Low Temperature Cold Store

[iceman007]

I have been asked to build a low temperature cold store. The store itself does not have to be that big-probably npo more than 2.5 metres by 3 metres and about 2metres high. However it needs a heavy gauge stainless steel interior and has to maintain -40 degrees, so would need to evaporate at -47 or -48 degrees. I can't get the plant from any normal suppliers as -40 evaporating is the lowest, so I think I have to try Grasso or perhaps maybe think about two stage compressors.
Has anyone an idea of where the plant can be obtained (I have been recommended a cryogenic chamber builder, but feel it might be a bit too much).

James

[RSFN1974]

It should be possible to get a plant that can do that. At my former job we built a container for -45°C. We used a Bock plant (don't remember which) running on R404A. Of course you will have to go very low on pressure (subzero). But there were no problems in getting the temp. down.

R Nielsen

[chemi-cool]

Hi James,

Good to see you. Here is the answer for your problem.
Note the lines:

Any project

Any size

Any place

http://www.coldstoragemfg.com/


I think it worth a quote.

Chemi

[iceman007]

Hi Chemi,

Aren't they based in California ???
I don't get asked for these sort of temperature applications, maybe -20 at the most. I reckon I can build the store, but I am having to think of the easiest way to get an evaporator temperature of nearly -50 degrees.

James

[Brian_UK]

Have a look at http://www.stancold.co.uk they do at least mention a -40°C coldroom.

[Cofreth]

I think a cascade system will be preferred for temperatures of -40 C and below.

[Peter_1]

Helllloooo James,

Busy again I see?

I should use R507 (-47°C at 0 bar) which will give you a safer margin of 1 K compared to R404a or 404a (-46°C at 0 bar).

Select an evaporator, running with a DT of 5 K so that you have also with this component a safe margin of 2 K (if you should run on R07)

Make sure that you have a controlled airflow (air turns at the end of the room) or even better, install the evaporator in a small false ceiling

Use a very small liquid subcooler (plate HE) to increase capacity of the cooler.

Select a compressor a litlle bit too heavy for the given evaporator capacity and use anadditional small throttling capacity valve (injecting controlled hot gas in the suction) to maintain a stable suction pressure, just above atmospheric pressure.
You will then be sure that compressor will evaporate allways at the same pressure, whatever the load may be.

Or even better, use a VFD for the compressor, it will at least be a very small one.

And use a Bitzer for this (my personal favor)
What cooling capacity do you need? Don't forgetat these low evaporating pressure that capacity drops serious. So don't forget to add the power of the fans, some heat of the door heating will enter the room,

Panel thickness used?

Give some more info here, I'm glad to help you.

I can ask at Goedhart or Kuba, they've done it before and even with much lower temperatures.
Guntner perhaps

[Peter_1]

http://www.coldstoragemfg.com/

Hopes that the quality of their work is better then the quality of their website.

[iceman007]

Hello Peter,

Always seem to be busy at the moment.
I had been thinking about this sat at home in front of the fire. I had originally thought to use either R507 or R404a. The room itself only needs to be about 20m3 or so. They want it lined in heavy gauge stainless steel (that in itself should be fun if I can find someone to build the panels to save me doing it). I estimate 80mm insulation thickness. This room is to store fuel tanks in (quite small ones, and a minimum of 10), probably 500 litres at any time, so a fair amount of heat to remove. I was speaking to one of my own colleagues and we had thought that as this is quite a small area to chill/freeze we would use a rotary compressor, and a 4 or 5kW duty, with aluminium/steel coils and pipes etc, electronic expansion valves, and as we thought we may (in the case or R404a be running low on pressure to fit an air purger. Defrost might be a problem, I think we cannot use hot gas, reverse cycle a bit more expensive, and electric (well the fuel storage might be an issue). We have designed everything to be non-sparking explosion proof. Possibly we will have to fit a sniffer alarm which shuts off all supply if there are fumes and vents the area. I had considered a Bitzer earlier on but had been talked out of it by a contact I have, but perhaps now I might use one. I dread to think how much it will cost them, but they paythe money and take the choice !!!

