freezing dog food

[knighty]

hi guys (im new)

I own a small factory making frozen pet food and I'm having trouble freezing it all

the local refridgeration companies dont really know what there doing... the good companies are so expensive there out of my dog food making price range.

I have one main freezer for freezing the dog food and another for storing it, the dog food is in 1lb bags and on trays in a rack to maximise surface area.

im not sure of the size of the motor, but the compressor is taking 8 amps on each of it's 3 phases (i suspect this compressor will be scrap soon, it's been blowing fuses)

the freezer is 8x6x12 (feet) and we only run it 6pm to 7am

on a bussy day we put maybe 2000lb of dog food in the freezer... im not sure about the specific heat capacity for any of it...

I'm thinking when this compressor dies I'll get a new (much bigger) evaporator too... I'll get one cheap an an auction soon hopefuly (lots of meet factorys closing down latly so good supply ar rock bottom prices)

the thing is what size compressor should i aim for, and could I run 2 compressors in parralel ? so maybe i could run 2 when theres a lot of stuff in there and just run 1 the rest of the time... (out electrisity bill is £1000 a month, - about 2000USD)

also... i've always been told i need to match evaporators and compressors...but why? no one can give me a good answer for that, i was thinking as long as the evaporator can out-preform the compressor theres not a problem...
i can see who if the evaporator is not bit enough it would just ice up

so,
6x8x12 foot freezer
2000lb of meat
hot big a copressor do i need
can i run 2 in parallel
link between evap and compressor sizes

wow thats a long first post, thanks for any help you can give me guys, and im sorry about any spelling mistakes, im dyslexic and my spell checker checked out on me

[US Iceman]

Hi Knighty,

I have a couple of questions for you to start with. Most of the information you provided is a good start, but you also need to provide the following information:

1) What is the meat temperature when it is placed in the freezer?

2) What temperature do you want the meat to be at after it is frozen?

3) What are the freezer walls constructed out of and how thick are the wall panels? Is there an insulated floor panel? The freezer also needs a pressure relief port.

4) What is the door size and how long (and how often) is it opened?

5) What is the ambient temperature surrounding the freezer? (need dry bulb and relative humidity)

Whoever helps you with this will need this information (maybe more). Most refrigeration people who know what to do may be expensive, but they can also help you to minimize your total costs while doing a first rate job.

Using two compressors could provide the full capacity when freezing is required. One compressor could operate to maintain the temperatures after the meat is frozen. There are a lot of variables to determine which is the best course of action though.

The evaporators and the other components (condenser, compressor, expansion valve, etc) need to be carefully selected to ensure their performance provides the desired effect.

As an example, an evaporator of a specific capacity will need to matched with a compressor that is capable of producing the same capacity at the desired temperature.

All of the refrigerant piping connecting these components will also have to be correctly sized to ensure the system capacity is not adversely affected.

Defrosting is another task that needs to be reviewed.

My recommendation is to find a competent refrigeration company in your area and use them to help you. If the people you ask questions of cannot explain it to your satisfaction, find someone else.

I'm sure there is someone in the UK close to you who can assist.

I do hope this is useful for you.

Best Regards,
US Iceman

[botrous]

Welcome to the forum Knighty . . . . .hope you enjoy your stay

[Brian_UK]

...the freezer is 8x6x12 (feet) and we only run it 6pm to 7am...

Welcome Knighty, I assume that name is due to your working hours ??

Anyway, I am not going to add anything to the previous replies because it is not my field however;

If you are only running your freezer for 13 hours a day why are you expecting it to be able to freeze you products ?

It must be taking at least several hours just to recool itself never mind cooling down and freezing the product.

So, what is the temperature of the freezer at 6pm when you turn it on and how long does it take to get to your required temperature before you start adding product ?

[knighty]

hi guys, thankd for the help

for those questions...

the meat varies in tempriture when its put into the freezer, but it should all be below 10'C

as long as the meat is frozen solid when we take it out of that freezer to box it that will do, it can always continue to cool once its in the storage freezer

the freezer walls are about 10cm thick, foam in the middle sandwiched between 2 thin sheets of aluminium, the floor is insulated too

the door is about 6 feet high and 3 feet wide

ambient tempritire is.... the weather in the UK... so all over the place.

the frezer is filled during the day (when its turned off) then closed and turned on overnight, it stays pretty cold in there, and on the hotter days we turn power on for a few hours during the day.

the freezer used to bring the tempreture down to -25'C by the morning... but now its only going down to about -10'C .... (the motor windings are on the way out in the compressor)


I'm not aiming to have the exact right compressor for the job, I'm hopeing I can have one compressor that can maintain a low tempreture in the room and another which will be much larger and will pull the tempreture down...

the way i see it is that is the larger compressor uses twice as much power as a smaller one... then it will only run half as much.... or close enough to keep me happy anyway.

I can get a really big compressor and evaporator cheap from any number of auctions... (no-one ever buys themfrom a closing slaughter house)

I just dont know about matching compressors to evaporators.

