Solar, Gas or Heat Pumps?


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We’re all trying to do our bit for the environment by saving water and electricity. And since hot water costs can comprise up to 60% of our electricity bill, it makes sense to look at water-heating options that can reduce the load on your wallet and your meter.

In addition, due to South African National Standard act 10400-XA 2, a maximum of 50% of a new building’s water heating can come from an electrical resistance element – in other words, all new buildings have to have half their electrical needs supplied by alternative energy sources.

So what are the options? The best are a solar system, a gas water heater or a heat pump. When sized correctly, a solar system has the potential to generate hot water at virtually no cost, provided you don’t need to use a backup electric element. Sunshine provides one eight-hour heating period every day and most hot water usage occurs in the morning and in the evening. It is therefore advisable to double the size of the water tank when replacing a conventional geyser with a solar system, to ensure there is 24-hours worth of water stored. Even so, the downside is that your water will be luke-warm or cold on very overcast days.

If you use a backup heating supply (whether gas or electricity) to warm the water when there isn’t enough solar power to do so, you will incur the running costs associated with that. This cost works out to about the same as the annual average running cost of a heat pump system.Heat pumps use electricity to generate hot water, but almost 70% less electricity than a conventional electric geyser. 

Certain gas water heaters work without any mains electricity supply, and provide hot water no matter the weather conditions. But compared solar and heat-pump systems, gas has a relatively high running cost.Taking running costs and availability of hot water into account, a heat pump looks like the best option, yet of the three options, it is the one with which South Africans are least familiar.

“A heat pump is a bit like a reverse-action air-conditioner,” explains Mike Alton, co-founder of HydraTherm. “Where the air-conditioner transfers heat from the air inside a room to the atmosphere outside, a heat pump transfers heat from the air around it to the water in its geyser. Its application has significant benefits for the environment and consumers’ pockets.”

HydraTherm’s integrated heat pump is a hot water cylinder or geyser that uses minimal energy to move heat from the surrounding air to water by means of a compressor and an air-to-water heat exchanger.  “It requires roughly a third of the electricity used by a conventional geyser to heat the same amount of water.”

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Issue 39