Project Info

Project Title 
Fan Cycling Control Technology Assessment
Project Number 
Investor Owned Utilities 
Commercial, Residential
Project Year(s) 

Single zone, constant volume packaged rooftop units (RTUs) are the most common air conditioning configuration for small-to-medium commercial facilities like offices or retail buildings. RTUs typically provide cooling, heating, and ventilation to a space in a building. In the past, building codes generally required a minimum amount of ventilation air to be supplied to a space during all times that the space is normally occupied. Recent modifications to codes allow for the RTU’s supply fan to be cycled off for up to thirty minutes at a time as long as the average ventilation rate is maintained. This modification provides the opportunity to reduce the fan energy required for ventilation through the application of retrofit controls. 

This technology evaluation tests a package of controls that cycles the supply fan off for up to thirty minutes while using an algorithm to ensure the average ventilation delivered meets the ventilation requirements of the space. The controls also incorporate Demand Control Ventilation (DCV) controls that set the ventilation requirement based on CO2 concentration in the space. In addition to fan cycling and DCV control, occupancy sensors are used to increase the cooling setpoint and decrease the heating setpoint when there are no occupants in the space. In combination, the controls have the potential to reduce supply fan energy as well as heating and cooling energy. 

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