low velocity on evaporator fans ?!?!

[cruzeiros]

hello..i have a question please...

i have a large ( 15 x 10 x 7 m ) room insulated with polyuretan 100 mm and i want to preserve fruits for a long period of time..and i understand that the air speed must be around 0,2 m/s.

How can i do this..? 10x

[US Iceman]

There are several other requirements besides air velocity. The fruit you wish to store will have a specific long term storage condition that must be maintained.

Air velocity is only one part of the problem. The refrigeration system has to be designed for sufficient cooling capacity to keep the room at the desired temperature.

The evaporators have to be selected for the appropriate humidity control, cooling capacity, and location.

The entire system also has to be designed for all operating conditions, i.e., full capacity or partial capacity. This can change by season, or time of storage for the cooler.

In some cases, the cooler atmosphere is controlled (oxygen content, CO2, etc). This depends on the fruit you want to store.

If you can supply additional details perhaps we can help you with answers for general questions. This is a job for a design engineer that you can work with.

[Peter_1]

How we have done it already.
The speed of the fans is slowed down the closer the setpoint is reached. There is a minimum allowable speed and a maximum allowable speed.
The curve between the these 2 points can be programmed freely.

You will come then to a situation where there just enough flow to maintain temperature.

If you have a watercoil, then there will be no problem.

If you have on the other hand a DX evaporator, the reduced flow means reduced capacity.
As the capacity is reduced, the TEV will try to maintain the SH but will soon go out of range and starts hunting or overfeeding, call it the way you like.

So you then need a smaller TEV for this reduced capacity or better, an EEV. An EEV will follow very precise the reduced capacity.

But then the compressor will then start to evaporate at a lower evaporating temperature unless you have foreseen this with a capacity control or a VFD on the compressor. We used a VFD for this.

It's the ultimate precise control and this is in fact almost exactly the same a VRV or VRF is doing.

Carel has a regulator which can perform all this tasks in one enclosure.

You can also increase evaporating temperature the more you approach the set temperature so that you dry less the products, it runs the compressor with a higher COP, and the cold feeling you will encounter then (for example in a meat cutting rooms where peoples are constantly working in cold conditions) will be better.

[cruzeiros]

thanks for your answers.. i know about controlled atmosphere and i have the equipment to do this and the advice of a supervisor from the producer. the fruits will be grapes in 50 % of the space and the rest in divided to apples and pears. for grapes is a special treatment with sulfur also..but this isn't the problem..
It seems that the refrigeration part will make us some hard time... first is this low speed of air over the products..then..in one room for almost a week the temperature must be 7-10 degrees celsius then it gets slowly to 0-2 degrees...
in another room..the product temperature after 24 hours must be -1 and then keep it that way..
(and i'm not so pleased about this..to work hard for a day and then to sleep 9 months)
in the first place i said to go with DX evaporators but now i'm starting to think of something else..
i was wondering...anybody has a link for this air velocity problem..?
10x and sorry for long message

[Peter_1]

You were thinking about something else, instead of DX evaporators...what were you thinking then?

The control of air speeds and different temperatures, I think it's all in my first reply or am I missing something?

Will the rooms have different compressers of will you use a pack?

Going in 24 hours to -1°C , I suppose the goods may not be frozen.

Give some more info about size of rooms, what you think to use for the compressers, brand name of evaporators and how you think to control this.

[US Iceman]

in another room..the product temperature after 24 hours must be -1 and then keep it that way..

This sounds like an apple storage room I worked on in the past. However, I am surprised that the product temperature must be decreased to -1C in 24 hours. This can be a very large cooling load for such a short time.

You have many different requirements, and also many different operating conditions.

Peter_1 provided some very good information. If I may add to his comments; I have used variable frequency drives (VFD's) on DX evaporators also, but caution you on reducing the fan speed below 50% of the normal speed. The TXV's tend to hunt and loose control of the evaporator superheat as Peter_1 said.

