Retrofit & Renewables

March 17, 2023

We have been working on a number of retrofit projects as a practice which is rewarding work and inspiring to see existing homes upgraded.

As our blog post on 3rd March discussed, we always propose that clients focus on a fabric first approach.

We been having a number of conversations with companies that install renewable heating solutions and 'heating our homes currently accounts for a huge 13-14% of the UK’s total carbon emissions'(1) so it's an important area for architects to address and engage with.

In the new homes that we design, we almost always specify ASHP with thermal stores and PV panels if budgets allow. In some extensive retrofit projects we are also proposing similar systems for heating & hot water. The information below sets out some of the key principles and rough costs associated to upgrade to a full electric system. These estimates depend on the size of the home, what it's made from and other factors.

Most traditional gas heating systems have been designed to run water through their radiators/UFH at 65/80oC whereas the much more efficient low temperature ASHP pumps run at 45oC. ASHP typicality supply heating at 45oC and hot water at 55oC. Therefore it is often necessary to upgrade more than just the primary heat source (boiler to ASHP). This typically means a full upgrade to an existing heating system that currently relies on gas. We have recently received quotes for such upgrades that estimate: £12.5-£15k for the heat pump and a domestic hot water cylinder and up to £16-£18k to include the other upgrades necessary. There is no VAT for Energy Saving Materials as this has been recently reduced to 0% VAT.

The upfront cost is quite significant. For a comparable three bedroom home, having a new gas boiler system installed would be in the region of £6000. However electric heating is the way the industry is going and a new gas boiler installation now may mean a replacement sooner than the life of the boiler and a doubling up of costs.

The advice we have been receiving from suppliers is, 'if you do install a new gas boiler, ensure that the radiators are specified to be compatible with a future upgrade to an ASHP'.

There is also currently a grant available of £5,000 to support the transition from gas to electric. However in relation to retrofit projects the grant is not applicable until any outstanding recommendations for loft or insulation has been done. This again pushes a fabric first approach. Reduce demand requirements first.

An ASHP combined with a Solar PVArray (typically a 4kW / 12 panel) installation is a good combination with an ASHP. Prices we have received for these are around £6-£7k depending on the technology used.

There is no longer a Feed in Tariff available but some energy providers, such as Octopus Energy are providing a Smart Export Guarantee payment and will buy back any excess electricity that you export at around 5.5p per kW. PVs would expect to see a rate of return on investment at around 6-10% but this is dependent on location and orientation and is site specific.

Another good option if a solar PV array and an ASHP is proposed is to use energy diversion equipment that re-directs any excess solar energy (PV electricity) that isn’t being used by the home an occupants at the time directly into the hot water tank, reducing the demand on the ASHP and heating your hot water by the sun for free. This extra costs around £595.00 as part of a solar installation so is relatively cost effective.

Battery Storage Systems is something that some of our clients are considering as a way to capture the energy produced by the solar array that can then be utilised later in the evening. However this adds quite significant additional costs. We have recently been quoted in the region of £5.5-£9k depending on the technology used and the size of the storage. Eg: Storage systems from SolaX, GivEnergy and Huawei providing 3.5-10kW capacity whereas Tesla Powerwall 2 storage system have a capacity of 13.5kW.

It is necessary to check the capacity of the local electricity network as depending on the systems proposed it may be necessary for the local energy supplier to reinforce the network to allow your connection to be made.

1. https://www.goodenergy.co.uk/products/heat-pumps

2. Thanks to ecoNRG based in Modbury, Devon for the data

Image credits:

https://www.dysonenergyservices.co.uk

https://www.premierconnections.co.uk

https://www.solarguide.co.uk