Absorption Fridges

[Brian]

I?ve just had an expensive few days - the ?three way? fridge in our motorhome died on our last trip. It was just out of warranty and, of course, it was the absorption (coolant) system which had failed, which isn?t repairable. To add to the joy, getting the old one out and the new one in wasn?t easy- the fridge is wider than the habitation door. They fit out the inside before putting on the roof when building these things. Fortunately, it did fit through the front door ( passenger door) but this required it to be lifted over the front seats etc.

Anyway, the new one is in- I replaced it with a compressor type, which are becoming more popular. They only run off 12v but seem remarkably efficient.

But, back to absorption fridges.

When ours first failed, I did some diagnostics - checking the gas or electric heaters were working etc, which they were. The fridge just wasn?t cooling. A call to a friendly engineer who services motorhomes etc confirmed my fears etc.

On returning home, trying to find someone to replace it promptly turned out to be a problem.

I also stumbled across mention of ?burping? absorption fridges. Basically, turning them upside down one or more times for varying times. How many and how long seems to be a black art.

I opted for what seemed the most common mix, three or so inversions for an hour or so.

After fitting back into place ( the inversions were done in the motorhome, the delights of getting it out the door were yet to come), I drove to a level spot (our drive slopes and absorption fridges need to be within 5 degrees or so of level) and fired it up on gas. It worked. Within 2 hrs the freezer section was down to -18 and the fridge at 4.5 degrees. Turned it off and headed home. I?d try again in the morning, if it worked I ?d saved £1200 ( these fridges are grossly over priced).

Let us just say, the next morning I was ordering a new fridge- which is now fitted.

However, I?ve become intrigued by Absorption fridges. I understand they are still used domestically- some of the small fridges like those in hotel rooms are apparently absorption ones. I recall people have gas fridges. Three way fridges used in caravans etc are often absorption ones so they can use gas, 12 V when being towed, and 240v if available.

They have no moving parts ( ignoring doors etc). Are all but silent - you can just hear the burner if on gas when it fires up.

They can have a very long life.

They can also die early, as ours did, I suspect due to being idle during lockdown etc.

Does anyone have an absorption fridge in their house?

[Steve Walker]

Many years ago, I fitted a sizeable transformer and rectifier to my parents' caravan, to allow use of the gas/12V fridge, 12V lighting and water pump from mains hook-ups.

[williamwright]

They are brilliant. Absorption is a joke by comparison.

Bill

[Paul]

You might want to compare the efficiency figures.

"Absorption coolers and heat pumps usually only make sense in homes without an electricity source, but they have an added advantage in that they can make use of any heat source, including solar energy, geothermal hot water, or other heat sources."

In other words, when you have a low-grade energy source which is "free", absorption might be a big win.

Burning gas, could be an expensive proposition, depending on the COP.

"In practice a typical COP for an absorption cycle in air conditioning would be about 0.7, compared to about 3.5 for a vapour compression system."

Even though these descriptions don't say "refrigerator", the same principles apply. The COP just isn't the same.

This means if you resistively heated your old absorption refrigerator, the COP would be the 0.7 number. By using a compressor, which generally requires a higher grade of energy input, the COP happens to be higher on those. They might both use electricity as the energy source, the compressor is more efficient.

Paul

[mm0fmf]

Done this on rented motorhomes. Removal and inversion for an hour. The second time the 12V cable connected to a chocolate-block connector where a wire was loose and it had arced and burnt. It still needed inverting after replacing the chocolate block.

The first time was on a camping site. The second was in a Parkplatz on the Autobahn near Stuttgart.

[Andy Burns]

My parents did in the early '70s, mainly because d ad worked for the gas board and got good discounts (we had a gas tumble dryer too). I think they're common in hotel rooms.

[Chris Hogg]

My parents had one in the early 1950's and it lasted into the 1960's. It used ammonia as the 'coolant' and ran on gas with a little burner in the back somewhere, but confusingly was made by Electrolux. Quite a large beast, IIRC.

Towards the end of its life, the cooling circuit developed a pinhole leak in the pipework just before the condenser fins - the kitchen started smelling slightly of ammonia. I repaired it by binding the leak with several layers of hairy string heavily impregnated and smothered with araldite! It worked, and gave the fridge another few years of life!

[Colin Bignell]

On 18/04/2022 00:32, Brian wrote: ...

I have a mini-fridge that is designed for hotel rooms. It is thermoelectric, rather than absorption, which will achieve 4C inside.

[Brian]

The 12v - at least the high current 12v - is normally only used when the engine is running. It powers a 12V heater and draws a lot of current. I?ve heard of people modifying 12v / gas only ones to use a mains power supply.

I didn?t check the 12v heater. The 240v one and gas burner certainly worked. The fridge was cold when we arrived so the 12v heater worked en route. Regardless, we need all three and it wasn?t a heater issue.

[Brian]

That seems to be the consensus.

