The move towards net-zero within the residential, construction and architecture industry is only made possible through collaboration.

We work closely with our partners to pull in expertise from all areas, and to share ideas and processes for the most effective outcomes. Carnell Warren Associates carry out the design of Mechanical, Electrical and Public Health Engineering Services. Carnell Warren specialises in the high-end residential market, with over 30 years of experience, their innovative solutions are based on tried and tested engineering principles.

Involved in a number of sustainable housing projects, RHA and Carnell Warren have worked together on renewable energy and technology solutions within the home.

Here, Director Will Harrington, explains what energy saving solutions are currently available to home-owners, the upcoming initiatives, grants and legislation from the government.

Q: RHA and Carnell Warren have often worked together on projects where heat pumps have been recommended as a more sustainable way of heating homes. Do you think the government’s proposal to subsidise heat pumps will allow more projects to follow this suit?

WH: The government scheme, the Renewable Heat Incentive (RHI) is coming to an end in March 2022. This scheme is planned to be replaced with another similar scheme, the Clean Heat Grant that will pay a one-off grant to homeowners installing a renewable heating system. These include Biomass, Solar Thermal, Ground Source or Air Sourced Heat Pumps (ASHPs). This scheme will pay a single payment of up to £4,000. This is less than what was available over the full term of the yearly RHI grant payments.

 Carnell Warren have found that all clients are interested in exploring other heating options than the traditional gas fired boilers. This is in part due to the grants available, but increasingly it is due to the increasing cost and uncertain supply of gas and the government nudges to move to a natural gas free future. The government are restricting the installation of gas boilers within new properties but there is currently no definitive date on when this is planned to come into effect.

 The incentives that exist are helping to increase the number of air source and ground source heat pump installations, which increase the confidence in the systems and will in turn reduce the installation costs. At some point in the future, I can see that the decision will be to choose an air source heat pump purely based on economics of installation rather than a government incentive. Sustainability then becomes a happy biproduct of the market changes.

 Planning becomes a contentious item on nearly all projects with ASHPs. If the government and planning bodies would take a more pragmatic approach to the installation of air sourced heat pumps this would reduce the costs, time and practicalities in installing them more often and would increase the uptake overnight.

Q: How exactly do heat pumps work?

WH: Heat pumps operate on a vapour compression cycle. In simple terms, they use the phase change (liquid to gas and back to liquid) through this cycle, and via a small amount of electric work they can extract energy from a source and turn it into useable heat. They can do this very efficiently using the thermal capacity of refrigerant gases and the latent energy from the phase change to effectively absorb heat.

Q: In retrofitting an existing home, is there anything else that homeowners will need to consider? We often try to increase the insulation of a home on the projects we work on. Does a fabric first approach need to be taken to make sure the heat pumps work efficiently?

WH: Yes, this is the number one sustainable measure you can take. Reducing the heat loss from the property reduces the size of the heat pump you have to install and decreases the reaction time of the system and can potentially reduce the temperature the system runs on, therefore increasing the efficiency of the system.

Q: Where can heat pumps be located and are they noisy?

WH: Heat pumps have to either reject heat or gain heat from the air. If they cannot do this effectively, they may overheat or undercool and freeze. This means the best place for them is in the open air. However, often there are planning restrictions over their placement, which means they are often enclosed or located below ground.

 This can all be designed out with require careful consideration and design. The units themselves are not that noisy, but everyone has different thresholds to noise and so this is a very individual view. Ultimately it is the client’s plant and so if it is an issue, it can be turned off during critical times. Usually, the planning restrictions of being 10-15dBA below the lowest recorded ambient noise level means that the units are pretty much silent after acoustic attenuation. 

Q: Can they be plumbed into more traditional central heating systems such as radiators and are hot water cylinders required?

WH: Short answer is yes! They can, modern ASHPs have multiple heat exchange processes which means that they can get to high temperatures of approximately 75degC which is similar to a traditional gas or oil-fired boiler.

Q: As well as heating, can they be used in reverse to cool homes in a more sustainable manner?

WH: Cooling has only every been provided by the same heat pump cycle that is provided by ASHPs, it is the same process that you will find in a domestic refrigerator, just operating in reverse. However, the units installed for heating can often be used for cooling as a biproduct of their type and installation. The government try to restrict grants for units used in cooling, however for larger projects the savings offered by government grants are insignificant to the savings for installing a system that can cool as well.

Q: Do you think there are any other technologies that governments could subsidise to help us reach zero carbon. Are mechanical ventilation heat recovery units possibly the next step, for example?

WH: I believe the best action the government can take to encourage the use of ASHPs and other green technologies is to remove the planning constraints that surround them. Mechanical Ventilation Heat Recovery Units (MVHR) are a good option for new build projects with extremely good air tightness, but they are not suitable for refurbishments, and they do not offer the scale of energy use reductions that are required for a zero-carbon home.

 The single biggest factor that all users can take to reduce energy usage is by reducing the temperature we heat and cool our homes, which is best done through insulation and the provision of sustainable heating and cooling options such as air and ground source heat pumps.

Speak with our team to enquire about your own project.