What is the difference between 2 way & 3 way control valve in AHU chilled water arrangement?

3WAY VALVE  :  Bypass the water flow through the bypass line if the valve in operation (open and close), so attain constant flow in the chilled water line circuit and also can use constant speed chilled water pumps.

2WAY VALVE : It is a modulating valve, so the water flow will fluctuate when valve open and close. required have to use a variable frequency dive motors for 2way valves.

3-way modulating valve (either diverting or mixing) is usually seen in low capacity/size system where constant speed primary pumps are employed for chilled water recirculation. In this case, the3-way valve's ability to have proportion of mixing or diverting chilled water is witnessed through adequate communication with BMS/BAS having responsive field sensors such as thermostat.

 

2-way valve is generally seen in a system with primary-secondary pumping scheme. Such system are big in size & the investment of employing primary-secondary system seems feasible. This contributes to the low cost of operation to a great extent. A combination of solenoid valves & de-coupler header in communication through BMS/BAS plays a major role to have an energy efficient system.

Two Way Valves are used to Control the Flow hence the Temperature by Shutting down or Opening the Cooling Coil,,this involves a Variable Speed motor pumps,,

,,,While in 3 Way valves,,it depends on By passing the cooling coil without shutting off the flow,,and in this case ,,constant speed pumps are used

Dear Mohammad ! 

Two way control valves are used near the A.H.U in supply and return lines, so that the chilled water from the machine transfers to the primary pumps of the chillers. 

Three way control valves are used near the A.H.U whenever the temperature of the chilled water does not decrease more than 12 degree Celsius it returns the water back to the A.H.U.  

Credit - Eng. Zeeshan (Sr. Mechanical Engineer, El Concorde co. Riyadh, KSA) - Mobile (0561237869)