Impact Of Evaporator Coil Air Flow In Residential Air Conditioning Systems

The performance of conventional split system residential air conditioners is highly dependent on adequate air flow across the evaporator coil. Sufficient air flow is necessary to achieve a proper balance between sensible and latent cooling capacity. Typical target air flow rates are approximately 350 - 450 cubic feet per minute per ton (581 - 747 L/S per kW) of cooling capacity. The authors have measured the air flow across the coil in 27 installations in Florida. Both flow hood and strip heat resistance methods were used to measure air flow with an established protocol. The installations measured ranged in capacity from 2 to 4 tons (7 - 14 kW). Measured air flows ranged from 130 to 510 cfm per ton (216 - 847 L/S per kW) with an mean of 320 cfm/ton (538 L/S per kW). Reasons for inadequate flows included undersized return ducts and grills, improper fan speed settings, fouled filters and cooling coils. High distribution system static pressures were due to long, circuitous runs and pinched or constricted ducts. Recommendations are made to improve current practice