Refrigerated Cabnets _ Design Fundamentals

[Rayin]

Dear All
It is indeed a very good site for every one interested in Refrigeration and Air
conditioning. It seems many members out there, are dedicated their whole time for helping
others by providing valuable replies. I am very grateful for the replies/ comments I got for
my previous postings.
Now I am agian seeking another help.
I am in the process of designing a refrigerated cabinet (work top refrigerator) for
vegetable storage, as per the attached Drawing. The overall external area of the cabinet is
5.62 sq. meter. The useful internal space is 0.352 Cubic Meter. The cabinet wall is 50 mm
thick, insulated with PUF (injected in place). The inner most & outer most surface of the wall is of 0.8 mm thick stainless steel sheet. The Cabinet has 2 no. doors of opening size 400x580 mm. This cabinet will be used in a Restaurant kitchen, where the temperature will be +22 to +25 Deg. C. The inside temperature of the cabinet should be +4 Deg. C. Products to be stored are Lettuce, Carrot, Tomato, Spring Onion etc (salad items)
Now my questions are:
1. When calculating wall heat load shall I neglet the 0.8 mm thick stainless steel sheets on
either side of the wall and just consider 50 mm thick PUF only?
2. How to calculate Air Change load?/ Infiltration load ?
3. To calculate product heat load (respiration heat load also), do I need to assume that the
whole cabinet will be filled with products? From where can I get specific volume of
products? As it is for different products, during load calculation, should each product be
taken as equal quantity?
4. The products are brought from super market in refrigerated vehicle, unload in a non-
airconditioned space, then taken to airconditioned (+22 to +25 Deg. C) kitchen, wash and
store in the proposed cabinet. What should be taken as product entering temperature? (I am
in the United Arab Emirates. Here non-refrigerated space temperature can vary 20 to 49 Deg
C, depending on season)
5. Generally what is the pull down time for these type of refrigerated ucabinets?
7. What should be the relative humidity inside the cabinet to keep leaves fresh? How to control RH without using humidity controller?
8. Once the heat load is known shall I use the equation A = Q/(U * Diff. in temperature) to get the evaporator coil length? (Area/ circumfrence)
Anticipating valuable replies, as usual, and thanking all the ladies and gentleman out there
With regards
Rayin

[Rayin]

Hi Dears,
May someone can explain how to calculate product load for a refrigerated cabinet supposed to be stored different products? What is the pull down time of normal work top/ reach in refrigerators?
With thanks and regards
Rayin

[RCassist]

Dear Rayin,

a lot of questions, and a lot of time since my last heat load calculation. I'll try to answer to those I remember. Hope it will help anyway.

1.) Do not consider the steel thikness, as the Lamba-value (heat transmission index) is given only by the isolator and his thikness.
2.) No answer
3.) I would consider the heat load related to the biggest "heating" product, in full cabinet condition, integrating a certain percentage of product turn-over. This way you should have the worst case condition allowing you to cover every requirement.
4.) I do not know really what to answer, but here in Europe theoretical transport temperatures are in practice also higher. I would consider something like 30-32°C.
5.) Depends on product an cooling unit. For meats you can cosider that cold penetrates mass with 1 cm/hour.
7.) For leaves you should consider 85-92% of RH in %. The only way to control it without humidity control is by dimensioning your evaporator exchange area wide, in order to keep an average DeltaT of 4-5 DEG.
8.) .....

Hope it helped. Have a nice day.

[harsadjanneh]

Dear All,

I am in the process of getting assembled , Drop in refrigerated frost top for mixing ice cream , just like cold stone and marble slab. I need assistance with the laying of frosted pipeline in between the stainless steel top on which granite is to be placed. I need drawing of the pipeline to lay in the top, size of the pipe, length of the pipe and other specs. Your help will be appreciated.

[Rayin]

To RCassist
Thanks for your reply. But still I am looking for more detailed answer. Any how I am trying to get copy Fundamentals of Refrigeration Hand book of ASHRAE.
Again many Many thanks for your reply

To harsadjanneh
I can't answer your query, but if some one can answer it, indeed more details you have to provide. Like size of table, Room temperature, quantity of ice cream mix, if 4 sides of the top is exposed to room temperature, how do you plan to do maintenance work of the coils/ evpaortaor fan etc. If you provide these details and many others, I may have missed, I hope many memebers can help you.
Wishing you all the very best.
Regards
Rayin