Paul Bennett, registered professional energy consultant with the Energy Institute and Executive Chairman of BSSEC, looks at the technologies available for electric heating and the building regulations you should be aware of…
As a technology, electric heating has been with us since the invention of electricity in the late 1800’s with the first available electric heaters being used in the 1900’s. Electric heating has developed greatly over the last 115 or so years, from electric resistive heaters that have been used in panel heaters, night storage heaters, radiant heaters to warm air heaters and more complex heat pumps.
At the same time, the way electricity is generated has changed dramatically from coal-powered electricity generating stations, to gas and nuclear and now onto greener hydro, wave, solar and wind-powered methods.
Electric heating is a controversial choice to heat a building. On the one hand, it is seen as the most carbon intensive method to provide heat for thermal comfort and the most expensive to run. When compared against gas heating, electric heating causes carbon dioxide emissions that are approximately 2.7 times higher, and energy running costs are approximately three times higher. However, owing to cleaner and greener methods to generate electricity, electric heating can have zero-rated carbon emissions. Green electricity can also benefit from government subsidies.
Technology has moved on tremendously, and electric driven heat pumps can dramatically reduce the carbon dioxide emissions and energy costs further owing to their high efficiency – termed as Coefficient of Performance (CoP). The CoP rating is the multiplier of input energy to the heat output. A CoP of 2 would mean that, for every unit of electrical energy input, twice as much heat output can be achieved. The seasonal CoP rating for an air source heat pump in a heating mode is typically 2.5. However, if the heat pump takes its heat from a more stable source than the air, for example the ground, then the efficiencies improve to around a seasonal CoP of 4.
What do the building regulations say about electric heating?
Part L2 of the Building Regulations requires that the actual Buildings Emissions Rate (BER) is determined using software and is compared against a building regulation compliant Target Emissions Rate (TER). In order to pass, the BER must be lower than the TER. The TER is based upon a notional building specification that typically includes standard thermal resistivity ‘U values’ for elemental constructions (e.g. roof, wall, floor, and windows) and a building air permeability standard that restricts air leakage from buildings.
In terms of systems, it assumes a heating efficiency (gas heating and hot water) of 91%. Heating is only one of all the building services that consume energy and systems such as lighting, ventilation and cooling collectively make up the TER. So it is important to understand that the heating system is only a part of the overall TER.
The choice of heating impacts the whole BER and can therefore affect the choice of other building services. This is the concept of the trade-off. For example, a highly efficient heating system can enable the provision of a lower efficient ventilation system to achieve compliance. Most designers would prefer to opt for the highest efficiency choices – where the budget can afford the best systems.
The Building Regulations are technology neutral and do not require that any specific heating system be provided. However, these regulations do recognise that low and zero carbon options exist and can help.
These include co-generation (using Combined Heat and Power (CHP) techniques), district heating (from a centralised heat network that feeds many buildings, typically from biomass or CHP), energy from renewable sources (including solar, geothermal water, biomass, biogases) and heat pumps.
As far as the Building Regulations are concerned, the best choice for a compliant electric heating system, is whether it is going to be a form of heat pump and whether it being air/water/ground source. There are also options for using heat pumps to recover waste heat.
Taking technology and legislation into account, in my personal opinion, electric heating using heat pumps that are fed from green energy is the ideal heating solution. It can be zero carbon and very efficient (with seasonal CoP’s at 4), meaning that running costs can be cheaper than gas. They can also attract Renewable Heat Incentives making the business case quite attractive.
Looking to the future and thinking about how we heat our buildings in the UK, my own prediction is that, as battery technology continues to improve at a dramatic rate, we will see some very clever takes on the simple storage heater design that are linked to heat pump designs. Watch this space!
Paul Bennett is a Chartered Engineer, Chartered Director and Executive Chairman of BSSEC. He is an approved ESOS Lead Assessor and accredited with the Energy Institute on its Register of Professional Energy Consultants. ■
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Building Services Sustainability & Environmental Consultancy (BSSEC)
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