Domestic hot water system combining solar and waste heat from thermoelectric air-conditioner

Abstract

This paper investigates the performance of a new hybrid domestic hot water system that combines solar energy with waste heat from a thermoelectric (TE) air-conditioner. To this end, 30 TE modules model no. TEC1-12704 (module specifications: 40 × 40 mm, maximum operating voltage and current: 13.5 VDC and 4.4 Amp) were used. The collector/storage tank capacity was 120 litres. The volume of the testing room for cooling was 2.5 m³. Investigations were undertaken by varying the voltage to the thermoelectric module (50, 100, 150 VDC), water mass flow rate and air velocity passing through the TE heat exchangers: 10, 15 l/min and 2.5, 5 m/s, respectively. It was found that this system can heat up the 120 litres to 50°C within 2 hours. The cooling capacity was 176 W. After that, the cooling capacity decreased as a result of the increase of water temperature returned from the tank and circulated through TE water/solid heat exchanger. Finally, under design consideration used in this study, the optimum conditions for operating the hot water production and cooling as well are: 100 VDC, water flow rate of 15 l/min and air velocity at 2.5 m/s. The corresponding highest coefficient of performance of the hybrid system is about 3.12.