Shower water heat recovery in high-rise residential buildings of Hong Kong

Abstract

This paper investigates the potential for shower water heat recovery from bathrooms equipped with instantaneous water heaters in high-rise residential buildings of Hong Kong. A simple single-pass counter-flow heat exchanger installed horizontally beneath the shower drain is employed as a localized heat recovery measure for preheating cold water going to a water heater. The thermal energy exchange is evaluated using the effectiveness-number of transfer units (e-NTU) approach. Shower usage patterns including shower operating time and water flow rate sampled from an interview survey via the Monte-Carlo sampling technique, together with the water temperatures at the shower heads, shower drains and cold water supply mains recorded in sample shower operations, are the input parameters. The results indicate that 4-15% shower water heat can be recovered through a 1.5 m long single-pass counter-flow heat exchanger for a drainage pipe of diameter 50 mm.