I need HELP : 16m is the height

[Mahmoud]

Dear All,,

I have a very big refrigerated warehouse to be controlled at 4C, dimensions are 90x18.5x16m, 16m is the height, i am having a doubt about POSITIONING THE UNIT COOLERS, actually it is divided to 4 levels with automated storage system, but each level is opened to the other, so you can consider it as one space, please note the following:

1- It is a multiple power rack system for the warehouse
2- I want to place unit coolers in each level for better air distribution.
3- That coolers will be connected to a rack system.
4- At the Heighest level (The last level), there is products to be stored in, and the hight of the last level is only 2.6m only, so if lets say we want to place all the coolers just below the ceilng it wont fit.

Now my doubts are:

1- Is it correct to position coolers in each level ?? coz the cold air will flow from the heighst level to the lowest by means of higher density of cold air.

2- If the cold air is going down from level no. 4 to 3 to 2 to 1, level 1 coolers' inlet air temperature might reach the design temp. before the other levels. and also level 2 before 3 and 4 and level 3 before level 4.

3- Accordingly if the deisgn temp. is achieved the rcompressor racks will trip off one by one, ok , let it be, but am afraid of short cycling coz maybe the actual temp. will flucuate because coolers might have the temp. of the supply air of the higher level(s) coolers. so is it safe the place the coolers on all levels? is there actual limitations ??

4- Accordingly is there any considerations for the distribution of total refrigeration load on all the levels, i.e. as the lowest level (level no.1) will have the coldest air bu natural gravity.

5- Finally, this is a well insualted warehouse (150mm polyurethane panels for walls,floor & ceiling) and products is mixed fruit and veg. entering chilled @ +15C max, with 36 roll up doors, out side ambient is 43C, so what is the approximate Watt/cubic meter for this warehouse (specific capacity)

I know i have wrote too much, but i have to submitt the design as soon as possible, please your help, and thanks in advance.

4-

[smpsmp45]

Before stydying all the details, I can say for sure that the coolers must be at the top most levels.

The floors should have wire mesh type structure so that Air can freely circulate. Do not place the coolers on each levels, if there is no separation of the floor level.

[Mahmoud]

Hello smpsmp45,,

Do u mean that it critical due to the return air??
there is no space for ceiling mounted coolers..

any ideas?

[Paulajayne]

Hi

Warm air rises, so coolers should be as high as possible.

Wall mounted? but remember to leave working space around them as well as access for things like fan exchanges.

Instead of direct assess from outside to the cold store consider a pre-cooled loading bay (buffer zone) - in the long term it will save on cold store cooling costs.

Paula

[The Viking]

Mounted at mid level or outside and ducted to high level?
Roof mounted and ducted?
(OK, not standard for cold rooms but it can be achieved if you size the fans accordingly)

[chillin out]

Mounted at mid level or outside and ducted to high level?
Roof mounted and ducted?
(OK, not standard for cold rooms but it can be achieved if you size the fans accordingly)
Thats what I was goi9ng to say.

Chillin:):)

[US Iceman]

Why not use units that have a downward discharge and mount the coils as high as possible. Cold air falls and warm air rises , so this would work with your high storage areas. And, it works off of basic principles to help ensure air circulation.

You do need to provide a sufficient number of units to effect even air distribution through the storage area.

I do not care for duct work. It's expensive and it requires some additional power input to overcome the increased static pressure due to the duct work.

[Mahmoud]

Dear All,,

Those was good ideas, BUT:

I dont have space even for downward flow coolers, the case is that some floor level areas are closed, i have thought about this, there will be a non uniform air distribution, plus even if we considered that there is a space, then the heighest level stored products will be extra chilled and might get frosted since the cold air supply strem might be at 0 since the room is 4 and the product will be spoiled ... and later on .. i will be fired for sure :)

About ducting system, i'll be using conventional cunic coolers, i think it wont work, so i might go to centrifugal type coolers,, ok but where to place them? if placed out side, whcih will lead tht i have to place them on the roof, where we do have extrmem ambient temp. like 43, ok i'll insulate the suction and discharge duct, but what about the cooler ?? is this practical ??!

one more thing,, the manufacturs supplies the fans with different static pressures, so if the static pressure required is more than available, what is to be done? is it practical to install additional fan in the duct line to increase the static pressure, and how ill select it's flow since the air is already flowing at a specific rate rated by the manufacturer ?

Is it too complicated or i am making it ?!

help me out please.

[Brian_UK]

I think that you need to inform the client of the limitations regarding getting cold airflow around the warehouse.

There are some occasions when it is wise to ask for help from an expert elsewhere but get the client to pay for the design service.

If you make an error and the system does not work then you will have to carry the cost. If you get the client to get a designer in then you are only responsible for the installation.

[Sledge]

I have only one experience with large warehouse. In that example it was ammonia and they were set for -20c. They built small insulated rooftop air supply houses, housing fans and coils, with machine rooms and condensor also on roof, mounted directly beside them. This worked fine for them, but am not aware of cost, capacity and efficiency.

[Samarjit Sen]

You have said that each floor is open to each other. If that be the case you should provide some unit coolers at the level 4, some in level 3 and some in level 2. You have to ensure that Unit Coolers have suffecient Air Throw and accordingly you locate them away from the walls.

How many air cooler units you propose to install. Since the Cold Air will fall down, there is no need to install any units in level 1.

If you can kindly provide more details such what is the floor of each level which I presume is mesh type to ensure passage of air, number and capacity of each unit coolers and the air throw of each, may be you will be able to get a more detail information and suggestions from the Forum.

[Samarjit Sen]

Are there any pillars inside the Room, if so the location of the same may be intimated.

