Ffuit cooling

[MilosBog]

Hi all,
could somebody check is everything OK in Here. I have a approximately 30kW cooling chamber for fruits and this is equipment which is selected
3849

3850

3851

I am totally tired and I am new in Germany and my new company is working only with this 3 producers from which equipment is selected. I am not familiar with bitzer and also with Guentner so any help would be appreciated.
If there is a mistake, please, don't hesitate to point me where it went wrong cause that is the learning process.
Best regards to all

[chemi-cool]

Most important, get some sleep, if you are tired you will make mistakes.

What sort of fruit are you talking about?
What % of humidity is required?
What about controlled atmosphere in the cold room?

And My last question, -25°C evaporating temp??? Are you going to freeze the fruit?

[MilosBog]

Hi there,
that was quick
mainly the apples are stored and needed chamber temperature is from 0 to 2 Deg Celsius. I have chosen the evaporation temperature of -25 because investor shall probably later on store some other things. The idea on the evaporator is to control air temperature by its flow so the air outlet air temperature is -4.9.

[chemi-cool]

I am not an expert with apples, The English techs should know more but you you have to take into consideration the atmosphere required for storing apples.

And by the way, the equipment you have chosen look fine to me.

[MilosBog]

I am afraid that something is missing, especially something about electronics..I will make until Wednesday the bill of materials and i will post it here together with schematic view so hopefully it will be relatively good...thanks a lot friend
:D

[MilosBog]

And relative humidity is 80-90 percent....

[NoNickName]

Definitely a wrong selection. Working at -25°C for fruit storage is not ok, and you can't even increase it because the working condition is on the right edge of the envelope.
Please return to the drawing board for this.

[MilosBog]

Yap you are right,
i have listened to the advice from one older colleague and i have noticed that every time he tells me something, later on it goes wrong...

I always thought that evaporation temperature should be 5-8K lower than the outlet air temperature so if i am right, the evaporation temperature should be around -12 to -13 degrees C?

I will check the P-S diagram for this...

P.S. Thanks, any comment is more than appreciated

[nando]

for fruit coolling is it importent to know how long the apples stay in the cooling
we work always in belgium, holland, germany... the customer will not be happy when the fruit dry out.
the evaporator temp. is very importent

[NoNickName]

I always thought that evaporation temperature should be 5-8K lower than the outlet air temperature so if i am right, the evaporation temperature should be around -12 to -13 degrees C?


Yes, and the warmer the better.

[mad fridgie]

Are you cooling the apples (if so over what time), or holding the apples for storage. Keep suction pressure high as possible.

[MilosBog]

Hi there,
the new selection of equipment...The system is designed for a storing the apples.
Is now a selection relatively OK?

[nando]

for fruit: evaporater has to be bigger in capacity than de compressor. this is 1 on 1, not good.
-12 is to low, regulation by valva for apple: -5 and for pear -7
evaporator is wrong: fan have to blow and not to suck (dry out)

[MilosBog]

Now i am totally confused..I mean, if the evaporation temperature is high and i need a 0 degrees in the room, than the temperature difference between inlet and outlet air is small so i need than a bigger air flow to be capable of cooling down all the loads...And if the flow is to big, fan cannot handle it because of pressure drop on the coil....

Everybody, don't think that i don't want to accept advices, but i woul like to have a physical explanation rather than just a statement.
Please, don't get me wrong,i really don't want to offend anybody or to underestimate the knowledge of people on this forum. I have came here to learn something and also to share my knowledge with all.

p.s. Why is recommended that evaporator capacity is larger than compressor capacity? It has logic but in which ratio?

p.s.s I think that this evaporator blows the cooled air, at least i have seen it in the drawings although i couldn't find where is a air inlet(it is not drawn)

[mad fridgie]

