CHP FAQ: Drafting a Quality Specification

Posted by John Hyde on 28-Mar-2017 11:00:00

We ask the ENER-G experts the key specification questions for optimal CHP projects.

Will it always be possible to connect CHP to the grid?

In the majority of cases a grid connection is feasible, however, there are parts of the country where the grid has little capacity to accept any connections. Consult with the Distribution Network Operator (DNO) at an early stage to determine whether there is capacity for a connection.

How should a thermal store be sized?

A thermal store should be able to store all of the heat from the engine in a period of 1 to 1.5 hours, which may require volumes of 10,000 to 15,000 litres. The amount of heat can be estimated from the hourly output in thermal units and the difference in the flow and return temperatures.

Why should CHP not be sized purely on the basis of building regulation compliance calculations, such as SAP and SBEM?

Both SAP and SBEM calculations can provide a useful guide, but they only consider the historical monthly heat and power requirements, rather than the hourly demand required for accurate sizing. Failure to take the full energy demand requirements into consideration could result in an oversized CHP unit, which will not operate efficiently.

Can CHP be the sole heating appliance for a building or development?

Normally this is not the case. A gas-fired CHP engine running full-time will have some maintenance shutdowns each year: other heat sources will be required to cover those periods. Also, electricity and heat demands vary from day to day and by season, with a CHP sized to the baseload (as per best practice) supplementary heat or power at may be required peak times.

How can the need for catalytic treatment of exhaust gases be assessed?

The need for treatment of exhaust gases depends on the emissions from the CHP unit, the dispersion achieved by the chimney and local environmental conditions. Catalytic treatment is likely to be required in areas of poor air quality, where a Local Air Quality Action Plan is in place. Alternatively, ultra-low NOX CHP technology is available without the need for catalysts. 

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Topics: CHP / Cogeneration

John Hyde

Mechanical & Manufacturing Engineer with over twelve years’ experience in the UK, USA & European Low Carbon Technology industries. Based in London, John works with consultants from early feasibility stages to investigate variables which influence CHP design. Endeavouring to increase awareness of the economic implications and best practice design of CHP through presentations of CPD seminars.