How CHP works
A CHP system consists of an engine, generator, heat exchangers, and monitoring/control computers. (See Fig. 4) CHP systems can be designed to run on a number of fuel inputs, including natural gas, bio-gas, diesel and bio-diesel, depending on the economics and availability of fuel sources. Generally natural gas is the most readily available fuel and provides the best economics, while still dramatically reducing GHG emissions.
Figure 4. CHP Unit
The engines specified for cogeneration are heavy, industrial strength engines. They are designed for continuous operation, 24/7, throughout the year, with a 12-18 year life span. (Generally a 90% uptime is assumed, to allow for scheduled maintenance including oil, filter and spark plug changes.) Fuel is burned in the engine, to drive reciprocating pistons which turn the drive shaft and gears. These in turn spin a generator at 1200 to 1800 RPM’s to produce electricity. Heat exchangers capture the heat off the engine jacket as well as the exhaust pipe (or flue). This heat can then be used for domestic hot water, space heating, and even for cooling in tri-generation systems (described below). The automated control and monitoring systems are very advanced, in order to continuously optimize operation of the CHP unit in terms of fuel use, matching engine speed and electrical output to building load requirements, and monitoring over 200 operational parameters to ensure proper function.
Correct system sizing is critical to maximizing CHP system efficiency and ROI, since CHP systems are most efficient when there is a good match between electricity and heat produced by the unit, and the electrical and heating needs of the building. CHP systems are typically employed in larger commercial buildings or multi-residential facilities, where there is a significant heat demand. CHP installations that Nexus personnel have been involved with provide electricity and heat to hotels, apartment complexes, bank buildings, seniors’ residential homes, sports and recreation centres, and other commercial building types. CHP systems are also particularly well suited to provide heat and electricity to greenhouses, resulting in meaningful energy and financial savings