Analysis of Zone-by-Zone Indoor Environmental Conditions and Electricity Savings from the Use of a Smart Thermostat: A Residential Case Study

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Smart thermostats are becoming an important tool that saves Heating, Ventilating, and Air Conditioning (HVAC) system energy use by optimizing thermostat settings. This paper presents the results of an analysis of measured, zone-by-zone indoor environmental conditions and electricity savings from the use of a smart thermostat that includes temperature and occupancy data from each zone in a single-family residence. In this analysis, statistical indoor air temperature profiles were developed for each zone before and after the installation of the smart thermostat. The analysis shows that the temperature and occupancy-based control of the system produced significant changes to the indoor air temperature profiles in each zone. Although these indoor condition changes were acceptable to the homeowner of the case-study residence, the changes to the before-after indoor air temperature profiles also present new challenges to simulating the annual savings with a calibrated building energy simulation program. The results also show that a residence with a single-zone HVAC system controlled by a single thermostat that was retrofitted with wireless occupancy and temperature sensors in each zone achieved significant electricity savings for the homeowner, as well as electric demand reductions for the electric utility.