[Mahmoud]

Dear All,

It is a design and build contract, so i am considered as the consultant and the contractor..

The floors are not mesh type, there is rail ways with base in the middle of the room for the open vegetables containers handling and storage to the desired spaces, and even if it was a mesh, these containers will act as a partiotion for the below level.

Cancelling the first floor level evaporators is a very good idea, coz i believe that air must and only must go down anyway, this is very good idea, guys what if also cancelled the second level's evaporators ?!! or if we placed the coolers at the top and the middle of the height of cold room, is this applicable, does the air return sensor behind the middle heigh coolers will read the room temp. instead of the discharged air from the above coolers ?!!

thanks for the support, am getting fruitfull ideas instead of asking an expert..!!

[Samarjit Sen]

Hello Mahmoud,

While designing structures, kindly ensure that the floors of each level hasmesh type or rails with gaps in between for air to pass. Even the storage should be such that there are suffecient air circulation.

These types of projects have been installed by us and also I had to inspect them for non performance. Unforunately air circulation and throw is not given any importance. It will be effective if you locate the Coolers at the top floor and the 2nd level. This way you will have a very effective performance..

Keep informing the Forum about the progress and you will get much benefit and knowledge from the members.

[US Iceman]

Unfortunately Air (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=17) circulation and Throw (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=52) is not given any importance.


I agree. Good temperature control of the product does not occur without good air circulation patterns. These are dependent on the location of the coils, the volume of air being circulated, and the throw (linear distance) of the air.

I have seen product spoil or melt in a storage area where the temperature in the aisle was acceptable, but certain locations in the same area were badly needing attention.

16 meters of ceiling height is nothing to get excited about. You want good air circulation and distribution of the air throughout the space, especially towards doors opening to the outside or shipping docks, and against the outside walls. The outside walls forming the perimeter of the building is one location you want a lot of clearance for free air flow.



thanks for the support, am getting fruitful ideas instead of asking an expert..!!


You need to be aware that any help any of us provide is based only on the information you provide. So far, all we have to work with is your descriptions. Without really good information or documentation to work with, I fear you are trying to design this system by consensus, or in agreement with some other party (possibly the owner).

You mentioned in an earlier post you had 2.6 meters of height at the top. Is this 2.6 meters above the highest rack? If so, that should allow sufficient space for medium to high profile coolers to be installed; with the return air having about 2-3 meters distance from an outside wall. In this case the air would be blowing towards the center of the room.

[Peter_1]

Such a big cooling place and no room for the coolers?
Who designed this place?
You better make a small schematic for us because we're guessing now a little bit.

[Peter_1]

=Mahmoud;69756... .. i will be fired for sure :)
You will be fired anyhow if you try to make something which is dommed to fail.
Better face the problem and explain your client why it won't work. Better now client at all then an unsatisfied client.

[Eeram]

Mount the evaporators if there is an isle, with the air entry back to back with about 2-3 meter space in between, blowing towards the racks. A photo or 2 of the warehouse layout can help.

[Samarjit Sen]

Hello Mahmoud,

How is your project coming through. Kindly keep us informed so that we may learn something and at the same time offer some assistance if required.

[Mahmoud]

Dear All,,

We have a lot of meetings with the client, and the client agreed to raise the height so we can place the coolers, now the issue is:

The cold store will be served with Bitzer screw racks, our ambient conditions are extreme, 45C ambient temperature, the compressor can reach 60C condensing temperature @ -6C, I HAVE 2 QUESTIONS:

1- the room temperature is 4C, at which suction temperature i should select the rack, the capacity of each rack should be 850KW, and am designing on DT of 8 to maintain +4C room temperature, what is the evaporating temperature i should select the rack on, -4C or below? piping to the last cooler will be 100m max., so what could be the maximum pressure drop, and how this will lead me to select at a specific suction temperature ?

2- Can i go with air cooled condensers OR IT IS A MUST TO GO WITH EVAPORATIVE CONDENSER?

Finally, if i have to go with evaporative condenser, what is the selection parameters to select the same, by the way the water suuply tempeature there is almost 43C and the ambient is 45, is the water supply temperature for the evaporative condenser is a variable, or it is just the wet bulb temperature.. please advise.

Thanks all in advance.

[gas_n_go]

To me the easiest solution is to either create barriers between floors or to figure out heat losses between floors the way it is now. Pipe in at least 4 seperatly controlled circuits, one on each floor. Most likely the largest coil on the top floor and the smallest coil on the bottom. I guess its a mute point now because the customer has already decided to redesign the space but that is what I would of looked at doing.

[Samarjit Sen]

Hi Mahmoud,

It is nice to know that your clients have accepted your suggestions. Could you please tell me what is the total heat load, product, product load and incoming temperature of the product.

For 45 Deg. C I would not like to use air cooled condensers. It would be better if you use an evaporative condenser.

[US Iceman]

...45C ambient temperature, the Compressor (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=60) can reach 60C condensing temperature


A 15K temperature difference on an air-cooled condenser? :eek:

That seems like a high number to use. I would have thought you would use one half of that (about 6-7K)to size the air-cooled condenser.

[Mahmoud]

Dear All,,

I have selected an air cooled condenser with a DT of 10K, the ambient is 45C and the condensing will be 55, and the compressor envelop can go up to 60, i am evaporating at -4C suction, but the condensing capacity (refrigeration capacity + power input) was calculated at 0C in order to extend the operating band of the system ..

Any comments ?

[Andy]

Dear All,,



Any comments ?


I would assume you are using aircooled because water is a premium:confused:

What about assisting the aircooled with a water spray system.


What about Geothermal, using a closed ground loop system to dump the heat to the ground:)

Kind Regards Andy D:)