Exhaust Air Heat Pumps in Multi-Unit Residential Developments

High efficiency, renewable, low cost…These are all buzzwords we hear when asked to develop energy strategies and designs for our clients. It will be no surprise then, specifically for high-density housing, that delivering a heating system that ticks all these boxes is becoming an innovation hotspot for the industry. Low carbon heating is becoming more and more prominent as we reach closer to the UKs target of Net Zero emissions by 2050.

Research has suggested that there are alternatives away from traditional community heating schemes (such as communal pipework through the building), with lower installation and running costs. However, nothing is ever straight forward, with one of the biggest challenges being planning policy compliance.

Not only this, there are also concerns from many parties on the increasing cost and complexity of heating systems. The rated capacity of such systems has increased too. For example, a standard home gas boiler was less than 12kW only a few years ago. Today, boilers and district heating modules within apartments are typically 35kW or larger.

One thing that is certainly happening is that heating demand is reducing significantly within dwellings, primarily through good passive design and improvements to building fabric. As a result, the continued use of district heating systems and communal plant has resulted in higher service charges to occupants (which includes costs for plant, distribution losses, maintenance, and management). So much so that this cost is becoming as much as the occupant’s metered energy bill.

As the Standard Assessment Procedure (SAP) changes continue to acknowledge the increase in network losses, SAP10, the capital costs and services charges will continue to rise.

Exhaust Air Heat Pumps look to break this mould by providing an ‘individual home solution’ that is not only low carbon, but also offers reduced capital and running costs to homeowners and developers.

Put simply, EAHP uses the warm air that is extracted from the building to provide domestic hot water and/or space heating. Inside the unit, this is driven from an internal air source heat pump which is highly efficient due to the temperature of the exhaust air. The EAHP type suitable for the dwelling will be dependent on the ventilation strategy used. For dwellings using continuous Mechanical Extract Ventilation (MEV), referred to as System 3 in Part F of the Buildings Regulation, a single stage EAHP would be selected. For more airtight dwellings, where a mechanical ventilation with heat recovery (MVHR) is used (System 4), a two-stage EAHP would be your unit of choice.

EAHPs are limited in their heating output ability, which is one of the reasons they are installed in buildings with good fabric standards to promote ‘heat autonomy’, conserving and recycling the heat already within the dwelling. It will be no surprise that two-stage EAHP are more cost effective and produce lower annual CO2 emissions in comparison to single-stage EAHPs. With a single-stage EAHP, the fresh air supply entering the dwelling must be constantly reheated.

The two-stage EAHP gets its name from recovering heat from the exhausted air through two separate stages. The first is through the MVHR system using a high efficiency counter flow heat exchanger to warm the fresh air supply. The second is heat recovery from the exhaust air heat pump which provides domestic hot water and tops up the fresh air supply if needed.

Key considerations

Cooper Homewood have carried out an in-depth review of the EAHP system and understand what needs to be provided to ensure that the system works to its optimum.

Ø  The suitability of the EAHP in relation to the size of the property.

Ø  The optimum levels of fabric performance.

Ø  heating output from the EAHP system and its limitations.

Ø  For dwellings with hot water usage, reheat times need to be considered against the client’s performance requirements.

Ø  Layout and performance of the ventilation system needs to be reviewed and carefully considered.

We believe the exhaust air heat pump is a great low carbon technology but has its limitations. With careful design and consideration of its constraints, this technology is a mover and shaker in the industry.

Of course, on larger mass-residential schemes, particularly in London, there are also challenges complying with planning policy requirements. Policy requirements typically ask for a centralised heating system, such as a communal network over individual systems within each dwelling. But don’t worry, we have extensive experience in this area and will ensure that proposals that we believe are appropriate will get through.

If you would like to discuss the suitability of an exhaust heat pump for your project, get in touch with our team and we would be happy to help.