Combined heat and power (CHP)

What is Combined heat and power (CHP)?

CHP is a system that takes the heat from exhaust gases that are produced from a generator, and uses them to heat your household for heating and hot water. Another system that can be used is in conjunction with water cooled generator engines. This system transferrs heat to a secondary water circuit which is then used to provide heat to your home and your hot water supply.

How does CHP work with generators when an engine contiunes to run even when heat is not required?

The heat exchangers have stainless steel tubes, tube plates and shell and cast iron end covers. In order to make sure that they are always full of water, they are to be installed with the water connections on top. This ensures that there is always a flow of water throughout the heat exchanger, even when staring the generator from a cold start.

Equipment that provides an automatic shutdown through the use of temperature probes should be utalized inside the exhaust heat exchanger and the engine.

In the unlikely event of a tube leak occuring, the heat exchanger should be installed below the level of the cylinder head to prevent any water from leaking back into the engine.
  air cooled chp system 1

The diagram above (System 1) shows waste heat recovery from an engine and alternator. This setup consists of a shell and tube engine water/secondary water heat exchanger. This is for transferring heat away from the engine water to the secondary water circuit, and also features a radiator that is utalised for dissipating all the heat if it is not required for any useful purpose. The radiator should be slightly larger than would be expected on a normal system. This is due to the additional heat produced from the exhaust gas heat exchanger.

Two by-pass thermostats are shown in the diagram above. 'A' set is at a higher temperature of around 90°C, and a second set 'B' which is set at a lower temperature of around 80°C. When the engine is cold the water will by-pass the radiator and the engine water / secondary heat exchanger. When the heat of the engine water reaches the setting of 'B' (80°C) it will continue to by-pass the radiator, but will now also pass through the engine water / secondary water heat exchanger.

If the heating requirement is not enough to equal out the temperature required for the engine water and it continues to rise, at 90°C (setting 'A') the thermostat will open and will pass engine water through the radiator.

Please note that if the engine is driving a heat pump and is stopped when there is no heating requirement, a radiator is not required and an installation can be arranged as shown in diagram shown below.

How does CHP work with generators when there is no heat requirement due to a heat pump stopping it?

This type of installation can be used with one of our combined heat exchanger/header tank assemblies for transferring heat from the engine water to the secondary water circuit.

With this setup, an automatic engine shutdown system should be utalised with a temperature probe inside the shell of the exhaust gas heat exchanger and the water outlet from the engine.


Please call us on 01270 509 296
for more information on CHP.

  air cooled chp system 2