An experimental investigation on the operational characteristics of a novel direct expansion based air conditioning system with a two-sectioned cooling coil

Abstract

Abstract For controlling indoor thermal environment, only indoor air temperature is usually considered when using conventional direct expansion (DX) based air conditioning (A/C) systems. Therefore, based on the previous experiences in developing novel A/C units to provide an enhanced moisture removal capacity, a novel constant speed DX A/C system with a two-sectioned cooling coil (TS-DXAC) has been proposed. In the proposed TS-DXAC system, to reduce its size, the two sections were arranged in parallel with their respective matching variable speed supply fans, and the mass flow rates for both refrigerant and air to each section could be adjusted. The total air flow rate of the system remained however constant, so as not to affect indoor air flow distribution and occupants’ thermal comfort. The inherent operational characteristics of a prototype experimental TS-DXAC system have been experimentally studied. The study results showed that the variations in the mass flow rates of refrigerant and air to the two sections would result in different combinations of the output total cooling capacity (TCC) and equipment sensible heat ratio (E SHR) from the prototype, and that the TCC – E SHR relationship was constrained within an irregular area. Furthermore, different inlet air temperatures and humidity levels would also influence its inherent operational characteristics as reflected by the changes in the positions and shapes of the irregular areas, with the latter influencing more on the operational characteristics.