how to size a chiller 1

[bragamor]

We need to buy a new air cooled water chiller for our chemical plant in Texas. The water flow in the system is 150 gpm so I have calculated that we need a 100 TN chiller.

CHILLER SIZE=150 GPMx60x8.33x12*x1.15**=102 TN=1,224,000 BTU
* delta T
** security factor in case we want to expand the system in the future

This chiller is feeding 10 exchangers, and here is where I have my biggest problem. To optimize the performance of the system, does the BTUs of the chiller has to be bigger than the BTUs of all the exchangers?

Thanks for you help on this one

 

[Montemayor]

Your statement is wrong or your calculations are wrong.

You do not show a calculation that reveals you need a 100 tons of refrigeration. Your calculation should show you need:

(150 gal/min) (60 min/hr) (8.33 lb water/gal) = 74,970 lb/hr

Heat Capacity of water = 1.0 Btu/oF-lb

Heat Transferred = (74,970 lb/hr) (1.0 Btu/oF-lb) (Delta T) = (74,970 Btu/ oF-hr) (Delta T)

If your Delta T = 12 oF (which you haven’t defined), then:

Heat Transferred = (74,970 Btu/ oF-hr) (12 oF) = 899,640 Btu/hr

Allowing for a 15% Contingency,

Heat Transferred = (899,640) (1.15) =1,034,586 Btu/hr = 86.21 tons of refrigeration

You fail to specify your units and your basic equation. You cannot expect to have your calculations checked if you don’t specify your units and your basis for equations.

The BTUs of the chiller has to be bigger than the BTUs of all the exchangers because of the inherent refrigeration losses you will suffer through the insulation on the equipment and the piping.