The error message

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This error can occur when looking at mixing circuits, and is best understood through this simple example.

Open

In this simple system there is an end unit which requires 1 kW at 70/50°C, fed through an active mixer and a boiler. In this case, there is no need for mixing and Hysopt will optimise the 3-way valve to a KVS-value with a nearly fully open authority.

If however, the “primary supply temperature override” is filled in, (which is needed to define the larger supply temperature of a system for proper working) Hysopt can calculate the needed mixing authority, like below. You see that the full load valve position is now decreased to 88% instead of 100%

Now, if you fill in the “primary supply temperature override” with a value equal to the propagated value (in this example this is 70°C). Hysopt expects to perform a calculation to design this full load valve position, but can’t as getting 70°C while mixing a supply of 70°C and a certain amount of smaller return is impossible. This will cause the error to pop up that there is no valve position for the desired mixing ratio.

The solution to this error is simple. Delete the primary supply temperature override as it is not needed in the propagation.