Optimizing Energy Efficiency and Improved Dehumidification Performance of Variable Capacity Air Conditioning Systems

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Dehumidification; Energy Efficiency; Air Conditioning; Buildings


High-performance homes promote high efficiency, but some of these homes, with very low cooling loads, may have greater challenges in delivering acceptable comfort. This paper discusses challenges and options regarding energy-efficient comfort control in homes with ducted and ductless variable capacity air conditioners based on recent research in occupied homes and house lab tests. Air conditioners cool and dehumidify. Well-designed homes can usually maintain acceptable temperature, but the likelihood of maintaining acceptable indoor humidity all the time is less certain. This is due to low sensible loads, variability in moisture removal effectiveness of air conditioning, and variability of moisture sources. As a result, some builders and highperformance home programs resort to using dehumidifiers. While dehumidifiers can improve relative humidity control, they present a different set of challenges and may cause significantly higher building energy use than owners expect. Variable capacity cooling energy savings typically around 20%-30% have been measured compared to fixed capacity systems in controlled house lab study. Research also found that better dehumidification is possible that limits overcooling and energy use. Recent testing of a new variable capacity system measured indoor humidity reduction of up to 15% RH points during low cooling load periods. Optimized variable capacity air conditioners may adequately control humidity at moderate levels without need for supplemental dehumidifiers. Such systems would require less annual space conditioning energy than sub-optimal variable capacity systems that require supplemental dehumidifiers in low sensible load homes. This paper will present research that shows how performance can be optimized, and discuss the importance of considering how cooling performance metrics impact cooling and dehumidification energy use.

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Buildings - Air Conditioning; Buildings - Dehumidification; Buildings - Energy Efficiency

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