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Chilled Water System , Confusions

Chilled Water System , Confusions

Chilled Water System , Confusions

I working on a project , with a Primary (SC) and Secondary (VS) Pumps system , additionally 3 chillers 191 Ton each ,
its my first time working on chilled water system , so i have many confusions ,

i have been searching online from quiet some time for these confusion and unfortunately couldn't find any clear answers ,
i know theirs no quick way to learn a complete system the easy way , since at job i am surrounded by such people , whom don't share any knowledge and even on asking no clear answers , ( kind of people don't wanna see other grow ) any ways .

the confusions i have are as "

1) how do we determine the system working pressure ?? as per my knowledge the circulating or primary pump head is not the working pressure of the system , so what will the system pressure and at a phase of testing and commissioning , what volume of water to be filled in the system and at what pressure should be the system be pressurised and then run it .

2) the makeup water line can be connected to any on the branch lines for the air separator or the expansion tank ??

3) the chemical doing system is selected on what parameters , method/location of chemical doing system piping to chilled water system and what are the chemicals been used for chilled water system ??

4) what are the chemicals used for the flushing processes ( for carbon steel pipes ) ??

sorry for stupid systems .

guys please share your valuable knowledge with me


RE: Chilled Water System , Confusions

This topic has been discussed on this website before in great detail. Do a search.

The expansion tank should usually be installed at the highest point in the system. The pressure of this tank establishes the lowest "system" pressure through the use of a water pressure regulator, which adds water as needed to maintain pressure. An air vent valve removes any air that might accumulate beyond the set level (usually half of the expansion tank).

RE: Chilled Water System , Confusions


I understand the expansion tank should be at the no pressure change location , but the point is what should be the Pre-charge of the pressure tank, now this depends on the pressure of the system , how to we know that means ,

for Example i have all the system ready with all piping for chiller , primary pumps , secondary pumps , ahus and fcus

now the system should be filled and pressurized before running the system . so at what pressure we need to pressurize the system before run it ,

RE: Chilled Water System , Confusions

You should seek the help of a more senior Engineer where you work.

RE: Chilled Water System , Confusions

I think these are actually pretty good questions for someone approaching their first CHW project, it is a shame your colleagues are not helpful.

For the first 2 questions, as mentioned earlier you should do a search of this forum. http://www.eng-tips.com/search.cfm?pid=403&act...

Manual chemical dosing pots are normally connected across a circulation pump, the pump forces water through the pot and introduces the chemical to the system.

Here is a good article on chemical flushing

RE: Chilled Water System , Confusions

Tank pressure is most often about 15 to 20 psi, but could be different for quite a number of reasons.

RE: Chilled Water System , Confusions

Know that a cubic ft of water at standard condition weights 62.34 lb.
Thus the pressure exerted by 1 ft high water column is 62.34/144 psi = 0.4329 psi

For closed piping system, if the pump suction is located say 200 ft below the highest piping (usually assumed at roof of the building) we typically add about 6 ft more water pressure so air will not get into the piping if the highest valve is opened to athmosphere. So the design pressure at pump suction should be .4329 x 206 = 89.2 say 90 psig. This is maintained by using an expansion tank that has a bladder precharged with comprssed air to about 12 psig and a pressure regulating in the makeup water line connection to the closed loop circuit. Now the pump when it runs produce its design pressure (say 85 ft head or 36.8 psig) at the design flow. So with pump running pump discharge pressure = 90+36.8 = 126.8 psig. Check piping and equipment submission on the project for their maximum operating pressure. If this is 150 psig and say you want to limit maximum pressure to 145 psig then the maximum allowable pressure you can tolerate in the system if the pressure regulating valve fails would be 145-126.8 = 18.2 psig. To safeguard the closed loop system from overpressure provide a safety relief valve downstream of the pressure regulating valve set at 90+18.2 = 98.1 psig.

If you are working for a consulting firm there should be master specifications that would state water treatment requirements. Also see previous projects, design drawings, specifications and project equipment submissions. Also ask google. So much information now is available on the internet.

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