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Heat your water at the right time to save electricity
Author: Corporate Communication / Korporatiewe Kommunikasie [Alec Basson]
Published: 05/10/2018

​​​With electricity prices set to increase significantly in the next three years, South Africans will have to be resourceful to keep the costs down. One of the ways to achieve this, would be to use less electricity to heat your water for that daily shower or bath.

A study at Stellenbosch University (SU) found that scheduling your water heater correctly according to the amount of hot water that you use saves more costs on water heating than a thermal blanket or lowering the set temperature of your geyser.

“The best way to save on your household electric water heating, is to start heating water two hours before and stopping before taking a shower or a bath," says Prof Thinus Booysen from the Department of Electrical and Electronic Engineering at SU. He conducted the study with colleagues Philip Nel (Department of Electrical and Electronic Engineering) and Brink Van der Merwe (Department of Computer Science). They tried to find an answer to the age-old question of how to best save energy used for household water heating.

Their research findings were published recently in the proceedings of the IEEE International Conference on Innovative Smart Grid Technologies.

Booysen says because of the inefficiency and costs of household water heating, which accounts for as much as 32% of household electricity consumption where electric water heaters are used, they decided to evaluate the impact of various energy savings actions for these water heaters. These include, among others, lowering the thermostat temperature, reducing volume consumed, using a thermal blanket over the tank and the piping, and using optimised scheduled heating control.

Booysen adds that people often struggle to make sense of these savings approaches and to choose the right one for the right use.

To find out which of these methods are the most cost effective, the researchers compared them using eight typical household usages (e.g. from a showering one-person apartment to a four-person bathing household). They also compared the impact of environmental factors, such as changing the ambient temperature around the water heater and the temperature of the cold water inlet.

Booysen says they used a two-node physical model of an electric water heater to simulate the energy consumption of an individual electric water heater and tested it by analysing usage data from actual household water heaters.

Effective schedule

“Our results show that, in general, schedule control achieves by far the biggest saving, resulting in savings ranging from 9% to 18%. The biggest savings, as expected, are the scenarios where only one small usage event (e.g. a short shower) occurs per day".

“We found that schedule control saves as much as 18% for households that take only one bath or shower per day, and an average of 12% for all the different usage patterns assessed."

“Ones with two baths (one in the morning and one in the evening) per day could save 10% and ones with two showers (one in the morning and one in the evening) could save 9%."

Booysen adds that schedule control is efficient because it shouldn't require any sort of behavioural change if implemented correctly.

“An effective schedule will be able to deliver hot water on demand while minimising the standing losses of the electric water heater. Standing losses result from the temperature difference between the water in the heating tank and the temperature of its surroundings."

He says schedule control also has the most significant impact on the standing losses (thermal energy lost to the environment) of water heaters for both single- and three-person households.

Booysen points out that the second most effective savings are achieved through insulation of the pipes and the tank, with savings ranging from 5% to 12%.

“Thermal insulation saves as much as 12% for low-volume infrequent use, and an average of almost 9% across profiles."

He mentions that implementing schedule control, pipe insulation and a thermal blanket in combination will result in total average energy reductions of 25.1% and 14.7% for single- and three-person households respectively.

According to Booysen, it also important to pay attention to the cold inlet water and to set the right temperature for the water heating tank, especially in a single-person household.

“The results shows that the temperature of the cold inlet water has a significant impact on energy consumption, with a 5°C increase leading to an average saving of 13% savings, compared to only 5% for the same change in ambient temperature."

“By simply decreasing the set temperature of the water heater by 5°C (to 60°C), a single-person household can achieve a similar total heater energy reduction as reducing his/her warm water consumption by 20%. This same reduction can be achieved by installing a thermal blanket and pipe insulation," says Booysen.

  • Source: Nel, PJC; Booysen, MJ; Van der Merwe, B. Saving on household electric water heating: What works best and by how much? IEEE International Conference on Innovative Smart Grid Technologies.


Prof Thinus Booysen

Department of Electrical and Electronic Engineering

Stellenbosch University

Tel: 021 808 4013


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Martin Viljoen

Manager: Media

Corporate Communication

Stellenbosch University

Tel: 021 808 4921