How Users Overriding Smart Thermostats Affects Energy Performance
From ASHRAE Journal Newsletter, March 23, 2021
People widely assume that overriding programmable thermostats is detrimental to potential energy savings. In a Science and Technology for the Built Environment article, researchers explored how users override schedules and what their energy consequences are. Researcher Brent Huchuk, Student Member ASHRAE, spoke with ASHRAE Journal about this work.
1. What is the significance of this research?
Schedule overrides (aka holds) are a common method for users to temporarily adjust the setpoints on their thermostats. Historically, studying how they have been used has relied on surveys of users or basic analysis, often leading to broad characterizations of their impacts. We were able to investigate, using a large dataset of smart thermostats, how the overrides were actually being used by individuals and what the relative impacts of these behaviors were. The results showed that a much more nuanced pattern of behaviors and smaller runtime (and energy) impacts exists than may be initially believed.
2. Why is it important to explore this topic now?
Particularly as thermostats in homes are being included with home energy management systems and as part of large grid-flexibility programs, being overridden reduces their utility and savings potential. Understanding how the overrides are being used is important to be able to anticipate or mitigate the effects.
3. What lessons, facts, and/or guidance can an engineer working in the field take away from this research?
Engineers working in the field should note that at least for these thermostats, when looking for meaningful reduction to the energy use, reducing overrides may not be the easy savings opportunity some evaluations may insinuate. In addition, instead of trying to prevent overrides it may be more effective to look at mitigating the effects of those overrides that do occur.
4. How can this research further the industry's knowledge on this topic?
The industry should take away the incredibly diverse ways in which thermostat overrides are used and that naïve or basic analyses can result in improper conclusions. For instance, only a small subset of users was found to continuously have their thermostat overridden and never change their setpoints. Additionally, our methods could be applicable to data from other smart thermostat manufacturers who would treat overrides differently and whose products this data could be compared against.
5. Were there any surprises or unforeseen challenges for you when preparing this research?
Initially we wanted to find if individual thermostat were repeatedly overridden under similar conditions, allowing for the overrides to be predicted. It was surprising how different the conditions were when the overrides were initiated and generally how few examples of overrides being initiated could be found for a majority of thermostats.
6. You mentioned several possible areas for future study. What do you think is the most logical next area for study?
An immediate next step for analysis would be quantifying the same metrics with another manufacturer’s data—hopefully one with different default override values and with a different user experience around setting the overrides. With this contrast it would be possible to understand which approach is generally more effective at mitigating undesirable (from a control standpoint) user behavior.