What is a heat exchanger?
A heat exchanger is a component that transfers heat from one liquid or gas to another without the two coming into contact. A thin wall of a conductive material such as stainless steel, copper or aluminium separates the flows, and heat passes through it from the warm side to the cold side.
Types
- Plate heat exchanger: a stack of thin, pressed plates with the two fluids flowing in alternate gaps. Compact and efficient; used in combi boilers, heat pumps and heat interface units.
- Coil or shell-and-tube: for example the coil inside an indirect hot water cylinder.
- Air-to-air: in MVHR units, usually a counterflow core.
- Ground heat exchanger: pipes in the ground exchanging heat with the soil.
- Shower drain heat exchanger: recovers heat from outgoing shower water.
Counterflow and parallel flow
In counterflow the fluids run in opposite directions, so a temperature difference remains along the whole length and heat transfer is greatest. Parallel flow is less efficient; crossflow lies in between.
Maintenance tips
- Limescale is the main enemy of hot water heat exchangers. In hard water areas, have them descaled or consider a softener.
- Sludge and magnetite in heating water block plate heat exchangers; a magnetic filter helps.
- Change MVHR filters on time to keep the core clean.
- Pressure changes: a heating system whose pressure keeps rising or falling may have a leaking heat exchanger; have it checked by an engineer.
Related terms
- Ground heat exchanger
- Central heating boiler
- Heat pump
- Heat recovery ventilation
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