Are there any up to date reviews available for best options for camping fridges please?
on 27th Aug 2021 at 2:47 pm
Haven’t seen any for quite a while now and it was always quite a controversial topic.
Personally I have been using my 40lt 3-way Dometic fridge\freezer for some 7 years now and have never been let down as yet. Our longest trip was Cape Town, Namibia, Botswana and back.
No need for a duel battery system, solar chargers etc.
Whilst travelling used the car battery to run the fridge/freezer
Whilst camping used 220v campsite supply
When no electricity at the camp site used gas.
A 5kg gas bottle can last me up to 4 days continuous 24 hr use with my Dometic.
So I found this combination suited me just fine.
The only modification I made was to fit a small “computer” type fan below the radiator coils at the back of the fridge to improve air flow to remove excess heat on some of those very hot days (>30 degrees C). Other wise the freezer section kept the frozen stuff frozen and the fridge prevented the milk going sour,l meat fresh but more importantly I always had a cold beer on my arrival at each camp site.
Hope you find something suitable
on 27th Aug 2021 at 5:21 pm
I also have a Dometic absorption fridge in my caravan, and it works OK until you look at the energy wastage compared to a compressor fridge.
Using your figures of 5kg of gas every 4 days, that works out to 1,25kg per day, or 57,5MJ per day.
A compressor fridge on the other hand draws 3A from the 12V supply, with an average duty cycle of about 50%, which works out to 3(A) x 12(V) x 12(h) x 3600(J/h) = 1,5MJ per day, or 2,5% of the absorption fridge’s power consumption.
The only advantage of the absorption fridge is that it can run on gas. That’s nice to have, but it’s also a very expensive nice-to-have.
One solar panel that can deliver 4,5A (which all the full-sized ones can) for 8 hours per day, will deliver the entire 1,5MJ-per-24hour requirement, and any excess energy can be saved in a battery for a cloudy day (when the solar will still deliver some energy).
So yes, the solar panel, plus a regulator (essential) and a suitable battery will cost the same as many kgs of gas, but the writing is nevertheless on the wall for the dinosaur gas-guzzler absorption fridge.
on 28th Aug 2021 at 2:44 pm
Hi Simon. I’ve often wondered why the absorption refrigeration system was so inefficient, and extensive research has not produced many answers.
The energy cost of running a compressor fridge are twofold:
The friction and electrical losses in the motor/compressor assembly,
The quantity of energy removed from the fridge contents.
In the absorption system there is no compressor, in fact no moving parts at all, so the friction and electrical losses fall away, leaving only the cost of extracting the energy from the evaporator side of the circuit.
BUT then there’s the latent heat in water that gets vapourised as a by-product of the ammonia being boiled out of the water in the heating section. That water vapour will condense out in the cooling coils. That energy is dissipated in the initial cooling phase where the water trickles back to the tank and is energy entirely wasted.
It’s impossible to know how much exactly water is vapourised in this way, but I’m pretty sure this is at least part of the answer. And sadly there’s no cure for it that I can see.
on 28th Aug 2021 at 4:36 pm
Oh dear I didn’t mean for this to become another who’s right who’s wrong debate sorry for raising it but was just giving my own personal point of view. The science behind both forms of refrigeration are equally interesting and both have their pro’s and con’s I dont believe either is better than the other as it all depends on what they are to achieve under varying conditions.
Yes obviously the compressor type will be more efficient but that is not what I was trying to portray. (even though we know absorption fridges are extremely efficient running on gas).
My mention of the time that a 5 kg gas cylinder will last is based on the most inefficient use of the gas wherein actual reality a 5 kg gas cylinder should last just over a week running at approximately 30gms/hr.
Firstly I generally would not be using gas continuously over a long trip as most of the time either electrical supply is available or 12v whilst travelling. But when there is no electrical power available two 5kg bottles of gas would give me at least two to three weeks of refrigeration before having to refill the gas bottles.
That was my point and with a compressor fridge with no electrical supply other that say the two deep cycle batteries and solar panels and a week of poor weather like lots of rain etc then it would become an issue, sure one can start up the vehicle every second day and charge the batteries at the cost of the fuel to run the engine/alternator.
So once again it was not to say which system has a better COP as we know the answer to that or even the cost of running either systems.
I certainly would not say that the absorption fridge is a dinosaur (or gas guzzler) as I can assure you the absorption fridge technology is very much alive and continuous developments are still taking place and research been done to still improve the performance of this type of refrigeration. Already they are looking at nanoparticle technology to be incorporated into the system. So rest assured the 3 way absorption fridge is not going away by any means just yet. Even though it’s been around since the middle 1800’s and in the good old days we had both an absorption fridge and a freezer both operating on paraffin, as a heat source, and for decades they worked well as we still had no electricity at our beach cottage on the wild coast.
