Multi drain heat recovery system – Thermal modeling, parametric analysis, and case study

Abstract

The present work concerns parametric analysis and case study of the performance of a newly suggested Multi Drain Heat Recovery System (MDHRS) that uses the relatively hot water of different drain sources such as the shower, the dish washer, the washing machine, and the sink simultaneously to heat/preheat residential cold water. To proceed, an appropriate thermal modeling along with its associated in-house code are developed. The heat rate error between numerical and experimental results is always below 14.2% for different inlet cold water temperatures and for different cold and hot water flow rates. The parametric analysis performed treated the effect of the hot and cold water inlet temperatures and flow rates on the performance of the system and allowed to raise practical recommendations in terms of application of the suggested concept. In the case study presented, the monthly amount of energy reduced, the monthly amount of money saved and the monthly amount of CO2 emissions reduction are considered. It was shown that when the heat exchanger length increases from 0.2 m to 1 m, the monthly amount of reduced energy increases from 102.2 kWh to 410.9 kWh, the monthly amount of money saved increases from 13.3 $ to 53.4 $ and the monthly amount of emissions reduction increases from 72.5 kg to 291.7 kg for a drain water temperature of 25 °C for the case of Lebanon.