Fan Coil Unit Piping And Valves Connections

[irfansiddiqui]

Dear All,

I have am recently appointed as design engineer n an hvac firm,, I have an issue with an standard detail available here of fan coil units connections.

according to detail:
tow way motorized valve is sussed for by-pass on CHWR line and then double regulating valve(Balancing Valve) is also used

I want to understand here connection with each other,, either it is a good approach to have both in same line ? or this system can be enhanced in more better way??

 

[willard3]

Do you have any training or experience in the HVAC field? If not, find someone in your office who does.

I don't understand your question and the language is not clear.

 

[Drazen]

plot the detail to pdf and submit it here.

 

[irfansiddiqui]

Please find attached link of connection's detail,
Please comment if i can improve this detail by changing valves

 

[cdxx139]

Yes its good to have both in the same line. The regulating valve is set at max gpm required for coil. And motorized valve will modulate to maintain setpoint.

knowledge is power

 

[EnergyProfessional]

one improvement would be to use a pressure-independent control valve.
You would want pressure taps at the coil to verify flow for those.

 

[DRWeig]

Another improvement would be to get rid of the balancing valves and let the system operate pressure-dependant. That'll get rid of the always-present extra pressure drop of the balancing valve and save lots of pumping energy. The same waste is apparent in pressure-independant control valves too.

Looky here:

http://www.kele.com/templates/content.aspx?id=4946

and here:

http://www.kele.com/templates/content.aspx?id=4942

and here:

http://www.kele.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=4799

and here:

http://www.kele.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=4798

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[SAK9]

If the fan coil is under 2 ton,I would go for an on/off valve rather than modulating.

 

[irfansiddiqui]

Thanks to all for prompt response...

cdxx139 yes it is a good practice, just want to improve it.

HerrKaLeun Thanks for a good suggestion.

DRWeig Sir, you have sent me good material i will study it and obviously it is better to reduce pressure drop on pump head by using it. I will try to make it better and will let you know. Thanks a-lot Sir.

SAK9 you approach is good n thanks.

 

[EnergyProfessional]

SAK9: not sure why the coil size determines modulation or not. but the valve cost is not really different, and comfort and other issues can appear with on/off. I would even use a VFD fan for an FC for that reason...

 

[NegativeZero]

depending on the size of the pipe the two way could be on/off- fail to open. Because we are not talking about a lot of water flow if its less the 1". So half open or full is not much difference. Depending on what its serving, will the fan come on/off based on room temp? I think because you have a modulating valve I see no need for the regulating valve when I can adjust max flow with my ball valve. (Change the gates to ball) if your worried about temp or comfort a three way would be nice to controlling discharge air temp. but that just over kill for a simple fan coil unit.

and I'm assuming this is a fan coil and not a heat pump.

personally I wouldn't use the auto vents because they suck. leave the stop cock to manually bleed air or get rid of them all together and add another hose connection after the two way so I can flush out the coil in either direction or blow out air fast with a hose and bucket. the maintenance guys will love you.

I don't see any unions anywhere unless they are at the flex connectors.

 

[EnergyProfessional]

Negative Zero: I don't understand why you compare to 3-way, you can modualte with 2-way valves as well.
with on/off you also have more valve movement becasue of cycling.

and how do you maintain DAT if you have on/off? Depending chilled water tmep you may get 50 or 60°F or whater DAT if you have on/off.

DRWeig: I thought about your idea of not having balancing valves. your ideas, as ususally, are pretty good and well researched.
One thing I woudl be cocnered with woudl be rogue zones or failed valves that will steal all the water (or at least unnecessaarily increas pump speed and reduce dT).
But I think either going to the expense of PICV, or no balancing valves. All that balancing valves do is provide an opportunity for generatiosn of people to randomly play with them and they never are actually balanced anyway.

 

[NegativeZero]

well if you had said you want to control DAT then of course modulating the valve is correct. the three way would work if you really want to have on demand cooling. Sometimes the legs off a supply line are long and the water warms. depending on how sensitive the controls you have, it will sense that warm air and drive that valve wide open until it cools. With a three way the cold is always there. But again its over kill, it was just a thought.

if your Modulating the valve a balance valve is not really necessary and if its part of several off a main I would think you have a circuit setter valve for the loop.

I want to correct my last post. I would keep the gates just for isolation, but I like ball valves. I hate when I go to a job and the one and only valve leaks and I have to drain the line or system. cost a bit more but well worth the redundancy.

 

[EnergyProfessional]

Negative Zero: you may still need balancing in case this is a rogue zone. Unless you have a really good hydronic design, and maybe if that FC is really far away.

you always want isolation valves, correct.

not sure hwy you differentiate between balancing valve and circuit-setter. afaik this is the same thing in what they do, just different names. I think traditionally in CV pump systems pump still had balancing valves, and the branch balancing valves ere called circuit setters. Obviously with Variable pumping only the branches need balancing.

 

[NegativeZero]

yes, balancing valve and circuit-setters are the same in my book, but reading the links DRWeig posted, like this one

http://www.kele.com/templates/content.aspx?id=4946

MYTH: The coils will not get their design flow if balancing valves are not used.

FACT: If the control valves are sized properly and the actuators are large enough to position the valve plugs properly, the system is self-balancing. Each coil will receive only enough flow to satisfy the load.

I just think we just do what is always done because its CYA. I cant tell you how many buildings I have been in where every balance valve, circuit setter, butterfly valves are wide open and they have no issues. I said to a building manager, this is amazing that an engineer figured out everything exactly so you don't have to use or need all these extra parts you paid for and installed.

So going back to the OP question, the drawing is fine. it will work. But Just give me two isolation valves, two drain hose connections and a properly sized modulating valve and a y strainer. and maybe gauge ports so I can read pressures maybe once a year. anyway, not really knowing what this coil will be used for, its just some ideas for value engineering.

I have been getting into more closed loop heat pump condensor loops using VFDs. So this subject in interesting to me. I'm not convinced the ROI is worth it, to change from a CV system. But I'm sure someone will show me the light.

 

[SAK9]

HerrKaLeun: On/off valve is very common on fan coils.I would suggest you superimpose the fan coil's capacity-gpm curve against the two way valve characteristiccurve.You could then see how much of a difference it makes.