Fridges for Motorhomes and Caravans
It is probably a reasonable assumption that nearly 100% of caravans and motorhomes have at least one refrigerator. Let’s face it, warm beer is only slightly more palatable than sour milk in your coffee.
Refrigerators for motorhomes and caravans are available in two very different types – gas fridges (often called 3-way), and compressor fridges.
(There is a third type of fridge available utilising the peltier thermo-electric cooling system, but as these are only suited to tiny refrigerators (ie 4 cans), they will not be discussed here.)
In this article I would really like to focus on the compressor variety – but let’s first look at the differences between these two types.
Gas fridges have no moving parts and work by applying heat to a water/ammonia mix in a sealed system. The combination of convection, pressure and gravity cause the fluid to circulate and the evaporation of the now liquid ammonia causes a cooling effect. This method of cooling does not require any electricity – any source of heat (when applied to the right part of the cycle) will do. This means that gas, kerosene or an electric element can be used to provide that heat. The three ways referred to are typically:
- A 12 volt heating element
- A 240 volt heating element
Advantages of gas refrigerators
- Can operate without electricity
- No moving parts
- No vibration
- Almost silent
Disadvantages of gas refrigerators
- Consumption of gas can be quite high (and expensive)
- Need to be close to level for correct operation
- Should not be used on gas when the vehicle is moving
- Can struggle in warmer climates (depending on the type)
- Should not be operated from battery or solar systems (unless they are supplied from the vehicle alternator)
- Difficult to diagnose and repair
- Have a far greater energy consumption for a given cooling capacity than compressor fridges.
One other important point about gas fridges is that they are always designed from the ground up as a gas fridge (i.e. not a conversion from another type of fridge). They typically have extremely thick thermal insulation in an effort to combat the warm climate issues. They are typically more robustly constructed (and thus heavier) than compressor fridges.
The method of operation for a compressor driven refrigerator is very different (although heat is still removed from the insider of the fridge through the process of evaporation). A small compressor compresses an oil gas mixture to the point where the gas becomes liquid and mixes with the oil – heat is produced at this stage and this heat is released into the air (this is done through the grill system normally located on the back of the fridge). This gas/oil mix is transported to evaporators inside the fridge and allowed to rapidly decompress. The decompression of the gas causes it to boil and evaporate and it is this evaporation process that draws heat from the inside of the refrigerator. The gas is then returned to the compressor and the cycle begins again.
This process is now highly evolved and many years of research and development has led to huge advances in both the efficiency of the compressor and the production of newer and more efficient gas/oil combinations. Some of this research was driven in search for materials to replace gasses that have an ozone depleting effect.
The compressors for use in household (240v) refrigerators are manufactured all over the world by many different companies. In contrast, just two compressors have for many years dominated the low voltage compressor market. The Sawafuji Swing Motor is only used in Engel branded fridges and all other low voltage refrigerators (up until very recently), have a Danfoss compressor as its heart.
These German engineered and manufactured compressors are truly amazing feats of design and craftsmanship. I have a friend who decided to build his own motorhome refrigerator. He (probably incorrectly) selected the smallest available Danfoss compressor. Being somewhat under powered for the task, the compressor ran 100% of the time (that is the thermostat never turned the compressor off). After 8 years of full time operation, that compressor is still providing cold (home brewed) beer every night. That is over 70,000 hours of run time! (I have heard many such stories about Engel Sawafuji driven fridges as well).
In the last few years, we have seen a growing number of low voltage refrigerators using a Chinese copy of the Danfoss compressor. Although cheaper, I seriously doubt their ability to match the longevity of the original.
Advantages of Compressor refrigerators
- Produce less heat than gas fridges
- Operate well regardless of climate
- Very well suited to solar operation
- Typically easy to diagnose and repair (every fridge tech understands the technology)
- May be left on while the vehicle is travelling
Disadvantages of Compressor refrigerators
- They make more noise than gas fridges (although no more than a modern household fridge)
- They need a constant and reliable supply of electricity
- Often poorly insulated (more on this below)
- Often less robustly constructed
When talking about low voltage, upright refrigerators and fridge/freezers, it is most likely that you will be looking at a conversion. By this I mean that the supplier of the fridge simply purchased a standard household 240v refrigerator (or at least the body) and fitted a Danfoss (or Danfoss copy) compressor. The major issue with this is the design and in particular the insulation type and quality. Until fairly recently, manufacturers of household refrigerators did not give too much thought to energy consumption, and a slim sleek looking fridge will sell more than a bulky, over weight looking one. The result is thinner walls and less insulation. Another issue is the type of insulation – some household fridges use low or medium density fibreglass for insulation – cheap and well suited to household applications. Not however ideal if you are going to take that fridge over corrugated roads. The fibreglass slowly separates and settles – thus vastly reducing the already poor insulation even further.
Our Danfoss driven compressor fridge used to happily maintain -18degC in the freezer compartment while operating about 20min every hour. After eight years of travelling very corrugated roads, it now struggles to maintain -11degC and runs almost full time. (I am about to embark on a project to attempt to restore and enhance this failing insulation. I am taking daily power consumption readings to give me a baseline so I can report on the effectiveness – more about this in another article).
Recommendations and conclusions
From the tone of this article, you can perhaps tell that I am not a big fan of gas powered (three way) refrigerators. This is in part due to the less than satisfactory experiences we had with our (admittedly old) gas refrigerator – and partly due to my electrical background (I find it much easier to understand and diagnose an electrically powered compressor than some “smoke and mirrors” heat powered cooling device). That said, I have spoken to a large number of caravaners all over Australia in the last eight years. I can say that without a doubt that the owners of compressor fridges are the ones most likely to be drinking a cold beer at the end of a hot day.
If you are in the market for a fridge for your motorhome or caravan, I suggest you consider the following:
- Think about the ongoing costs of feeding a gas fridge.
- Consider the climate in the area where you intend to travel.
- If you select a compressor fridge, be very sure you have sufficient power production to provide power to the fridge 100% of the time.
- Look for a compressor fridge with a genuine Danfoss compressor.
- Select a fridge that has been designed (from the ground up) as a mobile fridge.
This is part one of a three part series on motorhome and caravan refrigeration.
In the next article I will discuss how to diagnose problems with compressor fridges and explain how you can make a $2 diagnostic tool to catch problems before the beer gets warm and all the steak defrosts.
As always, I welcome comments and would love to hear about your experiences with either type of refrigerator. Use the comments box below to tell us what you think.
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