Ask the Expert – Delivering low carbon

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Like a lot of self-builders, you may be looking to stay clear of fossil fuel heating systems and install a heat pump in your home. However, you may be asking how exactly does a heat pump work – and will it work for me? Phil Hurley of the Heat Pump Association has the answers

HOW DOES A HEAT PUMP WORK? 

A heat pump harnesses the natural warmth from the ground, air or water to provide hot water and heating to homes. Each type of heat pump (air source, ground source, water source, exhaust air, and hybrid) works in a slightly different way, but all provide an efficient, low carbon solution. Two of the most commonly used heat pumps in new builds are explained below.

AIR SOURCE HEAT PUMPS

An air source heat pump absorbs low temperature heat from the outside air into a fluid that is then passed through a compressor to increase the temperature and transfer heat and hot water to the home. The system has various components similar to other types of heat pumps, but it also has a thin evaporator coil to draw ambient latent energy from the air and use it to warm up the refrigerant that sits inside the coil so that it begins to evaporate. This gas then moves through the compressor to increase the temperature, which is released inside the building through air ducts or radiators. Air source heat pumps are particularly well suited to smaller plots where space is at a premium. 

GROUND SOURCE HEAT PUMPS

A ground source heat pump takes low temperature heat from the ground to provide heat and hot water. There are various ways this thermal energy can be collected, with the more common methods including ground collectors – where the pipe is buried horizontally into the ground – and boreholes, where pipes are vertically inserted. In both cases, a water mix (with glycol) is then inserted into the pipe and circulated to and from the heat pump, pressurising the system to produce heat and hot water. Once the pipes are in the ground, they have a long lifespan of between 50-100 years and are largely unaffected by air temperature, providing a stable efficiency all year round. Building a home is an ideal time to install the infrastructure for a ground source heat pump as it requires some groundwork, however they are very efficient and worth the extra effort, plus the ground collectors are barely noticeable once complete. 

If you are lucky enough to be building a home near a lake, reservoir, river or even the sea, you may want to consider a water source heat pump. They work in a similar way to ground source heat pumps but extract heat from a body of water rather than the ground.

WHY INSTALL A HEAT PUMP? 

Over the last few years, the Government has indicated that heat pumps will be the technology of choice when it comes to replacing gas boilers in new homes. The focus on heat pumps as a low carbon heating solution is no coincidence. They offer huge carbon savings at around 65% versus a natural gas boiler and have the potential for further reductions as the grid continues to decarbonise over time. To put this into perspective, the projected savings of a heat pump in comparison to a gas boiler could be around 95% by 2050.

HOW DO HEAT PUMPS COMPLY WITH CHANGING BUILDING REGULATIONS? 

From 2025, when the Future Homes Standard is introduced, an average home will be required to cut carbon by at least 75% compared to current standards. In addition, interim changes are due to come into force from this month, requiring a 31% carbon reduction. This makes perfect sense given that the installation of the technology is easier and less disruptive, while avoiding the need for costly retrofits at a later date. Research by the Climate Change Committee (the official climate advisors to the Government) has also shown heat pumps to be cost comparable to gas boilers in new builds already.

WHAT KEY DESIGN POINTS NEED TO BE CONSIDERED? 

Understanding the use and thermal dynamics of your property is key to designing and specifying a suitable heating system. Some key design points to keep in mind include heat loss and hot water usage, external and internal pipe runs, central heating pipe sizing, placement of hot water cylinders, and consideration for sound and comfort. 

WHAT ARE THE PIPEWORK REQUIREMENTS? 

It is important to ensure that the outdoor unit fits within the setting of the property so that it is considered part of the external design, fitted in close proximity to the property to minimise pipe runs, for example. The pipe length from the unit to the water source within the home varies depending on the heat pump, but an eight metre heat pump head typically has a pipe run of around 15-20 metres.

WHAT FUNDING IS AVAILABLE FOR HEAT PUMPS? 

Upfront financial support towards the cost of a heat pump is available through the Government’s Boiler Upgrade Scheme. This has now been launched, and is open to any installation commissioned (with a MCS certificate issued from) 1 April. Grants of £5,000 are available for air source heat pumps or £6,000 for ground source heat pumps. It’s worth keeping in mind that self-build homes are eligible for the scheme, while other types of new build homes are not.

Phil Hurley is chair of the Heat Pump Association