2way valve PICV valve 1

[Jamsith]

Hi dears,
Please explain to me the control methodology for this Two way valve & PICV Valve. What I understand, this both valves are creating pressure inside the system by closing the path of the fluid, then the VFD system reduces the speed of the pump to reduce the system pressure accordingly. But what I want to know, from the where this VFD getting signal regarding this pressure increase ? There is an differential pressure sensor, but the location of this sensor will be where? is it next to suction or discharge of the pump? or should we have to add each pressure sensor to each FCU's ?

Please explain to me, and the this control terminology is same for 2 way & PICV valve or difference?

 

[GT-EGR]

There are a lot of nuances to this, but for the basic answers to your question:

The two-way valve, of most types, will open and close itself along the range (%open min to %open max) that you'll allow it. It will do this based on something sensed that you are trying to control. An example would be room temperature, as temp goes above or below a setpoint, the two-way valve will open/close to keep your space temp where you want it.

A PICV valve, is an upgraded version of a two-way valve. It does the same things mentioned above, but it also ensures that your system doesn't allow more flow through the valve than you select it for. So if your system pressure is rising, your two-way valve at full open will always produce the same flow, regardless of the pressure on the inlet side (from the pump).

Two-way and PICV valves are different because the PICV valve is a two-way that also includes a calibrated spring and orifice, to make sure that your max GPM stays below your design number. Your two-way valve will just open and close to meet a setpoint, it doesn't care how much flow it lets through to do that.

As for your pump control, the typical way would be based on differential pressure sensed somewhere in the system. As your pressure rises, your VFD slows down, and vice versa. You'll get a lot of different and probably correct answers on where to put this. If you have a critical location in your distribution, you'll want the sensor on that part of the run. If you have an area of the building that is best representative of your system load, that is where you want the sensor. If you really don't know where to put it, have multiple sensors and some logic to make sure all those points are considered and satisfied.

Newer control strategies that track your two-way valve position make this reading even less critical, but it's a more costly install plus some additional programming you reset your pump differential pressure target based on all the valve positions at any given point in time.

 

[ChasBean1]

Read GT-EGR's answer again. It is perfect. One note to add, water systems typically have the controlling DP sensor near the end of the loop. Air systems, 2/3 down the duct. You can't always achieve this on a water or air system, but these are the "general" rules.

 

[lilliput1]

The worst case piping run and associated fitting and equipment pressure drops would have to be determined to size the pump and determine optimum location of pressure sensor(s) to control the pump VFD.