Destined to Disappoint: Programmable Thermostat Savings are Only as Good as the Assumptions about Their Operating Characteristics

Programmable thermostats commonly account for a large percentage of energy savings for many residential and small business energy efficiency programs. For some portfolios, because of the limited number of devices that can affect gas savings for these sectors, programmable thermostats are the primary equipment aimed at attaining gas savings goals. However, evaluations reveal that actual energy savings for these devices often fall short of expected savings. Such discouraging results led ENERGY STAR® to suspend labeling programmable thermostats in 2009, citing that the device itself does not save energy, but instead, actual energy savings depend on user behaviors. This paper discusses the impact of assumptions about customer behaviors on actual savings, using the results of a recent evaluation for illustrative purposes. Typically, it is assumed that old thermostats were operated with constant settings while new thermostats are operated programmatically. While the results of this evaluation reveal the latter is generally true - most customers did operate their new units programmatically - there is little support for the former. In fact, the evaluation results showed that two-thirds of customers participating in the program already practiced energy conserving behaviors by manually setting- back their old thermostats for non-operating hours. Thus, the vast majority of the expected energy savings never materialized. Overall, the results show that for programmable thermostats to manifest expected realization rates, attention needs to be allocated to defining accurate assumptions about user behaviors. Implications for energy efficiency program design will be discussed, highlighting the need for more focus on understanding customer behaviors.