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Integrating CHP for optimum carbon reduction
It’s important to ensure that CHP units will integrate easily with other technologies and systems. Ian Dagley, general manager at Hoval, discusses the importance of electrical power output and the significance of the EREC G99 standard
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f the UK is to meet its carbon reduction targets, we need alternatives to the traditional arrangement of locally sited gas-fired boilers and electricity from remote, inefficient power stations to run our buildings. In fact, we need to deploy a range of different technologies to achieve carbon net zero. Renewable energy sources – especially wind and solar –already play an important role and will do so increasingly as the renewable infrastructure continues to expand. Nevertheless, when the wind stops blowing and the sun is obscured by cloud, we need to have suitable back-up sources of electrical power to ensure security of supply. Solar thermal systems also need to be backed up for the same reasons.
Currently, most electricity back-up sources are fossil fuel power stations that waste the heat they produce and are subject to major distribution losses. Thus, there is a strong argument for increased local power generation close to the buildings where the power is being used. Combined heat and power (CHP) is a key element of such a strategy, generating power alongside public distribution networks. Consequently, it is vital that the CHP units selected can be connected to the electricity distribution infrastructure and this is where EREC G99 comes in. Issued by the Energy Networks Association, EREC G99 replaced the G59 standard and ensures harmonised network standards (Requirements for Generators) are incorporated into Great Britain’s distribution and grid codes for CHP and other power generators with capacities between 0.8kW and 1MW. As a result, specifiers can be assured that G99-compliant CHP units meet all of the technical parameters and considerations relating to connection to the networks of licensed electricity distribution businesses throughout Great Britain. A CHP which has been tested to ensure that the design meets the relevant technical and compliance requirements of EREC G99 can be placed on the
Hoval’s PowerBloc CHP
Energy Networks Association’s type test register. The register gives specifiers access to a list of products that hold fully compliant status to G99, giving further assurance the correct product is selected. Fully compliant products will not require on site witness testing by domestic network operators. A major efficiency benefit of CHP is that it generates both heat and electricity, though you can’t have one without the other. The design of the system should therefore ensure maximum run-times for the CHP to maximise power production – as well as optimising the efficiency of heat production. However, CHP is typically used alongside other heat sources, possibly serving a heat network from an energy centre. Ensuring maximum run-times for the CHP therefore necessitates an integrated system that uses each heat source in the most efficient way. For example, the CHP could be sized on thermal output to achieve a constant base load throughout the year, with the power generated by a G99- compliant CHP unit being used onsite, exported to the grid or both. Surplus heat in summer can be used to drive an absorption chiller to generate chilled water for air conditioning. Sizing the CHP to meet the base heat load through the year is often a good way to maximise run times.
As noted earlier, excess electrical power can be exported to the grid but there is growing interest in
Combined heat & power
Ian Dagley, general
manager at Hoval
A plant room with mixed heat sources
storing it locally to increase system resilience and security of supply. Battery storage is one option, or it may be more cost-effective to use surplus electricity to pre-heat domestic hot water via an immersion heater in a cylinder. In this way, less heating is required by other heat sources to bring it up to the required storage temperature.
With so many options available the control of this mixture of technologies becomes increasingly important. Indeed, failing to establish precise control will prevent optimum efficiencies, yet experience has shown that controlling multiple heat sources with different controllers is extremely difficult. Fortunately, the latest generation of heating controllers is able to effectively handle a range of heat sources as single units or in cascades to optimum effect.
All of these parameters, alongside the specifics of the project, will feed into the best design that uses the most suitable technologies to maximum effect. It seems clear that G99-compliant CHP will continue to be at the heart of these designs.
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