The one negative is going ?off grid?. The spec claims 3 days with two 95Ahr batteries ( is ?consuming?) 95Ahr in 3 days, allowing for the 50% rule.

[Brian]

Sorry, I intended save the above to drafts and complete it later:

That assumes you aren?t using the 12v for other things and aren?t charging either. You can, of course, exceed 50% discharge a few times, change to Lithium batteries, add solar, ?.

We generally stick to sites so have mains and the 12v system has a 20A smart charger and 2 100 or 110 Ahr batteries. We rarely go ?off grid? but only for the odd night. At worst I have a generator. That said, I was considering adding solar before this episode and will almost certainly do so now - I recently up plated by adding air assisted suspension and changing rims and tyres to a higher load rating so I have the payload to play with.

One major advantage for us is we can now pre cool the fridge and freezer before trips. The three way was an issue as our drive slopes and it is difficult to get the MH within 5 degrees.

[ajh]

In the past I believe they were used on trawlers which had a hot engine all the time. however I also thought they needed stability for the vapours to settle so I don't know how they got round that.

[Brian]

I don?t doubt it. I looked at the numbers when deciding whether to buy another 3 way or go compressor. We rarely use gas to power the fridge and the electric cost is always in our experience included in the pitch fees but, even so, the numbers are significantly different. On the back of a compressor fridge, most of the heat is pumped from the interior of the fridge freezer. On an absorption one, you?ve got a gas or an electric heater. When ours failed, it was as warm as normal ( as far as I could tell by touch) yet the fridge / freezer was at room temp.

From memory, this new beast claims to use about 0.4 kWhr per 24 hr at 25 degrees. A fraction of the equivalent 3 way one.

3 ways are, of course, all but silent- on gas the make a slight noise when firing up. The compressor one makes a little noise but not enough to be a problem. It has a ?night mode?, which I?ve yet to explore, which is even quieter, if I?ve understood the manual.

Otherwise, the replacement is pretty well like for like. It fitted into the hole with minimal changes- nothing visible.

The changes to the 12V supply were simple etc. The old gas supply now feeds an external BBQ Point. The old mains supply and external mains socket. Both can be isolated when not in use etc.

I did find investigating absorption fridges interesting but it was a darn expensive exercise. A domestic fridge / freeze of the same size would cost perhaps £300 tops. This was £1200, the RRP is far higher.

I can see that, if you have a VERY cheap heat source, an absorption fridge may make sense but otherwise?.

[Brian]

That is interesting.

The suspected failure mode for mine is lack of use during the lockdowns. During my research, I found numerous stories of, mainly in the US, RV fridges which had been left unused for long periods and not working. After being inverted (burped) some recovered.

Theories as to why this works vary. One is an ?air lock?. The other is that the coolant can either crystalise and block a pipe / pipes or collect it the ?wrong? part of the system so it can?t be heated. Inverting, shakes it around and, if you are lucky, clears the pipes etc.

Certainly my inversion attempts seemed initially to work but only for a short while.

Our MH is parked on a slope when not in use. Looking at where the holding tank is, I suspect the coolant isn?t collecting there when parked. Normally we use the MH quite often but, during lockdowns, it wasted used. We have used it since and did notice the fridge wasn?t as cold as usual - we needed to increase the settings- so I suspect the problem started during lockdown.

[Dave Plowman (News]

First domestic fridge I had was a gas one in a rented flat. Large Electrolux. Well known in those days inverting it once in a while made it work better.

[Brian]

Interesting.

As I posted previously, I thought it seemed to be something required when they have stood idle. I assume yours were in near constant us.

I wonder if the coolants have something added now which alleviates whatever the mechanism is.

[Fredxx]

Absorption fridges used to be popular on narrowboats too, but the idea of venting burnt fumes into the cabin means you can no longer buy one. I think new rules forbid new builds from having one fitted.

In terms of efficiency you have to take care comparing like with like. Modern 230V fridge freezers take little power, and there is a thought it is best to switch an decent inverter to provide the necessary power from

12V to 230V.

YMMV

[Fredxx]

I also question why you need a fridge-freezer. Fridges consume much less energy to keep cool. And still work at low temperatures.

[Andrew]

I've had two electrolux 'under counter' silent fridges.

I took one with when I was working in Fiji and ended up giving it to some US Peace Corps volunteers.

The other one I bought 2nd hand on my return and it bumbled along for about 10 years until I bought a more modern compressor fridge that had a 3 * freezer compartment that the electrolux one didn't. (only 2* I think.

Electrolux could supply a kit for running it on gas or kerosene for 'tropical use'. I'm not sure if they are cheaper to run compared to a compressor type.

There was one in the Haematology lab for reagents and one day the ammonia leaked and we had to call the fire brigade to go in with breathing apparatus and remove it.

[Andrew]

The BHF charity shop in Worthing had 4 of them for sale after lockdown. Apparently the charity was given about a 100 of them by a large London hotel owner doing a refurb and they were distributed around the country.

£45 each and were snapped up PDQ.