In this two-part feature, Collyn Rivers tells you all you ever wanted to know about fridges but were afraid to ask!

People have been refrigerating things for a surprisingly long time. In fact, the scientist Charles Boyle, was playing around with cooling some drinkables way back in 1691. He wrote "that part of the beer or the wine that was next to the sides of the bottle could be refrigerated.”. And that's a lot more than some motorhome owners can claim for their fridges over three hundred years later!

Joking apart, there are very few bad fridges around. Most fridges that people complain about don't work as well as they should for just three main reasons. These are:

* The fridge was not designed for the ambient temperature in which it's being used.

* The fridge is connected by inadequate wiring and/or has inadequate ventilation.

* Users have unrealistic expectations.

Before we get into this any further bear in mind that fridges do not generate 'cold', but rather pump unwanted heat out of their insides to somewhere where it does not heat the fridge up once again. Installing a fridge so that the heat is shifted effectively is not hard to do, but it's not as obvious as it might appear. But we'll return to this in the second part of this feature.

This, the first part of this two-part feature, discusses how to choose the right sort of fridge. This will hopefully clarify issues when buying or replacing a fridge. It also identifies the various things that affect fridge performance.

Buying the Right Fridge

There's a big difference between buying a fridge for use in an all-240-volt home, and buying one for a motorhome that is likely to be away from the mains supply for days or weeks on end. Buying one for home is easy. Pick one you like the look of, that is big enough for your needs, and is built by a reputable maker, and it's a safe bet that even on very hot days that fridge will work as you'd expected.

Selecting a fridge that will work well in a campervan or motorhome needs more thought - but there are basic elements common to both domestic and mobile use.

Large fridges use more energy than small fridges but not in direct proportion. If everything else is equal, a fridge twice the size will certainly use more energy - but not twice as much.

The amount of energy a fridge uses will also vary from brand to brand and, if marketed as being suitable for caravan or motorhome use, whether it has been specifically designed for that use. Only a very few big ones are. Most big 12/24-volt fridges are domestic units retrofitted with a Danfoss compressor. They use less energy after they are modified, but may lack adequate insulation for truly efficient operation.

Because cold air falls it escapes every time the door is opened, a door-opening fridge uses more energy than a top-opening fridge. But whilst top-opening fridges are more efficient, anything you want to get out will always be underneath everything else. This is due to Murphy's Law of Selective Migration and no one's beaten Murphy in this area yet (his brother is suspected of owning a door-opening-fridge factory in Ireland).

The biggest major difference between fridges relates mostly to whether they are designed to run only on electricity or whether they are (so-called) three-way units that run from gas whilst camping; from 12-volts from the vehicle supply whilst driving; and from the 240 volts mains when that's available.

Substantially Different

Electric-only and three-way fridges are substantially different. Unless you have a lot of spare money, which type to choose should be primarily influenced by where you mostly stay at night.

Electric-only fridges are effective and more convenient. But the bigger ones are only really practicable if you have access to mains power most nights. Or you have a large motorhome with plenty of roof space, and $5000 or so dollars of half a dozen big solar modules and all the bits that come with them. Running a big electric fridge from solar is technically feasible but I leave it to you to decide if that's economically feasible. A big electric fridge can of course alternatively be run from a generator, but this costs truly serious money - up to $100 a week unless backed up during the day by solar or, whilst driving, from the vehicle alternator.

Most small to medium-sized electric fridges intended for motorhome or caravan use are designed specifically for that purpose. They use about one-third of the electrical energy of domestic units of similar capacity. They typically draw 35-55 watts. A larger fridge that's designed specifically for that purpose draws 65-90 watts. The converted domestic units I mentioned earlier in this feature draw about 100-130 watts.

A 70-100 litre top opening fridge will run from two 80-watt solar modules, and a 250-amp/hour battery will keep one going for two to three days with no solar input at all.

A 110-litre door-opening electric fridge needs at least four 80-watt solar modules. A 180-litre upward fridge needs at least six modules, and 300-litre units need eight. With any electric fridge it's advisable to have a back-up generator, or be prepared to waste food from time to time.

Because of their energy draw, large electric fridges are really best suited to people spending most nights in caravan parks - and/or for those with large motorhomes and lots of spare money. Most work well regardless of outside temperature as long as they are correctly installed. Many aren't, and so they don't - but The Wanderers space restrictions being as they are, we'll have to deal with that in the second part of this series.

Three-way Fridges

So let's look now at three-way fridges - and if you've had bad experiences with earlier versions of these fridges, forget about them because today's higher ambient temperature rated versions are light years ahead of those of a decade or so ago.

Three-way fridges run from gas whilst camping (or from the 240-volt mains where that is available). Whilst driving they run off the vehicle's 12 volts system (never on gas). They do however draw a lot of power whilst running off 12-volts and whilst this is within the capacity of the vehicle's alternator, they draw too much for it to be feasible to run them from solar. A 180-litre unit typically uses a third of a kilo of gas each day.

What is essential to know about three-way fridges is this. These fridges are designed to work only over limited and defined ranges of ambient temperature. Only those specifically designated as having a Climate Class T rating can be totally relied upon to work satisfactorily in the very high ambient temperatures experienced in the north and northwest of Australia. And I use the phrase 'specifically designated as having a Tropical Climate Class T rating' to mean just that.

