Balancing Valves in HVAC Chilled Water System

A system diagram would help.

There are many cases in which balancing valves can be made superflous by proper piping design, such as looped return headers and precise pressure drop calculations. By eliminating the balancing valves, you can reduce the total pressure drop and often get by with a smaller pump, as well as save energy.

Ideally, balancing valves (and control valves) are typically on the discharge side of any coil- HW or CHW.

The reason is that the pressure drop the valves create MIGHT cause some vaporization (flashing) downstream of the valves which would compromise the heat transfer in the coil.

Properly sized control valves take nearly 50% pressure drop (45%of absolute pressure) at full flow to allow most effective control action. With hot HW, that pressure drop can cause an issue. On the down stream side of the coil, the HW is cooler and less prone to flashing. Not so much of an issue with CHW, but still a safe place for the valves and their pressure drop.

Hi Guest,

Balancing valves are as the name implies a way of obtaining the required flow thru' the associated load, either heating or cooling, in a system where there are several or many variable resistance factors; in an ideal system they would not be needed as the Kv value of every control valve would match the dynamics of load and media supply.

Oversizing of components is endemic in the HVAC industry and it brings with it inflated first costs and increased running costs throughout the lifetime of the installation.

It is worth revisiting an installation and examining the way things are controlling,or not, with a view of down sizing valves where ever possible and eliminating the balancing valves as they are only adding to the friction losses of the whole system

Personally I don't like the things as they tend to be used to overcome poor design and if you know enough about the available delta P and available flow then a suitable sized control valve will generally suffice.

The controls available nowadays with VSDs applicable to pump drives (with appropriate sensing either delta P or T) together with flow measurement devices can render the balancing valve virtually redundant. I would consider flow minimisation an essential first step in order to achieve as great a deltaT as possible which assists in keeping your overall plant efficiency high if allied to the measures mentioned.

There is no reason why you should not use either of the valves mentioned although you will need to derive a signal from either a flow meaurement device or differential pressure monitor as an input to your BMS. The charactistics of the globe valve are superior to those of the butterfly or disc valve in this context. You might also think in terms of introducing speed control to the circulating pump(s) as an additional control measure.

You may find the 'Crane Pressure/flow Manual' of assistance.

Hope this helps,

Massey.