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cadwaladr
10-06-2012, 01:15 AM
does anyone know if this is an efficient way to defrost evaporator coils on low temperature applications and which type of glycol is the most efficient if any?

RANGER1
10-06-2012, 07:03 AM
does anyone know if this is an efficient way to defrost evaporator coils on low temperature applications and which type of glycol is the most efficient if any?

I would say hot gas defrost is efficient if you have more than 1 evaporator.
Also depends what type of system you have, maybe you could describe what you have in mind!


Is the glycol question another question?

Grizzly
10-06-2012, 10:45 AM
Hi Cadwaladr.

Yours is an intriguing question!
I have never come across glycol being used to defrost evaps.

I assume that as Ranger may be implying you would use glycol as a heat medium instead of hot gas.
But as the thermal properties and heat exchanges of the 2 are completely different.

I would assume there is a good reason why I have not seen it before?

Obviously as you well know its used widely as a heat barrier in cold store floors or a low temp cooling medium.

It is also used to cool oil circuits on screws. But I doubt it would work on evaps?
Grizzly

cricri
10-06-2012, 11:28 AM
we frequently use MEG at 50% to defrost coolers in large coldstores, temperature is about 35°C. It's spécial coolers, with a second coil imbricated in the main coil. it's a standard for GEA Kuba coolers (some difficults with other brands), we use only for CO2 plants. The hot glycool is provided by heat recovery from the hight side of the cascade, can be from the oil cooling with an intermediate PHE (30% to 50% glycool).

Grizzly
10-06-2012, 01:27 PM
we frequently use MEG at 50% to defrost coolers in large coldstores, temperature is about 35°C. It's spécial coolers, with a second coil imbricated in the main coil. it's a standard for GEA Kuba coolers (some difficults with other brands), we use only for CO2 plants. The hot glycool is provided by heat recovery from the hight side of the cascade, can be from the oil cooling with an intermediate PHE (30% to 50% glycool).

Thanks for the knowledgeable answer cricri.
Sadly my experience of Co2 systems is nil!
But seeing as over hear they are still quite specialist it's not so surprising.
Grizzly

al
10-06-2012, 02:11 PM
I've seen a GEA ammonia plant with the same, discharge heats glycol, very very effective and quick. Glycol was also used to cool the chill rooms.

al

Grizzly
10-06-2012, 02:46 PM
It appears I need to get out more, guys!

Sadly I seem to be occupied in resurrecting the dead, or at least keeping old plant going nowadays.
Rather than bringing new (modern) plant into life!
I have always been a fan of Grenco / Grasso's kit!

You live and learn.
Grizzly

cricri
10-06-2012, 03:14 PM
90279028 it looks like that (Luwe coolers)

cadwaladr
10-06-2012, 10:08 PM
the reason i ask the question is i look after a system with this type of system ,the issue i have is the owner uses car type antifreeze glycol blue in colour and its heated by electricity very similar to a hot water system a tank with a immersion type heater in it,then its pumped into evaps it seems to evaporate because no major leaks to be found and i suspect we dont have enough to defrost the coils and more storage volume is needed to accomplish the defrost,or is the wrong type of glycol being used?

Gary
10-06-2012, 10:44 PM
Niagara Blower Company builds a system that sprays glycol directly on the coil to prevent frost:

http://www.niagarablower.com/nofrost_operation.htm