Are heat pumps just hot air?

Posted on: 22 May, 2024

Amid fierce debate in the UK, are heat pumps really the future of sustainable energy, heating and retrofitting in the built environment?

If we are to achieve the 2050 net zero target set out by United Nations, changes will be needed across the board. For instance, cities will need to adopt smarter urban planning models that minimise private transportation; car manufacturers need to introduce battery-power across their model range; building owners will have to consider retrofitting before proceeding with demolishing old housing stock, and construction companies will need to assess sustainable alternatives to concrete.

Mitigating our impact on the environment will also require action on the part of homeowners, too. More and more governments around the world are encouraging people to replace gas boilers with heat pumps, with the goal of reducing emissions and improving energy efficiency. However, the promotion of this technology hasn’t been without controversy – particularly in the UK.

So what exactly are heat pumps? How do they work? And are they really the future, or just hot air?

What is a heat pump?

A heat pump is a device that uses electricity to transfer energy from one location to another. The name ‘heat pump’ is itself somewhat misleading, as it can provide both hot and cool air to a building as required.

For instance, in the winter, pumps can extract heat from outside of a home and move it inside, while in the summer, it can transfer warmth from inside to outdoors.

How do heat pumps work?

While there are several different types of heat pump that all work slightly differently, generally this technology functions in a similar manner to an air conditioner, in that it makes use of a refrigerant liquid. However, unlike air conditioners, heat pumps can use refrigerant to heat a building as well as cool it.

4 types of heat pump

Here are the four most prevalent kinds of heat pumps in use today:

1. Air source

Air source heat pumps work by using thermal energy derived from the hot air outside a building. Using fans, this warmth is blown across a heat exchanger to heat up its refrigerant liquid.

This form of pump is the most prevalent, as it can be installed outside of a building with relative ease. They’re also effective in winter despite the lack of hot air, thanks to their ability to capture thermal energy.

There are two main types of air source pump. Air-to-air pumps use air from outside, feeding it into a building through fans. In contrast, air-to-water pumps feed air into a wet central heating system, and can produce hot water.

2. Ground source

The major difference between air source and ground source heat pumps is where they draw warmth from, which in the case of ground source is from underground. Also referred to as geothermal heat pumps, ground source heat pumps work by pumping brine, a mixture of water and antifreeze, through pipes in the ground, performing a similar function to a boiler. The brine passes through heat exchangers, which carry the warmth over to a refrigerant.

Ground source options are generally more expensive than air source heat pumps, as excavating paths to install the pipes underground requires specific expertise. However, they’re considered to be more efficient, as underground temperature is more consistent than air temperature.

3. Water source

Water heat pumps, as the name suggests, makes use of water instead of air or ground. It’s usually linked to a water source like a river or well, and is highly regarded for its reliability. As with ground source heat pumps, water has a more consistent temperature than air, and is also an efficient carrier of energy.

How well a water heat pump suits a building depends on various factors, from the quality of the water in the area to the depth of the available water source.

4. Hybrid

Hybrid heat pumps make use of a standard pump alongside another traditional heat source, such as a boiler. It can be used to augment an existing boiler, and provides a cost-effective option when completely overhauling a building’s heating system with a new pump isn’t viable.

Why are heat pumps important?

Conventional air conditioning is responsible for around 4% of all global greenhouse gas emissions. As such, pumps are seen as the ‘central technology’ in the mission to cut heating’s impact on the environment. Pumps can reduce carbon emissions by at least 20% when compared with gas boiler, and potentially up to 80% in countries with cleaner electricity.

What’s more, installing this technology can offer a variety of benefits for building and homeowners.

6 benefits of heat pumps

1. Reduced energy bills

The price of the gas and oil that fuels our boilers is prone to fluctuation – particularly in the wake of economic uncertainty and global conflicts like the invasion of Ukraine. Pumps represent a cheaper and less volatile option – building owners will save on the cost of ordering fuel and have the opportunity to eliminate their gas bills.

2. Increased efficiency

Heat pumps are known for their efficiency. They only draw one-third of their energy from electricity, which can potentially compensate for the price difference compared to oil and gas systems, and are at least three times as efficient as gas boilers.

