CHP FAQ: Best practice utility integration
We ask ENER-G experts the questions you want answered. This month, we’re talking about utility integration and local site connections.
How much disruption to heat and power supplies will there be from integrating the CHP equipment and connecting to utilities?
The CHP generated electricity supply is connected to the main site power distribution board behind a dedicated breaker. This means that the equipment is isolated until it is ready to use. No interruption to site electricity supplies would usually be expected during installation or commissioning.
Connection to the gas supply should also be straightforward as long as an appropriate isolatable connection point is available. No interruption to supply would usually be expected.
Site infrastructure may need to be upgraded before CHP installation. This might include expansion of the main site power distribution board, extending gas supply pipework, or modification to existing equipment and hot water circuits. Typically, this can be achieved with minimal disruption to supplies.
It is possible that some site-specific factors could require an interruption to supplies. These can be identified and planned for as part of the site preparation works.
Is it possible to store surplus heat when demand is weak?
It is possible to store heat in hot water storage tanks, but the capacity to store more than a few hours of supply is rarely practical or economical. Once any storage capacity is used up, surplus heat is vented to the atmosphere – typically through external radiators.
Venting heat is inefficient and prolonged operation under these conditions undermines the economic viability of the CHP. When sizing the system, it is important that it is designed to meet the base-level demand for heat, so that minimal wastage occurs.
During warmer periods, it is possible to utilise the surplus heat to drive chillers via a trigeneration or Combined Cooling, Heat and Power (CCHP). Here, absorption chillers use heat to cool water that can then be fed to a cold water circuit serving refrigeration and cooling systems, such as chilled water air conditioning.
Whose responsibility is it to acquire certifications and approval for utility connections?
Connections, approval, regulations and adherence to applicable legislation are all site specific issues. It is the responsibility of the site management to comply with all requirements and obtain the necessary approval and certifications, however reputable suppliers can often support and advise on this process.
How can a CHP system meet strict NOx limitations in low emission zones?
Conventional CHP can reduce NOx emissions by using a catalyst that facilitates a chemical reaction to reduce NOx to O2 and N2. This can be achieved by the addition of a catalytic converter (CAT) or a Selective Catalytic Reduction (SCR) system.
CAT or SCR systems add to capital and operating costs. They also have a large footprint which can require additional capital investment on equipment housing.
An alternative is to install a CHP system that has been designed to produce very low NOx emissions. A range of 'ultra-low' NOx emission CHP systems is available to use in locations with strict limits. Emission levels at 50mg/Nm3 @ 5% O2 which is about 50% of the strict NOx emission limits set by the Greater London Authority (GLA) Sustainable Design and Construction Guidelines and the most stringent BREEAM criteria.
The advantage of installing an 'ultra-low' NOx emission CHP is a reduction in the capital investment, physical footprint and the running costs incurred, when compared to a standard CHP with an external catalytic system.
Can CHP be used to meet intermittent demand?
CHP is designed to provide a constant amount of electricity and heat. Regular starting and stopping of the system can reduce the lifespan of the equipment and undermine the economic case. That said, some CHP systems can offer a limited degree of flexibility in output, but it should be understood that efficiency declines and savings are reduced when it is not operating at full capacity.