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DRVs and control valves are used to regulate the chilled water flow rate.
We need to balance the flow rate considering the pressure drop in the coils of the AHU/FCUs.Hence while putting the valves in the return the flow measured is considering the pressure drop in the coils also and therfore you will get the accurate water flow in gpm while water balancing.This is as per my limited knowledge.Hoe this would be helpful to you.
Dear all
Theoretically there is no problem whether to install control valve on either supply or return line.
Normally it is installed on the return line because of following reasons.
1. ASHRAE Recommendations.
2. The coil of the unit should be flooded in case the valve is closed.
3. With a control valve on the return side, the water is at a higher pressure through the coil, reducing off gas, thereby lowering dissolved oxygen content. Lower dissolved oxygen extends equipment life by minimizing the air entrapment.
4. If it is a hot system, some manufacturers have temperature limitations on the actuators. If there is a180°F limit on the actuator (common to some actuators), the return side is preferred as it will operate at a cooler temperature.
5. If it is a cold system, it is always better to have less thermal breaks on the colder side (e.g.42°F water) than on the warmer return side (e.g.,56°F water). The return side installation reduces sweating on the electronic actuator, which is more prone to failure when wet.
Hope this will work
The main reason to install DRV or to say double regulating valve on the return line is that the flow can be restricted or can be at a halt in the Fan coil unit (FCU) coil for a small amount of time this is very important as the heat transfer is efficiently used in overall we can say it restricts the flow to sense the temperature change according to the load and regulates the flow ,there is a term called by pass factor employed for calculating the heat load this is the same by pass factor which is to be kept used up and it is nothing but the area available for the air to pass over the coil to extract coolness from the coil.
this helps in increasing the efficieny of extraction of cooled from the coil and ADP is achieved.
Just to control the flow such that there will not be any change in the pumping system.
- if the question why not installing the hook up on the water supply line the answer is to insure that the coil is full of pressurized water even in maintenance process
- but if the question will be the same as mentioned so the answer is you are talking about two different systems CAV and VAV
for CAV we cannot make modulating control on the air side
for VAV we can control air using VAV units on the air side and we may use hook up if they VAV system is connected to a chilled water system
