UC Davis

A “smart” device will remain efficient only as long as the settings and other parameters allow it to be. Thus, the degree of usability is becoming an element of energy efficiency similar to other physical characteristics. We developed and tested a procedure to quantify the usability of thermostats. The procedure assumes that usability can be represented by a user’s ability to accomplish a set of tasks. Thirty one subjects were tested in their ability to accomplish six essential tasks on programmable thermostats. The tests revealed a wide variation in the subjects’ ability to accomplish the same task on different thermostats. Thus it was possible to discern thermostats that were more effective than others. We created a metric based on data that are easy to collect and unambiguous that appears to reflect the usability of a task. Metrics from different tasks can be added and an overall usability “score” calculated. This approach, as well as the metric, can be applied to other devices where poor usability may impede energy-saving behaviour.