Heating

Mixed temperature

Mix

40,0°C

Hot

6,00l/min

Cold

4,00l/min

Mixed temperature calculates the blend of two water flows for heating and domestic hot water. It uses the energy balance of flow and temperature. The result is the common temperature, or the part flows that reach a target.

Mix

40,0

°C

Hot share

60

%

Hot
6,00l/min
Cold
4,00l/min

Task

Save in —

How it's calculated

Mixed temperature follows the energy balance of two water flows: the common temperature is the flow-weighted sum of the temperatures. The other way, the cold, hot and target temperatures split a total flow into two parts. Equal specific heat is assumed. Losses and a third flow are not. The target has to lie between cold and hot.

Worked example

6 l/min at 70 °C and 4 l/min at 15 °C give 48.0 °C.

FAQ

Does this cover a mixing circuit?
Yes, for the temperature at the mixing point. The valve characteristic, the pump and the bypass are not included.
What if one flow is zero?
The mix is then the temperature of the other flow. Neither flow may be empty or negative, and they may not both be zero.
Why does a target outside the two temperatures fail?
With only two temperatures the target cannot be hotter than the hot flow or colder than the cold flow.
Are degrees Celsius and kelvin mixed?
For differences it does not matter. The calculation uses the entered temperatures, not absolute temperatures.