You are storing apples, so you do not need "very cold" air to remove heat from the apples. But you do need good air distribution, which normally means lots of air with little temperature change.
If the air is to cold and/or dry, the air will absorb moisture from the apples.
Which means the quality of the apples reduces and that the client will get less value for his apples (paid for by weight)
Without getting to complicated, the temperature of the refrigerant in the coils "SST" will determine the dehumidification effect on the air. The cold the SST, the more water is sucked out of the air, then the product.
So when it comes to evap sizing you are normally given a KW rating at a set of air on conditions and a fixed TD (air on -SST) normally 6C, so for example a 30Kw evap at 0C air on and -6C SST would give you 5Kw per 1C TD. (keeping it simple)
So you are best to keep your TD at 4C (SST-4C,) so you would need for 30Kw an evap that gives you 7.5kw per C TD, or a nominal KW rated coil of 45Kw. This will also give you your required air flow

[nike123]

I found this data in my notes:


Minimum air circulation for apple cold storage is cca 500m^3/h per 1kW of refrigeration capacity.
Cold storage temperature for majority of apple species is 0°C or slightly above (1°C).
Humidity should be kept at 85%. That mean evaporator TD of 6K-8K.

Also this:

Controlled Atmosphere Storage: Remembering that apples take in oxygen and give off carbon dioxide, in 1940 Dr. Robert Smock of Cornell University experimented with reducing oxygen and increasing carbon dioxide in storage facilities, resulting in the development of a new storage technology called controlled atmosphere (CA) storage. CA storage requires air-tight, refrigerated warehouse rooms that are sealed after the apples are placed inside. The oxygen content in the storeroom air is reduced from 21% to 2.5%, and the carbon dioxide level is increased from 0.25% to 2-5%, and high humidity is maintained.

And this:

The first objective in a refrigerated storage is to cool the fruit promptly and maintain a temperature at or near the optimum. If cooling is to be done quickly there will be a large demand upon the refrigerating machinery at harvesttime. A large volume of air must be circulated to distribute the refrigeration to all the stored fruit. Even after the apples are cooled, there is always some variation in temperature from time to time in a storage room, and the fruit in some parts of the room is necessarily warmer than that in other parts. Best storage conditions are those that will keep the variation in temperature to a minimum. In order to effect prompt cooling. and uniform low temperatures, three requirements must be met. The first is ample refrigerating capacity; in the Pacific Northwest this would be about 6 tons of refrigeration for each 1,000 field boxes of apples brought to the storage daily. The second is ample volume of air circulation; 1,000 cubic feet of air a minute for each ton of refrigeration is considered a minimum. The third requirement is provision for the air to move effectively among all the packages; this depends upon the arrangement of air ducts, freedom from obstruction to air movement through the room, and arrangement of the stacks of boxes to permit access of air.
The first and second requirements-ample refrigeration and air circulation--can be provided by machinery. A plant loaded beyond its capacity cannot cool the apples promptly.
The third requirement, good air distribution, is more than a matter of plant capacity; it calls for careful attention to detail in design and operation. A large number of methods of air distribution are in use. The simplest is to discharge the cold air through nozzles at one point in the storage room and pick up the return air nearby. This is likely to result in a relatively wide range of temperatures in different parts of the room. Perhaps the most elaborate method is to discharge cold air from a large number of openings in ducts spaced through the room, and to pick up the return in an equal number of return ducts. In that method, the air velocities through the room may be slow. The most effective placement of ducts for providing uniform air distribution is a single discharge duct along one wall of the room and a single return duct along the opposite side. For good operation, the air is delivered to and returned from the room at the ceiling or near it.
Whatever the arrangement of the ducts, it is necessary to have a clear space at the ceiling throughout the room. Girders that extend across the path of air flow or packages stacked too close to the ceiling prevent free movement of air. Failure to leave an open space between stacks of packages results in poor circulation.
Even with plenty of refrigerating capacity and air volume, and with the best possible air distribution, absolute uniformity of temperature cannot be had. The air leaving the room will be warmer than that entering. For that reason, the fruit nearest the delivery openings is exposed to the coldest air. In the most modern plants, the variation in temperature of the fruit at different points is held to a minimum by automatically reversing periodically the direction of air movement. By doing so, none of the fruit is continuously exposed to the coldest air, and none to the warmest. When warm apples are brought into a storage room, it is desirable that they be cooled as quickly as possible. Reversing the air direction periodically permits using air as cold as 22 to 25 F. to get rapid cooling without danger of freezing.

[NoNickName]

Now i am totally confused..

