Multiple perspectives of the value of occupancy-based HVAC control systems

Occupancy-based strategies for reducing energy used for heating, ventilating, and air conditioning (HVAC) benefit building owners and help meet state and federal energy and climate goals. However, this value has not previously been quantified beyond typical building owner energy savings. The objective of this research is to estimate the national-level potential added-value of occupancy-based HVAC controls in small office buildings relative to a constant setpoint or to programmable thermostats. Value is defined based on the building owner perspective (energy cost), as well as societal based perspectives of fossil fuels consumed and greenhouse gas, NOx and SOx emissions. A generic small office building with two different HVAC systems is simulated in EnergyPlus and applied to five climate zones representative of the United States. Specific building envelope, electricity supplies, utility costs and total area of small office buildings are adjusted for each climate zone. Results demonstrate that occupancy-based strategies for HVAC control are highly effective, yielding 22-50%and 47-87% reduction in electricity and natural gas use, respectively, compared to no thermostat control. Results vary substantially across climate zones and HVAC systems. With occupancy sensors installed in all small office buildings, the U.S. national savings would be 15 - 66 million GJ fossil fuel use, 0.9-3.7 million metric tons CO2e emissions, and 168 - 658 million dollars for utility cost.