Cold Room Air Circulation Rates

[georgedvf]

Hello!!!

Is there a ASHRAE recommendation about how many air changes per hour must be in a determinated Cold Food Storage room???

I've seen some tables from some refrigeration compressors/evaporators manufacturers (ex.BOHN) that recommends you a minimum air changes per hour, but I can't found the base of that recommendation, is that taken from ASHRAE???

Thank you!

[nike123]

Why would you change air in cold room if, for example, food is frozen and packed in vacuum packing.
If you mean air circulation rate in cold room, than that is totally different from what you mean by air changes.

[georgedvf]

Thanks nike132, that's the correct word for what I was trying to refer for.

Can you tell me how can I change the subject of the thread, or just the moderators can???

[frank]

Done......

[georgedvf]

Thanks Frank, but I meant that "Air Circulation Rate" was the correct word for what I was looking for. Could you change the "Infiltration" for "Circulation" in the subject please???

[frank]

The air circulation rate would just be the amount of air pushed around by the evap fan. Is this the information you need?

[georgedvf]

Yes, that's why I'm looking for. This is what I found on Heatcraft-BOHN engineering manual:

4. Type of Operation/Air Flow
Two important considerations in the selection and location of the unit cooler are uniform air distribution and air velocities which are compatible with the particular application.
The direction of the air and air throw should be such that there is movement of air where there is a heat gain; this applies to the room walls and ceiling as well as the product. The unit cooler(s) should be arranged to direct its discharge air at any doors or openings, if it all possible. Avoid placing the unit cooler in a position close to a door where it may induce additional infiltration in to the room; this can cause fan icing and a condition known as hoar-frost. Also, avoid placing a unit in the air stream of another unit, because defrosting difficulties can result.
For general storage coolers and holding freezers, there are not criteria for air velocities within the room. The total supply of air is such that approximately 40 to 80 air changes occur each hour. This is an air conditioning term which is calculated as follows:
Air Changes = (total cfm*) x 60
internal room volume
* includes all unit coolers and auxiliary fans
This equation disregards the air motion which is induced by the discharge air from the unit cooler. For simplicity, the gross volume of the room is used unless the product and equipment occupy more than 10% of the volume. Specific applications such as cutting rooms and banana ripening rooms have desired limits. The table below indicates the minimum and maximum quantities of air for particular applications. Recommended Air Changes/Hour: (here is the table)

This is regarding the Evaporator(s) selection criteria. Heatcraft says that you should select an evaporator which gives enough CFM so the air changes/hour is the recommended on the table.

[Magoo]

Evaporator air circulation rates are determined by the evapoartor manufacture for a given performance factor. Generally from my experience somewhat inflated, air volume to performance that is to say.

[Segei]

Major reason of air circulation to prevent hot spots in the freezer. Some old style freezers don't have air circulation at all. A while ago I saw freezer that had brine cooled by ammonia. In the freezer brine piping was on the walls and under the ceiling. No forced air circulation, but only natural convection.

[lana]

Hi there,

you always end up with more CFM than this table gives you. This is just an indication.

Lets try this : a holding freezer with 10m x 10m x 3m = 300 m³ = 10594 ft³
Using the equation with maximum air change 80 = 80=CFMx60/10594 CFM = 14125
For this room you would need at least two evaporators for good air circulation. When you select from the catalog then you will see that in total you have more CFM than 14125.

Cheers

[georgedvf]

When small rooms that's true, you always end up with more CFM than those that the table indicates.

But when the room is big, it is when I can't reach the air changes that the table indicates, I'm talking about rooms of 200,000 ft³. For example for a Holding Freezer application tha table says minimun 40 air changes/hour but the maximum I got with standar evaporators is 12 air changes/hour.

[georgedvf]

Does anyone has reference for this from ASHRAE or somewhere else????

[Magoo]

Circulations rates depend on the product stored, prefrozen, unfrozen, chilled what ever and a thousand other criteria items, traffic values, respiration rates, the list goes on and on.
Join ASHRAE and pay for manuals and be totally confused at the end of it.
My favourate saying is ASHRAE jockeys design the perfect system that never works. Design comes from practical experience and understanding your clients ACTUAL needs. Then apply all the experience and deliver the system that does operate efficiently and with in clients requirements.

Grumpy

[georgedvf]

I'll be glad if some other reference besides ASHRAE is presented. It's just that I've not seen another reference about this subject.

So nobody has any reference???

[Josip]

Hi, georgedvf :)


When small rooms that's true, you always end up with more CFM than those that the table indicates.

But when the room is big, it is when I can't reach the air changes that the table indicates, I'm talking about rooms of 200,000 ft³. For example for a Holding Freezer application tha table says minimun 40 air changes/hour but the maximum I got with standar evaporators is 12 air changes/hour.

For storage room/s (goods are at temperature) must be enough 20-40 air changes per hour - practical experience .... for process rooms for cooling or freezing of some goods there are other methods for calculation of cooler/s and fans ...

I assume, your room is about 90x90x25 ft, so you can utilize about 85% of your floor area and about 90% of your room height (for smaller rooms factor is smaller) ... i.e. from your 200000 [ft³] occupied is about 150000 [ft³] 200000x0,85x0,90 = 153000 [ft³] ... so you have 50000 [ft³] of air to circulate around ....

.. from your calculation (if I'm not wrong 12changes/h x 200000[ft³] = 2400000[ft³/h]/50000[ft³]=48 changes/hour with full room occupied and coming down when room is less occupied ...

I agree with Magoo ... there is a lot of criteria items having effect on circulation rate i.e cold room calculation and construction ... the biggest problem are our clients ... wanted always bigger room/s with very strong cooler/s (to be there just in case if they need it one day) and then keep it partially empty 8 months per year, accusing vendors for high electricity bills... so we need to find out what are real needs of our client and then deliver exactly that ...

Best regards, Josip :)

[smpsmp45]

I have one cold Room Manual & it has a chart for air circulation rates.
Type of application Minimum Maximum
Holding Freezer : 40 80
Packaged Holding Center 40 80
Meat Chill Room 80 120
Banana Ripening 120 200
Veg/ Fruit Storage 30 60
Blast Freezer 150 300
Work areas 20 30
Unpacked Meat Storage 30 60
Air Changes = Total CFM of air cooler x 80 / ( internal Cold room Volume)

[georgedvf]

smpsmp45: is this the heatcraft manual??? It's almost the same, only the Cutting Room is missing.

[smpsmp45]

This we got from cold room manual prepared by Erricson India

[RG-NH3]

SMPSMP45: Could you give us where we can download the document?