Four key things to consider when specifying installing Combined Heat and Power

1) Load Mapping
The most effective way to design a CHP system is to align the electrical output as closely as possible with the load of the application. A CHP cascade can track electrical load to a lower output when there is a reduction in demand, but this can also threaten efficiency levels. The full benefit is only realised when the number of hours that the system runs at full load is maximised, so having modules within a cascade tracking electrical load to lower outputs shouldn’t always be seen as the best option.

In the event there is no demand for heat and little financial saving potential, the maintenance costs of a multi-module cascade would make it uneconomic to operate.

A single module system can modulate both electrically and thermally to 50 per cent of the load. This may not be as large a reduction as with a three module cascade, but often when having a system designed to modulate for long periods, the cost generally far outweighs the benefit.

2) Plant Space
Careful planning of a plant room’s layout is needed before investing in CHP. A system of multiple CHP modules requires more plant space. Each module also requires a connecting buffer vessel and a certain amount of clearance to be able to operate to its design potential.

3) Standby
A key benefit of multiple module CHP systems is that if one unit fails, you can still rely on the remaining units to deliver a supply of heat and power. That said, the reduced collective output of a system where one module is down limits the financial gain of the system, as the capital cost of two or more units plus two or more maintenance contracts would result in a significantly reduced payback.

Manufacturers like ourselves offer a remote CHP monitoring system to observe and maintain CHP systems, responding immediately if a faulty connection occurs. CHP downtime can damage financial and carbon savings, but remote monitoring reduces this risk and offers stakeholders peace of mind when making this large scale investment.

4) Installation Cost
A suitably-sized single CHP module boasts the fewest complications in terms of the time and cost involved in the installation so is often the most cost-effective option. The delivery and installation of one module means that only one set of gas, electrical, BMS, and flow/return connections needs to be made, and only one meter required, so the installation and commissioning procedure should be straightforward.

Multiple units require more supporting equipment so take longer to install and have added labour costs. For example, a system including three CHP modules would need three of each connection to be made, three meters to be fitted, and three commissioning procedures to take place.

It is important to consider the pros and cons of single or multiple CHP systems before their design and installation, to determine which is most suitable for a given project. Many consultants and contractors tend to favour a cascade of multiple units but a single CHP module can be a more attractive option in terms of installation, maintenance, and that all-important payback period.

Ben Richardson, Commercial Technical Consultant at Bosch Commercial and Industrial