Fill water for Chilled Water Hydronic Piping System

[nicole10g]

I am working on the Chilled water Hydronic Piping System of a 10-story office building. The Chiller Plant Room is at the Ground Floor. The bladder type expansion tank is installed at the suction side of the Chilled Water Pump inside the Chiller Plant Room and the water pressure at the bladder type expansion tank is designed to be 70PSI. The automatic fill valve is also set at 70PSI and fed at the line where the bladder type expansion tank is installed.

I have a problem with the feed water supply.

The city main water supply is at 40PSI and goes into the transfer tank at the Ground Floor where the transfer pump lifts the water to the storage tank at the 8th floor. The transfer pump is set at 63PSI and activated by the level sensor in the storage tank at the 8th floor. The 8th floor have a hydromaxi pump running at 35PSI and supply water to 7th to 9th floor only. The rest of the floor is by gravity feed with a pressure reducing valve at the 2nd floor set at 35PSI.

By looking at the pressure profile of the domestic water supply, none of the pressure can reach 70PSI for my automatic fill valve. In order to have the correct pressure, I would have to

1. install a pump at the transfer tank at the ground floor and lift the pressure to more than 70PSI or
2. move the automatic fill valve to the point where the domestic water pressure is good enough to feed the water. Do I need to move the bladder type expansion tank too?

Is that supposed to be done or there is a better method for the feed water supply? Thank you.

 

[Drazen]

i feel some schematics is needed to understand what are you talking about.

what is the purpose of your storage tank? i would understand it as a tank that supplies pressure control system, but you are mentioning bladder expansion vessel, which leads to confusion for me.

 

[Compositepro]

Expansion tanks and fill valves should be located at the lowest pressure point in the loop, which is typically the highest point in the loop.

 

[nicole10g]

The simple schematic for the chilled water hydronic piping and the main domestic cold water piping is attached.

 

[LittleInch]

The position of the expansion tank and fill point is a little strange, but it's not hard to work out.

You don't say what heights are present here, but assuming for an office building that each floor from floor to floor is a minimum of 3m, the static head on the 8th floor from ground level is 2.4 barg (35 psig) minimum. If you add that to the 35 psig from your pump on the 8th floor and inject it into the system on the 8th floor (or any other floor, but the shortest pipe length is best), you will just get some flow in which is equivalent to 70psig or more on the GF.

I assume there is a vent at the high point you haven't shown for clarity and hence your 40 psig at the GF will be enough to first fill the chilled water system up to the 8th floor and then you can add from the 8th floor onwards.

If the height of your 8th flop pump is more than 24m above the 70 psi point on the GF then you're OK. This only works when the chilled water isn't flowing.

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

 

[SAK9]

Agree with Compositepro that expansion tank should be at the lowest pressure point or in other words on the roof.Once you have relocated,you do not require 70 psi anymore.

 

[LittleInch]

SAK9 - I beg to differ. You might not need 70 psi at the expansion tank location if you move it, but there will still be a requirement for 70 psi measured at the ground floor so the problem still remains as stated.

That though is one solution, i.e. lower the system pressure - 70 psi seems more than enough to keep the system flooded at the highest point so maybe 60 might do?

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

 

[RandomUserName]

Littlinch and SAK9 and bringing up great points.

We really need to know the floor-to-floor distances.

If floor-to-floor elevations are 15ft, then pressure in ceiling of floor 9 is about 65 PSIG. Expansion tank on floor 1 is set correctly at 70 PSIG, keeping a pressure in the hydronic system on the 9th floor of about 5 PSIG.

I agree with littleinch on how they probably fill the system; ground floor water pressure up to the 5th floor ceiling system (if floor-to-floor is 15 ft), then manual fill to the top, possibly with the hydromaxi pump on the 8th floor?

I also agree with littleinch on how relocation of the expansion tank will not change the 70 PSI requirement if the fill valve is left on the ground floor.

Nicloe10g, you need to clarify what your goal is with this system.

If you goal is to have the system automatically refill in the case of minor hydronic leaks, then I believe you need to relocate the expansion tank and fill valve to the highest point in the system. Set the expansion tank at the default 12 PSIG and the domestic water PRV as well; tie fill valve into hydromaxi pump for adequate pressure. Expansion tank will need to be resized as it should become drastically smaller. Where is your PSV on the system?

 

[Drazen]

I would simplify littleinch calculation a bit and say:

10 floors x 3 m + 5 m provision = 35 m, is 50 psi.

you have as much on pressure side of transfer pump, so catch there and change your automatic fill valve setting to 50 psi.

expansion tank position can be anywhere, it is just that pressure setting of the tank has to be adjusted, to work properly.

 

[RandomUserName]

Drazen,

I believe his issue is that city water is coming in at 40 PSIG. He cannot "set" the auto fill valve any higher.

I could be wrong or not understanding; would EDIT: NOT be the first time!

 

[LittleInch]

Drazen, If he sets the valve to 50 psi he won't have positive pressure at the highest FCU. Also 3m is probably a bit low for an office building - if it 4m then it doesn't work.

Of course maybe Nicole could just tell us what the heights of these things are....

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

 

[lukaiENG]

I agree with Little inch. the pressurized supply after the 8th floor pump should provide sufficient pressure at the ground floor (depending on floor to floor heights).

 

[nicole10g]

Thank you for all your replies.

1. There is an air vent at the highest point which I have added 5psi to it.
2. The floor to floor height is GF 8MH, 9F 5.5MH and the rest 4MH. I have marked it out in my revised attached drawing. I also indicate the static pressure on the drawing.
3. There is no space at the 9F ceiling to locate the expansion tank to be higher than the FCU.

