Secondary Author(s)

Hoak, David

Report Number




HVAC; Cooling; Buildings


An in-house research project at the Florida Solar Energy Center in 2013 was conducted to evaluate the potential of an evaporatively cooled mini-split heat pump. The mini-split heat pump modified was a 1.5-ton Fujitsu model with 19.2 SEER and 10.0 HSPF energy efficiency ratings. Cooling capacity of the system is variable and ranges from 7,000 to 23,000 Btu/h.

We demonstrated that it is possible to improve the energy efficiency of the evaluated mini-split air conditioner by 21% seasonally in Florida's humid climate using an evaporative pre-cooler. Further, we showed the same apparatus was able to improve air conditioner efficiency by almost 50% at a peak condition of 95°F outdoors. Cooling energy use was reduced in a very predictable fashion according to the difference between the outdoor dry-bulb and wet-bulb temperature. Performance improvements in temperate or dryer climates would likely average 25 - 35%. Average water consumption of the evaporator cooler was about 5.7 gallons per day -- a modest consumption given the large improvements in air conditioning energy efficiency. If condensate water was plumbed to the evaporative sump, estimated net water needs would be less than one gallon per day in Central Florida, although much more in drier climates.

The pre-cooler assembly is inexpensive with few moving parts and could be manufactured as add-on kits for mini-split air conditioners. Estimated retail cost would be $350 or less. Systems could improve seasonal cooling efficiency by 25-30% in most climates, with dramatic improvements in peak cooling performance- desirable for capacity constrained utilities.

Date Published


Local Subjects

Buildings - Cooling; Buildings - HVAC


FSEC Energy Research Center® Collection



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