Warm, moderate, or cool-liker? A Benchmarking Framework to Characterize Occupant Overall Thermal Preferences based on Large-Scale Thermostat Data

Humans could exhibit distinct overall thermal preferences when exposed to identical indoor thermal environments, leading to distinct preference groups such as "warm-likers" or "cool-likers", who consistently prefer warmer or cooler conditions than the average population, respectively. Currently, most thermal comfort modelling studies focus on capturing momentary or instantaneous comfort states/preferences, ignoring the overall thermal preference. This paper proposes a benchmarking framework to identify and characterize overall thermal preferences based on preferred setpoint/outdoor temperature relationships derived from ECOBEE Donate Your Data program. Using descriptive statistics, we establish 3 temporally consistent overall preference groups, including warm-liker, moderate and cool-liker, along with a temporally chaotic preference group termed random. Our results demonstrate that warm-likers' preferred temperature setpoints are above 21.5°C on heating days and 24-25°C on cooling days, while cool-likers prefer setpoints below 19.6°C on heating days and 22°C on cooling days. We observed that around 50% of users exhibit secondary overall preferences, implying that overall thermal preference could change over time. On average, overall thermal preference can be established in 10 to 16 setpoint adjustments. The study reveals varied responses to outdoor temperature changes among users: many maintain constant indoor temperature preferences, while a significant number adjust their indoor temperatures upwards by 0.1°C to 0.4°C for each 1°C rise in outdoor temperature. A smaller group prefers cooler indoor temperatures as it gets warmer outside, showing a unique negative adjustment trend of -0.1. We also found that climate interacts with the overall preference group, with warmer climates having more warm-likers and vice versa.