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2016-06-02 | story

Surprising finding: water heating behaviour in SA

CAPE TOWN: The single most effective thing that South Africans can do to reduce their energy use related to heating water in their homes, is to switch off hot water cylinders half an hour before they are most likely to bath or shower. Those people who do switch their cylinders on and off during the day, as an energy saving measure, tend to turn them off after the geysers have refilled and reheated, which is wasteful of energy. 

This is according to Dr Thinus Booysen, with the University of Stellenbosch’s Electrical and Electronic Engineering Department, who recently released some surprising findings about middle class South Africans’ behaviour associated with managing water heating in their homes, and their levels of knowledge around efficiency measures and the associated costs.

In South Africa, where the population is 54 million, just under half of people heat water in their homes either on the stove top, or in kettles. It’s only some 5.4 million households that have water heating cylinders to do the job, but that accounts for the lion’s share of household energy use here. Most of these cylinders are in wealthier households.

One of the ways people are urged by the national utility to save electricity, in order to stabilise demand on an increasingly overstretched grid, is to switch their geysers and other non-crucial appliances off during peak hours. But Booysen wanted to understand how widely this method is used, and how much people understand about their daily energy use associated with heating water at home.

Booysen teamed up with the University of Cape Town’s Environmental Policy Research Unit (EPRU) to design a survey which they ran on the social media platform Facebook. They managed to recruit 457 people to take part in it, mostly men, and mostly between the ages of 45 and 63.

The motivation was to test the market readiness for an experimental ‘smart’ geyser control device that Booysen and his team have developed, which can take the headache out of remembering to switch these cylinders on and off manually each day. It also draws up a tailored heating schedule that is optimised for the heating profile of each household, based on people’s actual consumption patterns.

His assumption from the start of the survey was that few people would bother to switch their geysers on and off manually, partly because of the inconvenience. Yet he discovered he was wrong on this score, finding as many as 70 percent of the survey participants practiced this method.

‘What surprised me is that most of people in the survey do turn their geysers on and off daily,’ he says, ‘and most of them do it manually, rather than using a timing device to do it automatically.’

The other assumption was that people wouldn’t have a good sense of how long it takes to heat up the water in a cylinder.

‘But because many of these people are switching the geysers on and off manually, they’re constantly testing the water to see when it’s warm enough to use, so they do know how long it takes to heat up.’

What these people don’t pay attention to, is how slowly the water in these cylinders cools down once they are switched off.

‘It takes as much as 24 hours for a geyser to cool down again. So the upshot of only switching off a geyser once it’s reheated the water, is that all that energy goes to waste. Many people in the survey were doing this - switching the geysers on ahead of needing to bath or shower, allowing it to refill, which means the water begins to heat immediately, and then only switch the cylinders off a while after using it.’

The survey turned up the fact that most of the participants didn’t know how much energy they would save by using these sorts of measures, or how to best manage the switching on and off, relative to the households water use patterns.

‘The best advice I can give is for people to switch off their hot water cylinders just before they’re going to bath or shower, use up the warm water that’s already there, and leave they geyser off until three or four hours before you need it again.’

He recommends switching it back on about three hours before a family’s peak demand, and then switch it off again about half an hour before everyone baths or showers.

‘You can get about three to four showers or two baths out of the geyser in short succession, even though the element isn’t heating the incoming cold water,’ he assures people.

As people use the geyser, the warm water flows out the top of the cylinder. The cool replacing water comes in at the bottom and doesn’t mix with the warm water immediately, so the already warm water doesn’t cool down if it’s used immediately.

However, Booysen’s smart device is geared towards taking the hassle out of doing this sort of thing manually. The gadget operates in three parts: a control box the size of half a shoe box is installed next to a geyser. The device then measures the water and electricity use in the geyser, and communicates the information via the internet to an online server that analyses the data. The system is designed to allow the user to control the geyser via an app either on a computer or smart phone.

This allows you to log in anywhere in the world, to see what the flow rate and volume of used water is in your geyser, and what the temperature is,’ Booysen explains. ‘The smart app allows you to turn the geyser on and off remotely with click of a button. You can set the timer and the temperature. This allows you to design your own schedule control.’

The gadget, which was recently tested outside of the Stellenbosch laboratory for the first time in the fives years his team has been designing it, has the potential to autonomously cut household water heating by up to 30 percent without users noticing a change to their hot water use habits. 

The paper, Energy perceptions in South Africa: An analysis of behaviour and understanding of electric water heaters, will be published in the journal Energy for Sustainable Development in June 2016. EPRU’s Prof Martine Visser, Dr Kerry Brick and doctoral economics student Samantha De Martino were instrumental in helping Booysen and his team design the survey questions.