Hot water defrost

[PaulL]

Hi there

Hope everybody is fine.
Please I would like to talk concerning the possibility of having water defrost in air coolers.
I have been asked several times during last period to provide this defrosting system
I have tried to find some literature in the web but without success.
Moreover, I have been asked by cooler manufacturer how I want this system to be realized, since they have no experience.
I assume I have to impose a specific fluid flow ( and determining an inlet glycol temperature and outlet)
This will determine mine surface needed.
Please, can anybody give me some hint ?
There are more and more requests, and my fear is to loose opportunities.
Thanks in advance !

[chemi-cool]

Air will freeze at -0C
Why not controlling the the inlet glycol temp?

[PaulZ]

Hi PaulL
Water defrosts can cause a lot of problems.
This type of defrost was use here many years ago but has pretty much been replaced now.
The evaporators of air coolers had a tray on top of the coil block.
This tray has a series of small holes that distributed the water over the coil, it was supplied with water from a tank which sometimes had a coil with some discharge gas running through it, this warmed the water.
The temperature of the tank had to be controlled otherwise it got too hot, from memory I think it was about 35oC.
Problems with this type of defrost was holes in tray blocked up, drains overflowed and water went of floor (big problem in a freezer), lots of condensation in room from hot water (lots of frost on walls and ceiling around evap), pump strainers blocking up due to debris being washed off coil, etc.
There are better ways of defrosting with less headaches.
Regards
Paul

[Magoo]

hello
please clarify, do you want warm water through the glycol coil or over the coil and fins

[cadwaladr]

Worked on a cold store with heated glycol,with dual circuit evaporator it worked well,but keeping the heat in the glycol was critical but a lot of engineering was involved on installation very good on energy consumption but high maintainence.

[PaulL]

Hi there

Many thanks for your answers.
Indeed I have not been clear enough
For water defrost I mean:
Let's consider the coil.
Into the coil there are
- circuits where refrigerant passes through
and
-some dedicated circuits into the coils that are designed in order to have hot water - or hot glycol -to pass in substitution of electrical heaters.

This was the construction I am interested in.
I do understand this is an headache construction, but I have a lot of requests on this (maybe to save electrical power consumption?)

Many thanks

[cadwaladr]

Well you would have to use glycol not water,and how big are the evaporator coils?

[RANGER1]

Hi there

Many thanks for your answers.
Indeed I have not been clear enough
For water defrost I mean:
Let's consider the coil.
Into the coil there are
- circuits where refrigerant passes through
and
-some dedicated circuits into the coils that are designed in order to have hot water - or hot glycol -to pass in substitution of electrical heaters.

This was the construction I am interested in.
I do understand this is an headache construction, but I have a lot of requests on this (maybe to save electrical power consumption?)

Many thanks

I think issues with water, as small tubes, can't drain out , so would freeze.
Glycol needs a system to store, pump, heat up & concentration so it won't freeze.
Would also need to be pretty warm to get heat transfer, assuming we are talking freezer.

If a system with a number of air coolers on it, hot gas defrost is an option, but some expense setting it up.

Think water over evaporator can still be used, but can be problematic if not monitored carefully.

On some larger purpose built applications, ambient air defrost can be used, with purpose built doors open to outside, while sealing it off from refrigerated space, run fans to circulate outside air over it.