Green Homes Network

As a sustainability professional, David S. wanted to improve his 70-year-old detached home's energy performance certificate (EPC) to an A rating. He bought the house in Pittenweem, Fife, in 2005 and began by replacing the gas heating system and installing insulation, which improved the building to an EPC D rating.

Over the years, he made more and more improvements to finally attain the desired A rating. This included several renewable energy technologies, such as an air source heat pump via radiators and underfloor heating, a biomass stove, solar PV and electricity storage, an electric vehicle and chargepoint (installed by Everwarm), and solar water heating. It also included many energy efficiency improvements, including mechanical heat recovery ventilation, A-rated appliances, draughtproofing, low energy lighting, triple glazing, and a smart meter.

Keeping the heat in

From 2005 to 2010, David spent around £10,000 on the following insulation measures:

·       Blown cavity wall insulation installed through a utility company scheme

·       rigid polystyrene underfloor insulation between the joists

·       room-in-loft insulation of 75mm Kingspan between the roof rafters, with 50mm Kingspan across the rafters

·       Warmcell loft insulation (David advises: do not use it if you ever think you may go into the space again, as when you move it, it gets everywhere).

The insulation was all self-installed except the cavity wall insulation. David also opted to triple glaze five windows and the front door for £16,000.

Combining a heat pump with solar thermal

In 2008, David had a solar thermal system installed – 2m² AES flat panel with polycarbonate cover (which generates an average of 1kWh heat per hour) with Resol controller – which took three days and was fitted by Glendevon Energy.

In 2021, David saw the Department for Business, Energy and Industrial Strategy's (BEIS) Electrification of Heat project on Facebook, which offered free heat pump installation. He applied for it and was accepted, which resulted in having the following installed by McInnes Group:

·       Vaillant aroTHERM plus 7kW air source heat pump

·       Joule twin coil 200L hot water cylinder

·       Stelrad Elite K3 radiators

·       Sontex Supercal Heat Meter

·       Eastron electricity meter

·       Passivliving data gateway to send energy data to BEIS as part of the project.

It took four days to install everything – during two of which the home had to be vacated – and cost £12–15,000, which was fully funded through the BEIS Electrification of Heat project.

The contractor's quotation for this project included expected annual heat losses and running costs. The contractor quoted a heat demand of 22,000kWh, which gave a running electricity demand of 6,800kWh. However, by using his gas consumption over the previous years, David realised this quotation was an extreme worst-case scenario, which accounted for continuous heating at a standard room temperature based on educated assumptions about the fabric of the building. David therefore advises that before installing a heat pump, you should improve the fabric of the building first. After one year, it was clear the heat pump only needed to deliver 7,200kWh of heat, using 2,000 kWh of electricity (less than 30% of quoted electricity demand).

Due to the lower heat flow temperature, the new radiators installed as part of the new heating system were three times the size of the existing ones. A new electrical sub-distribution board was installed as well, along with a SMETS2 smart meter installed by David's electricity supplier. David had previously intended to install electronic controls on all the radiators to allow for zonal heating, but after some research opted for a single Vaillant control system instead, which works well.

When the air source heat pump was installed, some changes had to be made to the existing solar thermal system, which comprised a 200L open-vented hot water cylinder, with an additional coil for a back boiler in a 6kW Hunter Herald wood-burning stove and an immersion heater. The hot water cylinder was replaced with a pressurised cylinder which was not open-vented, meaning they had to remove the back boiler from the wood-burning stove. The installer also disconnected the existing solar thermal system but would not reconnect it, so David had to call out the original contractor, which cost £600. However, David says this was worth it as solar thermal provides the majority of his domestic hot water.

Generating electricity from the sun

In 2022, David decided to look into solar PV and battery. After extensive online research, he got four quotes from different suppliers, and chose EVi, a small, Fife-based installer, who he would recommend. The installation took two days, cost £10,000, and included the following:

·       10 Trina Vortex S 400W panels with Tigo optimisers totalling 4kWp

·       GivEnergy 3.6kW hybrid inverter

·       GivEnergy 8.2kWh LiFePO4 battery storage system

The solar PV hybrid inverter produces up to 3.6kW of electricity, but the battery can only discharge at 2.5kW. In summer, the solar powers the house and charges the battery for use after the sun goes down. In winter, the battery is charged on cheap-rate electricity and used to run the house during the day.

An energy conscious household

David is now much more conscious about how much electricity he uses. He has an electricity meter and heat meter that measure the electricity in and total heat out of the heat pump. In 2022, it consumed 2,020kWh electricity and produced 7,162kWh of heat. In July, the solar thermal system produced 94% of all the hot water used, and 35% in December, meaning 67% of his annual hot water is produced by the solar panel.

After installing all these technologies, David received not just the EPC A rating he desired, but also a very warm, comfortable home and drastically reduced energy bills. Based on his January 2023 energy rates, he is looking at savings of £1,210 annually. The heating system flow temperature is only at 25–35 Celsius, which keeps the house toasty, and he barely uses the wood-burning stove any more. He is very happy that the house's carbon footprint is down from 2.7 tCO2e in 2020 to 0.6 tCO2e in 2022, and believes that if he sold the house in ten years, an EPC A rating could add to its value.

And David's not stopping yet: he's now self-installing a mechanical ventilation heat recovery (MVHR) system, which, although proving difficult as it requires ductwork throughout the house and holes in ceilings, he believes will be worth it. PAUL Heat Recovery Scotland designed the system and will commission it when it's completed.

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