The best systems to use VFD's on (in my opinion) are flooded or liquid overfeed evaporators.

Also, in my experience, TXV's do not react very well with large load changes, or small, fast load changes.

Part of the velocity problem is the air circulation over and through the product and containers. The racks and storage containers must provide for uniform airflow also.

Do you have to maintain a 0,2 m/s velocity over the whole room, or at several measuring stations?

Can you provide some additional information please?

Are you required to have humidity control also?

[cruzeiros]

1.When i was saying something else i was thinking not to use evaporators in the rooms. My idea was something more like an air handling unit (air duct system) for a better distribution of air and for control of the fan speed. ( Making this to an evaporator i suppose is not very good because the liquid would get to the compressor..?!?!)
2.In the first place i was thinking to a pack but now..?!
3.The recomended temperature to store pears for a long period (from 3 different sources ) is -1..0 celsius.
4.Guntner is the name, the rooms are anyway to big to have a corect speed over the product with an evaporator...and keep this in mind: "I'm new to refrigeration engineer" (for you it may be easy..but for some of us..., we are just starting to understand some things...with your help of course) 10x.

[cruzeiros]

the speed will be measured in several points between the containers and yes..humidity must be 85-90 % for grapes and 90-95 for others. 10x for informations...

[Peter_1]

1.... an air handling unit (air duct system) for a better distribution of air and for control of the fan speed.
2..... pack but now..?!
3.The recomended temperature to store pears for a long period (from 3 different sources ) is -1..0 celsius.
4.Guntner is the name, the rooms are anyway to big to have a corect speed over the product with an evaporator...

1 an AHU is not airtight enough for an ULO room and is also too expensive. You can control speed not better in an AHU.
2. Best choice is in my opinion a pack.
3. Here in Belgium, storage temperature is determined by the sugar content of the pear and is mostly something around -1°C. I think everyone has his own method for this.
4. Guntner is a very good product. They have also evaporators with larger fans to increase static height. If room is that big, install additional circulating fans and use the evaporators only to cool the room.

We installed twice an ULO room and once all the products are cooled, air circulation is not that important anymore because the stack them beside each other with a spacing of +/- 2 inches (5 cm) and 12 ft or 4 m high in wooden boxes.
While cooling (+/- 2 weeks), they spread the boxes more wide open.
Set a safety thermostat in serie with the first one in case the main hangs for some reason.

Some suggestions:

Make all the electrical connections to the outisde of the room because you can't work in the room afterwards to repair something (oxygen is gone and goods are stacked to high) If a heater fails or a fan, you can allways disconnect them and run with one less.

Try to install at least 2 evaporators/room with more then 1 fan/evaporator.
Once the room is on the set temperature, you can run 2evaporators at +/- half fan speed and reduce compressor capacity with 50%

Install the TEV and the SV outside the room.

Make that all your feed-throug are made gastight.

Let the drain flow on the floor in the coldroom so that the water stays in the room.

[US Iceman]

My idea was something more like an air handling unit (air duct system) for a better distribution of air and for control of the fan speed.

I do not like to use duct work in food processing or storage areas. Ducts will accumulate dust, bacteria, etc. that can lead to other problems. It is hard to clean metal ducts. (see one option below)

If you use galvanized duct, it will eventually rust. Stainless steel is better to eliminate the corrosion problem, but the dirt issue is still present.

Of course the discharge air velocity will be greater from a ceiling hung evaporator, when compared to the discharge velocity of ducted louvers.

These have been used with good success in food processing areas, since they are fabric and can be washed regularly. Good air filters can help also.

http://www.ductsox.com/

One idea for you to consider....

Making this to an evaporator I suppose is not very good because the liquid would get to the compressor..?!?!

In either case if you use refrigerant as the primary coolant, you can have potential flood-back issues with liquid refrigerant due to the varying loads with TXV's.

You will need liquid/vapor separators on the suction line before the compressors for sure.

