Air Changes in a Refrigerated Room

[gwapa]

How many changes of the volumen of a Room must one change per hour in order garantee room conditions?
Thanks
Gwapa

[smpsmp45]

I think your question is not very clear. It shall depend on the application & nature of persons present in the Room.

[gwapa]

A freezer at -28ºC to storage fruit pulp how many air changes should have?

A freezer at -28ºC to storage fish (tune) how many air changes should have?

A refrigerated room at +5ºC to storage milk and butter How many air changes should have?

A storage meat room ?

A procesing meat room with people inside at 10ºC?

This are some applications

[US Iceman]

I have never heard if using "x" air changes per hour for refrigerated spaces. This is typically only used for occupied rooms (processing, etc) and not for product storage.

If anything, I would be more concerned with air throw and spread.

Air throw is the distance the air will travel. At this distance the terminal air velocity is achieved. Some evaporator manufacturers may list the air throw but they may not list the terminal velocity. If not, you should ask them.

The terminal velocity is important because you may need a sufficient air flow over the product. Air throw is important since you need to provide air flow to an adequate distance.

Spread is how far the air spreads out. Think of it as a isosceles triangle. The point of the triangle is the center of the fan. The base of the triangle is the spread at the required distance. As the air leaves the fan tips the air starts to decelerate and mix with the room air. This deceleration causes the air to spread out from the radial flow it started with.

If you provide a sufficient quantity of evaporators that are installed to circulate a uniform terminal velocity at the required distance with the spread providing adequate coverage, you should be good to go!

[gwapa]

US ICEMAN
I agree with you .However I found the attached file as a part of a Handbook of a Manufacturer .

I couldn´t achive to such figures It look to me very high.

What I know is that lowering the TD I will increase the air flow required for the same load

But this figures in the attached file look to me wrong

Could you please comment
Best regards
Gwapa

[US Iceman]

I couldn´t achieve to such figures It look to me very high.

Not without using a lot of fan power I bet!

I would not worry about air TD, only the evaporator TD. Pick the coils for what you want to achieve.

If the cooling capacity is too high the air TD will be lower also.

Seriously, I don't know where those numbers came from. That is a lot of air to circulate...

What book did you find that in? I agree with everything except the air changes.

[Yuri B.]

What is the story about?

I couldn´t achive to such figures It look to me very high.

Quite contrary, the figures in that table should be very low for your total cfm multiplied by 60/ volume of your cold room.
The formula is inadequate and they stress it themselves. How had they come (and how one should) to the figures in the table they did not explain.

[smpsmp45]

Probably the Air changes word is more confusing. Typically the air flow quantity in the cold stores / freezers should be based on these factors.

So many a times even if you get less air flow by your calculations, may be you have to ensure that still the Air quantity is as per the table.

We have come across these situations many a times, & in a floriculture applications these tables are not useful as the flowers get damaged due to high velocity.

[davidlleida]

Hi,
the only thing i can say is that these factors are important to know for storage of vegetables specially fruits or products that can get damaged for high air speed across the product wich causes dehidration (water loss).
But this means also that the product must be correctly "stored" in the room.
I mean that the owner must kepp some distances beetwen pallets (if it's the case) to allow the air pass through the product at a velocity slow enough.
Also you must be sure that the air is not by-passing to the evaporator without passing through the product.
I would not take care only of having a minimum air in the room but also at hese other factors.
I hope these ideas are useful.

[Josip]

Hi,


... this is coefficient of air circulation i.e total volume of empty chamber which must pass through the cooler/s in one hour ....


all is logical... for work areas/cutting rooms very small 20-30 changes/hour and for blast freezer 150-300 giving a clearer idea of air movement.

Best regards, Josip