thermostats based on this methodology. We expect that minimum usability requirements will eventually be incorporated into future MEPS after these techniques are perfected.