Mixing loop, single shunt with 2-way valve

A single shunt mixing loop is used when variable flow or variable temperature or both are desired on the secondary side.

The flow on both sides is reduced for most of the year in order to meet the variations in heating load. This results in excellent energy savings. The temperature and heat loss on the return flow pipe is reduced as well. The single shunt system has a low initial cost, and can be fitted with 2- or 3-way valves. A single shunt system is suitable for condensing boilers due to its low return flow temperature.

  • Secondary side:
    The load will normally be a heat surface or a radiator system where there is a demand for a variable temperature.
    Due to a reduction in the flow temperature, the flow in the secondary side will normally be higher than in the primary side.
    The flow can be constant or variable, depending on the system.
    The valve can be placed either in the flow pipe or in the return pipe.
     
  • Primary side:
    The flow decreases when the valve closes. If an uncontrolled pump is installed on the primary side, the differential pressure at the connection point will increase when the flow is decreasing.    

Interaction with speed-controlled pumps:

  • Secondary side:
    Due to the higher flow in the secondary side, a speed-controlled pump will have the authority in secondary systems.
     
  • Primary side:
    The pump will reduce its speed when the valve is closing. Normally proportional pressure control is recommended in systems where the pressure loss in the control valve is below 50 % of the total pressure loss in the system. 

 





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