Performance analysis of small-scale direct expansion air conditioning system with indirect evaporative cooler as dedicated ventilator

Abstract

Split-type and window-type air-conditioners are typical small-scale direct expansion air-conditioning (DXAC) system widely-used for household applications. However, lack of controllable ventilation can be a serious problem leading to health problems for such air-conditioning (AC) systems. To improve the indoor air quality of a home space equipped with small-scale DXAC system, an indirect evaporative cooler (IEC) is used as a dedicated ventilator, on one hand, to guarantee proper outdoor air supply and on the other hand, to provide sensible cooling under certain climatic conditions. Validated numerical component models of IEC, DXAC and indoor thermal balance were established and coupled in series to form a closed-loop model of DXAC with IEC ventilator (DXAC-IEC) system. The effects of ambient humidity, ambient temperature, sensible heat ratio and ventilation rate on the system performance were investigated, with comparison to the standalone DXAC system. The results show that the IEC can enhance the system performance under moderate hot and dry ambient conditions (tamb ≤ 33 °C, RHamb ≤ 60%) by reducing the cooling load of DXAC. But it would bring extra moisture from outdoor in humid conditions (tamb ≥ 30 °C, RHamb>50%) for sacrifice of improved indoor air quality. Optimal fresh air ratio exists for the DXAC-IEC system to achieve the maximum coefficient of performance. The findings will be beneficial for the design and optimization of DXAC-IEC system.