The refrigeration system design is very involved; humidity control, temperature control, and very large cooling load requirements (full capacity to partial capacity, also).

You may need a separate pack on the -1C room for sufficient capacity when it is filled with fruit. The wide range of capacity required is a good application for multiple compressors and VFD's on one or more compressors.

for you it may be easy..but for some of us..., we are just starting to understand some things...with your help of course

We all started in the same position. We learn as we get older.

[US Iceman]

Peter, I am not familiar with the term "ULO". What does this mean?

Thanks,
US Iceman

[cruzeiros]

"ultra low oxygen" and thanks for all

[US Iceman]

That makes sense. We call then CA (Controlled Atmosphere) rooms here.

Thank you for the explanation.

[reeferman]

That makes sense. We call then CA (Controlled Atmosphere) rooms here.

Thank you for the explanation.

I just wanted to add that ULO and CA are similar, but not the same.
ULO goes down to 1% oxygen and CA has 2% minimal.
Because of this fact a ULO Room has to be better sealed than for CA.
See also:
http://www.tis-gdv.de/tis/tagungen/s...7/wild/14a.gif

[Peter_1]

Here are some pictures of the ULO we installed.
Will take some pictures the next time we're there of the crubber/air washer (not installed by us but by Van Amerongen The Netherlands)

[NoNickName]

Carel has a regulator which can perform all this tasks in one enclosure.

Don't expect it to work, though. They are able to forget disabling the hour counters for non-existing standby pumps, let alone controlling a EEV and a VSD.

[Peter_1]

Why you 're the only one having problems with Carel?

We have now tree packs running on them and they work perfect.

In one pack, we throw out completely the Omron PLC.

And their Plantvisor, mmmmmmmmm...Dixell is nothing compared with it.
But we have field experience with it...which means...we design it...we build it...we install it...and we service it...
and this since almost 25 years.
Perhaps that's the difference.

[Peter_1]

And... I forgot to say...we do more then making and installing chillers.

We have also a wide experience...from NH3 to R114, from R23 to ethylene, propane, yes even R12 and R502 (those good old days), cascade systems, autocascade systems, freezers, blast freezers, heat reclaim, ice machines (installed a 10 ton unit), switch cupboards PLC and HMI controlled...ohh...and chillers.
But if we have time, we make them ourself.

[NoNickName]

Maybe because I'm trained with Easytools, and I know what's behind it.
Let's make an example: pCO1 with I/O expansion module. Digital inputs are acquired from the XM in no less then 22 seconds, set aside analogue conversion.
Pump switching on the expansion module let a chiller stop for flow alarm.
Or, shall we talk about the programming keys? I mean the ones you have to open in two like a nut to let them work.
Or the backlight of the PGD, who have a life of 5000 hours and the backlighting is not replaceable.

I have a drawer full of anecdotes, in much less than 25 years. One day I'll post in off topic area and will have a laugh.

[Peter_1]

What's Easytools?
Something like Multisim?

[NoNickName]

Easytools is the Development Environment for pCO software

[Dan]

1 an AHU is not airtight enough for an ULO room and is also too expensive. You can control speed not better in an AHU....
Some suggestions:

Make all the electrical connections to the outisde of the room because you can't work in the room afterwards to repair something (oxygen is gone and goods are stacked to high) If a heater fails or a fan, you can allways disconnect them and run with one less.

Try to install at least 2 evaporators/room with more then 1 fan/evaporator.
Once the room is on the set temperature, you can run 2evaporators at +/- half fan speed and reduce compressor capacity with 50%

Install the TEV and the SV outside the room.

Make that all your feed-throug are made gastight.

Let the drain flow on the floor in the coldroom so that the water stays in the room.

Peter, that is a very nice package of advice. Especially your suggestions.

[Ke-Fibertec UK]

We recommend F7 filters for our High dust holding capacity ducts, and F8 for low duct holding capacity.