Operating principle

The active mixing circuit controls the net thermal power passing through the circuit by mixing cold return water (coming from the end unit return pipes) with hot water from the primary production side. In full load operation the inlet gate of  the 3-way mixing valve is completely opened whereas in partial load conditions the 3-way mixing valves is positioned in function of the process value (measured water temperature) and set point (heating curve). The premix balance valve ensures that the supply temperature to the end unit is lower than the supply temperature leaving the 3-way valve by mixing cold return water from the end unit. This type of base circuit is mostly used for floor heating in combination with high temperature end units (radiators, convectors, ventilation batteries, ...).

Individual components and parameters

1. Secondary pump 
2. 3-way mixing valve
3. Balance valve for pump
4. Balance valve on the 3-way valve bypass
5. Balance valve to limit maximum temperature (premix)

System check 

As this mixing circuit is a so called 'active' mixing circuit, the embedded pump is able to extract hot water from the primary side by itself. In fact this circuit must be connected to a pressure less header/collector. If the software encounters a pump on the primary side of the active mixing circuit, it will report this as a problem while running the system check. 

Note that when the primary pump is not removed the pump and valve optimization is no longer supported, it is still possible to simulate the system as a reference case but the user needs to fill in the parameters.

Related models:

•  TOKEN  - NjIyfDdQUG5RWHU0 - Active mixing circuit with primary pump (demonstrates the distorted control behavior due to the primary pump)  

Design flow and temperature regime propagation

By running the action "compute design flows" all the design flows are calculated based on the power and temperature regime of the end units. In case where there are multiple types of end units (radiators, floor heating, ...) the supply temperature in regime may differ. In order to guarantee the maximum supply temperature (45°C) of the floor heating the flow through the premix balance valve needs to be calculated to achieve this. In the example below the premix balance valve is calculated by filling in the primary supply temperature override. Note that the primary temperature difference from the floor heating is larger than that of the radiators, which will influence the design flow.

Related models:

• TOKEN  - NjI1fFpqc3BuN3ZZ - Primary regime change