Caravan Fridges and Fridge Vent Fans.

[Paullus1959]

While browsing YouTube yesterday I came across several videos including one from Dan Trudgeon on the subject of caravan fridge performance in hot weather and fitting fans to improve circulation through the side vents in the caravan.
I have a Thetford fridge in my caravan and I've not really noticed any problem with the fridge not getting cold enough in hot weather.
I thought fridges worked better in hot weather and was the reason for fitting vent shields in the Winter to increase heat and heat transfer.
My fridge does get cold quicker when running on gas and the freezer compartment seems to be colder on gas too, which I believe is due to gas burning hotter than the electric heating element does.
I have a freezer in my garage that is designed specifically to work in colder places because ordinary freezers and fridges don't work efficiently in cold environments.
So, are caravan fridges different?
I am now confused about the science behind fitting vent fans so if someone can enlighten me please I'd be very grateful
Thanks.

 

[otherclive]

I fitted one for trips to southern France. It just aided the natural convective flow of air across the heat exchanger. In normal British temperatures it did not switch in.

ps edit. It was a Vento kit, but some use PC fans as an alternative option.

 

[ProfJohnL]

Excluding Thermo Electric (Peltier) coolers, conventional domestic and caravan fridges use a sealed closed circuit refrigeration process which relies on a cocktail of chemicals with naturally low temperature boiling points that can experience a reversible phase and pressure change between liquid and vapour and back again within the circuit. The circuit is designed to cause the chemicals to evaporate and absorb heat energy in the section of the circuit inside the fridge compartment ( the Evaporator), and to condense and give up the heat of latent vaporisation in the section of the circuit that s outside the fridge. (the Condenser)

Heat energy can only move if there is a temperature difference, and it always moves from high temperature energy levels to lower temperature energy levels, so both these systems will suffer a reduction of efficiency if the external ambient temperatures are close to the temperature of the external condenser radiator, but the major difference between the Compressor driven and absorption systems , the compressors are more efficient and can realise higher condenser temperatures, and thus are better able to operate in high ambient temps. By contrast absorption fridges can't produce such high condenser temperatures so they can struggle in high ambients, which is why it may be necessary to assist the air flow over the condenser radiator.

But there are also differences in the cocktail of chemicals used in both systems. Because the compressor system is mechanically compressing the refrigerant, it's much more predictable and can use a refrigerant with a wider (especially temperature) operating parameters. By comparison the absorption process is far more sensitive not only to temperature ranges, and the cocktail needs other characteristics the application of external heat to drive the system, consequently the Absorption process has a narrower range of ambient operating temperatures.

However and despite the fact that Domestic compressor fridges and freezers are more efficient, like absorption systems they can be optimised for different ambient temperature ranges, for example indoor/outdoor, and of course for different regions of the world.

IF in doubt check with the manufacturer.

 

[Mr Plodd]

A caravan fridge works by drawing heat out of the fridge and dissipating it to the outside air. That's why you feel warmth at the external vent. However it requires a difference in temperature for the heat to move from the coils at the back of the fridge into the pasding air (convection current moves the air). The less the difference in temlerature between tge two the less heat energy can be moved between them.

Think pf this in terms of a cold water tap and your hand. If the tap is just running and you put your hand under the flow it cools down a little, if you turn the tap open more then your hand gets cold because more heat energy can be transferred from your warm hand into the greater flow of cooler water.

Fitting a fridge fan increases the flow of air over the fridges heat exchanger so more heat is taken away, and the inside gets cooler. The higher the ambient temperature the greater the flow of air needed to absorb the same amount of heat energy.

I have fitted fans to numerous leisure vehicles, they do improve the fridges performance once the ambient temperature gets to the mid 20's and beyond. Below that I have never noticed any difference.

External vent covers are for use in the winter to limit the flow of cold air over the heat exchanger because otherwise the difference in temperature means too much heat is absorbed by the cold air, and the inside of the fridge gets too cold!

If travelling abroad these fans can be beneficial, but less so in the UK.

I never use the proprietory kits as a computer fan, a few zip ties, a switch and a couple of hours of my time cost an awful lot less. About £10 compared to £50+

 

[Jcloughie]

If you look at Dometic fridge fitting instructions, they suggest that the gap behind the condenser should be reduced to about 25 mm. This is contra to what many would think. The reason is to create a Ventura or chimney effect, which speeds the airflow where it is needed.

As caravan manufacturers don’t seem to comply. Using a fan or two can have the same effect.

like Mr Plodd, I made my own. I used two fans behind the top vent. They went too fast, so too noisy. So I then wired them in series which fixed this nicely.

I switched mine with a thermostatic switch with the sensor strapped to the top of the condenser. It worked well. It only worked in warmer weather. And would cycle on and off as expected. The switch went in a small plastic box and sat on top of the fridge, Once set, it could be left alone.


John

 

[otherclive]

Practical Caravan had an article on fitting a proprietary fan kit a while back. Same bits and pieces can be widely obtained for custom fitting.

How to fit a CBE fridge fan kit - Practical Caravan

Installing a fridge fan can boost your fridge’s cooling power, which is especially useful in hot weather. Nigel Hutson shows you how.

www.practicalcaravan.com

 

[Buckman]

People fit fans to aid the frdige in cooling although they probably would not be necessary if the manufacturer sealed the fridge in properly. ?

 

[ProfJohnL]

People fit fans to aid the frdige in cooling although they probably would not be necessary if the manufacturer sealed the fridge in properly. ?

In most cases its the external ambient temperatures which necessitate the fitting of a fan, It's very unlikely the poor sealing of the fridge to internal furniture would affect this specific need.

 

[Woodentop]

If any reader goes down the DIY route and uses 12V computer fans, fit one behind each grille taking note of the air flow direction embossed in the side of the fan case, and wire the fans electrically in series. They will run slower and make very much less noise but be just as effective.

 

[Buckman]

We have spent weeks in Spain and France in really hot weather and also the fridge vents out into the awning. On our current 2018 caravan we have never found the need for fans as fridge work perfectly probably due to a decent airflow over the fins as the fridge was probably fitted correctly. Our previous Lunar caravan gave us a lot of grief in hot weather and we had to use a fan to force the air up over the fins.

 

[Mr Plodd]

I have always fitted the fans to the top vent only (and I buy silent running ones)

My theory (which has served me well for 20+ years) being that I want to extract the air once it has done its job of absorbing heat from the heat exchanger fins, rather than trying to force it in. The greater the airflow the greater the cooling effect so by positive extraction the flow is maximised

Extractor fans in kitchens always suck air out , they don't blow it in !

 

[shouldknowbettor]

Distance from the fan to the fins will be the main condition for effectiveness I would think. Whether extracting on inputting air, if the back of the fridge is fully sealed the effect will be the same, if not fully sealed (as is likely) the amount of air flow over the fins themselves will be the deciding factor, the closer the fan is the more air will flow over the fins rather than forcing air through the gaps (or sucking it)

 

[Buckman]

I have always fitted the fans to the top vent only (and I buy silent running ones)

My theory (which has served me well for 20+ years) being that I want to extract the air once it has done its job of absorbing heat from the heat exchanger fins, rather than trying to force it in. The greater the airflow the greater the cooling effect so by positive extraction the flow is maximised

Extractor fans in kitchens always suck air out , they don't blow it in !

We have never needed to have an extractor in the kitchen to cool down the fridge. Our extractor is used to expel humidity and smells from the kitchen. Maybe you need to invest in a new fridge for your kitchen at home?