Closed Loop Chilled water Makeup Water / Expansion Tank / Air Separator

[AliNaseem2]

Hello Everyone ,

I have a Closed loop chilled water system , its a Primary (constant Speed) and (Secondary variable Speed) System , all the Pumps and the Chilled are located at the Roof Top and the Loads(ahus,fcu) at Ground level .

The Closed loop System Should be Pressurized at a Specific Pressure to run Normally , i have makeup water pumps , to initially fill the system and then maintain the Pressure in the System , in case of leaks or drain the pumps should refill the system and pressurize it again automatically ( if Possible ), where should i make the connection for the makeup water in the chilled water system , how do i balance this point , and control it to keep the system full or at a desired pressure at all times , in practical how this can be done , and what controls are required to achieve it


Attached Not to scale Sketch for my system , where should be the connection for the expansion tank and makeup water should be ??

The green pipes are related with primary suction and discharge
and the Blue with Secondary

 

[MFJewell]

I'd put it in the chilled water return (the warm side of the system). Use an automated control valve to control the make-up. Also not sure why you would want to control system pressure with make-up. The chilled water pumps should be used to maintain the system at normal operating pressure. Make sure your make-up pumps have high enough discharge pressure to push water into the chilled water system.

 

[AliNaseem2]

Dear MFJewell

so the purpose of the Chilled water makeup pump is to fill the system only , so select the pump to fill the system at the top most point ??

i think the Pressurization unit is same as the makeup water pumps with pressure vessel ?? or i am mistaken ? so if there a leak in the system ,

the makeup wont automatically fill it ?? and whats the Expansion tank for in the Closed loop Chilled water system , to accommodate the expanded water only

during off cycle ???

 

[lukaiENG]

AliNaseem2,
I would disagree with MFJewell's position that the CHW pumps maintain the system pressure. In a closed system, the primary and secondary pumps are purely there to maintain flow by overcoming the frictional pressure losses of the system.

As you understand, you should have a make-up water pump and an expansion tank (tank maintains stability in the pressure as the pump cycles on/off). These can often be procured as a packaged system sized based on you system volume.
You should locate the make-up/pressurization unit at the rooftop level, feeding into the return. The reason for this location is that the make-up pump has to do the least about of work as this point in the system will have the lowest pressure (both static and dynamic).

 

[lukaiENG]

I should add, if you're building is relatively short, there is not a big issue with installing the make-up unit inside the building at lower levels, the pump will just have to work a little harder to put water into the system. As buildings get taller you need to look closely at the static pressure rating of system components installed at lower levels.

 

[MFJewell]

Maybe I am used to large chilled water systems. Our headers are 60" diameter. We use make-up for losses due to leakage at customer sites. Our make up line is 4". The chilled water pumps (23 in total) are used to maintain header pressure (some are on VFDs).

 

[LittleInch]

Not simple to answer without a schematic of the whole system, but on the basis of the data to date:

I think filling and pressurisation are two different things. Filling is ideally undertaken from the lowest point so that you're filling from under the water / air boundary and it makes venting the air easier. However on tall buildings this can be a high pressure to fill all the way to the top.

Expansion vessel and prssurisation pump I agree with others - the return line on the roof is the easiest place and reduces pressure rating of the equipment. In terms of what pressure to maintain - it's a balance between making sure the pressure is always positive and creating a high pressure downstream your main circulation pumps at the lowest point. 2-3 bar seems reasonable to me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AliNaseem2]

Deal All ,

The Highest point of system is only 6 meter's higher than the makeup water pump set , its already located on roof top ,

Can i just simply connect the Makeup Like to the Main Line of Chilled Water return , or should i make the Connection into the Air Separator ,
The Air separator vent pipe extended above the air separator , is the most highest point the whole system ??


