So-called ‘smart thermostats’ are beginning to fill the gap left in efficiency programs
after researchers and policy makers discovered that in practice, simple programmable
thermostats do not guarantee energy savings. As a result, EPA ended EnergyStar certification of
programmable thermostats in 2010. Many recent pilots for communicating thermostats,
occupancy-responsive thermostats, and adaptive control schemes have shown significant annual
HVAC savings on the order of 10-20%. However, the form and function for technologies in this
space vary widely. Some controls merely allow for remote management (e.g., web-based setpoint
scheduling or smart-phone interface and control), while other devices monitor occupancy
and automatically adjust set-points when a space is vacant. Still other technologies automatically
adapt to user behaviors and preferences in order to anticipate changes and adjust HVAC
operation. These differences have different savings implications. Further, the application into
which any of these technologies is installed also impacts savings potential.
The study focuses particularly on a series of pilot evaluations conducted with one
occupancy-responsive adaptive thermostat system that resulted in very little energy savings
during normal operation in university residence halls. These results came as a great surprise to
the research team, especially since the HVAC system run-time for vacant zones was reduced to
nearly zero in the buildings. The detailed evaluation of this case forms a conceptual basis for
explanation of the limitations for smart thermostat devices. The research shows that considerable
savings can be had in certain instances, but that the impact is sensitive to technology and
application. The study also reviews previous research on the technology and recommends
methodological improvements for future studies
