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Want to save 60-85 per cent on energy costs and cut carbon emissions? This technology is gaining favour in an energy-starved world.
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Heat pumps are becoming all the rage around a world that must slash carbon emissions rapidly while cutting energy costs. In buildings, they replace space heating, water heating, and provide cooling as a bonus.
A heat pump extracts heat from outside, concentrates it (using an electric compressor) to raise the temperature, and pumps the heat to where it is needed. Millions of Australian homes already have heat pumps in the form of refrigerators and reverse-cycle air conditioners.
Even before the restrictions on Russian gas supply, many European countries were rolling out heat pumps, even in cold climates. Now, government policies are accelerating change.
The Australian Capital Territory (ACT) government is encouraging the electrification of buildings using heat pumps. It is considering legislation to mandate this in new housing developments.
The Victorian government recently launched a Gas Substitution Roadmap to reframe its incentive programs toward heat pumps. Other states and territories are also reviewing policies.
Relative to an electric fan heater or traditional electric hot water service, a heat pump can save 60-85 per cent on energy costs.
Comparisons with gas are tricky, as efficiencies and energy prices vary. Typically, a heat pump costs around half as much for heating as gas. If instead of exporting your excess rooftop solar output, you use it to run a heat pump, it can be up to 90 per cent cheaper than gas.
Heat pumps are also climate-friendly. Calculations show a typical heat pump using average Australian electricity from the grid will cut emissions by about a quarter relative to gas and three-quarters compared to an electric fan or panel heater.
If a high-efficiency heat pump replaces inefficient gas heating or runs on solar, reductions can be much bigger. The gap is widening as zero-emission renewable electricity replaces coal and gas generation, and heat pumps become even more efficient.
Heat pumps available today achieve 300-600 per cent efficiency. For each unit of electricity consumed, the pumps produce three to six units of heat. Heat pumps can operate in freezing conditions too.
How is this possible when the maximum efficiency of traditional electric and gas heaters is 100 per cent, and cold air is cold?
It is not magic. Think about your fridge, which is a small heat pump. Inside is a cold panel called an evaporator. It absorbs heat from warm food and other sources because heat flows naturally from warmer objects to cooler objects. The electric motor under the fridge drives a compressor that concentrates the heat to a higher temperature, which dumps it into your kitchen. The sides and back of a typical fridge get warm as this happens. So, your fridge cools the food while heating the kitchen a bit.
A heat pump obeys the laws of thermodynamics, which allow it to operate at efficiencies from 200 per cent to over 1,000 per cent in theory. But the wider the temperature difference, the less efficient the heat pump is.
Remember, your fridge keeps the freezer compartment cold while pumping heat into your kitchen. The laws of physics are at play. What we experience as a cold temperature is quite hot: it is all relative.
Outer space is close to a temperature known as absolute zero, zero degrees Kelvin, or –273℃. So, a temperature of 0℃ (at which water freezes), or even the recommended freezer temperature of -18℃, is quite hot relative to outer space.
The main problem for a heat pump in “cold” weather is that ice can form on its heat exchanger as water vapour in the air cools and condenses, then freezes. This ice blocks the airflow that provides the hot air to the heat pump. Heat pumps are designed to minimise this problem.
Selecting a suitable heat pump can be tricky. Most advisers are used to discussing gas options. Resources such as yourhome.gov.au, choice.com.au and the popular Facebook page My Efficient Electric Home can help.
All household units must carry energy labels (see energyrating.gov.au): the more stars the better. The independent FairAir web calculator allows you to estimate heating and cooling requirements for a home and the size needed to maintain comfort.
Bigger heat pumps are more expensive, so unnecessary oversizing can cost a lot more. Insulating, sealing drafts and other building efficiency measures also allow you to buy smaller heat pumps that use less energy and provide better comfort.
When using a heat pump, it is especially important to clean its filter every few months. A blocked filter reduces efficiency and the heating and cooling output. If you have an older heat pump that no longer delivers as much heat (or cooling), it may have lost some refrigerant and need a top-up.
This article was written by Alan Pears and first appeared in The Conversation.
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