Compressor sizing for both chiller & freezer (1 comp for 2 room)

[helm_n]

Hi all,

I'm new here.

Appreciate the help & info.

How do we sizing compressor based on below condition:

One compressor (common) to cater for both chiller & freezer room.

Chiller room operating temp at 4 degC (evaporating temp -4 degC)
Capacity required : 10,000 btu/hr

Freezer room operating temp at -25 degC (evoporating temp -33 degC)
Capacity required : 14,000 btu/hr

Refrigerant : R404a
Condensing temp : 50 degC (Air cooled with 35 degC ambient)


This kind a new to me as I normally do one compressor to one room system with straigthforward when selecting the compressor.
But to sizing compressor with different evaporating temp, I dont' know how to properly do that.


Thanks in advance all the info.

[mad fridgie]

You should not!

[mbc]

you should design your system for -33 deg C
the capacity of compressor as much as more is better
and you need CPR (crankcase pressure regulator) and other equipment to do this kind of works
mail me to send more information and drawing of that to you.
gholbehan@yahoo.com

[helm_n]

mad fridgie,

Common practice in refrigeration provision system this is. One compressor in duty mode, another in standby/backup mode.

[helm_n]

hi mbc,

dont want to oversize it too much which will affecting the cost. Definitely not to undersize either.
Understand it will also need evaporator pressure regulator at suction line of the chiller room. is it the same as crack case pressure regulator?

Appreciate the info provide.

[mad fridgie]

Is this one room at 2 different set temps or 2 different rooms running at different temps

[abidmech]

Dear

For different temperatures applications means below zero degree and above zero degree then you will need the booster or two stage compressor operating at -42C evaporating temperature and -4C evaporating temp.
For further detail, please feel to contact me.

Regard
Abid Ameen
abid.ameen@dec.com.pk

[mad fridgie]

If you are using a single compressor for 2 rooms (say for instance a Copelend scroll) then you will be using approx 2Kw more power than if you had 2 compressors sized for each duty.
heres the numbers
2Kw * 18hrs a day = 36Kwhrs
36kwhrs * 365 = 13140Kwhrs/year
13140 * $0.1/Kwhr = $1314.00
10 year life, saving $13,140.
No need for for one large compressor or EPR, (so yes has slightly higher install cost, but which is the best value for money, and what is best for the enviroment?)

[helm_n]

This is mostly for off-shore unit, freezer & cold room on ship/rig. Such design offer more convenient when do trouble shooting when one of the system fail. Having 2 system separately will also have space issue.
I also have other request with 2 compressor running with 1 backup comp.

I've generated (attached) a diagram for reference. Pls comment.
Now to properly size the compressor is an issue for me. Compressor will
be Bitzer semi-hermetic reciprocating.

Thanks all.

Mad fridgie,
This is for two room with different temp setting but with common refrigerant line.

[mad fridgie]

Compressor sizing should be based at lowest SST (suction pressure) add both duties together. You could derate slightly to cover diversity, you need to find out how the duty for each room was derived.
Nothing wrong with Bitzer.
I presume refrigerant, TEVs, are a standard spare part off shore!!?
If you truly want back up you could look at interwoven coils (seperate refrigeration circuits within a single evap configuration)