Dehumidification performance of a variable speed heat pump and a single speed heat pump with and without dehumidification capabilities in a warm and humid climate

Abstract

Conventional air conditioning systems in houses respond to thermal loads by means of controlling dry-bulb temperature through the thermostat. As part of the process to control temperature, dehumidification is also provided. However, as houses are becoming more efficient, supplemental dehumidification is often necessary for homes located in hot and humid climates to control relative humidity intentionally. This study compared the dehumidification performance of a residential air conditioning system working in three operations modes to emulate three different systems: a system with a variable speed mode, a single-speed system with an enhanced dehumidification mode, and a single-speed system operating in a traditional or normal cooling mode. With operation mode changes achieved through software, this study constituted a novelty in the topic of humidity control by using a single machine, with the same exact physical set-up to directly compare the dehumidification performance of three types of systems.Two types of days were of interest in the study, hot and humid days (summer season) and mild and humid days (Fall shoulder season). After assessment of the dehumidification performance, the variable speed mode was able to maintain relative humidity between 50% to 52% on summer days. In the single-speed with enhanced dehumidification, a slightly less effective humidity control was achieved on summer days with the mode keeping the relative humidity between 53% to 55%. In the normal cooling mode, which resembles a conventional system, the humidity levels were controlled between 55% to 60%. In the shoulder season, the variable speed and enhanced dehumidification modes maintained the relative humidity between 55% to 58% and 53% to 56% respectively. In the shoulder season, the normal cooling mode kept the indoor relative humidity near or above 60%. In terms of dehumidification efficiency expressed as a function of the amount of water condensate per unit of energy, the variable speed was determined to be more efficient than the other modes.