For the Expansion tank (bladder type ) i will Connect to Suction Header of Circulation Pumps / Return Line , for example a 10'' Main Header with a 2-3'' Branch Line Directly to the Expansion Vessel , how to i balance this line/point/Connection , What Should be the Pressure Setting Here ,

Briefly The System i have is Consist of 3 Secondary Pumps ( Variable Speed ) and 4 Primary Pumps ( Constant Speed ) and 3 Chillers ,
the Secondary Pumps will Maintain the Dela P in the System , atleast a 2-3 bar at the remotest Point ,
The Job for the Primary Pumps are for Circulation (return) the Suction Pressure of the Primary Pumps will be the Friction losses form the last return up to the Pumps Suction and Discharge into the Chillers and From chilled goes to the Secondary Pump , the Discharge Pressure for the Primary Pumps Should also satisfy the Suction Pressure of the Secondary Pumps , which will be the Loses in Chiller and its Valves ,

So Now if the Expansion Tank is Connected to the Return Line and Pre-Charged to be , For example lets say ; 2 bars , The Suction Line Pressure Should be also 2 Bar to 1:1 each other out , and the Expansion Vessel will compensate water only when the line Pressure increases and this is on the system is off and the water temperature risers or when the system is suddenly shut down water surge , but this sill happen on the discharge side where we have the Check Valves ,

Why called the No pressure Change side , the expansion tank should be , well the pressure never changes at this point ??

 

[lilliput1]

The expansion tank should be located between the air separator and the suction of the main pumps. The expansion tank must be pressurized to match the static head of the water equal to the highest point of the water piping above the expansion tank plus about 6 feet of water. This is to make sure that all part of the piping is under pressure so any valve open anywhere would not let air in. Connect the makeup at the expansion tank piping connection to the system. In the makeup line put in a pressure regulating valve set to maintain the above expansion tank pressure. Downstream of the pressure regulating valve put in a safety relief valve set for the pressure that when the pressure regulating valve fail and the head pressure of pump is added will not exceed 145 psig(150-5 psi safety). To size the expansion tank you have to calculate the volume of water in the entire system and figure out the water expansion from its lowest temperature to the highest (when chillers off). Look at Amtrol web site to see sample calculation to determine expansion tank acceptance volume required. Because of the expansion tank location at pump suction, static head and use of pressure regulating valve this is the point of no pressure change. Upper level location will result in smallest expansion tank. Do not have more than one expansion tank location in a system. Put all expansion tank required with system expansion in one location/tie-in. Expansion tanks are more critical in hot water systems. Glycol expands more than water and will require larger expansion tank. Go for ASME rated bladder type expansion tank. select vertical or horizontal. Give all equipment weight and location to structural engineer for proper structural design.

 

[BronYrAur]

I don't see a decoupling bridge in your piping diagram. Your primary and secondary pumps appear to be in series with one another!

 

[quark]

In a closed loop, you should add make up at zero energy point (the point where gravity head starts). Generally, this is where your return starts downward, towards suction of the pumps.

 

[ChasBean1]

To be most effective, the air separator should be placed at the lowest pressure, highest temperature point of the system. The expansion tank should be in a similar location. This usually turns out to be high in the building and at the pump return/suction line. The makeup pressure reducing valve (PRV) should be set to the minimum system pressure you’d like to maintain.

Without going back to Fluids 101, the top of your loop (highest elevation point) should have about 15-20 pounds per square inch, gauge (psig) pressure. You can compensate for pressure or water losses via the makeup water PRV at any point in the system. If you provide makeup at the top of the system, set the PRV to about 15-20 psig. If you pipe the makeup water to a lower point in the system, adjust the makeup pressure based on fluid column height:

If the makeup point is 50 feet e.g., 3-4 floors below the top of the loop: (50 ÷ 2.31* = 22 psig). 15 psig at the top, plus 22 psig of head is 37 psig. Set your makeup water PRV to provide 37 psig.

* 2.31 feet of head of water is equal to 1 psi pressure.