3. Low maintenance

Modern heat pumps are far more reliable than their predecessors. If properly maintained, they can last up to 20 years. They also require less maintenance than traditional heating systems.

4. Reduced carbon footprint

Around 70-80% of the energy provided by an average heat pump is renewable. What’s more, research from EDF found that installing a pump can cut your carbon emissions by over 23 tonnes of CO2 over a decade, making it an attractive option for businesses and residents looking to reduce their carbon footprint.

5. Save storage space

Unlike gas boilers, heat pumps tend to be outside of a building or underground, meaning building and homeowners can make use of the extra space for storage.

6. Government incentives

The UK, USA, Germany, New Zealand and many other countries offer subsidies, incentives and grants for the adoption of heat pumps that can help with the significant cost of buying and installing them.

Why heat pumps are so controversial?

While the UK government has been very active in promoting heat pumps, interest in them among homeowners remains low, according to research.

A YouGov survey found that just one in ten people want to replace their gas boiler with a heat pump and, instead, around half would rather use hydrogen power as part of their existing gas supply. This is despite the implementation of the Boiler Upgrade Scheme, which is designed to support the decarbonisation of homes and small on-domestic buildings in England and Wales by offering grants of up to £7,500 for the installation of heat pumps.

In contrast, heat pumps outsold gas boilers in the USA in 2022, and an investment of $63 million USD was pledged into the manufacturing of this technology from the Biden-Harris administration earlier this year. What’s more, the EU is the fastest growing market for heat pumps and the technology is already well established in Asia, with China boasting the largest number of installations, according to the EU.

So why does there appear to be so much opposition to this technology in the UK?

Heat pumps have significantly evolved over the last few decades, but many will still remember the earliest incarnations of this technology being poor and ineffective. The significant outlay required to install pumps – even with government grants – is also enough to put off many, with just 12,000 people in the country taking advantage of the Boiler Upgrade Scheme as of last August.

Learn more: 10 heat pump myths, debunked

The rollout of heat pumps in the UK has also come under fire. The National Audit Office (NAO) – the UK’s public spending watchdog – found that installations of pumps will need to increase 11-fold to hit the government’s 2028 target of having 600,000 installed per year in homes.

Outside of the issues around their implementation, heat pumps aren’t without their downsides.

The drawbacks of heat pumps

1. Increased electricity consumption

While an effective heat pump installation can all but eliminate the need for gas or oil, it will drive up a building’s electricity usage. And in an uncertain economic climate, electricity typically costs three times as much as gas, unit for unit.

2. High upfront cost

Heat pumps can pay off in the long term thanks to their increased efficiency, but their installation does require upfront expense (hence the government grants being offered in the UK). From the installation itself to potentially having to purchase new, larger radiators to digging underground pipes, fitting new pumps is an expensive process.

3. Installation challenges

There are various factors that determine what kind of heat pump is suitable for a particular building, with ground and water source pumps, for example, requiring a significant amount of work to install. Even cheaper and more simple air source heat pumps can require significant modifications to a building during installation.

4. Sustainability implications

Heat pumps may be a more sustainable alternative to traditional gas boilers, but their reliance on electricity means they will never be truly carbon neutral – even if this can be somewhat mitigated by fitting solar panels. The refrigerants and fluids used in heat transfer also present issues for sustainability and the environment, particularly if they leak.

Heat pumps and retrofitting

While they’re most commonly associated with new builds, heat pumps have potential for retrofitting projects, too. Although outdated parts and components may have to be replaced, they can be compatible with existing heating and cooling systems. However, as with many of the downsides of pumps listed above, they can require invasive work, such as opening walls and changing pipes.

The heat is on – are pumps really the future of sustainable housing?

Heat pumps have enormous potential to reduce the significant damage that heating and energy consumption have on the planet every year. While their implementation requires significant upfront cost, their potential to save costs and energy, coupled with incentives from governments, will make them an attractive and viable option in the long run.

Sustainability isn’t a passing trend – it’s here to stay and is constantly evolving. If you want to inspire and action change in your career, UCEM’s MSc Innovation in Sustainable Built Environments will give you the skills you need, both now and in the future.

Find out more: MSc Innovation in Sustainable Built Environments – University College of Estate Management