Title

Design of a Very High Efficiency Evaporatively Cooled Mini-split Air Conditioner

Report Number

FSEC-RR-464-14

Keywords

HVAC; Cooling; Heat Pumps; Buildings

Abstract

An in-house research project at the Florida Solar Energy Center 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 in the summer of 2013 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 drybulb temperature and wetbulb. Performance improvements in temperate or dryer climates would likely average 25 - 30%. 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.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 performance by 25-30% in most climates, with dramatic improvements in peak cooling performance- desirable for capacity constrained utilities.A brief patent search revealed no similar prior-art for evaporative coolers used with mini-split air conditioners. Also, based on recent research, we are certain performance improvements in the concept are obtainable (6' media, sub-cooling, AC speed control). These would enhance annual efficiency improvements by 5-10% to the 30-40% range. We aim to test the further improvements in the summer of 2014.

Date Published

1-2-2014

Subjects

Buildings - Cooling; Heat Pumps; Buildings - HVAC

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