Energy and thermal comfort performance evaluation of thermostatic and electronic mixing valves used to provide domestic hot water of buildings

Abstract

Building codes require domestic hot water supplied to high-rise residential buildings to be stored at 60∘C or above to avoid bacterial contamination (e.g., Legionella), while the supplied water delivered to residential units should not exceed 49∘C to avoid scalding. Inefficient mixing of hot and cold water to lower the water temperature can cause temperature and pressure fluctuations of supplied water resulting in resident discomfort, higher energy consumption and risk to plumbing fixture. This work compares the efficiency of two mixing devices (a) an electronic mixing valve (EMV) and (b) a thermostatic mixing valve (TMV) experimentally and numerically. The energy savings, pressure drop, and temperature fluctuation caused by each device in the same building are presented. Each 24–hour period is divided into 4 time periods based on hot water demand. The results show that the EMV can provide steadier temperature during the transition between low demand period overnight and peak consumption in the early morning, and lower pressure drop in the hot water system. In addition, depending on the circulation flowrate in the building, the EMV can potentially reduce energy consumption by more than 40% particularly during low demand periods.