We’ll be running a series of controlled tests in the Salford Energy House to understand the system efficiency of air-to-air heat pumps used with an intermittent and/or zoned heating pattern, and how their efficiency for these patterns differs to air-to-water heat pumps. 

Depending on the results, this may allow us to confidently recommend air-to-air heat pumps as a low-carbon heating solution for contexts where it’s undesirable or unfeasible for homeowners to adapt to the continuous heating patterns required for air-to-water heat pumps to provide optimal comfort and efficiency. This might include social housing tenants, as well as those with jobs or lifestyles that mean they’re away from the property for extended periods of time.

The continuous, whole-home heating pattern that is usually required for an air-to-water heat pump to provide optimum efficiency, comfort and running costs doesn't always work for everyone. For example, those in social housing may be more familiar with intermittent or zoned heating patterns, where heating is only turned on for shorter periods of time or only in certain rooms. Others may have jobs or lifestyles that keep them away from home for extended periods of time. As such, many may find it counterintuitive or undesirable to use a continuous heating pattern.

Although air-to-air heat pumps also provide the best efficiency and comfort when used with a continuous, whole-home heating pattern, they may also be able to be used for intermittent or zoned heating without as significant an impact on comfort, efficiency or running costs as an air-to-water heat system. Interviews with air-to-air heat pump users have provided anecdotal evidence of this. 

However, further evidence is still required to be confident in this use case, especially as there will still be a negative impact on efficiency when air-to-air systems are used for intermittent and zoned heating, even if it is expected to be much smaller. 

Therefore, quantitative research is needed to determine the size of these efficiency reductions, and the interplay between efficiency reductions and the energy savings gained from not heating a home continuously or only heating certain rooms at certain times.

Conducting research to address this will also have an added benefit of building on the existing data that allows for a comparison between air-to-air and air-to-water heat pump efficiency when used with their optimum continuous heating patterns.

Building this evidence base could increase confidence in air-to-air heat pumps as a low-carbon heating solution across a variety of contexts. This can help with our aim of accelerating the decarbonisation of home heating in the UK by demonstrating the utility of a solution for contexts where an air-to-water heat pump may be less practical or desirable to install.

We will be running six air-to-air heat pump tests in the Salford Energy House, testing different heating patterns and outdoor temperature. The Salford Energy House is a traditional Victorian end-terrace house built within an environmental chamber. This means factors such as the outdoor temperature can be controlled and kept consistent between each test, allowing us to run tests in a controlled and comparable way.

In each test we’ll be measuring the following factors, which will allow us to compare how they’re impacted by different heating patterns:

1. electricity use
2. heat pump efficiency
3. how quickly the desired room temperature is met and how well it is maintained
4. room humidity
5. fan noise from the internal and external air-to-air units

We’ll also be comparing the results of these air-to-air tests to air-to-water tests that have previously been conducted at the Salford Energy House.