A Case for Thermostat User Models Bryan Urban and Carla Gomez Fraunhofer Center for Sustainable Energy Systems Cambridge, MA, USA

Misconceptions of Thermostats An on/off switch A dimmer switch An accelerator Turning down the thermostat has little or no effect on energy consumption

How People Use Thermostats Overrides – Temporary override – Long-term override – Permanent hold Use to turn heating system on and off Leave on and open windows 20% are set to the incorrect time

Field Study 82 apartment units tested Installed – Programmable thermostats – Temperature/RH sensors – Furnace state sensors 60 units provided adequate feedback

Infrequent Override Fixed SetpointsSchedules Frequent Override

Infrequent Override Fixed SetpointsSchedules Frequent Override 72.2 °F st. dev. 2.8 °F 73.0 °F st. dev. 4.7 °F 71.0 °F st. dev. 2.6 °F 71.3 °F st. dev. 5.0 °F

Infrequent Override Fixed SetpointsSchedules Frequent Override 77 therms st. dev therms st. dev therms st. dev therms st. dev. 56

Conclusions Misconceptions about thermostats lead to unexpected usage patterns Behavioral differences lead to large variation in energy consumption ASHRAE 90.2 did not accurately describe real setpoints or schedules Existing energy modeling tools can model behavioral variability in thermostat schedules