Heating water accounts for a whopping 32% chunk of typical household electricity consumption, and with electricity prices going only one way, cutting down on that usage is increasingly important.
But South Africans may be going about it all wrong.
According to a new study from Stellenbosch University (SU), scheduling your geyser can beat other tried-and-tested methods including lowering the thermostat temperature – as is often recommended – as well as using a thermal blanket or reducing the use of hot water.
“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 professor Thinus Booysen of the SU department of electrical and electronic engineering.
A team of researchers from the university compared these methods using eight typical household usages, from a one-person apartment shower 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.
“The biggest savings, as expected, are the scenarios where only one small usage event (e.g. a short shower) occurs per day,” said Booysens. “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 of a geyser 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 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.
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.”
Implementing a combination of all three would result in a total average energy reduction of 25.1% and 14.7% for single- and three-person households respectively.
Although timing is the single most effective intervention, turning down the temperature on a geyser is still not a bad idea – and far better than trying to cut down on showers or taking shallower baths.
“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,” said Booysen.
The research was published at the IEEE International Conference on Innovative Smart Grid Technologies.