If you want to e-mail me back you know where I am.

Many Thanks
James

[iceman007]

Finally sorted out. I've got someone to do the panels, and the plant- I shall use a bitzer compressor, subcooler etc etc etc, running on R507 (thanks Peter)

Many thanks.

PS Thanks especially Peter, and Chemi for your assistance-always there at the right time !!!!!!!!!

[Peter_1]

Just found now some time for a reply.

These are the fine jobs, here you can prove that you know your job. Something complete different than connecting two tubes between an indoor and a prewired and prefilled outdoor unit.

James, for a -20°C room ,we use at least 10 cm and for a -25°C room, even 14 cm panels.
Pressure differential valve in the panel?
Will you cover the inside walls after wards with stainless steel plates?
We have two manufacturers who can make this in stainless steel.
Viesmann has these rooms standard in stock as far as I can remember. (they're not cheap)

A standard condensing unit will do the job fine I think, only one thing, when you evaporate at -46°C, almost no heat will be pumped to the condenser which was initially designed for a higher evaporating temperature.
If this unit is installed in a cold environment, then a HP control will be needed.

Indeed, the fuel can cause some headaches but that can be solved anyway.
The sniffer alarm is a good idea but will it work also at -30°C?
Indeed, you should better use a reverse cycle to defrost the coil.
Or http://www.bmil.com/ballyrefrig/thermosaver.htm

What with the drain heater you will need? Feeding the evaporator with the liquid supply via the drain? (perhaps a silly idea)

This is such a nice job which you may not let it slip out of your hands.

We often install on such a systems an automatic telephone dialer - the same they use in domestic alarm burglar systems - when something happens with the unit (4 spoken messages to 4 different mobile numbers for +/- 150 €) We mostly connect the first contact to the temperature alarm of the controller, the 2nd when we have lost the power, and some critical alarms connected in parallel on the Th (motor current tripping, Kriwan, Oil pressure and HP, all connected to one auxiliary alarm relay) and non critical to the 4 th (1 of the fans of the condenser or evaporator is tripping, ***** sniffers alarm, safety time of defrosting exceeded,.. .. )

5 kW will be big enough, even a smaller one will do the job. But with 5 kW, you will have a safe margin.

Bitzers are relay superb German class products, makes almost no noise, less vibration and are not more expensive then a Copeland.
Bitzer is doing also a lot more R&D for their products. Look to their screws and semi-hermetic screws where you even don't need an oil separator. A real masterpiece of technique if you ask me.

Let us know if you won the job.

[chillin out]

What with the drain heater you will need? Feeding the evaporator with the liquid supply via the drain? (perhaps a silly idea)

Good idea that Peter, but what if the drain blocked up and froze?
Would it burst the L/L pipe?
Also it would be a hard job getting theL/L round the trap.

Chillin

[iceman007]

Hi Peter,

200mm insulated panels (polyisocyanurate), stainless steel inside 304 gauge, manufacturer can do this-wider door opening for hydraulic lift, minimum 500kg load bearing, bitzer compressor probably might use 4.7kW, HP control, reverse cycle defrost, drain heater haven't fully decided on how to do yet, but that's a small detail, we might be able to use electric heater, with all electrics contained in a plenum or something (Bitzer are having a think about it as well). We have to put remote monitoring on there, the control panel we can build, and we should be able to sense or sniff down to -40 degrees (I have a specialist guy who can build specialist sensors etc) Once we detect a rise above a certain level, power shuts down, and activates a dialer and vents the room via a extract to outdoors (drawings are being done this week).
I agree, this is a better test than putting pipes and a cable between packaged units (I better be careful what I say here)

verschilt de mensen van de jongens (Ik hoop u dat kunt begrijpen)
James