Chilled water system

[Rabindra]

Can any one please tell me the working and advantages and Disadvantages of Three way Mixing Valve and Diverting valve as control for the modulation of the chilled water through air handling unit. Also please tell where I can see the diagram/sketch of the Three way mixing valve and diverting valve.

Thanks
Rab

[The Viking]

Well,
It won't affect the AHU much.

What it will do is maintain the water-flow through the system.
Whereas the 2 port valve will shut the water-flow off, the 3 port version diverts it.
which one you prefer is down to system design

[Ben-Hur-Cool]

The 3-way diverting valve is prefferable for every chilled water systems. You have to keep waterflow going or else your evaporator could cool down too much and you could risk refrigerant fluid going back to your compressor.
As which some airco's are protected from this trough a flow-switch or a sensor placed on the outgoing conduit of your evaporator.


Ben

[Brian_UK]

If you had done a search on the forum you would see that this subject has been discussed before, however I will repeat my earlier answer...

It depends on which type of valve it is - it may be a 'mixing valve' or a 'diverting valve'.

See here for details on a Mixing Valve
http://bahercs.com/THREEWAY%20MIXING...%20TRI%20M.htm (http://bahercs.com/THREEWAY%20MIXING%20VALVE%20TRI%20M.htm)

and here for a Diverting Valve
http://bahercs.com/3WAY%20DIVERTINGVALVE%20TRI%20D.htm

[Tesla]

Hi Rabindra
I don't think I've seen mixing valves on a chilled water system. Diverting valves allow chilled water to bypass the coil when cooling is not required. A chilled water bypass valve may not be required with a three way valve - but is always required with two way valves - This is to maintain a minimum water flow across chiller vessel to prevent an ice up. One advantage of a three way valve is the temp of water in loop will be cooler and more stable, dissadvantage is wasted pump power. Mixing valves I've only seen on hot water systems like for the tap in a toilet mixing hot + cold to get warm so as one is no burnt by the hot water.

[wambat]

Hi Rabindra
Three-way valves are generally classified as mixing or diverting. This refers to the
internal construction of the valve, not the application. The internal differences are
necessary so that the valve seats against flow. Mixing valves have two inlets and one
outlet . Diverting valves have one inlet and two outlets
Either valve may perform a temperature-control action (mixing application) or a flow control action (bypassing application) depending on its location in the system.

Diverting valves, however, should not be substituted for mixing valves and
vice-versa. Using either design for the wrong application would tend to cause chatter.
Another type of three-way valve is used in the supply line to coils in a three-pipe system. This valve has two inlets and one outlet. One inlet is supplied
with heating water and the other is supplied with chilled water. Depending on the thermostatic controls in the occupied space, the valve opens to allow either heating water or chilled water into the coil. The diverting valve is normally installed before the cooling coil where as the mixing valve is usually installed after the cooling coil
:)

[Rabindra]

Hi,
Thanks
Rabindra


Hi Rabindra
Three-way valves are generally classified as mixing or diverting. This refers to the
internal construction of the valve, not the application. The internal differences are
necessary so that the valve seats against flow. Mixing valves have two inlets and one
outlet . Diverting valves have one inlet and two outlets
Either valve may perform a temperature-control action (mixing application) or a flow control action (bypassing application) depending on its location in the system.

Diverting valves, however, should not be substituted for mixing valves and
vice-versa. Using either design for the wrong application would tend to cause chatter.
Another type of three-way valve is used in the supply line to coils in a three-pipe system. This valve has two inlets and one outlet. One inlet is supplied
with heating water and the other is supplied with chilled water. Depending on the thermostatic controls in the occupied space, the valve opens to allow either heating water or chilled water into the coil. The diverting valve is normally installed before the cooling coil where as the mixing valve is usually installed after the cooling coil
:)