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How does this floor heating mixing unit work?

  1. May 14, 2016 #1
    I've come across this floor heating mixing unit from Watts in an appartment. The image shows how things flow (I could only find this with some russian-looking annotations). To the left of the return connection there is a water meter - not an energy meter - it only shows the accumulated amount that has flown through it from the day of installation. My question is - will this meter to some extent also run when no water goes to the floor loops? I suspect it will due to water being forced through the pump by the pump in the boiler room somewhere. Any ideas?

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  3. May 14, 2016 #2
    Know anyone who reads Russian? There could be someone who could directly read the diagram. I'm guessing the large piece of equipment is a mixing valve, mixing hot water from some source with cold return from the distribution and back out to the distribution. Part of the warm flow goes back to the (boiler? heater?).
  4. May 15, 2016 #3
    The large piece is indeed a mixing valve. The russian points to - and explains - a couple of thermometers, and the thing on the top is an overherating-device that shuts down the pump to prevent too hot water from reaching the floor.
  5. May 18, 2016 #4


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    I have similar manifold at home although it's a slightly different design and set up.

    The manifold is usually controlled by a Wiring Centre. This takes electrical inputs from the room thermostats and generates outputs that control actuators on the manifold. In a small house there might be one thermostat per room each controlling one actuator feeding the loop for that room. In larger houses with big rooms one thermostat might control two or more floor loops.

    In most cases the wiring centre also generates a "Boiler Enable (BE)" signal that is the logical OR of all the thermostats. The BE signal is used to control the manifold pump, the Boiler and it's pump. That way if no room stats are calling for heat everything is off. This is sometimes called an Interlock. I think it's mandatory to have an interlock in some countries.

    On some systems there is no interlock. The boiler is either enabled 24/7 or is controlled by a time clock. What happens is that when the floor loops stop calling for heat the manifold stops taking hot water from the boiler. That causes an increase in pressure that opens an automatic bypass between the boiler flow and return. That causes the boiler return temperature to rise. If the burner is still running the flow temperature will also rise eventually causing the burner to shut off.

    Unfortunately there are numerous variations so it's quite difficult to be sure how your works and what that means for the flow meter.
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