With Programmable Thermostats, User-Friendliness Doesn’t Necessarily Mean Energy Savings

This week, Fraunhofer CSE presented preliminary results of a field study at the Garrison Institute’s “Climate, Buildings and Behavior Symposium”. In this project, partially funded by the US Department of Energy’s Building America Program, our Building Energy Efficiency team investigated if increasing usability in programmable thermostats (PT) actually facilitates energy saving behavior. Here, we want to share some of the most interesting insights from our study:

The majority of U.S. households use either manual (48%) or programmable (37%) thermostats (PTs) to regulate their heating. In theory, these thermostats can not only save consumers’ energy, but also leave more money in their pockets thanks to lower heating and electric bills. As a result, in 1995, the U.S. Environmental Protection Agency (EPA)established the EnergyStar programmable thermostat program, which actively promoted PTs as a means of saving energy. If homeowners don’t actively program their thermostats and use energy-saving settings such as daytime and night-time setbacks, there are no significant energy savings to be had. But that’s where the problems start. Programming thermostats is a complicated endeavor: the typical device includes a wide range of functions such as separate schedules for weekdays, weekends, vacations, and a hold or override option. Other user issues with PTs include abbreviations and terminology that many people don’t readily understand, confusing lights and symbols, or illogically positioned interface elements. So, here is the question: Are people with an easy-to-operate thermostat more likely to use its energy-saving settings, such as nighttime setbacks?

To tackle this question, Fraunhofer CSE’s Building Energy Efficiency team installed a combination of touch screen thermostats—models the Lawrence Berkeley National Laboratory (LBNL)  found to be more user-friendly—and more traditional button interface thermostats in a multi-family building managed by our partner, WinnResidential. In addition, non-intrusive sensors were installed in each apartment to collect temperature, humidity and the on/off state of the furnace every 10 minutes for most of the heating season (December-April). After randomly assigning participating households either a high-usability (touch screen) or low-usability (button interface) model, Fraunhofer engineers collected and analyzed sensor data to infer thermostat settings in each participating apartment, allowing them to establish whether the occupants were actually using the thermostats’ energy-saving settings.

Here is what we found. Thermostat usability does not seem to have a meaningful effect on how often home occupants use default energy-saving settings on their thermostats. Only 3% of households used programmed default nighttime setbacks (62°F) on the coldest nights of the past heating season—independently of whether they navigated the more user-friendly touch screen or the basic button interface thermostats. What does this mean? Prices for thermostats range from about $20 to $140, depending on the functionality they offer. Although a price difference of more than $100 may be justified by superior aesthetics and quality, it does not automatically translate to an equivalent increase in energy savings. Even the most cleverly designed thermostat will not provide any energy savings if consumers lack the motivation to change their energy consumption habits.

Our results are a first step in understanding how consumers use PTs. In our next research phase, we will turn to a number of more specific questions—for instance how satisfied study participants are with their thermostats, or what their preferred temperature is based on their energy settings.

Additional publications and presentations are scheduled for later in the year—we look forward to keep you posted!

About author
I'm a former marketing intern at Fraunhofer CSE, having supported CSE's communications activities in a number of areas over the spring and summer of 2012.
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