Reducing Greenhouse Gas Emissions From Energy Used In UK Homes

Recent climate change protests by Extinction Rebellion are a good prompt to take a look at energy consumption in the home and how to reduce Greenhouse Gas emissions. This article’s focus is on domestic central heating systems, responsible for around 80% of a typical home’s energy consumption, and how individuals assisted by the UK government can make a difference. The financial impact of particular choices will be the focus of a future article.

The challenge is explored using an example “typical” three bedroom house, with total floor area 80m² which produces 3,800 kg of greenhouse gases each year. The following steps look at the way a homeowner can reduce these carbon emissions to below 1 tonne (1,000 kg) per year:

1. Reducing the energy required for space heating, by improving the fabric of the building to reduce heat loss
2. Improving heating system efficiency, by switching from a gas boiler to a heat pump
3. Greater use of zero carbon energy sources such as renewable electricity and “green” hydrogen.

The conclusion is that an individual homeowner can make significant differences by improving the energy performance of their own home. This could involve an EnerPHit upgrade and a switch to low carbon forms of heating, such as an Air Source Heat Pump, and away from fossil fuel heating using natural gas. These solutions use technology and building techniques available to homeowners today and would result in the home’s annual carbon emissions falling below 1,000 kg by 2025. This figure could be achieved earlier if a 2.5kW peak solar panel array is also installed on the house roof.

Government needs to drive changes, by further reductions in Greenhouse Gas emissions from electricity generation and by encouraging the use of “green” hydrogen as an alternative to natural gas. This could help a home achieve close to zero emissions overall.

Government also needs to ensure that new homes built in the future have low carbon heating and are built to standards similar to PassivHaus, requiring much lower heating energy (of the order of 15kWh m² of floor area per year).

Let’s see how that conclusion is reached….

Where Are We Now?

Figure 1 shows that the typical 3-bedroom house uses 17,700 kWh of energy annually ¹, producing 3.8 tonnes of carbon dioxide equivalent ² (CO₂e). The majority of this energy use is natural gas for space heating (11,600 kWh) and water heating (2,500 kWh) with the remainder from electricity use for cooking and domestic appliances (3,600 kWh). Reducing the energy needed for space heating is the best way to reduce a home’s Greenhouse Gas emissions.

Focusing more narrowly on space heating, Figure 2 shows the annual energy demand for space heating in different types of houses.

A home built in 2009 to building regulations operating at the time requires around 9,300 kWh/year of space heating, 20% less energy than the typical house (11,600 kWh/year) and one built in 2019 would use around 52% less.

If a new home is built to the more demanding PassivHaus standard then annual energy use would be around 1,200 kWh, only 10% of the energy required for space heating in a typical house. There is also the option of refurbishing an existing house to EnerPHit standard (2,000 kWh/year), which is similar to PassivHaus but recognises the energy consumption compromises of upgrading rather than building from new.

Whilst newer homes require less space heating due to improved insulation and air tightness levels, the energy used for water heating and running appliances is about the same as a typical house.

How does you own home’s energy performance compare to the typical home? Explore this by trying Great Home’s Average Energy Consumption Calculator (opens in new tab).

Step 1: Reducing the energy required for space heating a home, by improving the fabric of the building to reduce heat losses

If you feel you should do your bit to help address climate concerns then upgrading your home to modern EnerPHit standards would reduce space heating energy use to 2,000 kWh/year and related carbon emissions by around 83%. There are significant costs associated with doing this (£400-£800 + VAT per m² of house floor area), which for an 80m² home would be £38,400 – £76,800 inc VAT. These costs can be lower if:

• A new house is being constructed with modern features built in to start with (which may increase costs by as little as £5,000)
• An existing house is undergoing a major refurbishment
• More modern windows and doors have already been fitted
• The heating system requires replacement anyway
• The UK government removed the 20% VAT rate on building work driving reduction’s in energy use.

The wide range of pricing is also because there are economies of scale when a whole estate is upgraded, or thousand of similar homes are being upgraded each year.

