How heat pumps of the 1800s are becoming ...

Zhibin Yu, a thermal engineer, had been grappling with an engineering problem for years. During the first UK lockdown of the COVID-19 pandemic, he found the perfect opportunity to tackle it. With more time on his hands, he focused on improving the efficiency of heat pumps, which move heat from the outdoors into homes.

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While heat pumps are more efficient than gas heaters, they often ice up, reducing their effectiveness. Yu, based at the University of Glasgow, UK, spent weeks pondering the issue before a breakthrough: capturing and rerouting the heat waste produced by standard heat pumps. This innovation could solve the defrosting problem and improve the pump's overall performance.

Recent Innovations and Their Global Impact

Heat pump technology, dating back 200 years, is becoming more efficient today. According to the International Energy Agency (IEA), only about 10% of global space heating needs are currently met by heat pumps. Given the ongoing energy crisis and the push to reduce fossil fuel consumption, the importance of heat pumps has never been more pronounced.

In a research paper published in the summer of 2022, Yu and his colleagues introduced a prototype heat pump design. This model stores leftover heat in a small water tank, enabling the device to defrost itself without halting the home’s heat supply.

How Heat Pumps Work

Heat pumps operate on a simple principle: capturing and using environmental heat. Unlike traditional heaters, heat pumps transfer heat from the outdoors into homes. Refrigerants within the pump absorb and release heat, facilitating this process. The efficiency of heat pumps is measured by their coefficient of performance (COP), with a COP of 3 indicating 300% efficiency.

The concept of heat pumps isn’t new. Lord Kelvin proposed their use for space heating in 1852. The first heat pump was designed shortly thereafter, and by the 1950s, they were discussed in the British Parliament as a heating alternative during coal shortages. The 1973-74 oil crisis spurred further interest in heat pumps as a sustainable option.

The Current Energy Crisis and Heat Pump Adoption

The Russian invasion of Ukraine in February 2022 spiked gas prices, making heat pumps more attractive. Bill McKibben's blog post "Heat pumps for peace and freedom" highlighted their potential to reduce reliance on fossil fuels and counter geopolitical challenges.

Environmentalist Karen Palmer, an economist at Resources for the Future, emphasizes the role of heat pumps in combating climate change, especially when powered by renewable electricity sources like domestic solar panels.

The IEA estimates that heat pumps could reduce global carbon dioxide emissions by at least 500 million metric tons by 2030—equivalent to the annual CO2 emissions from all European cars.

Barriers to Widespread Use

Despite their advantages, heat pumps are not yet commonplace in some countries due to costs. They are more expensive than gas heating units, and historically cheap natural gas has dissuaded homeowners from switching. Cold climate performance is another concern, especially in poorly insulated homes. However, modern heat pumps can work efficiently at temperatures as low as -10°F. Norway leads in heat pump adoption, showing their potential even in harsh climates.

Innovations continue to improve heat pump efficiency and suitability for varying housing conditions. Yu's new air source heat pump design, for instance, promises to improve COP by 3-10% while being cheaper than comparable models.

Future Prospects and Community Heating Systems

High-temperature heat pumps are being developed, such as those by Vattenfall and its subsidiary Feenstra, expected to launch in 2023. These systems use CO2 as a refrigerant and are designed to replace gas boilers without extensive home insulation upgrades. Pilot trials have shown promising results with homeowners preferring heat pumps over returning to gas boilers.

District heating systems are another promising solution. Star Renewable Energy in Glasgow, for example, has built systems that draw warmth from nearby water bodies, providing efficient heating for entire communities.

While not every home or budget can accommodate a heat pump, their efficiency and increasing adoption make them a crucial option for the future. "Eventually," predicts Yu, "I think everyone will switch to heat pumps."

Chris Baraniuk is a freelance science journalist and nature lover based in Belfast, Northern Ireland. His work has appeared in BBC, the Guardian, New Scientist, Scientific American, and more.

This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews. Sign up for the newsletter.

Most common type of heat pump

This article provides details about the common type of heat pump. For general information, see heat pump.

An air source heat pump (ASHP) absorbs heat from the outside air and releases it inside a building. Using the same vapor-compression refrigeration process as an air conditioner, but in reverse, ASHPs efficiently heat individual houses or flats.

Air-to-air heat pumps provide hot or cold air directly to rooms, while air-to-water heat pumps use radiators or underfloor heating to heat entire houses. ASHPs typically gain 4 kWh of thermal energy from 1 kWh of electrical energy, optimizing flow temperatures suitable for buildings with low-flow temperature heat emitters.

