Mixing valve
The mixing valve influences the ratio of two volume flows . It is a variant of a control valve with two inputs and at least one output. The rotary valve built into the mixer is also called a plug . The position of the mixer plug can be done manually or via an electric drive (mixer motor).
In hot water heating systems , the mixing valve is used to keep the flow temperature constant or to increase the return temperature ( return increase ).
Heating mixing valve
Three- way or four-way mixers are mostly used in heating circuits .
The three-way mixer has three connections like a switch valve and is usually switched as follows:
- Connection A: from the heat source (control gate)
- Connection B: Branch line from the heating circuit return (bypass gate)
- Connection C: to the pump of the heating circuit (flow) (Summentor)
The mixer has two extreme positions:
- "open" - the heating circuit is completely fed by the heat source (A), the branch line to the return (B) is closed
- "Closed" - the heating circuit (C) runs in a closed circuit via the branch line (B) (also called short-circuit or bypass line), the connection line to the heat source is closed
With intermediate positions, the mixer can direct more or less volume flow from the heat source into the heating circuit and, through the temperature mixture, control the heating flow temperature according to the heating curve according to the outside temperature.
Depending on the required flow temperature, the heating control switches the servomotor either in the "open" or "closed" direction for a few seconds. The interval times in between are in the range of minutes and can be made dependent on the difference between the target and actual temperature in order to avoid overshooting of the temperature control.
The four-way mixer is connected to the flow and return of both the boiler circuit and the heating circuit. It now mixes cooler return water into the heating circuit as required and warmer flow water into the boiler return (return increase). Due to the use of modern low-temperature boilers and even more so today due to the spread of condensing boilers, this design is becoming increasingly less important. It is still used, for example, for the subsequent integration of a fireplace insert with a water pocket into a heating circuit network.
In addition, other types of multi-way mixers have developed in recent years . For example, you can take water from a buffer tank according to its temperature stratification at the height of the desired temperature level, so that the mixing in the buffer is lower and the temperature level in the upper range is higher and thus the efficiency of the system is increased. Another area of application of such mixers is the use of a high temperature level in a radiator heating circuit return to supply an underfloor heating circuit . There, the boiler flow is only added to the underfloor heating flow when the temperature of the radiator return is no longer sufficient. Here, too, the intention is to keep the return flow of the overall system as low as possible in order to increase the efficiency of a condensing or bivalent solar thermal system.
literature
- Ross, Hans: Hydraulics of the water heating . 5th edition. Oldenburg-Industrieverlag, Munich 2002, ISBN 3-486-26529-6 ( three-way valve in the Google book search).