How to Design Refrigerated Cabinets

[Rayin]

Hi All...:)
I am working in a factory fabricating refrigerated cabinets as per client requirement. The technicians, not doing any calculation put one model of compressor, usually higher capacity than required.(Danfoss, Made in Germany, Hermatic models) Then fabricating either fin & tube type or tube_wound_around_inner tank type evaporator. Gas charging is little more funny. They start charging and if the discharge line near the compressor feeling cold, will stop the charging. If the client complaints about improper cooling, first will increase or decrease the refrigerant, even if no effect, then will replace the condensing unit. I am sure it is not the proper method. My question is how to Design a refrigerated cabinet.? I know the 4 components (1. Transmission load, 2. Air Change. 3. Product Load. 4. Miscellanneous load) of heat gain to design a walk-in cold room. same method can we use in refrigerators? Then how to design a custom evaporator?
How to calculate the amount of refrigerant?
What should be the low & high pressure?
Refrigerant is R134a for Coolers and R404 for freezers. Ambient temperature: 40 degree C
Inner and outer wall of our cabinet is 0.8mm thick stainless steel and in between 50 mm thick PUF insulation, (40kg/m3), injected.
I know the storage temperature and humidity conditions required for almost all products our clients are using.
As part of my Mechanical engineering course, refrigeration was one of the subject of study, more focused on theory than practical. So I need help from the refrigeration Gurus to connect the theory with actual parctice. Considering the case of a cabinet with inner size: 1900mm Length x 600 mm width x 600 cmm high with 3 no. 500x500 mm opening on length side for doors, to store fruits, can anybody explain me the design process?
With many many thanks in advance
Rayin

[Kevin Yeo]

Hi Rayin,

Is your 'refrigerated cabinet' fully enclosed? If so, you can almost use any heat load calculation software to calculate how much capacity required by the cooling coil with consideration of glass doors isn't it.
But if its used to store fruits, you may need to consider lower KTD1 to maintain relatively higher humidity. Assuming required temperature +5 deg C, using KTD1 of 5k your evaporating temperature should be 0 deg C. Size a condensing unit with 0 deg C / 50 deg C (since you mentioned ambient is +40 deg C). 10k difference between SCT and ambient should be used to size a condenser.
Hope it helps. By the way, do you export these showcase? Do you mind to email to me the pictures of them :) Thanks

Rgds,
Kevin

[Rayin]

Dear Kavin..
Thanks for you reply.
I attach image of one of our products. We manufacture only for order (It's job order shop) I need some more details like, how can we do the condensing unit selection calculations manually? Also how much long should be the evaporator coil? The amount of refrigerant required ?etc. What is the correct charging procedure?
Thank you very much again
Regards
Rayin

[taz24]

Also how much long should be the evaporator coil? The amount of refrigerant required ?etc. Rayin


Hello Rayin.

When sizeing up a system you always start with the size of the evap and take it from there.
You need to know the heat loads of the products in the cabinate, the outside ambient influence (heat gain through the walls), defrosts and also somthing people forget about is the internal heat sources such as evap fans and trim heaters.
When all this information is known then a calcalation for the size of evap can be made.

Cheers taz.

[LRAC]

Hi Rayin

This is not exactly the correct way to do it, but i was involved with cabinet designs at a refrigeration manufacturer in Dudley. We kept our research and design costs very low.

Simple when a store refit was in hand we would remove the old cabinets,multidecks etc and completly gut them back at the factory to see what made them tick, or as soon as a competitors cabinet came on the market we would purchase one and do exactly the same.

Might be worth you following the same procedure?

OK guys i know its the wrong way round but all industrys do it.

Regards
Lrac

[Rayin]

Dear LRAC,
We also do the same trick!. But it does not make satisfy me. That is why I posted the thread!!
Anyway thank you for your response!!