I have two proposals:

1. Relocated the bladder type expansion tank and the automatic fill valve to the 8F and set the expansion tank pressure to 18PSI. The domestic water supply from the hydromaxi pump with 35PSI can be used to automatically refill system.

2. To extend an extra pipe tapping from the hydromaxi pump directly to the Chiller Plant Room. This water pressure arrived at the Chiller Plant Room will have 86PSI that could do the job. The point of this proposal is to have all the major equipment to be at the same room but with the extra cost of extending the water pipe.

Which one is a better proposal? Or there is be another alternative.

Thank you.

 

[LittleInch]

Nicole - you haven't attached the drawing, but the dimensions and pressure make sense to me.

If you have room I would put the expansion tank on the 8th floor - less pressure on it and less pressure for the fill pipe and no new equipment, but separates the kit.

However if the fill flow and volume is small, then your pipe from 8th floor to GF might only need to be 1" or so, so a small cost and avoids moving things now.

Alternatively just add a small pressurising pump to the tank on the GF with a discharge pressure of >70 psi. Again if the volumes are small and irregular (topping up), then this pump can be small - I would go for a small PD pump myself, but a small centrifugal would do.

Only you can do the option costs and cost of revising the design, which may be lots more than the cost of the fix.

Let us know what you decide. LI

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

 

[Drazen]

littleinch, i clearly showed in simple equation that it will be sufficient pressure for imagined height. 5 m addition is arbitrary, new standars allow zero for small system, anyhting between 3 and 5 m for larger system, all what is needed is to have slightly higher than atmospheric pressure.

with given heights, though, required psi goes to at least 80 if filled from the bottom. you can, of course, move fill valve on the top downstream of so called hydropump, but the statement how automatic fill valve cannot be adjusted have little sense to me. if that's true, drop it, and buy one spring overflow valve plus one non-return valve (or backflow preventer if code requires so).

again, that has nothing to do with expansion tank, fill point at the expansion tank is made customary, but is not rule carved in stone. you just need to adjust expansion tank to real static pressure.

 

[nicole10g]

Thanks LittleInch for the advice and I have attached the drawing now.

The building is still in construction and will be commissioned in 2 months time. The expansion tank is not yet installed, in fact it is not yet purchased. The hydromaxi pump room is beside the main chilled water pipe riser and there is ample of space to house the expansion tank. Therefore, I will advise the client to install the expansion tank there with the charging pressure of 18PSI and the automatic fill valve to set at 18PSI too.

 

[Cjrac]

add a system feeder (axiom or similiar) and tie into expansion tank..provide a hose bibb connection adjacent to the system feeder to fill the system feeder tank .

 

[nicole10g]

I was thinking with the reduced pressure for the pressure tank, I could have reduced the tank volume capacity too.

The original tank sizing is as follow:

1. Chilled water temperature is 44degF (take 40degF and SV1@40degF = 0.01602
Max ambient temperature is 104degF (take 100degF and SV2@100degF = 0.01613
Total volume of chilled water V1 = 55000Litre

Expanded Volume = V1*[(SV2/SV1)-1] = 55000*[(0.01613/0.01602)-1] = 377 Litre

2. The chiller safety valve is set at 135PSI and the CHWP head is 35PSI
Min pressure at the tank P0 = 70PSI and max pressure at the tank P1 = 135-35 = 100PSI

Acceptance Factor = 1-[(P0+PA)/(P1+PA)] = 1-[(70+14.7)/(100+14.7)] = 0.2616

Total tank volume = 377/0.2616 = 1441Litre and choose 1500Litre tank

Now with the pressure move to 8F @ 36MH (118ftH or 51PSI) from GF and piping design is 4ft/100ft drop, therefore pipe drop = 2PSI from GF to 8F
Min Pressure at the tank P0 = 18PSI and max pressure at the tank P1 = 135-35+2-51 = 51PSI

Acceptance Factor = 1-[(P0+PA)/(P1+PA)] = 1-[(18+14.7)/(51+14.7)] = 0.5023

Total tank volume = 377/0.5023 = 7501Litre and choose 800Litre tank

Can I size the pressure tank as above formula and calculation?

 

[EnergyProfessional]

Some things to consider:
- expansion tank and water supply should be at the "point of no pressure change", which is suction side of pump.
- this may be at ground floor, or highest floor. while highest floor may be preferable to reduce pressure, this may not be possible if the pumps need to be by the chiller etc.
- If you install it not at "point of no pressure change" the pump activity will increase the pressure based on pump operation (your 70 psi plus whatever the pressure the pump generates, which will vary). not good at all.
- at the highest point your pressure should be above ambient pressure (0 gage pressure, or 14.7 psi absolute pressure). This is to allow de-aeretors to work. If at the high floor the system pressure is below normal air-pressure, the de-aerator will suck air into the system instead of purging it.
- that "point of no pressure change" and the elevation difference to highest system point determines the system pressure you need. Every 2.31 ft of height, 1 psi in case of water Fluids with different densities (glycol) are different.
- with your 70 psi gage pressure (above ambient pressure) your highest point cannot be more than 160 ft higher (70 psi x 2.3 ftH2O/psi). Obviously you want some safety, so have 10 psi at the highest point etc.
- all your equipment in the building needs to withstand the pressure. At discharge side of pump you have 70 psi + pump pressure. so you may need 150 psi devices on ground floor etc. At highest floor they only need to withstand less. So you may be able to use less expensive device upstairs.
- if city-water does not provide 70 psi, you need a booster pump. No free lunch in thermodynamics, sorry.

 

[Compositepro]

Everything energyprofessional points out is correct and is satisfied by doing as I said is the standard practice, in one sentence.