I do agree the compressor fridge is more efficient even though they are expensive and are more prone to wear and tear and the back-up technology more complex and also not cheap.
I don’t think modern caravan manufacturers, like those in England and Europe, would still be fitting absorption fridges into their caravans in 2021, if it was not justifiable or they were dinosaurs!
So finally yes the compressor type is far more effective but maybe we shouldn’t discount the absorption type either.
on 29th Aug 2021 at 3:39 pm
My experience of absorption fridges (I used them exclusively for the 10 years I lived in the Mozambique bush) was that they burned 0,4kgs per day, say 18MJ.
Apart from the cost of the gas, which you grow accustomed to, my major beef with the technology was that the effectiveness of their cooling would drop off rapidly when the ambient temperature exceeded 30C. I put that down to the failure of the ammonia gas to liquefy under the given hydrogen pressure, which must have been about 12bar, though impossible to measure of course. It may indeed be premature to use the term ‘dinosaur’, though as with the diesel engine, followed by the petrol engine, they are on their way into history.
Happily I won’t be alive to see it but the world is going all electric, either nuclear or renewable electric, but electric nevertheless. Our grandchildren will preside over the transition to world where no energy is derived from combustion of any kind. And absorption fridges are just on the wrong side of history, along with lots of other useful devices.
on 1st Sep 2021 at 10:25 am
Apart from the cost of the gas, which you grow accustomed to, my major beef with the technology was that the effectiveness of their cooling would drop off rapidly when the ambient temperature exceeded 30C. I put that down to the failure of the ammonia gas to liquefy under the given hydrogen pressure, which must have been about 12bar,
You’re right in that they target 35°C as the highest ambient operating temperature. And by increasing the hydrogen pressure to say 20 bar you would increase that to closer to 50°C, but the resulting problem would be that the evaporation temperature of the ammonia would increase commensurately, meaning even more gas required to run the fridge, not to mention higher temps all around the chimney and a longer cooling coil before the evaporator.
Better to bend with the wind and go for a low-power compressor system. They just work a whole lot better.
on 19th Oct 2021 at 11:57 am
(You’re right in that they target 35°C as the highest ambient operating temperature.)
That is true but according to Dometic, IF the ambient temperature rises above 35 degrees C then by using a fan to either extract or blow over the radiator would resolve the problem.
This I did, by using the top outlet air vent for the fridge and the pictures below illustrate the three fans. These were set in series and made sure they extracted air from above the radiator through the vent to the outside. Tested the fridge on the last trip to Kruger with outside ambient >35 degreesC and temperature above the radiator >50degreesC and the freezer measured -8 degreesC and fridge section +4 DegreesC (hope the pictures come out)
A fan is not going to lower the ambient temperature the way it appears to cool the human body.
When a fan blows air at you it actually just moves the boundary layer of air attached to your skin which will have been heated by your skin and is also saturated with moisture from evaporating your sweat.
Since the cooling coils of the fridge do not exude water there is nothing to evaporate and no cooling from the phase change of water into vapour. Since the cooling coils also do not have hair to retain a boundary layer, convection will immediately cause the heated air to rise to be replaced by cooler, denser air from below. As long as this convection is allowed to vent upwards without restriction adding a fan will serve no purpose. No fan can lower the ambient air temperature, a fan can only assist the movement of hot air from where it is being heated to somewhere else.
If your fridge burns 0,4 Kgs of gas per 24 hours, this is equivalent to a 213 Watt electric element in the fridge compartment, which means you need to move over 200 litres of air out of the top of the compartment every second if you don’t want the temperature in the fridge compartment to rise more than 1 degree C.
And for that you definitely need a few fans.
on 21st Oct 2021 at 9:59 am
My calculator says the speed of airflow through those 2 fans needs to be 45Km/h. Is that even attainable?
How much above ambient can you tolerate in the fridge compartment?
on 21st Oct 2021 at 11:42 am
The unkown factor here is the sixe of the bottom air inlet. You can have fans as big as you like up top but if the lower air intake is too small the fan will just create circulation around itself.
The caravan builders should provide huge vents that can be closed for transit and offer almost unimpeded airflow when open. Just as if it’s standing in your kitchen at home.
on 21st Oct 2021 at 6:05 pm
What’s frightening is that Dometic is telling people that a fan can lower the ambient temperature.
