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 32 transfer units (ε-NTU) approach. Shower usage patterns including shower operating time and 33 water flow rate sampled from an interview survey via the Monte Carlo sampling technique, 34 together with the water temperatures at the shower heads, shower drains and cold water 35 supply mains recorded in sample shower operations, are the input parameters. The results 36 indicate that 4-15% shower water heat can be recovered through a 1.5 m long single-pass 37 counter-flow heat exchanger for a drainage pipe of diameter 50 mm. 38

Carbon Dioxide Reduction Targets of Hot Water Showers for People in Hong Kong

“…The maximum CO2 reduction calculated from all of the measures listed in Table 2 using Equation (19) is estimated to be 52%. Table 2 summarizes the maximum CO 2 reduction estimates from various measures, including water conservation programmes that target P sh,35 ≥ 0.5 and T sf ≤ 5 • C, water efficient products, shower drain water heat recovery, and energy efficiency improvements for water supply systems [11,12,16,17]. The influence of users on CO 2 reduction is found to be significant and compatible to that of water efficient showerheads.…”

“…According to the survey, all occupants would take at least one shower per day [17]. A total of 597 occupants were interviewed; 269, 289, 37, and 2 of them would take one, two, three, and four showers in the summer while 537, 57, 3, and none of them would take one, two, three, and four showers in the winter respectively.…”

“…Symbol '' represents data from reference [17] Figure 2 graphs the expected number of showers per occupant per day determined by Equation (3). Averages (i.e., Tsf = 0 °C) from a previous study are also shown for comparison.…”

Shower heat exchanger: reuse of energy from heated drinking water for CO<sub>2</sub> reduction

“…Moreover, its CO 2 emission would be only 76.9 ton yr −1 . Another study done by Wong et al (2010) also showed the high energy saving potential of a shower heat exchanger (Wong et al, 2010). They tested the efficiency of a horizontal shower heat exchanger, and estimated that an annual energy saving of 4-15 % can be achieved in a 40 floor (20 apartments per floor) high-rise residential building.…”

<b>Analysis of absorbed energy and efficiency of a solar flat plate collector

“…One of the most promising sources is the use of solar thermal energy for water heating proposed by Wong, Mui, & Guan (2010) and Altoé, Oliveira Filho and Carlo (2012).…”