Water Chiller Flow and Pressure Graph

[Worker7]

1. If a chiller is designed to provide 3 gpm at 80 psi and we have a pressure drop of 20 psi in the equipment cabinet we are cooling, would you still have 3 gpm flow through the copper tubing in the equipment cabinet?

2. When our equipment is turned on and heat is being generated and the chiller is running at 3 gpm, if we want to maintain 3 gpm but at the lowest possible pressure, could we reduce the pressure to where we want it without affecting the 3 gpm flow as long as we don't reduce the pressure lower than what is needed to overcome the pressure drop in the equipment cabinet?

 

[drawoh]

WorkerZ,

What kind of pump are you using? If you use a positive displacement pump like a gear pump, your flow should be approximately constant, regardless of the back pressure, at least within the limits of the pump. I cannot image a centrifugal pump, a small one anyway, putting out 80psig. The 80psig actually has nothing to do with your pump. It is a function of your flow rate and the fluid resistance of your system. If your pump is capable of 80psig, it will pump 3gpm. Are you sure your output is at 80psig?

If you want to maintain your flow rate but at lower pressure, you must reduce the back pressure in your system. Making your tubes and pipes bigger has a huge effect. If you are concerned about the absolute pressure in your system, you need to move your high pressure drop components like radiators and flow-switches, upstream of your system.

When I did this analysis, I found that the chiller's cooling rate was not very sensitive to flow rate. You should look into this. We were concerned about maximum pressure, and I unsuccessfully argued for a centrifugal pump. The gear pump we used absolutely needed a pressure relief valve.

--
JHG

 

[mk3223]

For the question #2, IMO, you may need a bypass or circulation line to maintain the constant flow of the system while adjusting the operating pressure to suit the system demand.

 

[drawoh]

mk3223,

If you bypass the equipment, you are not chilling it. What is the point?

--
JHG