Is this doable, building your own specialised fridge ........... let me explain!

Hi,

I go hunting on a regular basis and have a requirement to store venison in a cool climate over an extended period of time, up to 12 hours when travelling. So this is my thinking, build a "chest type" box that can easily be dropped into into a trailer (6'X4'X2' high).

My tow vehicle is currently fitted with a dual battery system and a 700W pure sine wave inverter capable of 1400W at startup. So that is how I intend to power it.

I also have an old upright ~ 200l refridgerator / freezer, my dear wife put a hole into the freezer evaporator unit with a sharp knife (DON'T go there). The cost to repair is such that I was going to toss it until this project came to mind. So I have a 220V compressor (details as to size can follow), condensor unit but will need an evaporator. I was hoping to make the evaporator unit from coiled copper and the bin of the chest fridge from aluminium that will be seamlessly welded.

Once assembled the fridge will be connected and gassed by a professional. I will undertake all other mechanical and electrical work which is well within my competance.

It is probably uneconomical but hey, it is custom.

Any opinions or am I flogging a dead horse.

Hi Andrew

You should be OK carrying out the construction side, but yes it will need to be commisioned by a licenced professional. Unless of course your counntry hasn't signed up to the Montreal and Kyoto protocol, then you could do it your self.

Even if we had not signed up I would still like a licenced professional to do it.

Where do I start? Obviously I would need to size the box to the compressor size. Can you point me at a resource that I can start studying and learning from so that I can start the theoretical calc's.

Cheers

You need to work out how much meat you want to chill (kg) over what period (time) and the start temperature and the end temperature (t1 - t2)

This will give you the refrigeration load. From there, you will be able to see if your compressor is up to the job.

Post some details and we can work from there.

What is the compressor model no.?

if comp big enough buy a eutentic beam on provision there available in your area precharge it on stanby and on the road you dont need to run with power we run two boxes for a customer who drives a hurst, you no what i mean, one beam cools well even in our summer on a 13 cuft chest freezer comp he runs them under suspicious circumstances aparantley

Hello Frank,

thanks for the offer of help. Generally the farms on which we hunt have refrigerations facilities. One it assists in ageing the venison and two it is easier to break the carcass into cuts of meat when cooler. Decent farms can get the meat to about 5 to 8 dec C. So Delta t would be in the order of 5 degrees. Thast would have me at a mean temperature 3 deg C. This may well be over the top and I would think that if I could keep the product at 5 deg C that this would be first prize.

The mass of meat to keep chilled would probably be a maximum of 150kg. We tend to remove all the bone etc. etc. for efficient transportation.

The average ambient temperature in winter (hunting season) when travelling would be in the order of 25 deg C in summer about 35 dec C. We do hunt on occasion early summer and late autumn. So for this exercise lets assume that we need to cool 150kg of meat, by 5 dec C and maintain a temperature of 3 dec C in an ambient of 35 dec C. The compressor may not be able to cope but if the meat transports at 10 dec C it is still better that we currently have.

The fridge is an old GE Model WGR 308 (wife says it is the Noah special edition model). The rating plate on the compressor reads;

AE130 JS351
25C81 075433 AE1343A
220/240V 50Hz LRA -9.5
TECUMSEH SICOH BRASIL

On the top of the compressor appears the coltage and frequency as well a "Watt Input 150"

The fridge has a total internal capacity of 308l (267l Fridge and 41l Freezer).

Kind Regards
Andrew

Tecumseh AE1343A
Refrigerant R12
Rating:
60Hz 450btu/h
50Hz 390btu/h
Evap -34.4°C <-> -12.2°C

Thanks Brian,

my inverter has a dip switch that allows me the set from 50Hz to 60Hz so that means I have 450btu/h potentially available. Does one gas differently depending on the frequency? If this is the case I will need to design around 50Hz to make it useable on mains electicity.

I am going to hunt for formulae now. As space nor aesthetics (it will still need to look presentable though) is not the primary consideration here I can afford myself the luxuty of decent wall thickness. Does one use a liquid expandable foam or are there other products that are less "lossy".

Cheers
Andrew

Quote:

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Originally Posted by charlie patt

if comp big enough buy a eutentic beam on provision there available in your area precharge it on stanby and on the road you dont need to run with power we run two boxes for a customer who drives a hurst, you no what i mean, one beam cools well even in our summer on a 13 cuft chest freezer comp he runs them under suspicious circumstances aparantley

---

As I already have the power source available would this not be an unnescessary expense or are there other advantages. I will google it now.

OK,

been doing some google work lookig for formulae and downloaded the program Coolpack. Frankly I can make no sense of it yet. Where can I find a logical sequence of formulae that will get me a result. As I am working backwards it should be much easier. I was thinking of the big picture stuff so using rule of thumb perhaps someone can help.

Known factors

Fridge is 308l. If cooling is a linear function then would this be a fair assumption?
Fridge currently cools 267l to to 3-5 deg C in ambients of 30 dec C. There is the 41l freezer compartment that is cooled to say -18 deg C, would it be fair to say that converting this energy from freezer to fridge would increase the 41l by roughly 4X. This would bring the effective "fridge" volume to 267l+164l=431l. Now 431l may well be too much volume so I was thinking of making the volume 400l giving some more headroom in the compressor.

On this basis I am assuming that the compressor would cope with cooling under normal household fridge conditions. What I don't know is how to calculate the cooling effect on a 150kg meat load ( a load which I am sure well exceeds any normal 400l fridge), assuming the meat from the coldroom is at 10 deg C and placed into an already pre-ccoled fridge at 5 dec C.

If the above is true then no fancy calc's are required, if not true I would need some serious backup from the forum.

All that would remain would be to decide on the condenser coil and shape and the evaporator coil. I was hoping to use a couple of turns of copper tubing around the inside of the fridge compartment such that the cold air decends on the contents of the fridge? Is this stupid or should I be blowing cold air into the compartment. The coils just sounded more efficient as cooling fans would not be required. The current condensor is flat and mounted to the rear of the fridge so that will probably be impractical so I will buy one of those more compact units with the cooling fan.

Am I oversimplifying the matter? It would be impractlcal for me to learn how to design a fridge for a one off "redneck" type hunting fridge that could have latitude in it's perfomance.

Thanks for the help thus far.

Cheers

I think I have answered my own question on the frequency. The compressor is designed at 60Hz, here in S.A. we run a 50Hz system so I would have to assume that either is fine but that at 50Hz that the fridge was underperforming a little.

From the input data of 150W I assume this is the average load when running so the load current would be 0.68A. Typically startup currents are in the order of 8-10X load current so that would leave me at 1200 to 1500W on startup, my inverter handles 1400W so I should be OK on that.

Gonna keep you boys busy :D.

As the fridge will be bouncing around would one still want to mount the compressor on some form of suspension or would it be better to make it a rigid mount.


Cheers
Andrew

Hi,

would it help to roll the copper tubing slighly flat for a more intimate contact with the walls of the fridge? We have a rolling mill at work that I could use.

Andrew