Low-carbon heating systems in UK homes

With the implications of the latest conflict in the Middle East beginning to unfold, many self-builders and renovators are asking how they can reduce their homes’ reliance on fossil fuels. The concept of an ‘autonomous’ house — largely self-sufficient in meeting its own energy demand — has existed since the 1970s. Early designs focused on passive solar gain through large south-facing windows and the use of thermal mass in floors and walls to retain heat (these ideas have largely been superseded due to the risk of overheating).

With technologies such as air source heat pumps and domestic battery storage becoming more mainstream, the prospect of a self-sufficient home is now more achievable.

Air source heat pumps (ASHPs) are highly efficient electric heating systems that extract heat from the outside air to provide space heating and hot water. An ASHP consists of an external unit where heat is transferred via a heat exchanger. Heated water is then circulated into the home to supply the hot water cylinder and the heating distribution system, such as radiators or underfloor heating.

In both refurbishment projects and new builds, it is important to identify suitable locations for the external unit and associated internal equipment early in the design process. Retrofitting these elements into a developed design can be challenging if space has not been allowed for them from the outset.

Because heat pumps rely on extracting heat from the surrounding air, they require adequate ventilation. Typically, this means allowing at least a 300mm gap behind the unit and 1m of clear space in front. For this reason, placing an ASHP in a narrow side passageway is usually unsuitable.

The external unit in our eco-house project

Noise is another important consideration. ASHP installations must comply with a strict noise limit of 42dB at the nearest neighbouring door or window. This constraint can make siting the unit at the rear of a narrow terraced property impractical.

Ideally, the ASHP should be positioned close to the internal hot water cylinder to minimise heat losses. Where the unit is located further from the house, pre-insulated underground pipework is used to carry the flow and return water. If the pump is close to an external wall but the plant room is some distance away, the route for this pipework must be carefully planned.

The space required for internal equipment depends on the size of the house and the number of bathrooms. In a large four-bedroom home with underfloor heating, the plant room may include a hot water cylinder, buffer tank, one or two expansion vessels, and the associated pipework. Arranged linearly, this can require at least 1800mm in width and 650mm in depth. Smaller homes may need only a cylinder and a single expansion vessel, but this still occupies more space than a standard kitchen cupboard. These items are often located in the utility room, but sometimes it is better to plan for a separate, dedicated plant room.

The internal cylinders and solar inverter in a full house refurbishment in Redland, Bristol

Solar photovoltaic (PV) panels are a valuable addition, as the electricity they generate can be used to power the heat pump, effectively providing free heating and hot water. PV systems require an appropriate roof area and orientation; for example, a north-facing roof pitch is generally unsuitable.

There is, however, a mismatch between when solar energy is generated (during sunny periods) and when heating demand is highest. Domestic battery storage allows excess electricity generated during the day to be stored for use at night or during peak demand. This reduces reliance on the national grid, lowers energy bills, and moves the home closer to energy autonomy.

In our eco-house project in Somerset the combination of an air source heat pump, solar PV panels, and a domestic battery allows the building to be self-sufficient for heating and hot water for several months of the year.

The internal cylinders, solar inverter and domestic batteries in our eco-house project in Somerset

Conclusion

Integrating a low carbon heating system in a new home or a major domestic refurbishment is a complex task which involves specialist knowledge. DHV Architects and their team of builders and installers have the skills and experience to guide our clients through every stage of the process and create beautiful spaces tailored to their needs. Contact us for a no obligation discussion about your project on 0117 914 8317 or email info@dhva.co.uk.