Use of condensate drain to pre-cool the inlet air to the condensers: A technique to improve the performance of split air-conditioning units

Abstract

In hot ambient conditions, split air-conditioning (AC) systems experience a drop in their coefficient of performance and an increase in power consumption due to the direct relationship between the condensation temperature of the unit and the prevailing ambient temperature. In this work, the enhancement in the COP and the reduction in power consumption for a split AC unit are evaluated when a direct water spray evaporative cooling system is used. The study focuses on minimizing the amount of water needed to cool the condenser by utilizing the wasted water from the condensate drain, synchronizing the water injection with ON–OFF compressor operation, and determining the optimal hourly periods for the injection system to achieve a reduction in energy consumption. The objectives of this work are threefold. The first objective is to conduct experiments inside an environmental chamber to determine the effectiveness of the evaporative cooling system at different ambient conditions and to derive correlations that predict the outlet air conditions and the water consumption. The second objective is to develop an integrated mathematical model to simulate the performance of the evaporatively cooled split AC system in a controlled space under certain operational conditions (using steady-state performance data supplied by the manufacturer and taking into account the transient effect during the ON–OFF compressor cycling) and to experimentally validate this model. The third and final objective is to evaluate the model under “real environment conditions” for a case study where the thermal conditions and energy demand of a typical office space in Beirut during three months (June, August, and October) are investigated and where the “sufficiency” of drain water is the limiting factor. The simulation results have shown that the drain water would be sufficient in October only, resulting in 5.3% energy saving throughout the whole day. On the other hand, the synchronized spray of water is found to last for six operating hours in a June day and eight hours in August; this results in a total daily reduction in the consumed energy of 5% in June and 4.5% in August.