Question, Chilled Water Tank Sizing

[Pete_K]

Hi All,

First, if this question should be somewhere else, please let me know...i am new to this forum.

I'm doing work for a customer on a piping system upgrade. The system supplies chilled water (~60 F) from an open tank to molding machines, and returns the water to a partitioned side of the same tank it came from. Water in that partitioned area either goes thru a chiller or a heat exchanger to bring the temp down. The temps of the streams into the "cold side" are probably within 10 degrees F of that 60 degrees outlet temp.

My problem is, the customer is looking to us to provide direction on sizing the tank. The output flow is ~900 gpm. All they have offered is that the chiller requires to have 1000 gallons of water in the tank. This kind of work is not in my background - I'm more of a machine designer. The closest experience i have to this is sizing large reservoirs for hydraulic oil for oil bearings. In those cases typically there is a "retention time" that you are aiming for, so if my desired retention time in this case was 3 minutes, i'd need 2700 gallons.

Is there some "rule of thumb" or other sizing rule in this case? My typical efforts of researching on Google have not been fruitful, so any help i could get would be much appreciated. I have a feeling that the tank will end up around 3,000 gallons, but I would like to be able to back that up with something.

Thanks in advance.

p.s. i am going to post this question as well in the HVAC forum.

 

[bimr]

If the chiller supplier says all you need is 1,000 gallons, then that is all you need.

One would think the issue has more to do with the number of start/ stops of the pump. Pump motors are designed for a typical number of start/ stops per hour. The reason being is that more heat is generated during the pump start than during the pump running. Too many starts per hour will burn up the pump motor.

You need to analyze the operation and design the system so that the pump is not continuously cycling on and off. You have not presented enough information to do this.