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.