What is the criteria to use 2 or 3 way control valves in chilled water lines? Where to use 2 way and not 3 way and where to use 3 way not 2 way and why?

This is how we look to the the story:

1. 2Way Valve:
   • 2Way (Or2 Ports) Valve is passing the water in one direction only. so if the valve is fully close it will trap the water before it.
   • this will lead to a pressure increase in this branch
2. 3 Way Valve:

• 3Way (Or3 ports) Valve is passing the water in2 directions.
• so if the valve is fully open the full amount of water will be moving in one direction, if it closed the water will pass to the other direction, if the valve is partially open then percent of the water will flow through direction1 and the remaining will pass through the other (for Diverting Valve which installed in the supply line).
• In another cases if we install the valve in the return line so if the valve is open water will flow through the unit (Cooling coil as example) then pass through main direction. if the valve is close the water will by pass the unit and then flow through the other direction through the valve (Mixing Valve which installed in the Return line).
• this will not cause the pressure rising.  

Why we use the2 way valve? when you use the2 way valves in HVAC system in all the equipments in your building this means that you will not need all the chilled water to go through your system all the time if you don't need much cooling. so you will be able to reduce the speed of the secondary pumps of your system. this will lead to a huge energy saving in the running cost of your building (depend on the number of Pumps and thier sizes). Also you will be able to reduce the size of your pumps. But in this case you have to use Variable Speed Pumps. Also you should have2 sets of Pumps, One set constant with Speed for Chillers and another set to serve the building. ans also By Pass Valve to gurantee the min flow of the chillers. Otherwise you can use one set with a variable flow chillers. This has to be a decision in the mechanical design stage depend on the cost calculation of the project.

Bottom line is:

use the2 way Valve in the system that can withstand the variable water flow

use the3 way valve in the systems that needs a constant water flow.

 

WHEN THE PUMPS VFD2 WAY USED, AND IF IT CONSTANT SPEED THE3 WAY VALVE USED.

The2-ways valve closes when cooling is not required in the space and the set point of the room thermostat has been achieved, thus the CHW pump still running rises the CHW pressure in the supply lines to the coils, to regulate this pressure increase a DPT-pressure transmitter/transducer wired to the PLC sends a signal to vary the CHW pump flow, by varying the pump motor speed using a VFD-variable frequency converter on the motor, by pump affinity laws, for a constant impeller diameter and variable speed, new flow= old low x (new speed/ old speed ).

if chilled water pump has varaible speed we use2way valve . if chilled water pump has constant speed we use3 way valve because when temperature comes3way valve by pass chilled water to return line . in varaible speed chilled water speed decrease and increase according to temperature requiredment.we use2 way valve.

In Chilled water line Criteria to use2 or3-way valve depends on the application type: 1.
 2-way valves are recommended in Chilled water piping with primary const.
flow and secondary Variable speed pump. 
3-way valves are not suitable for this system.
2.
 2-way valves are recommended in Primary only Variable speed pump. 
to maintain a minimum flow across chiller, a motorised bypass valve is used across the headers in this system  3.
 When there is a primary only constant speed pumping system is used,3-way valve is recommended.
for this application2-way valves are not best suitable.

2 Way is used in the case of a Bay bus line between expulsion and public clouds2 / when there is a variable speed with cold water pumps / If not available supply only uses 3 Way

2 way v/v is using with VFD drive that control the motor RPM, Compair to 3 way v/v it has no vfd drive to control motor rpm it has constant speed so if room temperature reach then third ie bottom side v/v open and water goes through by pass line

Best way to save working cost we generally use the system in which chilled water primary pump is constant flow with varying delta but at same time secondary pump is varying flow but fixed delta that is  y we use3 way valve to regulate the flow rate in the system with constant flow rate 

but in case of variable flow the flow adjusts that is y we use2 way valve 

 

The two-way valve that controls the flow of refrigerant through single line. The three- way valves with an inlet that is common to two opposite openings .lt controls refrigerant flow in two different lines The four-way reversing valve used on heat pumps. Solenoid valves may be activated by a thermostat. These valves are used to control the temperature of a regulator or a room, Three-way solenoid valves are used mainly on commercial refrigerating units. They may be used to control two separate refrigerant circuits for defrosting, two temperature evaporators etc. In the three way solenoid valve opening is the common opening and is never closed-As the electromagnet is de 'energized, the following occurs :The weight of the solenoid plunger assembly holds the valve against the lower seat .The force of the upper spring also holds the valve firmly against the lower seat .This action closes port B to the common port and opens C. When the electrical circuit is closed the solenoid becomes energized .The Piston with the tow valves attached to it will move in the opposite direction.

2way used when scwp have vfdsped

3way valve uosed when schwp is constant speed

2way valve uosed to safing power

Primary type chiilled water system    3-way valves

Primary-secondary type chilled water system 2-way valve

beyond that initial and running cost issues in terms of power saving and installation cost  vfs pumps are so expensive comp to constant speed ones

pipng cost as high flow requires large diameter pipes even schedules sometimes play a role

things are interrelated 1st 2 lines i guess the coclusion