Evaporators Location

[gwapa]

Hi everybody

In a walk-in warehouse which would be the best locations of the evaportors ?

blowing the discharge air from the evaporator in the same way as the Rack (shelves) are located
Blowing the air perpendicular at the RAck (Shelves)
Thanks for your thought
Regards
Gwapa

[smpsmp45]

The Air should not into the pallets as it shall then short cycle.

Location is not then important if you can achieve this.

[gwapa]

Hi Smpsmp45

In both alternatives I posed the evaporators are located in the higher zone of the warehouse and at one meter from the panel walls. There will be in both alternatives one meter from the higher part of the products and the panel ceiling.

So I have two alternatives a) Locate the evaporators blowing in the same direction as to the rack go.or b) Locate the evaporator blowing in perpendicular way to the racks.
Thanks
Gwapa

[US Iceman]

My main concerns are the ability to deliver the air through the space above the racks. If you can get good airflow from the evaporators without any barriers blocking the flow then this is best in my opinion.

The evaporators usually have a distance they can distribute the air with only the fans. Some manufacturers offer a long throw adapter for the fans also. This adapter is just a cone that is placed on the fans to increase the air throw distance.

Another concept to visualize is the air spread. This is the angle the air spreads out to at the end of the air throw.

Additoinally, at the end of this air throw where the spread is at it's maximum you also need to know the terminal or final velocity of the air as this affects the air circulation and cooling of product.

If you can visualize these concepts and apply them to the space I think you can see how this works.

Then the last comment is: Cold air falls and warm air rises. I prefer to have some airflow over the doors to reduce frost formation above the doors.

[gwapa]

Thanks US Iceman
The concepts are clear and I agree with you. However some engineer think that locating the evaporator with the air flow perpendicular to the rack will be much better due to the fact the air flows throught the rack and araund the products . In other hands if you locate the evaporators flowing in the same way as the rack the air will go throught the ailes and will form a short circuit.
please your coments are wellcome
Regards
Gwapa

[bobby]

hi gwapa

with every coldstore installation i have been involved in we have always positioned the evaporators flowing the same way as the racking.it does not matter that some of the thrown air travels down the aisles as it is a coldstore application where you are looking for a mean average temperature across the room and not a blast freezer where you want the air to flow around the product and at higher velocities.
locating the evaporators the same way as the racking can also benefit you when it comes to maintenance as they are easier to get at.
don`t make the same mistake alot of companies are doing by installing the evaporators on the wall side where the the main doors are, this can cost a fortune in needless defrosting.
as previously mentioned by the iceman if you don`t get the air throw calculations correct then it will never work correctly. i have seen with longer stores booster fans being installed half way down to pick up the air and throw it further but personally i think it is a bad idea, because if you don`t get it right then you can end up with two different average room temps

regards
bobby

[US Iceman]

Blast freezing or cooling is completely different than cold storage. For cold storage think of the building as a large container full of cold air. If warm air blows into the space, you have warm spots. You can also have warm spots on the walls if the air circulation is insufficient.

I have seen product spoil stacked in a corner of a freezer with no air flow.:eek:

You want air flow direct to the walls so that the air flows over the racks/product and then through an ample space between the wall and product. If the circulation is good through the entire building, it does not matter which way the racks are installed.

However, having just said that.... you want to minimize the objects the air has to flow around in the path of the air discharge. If the air can't discharge to it's catalog capability then the air is short circuited.

At a minimum you want the air flow to discharge from the coils and cleanly flow to it's farthest potential distance (which is hopefully a wall or a door). This usually means the evaporators are above the highest product in the racks so that the air flows over it.

Another point is one where I have seen some problems... People sometimes like to place coils back-to-back with air entering side opposite of each other. This is OK as long as you have at least 3-4 fan diameters between them to ensure adequate room for return air flow into the coils. Having said that, this space of 3-4 fan diameters would be about equal to an aisle in the building, so this would be an ideal location for the return air flow into the coils.;)

And... I can't emphasize enough the direction of air flow over the doors. Warm air wants to rise and the moisture in this air will freeze onto the walls, racks, and product which makes a big mess.

Having cold air discharge over the top of the door way provides an air curtain to mix with the warm air and in turn absorb the moisture from the warm air. Voila, the frost problem is minimized.

All of this is just like an open display freezer case in the supermarket. If you disturb the air curtain the case cannot maintain temperature.

[Sergei]

I agree with you Mike.
However, I think that evaporator coils should be located as far as possible from the doors. Warm moist air enter the freezer and goes up. Some of his moisture increase humidity in cold room and the rest will form the snow. It is better snow on the ceiling than on the coils, otherwise coils will be plugged very quickly.
What do you think about evaporators in penthouses?

