Defrosting Low Temperature Cold Evaporators

[Grizzly]

Hi Guys.
Has anyone every heard of the above being carried out using Hot water / Steam?
Grizzly

[Segei]

Some tunnel freezers use warm water for the defrosting.

[Emmett]

Ive seen Hot glycol, never water or steam though. Interesting question. The number one issue I have with some low temp enviornmental chambers on site, is with defrost. I recently had discussions with a manufacturer regarding using hot gas defrost, would use steam heat exchanger to superheat the hot gas before and after the evap coil. It appears they are not very interested in going down this path. I do not like the embedded heaters since when they do go bad it is often impossible to remove them, has anyone else had any luck controlling these heaters to precise temperature where you do not flash off the ice/frost to vapour?

[cadwaladr]

i have a glycol defrost system and want to use a solar panel to heat the glycol via a water/glycol exchange has anybody seen this before?

[Magoo]

Hi Grizzly,
I have worked on one that had warmish water, around 35'C, it created a lot of snow build up on ceiling around coil. Would imagine hot water and or steam would be worse.
magoo.

[Segei]

Actually you should reduce hot gas superheat to minimize sublimation of the frost. Refrigerant condensation give us 80-90% of heat for hot gas defrosting. Superheat gives small portion of total heat, but it is a reason of frost sublimation. However, hot gas supply, refrigerant condensation and refrigerant condensate draining should be set up properly.

[Grizzly]

Actually the Thread should of read Defrosting Frozen up Cold Store Evaps in situ With Hot water / Steam.
Yes, I have witnessed 2 very frozen large Cold store evaps being cleared of ice using a high pressure steam/hot water lance.
OK the chamber temp was up to around -15 (lack of air flow due to severe iceing the main culprit) whilst this was going on and still these guys cleared the whole evap with very little water overspray.

In fact everyone, the Store staff and our entire engineering dept. All felt this was a disaster waiting to happen.
With the prospect of large amounts of water / ice needing to be cleared up after the relevant evap was washed out.

The small amount that overshot the drain tray (slightly to much added, which the drain hole could not cope with,) was caught on the tarpaulin sheets that had been spread out underneath the evaporator.
Which were just dragged outside into the yard and brushed off after a short while in the sunshine.

Truly amazing, I did not believe it could be done!
2 more being done tomorrow.
Grizzly

[james10]

I've heard horror stories of people throwing buckets of water on evaps and causing them to tear open and believe it or not I caught someone on site defrosting a heat pump condenser with a turbo torch

[Magoo]

Hi Grizzly,
all becomes clearer, were the coils pumped before defrosted, and what was the standing pressure in system, must have been below safety releif settings.
I had a client that decided to use steam heated water to defrost flooded ammonia coil between shift changes, for extended production run. Wrong, the safetys let go at + 35'C SST. Dramas plus,,, Fire Service. Full evacuation of plant. Local area evacuation.

[cool runings]

.

I have used power washes that use hot water for derfosting / cleaning evap coils.
I have done it countless times in large coldrooms and with very little distruption or mess.

The only problem is the evap fans (the fans do not like high pressure water up em Pike) .

But if you take precautions to protect electrics it can be a very quick solution to iced up evaps.

coolrunnings

.

[Grizzly]

Coolrunnings.
You are lucky to have had that option within your armoury.
Despite over 20 yrs cold store experience I nor any of my colleagues had heard of a "more ridiculous option".
There were guys within our company that knew better and hat's off to them.
You are correct apparently Fan terminal boxes etc can fill with water.

Magoo.
These evaps were so badly iced up that even repeated defrosts, with fully functional heater rods (although that has only been proven since clearing the side of the evaps) could not maintain a decent airflow.
So as a consequence the system suction pressure was really low even when running. So you could say they were running almost pumped down anyway.
The heat introduced to the system whilst the evaps were turned off will of been negligible.

We were all convinced that the heater rods were in a poor state but in hind-sight the malfunctioning Main access door is looking favorite to me. Despite assurances that it does not stay open often!
Grizzly

[chemi-cool]

Falling film chiller usue water for defrost.
Any SS ice builder, uses water to defrost.

You must have a SS made evaporator to be able to use water, once ice start building around the copper tubes [mainly at the bottom of it] squeeze them like soft nylon and causes leaks and blocks them form refrigerant flow.

Every machine have its life span including evaporators.

[Emmett]

I had no idea you were talking about literally using steam/hot water on the exterior of the coil I assumed you were asking about using it in a parrallel circuit to defrost the coil. I would never have even considered using steam to clear a coil inside the cold room.

[cool runings]

.

Yep used this method for decades and it has proven to be
an extremely good quick method for defrost.

Most big factories, cold stores and supermarkets have
steam cleaners in use for washing wharehouse yards and the lorries.

Just take a few obvious percautions, electrics and over spray being easy.

Pump down the evap (the whole system if needed) the whole opperation
when completely set up and ready to go only requires you to be in the room
for less than an hour, so no products are put at risk.

Keep the pressure washer on the lowest setting and avoid hitting the evap
at an angle because the fins will bend.

But I have used this method as one of the tools in my tool kit on and off
for more than 30 years. I have had a few catastrophes over the years but
preperation prevents p1ss poor performance .

All the best

coolrunnings

.

[Segei]

.

Yep used this method for decades and it has proven to be
an extremely good quick method for defrost.

Most big factories, cold stores and supermarkets have
steam cleaners in use for washing wharehouse yards and the lorries.

Just take a few obvious percautions, electrics and over spray being easy.

Pump down the evap (the whole system if needed) the whole opperation
when completely set up and ready to go only requires you to be in the room
for less than an hour, so no products are put at risk.

Keep the pressure washer on the lowest setting and avoid hitting the evap
at an angle because the fins will bend.

But I have used this method as one of the tools in my tool kit on and off
for more than 30 years. I have had a few catastrophes over the years but
preperation prevents p1ss poor performance .

All the best

coolrunnings

.

Some plants have 100+ evaporators. How are you going to defrost them twice per day?

[stufus]

Some plants have 100+ evaporators. How are you going to defrost them twice per day?

If you have a plant with 100+ evaps ice locked everyday ,someone isn't doing their job or the person doing the job doesn't know what they are doing.
(Obviously not you personally Segei)
Cheers
Stu

[cool runings]

Some plants have 100+ evaporators. How are you going to defrost them twice per day?

No Segei you miss the whole point of this method.

The evaporators defrost automaticaly.

This method is only to be used when the evap is so iced up due
to a fault and therefore no longer able to defrost automaticaly.

All the best

coolrunnings

.

[Segei]

Put defrost on manual and"cook" the evaporator.