Saving on household electric water heating: What works best and by how much?

Abstract

Abstract-Electric heating of water for domestic use is a substantial component of total household energy costs. Thermal energy in a water heater is either used (as warm water) or lost to the environment. Various approaches to reduce the losses and improve the efficiency of these notoriously inefficient and costly water heaters have been proposed and are employed. However, given the complex factors at play, making sense of the savings approaches and choosing the right one for the right use case is not a simple task and often misunderstood. This paper addresses this problem by comparing some of the commonly employed approaches, including schedule control, change in set temperature, use of thermal insulation, and reduction in consumed volume. We also compare the impact of environmental factors, such as changing the ambient temperature around the water heater and the cold inlet temperature. The results show that for the consumption profiles and use cases evaluated, schedule control is the most effective, followed by insulation of the tank and piping. Combined, these two interventions save up to 25%. We also find that the effect of the temperature of the cold inlet water dwarfs that of the ambient temperature, is in line with other approaches, and means the installation status quo needs to be reconsidered.

How much energy can optimal control of domestic water heating save?

“…The reduction is shown in Figures 3 (e) and (f), with respective energy and percentage reductions from the TC baseline of 1.4, 1.5, 1.7 kWh/day and 12.8, 17.8, 26.3 %. These results are in line with the simulated and field-measured and/or energy-matched results reported by Booysen et al (2013); Kepplinger et al (2015Kepplinger et al ( , 2016 and Nel et al (2018). The median standing loss for this strategy was a mere 1.0 kWh/day, a reduction of 1.4 kWh/day (58 %) from TC's 2.4 kWh/day.…”

“…And given the coal-intensive energy generation typical of these countries, any change in energy used usually implies a proportional change in greenhouse gasses emitted. Nel et al (2018) evaluated typical strategies that people use in developing countries to save on domestic water heating, such as insulating the heater with a blanket, using less hot water, lowering the set-point temperature, and applying an on-off schedule. They simulated various hot water usage profiles (e.g.…”

“…We compare the strategies by using field-measured hot water usage patterns that were sampled every minute from 30 water heaters over a period of 20 days using a simulated thermal model. The water heaters were part of a research project in which users from South Africa's Western Cape, Gauteng, and Mpumalanga volunteered to trial smart water heater controllers Reported energy savings (%) Fanney and Dougherty (1996) 4-6 Goh and Apt (2004) 5-6 Booysen et al 201314-17 Kepplinger et al (2014) 5-13 Kepplinger et al (2015) 10-12 Kepplinger et al (2016) 12 Booysen and Cloete (2016) 29-34 Gholizadeh and Aravinthan (2016) 6 Cloete (2016) 6 Nel et al (2018) 9-18 Matos et al 201939…”

Optimal schedule and temperature control of stratified water heaters

“…Kepplinger et al (2014) and Booysen et al (2019) use dynamic programming for optimal schedule control. Fanney & Dougherty (1996) 4-6 Goh & Apt (2004) 5-6 Booysen et al (2013) 14-17 Kepplinger et al (2014) 5-13 Kepplinger et al (2015) 10-12 Kepplinger et al (2016) 12 Booysen & Cloete (2016) 29-34 Gholizadeh & Aravinthan (2016) 6 Cloete (2016) 6 Nel et al (2018) 9-18 Booysen et al (2019) 8-18 Xiang et al ( 2019) 4…”

A potential source of undiagnosed Legionellosis: Legionella growth in domestic water heating systems in South Africa

“…Water heaters nominally heat water to 65 • C, although temperatures of as low as 40 • C are considered sufficiently warm for user satisfaction (Belov et al, 2015;Nel et al, 2018a). The energy consumed by a domestic water heater can be reduced by 29 % through schedule control and lowering the thermostat's target temperature (Booysen and Cloete, 2016;Nel et al, 2018b). Despite the financial benefit to the user of operating at these lower temperatures, the heater and its hot water distribution system could be creating ideal temperature niches for the growth of the L. pneumophila pathogen.…”