Hot gas defrost vs Electric defrost

:confused::confused::confused: Hi, i am new for this site, im from Indonesia so im sorry if my english is hard to understand.
I wonder if someone could help me, i have a basic question, when do we need to use electrical defrost and when do we need to use hot gas defrost??
All i know is hot gas defrost is cheaper than electric defrost, and if we use electric defrost in a freeze room, room temp. will be affected dramatically...:( Is this statement's right : we better to use hot gas defost for pump evaoprator only??

Hi and welcome to the RE forums.

If you are using a pumped refrigerant system a hot gas defrost is very simple to use, if the evaporators were designed for it.

Electric defrost is used so often in commercial refrigeration because it is easy to install. Hot gas defrost systems can be more complicated, but yes, they are less expensive to operate. No additional energy is needed.

Thanks Iceman...
I have another question grandpa, is there any constraint if we want to use hot gas defrost for dx systems? [what parameters should be considered]

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what parameters should be considered

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Well, you might want to show more respect if you expect another free answer.

:rolleyes:

Using DX and hot gas is acceptable if the coil is designed properly.

http://www.refrigeration-engineer.co...c/progress.gif

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Originally Posted by US Iceman

Well, you might want to show more respect if you expect another free answer.

:rolleyes:

Using DX and hot gas is acceptable if the coil is designed properly.

http://www.refrigeration-engineer.co...c/progress.gif

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Iceman the use of "Grandpa" may be a translation issue - "Grandpa" is in many places a title of a person of great wisdom.

Don't you dare call me Grandma though -- :D

Paula

Hot gas defrost do a quick or faster defrosting action .
Normally if there is a fan , it shall be stop when defrosting, and will not run up to the temp at the evaporator reach a low temp near set point temperature.

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Originally Posted by herdian

Thanks Iceman...
I have another question grandpa, is there any constraint if we want to use hot gas defrost for dx systems? [what parameters should be considered]

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Hot gas defrost works by injecting the hot discharge gas straight into the evap.
This method works with DX systems very well when designed correctly.
There are two methods of getting the gas to the evap.
One method is to have a third pipe carry the hot gas straight to the evap
Another way is to let the hot gas travel down the suction to the evap.

What method you choose will depend on the system and application.
How many evaporators is on the system?
How many compressors are on the system?
If you are single comp and evap then the third pipe method may work.
If your system is multi evap then the hot gas down the suction may be better.
The one consideration you must allow is what do you do with the used hot gas once it has passed through the evap?
You could let the gas condense in the liquid line or you could let it return back to the comp.
Both have there advantages and disadvantages.
If you let it return to the comp then the compressor will over heat so timeing is critical.
If you let it enter the liquid line then you must create a pressure differance to alow the correct flow.

Cheers taz.

Mike if you are a grandpa, then I am great grandpa.

With a hot gas defrost system, I have seen it is better to use a cpr valve in the suction line just before the compressor.

Hi Samarjit,

Yeah, I received a PM from another member who said he thought this was funny, since he had a son almost my age.

Now I feel younger.:D

Mike, it is good to know you feel younger. I also feel very young, when I visit the President of the Cold Storage Association who is 84 years of age and still active.

Mike, how does she know you so well.

Like he said, electric defrost is normally used a smaller stand alone systems. Generally to use hot gas, you do not want to defrost more than 1/3 of your coils at anyone time. There are some commerical manufactures that do use a reverse cycle hot gas to defrost one coil on one condensing unit.

It would help if you tell us a bit about the system you are looking to use...refrigerant, temperature and number of evaporators and compressor/condensing units or is it a rack.

Ken

Hi Ken,

Doh, as Homer would say!

If grandpa is supposed to be an honorific title, Paulajayne should also be willing to go along with the gender specific version also.;) If not, then I'm going to request to abstain also.:D

Hi everybody who participated in this post

I would like to request Cheers taz, to explain bit more on the hot gas travel down the suction to the evap. I you could explain how it works and if possible a diagram of the piping along with the necessary accessories. In my blast freezer I have installed the hot gas defrost with a crankcase regulator valve which is very quick.

Hi Ken is it same thing, that you are talking about the reserve cycle hot gas defrost system. Please explain it in length.

Furthermore I would like to request you all to drag herdian into the lead as he had disappeared once again as usual. Therefore I would once again kindly request you all to drag the original person who posts a thread to participate until he gets resolved the problem. As such I urge the moderators and the senior members must find a solution for this.

Suny

Normal hot gas systems will have multiple evaporators, and you only defrost a maximum of about 1/3 of them ar any given time. This is so that your system will have a sufficient hot gas source to to provide gas for the defrosting unit(s).

In a small system where you have only one evaporator and one compressor such as a commercial unit with a single condensing unit, you basically run the unit in reverse cycle like a heat pump to put heat inthe coil to defrost it.

In defrosting larger coils, you have to feed the coil with a hot gas and control the pressure with a regulator to defrost the coil. Pressure is released to the suction and liquid will build in the coil. In taking the coil into and out of defrost, you need to have smaller feed solenoids to reduce the flow of gas into and out of the coil at the initiation of defrost.

This is often referred to as a soft-gas solenoid. The purpose is to prevent sudden shock to the coil, both thermally and hydraulically.

You can find an article in this months RETA Breeze in The Technical Report. Additional information can be found in the Parker/RS catalog on the valving used on a hot gas defrost system.

I can not tell you how to best design the hot gas defrost system until you tell us a bit about your system. Is it a single coil or multiple coils, temperature level, refrigerant feed (believe you said it was DX), presumably a down feed design, defrost in the pan or not, plant a two stage plant or single stage?

But I feel it is best if you research the Parker site and determine which system best suits your application. Then show us what you plan to do and see what we think. This is the best way to learn.

Mike, by the way, nice article in RETA Breeze on What is Your suction Pressure.

Ken

Thanks Ken. What did you think of the R/S article? I think they did a nice job of addressing the various problems.

BTW, would you have any interest in writing a short article for the Tech Report? They are always looking for some technical articles from guys with field experience, etc. Theres no money in it, so all you get are bragging rights.;)

ha ,ha ,ha, that tickled me iceman, grandpa "eh",if that was a cash job it would have ended up expensive dont you think.:D

Thanks Ken for ur lengthy explanation. Now it is late night here. I will give u full details. Pls excuse for t moment.
Suny

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Originally Posted by old gas bottle

...if that was a cash job it would have ended up expensive dont you think.:D

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Was I that transparent?:cool:

Mike, the RS article was a good summary of the problems. There have been more detailed papers presented at IIAR in the past.

Like a lot of the design in industrial refrigeration, it is part science and part magic. I tend to error on the side of safety when it comes to system design and go with what I know works. I do like to look at new designs and will keep an eye on the info and see if it does pan out. If I try to do something different on my own, I try to leave myself a way out if there is a problem.

Send me an email and let me know what sort of topics they might be in need of.

Ken

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Originally Posted by Paulajayne

Iceman the use of "Grandpa" may be a translation issue - "Grandpa" is in many places a title of a person of great wisdom.

Don't you dare call me Grandma though -- :D

Paula

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Indeed a term of great respect, it is a compliment to him!