Cold room dimensioning - ratio volume air flow

[MrReds]

Hallo To everybody.
I am facing for the first time to following situation and I would be grateful for each kind of suggestion and comments.

I have to regulate temperature in a room of approximately 300 m³
The capacity I need is around 220kW
Owing to request, I can utilize only a cubic cooler in one side of the room.
I realized the selection, and I found out that the ratio between the air flow of the cooler and the volume of the room is around 240 !
Is this a correct value to refer to ?

Face velocity of the cooler is around 3.3 m/s

Please, could you tell me if what I am doing is totally rubbish ?
Are there any risk of recirculation when facing with this situation ?

Is there anybody who could suggest me some different figures to keep as reference when dimensioning the climatization of a room ?

Thanks in advance

[Samarjit Sen]

Hi MrReds,

For designing a refrigeration system for a Cold Room there are many factors to be considered. What is the product to be stored, what is the product load and the incoming temperature, what is the Room Temperature and RH desired to be maintained, pull down time, the period of storage, dimensions of the room and the insulation details. In absence of this it is very difficult to help you with your question.

Kindly provide these details so that I may suggest something which may be of use to you.

[MrReds]

hallo & apologizes for the delay of answer.

according to the dimensions of the room, the maximum heat load and the insulation I calculated that required capacity is more or less 220kW.
Dimensions of room are 13 x 5 x 4.6 (h) m more or less.
Concerning the product, as a matter of fact there is no product to be stored, but what has to be cooled is a huge series of compressors.
Hope this is useful.
Anyhow my concern was the high air velocity and the ratio between the air flow of the cooler and the volume of the room, so that there could be a problem of recirculation.

Hope this is useful to help me, should not be enough, please write back

Thanks in advance

[Brian_UK]

HI, you say that the room will contain compressor, what type of compressor are they? refrigeration or air?

It is possible to just provide air flow ventilation to remove the excess heat?

[smpsmp45]

Are you putting up a simulation chamber or something?

We too had done similar project wherein Entire Truck was kept in the chamber, & even the temp were lowered upto -40 deg c to check up the AC performance at such low temperatures. & check the electrical components etc.

But there was no restriction on the time frame to bring down the temp to the desired level. It seems in your case, you have certain time span to bring down the temp of the compressors to the desired levels. In case you can get some relief on that point - increased no of hours, the system shall look more practical .
But still it is definitely an interesting application.

[The Viking]

220 kW = 220.000W
This in an area of 65 square meters...

What is the desired resultant temperature?

If you just looking at cooling the compressors then:
65x150=10kW to keep the room at constant temp (ROUGH ESTIMATE)
Are those compressors really pulling over 200kW of power?
(ignoring powerfactors, assuming 415V-3phase and so on, 200.000/3 = 67kW per phase = ~169 Amp per phase !!!)

If you let us know a bit more about your design criteria, like desired room temp, energy consumption of the compressors and so on, then I'm sure several of us here are happy to check your figures.

[750 Valve]

Are you saying you can only use 1 evaporator at one end of the room, the resulting ratio between your evap air volume and your room air volume is 1:240?
So you'd be looking to push that air the 13m length of the room? or the 5m length? Whats the throw on the fans you want to use?
Do you have a product pulldown requirement or will these compressors just produce heat from running? If there is a pulldown requirement then the air volume ratio will be more critical but either way air circulation must be a priority. Multiple evaps all along the 13m wall blowing 5m would be ideal, 1 evap on the 5m wall blowing 13m is asking a bit - depends on the air throw.

[Samarjit Sen]

Sorry for not replying earlier as I was busy with my projects,

What type of Compressors are these which require cooling. (2) What is the end temperature that is required. (3) Are there any restriction in putting multiple air cooling units. (4) What is the pull down time.

I personally feel that installing multiple air cooling units will be more effective than putting a large coil.

[frank]

I personally feel that installing multiple air cooling units will be more effective than putting a large coil.
And this will also give back up if one unit requires maintenance or fails.

[Samarjit Sen]

Yes Frank you are right. Other than the backup, this will ensure uniform air circulation and temperature.

[sakly]

you are right the air changes doesn t mean any thing in cold room design. so the ACH = 240 is not rubbish at all.
good luck

[John Hunter]

It appears to me that you are attempting to Ventilate a Plant room rather than a product holding cool store. The fact that the heat source is electric motors the air will be "Dry". So here is the basics. Assuming the air is at NTP the density will be around 1.2 kg/m3. The specific heat will be 1 kJ / kg.C. Assuming that the cooler is refrigerated and has a deep coil with the face velocity of around 3 m/s the TD across the coil I would estimate at around 3.0 C.
The heat removed per m3 will be 3.6 kj/s = 3.6 kw. So to handle your heat load the air flow will be around 55.5 cubic metres per second. At a face velocity of 3 metres the face area of he coil would be around 16 m2. One unit as described will not handle this loading. It appears to me that there is a tremendous concentration of heat generating energy in a relatively small area. The design of the space may be due to some environmental reasons which is not clear but I would suggest the concept be revisited. I have ventilated large plant rooms using ambient air where the external air is around 25-27 C . Properly designed this will give an internal room temperature of around 32 to 35 C . Where possible try and ensure a room height of at least 6 metres with either sufficiently sized extract fans or static roof vents to induce stack effect. One thing worth remembering if the fan is at inlet the heat load of the fan motor is adding to the general heat load where as when the fan is extracting the fan motor heat is directly rejected.