[US Iceman]

Hi Sergei,



However, I think that evaporator coils should be located as far as possible from the doors. Warm moist air enter the freezer and goes up. Some of his moisture increase humidity in cold room and the rest will form the snow.


I agree 100%. What I have observed is if the air flow from the coils is directed above the doors, the air then flows down. This prevents the warm moist air from rising and also causes the moisture in the warm air to be absorbed by the colder, drier air.

None of this means the doors should not have plastic curtains or other devices, because they help to reduce the total volume of warm air that does enter the space.

I have also seen installations where the coils are installed above the doors, thinking this will prevent the frost and ice problem. It actually makes it worse because the frost now collects all over the drain pan and coil housing.:eek:

Personally, I don't like penthouses at all. If one coil goes into defrost the other coils is affected by the defrost cycle taking place. The air flow with this is less directional than ceiling mounted units and you have to pay for the additional fan power with the discharge duct static pressure.

I know contractors like these because they are easy to install and pipe. From an owners perspective I think they are more expensive to purchase and operate. I don't have any hard numbers on this... just my opinions.:D

[gwapa]

Thanks for this very nice discution;)

[Sergei]

Hi Sergei,



I agree 100%. What I have observed is if the air flow from the coils is directed above the doors, the air then flows down. This prevents the warm moist air from rising and also causes the moisture in the warm air to be absorbed by the colder, drier air.

None of this means the doors should not have plastic curtains or other devices, because they help to reduce the total volume of warm air that does enter the space.

I have also seen installations where the coils are installed above the doors, thinking this will prevent the frost and ice problem. It actually makes it worse because the frost now collects all over the drain pan and coil housing.:eek:

Personally, I don't like penthouses at all. If one coil goes into defrost the other coils is affected by the defrost cycle taking place. The air flow with this is less directional than ceiling mounted units and you have to pay for the additional fan power with the discharge duct static pressure.

I know contractors like these because they are easy to install and pipe. From an owners perspective I think they are more expensive to purchase and operate. I don't have any hard numbers on this... just my opinions.:D
I like penthouses.
Defrosting. Many people don't understand the reason of poor defrosting in penthouses. Operating coils create slight vacuum in penthouse. When one coil goes on defrosting, other operating coil pull the cold air not only through freezer opening, but through defrosting coil as well. Cold air move through the coil and will refreeze the melted frost at the bottom of the coil. To prevent this, I defrost 2 coils simultaneously and 2 other coils are OFF. Sometimes I defrost 4 coils simultaniosly.

[kelvin_27_84]

Hi, I usually like to place coolers at the short end of the warehouse, facing the long end (that is provided your layout is not a square. and awkward position) with that, 1m spacing from the wall with valves stations above the insulation panels and as high as possible. (this is assume that we are talking about guneter's evaporators) this is because, guneter's evaporators have a tilting angle of 3-5 degrees to make sure the air travel at the top of the insulation panels before falling down. With that guneter's has a certain technology call the streamers, this is a guaranteed air throw of at least 75m (without that it could be about 30m) Hope that helps

[US Iceman]

To prevent this, I defrost 2 coils simultaneously and 2 other coils are OFF. Sometimes I defrost 4 coils simultaniosly.


That would solve the frost problem.:) I think the issue is there are certain things you have to do to make a penthouse work right. That doesn't mean they are bad, it's just something you have to be aware of.

[smpsmp45]

Dear Sergei,

The point is noted on defrosting. Good idea.

[Sergei]

About the throw.
I think that should be different approach to design of evaporators for ceiling and for penthouses.
Ceiling evaporators. Throw is very important, because air should be pushed to opposite wall to eliminate hot stop in top corner beside this wall. I call it push approach.
Penthouses evaporators. Penthouse usually located in the middle of the freezer and air can be pulled evenly from each side of the freezer. Evaporators suck the warmest air in the freezer located under the ceiling. It means that regardless of the throw we won't have hot spots. This is the pull approach.

[US Iceman]

I prefer to think of the air circulation in the term of displacement. The primary purposes of evaporators are to provide sufficient cooling capacity and to discharge sufficient air volume to displace the warm air, creating a uniform temperature distribution within the temperature controlled space.

To achieve this you have to look at the building floor plan. Is it square, rectangular, or a variation of these?

Placing the evaporators down the center of the long dimension with air blowing left and right is the same principle as a penthouse. It just centralizes the locations of the evaporators and the air distribution. The same thing is achieved with the ceiling hung evaporators in the center blowing either direction.

The main issue is air distribution. Air throw on an evaporator is the same thing as on a penthouse unit.

No matter which one is used, you still have to deal with the doors and dock area or you will have frost problems.

There is nothing wrong with penthouse units, you just need to understand how they work (and defrost) to apply them properly. What I don't like is when one large penthouse is used for an entire space. Very large coils in defrost (with hot gas) suck up a lot of hot gas so you have to pay very good attention to how the defrost piping is designed and installed.