As of 2023, ASHPs account for about 10% of global building heating. They are pivotal in phasing out gas boilers to reduce greenhouse gas emissions. ASHPs move heat between outdoor and indoor heat exchangers, sometimes heating water for domestic use. They are relatively easy and inexpensive to install, achieving COPs of 2-5 in mild weather, and 1-4 at temperatures below -8°C (18°F).

Newer models with variable-speed compressors maintain high efficiency in freezing conditions, making them viable even in cold climates like Minnesota and Maine, USA.

Technology

Air source heat pumps operate by transferring heat between outdoor and indoor environments. Air-to-air systems can heat or cool interiors, while air-to-water systems provide space heating and hot water. The system includes an outdoor evaporator and indoor condenser coils, similar to a refrigerator or air conditioner.

Most ASHPs are reversible, providing both heating and cooling. Heat is transferred via refrigerant, which absorbs ambient heat outdoors and releases it indoors. Modern ASHPs can operate efficiently in a range of temperatures, making them versatile for various climates.

Replacing Gas Heating in Existing Homes

Good home insulation is essential for ASHP efficiency. ASHPs are bigger than gas boilers and require outdoor space, making the installation process more complex and potentially expensive. Proper sizing is crucial to avoid high running costs. Retrofit challenges include replacing radiators and pipes or installing low-temperature underfloor heating systems.

High-temperature heat pumps can retain existing heat emitters but are more costly to buy and run, suitable for buildings hard to alter or insulate. ASHPs maintain even temperatures, filter air, and reduce allergens, potentially better for health than fossil-fueled heaters.

ASHP Performance in Cold Climates

Standard ASHPs are not recommended below -10°C, but models designed for very cold climates can operate down to -30°C. Variable-speed compressors enable operation in extreme conditions, although electric resistance heating may be more efficient below -25°C.

In cold weather, ASHPs defrost by switching to cooling mode briefly, using heat from circulating water or air. Modern ASHPs can meet heating needs even in freezing conditions, although hybrid systems or multiple units may be necessary for large homes.

Noise Management

An ASHP's outdoor unit includes fans that produce noise. Modern units offer silent mode operation and acoustic enclosures to reduce noise in sensitive areas. Proper placement and scheduling can mitigate noise issues.

In the U.S., the maximum allowed night-time noise level is 45 dBA, while in the UK it's 42 dB from the nearest neighbor. Germany's limit for residential areas is 35 dB. Ground source heat pumps, which don't require outdoor units, eliminate this noise concern.

For more information, visit OUTES.

Efficiency Ratings

The efficiency of ASHPs is measured by COP, with higher COP indicating greater efficiency. In mild weather, their COPs range from 4 to 6, but efficiency decreases as outdoor temperatures drop. Ground source heat pumps maintain more consistent efficiency due to stable ground temperatures.

Design improvements, such as variable-speed compressors, enhance efficiency by allowing slower operation and better moisture condensation. Regular maintenance, like changing filters, can improve performance by 10% to 25%.

Impact on Decarbonization

Heat pumps are crucial for reducing CO2 emissions by replacing gas boilers. The IEA predicts significant emission reductions by 2030. However, concerns remain about winter electric load peaks, especially if ASHPs are used with electric resistance heating.

Wind farms, like those in Canada's Yukon Territory, complement ASHPs by increasing winter electricity supply. Heat pumps can also stabilize grids through demand response, aided by thermal energy storage solutions.

Economic Considerations

ASHPs have higher initial costs but lower lifetime expenses compared to gas boilers and air conditioners, especially with government subsidies. Market adoption varies, with Norway, Australia, and New Zealand leading in heat pump usage. As of 2023, heat pumps outsold fossil fuel-based heating in the U.S. and France.

Maintenance and Reliability

ASHPs typically require less maintenance than fossil fuel heaters. Proper sizing and installation are essential for longevity and efficiency. Consumer surveys indicate that heat pumps are durable, though some may experience issues within eight years of ownership.

Historical Context

Heat pump technology evolved from chemical refrigeration techniques developed in the 19th century. Key milestones include Jacob Perkins' ice-making machine and Fusanosuke Kuhara's early air conditioner. Modern heat pumps replaced harmful refrigerants like CFCs with more sustainable options, driven by international environmental treaties.

In 1989, Gustav Lorentzen's method for using CO2 as a refrigerant marked a significant advancement in eco-friendly heat pump technology. This innovation led to widespread adoption in Europe.

Manufacturing Trends

Demand for heat pumps has surged in the 21st century, with governments promoting them for energy security and decarbonization. European manufacturers focus on air-to-water systems, while Asian countries, especially China, dominate production with air-to-air systems.

For further details, visit Commercial Air Source Heat Pump Manufacturer.