Get the most from a heat pump

The site survey for the installation of a heat pump should take into account the thermal efficiency of the areas to be heated

Get the maximum from a heat pump

Kevin Potter takes you through the essential steps to be taken to get the most from a heat pump – from initial sizing and location to installation and to educating users

Kevin Potter

National sales manager at Hamworthy Heating

www.hamworthy-heating.com

he energy efficiency of heat

Tpumps is not in doubt; they are up to three times as efficient as a gas boiler. But to maximise the energy efficiency of a heat pump, there are four key aspects that need careful consideration: building fabric, building services, heat pump system design, and usage.

The design of your building and the material it is made from will impact the energy efficiency of your heat pump. The aim is to minimise heat loss through, for example, the uncontrolled flow of air through gaps in the fabric of a building. The more thermally efficient the building, the more energy efficient it will be. Consideration therefore needs to be given to all aspects of building fabric, including insulation, glazing, etc. However, these considerations should also apply to buildings heated with gas-fired boilers.

Undertaking a building survey will enable you to identify heat loss within your building and remedial work that needs to be done to reduce this.

Survey addresses services

A building survey should also address the services within that building, including the existing heating system to see if it is fit for purpose when it comes to running efficiently with a heat pump. Key to the success of a heat pump-based heating system is the ability for the building’s heating system to be able to operate on lower temperatures. That means correctly sized radiators. In the UK, we are relatively poor at sizing radiators as we often base the decision on aesthetics which normally translates into smaller radiators. With a heat pump, the temperature running through the radiators is lower than that provided by a gas boiler, so the radiator must be of a size and nature that provides it with ample opportunity to deliver heat to that area. In many cases, that will mean larger radiators than we are used to.

For the same reason, heat pumps are particularly well suited to use with underfloor heating systems, which have a large surface area from which to disperse heat.

When it comes to gas boilers, most installers will head straight for the plant room and will be able to specify the boiler pretty accurately from that and a cursory look around the building. With a heat pump, the plant room is no longer the first port of call. Instead, to correctly specify a heat pump, the thermal efficiency of all the areas to be heated – including aspects such as window sizes and the building’s materials - need to be measured and calculated. It needs a skilled person to conduct a survey of this nature, although Hamworthy Heating will shortly launch a sizing

Educating the building occupants to the new heating system is important

tool that will make this process much easier and will automatically calculate the size of appliance required.

Correct sizing matters

In the world of gas boilers, it’s standard practice to oversize them, which doesn’t really matter as the boilers just work less hard. Oversizing a heat pump however doesn’t mean you’ll benefit from more heat, but it does make it less efficient, so correct sizing matters.

The location of a heat pump is also completely different to that of a gas boiler, as a heat pump requires external air flow to function so must be installed externally. Units are commonly installed at ground level or on the roof depending on the building type, but the key requirement is adequate clearances to ensure good air flow. Manufacturer’s specifications must be adhered to and whatever you do, don't cover the heat pump or even put a roof over it. Impeding the air flow to a heat pump will negatively impact performance and can result in higher running costs.

Another aspect that differs from gas boiler installations is the use of a buffer tank, but this has an important role to play when it comes to heat pump energy efficiency. A buffer tank keeps a minimum volume of water ‘in circuit’ at times when the heating load is very low. It prevents the heat pump from short cycling and provides a bypass route to maintain the minimum flow rate through the heat pump if most of the heating zones have shut down. Short cycling not only impacts energy efficiency and comfort levels but can also reduce compressor life.

Understanding the building

As with all heating systems, understanding the building and its usage is important to identifying what you want to achieve from your heating system. This then needs to be translated into a good control strategy for maximum energy efficiency. Heat pumps are capable of everything that boilers are capable of when it comes to control, and can readily be integrated into a BMS.

Educating the building occupants to the new heating system is an important consideration, but one that mostly gets overlooked. With a gas boiler, if the temperature drops you can turn it up and in a relatively short timeframe the building reaches the required temperature. With a heat pump, you need to maintain a base heating temperature over a long period of time. Opening windows or messing around with thermostats will cause an imbalance in the system that will take time to rectify. ■