Yes, you are. Why instead of trial and error, just have a look at the appropriate papers from ASHRAE. They published a very comprehensive guide for food processing and conservation.
Your selection is still very wrong.

[mad fridgie]

Yes, you are. Why instead of trial and error, just have a look at the appropriate papers from ASHRAE. They published a very comprehensive guide for food processing and conservation.
Your selection is still very wrong.
How True!
Also look at useful superheat on unit selection, it is not 100%
You have picked high ambients, so becareful when load is lower and cond is lower that you again do not end up with low SST conditions

[nando]

i cannot say it better than what they wrote here, perfect

[Gary]

Lower evap temp = more moisture removal = drier air = drier fruit = less product weight = less profit

[MilosBog]

Hi people,
you are right, instead of trail an error it is better to take some literature..But as you can see i am 26(not a perfect age for engineer) an i have changed a job to one better payed but the company is just starting with refrigeration so i don't have any help inside or project in which i can take a look. And also, standards will be bought only when we inside the new department make some results in this field. Tanks a lot for the help, i will recalculate all this stuff a bit better later on and i will come back with questions once agai

[nando]

again made somebody happy

[Gary]

Hi people,
you are right, instead of trail an error it is better to take some literature..But as you can see i am 26(not a perfect age for engineer) an i have changed a job to one better payed but the company is just starting with refrigeration so i don't have any help inside or project in which i can take a look. And also, standards will be bought only when we inside the new department make some results in this field. Tanks a lot for the help, i will recalculate all this stuff a bit better later on and i will come back with questions once agai

Keep in mind that it is not just about temperature, it is also about humidity. This is true of air conditioning as well. Since you are more familiar with A/C, perhaps this will help clarify your thinking:

http://www.uigi.com/UIGI_SI.PDF

Let's say we want an A/C system to give us 22C@50%RH. Find where the 22C vertical line intersects with the 50%RH curve. Draw a horizontal line from that intersection over to the 100%RH curve. The vertical line at that intersection is the 11C line. This tells us that if the air contacting the coil surface is 11C@100%RH, then just enough moisture will be removed, so that when this air enters the room and is warmed to 22C, it's RH will be 50%. Ideal for human comfort.

Refrigeration works the same way. Identify the target temp and humidity, then trace the psychrometric chart to find out the ideal coil surface temp@100%RH (apparatus dewpoint aka ADP) and design your system accordingly.

[MilosBog]

Hi all,
i have rechecked most of the literature that i could find and that's it..now all the things are much more clear and i will do it in another way but next time, now one older colleague has done it - and he done the same... and i couldnt say anything 'cause he is a project designer for a 30 years now. But now i have only one , lets say theoretical question : With all the traps in the refrigerant piping, the refrigerant shall condense definitely in off periods, what to do to remove the condensate refrigerant from steam pipes? is there any post regarding this stuff?

[nike123]

Refrigeration works the same way. Identify the target temp and humidity, then trace the psychrometric chart to find out the ideal coil surface temp@100%RH (apparatus dewpoint aka ADP) and design your system accordingly.

Explained:

http://courses.washington.edu/me425/425-8-Coil%20Load%202006.pdf

[NoNickName]

what to do to remove the condensate refrigerant from steam pipes? is there any post regarding this stuff?

You mean vapor, not steam.
You do nothing.
Traps are there for a reason, and even if refrigerant condenses in the condenser pipes, there's no problem whatsoever. For the suction pipe, liquid accumulator should be there just to avoid liquid slugging.

[MilosBog]

hihihihi...In my mother language is a steam so i haven't expressed myself quite OK :)

[MilosBog]

Hi All,
one more thing and maybe that's it..maybe...As i come from the AC side i have selected the condensing unit for the high outdoor temperature. It is a standard for a Germany (the 32, have done the selection for 34). Now, i have seen one project in which the condensing unit is selected for a outdoor temperature of 20% but in Balkans. What to do if the outer temperature is around zero or lower? . Although the EC fans are included in delivery i am not sure how it will work or can this thing work.I will check which controllers is selected..

[NoNickName]

You need to make sure that condensing control by fan speed regulation is supplied and setup.