Valves on FCU, AHU

[nevinjohn]

Hi,
2 way vales
3 way valves
Balancing Valves.
One amongst the three are used in most of the installations. Can someone explain what function each does. When we adjust the thermostat, is it the balancing valve or the other which varies the chilled water flow.

Secondly, if we need to design the system for a high rise building, the pressure of water colum acting on the FCU/AHU in the buildings basement would be very high.! Can Pressure Reduction Valves be used? How can we determine, till what height these vales are required?

[frank]

A 2 way valve is normally either open or shut and is often called a Zone Valve, in a chilled water circuit. Solenoid valves are also 2 port valves.

3 port valves can be either modulating or port specific, that is, the valve will either modulate to serve 1 or both ports, depending on the value of the signal input ( 0 - 10v or 0 - 20ma), or will motor to serve the duty port or bypass port

A balancing valve can be adjusted to regulate the flow through the valve, to ensure that the correct design flowrate is available at each fan coil, radiator, AHU coil, etc.

Have a look on Wikipedia for lots more information http://en.wikipedia.org/w/index.php?search=3+port+valve&title=Special%3ASearch

When you need to pump chilled water vertically in a high rise situation, you need to calculate the 'Head' of water and select your pump to match it. Not something to take a guess at.

[Tesla]

To add to Frank's good description above. The balancing valve can be used to ensure the correct pressure drop is maintained which is transferred to flow rate, this can also compensate for difference in head pressure such as AHU's on each floor of a building. Generally when a two way valve is used a bypass valve is used on the chiller or boiler so as to maintain flow through the heat exchanger when cycling off to prevent frozen tubes or cracked boiler plates. I'm sure there is much more ...