Overview — biomass vs heat pumps
Pete Downes put together this summary as a handout after a CPD event we presented for a group of surveyors and architects at The Abbey Group conference centre on Preston Road, Yeovil, on Tuesday 1st of March 2016, about Eco Homes/Renewable Heat Incentives + Tariffs.
Renewable Heat Incentive
The Renewable Heat Incentive (RHI) is a government scheme set up to promote the use of renewable fuels in this country, such as wood chip and wood pellet from sustainable sources burnt by biomass boilers, as well as highly energy efficient technologies such as ground source and air source heat pumps. It is available to businesses and individuals, and landlords, and private investors, but not to building developers, though a centralised or de-centralised plant can be installed that does qualify for the RHI.
Suitability of technologies
In broad brush terms, biomass boilers are ideal for use in old constructions where fierce heat is required that would otherwise be provided by gas or oil-fired boilers. They are also suitable for use in new builds, though on a small domestic new build property it is far less practical in terms of ROI and available space for the installation and fuel supply. Biomass can also provide attractive returns when installed as a heating plant servicing multiple dwellings via a district heating main. Significant savings can be achieved over the cost of multiple gas connections, and where a central plant room serves a block of flats no special considerations have to be given to the routing of the heat main, which would apply to gas services. Ongoing costs relating to serving and maintenance are also reduced over the cost of servicing multiple oil or gas boilers.
Heat pumps are generally the better choice for one-off new build houses where low grade heat is sufficient to heat the property via underfloor heating, fan coils or oversized radiators. Both ground and air source heat pumps can be installed on individual properties, or as a centralised plant serving multiple dwellings via a district heating main, with much the same benefits as biomass, though with the added benefit of even lower maintenance costs.
Another interesting concept is where the ground array containing the cold brine (glycol mix) is taken to each property via a simple main in much the same fashion as the standard district heating main. A very small ground source heat pump can then be installed in each property (some available that fit under kitchen units), thus minimising heat main losses and providing a virtually maintenance free source of heat for the property.
• Plant room or outbuilding of sufficient size to house boiler and buffer
• Adequate space for a fuel store/silo
• Route for the flue with sufficient height to evacuate and disperse the smoke at start-up
• Flue may require planning permission in certain areas
Ground source heat pump:
• Adequate electricity supply
• Sufficient land to serve the ground array, or boreholes
• Consideration must be given to low grade noise and vibration
Air source heat pump:
• Adequate electricity supply
• Sufficient space around the heat pump to prevent recycling of air
• Consideration must be given to low grade noise and vibration – more than GSHP
• Must be sited away from boundaries
• Planning permission required if there is another heat pump nearby or wind turbine
Added benefits with heat pumps:
• Can be linked to solar PV installations to achieve even lower running costs
• Some can be reversed during hot weather to provide cooling
• Low servicing and maintenance requirements
Energy efficiency in buildings
Key points for the design of new build properties:
• Build with high internal thermal mass
• Smaller north facing windows
• Larger south facing windows (solar gain)
• More underfloor heating pipe = lower running temperature = higher heat pump efficiency = lower running costs and lower CO2 emissions
• Heating pipe in screed upstairs and down
• Link heat pump to PV solar panels
• Use cheap rate electricity plans such as Economy 10 to run heat pumps
Future of the Renewable Heat Incentive
The crux of the latest government announcement is that there will be no change to the current arrangement until spring 2017.