4x4 PROFESSOR WHAT YOU NEED TO KNOW ABOUT FRIDGE/FREEZERS
If you’ve had enough of warm beer and spoiled meat, it’s time to consider a fridge/ freezer. We explain how they work, the best way to install them and the most efficient way to use them.
Fridge/freezers are typically divided into three groups based on size: compact, medium and large. A compact fridge (typically 12-25 ℓ) is small enough to fit between the front seats. You don’t need a complicated dualbattery system and simply plug it into the 12 V cigarette lighter socket. The disadvantage of such a fridge is that it probably doesn’t freeze. It is only suitable for water, cooldrinks and fruit. Expect to pay around R1 500.
Medium-sized fridge/freezers (25-65 ℓ) often have two compartments: one for frozen food and a second that merely keeps stuff cool.
Some of them work really well, but because the two compartments flow together, it can get tricky to regulate the temperatures in the two sections individually. These fridge/freezers cost an average of R7 000.
A large fridge/freezer (65 ℓ and more) has compartments that are physically separated with separate temperature controls. Here you can use one compartment to keep braai meat frozen and the other for veggies, eggs and drinks that shouldn’t be frozen. Large fridge/freezers definitely need a dual-battery system. Expect to pay at least R10 000 for these machines.
How do they work?
Volatile ammonia gas bubbles from an expansion valve into a pipe called the evaporator and coils on the inside wall of your fridge/freezer. The ammonia inside this evaporator is ice cold, and according to the second law of thermodynamics – that states heat flows freely to cold and never the other way around – heat flows from your groceries into the evaporator.
The ammonia gas heats up over time and a compressor pump extracts it from the fridge/freezer and compresses the slightly heated ammonia into a liquid. The warmer liquid coils along a second pipe, the condenser, on the outside of the fridge/freezer where the heat flows to the cooler outside air (again thanks to the second law of thermodynamics). Here there’s often a fan that blows the heated air away so cooler air can move in to absorb the heat.
The slightly cooled ammonia liquid returns to the expansion valve that allows it to again turn into a gas. The sudden expansion of the liquid causes the temperature of the gas to drop below freezing. It’s an evaporation process that scientists don’t yet fully understand, but it works.
Technically speaking, a fridge/freezer does not make something cold – the laws of thermodynamics say thats impossible – but it does remove the heat from your meat and beer until it equals the temperature of the gas in the evaporator pipe… a clever way to cheat the laws of nature.
Cool heads prevail
Large fridge/freezers often have better insulation and a stronger cooling system than small ones. They are obviously also more expensive, but for the money you not only get better cooling, but also more storage space.
Metal is a better conductor than plastic, and therefore a fridge/freezer with a metal shell will get hotter than one encased in plastic. However, metal,
especially stainless steel, is more durable than plastic and will therefore last longer.
By the way, we have bad news for campers who like aluminium glasses. Aluminium does not keep your drink cooler than other glasses as you may have believed. The reason why the metal feels so nice and cold in your hand is because heat literally streams out of your body into your drink. That second law of thermodynamics does not always count in our favour.
Should you cover up?
A fridge blanket works well to keep the stainless steel of your National Luna pristine. A cover also prevents the sun from deteriorating your Dometic’s plastic. But does it help keep your fridge/freezer cooler, is the burning question.
Do you crawl under a blanket when its hot? Many fridge blankets don’t fit snugly enough around the shell of a fridge/ freezer, allowing heat flowing from the cooling system to end up trapped under the material, despite vents in the cover.
Then, on top of that, some fridge covers are lined with reflective material on the inside – almost as if they want to bake the fridge, like a garlic bread in foil! If you think about it carefully, the reflective layer should actually be on the outside of the cover to reflect ambient heat away. We have also seen matt-black covers, which beggars belief, frankly.
For best results, simply keep a fridge/freezer away from direct sunlight and make sure the condenser gets enough fresh air. If you don’t mind your Engel getting the odd scratch mark, or if your Mobicool is always kept under roof, there is no reason to use a cover.
Putalidonit
A lid that hinges open at the back works well for small refrigerators that fit between seats so that you and your travel companion have access to the contents.
Medium-sized and large fridge/freezers work better when the lid is hinged to the side. Large fridge/freezers’ hinges that open at the back usually knock against the hatch of your bakkie’s canopy or the ceiling of your SUV. This prevents the lid from opening completely and makes it more difficult to remove a long pork rib or 2 ℓ bottle.
