Return increase
A return increase is used in liquid-led heating systems to quickly reach or maintain the minimum temperature required in the heat generator.
function
For this purpose, a variable part of the (hot) flow medium is usually added to the (cold) return flow using a mixing valve . In this way, a favorable temperature for the operation of the heating system can be reached quickly. This can be useful to, among other things
- to prevent corrosive pitting and stress cracks in the heat exchanger due to condensate (protection against damage ), as well as to
- to achieve the optimum operational efficiency of the plant early on.
Applications
Boilers, stoves
This prevents that within the boiler steam from the hot gases to the cold to the heat exchanger to condense can; the necessary minimum temperature of components inside the boiler depends on the smoke gas dew point of the fuel (oil 47 ° C, gas approx. 59 ° C). In this way, the risk of corrosion inside the boiler is considerably reduced.
In the case of wood-burning boilers, it is also important that maintaining a suitable minimum temperature in the heat exchanger (normally 60 ° C) prevents the formation of glossy soot on the surfaces of the heat exchanger.
Older boilers require an external return increase, more modern boilers are either already built to be corrosion-resistant or have a built-in return increase.
Condensing boilers use the latent energy still contained in the flue gases through systematic condensation and have heat exchangers made of stainless steel or aluminum. The lower the return temperature, the more moisture condenses in the boiler and the greater the additional heat gain. In this case, raising the return temperature would be counterproductive.
If a tiled stove heating insert with a downstream water register or a tiled stove boiler device is used for the heating connection, a properly functioning return increase is also important. As described above, this ensures that part of the hot water that has already been generated is diverted and fed back to the heat exchanger . Mixers that can be controlled manually as well as fixed systems are suitable here. The optimal temperature is at least 55 ° C. First of all, a return temperature that is too low is noticeable through an unpleasant "smoke smell". If the return temperature is then not increased, this leads within a short time to considerable soot formation in the exchanger surfaces and ultimately to total damage to the heat exchanger. Owners of tiled stoves should therefore only switch on the water heating when the system is operated at full load and check the return temperature at least once a week.
Solar technology
In solar systems ( solar thermal ) with heating support , the return flow of the heating circuit is cooled down by raising the return flow of the heating circuit, so that the use of the least amount of solar radiation is possible. Instead of adding the flow from the heating circuit, the return medium of the heating circuit is heated by a heat exchanger or by passing through the solar storage tank before it is returned to the primary heat generator. Since this only makes sense for heating systems with a low design temperature , the problem of increasing the return flow in condensing boilers does not arise here either.
Vehicle technology
In vehicle technology, the process of increasing the return flow is also used to bring the temperature of liquid-cooled internal combustion engines as quickly as possible to the optimum operating temperature and to keep it there.
In this case, temperature-controlled liquid is fed to the return via an internal or external short-circuit line until the optimum operating temperature is reached. Then the flow is opened via a thermostat , usually an expansion element , and a variable volume flow to the cooler - the place where the heat is emitted - is released.
Web links
Individual evidence
- ↑ Short-circuit line in internal combustion engines to reach the operating temperature PDF, "Description" for patent DE 19755024A1, online access on March 11, 2011.