Flow temperature

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The flow temperature in a heating or cooling circuit , the temperature of the heat - or cold -transmitting medium (eg. Water , that a) the technical system is supplied. The temperature of the medium flowing out of the system is called the return temperature .

Heating technology

In heating technology , the flow temperature is the temperature of the heat-transferring medium after it has been heated by a heat source (e.g. solar collector , gas heater ) that is fed into the heating circuit .

The level of the flow temperature depends on the heat-emitting surfaces and the heating requirements of the rooms. It used to be 90 ° Celsius. The reason for this was the gravity heating , which relied on a high flow temperature without circulation pumps in order to be able to move the heating water. In order to support the condensing technology with conventional radiator heating and due to better insulated buildings, the heating systems are designed for low temperatures (approx. 55 ° C). For use in connection with heat pumps and / or solar heating support, surface heating systems are suitable that only require flow temperatures of approx. 30–35 ° C. A further reduction to about 23 ° C provides the technique of thermal activation component .

The flow temperature should be selected as low as possible, so that the desired heating of the rooms is possible at every point on the heating curve . There are several reasons for this:

Heat distribution system losses
The heating medium reaches the consumer at a temperature that is slightly lower than the flow temperature. This depends on the quality of the insulation of the supply line between the heat source and the consumer. This inevitably means that the flow temperature must be higher than 22 ° C ( room temperature ). If the flow temperature is selected too high compared to the ambient temperature, the transmission losses of the system are correspondingly higher (for calculation, see heat transfer coefficient ). Losses occur in particular when the heat is distributed outside the building envelope to be heated, which is why the Energy Saving Ordinance stipulates a minimum level of insulation for this.
Losses due to unintentional ventilation
The heat output via heating surfaces is higher, the higher the flow temperature. Since the risk of ventilation losses is particularly high in the transition period in spring or autumn, these losses can at least be minimized by adjusting the heating curve .
Improved efficiency with modern heating technology
Heat pumps have a higher COP the lower the flow temperature is (1K lower increases the COP by 2.8%). It is similar when using solar heating support : the lower the required temperature, the higher the annual yield, because usable temperatures can be achieved even in times of low irradiation.

Cooling technology

In air conditioning and refrigeration technology , the flow temperature is lower than that of the return, as it is supposed to extract heat from the object to be cooled. Cold is thus a form of heat, but with the opposite direction of energy flow.

With recooling or liquid cooling , the flow temperature is higher than the return temperature. It is the temperature of the heat transfer medium before cooling down, e.g. B. in the cooling tower or heat exchanger .

See also

Web links

Individual evidence

  1. - Chapter 1.4.1 ( Memento of the original from April 17th, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF file; 44 kB) @1@ 2Template: Webachiv / IABot / www.lindau.de