Efficiency assessments of a compound cooling system for low-humidity applications

•Affordable and straightforward physical configuration for indirect evaporative cooling.•Concentric tower design able to be retrofitted to existing split cooling units.•Proposed design decreases 19% cooling load and 29% required electrical input.•Inclusion of the tower reduces operation time, and device footprint by ∼ 40%.•Economic investments are reduced by 36 to 39% depending on the implemented scheme. Present work introduces the utilization of a concentric vertical pipe heat exchanger for indirect evaporative cooling. The device is coupled to a heat pump cooler, i.e., vapour compression cycle, as a pre-cooler and pre-dehumidifier of outdoor fresh air, to reduce the cooling load exerted on the evaporator. The proposed configuration borrows concepts from cooling tower operation, which enables the recirculation of room exhaust air, stabilizing its temperature before purging, also reducing the thermal load exerted over the condenser. An experimental analysis of the setup was performed, obtaining an average temperature drop, between intake and exhaust, of ∼ 10 °C. Against standalone configuration, this resulted in a 19%, and 29%, decrease of the cooling load, and required electrical input, respectively. Moreover, the inclusion of the indirect evaporative cooling setup reduced operation time by ∼ 40%; from 36 to ∼ 18 min per hour, resulting in long-term economic savings between 41 and 44% against stock energy consumption. Based on the surplus of energy achieved, this paper conducts a redesign and optimization of the heat exchangers. Through an inverse heat transfer approach, the device footprint can be reduced between 35.8 and 38.9% in terms of its weight, and 45.5 to 44.4% in terms of its surface area; features particularly useful when it comes to limitations in structural load capacity and/or space availability. The conducted redimensioning analysis revealed initial investment savings, between 36.2 and 39.7% of total cost, which albeit lower than operational-related savings, are still comparable when it comes to the design and operation of an air handling unit. Based on obtained results, the integration of the proposed setup does enhance the performance of the stock heat pump cooler, without increasing overall energy expenditure costs, thus is presented as an affordable, retrofittable, option for air conditioning systems operating in arid and semi-arid climates.