What are the key considerations for designing a chilled water system?

[Francois4Pres]

Hi.

Im a post graduate student but worked in the HVAC industry for almost 3 years but mostly done refrigeration and VRV systems which i designed etc... Had done some minor chilled water system designs but never got to the construction phase.

Have a couple of questions and looking for some opinions from technicians and engineers as google give me some useless info and my boss is out of town with a supplier on a trip and the other engineers are electrical...

Here it goes:
1) What is the deference between a flow regulating valve and a pressure relieving valve? don't both of them doe the same job?

2) When doing calculations for a buffer tank/expansion tank for a chilled water system, how should one start of with the calculation?

Thanks
Francois

 

[Travis_King]

Pressure relief valves are generally system protection valves that discharge the pressurized medium until they reach a set point -- or "blowdown" -- at which point the valves reseat, ready to protect the system once again!

Flow regulating valves do just that. They regulate flow. They are usually control valves that you use when you need/want to, well, control your flow for certain conditions. They may be used as relief valves, if you want; they are not designed specifically as relief valves. "Regulating valve" is an extremely broad term and covers isolation valves, ball valves, gate valves, check valves, anything that controls flow, really.

 

[Francois4Pres]

Thanks.

I have found guidelines to sizing a expansion tank, now what is the main deference between a closed expansion tank and a open expansion tank?

Open tank is open to the atmosphere ... but a closed tank, does it have a air nozzle so as the pressure increases does it let out air? or does it keep that build up pressure inside?

 

[Travis_King]

A closed expansion tank would be used in applications where you have a closed loop system where you want pressure maintained, but still want the ability to protect against the expansion and overpressurization due to heating. They have relief valves and pressure check valves (Schraders [sp?], like a tire) or some digital read of the air pressure.

--If you didn't already know, these tanks are usually filled with air, so the overflow compresses the air when it expands and is allowed to maintain its operating pressure.


An open expansion tank would be used in applications where you aren't worried about the head downstream, or where the open tank is higher up than the rest of the system. These aren't generally used anymore (maybe for some specific applications) because, well, closed tanks are just plain better. They provide safe cushioning of pressure while maintaining system pressure at the desired level. Plus, open tanks, which are generally on roofs (because they have to be very high up to maintain head) are exposed to the cooler temps and contamination (fine for process water, but not for your potables).

 

[Francois4Pres]

Ok that makes sense...

And typically closed tanks has either a bladder (diaphragm) or a non bladder (plain closed).

Thanks again for your input. Think the rest I can do.