PICV
PICV
(OP)
Hi Experts,
PICV as the brochure is a combination of flow control that works to deliver the required chill water flow irrespective of upstream pressure pressure in the pipe line. When that is the case I believe there is no need to have double regulating valve or other control valves. As the AHU load decreases PICV closes irrespective of the upstream pressure in the chilled water pipe line. Similarly when pressure is high in the up stream pipe but AHU load is low PICV closes. Could you please throw light from your experience.





RE: PICV
I prefer the Honeywell, of very high quality while having less pressure drop than Belimo et al. Only 3 psi, which is less than regular valve and balancing valve.
You'll need a strainer and during flushing they need to take out the cartridge.
Very few application require pressure-dependent valves (i.e. bypass for min flow etc.). Other than that, PICV all the way.
RE: PICV
Not only have they been maintenance free (other than removing and draining/airing out cartridges) but oping by next year to have the primary pumps VFD run off the percentage open for the PICV's. Can't do that with a pressure dependent. If you think about the air side vs. the hydronic side, would you install pressure dependent mixing boxes?
RE: PICV
AFAIK for airside the only pressure-independent devices are VAV boxes with flow-station , and the CV American Aldes (or similar) devices.
RE: PICV
With refernce to HerrKaLeun's mention about VAV being an equivalent to PICV of a water line. Air being a compressible less density fluid, would that behave the same as that of PICV that effectively controls (flow rate) and manage Pressures.
RE: PICV
When i was starting in HVAC, pressure dpendent boxes were the norm, and pressure independent boxes were considered a costly fad. Thirty years later it is difficult to even find pressure dependent VAV boxes. I beleive that the same arguments, and the same control optimization, that was argued on the air side 30 years ago will be pretty much the same as the arguments I've been hearing for PICV for 5 or 6 years.
RE: PICV
RE: PICV
Please read the attached brochure to understand STAD-STAP combination in detail.
RE: PICV
in reality most balancers run the pump at high speed and squeeze the heck out of the balancing valves. sure more than 3 psi.
SAK9: in most cases i use a PICV or regular valve as bypass and control with flow-meter assuming a minimum boiler or chiller flow is what motivates you to have bypass (in variable primary). the exact method probably depends on why you want to bypass?
RE: PICV
RE: PICV
Obviously the one requiring active electronic control and a meter make it much different.
a regular valve is similar to a regular damper (= pressure dependent VAV "box")
RE: PICV
RE: PICV
I know Belimo etc. have higher dP, one more reason to use Honeywell.
RE: PICV
You can find that your entire loop is satisfied from a flow perspective without pressure independent valves at some value, say 10 psid. Now, if we have a system full of pressure regulating devices, that 10 psid might become 15 psid because under a dynamic condition, some remote loads might require that higher value to keep the 3 psid you mention.
My analogy was to Phoenix Control air valves, which are great for a number of reasons but it’s known that the central air delivery systems require a slightly higher pressure (and more fan energy) than a system full of Price/Nailor/Enviro-Tec VAV boxes.
That said, the 3 psid minimum value seems pretty good…
RE: PICV
VAV boxes are a real hassle for us, pressure sensors fail, drift, need recalibration. I have one that has almost 5 times the flow it "measures". So if there was something like the Control valve, even at higher dP, I take it if it is accurate and hasslefree. Also seems easier to replace with the drawband etc. Can even be retrofitted.
anyway, I don't fully follow your logic of the additional 5 psi. but using PICV really depends if you want a defined flow, or not. In some cases you may want to have a pressure-dependent valve (i.e. bypass valve). so it really depends. I've been using PICV for a while and really happy with it. Even if dP would be a bit higher, you would make up those losses with never exceeding flow. and if you ever talk to a balancer, you know the first thing your design needs to do is get rid of things that need balancing :)
RE: PICV
This could go in circles for a while. Back to 101, a fan serving a distribution system with volume dampers might require a half-inch static, max. You produce the pressure, leave the most remote devices open fully, then tweak back the others.
If each device becomes an EnviroTec VAV box, the half-inch becomes maybe 1.0 inches, because under dynamic conditions, boxes might need that pressure to deliver the flow that they require.
If each device becomes a Phoenix Control Valve, the common duct static might become 1.5 inches because each device needs 0.6” pressure across it to perform as needed.
The same goes with water. If you want guaranteed flow control at terminal devices, it will cost you with pump power and system pressure.
RE: PICV
Best to you,
Goober Dave
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RE: PICV
sorry for hijacking this thread to go from valves to VAV boxes :)
RE: PICV
RE: PICV
RE: PICV
RE: PICV
Thank you very much for the reply. Pl correct me if I'm wrong.
When the load in the AHU is less, the return water temp is also less than designed CHWR temperature which is sensed by the temp sensor located in the AHU return pipe. What does this sensor do? Send signal to BAS or directly communicating with the PICV?
Thanks in advance
RE: PICV
Discharge Air Temperature is compared to the set value. If DAT is too high, the cooling coil valve opens up. If it is too low, the valve closes. There also is a PID loop to control that etc... that is what the controller does.