When 3-port valves in HVAC plants are fully closed, false circulation can occur when hot water rises or when water is pulled away near rectangular pipe connections.
False circulation can be avoided by proper planning – with almost no extra cost – but remedy is usually very costly in existing plants.
Measures against false circulation
Observe guide value for the water speed: 0.5…1 m/s.
The lower the water speed, the smaller the risk that the diverted flow pulls water from the critical piping section. If required, balancing valves can be installed to improve flow conditions
Observe a certain distance between bypass and collector/header or short-circuit:
H ≥ 10 x pipe dia., minimum 400 mm
Installation of a check valve or gravity brake R with small spring pressure in the critical piping section, aimed at ensuring a minimum flow in the opening range