Figure 3 shows that, with an EnerPHit upgrade, energy demand for space heating would fall by 83% and overall energy consumed by the home would fall from 17,100 kWh per year to 8,100 kWh (-54%).

Step 2: Improving the efficiency of the heating system used to heat a home, by using a heat pump

Most homes currently have a condensing gas boiler fitted, which if properly serviced and maintained is likely to have an efficiency of around 90%. There are older boilers fitted in some properties, which have efficiencies closer to 50%, but these are not widespread. So to make significant difference, a different technology approach is needed. Fortunately there is an existing, well-established technology, already available to us: heat pumps.

Historically heat pumps have gained widespread use in appliances such as fridges and air conditioners and have gradually been developed for other purposes. In new applications they are designed to absorb heat from an external heat source and use it for space and water heating in the home. They are already becoming a popular heating option for homes without gas. By using the external heat, a heat pump can deliver more energy than it consumes to operate it: using 1 kWh of electrical energy can deliver around 3 kWh of heat ³ for space heating and around 2.3 kWh for water heating. The external heat could be taken from the:

• Air (from outside air)
• Ground (usually from a pipe buried in a horizontal trench or a vertical borehole) 
• Water (using a flowing river or open water)

Figure 4 shows that, by installing an Air Source Heat Pump (ASHP), the energy consumed for space heating reduces by 67%. Where heat pumps are used in combination with underfloor heating rather than radiators then efficiencies are higher.

The good news is that hot water can be heated in the same way, meaning that additional energy savings are achieved, although not at the same level as with the space heating system. This is because water heating requires a higher temperature to be achieved, upwards of a 55°C gain, and the ASHP is less efficient when delivering these higher temperatures. In comparison, space heating can be operated with lower temperature gains, typically 35°C. The average energy gains over the year are often described as the Seasonal Performance Factor (SPF) for the ASHP. The performance for water heating is lower at 2.3 than for space heating at 3.0.

Figure 5 shows that switching to an Air Source Heat Pump (ASHP), as an alternative to a boiler, reduces overall energy demand by 52%. By including an ASHP within the EnerPHit fabric upgrade, this can reduce overall energy use by 70%. This would reduce typical annual energy demand from 17,700 kWh down to 5,354 kWh. Switching to an ASHP means that all the heating energy will come from electricity and there will be no demand for natural gas.

You may wonder what the difference is between heating with gas and heating with electricity, in terms of greenhouse gas emissions. Latest figures (2018) show:

• Natural Gas: 210 grammes of CO₂e per kWh ^4,5
• Grid supplied electricity: 233 grammes of CO₂e per kWh

Figure 6 shows that carbon emissions for a typical house which switches to an ASHP fall by 49% overall to 1,934 kg CO₂e/year and if the home is upgraded to EnerPHit then carbon emissions fall to 1,188kg.

Grid supplied electricity is projected to fall to 41 grammes of CO₂e per kWh by 2035⁶ as the switch to renewable forms of electricity continues. So using electricity is probably the best way to go long term, if we want to reduce greenhouse gas emissions, especially as electricity also enables the use of highly energy efficient heat pump technology.

Step 3: Use zero carbon energy sources

Generally these are in the control of policymakers rather than a homeowner. However, for those not wanting to wait, installing solar panels may help a little.

Renewable Electricity From Solar Panels On The Roof

Electricity from roof top solar can make little contribution to home heating. Most solar generation is in the summer during the day whereas heating demand peaks in winter during the hours of darkness.

However it can play a part in supplying electricity for domestic appliances and cooking. A 2.5kW peak solar panel array on the roof of a house should generate at least 2,125 kWh/year of solar electricity. The profile of demand will usually mean around 60% of this is exported to the grid, with around 850 kWh (40%) used within the home.