I'm hopeing going for an evaporator thats overkill for the compressor will work out ok and solve any problems.

the son of a guy who works for e is a refridgeration engeneer.... he used to be a machanic and they gave him 1 weeks refridgeration training... so he's not much good to say the least... but means i have easy access to all the parts, gass, tools etc.. that i need

[botrous]

Hi knighty , how are you ?
What's the weight of meat per day you put in the freezer , 1 ton , 2 tons . . . .?
The weight is critical for compressor/evaporator sizing

regards

[knighty]

about 2000lb on a really busy day... so thats what to aim for. tho some days it's only half that much.

and I'd really like some overkill on this... compressors don't seam to last that long for us now, maybe 3 years and at £3000 a time !
I'm guessing were pushing them harder than they were really designed to go

[Abe]

t

he freezer used to bring the tempreture down to -25'C by the morning... but now its only going down to about -10'C .... (the motor windings are on the way out in the compressor)

U seem to be convinced its your compressor and not anything else.

If it did the job before it can do it again

Give us details of compressor and size of room, and we can work out if its up to the job

Have u considereyou might have a slow leak or something???

[Mahmoud]

Dear Knighty..

first of all welcome man,, now as per your requirement:

1- 2000lb/13 hours entering @ +10*C (proposed Meet)
2- 100mm plourethane panels.

your requirements is as follows:

- 9 KW of refrigeration @ Evaporating Temp. of -45*C (Proposed Ambient 32)
- Room temp. to be maintainded at -40*C

If you have a DWM-Copeland and Friga-Bohn dealer ask about those model:

Condensing Unit Model : Z9-6TA-1500 SUB (2-Stage)
Friga-Bohn Unit Model : NQ-2023 S +RVU+ ECK Kits

or search for equivalent with bitzer and bock .. but i preffer Copeland..

[Guy Hodgins]

You might want to consider a second hand horizontal packaged plate freezer. These units freeze products in trays into square blocks extremely quickly.

[knighty]

I've googled around a bit and that looks like a really nice compressos... but it looks expensive too

if i pick up a compressor and evaporator at auction.... how important is matching the two for output ?

I need something cheap

[Abe]

I've googled around a bit and that looks like a really nice compressos... but it looks expensive too

if i pick up a compressor and evaporator at auction.... how important is matching the two for output ?

I need something cheap

Matching the two is CRITICAL

[Peter_1]

What is very important for a freezer is the proper air guidance.
Add also additional fans to improve heat removal.

Mahmoud gave you the correct needed cooling capacity, 9 kW,... but for such an application I should evaporate at -30°C to -35°C, gives you a much better COP and you don't need a 2-stage compressor.

If you take in account 2 defrosts of 30 ', then you need 10 kW.

Enough air circulation, that's crucial for a blast freezer. Make that there is enough space between the meat blocks.

You can't push a compressor harder then it's designed for. If you stay within the specs and a competent mechanic services it (!!!), then it will last more than 10 years.
If you buy your equipmet at an auction, then you don't know what you're buying. You perhaps pay not that much but you buy also a certain risk.

I doubt that the son of one of your workers is competent enough to install this. It's not because he can give you the tools, the gas that he's also able to do this job the way it should have to be installed.

[Mahmoud]

Dear Peter,,

don't you think that a good temp. difference should be there ? in other words in blast freezing to achieve -20*C product temp. we should have -40*C room temp. ?

From my experience i havent did any blast freezer with single stage compressor or at room temp. less than -35*C, please explain this point peter..

The best..

[Double V]

Yo Knighty

Think about this carefully man! Your main aim is to produce frozen dog food. Why do you want to take a chance on something like this. Do yourself a favor & spend some quality money on a quality installation from a quality mechanic that won't dissapear when things go wrong.

I'm sure you won't be able to sell the dog food when it isn't frozen. A freezer that doesn't work means dog food wasted.

I've seen it happen so many times when guys want to save some money but land up doing the job a second time to have it fixed up properly. Make sure you get the right person the first time around.

[Mahmoud]

Double V. i agree with you completly..

[US Iceman]

Hi all,

don't you think that a good temp. difference should be there ? in other words in blast freezing to achieve -20*C product temp. we should have -40*C room temp. ?

I disagree with this point. A high temperature difference should not be used for blast freezing. A reasonable value to use is 5 to 6C, not 20C.

A larger temperature difference will require larger compressors, larger suction lines, more energy input, and two stage systems.

What is very important for a freezer is the proper air guidance....

Enough air circulation, that's crucial for a blast freezer. Make that there is enough space between the meat blocks.

I totally agree with Peter. Temperature is provided to produce a fast freezing process, but air circulation is what removes the heat from the product. More air circulation with minimal temperature difference produces a higher quality product. It is also a more efficient cooling process.

Knighty, if you are replacing compressors on a regular basis, it might be more cost effective to do it right the next time.

From what you describe, you are spending a lot of money on replacement parts and have continual frustration with the system. This is not normal and should not be expected.

How much money have you saved really???

The components have to be carefully matched! If not, you are bound to have more of the same problems you want to correct.

