How to specify the right heat pump for your residential project: Project design and site constraints

Heat pump specification for residential dwellings being built

With an increasing focus on finding ways to meet the UK’s net-zero carbon target by 2050, innovative heat pump and low carbon electric systems based on hot water heat pumps and ambient loops are being increasingly specified for residential projects. They can help meet the recent changes to Part L of the building regulations and provide future proofing as new regulations proposed by the government will likely phase out the use of fossil fuels for new residential buildings as early as 2025 with the introduction of the Future Homes Standard.

This blog is focussed on the considerations around site constraints that should be considered by Mechanical and Electrical (M&E) consultants and other building professionals when specifying heat pumps for residential projects. It is taken from the white paper ‘A technical guide to the specification of heat pumps for single dwellings and multi-occupancy residential or mixed-use developments’ to give you a taste of just one of the many important areas that can influence specification choices covered in this comprehensive white paper.

There are many heat pump options available to the specifier and we will show in this blog how understanding site constraints can help to optimise the choice of technology for a residential project.

Which site constraints are important factors in the selection of heat pumps during residential project design?

Site constraints around the ground area available as well as the robustness of the supply chain are important factors in the selection of a heat pump. Let us assume that a ground source heat pump (GSHP) installation is planned for a residential development. This is rarely the best route in terms of capital cost but works well as a simplified example. A large ground area could be required to accommodate the ground loop and heat exchangers. Where space is at a premium, both in terms of availability and financial value, boreholes and horizontal collectors may be required, and these could attract additional, high capital cost.

Skills shortages in renewable technologies mean there are often only a few companies available for the specialised excavations required. This lack of availability in the supply chain may affect the scheduling of the project. In this case, alternatives to GSHPs could be considered.

  • An air source heat pump (ASHP) or a closed-loop water source heat pump (WSHP) may be appropriate alternatives requiring smaller capital investment. ASHP units may be installed on the roof of the building requiring only sufficient airflow space to support the technology’s optimal performance.
  • For single residential dwellings, there is a choice of monobloc or a split system air source heat pump. These offer, amongst other features, the flexibility of placement and lower capital cost.
  • A closed-loop low-temperature network commonly referred to by the industry as an ambient loop with water-to-water heat pumps, would typically require a relatively small plant room within the building.
  • Solutions that incorporate hot water heat pumps (HWHPs) and ambient loops with compact in-apartment heat pumps, are a newer but proven technology ideal for specification in medium and large residential apartment developments. The most appropriate solution for a particular project can be selected by contacting a specialist in the design stage.

Energy Source, local geology, and weather conditions

The energy source on an intended site must be qualified to guarantee that the volume and stability of supply will meet the demand of a specific heat pump. If a GSHP is being considered, local geology should be investigated. This is to establish the thermal and conductivity properties of the bedrock for vertical and superficial deposits for a horizontal loop.

If an ASHP is considered, studies into seasonal forecasts of wind speeds and temperatures are pivotal in demonstrating its efficiency. The geographical height of the area, potential defrosting requirements, and the positioning of a building to avoid shaded areas, will all contribute to the viability of the energy source.

Open-loop WSHPs would require studies into the water supply’s depth, volume, temperature and quality.

A site chosen for a project may present an energy source of ideal natural qualities to support the efficient operation of a specific type of heat pump. However, it is more likely that multiple energy sources will be available with varied attributes. The end solution will have to be specified by employing a series of choices and should be based on thorough research, source qualification and calculations. The design of a modern heat pump can compensate for smaller deficits of the source.

A common challenge for new UK developments is establishing a sufficient gas or electricity supply at an acceptable capital cost. Overcoming issues with gas supply can be achieved by the specification of heat pumps to design gas out altogether. Revised Building Regulations will soon make this a logical decision from a compliance perspective and is another benefit of heat pump specification. This is particularly relevant when making specifications for phased projects that could be affected by the implementation dates of the revised Building Regulations associated with the Future Homes Standard timeline. Specification of high-efficiency heat pumps may also help with electricity supply constraints. If required, the heat pump design can go further and can be altered to combine buffer vessels with off-peak tariffs to act as a flexible energy supply.

Space constraints

One of the reasons for the specification of heat pumps is the freedom of design they offer. ASHPs can be installed on roofs, visually concealed, or enclosed in a specially designed casing, freeing usable space in a building. In general, heat pump systems for medium and large residential properties can be designed to command less overall space in the building than traditional heating systems.

In residential developments, especially in metropolitan and urban areas, the now freed space can be used to generate additional profit. The design of the distribution systems and emitters can be customised to suit the application, further building on these benefits. For example, underfloor emitter systems can maximise usable living space. While in-apartment heat pumps, which use an ambient loop, can provide comfort cooling without additional pipework and cooling plant taking up space in the building.

In residential homes, split system ASHPs allow for the heat pump to be installed further away from the property. Hot water heat pumps can be paired with direct-acting panel heaters, reducing the capital cost of the heating solution, and removing the need for a hydronic system to deliver space heating.

What other factors should be considered when specifying heat pumps for residential projects?

This extract from our Dimplex white paper has highlighted just one of many key areas that should be considered when specifying heat pump technology for residential projects. Others include:

  • Environmental and planning concerns
  • Efficiency, capital and running costs
  • Compliance and futureproofing
  • Installation

For more information, please download our white paper and, if you looking for low-carbon heating, hot water or ventilation solutions for your next residential project, please contact our team today who will be happy to guide you through the range of Dimplex solutions available.