Alan Pierce advises the Australian Energy Efficiency Alliance and the Energy Efficiency Council, as well as government and community groups such as Renew, on heat pump related matters.
Heat pumps are all the rage in a world where carbon emissions need to be cut quickly while lowering energy costs. In buildings, they replace space heating and water heating, and provide cooling as a bonus.
A heat pump takes heat from outside, concentrates it (using an electric compressor) to raise the temperature, and pumps the heat to where it is needed. In fact, millions of Australian households have purchased heat pumps in the form of reverse cycle refrigerators and air conditioners for cooling. They can also be heated, which can save you a lot of money compared to other types of heating!
Even before Russia restricted gas supplies, many European countries were introducing heat pumps – even in colder climates. Now government policy is changing at an accelerated pace. The US, which has had access to very cheap natural gas in recent years, has also joined in the craze, with President Joe Biden declaring heat pumps “defense critical” and ordering more production.
The ACT government is encouraging the electrification of buildings that use heat pumps and is considering legislation to make it mandatory in new developments. The Victorian government recently launched a natural gas replacement roadmap and is in the process of reformulating its heat pump incentive scheme. Other states and territories are also reviewing policies.
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I have calculated that a heat pump can save 60-85% on energy costs compared to an electric fan heater or traditional electric hot water, which is within the range estimated by the ACT government.
Comparisons with natural gas are difficult because efficiency and energy prices vary widely. However, as a general rule, heat pumps cost about half as much as gas. By not exporting excess rooftop solar and using it to run a heat pump, I calculated that it would be 90% cheaper than natural gas.
Heat pumps are also good for the climate. My calculations show that a typical heat pump using average electricity from the Australian grid will cut emissions by about a quarter compared to natural gas and three quarters compared to electric fans or panel heaters.
If high-efficiency heat pumps replace inefficient gas heating or run predominantly on solar energy, emissions reductions could be much greater. This gap is widening as zero-emission renewable electricity replaces coal and natural gas and heat pumps become more efficient.
Read more: The good news is that the clean energy gold rush is in full swing. We need it to deal with energy price volatility and the exit of coal
Heat pumps available today have an efficiency of 300-600%, that is, they produce three to six units of heat for every unit of electricity consumed. Heat pumps can also operate in freezing conditions.
How is this possible when conventional electric and gas heaters are operating at 100% efficiency and the cold air is very cold?
It’s not magic. Think of your refrigerator, it’s a small heat pump. Inside the refrigerator is a cooling plate called an evaporator. It absorbs heat from warm foods and other sources because heat is naturally transferred from warmer to colder items. An electric motor under the refrigerator drives a compressor that concentrates the heat to a higher temperature and pours it into the kitchen. When this happens, the walls and back of a typical refrigerator heat up. This way your refrigerator cools your food while heating your kitchen at the same time.
Heat pumps obey the laws of thermodynamics and can theoretically operate at 200% to over 1000% efficiency. But the greater the temperature difference, the less efficient the heat pump will be.
If a heat pump needs to extract heat from the environment, how does it perform in cold weather? Remember that your refrigerator keeps the freezer cold by pumping heat into the kitchen. The laws of physics work. The low temperatures we experience are actually quite high: everything is relative.
The temperature of outer space is approaching a temperature known as absolute zero, zero Kelvin or -273°C. So 0°C (the temperature at which water freezes) or even the recommended freezer temperature of -18°C is actually pretty hot compared to space.
The main problem with heat pumps in “cold” weather is that ice forms on their heat exchangers when the water vapor in the air cools and condenses and then freezes. This ice blocks the airflow that normally supplies the heat pump with “hot” air. Heat pumps can be designed to minimize this problem.
Read more: Heat pumps: UK to install 600,000 pumps a year by 2028, but huge investment required to keep up with them
Choosing the right heat pump (often referred to as reverse cycle air conditioners) can be a daunting task as most consultants are used to discussing gas options. Resources such as yourhome.gov.au, selection.com.au, and the popular Facebook page My Efficient Electric Home can help.
All household units must have an energy efficiency label (see energyrating.gov.au): the more stars the better. FairAir’s stand-alone network calculator allows you to estimate your home’s heating and cooling needs, as well as the dimensions needed for a comfortable stay.
Larger heat pumps cost more, so oversized can cost more. In addition, insulation, hermetically sealed ventilation and other building efficiency measures allow for smaller and less expensive heat pumps that use less energy and provide more comfort.
When using a heat pump, it is important to clean the filter every few months. A clogged filter reduces efficiency as well as heating and cooling capacity. If your old heat pump no longer provides as much heat (or cooling), it may have lost some refrigerant and needs to be replaced.