A scary as the motoring writers that imagine that Torque is some kind of superior alternative type of power engine power.
All products of local schooling no doubt. Post ’94 that is.
on 22nd Oct 2021 at 2:05 am
I read on the back of a powdered sauce packet, of which they must have produced millions, that you must add a quantity of RAPIDLY (their CAPS) boiling water.
They probably imagine that water boiling RAPIDLY is hotter than that just simmering.
The level of ignorance amongst the new generation is truly appaling.
on 22nd Oct 2021 at 3:04 pm
Sadly it would appear that there is a total misunderstanding as to what actually takes place during the operation of the fans in an absorption fridge modification.
Firstly the fans, in this application, have absolutely NOTHING to do with evaporation !
So all those calculations regarding water vapour and evaporation etc. in this application is unfortunately totally incorrect. No mention is made that I or Dometic or for that matter any qualified fridge mechanic or mechanical engineer, made the comment that the purpose of the fans is to “cool” the ambient temperature .
The purpose of the fans is primarily to REMOVE heat and that is exactly what transpires. They are not there to cool the incoming air!
Ambient air is drawn in from below the fridge (inlet vent) and passes over the radiator taking the radiated heat with it and exits through the top (outlet vent). Generally both vents are the same size so what ever volume of air is drawn in is the same as the amount or volume of air blown out. There is no differential pressure difference between the two vents. There is therefor no necessity to have a larger inlet vent compared to the outlet vent BUT what is extremely important is that the air flows through the radiator and not be allowed to bypass the radiator.
If you can understand how air cooled engines work like the old VW beetle, or motor bike engines (although some are now water cooled) or even just an electric motor this will make it easier to understand. Just disconnect the fan on an electric motor or block the air flow and see how quickly the motor heats up and if fitted with a thermal trip will stop the motor and prevent it from burning out.
After doing the modification to my fridge, I carried out numerous measurements with the fans off and with the fans on. I performed the tests with the ambient temperature below 25 degrees C and temperatures above 35 degrees C. (the maximum ambient temperature that I was able to do a test on was at Kruger NP where the outside ambient temperature was 43 degrees C). I have all the results to illustrate that in fact the fans do actually remove excessive heat build up behind the fridge and have a direct influence of the fridge operation and performance (these results are available for anyone who would like to see them) These results are therefor factual scientific results and not assumption or opinions. My results are therefor evidence based. Incidences where outside temp was 37 Degrees C and fan off the temperature inside the freezer compartment was only minus 1Degree C with the fans on the Freezer dropped to minus 8 Degrees C. If that’s not proof enough then I rest my case.
I have a thermometer permanently set above the radiator behind the fridge so I can read the temperature from inside the caravan. With out the fans on and the outside ambient temperature above 25 Degrees C the temperature above the radiator behind the fridge can reach temperatures of over 55 Degrees C . The design of these fridges are such that with an ambient temperature of <30Degrees C, the free flow of air from the inlet vent and the outlet vent will happen naturally and is so designed that the operation of the absorption fridge works as it is designed to as long as there is no restriction of the air flow. Because of the density of the inlet air and the outlet air are different, thus why hot air rises, this causes the natural removal of the hot air created from the radiated heat from the radiator. You will note that the radiator has fins on them which increases the heat transfer from the radiator to the air passing over them.
The fact is that when the ambient temperature get above 30 Degrees C, the natural flow is no longer sufficient to draw the hot air out but with the fans this is overcome and the temperature above the radiator, drops from well over 55 Degrees C, down to 38 to 50 Degrees C which is the highest temperature that an absorption fridge likes to operate effectively. The converse is true too for these fridges where, if the ambient temperature, falls below freezing point, the inlet air vent needs to be restricted to prevent air flowing over the radiator, as the function of ammonia evaporation will not take place as designed and thus the fridge will not operate efficiently.
Again it must be noted that it is NOT the speed of the air flow that is important it is the volume of air that can flow over the radiator fins that is important and thus the volume of air is not linear to the speed of the air flow (its just simple physics if one understands the basics of physical science.) So we are not looking for air pressure but simply air flow.
Oh and by the way there is a difference between rapidly boiling water and simmering water. It’s nothing to do with temperature but all to do with steam generation. That is why the old steam locomotives had huge fires to make sure the water was boiling rapidly to create as much steam as possible Can you imagine a steam engine operating with water just simmering at boiling point.
Again I am not for or against either compressor of absorbton fridges I just find absorption fridges fascinating.
on 22nd Oct 2021 at 3:46 pm
The instructions for boiling the water were on a sauce powder packet.