Conversion of AC condensing unit to refrigeration

[springmaster]

Hi All

I would like to confirm if we can do the following:
- we have a condensing unit of around 30 kW cooling capacity for AC, in good shape, wich we want to convert to refrigeration for a cold room. The unit has 2 MANEUROPE MT64 and for AC it use to run with R22, with a centrifugal fan;
- as said before, we want to use it for -20ºC Cold room, with -25ºC evaporating temp with R22, making cooling capacity of compresssors 3,09 kW , total = 6,18 kW at those conditions;
- when we calculate a condensing unit to match the compressors duties at those conditions, the Condenser capacity, according with a manufacturer catalog, is 9,0 kW at 10 ºC DT;

- we think that we can use the old condensing unit wit a speed regulator conected to the centrifugal fan to lower the rpm- Question- can we do this?

or

- can we use that condensing unit with 1 new compressor with cooling capacity of 30 kW at -25 ºC?

Please help

Thank you

[HVACRAU]

MT064 compressor -25ºC evaporating temp almost out of compressor envelopes. On -20ºC freezer room it will struggle. How big is the room size?

[springmaster]

Hi

The room size is 6 x 2,4 m x 2,4 m- an 20 feet refrigerated container. Note that we want to put 2 units running and the product is frozen mackrel coming in at -15/-18 ºC.

[HVACRAU]

That’s good you put 2 units, only if the insulation is Ok.
From compressor manufacturer’s data, -18^oC room /38^oC ambient will be a limit. You can try if you can make lower.

[springmaster]

Thanks.

Shall we use a variable speed regulator for the condenser fan or we can use the condenser as it is?

Rgds

[HVACRAU]

That will not improve the unit’s capacity.
Fan speed control normally use when condenser is big or low local winter ambient temperature or for noisy control. You need decide yourself.

[springmaster]

Hi again

As mentioned, the condensing unit is originally 30 kW cooling capacity for AC.

Question:
So is it ok if using for -25ºC wich will give us a total = 6,18 kW at those conditions? the condeser unit is 30 kW
or
we have to match the condesing unit capacity using a a speed regulator to give us the condesing capacity of 6, 18 kW?

Please help

Thank you

[Goober]

Not sure what your workings are, but from what you're saying the condeser is now oversized and that does make sense. Simple way would be to block off a portion of the condenser.....

[AlexG]

Springmaster, dont warry about condenser size. For your compressor at -25C evap T max condensing T is 43C. Maybe your oversized condenser will help you to have this T. If you have centrifugal fan take care about amperage. Without ducts can burn motor. And dont forget about defrosting system.Good luck.