And, most people just use the discharge plenums with elbows to direct the air flow. That has to be a huge static pressure penalty.

I just think we can do a better job than the ones I have seen.

[Sergei]

I think that we can blow air down without any throw(penthouses). Cold air will spread on the floor and gradually warm up and will go up. Minimum static pressure losses. Air flow is important, but not the throw. Modern freezers are tall and this is benefit to convection. I would call it half natural, half forced convection

[US Iceman]

You know, it would be fun & interesting to see this modeled with a CFD (computational fluid dynamics) program. Then we would have a real good idea of the temperature distribution throughout the space.

[kelvin_27_84]

Well i have to agree on penthouse, just that like what Sergei has said, it is located in the middle of the warehouse. With that kind of position, even constructing a maintenance platform may not be visible when warehouse space is to be fully utilize. Space = money. Having a platform for maintenance is going to be a issue. Some customers may not even want that. Thus the only way is to use scissor lift to do the maintenance, in the middle of the warehouse. I agree that that penthouse is good, but in cases of warehouse where space is important, I doubt it is good.

[Aik]

Hi Sergei,

I have also seen installations where the coils are installed above the doors, thinking this will prevent the frost and ice problem. It actually makes it worse because the frost now collects all over the drain pan and coil housing.:eek:

Quote from ASHRAE recomendation of "Refrigeration of Cheese Rooms"

One unit should be placed near the door to the room to cool the warm moist air before it has a chance to spread over the ceiling. Otherwise, condensation dripping from the ceiling or mold growth will result.
I suppose that evaporators must placed opposite the door, but sometimes there are situations when one evaporator plased near the door. If thise evaporator will switch off when the door open will it solve the problem with more frost ice on it?

[US Iceman]

If thise evaporator will switch off when the door open will it solve the problem with more frost ice on it?

No, the warm moist air still rises and collects on the coil fins and housing. IMO, the discharge air from a coil should be directed towards the door opening. This allows the colder air to mix with the warm entering air and absorb some of the moisture from the entering air. This should be sufficient to reduce or prevent any frost accumulation near the door opening.

[Aik]

IMHO, the discharge air from a coil should be directed towards the door opening. This allows the colder air to mix with the warm entering air and absorb some of the moisture from the entering air. This should be sufficient to reduce or prevent any frost accumulation near the door opening.
In addition, pressure in cold room is less than on the outside of the room, because the temperature in cold room is lower. When door is open than warm air goes to the room (owing to difference of pressure). If discharge air from a coil will directed towards the door then part of external warm air will stoped by dynamic pressure (velocity pressure) of this discharge air from a coil.


No, the warm moist air still rises and collects on the coil fins and housing.
I have a problem: evaporator installed near the door and I don't know how can I improve its work without removing it...

[Segei]

In addition, pressure in cold room is less than on the outside of the room, because the temperature in cold room is lower. When door is open than warm air goes to the room (owing to difference of pressure). If discharge air from a coil will directed towards the door then part of external warm air will stoped by dynamic pressure (velocity pressure) of this discharge air from a coil.


I have a problem: evaporator installed near the door and I don't know how can I improve its work without removing it...
Probably your evaporator has a drain line. Through this line pressures inside room and outside will equalize.
Can you give us more information about this room? Tem-re, size. How many evaporators do you have in this room?

[mad fridgie]

In rooms the static pressure is equal (equalizes over time) Air density is different. When you open the door the cold "falls out", this is replaced by warm air, a "natural convention current".
Re your coil by the door (ths does depend upon room size and type of load) Add a turning vain between the back of the coil and the wall. Reverse the airflow. The air flow will act as an air curtain, reducing the air infiltration. If the room is long (warm spot at the opposite end) add a simple phlenom, down the length of the room

[Aik]

Probably your evaporator has a drain line. Through this line pressures inside room and outside will equalize.
Can you give us more information about this room? Tem-re, size. How many evaporators do you have in this room?
Room temperature is -4 C, two evaporators in the room one near the door.

Reverse the airflow. The air flow will act as an air curtain, reducing the air infiltration. If the room is long (warm spot at the opposite end) add a simple phlenom, down the length of the room
Room has long length...phlenom - what is it? If the flow reversed then ventilators may overheat, because tempereture of income air is higher then outcome from coil...

[mad fridgie]

ventilators (fans) will not over heat.
phlenom= "a duct"

[Aik]

If fans automatically reversed when the door is open, what do you think about thise algorithm?

[mad fridgie]

If fans automatically reversed when the door is open, what do you think about thise algorithm?
Reverse rotation only, will only cuase air to feather, if you want truely reversable airflow, then you need double pitched blade (one set for each direction and rotation)