Building Energy Technology: Evaluation of Programmable Thermostats

Fraunhofer Center for Sustainable Energy Systems

A CSE Fellow prepares a thermostat for deployment.

Project Motivation

The majority of U.S. households use either manual or programmable thermostats 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. But are people with an easy-to-operate thermostat more likely to use its energy-saving settings, such as nighttime setbacks?

 

Assessing Thermostat Usability

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.

 

In the end, thermostat usability did 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.

 

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.

 

A Building America Project

The thermostat evaluation was one of several research projects undertaken by a Fraunhofer CSE-led research team under a task order from the US Department of Energy's Building America Program.