There are some great options for getting low-carbon heat and energy into your home, but which technologies are best, and what are the limitations? Darren McMahon, marketing director at Viessmann, shares a brief overview
The recent announcement by the government that no gas or oil boilers will be installed in new build properties from 2025, means switching to renewables is well and truly back on the agenda. If the country intends to be carbon neutral by 2050, then certainly, we are going to have to heat our homes differently. Already, we are seeing a surge of interest in training for our non-fossil-fuelled heating systems.
This really matters because the burning of fossil fuels to service buildings (providing space-heating, hot water, air-conditioning, and electricity for light and appliances) is a major source of greenhouse gas emissions. But of all the alternative technologies that derive energy from naturally renewed resources, which to choose? And in addition to reducing your carbon footprint and energy bills, could you also be entitled to receive payments through a government-funded incentive scheme?
If you are thinking of replacing or supplementing your current boiler, or are planning a new-build or refurbishment project, renewable technologies could be ideal. As a rule of thumb, off-gas homes have the greatest potential to save on fuel bills and decrease carbon emissions, but homes with access to mains gas can also benefit. It is crucial, however, to plan carefully, and to be aware of the various technologies’ requirements.
Choosing the best renewable technology
Choosing the best renewable technology for your home depends on the type of energy you rely on (gas, oil, LPG, wood, coal or electricity) and the quantities you use for heating and hot water versus the amount of electricity you use for lighting and appliances. A qualified domestic heating engineer will make heat-demand calculations to ensure you get a correctly-sized heat generator. The engineer will also advise on any hot water storage needs if you are moving to a low-temperature heating system.
The renewable technology that performs most similarly to gas and oil boilers, is the biomass boiler (and stove). These provide (high temperature) heat to central heating systems and hot water boilers through a process of direct combustion by burning logs, pellets and wood chips from quick-growing trees. Biomass boilers can be ideal for homes with big heat demands, but it is worth remembering that they tend to be large and will also require space for storing the fuel.
Ground source heat pump
A much more sophisticated solution and one increasingly favoured by the government is heat pumps. They can operate as a standalone unit or in conjunction with an existing heating system. A ground source heat pump (GSHP) extracts natural heat from the ground, using geothermal probes or collectors buried in your garden, to provide heating and hot water. This technology works well all year round because under the surface the ground remains at a fairly constant temperature. Ground-source heat pumps can also provide a cooling function during spells of hot weather by transferring heat energy from the home into the cooler ground. Underfloor heating is usually necessary to get the best out of this technology (if this isn’t possible, use large radiators), and good home insulation is vital because heat pumps generate a relatively low flow temperature and are most efficient when doing so.
Air-source heat pumps
Air-source heat pumps (ASHPs) work by taking heat from the air surrounding the home. On the reverse principle to a refrigerator, they use a fan to draw-in the ambient air and transferring this to a heat exchanger (evaporator) in the heat pump. Refrigerant circulating inside the pump changes its physical state and evaporates, then a compressor makes the refrigerant steam usable for heating and hot water systems. This type of pump can also serve as a cooling system on hot days. Underfloor heating is again preferable (or large radiators) and good home insulation essential.
With ground-source and air-source heat pumps, hot water has to be stored in large cylinders and these allow the heat pump to work for longer periods, reducing cycling on/off and increasing longevity. But both types of pump eliminate the need for fuel deliveries and storage, require minimal maintenance, and have a long lifespan. Air source pumps are easier to install, particularly for retrofit.
There are two more options, and both harness the free energy emitted by the sun. Solar thermal uses the sun’s rays to provide domestic hot water and is typically supported by a boiler or immersion system, to ensure the home has hot water whenever needed; solar photovoltaic (PV) panels convert the sun’s rays into electricity to power lighting and appliances, including heat pumps. PV modules can also be combined with power storage units to give you greater independence from the grid.
Power is nothing, however, without control. This is especially true of renewable technologies because they differ greatly but may have to work together. A large country house, for example, might have an integrated heating system which uses solar thermal and a ground source heat pump with a gas boiler for back-up. When renewable technologies are combined, the right kind of control system will decide which energy source is the most efficient to use at any time.
Get paid to go green
Ground source and air source heat pumps, biomass boilers and stoves, and solar thermal panels are all eligible for payments from the Domestic Renewable Heat Incentive (Domestic RHI), a government-funded scheme designed to help the UK reduce its carbon emissions and meet renewable energy targets. This pays, quarterly over a seven-year period, a set amount for every kilowatt-hour of energy produced. The Ofgem website specifies the permissible uses of the heat produced and contains a product eligibility list.
At the same time as qualifying for regular Feed in Tariff (FiT) funding, generating power at home will also dramatically reduce the amounts you have to pay an external supplier for electricity. This delivers desirable financial savings, but better still, you will also be doing your bit to help save the planet.
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