Keep the lid latched when travelling, because if it’s ajar, hot air will seep in – and then the compressor has to work hard to maintain the correct temperature.
Fill me up
Plan your menu before you leave and pack the food in the order in which you will consume it – in other words, day five’s steaks are at the very bottom while day one’s chicken satays lie at the very top.
Don’t be too hard on your travel partner if the lid is left open for too long. When opening, a lot of cold air wafts out, yes, but after that the remainder lies quietly and will not float away – perhaps you remember your science teacher explaining that cold air sinks and hot air rises? However, if you’re going to rummage in the fridge/freezer, you will definitely lose precious cold air.
If your fridge/freezer has baskets, don’t remove them to make space for an extra pack of boerewors as those baskets improve air circulation.
Beverages in cans get cold faster than those in glass bottles because the heat in them can be carried away faster by the cooling system. Don’t leave gaps after removing and consuming something; chuck in a bottle of water rather than wasting power to keep air cold.
Keep the lid latched when travelling, because if it’s ajar, hot air will seep in…
Strap in!
Never transport a fridge/freezer unsecured in the back of your bakkie or SUV. It will slide around and be damaged. And while driving down Van Zyl’s Pass, you definitely don’t want a heavily loaded fridge/freezer rushing you from behind.
It’s precisely for this reason that some fridge/freezers have mounts that you can bolt to a floor or drawer system. This is without a doubt the best way to transport a fridge/freezer.
Other fridge/freezers have special hoops through which you can attach ratchet straps, while others require you to tie straps to the handles. The latter isn’t ideal because all the shaking on gravel roads will eventually bend or break the handles.
If your fridge/freezer slides on a drawer system, you should preferably run the power cord over the top of the fridge/freezer where the runner can’t pinch it.
Try to mount your fridge/ freezer as far away from a window as possible, even if you have to install it in the middle of your SUV’s luggage space or your bakkie’s load bin. And don’t allow anything to block the vents. If the condenser pipe can’t cool off, neither will your provisions.
Treat meat sweet
Freeze your braai meat at home before packing it in your fridge/ freezer. This relieves the pressure on the compressor. Vacuumpacked steaks should also be frozen. Don’t believe people who tell you it will be fine in an ammo box. The bacteria in vacuum-packed meat can flourish using only the little bit of oxygen inside the tissue.
At camp, transfer the meat from the freezer to the fridge section to thaw it slowly if you plan to braai it the next night.
The meat you buy at a supermarket often has reddish water in the packaging called myoglobin. Discard it and dry your steaks with paper towels before freezing. You’re not going to consume the myoglobin, so keeping it around is just providing another medium for bacteria to grow in.
When placing fresh meat in a fridge/freezer, set the thermostat as cold as possible. If you don’t, the meat will freeze slowly, allowing large ice crystals to form inside the tissue, cutting the tissue, and making the meat sloppy when you thaw it later on. Quick freezing is less destructive, and once the meat is rock-hard you can raise the temperature to -18 °C to save power but still keep enzymes and bacteria dormant.
After your holiday, thoroughly clean your fridge/freezer and leave its lid open for a few hours so it dries out properly. Then store it for the next time.
Some history
1824 English scientist Michael Faraday builds the first ammonia-cooled fridge.
1940 Fridges become popular in households.
1960 Electrolux, a Swedish company specialising in electrical appliances, launches its subsidiary Dometic. Dometic further develops Electrolux’s camping fridges (the kind you find in older caravans), as well as other electric camping gadgets. Dometic later makes fridge/ freezers for the Waeco and ARB brands.
1962 The first portable fridge/ freezer as we know it today is manufactured by the Sawafuji company in Japan.
It is marketed under the Engel brand and thanks to its long history you can still buy Engel’s fridge/freezers (and spare parts) all over the world.
1989 The European Institute for Freezing – Institut International du Froid in French – determines -18 °C is the ideal temperature at which meat should remain frozen. Rapper Vanilla Ice releases his hit song “Ice Ice Baby” that same year.
2002 South Africa’s National Luna is the first fridge/freezer manufacturer in the world to come up with independently adjustable dual climate zones. Now you can keep meat at -18 °C and beer at 4 °C – in the same appliance using only one compressor!
2012 SnoMaster, another proud South African company, goes international.