Doble Temperature With Only 1 Evap/cond System

[georgedvf]

Hello everyone!
I'm new here, my native language isn't the english so if I say something stupid or non-understandable please hit me :confused:, I mean, let me know.

I'm wondering if any of you have ever designed a refrigeration system where, with just 1 compressor, 1 condensator and 1 evaporator you can get the room either at 2°C or at -18°C. The guy who is asking me to do the system calls it "double temperature room", the reason for this is that he would rent this room, so if a client of his needs to keep vegetables in there the room should be at 2°C, but if other client needs to keep meat or something frozen, the room should be at -18°C.

So I'm trying to figure if it is possible, and I thought, hey I found this forum full of experts, lets ask their opinion.

I hope you can help me!

Thank you!!

[gramcor]

Hello George
Is the same situation like in " no frost " refrigerator side-by-side .
Make -18 C in one room and redirect frozen air from this with an variable speed fan to refrigerations room.
must have two temperature loop control , one ( the main ) for -18C and other for fan speed .
Best regards
Gramcor

[Peter_1]

Welcome George.
Don't worry about your language, my native language is Dutch and most understand me very well.

It's possible with some restrictions: if you design it as a freezer and makes that your compressor can handle an evaporating temperature of -10°C (14°F), your condenser is big enough to handle the load while in cooling, then I don't see a problem.

[smpsmp45]

There are commercially developed units available with this conditions. We had used a few for veg as well as Icecream applications. But it had Two compressors. I am talking about 5TR system at -20 Deg C. So also the condener has sort of two circuits as at higher evaporating ( room ) temp, the heat rejection is more. So te other curcuit comes into play that time. But yes condenser is One as such split into two circuits. But Semi Hermetic compressors are designed specifically for various temp ranges - High. Medium & Low. So we need Two compressors One for LOW category & the other for Medium category.
But unit has a single box construction- Monoblock

[NoNickName]

Isn't it enough to have a dual setpoint microprocessor and a superheat controller?

[georgedvf]

Thanks to everybody!

Gramcor: If I understand well, you're talking about having a separate freezer room next to refrigeration room??? I need the same room, but in different months or years to become freezer or cooler.

Peter_1:
what about the evaporator?? does the distribuitor/expansion valve have capacity to handle such different drop pressures?

smpsmp45:
that's interesting, i guess those units are for small capacities??? I forgot to tell you the dimensiones of the room, it's 22.00m (long) X 7.00m (width)x 13.00m(height), so there will be like 3 large evaporators and 3 compressors/condensing units.

NoNickName:
I'd not reject any proposal, I'm happy to learn as much as I can, if you have some more information about the operation please it would be great.

Again thanks to everybody!!!

I know I'm asking too much, but, do you know where can I find technical information about designing refrigeration systems??? Industrial projects...

Thanks a lot!

[Peter_1]

what about the evaporator?? does the distributor/expansion valve have capacity to handle such different drop pressures?
This will be no problem, as long as you make the right selection.

[georgedvf]

Ok, this is what I did:
I designed it as a freezer, I couldn't find a compressor who handles such a wide range of temperatures so I chose 2 for low temp and 4 for normal temp (actually It's rack :eek:), so I had to use solenoid valves to control wheter the system should work as freezer or cooler. Then I looked for an expansion valve but couldn't find it either, so I chose an electronic expansion valve, problem solved.

Thanks to everybody

[david_pittsley]

Hi,did you consider using a back pressure regulator to control your evap. pressure.This will control your evap. temp.So you need to install two of them on the low pressure (suction ) side, and have a switch to control which regulator is on.They also make a motorized valve on the back pressure regulator which has a very large range of of temp.variations that you could use.You adj. the t-stat and the motorized valve will open or close and modulate to maintain your desired temp.What do you think,might this work for you?

[sonhdv]

This will be no problem, as long as you make the right selection.

Yes, I think that.
at 2 deg C line the evaporator temp is about -10 deg C to -5 deg C.
And the -18 deg C line the evaporator temp is about -25 deg C.
The problem is we have only one compressor, one condenser (in this case i think it is condenser/condensing unit) .
If we have only one room (using for two cases), we can choose for -18 deg C line (it's not problem for 2 deg C line).
But in the case we have two rooms (one for -18 deg C and one for 2 deg C), it mean the pressure is different.
Can we use one unit like above for it.
Tks so much, and If I have any mistakes, pls let me know.
Tks again

[mnazliay]

Hello everyone.

It is my first time wiriting to the forum.
I have been selling the "dual temp. refirgerating units" for very almost 15 years.

How we are doing it is : you get the compressor for dual temp, i.e which allows you to work with +5 /-30 C evaporating temp with the capacity control.
If you have a 4 cylinder comp, then you use it with 4 cylinder full load load low temp, and 2 cylinder for medium temp.
You design the unit for low temp-30 ev., then when you cut one head of the compressor yor evaporator and conndenser is always ok for half load.

The system works for preservation rooms without any problem, but of course for high capacity for medium temp like precooling will make the uit not suitable since to obtain the high medium temp capacity, you must have a very oversized compressor for lo temp.

I hope the information was helpful:

[herman]

the smartest solution!