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Rio69
13-05-2013, 12:31 PM
I am designing a refrigeration plant with single vertical plate freezer.
I am not sure how to design defrosting, since it is only one unit in the system, and I do not know how to provide hot gas for defrosting.
I have got some advices to install additional small air evaporator in space nearby, to provide hot gas, but I actually do not know how big it should be, and anyway I do not need it, have nothing to cool.
The system will be liquid overfeed with pump.I would prefere to use R404a, but I am avare of problems with oil managment. If somebody has experience, please help

I have experience with plate freezer and ammonia installation with hot gas defrosting, but it was always with several evaporators in system, and supplying hot gas was never problem.

Thank you in advance.

Iceman717
13-05-2013, 04:40 PM
any chance you could use multiple smaller units rather than just one?

Rio69
13-05-2013, 08:45 PM
I am considering using two smaller freezer. And how will I defrost the last batch..again have no hot gas, since freezer No. 1 is not working any more?

RANGER1
13-05-2013, 09:00 PM
Rio69, consider defrost like a harvest on a Vogt ice machine. They unload compressor to approx. 25%, keep it running to regenerate system & use gas off top of liquid receiver for defrost. Evaporator has a downstream pressure regulator with liquid receiver gas feeding in for defrost set at 2-5 deg C(harvest in ice machine's case).Best look up Vogt operation for details if you do not know already.

Tycho
17-05-2013, 04:56 AM
This is a fun one.

How can you make a liquid overfeed system with only one evaporator?

You can't, because you need to get hotgas from somewhere to defrost it, and without a second evaporator, you can't get any hotgas... or so they say...

what if you have a suction drum that can hold the whole charge of the system, and when you need to defrost, you reroute all hotgas to the plate freezer instead of to the condenser, push the liquid back to the suction drum, the liquid coming back to the suction drum would be enough to keep the compressor going, or so I hope, so it could keep he defrost and compressor running.

I built a system like that, but with LP floaters on the plate freezers, and there were two of them

AMP
30-05-2013, 06:32 PM
Hi Rio69,

It is very easy to defrost one single vertical plate freezer with hot gas. The condenser is there!!! You may take care of the valves sequence, where to put them and some pressures, but it is very easy. And you will not need complex automatons or expensive automatic valves or auxiliary components. The standard pump circulation system is compatible with defrosting a sinlge vertical plate freezer installation. We did it many times and it runs perfectly.

If you want further information, don't hesitate contacting me at alejandro@tucal.es I have the experience of more than 20 years of plate freezers behind me. In deed, I work manufacturing them.

Tycho
31-05-2013, 06:53 PM
made a quick schematic of how it could be done...
10450

The idea being, when you need to defrost, close the suction valve on the freezer and open the hotgas valve.
The ofv valve after the refrigerant pump ensures that the pump won't cavitate while the freezer is defrosting, and there will be no need to switch it off for the defrost.

I don't know why you want a system with a single plate freezer running with pump circulation, unless it is for future expansion of the system...

if it is not for future expansion, I would go with DX and a LP float valve on the plate freezer instead.
Allow me to demonstrate:
10451

Both systems should be as simple as closing the suction valve and opening the hotgas valve.
if the compressor is in reduced capacity, it may be beneficial to open the hotgas valve for a minute or so before closing the suction valve, to kind of short circuit the system so the compressor gets something to work with before you close the suction

AMP
03-06-2013, 12:34 PM
Dear Tycho,

I think it is simpler to "manufacture" a four-way valve with solenoids and use the condenser as evaporator. It is much more reliable, simple and also cheaper (which is very important if you don't reduce the quality). Also you don't have to take care if the compressor stops. The load will be there, on the condenser, so it will run.

About the DX system with a float, I understand you are proposing to use a gravity system. Sincerely, under my point of view I wouldn't suggest it. You have to take so much care of where you put all the components, its sizes, and you will loose efficiency during freezing. Even, starting the freezing cycle will be longer.