Climate Class Ratings

I need here to explain just what I mean. A number of fridges sold in Australia are marketed as 'tropicalised'. Whilst this is a reasonable description of their design and construction, the term 'tropicalised' can unintentionally mislead those not familiar with fridge technology.

The increasingly accepted European Union (CEN) fridge performance standard, includes so-called 'Climate Classes' in which the most stringent is Climate Class T. And that 'T' stands for Tropical. So in the way that 'oils ain't necessarily oils', a 'tropicalised' fridge ain't necessarily Climate Class T.

There are four (CEN Standard) Climate Class ratings.

Fridges rated 'SN', and 'N' (which stands for Sub Normal, and Normal respectively) are designed and rated to work up to 32 degrees C.

Fridges marked 'ST', (which stands for Sub Tropical) are designed and rated to work up to 36 degrees C. Those marked 'T' (which stands for Tropical) are designed and rated to work up to 43 degrees C.

A correctly installed fridge Climate Class rated fridge can be relied upon to work satisfactorily up to the highest ambient temperature for which it is rated. But once past that temperature, cooling performance is likely to drop off. If, for example, you have a Climate Class SN or N fridge (ie. designed for 32 degrees maximum), but it's 42 degrees outside, the beer in that fridge is likely to be up to ten degrees C warmer.

So if you are planning to spend time in places that are very hot, it is prudent to use a 'T-rated' unit. I have yet to encounter anyone even locally using a correctly installed 'T-rated' fridge that was not completely satisfied with its performance. And I live in the Kimberley which is one of the most consistently hot areas of this country.

Do note that the European Union Standard that includes Climate Class ratings is not obligatory in Australia. Nevertheless Dometic and a few other fridge vendors market fridges in Australia that have the 'Climate Class' rating noted on their compliance plate (which you'll find inside the fridge). Climate Class T fridges were for example fitted in several display Winnebagos on display at the Casino Rally and many CMCA members have recently bought them.

Be clear regarding this: a statement that a fridge is 'tropicalised' does not imply that it meets Climate Class 'T' requirements.

Dometic states that its fridges that do meet the 'T' standard (and are designated accordingly on the compliance plate) are the larger models RM 2453, RM 2553, and RM 4601. The company claims only that its smaller fridges are 'tropicalised'.

Quantifying Fridge Performance

Outside the EU Standards, it is extremely difficult to obtain any reliable guide to probable fridge performance. There are other more or less recognised standards, but they are really only of use for comparative purposes. Individual fridge performance is affected by so many variables, particularly regarding installation, but also of usage, that it's all but impossible to give typical data. A seller who seems evasive about this is probably being more honest than those who make specific claims!

What to Buy

Correctly installed electric-only fridges are convenient to use and can be virtually relied upon to work well despite the ambient temperature, as long as power is available.

Three-way fridges are designed to work only within a quite specific range of ambient temperature. They do however have the huge advantage of not being dependent on 12 or 240-volt power. Nor are they affected by rainy periods were you to be running on solar. They are also ultra-reliable.

If you have one of these fridges you are able to stay away for as long as you like from mains power, and with adequate refrigeration virtually assured. But as next month's Part 2 shows, you must install it correctly.

Approximate Consumption

As a very rough guide, 40-110 litre chest opening electric units such as Engel and Waeco etc draw three to four amps. Small door-opening units such as Waeco, Vitrifrigo, Frostbite) draw three and a half to six amps.

Big purpose-made fridges such as Vitrifrigo and Frostbite draw from six to eight amps. Big converted domestic fridges (BP, Fisher Paykel etc) draw seven to ten amps.

Three-way fridges draw a great deal more. Small-medium sized three-way fridges draw twelve to fifteen amps. Those over 170 litres or so draw fifteen to twenty amps. The 300-litre plus units may draw up to twenty-five amps. That's a lot!

Unrealistic Expectations

At the beginning of this feature, I touched briefly on unrealistic expectations. Most people know pretty much what to expect of a fridge, but I have come across others seriously complaining that their fridge cannot bring a warm carton of beer down to Australian drinking temperature in an hour or two! No normal domestic or motorhome fridge can do so. When you buy beer always obtain a cold carton and put it straight into the fridge.

Likewise no normal fridge has a chance of quickly freezing an ever-growing stack of newly caught fish. If you attempt this the fridge/freezer will draw power continuously - instead of cycling on and off - and energy consumption will double or even triple.

What you can expect is this. A fridge that is correctly installed and reasonably used can be made to perform as its maker intended. But if that intention was an ambient not exceeding 32 degrees, it is unreasonable to blame the fridge if it does not provide adequate cooling beyond that temperature. A few members have suggested that vendors should warn potential buyers of this.

Unfortunately marketing concentrates on what things can do, not what they cannot do, nevertheless a fridge's designed working temperature range is usually disclosed in vendors' technical data, but not necessarily in their promotional literature.
Part 2 coming soon - The second and final part of this series shows what is necessary to have fridges work as their makers' intended. The good news is that the cooling and energy usage of most fridges can be improved. Many can be improved dramatically. The even better news is that it costs little, if anything, to do this.

Further Information

Further information on both three-way and electric-only fridges is contained in Motorhome Electrics'. It even explains how to make your own. There's also a lot of information about running them from solar in my new book Solar That Really Works - Motorhome Edition (there's also a Caravan Edition so you need to spell out which you need). These books are available on the order form on our secure site. (Note: Solar book available in November).