hot gas defrost design

[lynark]

Hi guys,

just want to ask how to design a hot gas defrost for bare pipe in coldstorages

regards,

lynark

[sedgy]

hi lynark, can you elaberate on the quote = for bare pipes in coldstorage?

[McFranklin]

It will depend on the physical arrangement of the pipe array, the feed method, and the rest of the system.
I am assuming that we are talking about antique refrigeration.

Way back when, cold storage rooms had cork insulation (some used sawdust) the compressors were recips and instead of evaporator coils (with fans, tubes and fins) they ran bare steel pipe back and forth alond the walls and ceilings. The rooms depended upon natural air flow to move the warmer air across the piping to get the heat transfer. I saw a cut sheet from Frick advertising their Spiral Fin tubing which dated from the 1940's. If I recall correctly the pipe was 2" IPS.
And if that is what you have, we would need a lot more information, you have to deal with the liquid refrigerant at the start of the defrost cycle, the oil in the pipe, the hot gas condensate, the melt water, what the heat load will do to the rest of the plant, your supply of hot gas and so on.

[Magoo]

Hot gas defrost is best described as cool gas defrost by the time the actual gas gets to the evap coils, then the evap acts as a big oversized condenser before any ice disappears. Well that is my experience anyway. So you end up with an evap full of nice cold liquid.
magoo

[lynark]

It will depend on the physical arrangement of the pipe array, the feed method, and the rest of the system.
I am assuming that we are talking about antique refrigeration.

Way back when, cold storage rooms had cork insulation (some used sawdust) the compressors were recips and instead of evaporator coils (with fans, tubes and fins) they ran bare steel pipe back and forth alond the walls and ceilings. The rooms depended upon natural air flow to move the warmer air across the piping to get the heat transfer. I saw a cut sheet from Frick advertising their Spiral Fin tubing which dated from the 1940's. If I recall correctly the pipe was 2" IPS.
And if that is what you have, we would need a lot more information, you have to deal with the liquid refrigerant at the start of the defrost cycle, the oil in the pipe, the hot gas condensate, the melt water, what the heat load will do to the rest of the plant, your supply of hot gas and so on.


Yap thats the design of the coldstorage of our client... problem is there is "no" hot gas defrost in the system for the bare pipe so need to install one... but i gave limited knowledge in this type of system...

regards,

lynark

[RANGER1]

lynark,
Even if you had hot gas defost how would you manage the melting ice?

If you have a system of that vintage maybe you have a recip compressor with reversing
valve manifold on it already
ie 4 valve manifold that can be used for bypass start up, pumping out condensor into evaporator.These were used in days gone by for this reason.

[McFranklin]

It might be possible to set up a hot gas system. Depending on how your customer's facility is set up there might be several methods.
We are back at needing more details on the system.

[lynark]

Dear Ranger1 and Franklin,

Thanks again for the info. What are the details needed so we can start the hot gas design?

Regards,

Lynark