View Full Version : Evaporator Concerns-Use of a 30 TOR Unit for a 40 TOR System

29-06-2004, 04:07 AM
Would it be possible to use an underrated evaporator (say design at 30 TOR) for a chilled water system with design capacity of 40 TOR? If this is possible, are there any operation control procedures we need to implement or operational parameters we need to monitor to make sure the set-up would not pose any problems to system auxiliaries such as compressor, expansion valve and condenser. Due to marketing constraints we were forced to use this set up without us really knowing how it will affect the whole system operation. However, we were assured by our local contractor that this would pose no problem as long as system is operated at lower capacity than 40 TOR and initial charging of refrigerant also lower than the standard. Any inputs on this concern would be highly appreciated.

29-06-2004, 06:35 AM
You should have a licensed design engineer review the system to avoid potentially serious and expensive problems. An undersized evaporator (undersized in relation to the compressor and condenser) will operate at lower temperature. Besides being inefficient, there is the potential for freeze-up in a chilled water system unless water velocity and temperature are maintained high enough and safety controls are properly designed.

Unless your contractor is very experienced and willing to guarantee performance and provide an iron-clad warranty in the event of failure, it seems foolish to proceed without professional design advice.


29-06-2004, 07:11 AM
Much More information is required to give a fair answer. You say undersized evaporator what else would be undersisized. We are talking 25% undersize. Thank "god" you you don't need to licensed in the UK.

On the other hand as we don't use CFC's maybe it's a blessing so thank "god"

"GOD" = a higher being someone you believe in
(does not live in a white house or have a dad who used to live there) :D

29-06-2004, 09:45 AM
Thank you for the advice. We'll just operate the system beyond its rated capacity say at 66%. Anyway system is expected to operate only in week time after which we can hopefully install the new evaporator.

Our system operation:
a) 20 m3/hr, evaporator out temp @ 15C and evaporator in temp @ 30C
b) Capacity Control at 33%, 66% and 100%

29-06-2004, 04:34 PM
Hi Marc.

How about using hot gas bypass to maintain positive suction temp?


29-06-2004, 06:57 PM
Or replacing the gass with another one (for example R407c out and charging R134a in) and replacing the TEV, adjust LP and HP.
Has to be done by someone who know what he/she is doing.

29-06-2004, 08:12 PM
And fit a CPR to prevent excessive back pressures

30-06-2004, 11:47 AM

Whatever you do with your evapors, and I hope it will work OK for you, please come back and let us Know what you did and how did it work?

Good luck. :)


05-07-2004, 04:29 AM
Good morning to all!

Just to let you know that we've already commissioned the chiller system with a 30 TOR evaporator. So far the system is operating normally but of course at a reduced capacity. Correspondingly, our production operation has also been reduced to 60%-70% of the rated output. The following operational controls/guidelines are strictly being implemented to avoid problems:

a) Compressor is manually operated at 33% and 66% capacity control. Never in any instance would we allow the operations group to set the capacity control in automatic operation or manually set the capacity control at 100%. As additional protection, we bypassed the 100% capacity control such that it fully operates unloaded. Compressor motor ampere reading is also stable at 41 amperes (or 68%) compared to full load current of 60 amperes.

b) If process overloading occurs, corrections are made on the product side (say reduction of material feedrate in heat exchange with the chilled water) and not on the capacity control of the chiller system.

c) All controls were tested and assured to be working before we formally advised production to proceed with the operation. These included the oil pressure switches, low and high pressure switch cut-out, chilled water low temperature cut-out, etc.

Thanks and regards,


05-07-2004, 11:47 AM
Hi nrps.

Glad it came out OK. :)