Ventilation, Humidity, and Energy Impacts of Uncontrolled Airflow in a Light Commercial Building

Secondary Author(s)

Cummings, James

Report Number





Buildings; Ventilation; Humidity; HVAC; Ducts; Cooling; Air Flow


A small commercial building was monitored before and after energy saving retrofits to study the impact of retrofits upon ventilation rates, humidity, building pressure and air conditioning energy use. Duct airtightness testing identified severe duct leakage as a significant source of uncontrolled airflow. Differential pressure and infiltration measurements using tracer gas indicated an attic exhaust fan as another significant source of uncontrolled airflow. Duct repair resulted in a 31% drop (30.5 kWh/day) in cooling energy, and an increase in relative humidity from 72% to 76%. Turning off the attic exhaust resulted in an additional 36% energy savings (14.3 kWh/day), including fan power, and a decrease in relative humidity from 76% to 58%. Turning off the attic exhaust fan also significantly reduced the ventilation rate in the building by about 62 % from pre-retrofit ventilation measurements. The study of this building before and after retrofits illustrates the impacts that air leakage can have on light commercial buildings with non-airtight ceilings, the importance of using good diagnostics to discover all sources of uncontrolled airflow in buildings, and the importance in understanding what the duct zone environment is like in small commercial construction.

Date Published



Buildings - Air Flow; Buildings - Cooling; Buildings - Ducts; Humidity; Buildings - HVAC; Buildings - Ventilation

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