multiple evaps

[angryk]

Hello all. I would appreciate any opinions on the best way to set up a multi- evaporator system on one compressor.
I am refering to two to four evaps on one compressor with small h.p. or fractional h.p. compressor. My main thoughts are on oil return and superheat management during the various loads the system will see. I am asking this as a general question, not in regard to a specific sytem.

[Bones]

well, use non-return valves on all evap coils exept for the warmest coil... manual shut off valves for liquid and suction should you ever want isolate for repairs/service down the track... cycle coils through thermostat controling liquid line solenoid valves..

possibly a EPR valve, and if your specifically worried about oil return throw an oil separator in.

[Peter_1]

Must all the evaps run at the same suction pressure?
Attached you will find a drawing like we did already several times in vending trucks.

If you run at partial load, there is plenty capacity available and a also huge condensor capacity. Suction pressure remains allways the same and compressor is always working under the same load/conditions.

9 years ago, at the initial build up of such a system, our client asked us to use his old Comef compressor - if possible - which was then more then 20 years old. He's still running.

Safety cut-out thermostat in case liquid injection should fail and suction gasses becomes to hot.

Liquid injection is cut off is fed by an ESV (running together with the compressor) to prevent overflow in the accumulator.

With the system we use, the compressor always run at the same conditions,regardless of the number of evaporators running.

Never used an oil separator, but payed allways attention to lay tubes with a slope to the compressor and pay attention on suction speeds.

Or you can use a frequency controlled flat Hitachi scroll (did this once with good result) specially build for this application or the brand new capacity controlled scroll of Copeland (allready used in the newest Samsung VRV units)

[Peter_1]

Forgot to post the picture but as far as I could find out, unable to do this when editing. Is that correct?

Is the picture readable? Sorry it's a hand drawing but it takes too much time to draw it with the computer.

Peter

[chemi-cool]

Hi John,

the most basic unit is a domestic refrigerator with two doors (not no frost). it has two evaporators in line with the same evaporating temp. but different temp in each cabinet.

read cerfully what peter has to say cos he's got tons of experiance!

I did years ago a big high temp 7C storage for flowers before shipment to europe there was one compressor, oil separetor, three evaporators in paralell all in one room 200m2 one over sized suction line accumulator. pump down.
the system was operating with good old R12. and didnt have any problems.

I belive its still running today if they still have flowers.

chemi

[angryk]

thanks for the input everybody.