As Figure 7 shows, this would reduce emissions on an EnerPHit upgraded house with ASHP and 2.5kW solar panel array to 752 kg CO₂e/year, a reduction of 495 kg CO₂e, and well below our target 1,000 kg per year. However, as emissions from grid electricity are projected to continue to fall anyway, the same result would be achieved by not installing solar pv panels and just watching for about five years as annual grid emissions fall. This re-enforces the view that the best option, if you wish to reduce carbon emissions, would be to invest in low carbon heating methods, such as heat pumps, and remove the need for a fossil fuel powered heating system in the home.

Renewable Electricity From The Grid

Figure 8 shows that already agreed policy interventions by government should cause Greenhouse Gas emissions from grid electricity to fall to at least the 41 grammes of CO₂e per kWh currently projected for 2035.

Ignoring the contribution from a domestic solar panel array, Figure 9 shows that, assuming 2035 electricity grid levels of carbon emissions, a typical house using an Air Source Heat Pump would have carbon emissions 89% lower than one that used gas for heating. If the house also had an EnerPHit upgrade then emissions would be 93% lower.

Converting Natural Gas Network To 100% Hydrogen

There is also talk of phasing out natural gas, with its built in carbon emissions, and converting the domestic gas grid to “green” hydrogen which produces no emissions. Green hydrogen can be produced either by the electrolysis of water on a massive scale, or potentially as a stop gap measure by using carbon capture on fossil fuels. This is possible, probably over a twenty year time frame and government should explore this as another possible technology option.

This would be a massive undertaking, due to the energy demand the hydrogen would replace. However, a project to explore this has been proposed by Northern Gas Networks. This presents a detailed engineering solution to convert the gas network in the North of England, covering 14% of the gas network, to 100% hydrogen over the 2028-2034 period. It includes inter-seasonal storage of hydrogen in salt caverns able to deliver 8TWh of energy and sequestration of 20Mt per year of CO2. (Read more about this project at the Northern Gas Networks website). Gas boilers and cookers would have to be converted or replaced.

Figure 10 shows that for a typical house in 2035 fitted with a 100% hydrogen gas boiler and using electricity at 41g CO₂e per kWh, then annual Greehouse Gas emissions at 148 kg CO₂e would be lower than the EnerPHit upgraded house heated with an Air Source Heat Pump shown in Figure 8. This assumes at least part of the gas network is converted to green hydrogen by 2035.

Supplying 100% hydrogen via the existing gas network could create the potential for hydrogen fuel cells in homes, to generate electricity for use in the home, especially at time of peak electricity demand, as an alternative to using the electricity grid. It may also permit the refuelling of hydrogen fuel cell commercial vehicles such as buses and HGV’s.

Conclusion

This article points out a variety of actions a climate conscious homeowner can take if they really want to contribute to reducing carbon emissions. By upgrading their home to EnerPHit standard and using an Air Source Heat Pump would reduce Greenhouse Gas emissions from the home by 93% by 2035. Converting the existing gas boiler heating system to an Air Source Heat Pump (cost circa £5,000-£10,000) would reduce emissions by 89% over the same time period.

For governments, a combination of decarbonising the electricity grid and replacing the natural gas in the gas grid with green hydrogen would cover the vast majority of UK homes where other energy efficiency improvements were not possible.

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Notes

1. Assuming the occupants use gas for water & space heating and electricity for lighting, domestic appliances and cooking.
2. The e in CO₂e stands for carbon dioxide equivalent as there are a variety of gases produced in the combustion of natural gas, and adjustments are made to calculate the overall impact of these gases in terms of carbon dioxide.
3. Currie & Brown (2018). Cost of carbon reduction in new buildings. Available at: https://www.cse.org.uk/downloads/file/cost-of-carbon-reduction-in-new-buildings.pdf
4. Assumes A rated condensing boiler. Data from
   Houses of Parliament (2016). Carbon Footprint of Heat Generation. Available at: http://researchbriefings.files.parliament.uk/documents/POST-PN-0523/POST-PN-0523.pdf
5. UK Government GHG Conversion Factors for Company Reporting. Using natural gas at 87.5% efficiency
6. BEIS (2019). UPDATED ENERGY AND EMISSIONS PROJECTIONS 2018