A combined heat and power (CHP) plant earns its efficiency by using the engine's heat - for district heating, greenhouses, hospitals or industrial processes - while it generates electricity. But heat demand rises and falls with the season and the time of day, while electricity may be needed all the time. When nobody takes the heat, the engine still has to get rid of it. That is the job of the emergency cooler, also called a dump radiator or table cooler: a radiator that rejects the unused heat to the air so the engine can keep running at full output.
Where The Heat Comes From
In a gas-engine CHP unit, heat is recovered from several sources: the jacket water of the high-temperature (HT) circuit, the exhaust gas through an exhaust heat exchanger, and often the first stage of the charge-air cooler. The low-temperature (LT) circuit - second-stage charge air and sometimes lubricating oil - runs too cold to be useful for most heating networks and is cooled by its own radiator in any case.
The emergency cooler sits in the HT side of the heat recovery circuit. When the heat consumer takes less than the engine produces, a control valve sends the surplus to the emergency cooler; when demand returns, the flow goes back to the consumer.
Sizing For The Worst Case
The emergency cooler must be able to reject the full recovered heat of the engine at the hottest design ambient - because the worst case is a summer day with no heat demand at all. It is designed for the engine manufacturer's heat rejection, flow and temperature limits, and its fans are usually speed-controlled so that they run only as hard as the surplus heat requires. Together with the LT radiator it can be combined into one LT/HT radiator casing, which saves space and pipework.
The Parts Around It
An emergency cooler works within a hydraulic system: pumps, three-way control valves, plate heat exchangers that separate the engine circuit from the heating network, expansion tanks and instrumentation. Delivering these as a coordinated package - a heating module or pump skid together with the radiators and plate heat exchangers - avoids interface problems on site.
What To Consider
- Control strategy - how the valve and the fan speed respond to falling heat demand, so the engine never sees a temperature spike.
- Glycol and freeze protection - an emergency cooler may stand idle in winter and must not freeze.
- Sound - CHP plants often stand close to the buildings they heat, so night-time noise limits matter.
- Corrosion and fouling - fin materials and coatings suited to the site, and access for cleaning.
- Installation - free air around the unit so the warm discharge air does not return to the intake.
The emergency cooler is the component that lets a CHP plant follow the electricity market rather than the weather. Designed for the full heat at the hottest ambient and integrated with the heat recovery circuit, it keeps the engine running whatever the heat demand. Read more about TECS solutions for cogeneration, or send us your project data.
