The average temperature difference specifies the average difference between the flow and return temperature over a given period of time.
The temperature difference is important in connection with district heating, where there often are requirements in terms of an acceptable minimal value, above which the average temperature difference should be maintained.
This requirement is made to minimise the heat loss from the return pipe in the district heating system. It also minimises the flow rate of the medium that is circulated in the district heating network.
The temperature difference in a heating system depends on the components that are installed for heat emission. When using radiators, the cooling will often be sufficient, as the velocity through the radiator is low. In connection with floor heating where there is a risk of high flow, return temperature limiting valves are applied to ensure proper cooling of the district heating water.
A poorly regulated system or defective valves can also cause the heat-carrying medium to flow too fast through the heat emitters. This will cause an inadequate cooling of the medium.