Regards,
US Iceman

[Peter_1]

Mahmoud, the last blast freezer we installed was made for 11 ton chicken meat/night (8 hours)

We maintain a temperature of -30°C, evaporating at -37°C to -40°C (R404a which approaches almost atmospheric pressure)

Hot gas defrost.

[knighty]

your al right, im frustrated with having to throw good money after bad for system's that don't do what there suposed to do or dont last long enough.

I've only just taken over the business from my father but I've been working there since I was small and can remember the old belt driven compressors that used to last for pretty much forever.

I've just scrapped 3 smaller freezers and replaced them with one big one... but then I broke my leg in a car accident so everything is kind of up in the air at the moment.

once im back at work I'll move around the racks for freezing the meat and see how much it helps (we didnt have room for this before)

thanks for all your help guys, I'll hold off on replacing the compressor for now untill it breaks or untill the sumer at least .
(i can spread stuff around in different freezers etc.. or give it 2 days to freez if i get stuck, just its a lot of extra work)

on another point... what size compressor should be used for a 8x7x24foot box, 10mil walls, just to keep the stuff in there frozen (no freezing needed) a temp of about -20 would be nice... this new freezer will only get down to about -10.

once my leg is better I'll phone up a good refridgeration company, just i'd like some info first so i can tell if there any good

p.s. thanks for putting up with my dislexic spelling too, lots of people take offence thinking im just lazy

[knighty]

you know how the compressor and evaporator need to be matched... why is that ?

is it just the expansion valve that has to be right of the hole unit ?
I dont understand why it matters if the evaporaotor is of a higher output than the compressor/condensor unit.

also, how is evap temp set ? buy the expansion valve ?

sorry of all the questions guys, im searching the net like mad but nothing i can find goes into enough detail... either that or goes into way too much detail.

[US Iceman]

Knighty,

A brief explanation.

First we need to know how much refrigeration (cooling capacity) is needed. This is a calculated value. So many BTU's, kW cooling, kCal, whatever.

The number of evaporators is determined by the proper air circulation and capacity. A large room may require multiple coils, while a small room may be OK with one coil.

For applications that require periodic defrosting, the installed refrigeration capacity is increased to allow for the capacity lost when the coils are in defrost. Here again the system capacity must be balanced with the available run time.

The evaporator coil performance is rated in heat transfer per degree TD (temperature difference = room temperature minus evaporating temperature).

The evaporating temperature equals a specific pressure for a given refrigerant. The evaporating pressure of the refrigerant is higher than the compressor suction pressure.

The pressure difference between evaporating pressure and compressor suction pressure is the suction line pressure loss.

The compressor(s) is selected to provide the total cooling capacity calculated in step 1 above (corrected for time off during defrost ).

The expansion valves are selected on the basis of the evaporator cooling capacity and the available pressure difference between the condensing pressure and the evaporating pressure.

The condenser is selected for the total heat rejected by the refrigeration system.

It must all balance, if the system is to work properly. If any component is not properly selected, you will find a lack of capacity, longer freezing times, poor operation, frequent replacements, etc.

This is only a very basic list of the logic behind the art and science of refrigeration.

This is why it pays to hire a professional!

I hope this helps.

US Iceman

[Abe]

you know how the compressor and evaporator need to be matched... why is that ?

is it just the expansion valve that has to be right of the hole unit ?
I dont understand why it matters if the evaporaotor is of a higher output than the compressor/condensor unit.

also, how is evap temp set ? buy the expansion valve ?

sorry of all the questions guys, im searching the net like mad but nothing i can find goes into enough detail... either that or goes into way too much detail.

If Evaporator is sized too small it will ice up rapidly

Its just like a human body, the parts match the rest of the body, if arms were short, or legs longer.the body wont function or work, walk right.

Same thing here

You dont put a Chevrolet 6 cylinder engine into a mini do you??

[chemi-cool]

You dont put a Chevrolet 6 cylinder engine into a mini do you??

Oh, Yes you do!!!

Chemi

[Brian_UK]

I think that metaphor should have been the other way around Chemi don't you ??

[Mahmoud]

I disagree with this point. A high temperature difference should not be used for blast freezing. A reasonable value to use is 5 to 6C, not 20C.

A larger temperature difference will require larger compressors, larger suction lines, more energy input, and two stage systems.

US Iceman,, you've totally misunderstand me man .. the temp. difference am talking about is the diff. between the room temp. and the product temp. NOT the return air and evap. temp.. this would make me very silly man .. i had to mention that to clear the image

Peter, 11 tons of meat, what was the capacity of the system @ evap. temp. of -37.. and what was the product temp. finally freezed going out to be stored in the freezer..?

The best ..

[knighty]

i've got a smallish (about 1hp) compressor/condensor setup sitting on a shelf doing nothing at the moment from a fridge i scrapped... what about if i hooked this up with a heat exchanger cooling the high presure line going into the blast freezer ?

useing something like this...
http://cgi.ebay.com/ebaymotors/New-S...76601567QQrdZ1

would that help much ?

[Peter_1]

This is the pack for this, liquid reciever and the SV's with the hot gas defrost system on the dusty ceiling.