Guest post by National Luna

PART 1

Knowing how much power your camping fridge uses is an important step in knowing how much battery energy you need. It also helps when calculating your required solar-panel size.

While several factors affect your fridge’s energy use, ambient temperature is one of the most impactful. Other factors include:

  • Your preferred temperature setting
  • The thickness of your fridge’s insulation
  • The volume of your fridge
  • The overall design and engineering of the compressor and piping
  • How often you open and close the unit

Of course, it’s impossible to make any specific claims about power use when dealing with so many variables, however, by isolating the effects of ambient temperatures, we get to see how significant a role it plays. The following graphs present an example…

AMBIENT TEMPERATURE

The greater the difference between your fridge’s internal temperature, and the ambient external temperature, the greater (or faster) these two forces want to “equalise”.

This is why the quality and thickness of your fridge’s insulation is so pivotal because the insulation is the only thing that’s slowing down this equalising / warm-up effect.

However, no insulation is perfect, eventually, the fridge’s internal temperature will rise to a point where the compressor will cycle on in order to bring the temperature back down.

That said, the number of ON/OFF cycles is directly related to the ambient temperature. A higher ambient temperature means a higher number of cycles within a 1-hour period.

The graphs below highlight this fact on a single compartment fridge with 60 mm of insulation, and an internal temperature setting of +4ºC.

At a 21ºC ambient temperature, our example fridge has cycled on once within a 1-hour period. Put another way: The compressor has run for 18 – 20% of this time.
At 32ºC, the fridge has cycled on twice within the hour, or, it has run for 25 – 30% of this time.
Finally, if we “double” the ambient temperature to 43ºC, the number of cycles triples within the same period, and the compressor runs for 30 – 50% of this time. Likewise, the energy used is roughly 3 times higher.

By excluding all the other variables, and looking at the effects of the ambient temperature alone, we’re able to see how impactful the operating conditions are on a camping fridge’s energy use.

To be clear, it’s not that the compressor is working “harder” or “faster” at 43ºC (as opposed to 21ºC), it’s that the compressor is cycling on 3 times more often. The actual energy consumed – per cycle – is mostly the same at various ambient temperatures, however, the number of cycles considerably changes.

The final graph below combines the concepts of the previous 3 graphs, and stretches that information over 24-hours.

Given how impactful ambient conditions are, and the fact that they fluctuate throughout the day, the only truly accurate way to calculate a camping fridge’s power use, is to look at the energy consumed over 24-hours.
In this particular example, our test fridge used between 16 to 20 Ah over the course of the day. Assuming your auxiliary battery has 100 Ah of usable energy available, in this example, you’d be able to run your 12V fridge for 5 to 6 days. In reality though, you would have to account for all the other variables mentioned at the start of this article.

It’s important to note that these values are typical for this size- and type of fridge, however, some variations will exist between manufacturers and the actual usage of the unit. What’s more, these results are based on an empty fridge. If the unit was packed full of groceries, the ON and OFF times would both be longer as the contents of the fridge would “stretch out” the cycle times.

For the reasons explained above, it becomes obvious that the energy use of a camping fridge is irrelevant when stated as a snap shot in time. For example: It’s quite possible that a fridge equipped with thick insulation, drawing 3.5A, can be more economical over 24-hours, than a fridge equipped with thin insulation drawing just 2.5A over the same period.

Again, the efficiency of a camping fridge relates more to the insulation, than it does to the compressor itself. However, the benefit of using a more powerful compressor is that the unit can pull the temperature down a lot faster when you need it to.

KEY POINTS

Ambient temperatures are the enemy! The hotter the operating conditions, the more often the fridge will cycle ON and OFF. Insulation is the best defence against this.

Solution: Keep your fridge away from direct sunlight, and if possible, remove it from a hot vehicle.

Ventilation plays a key role in your fridge’s ability to extract heat. A fridge that can’t “breath” properly, will use more power.

Solution: Make sure your fridge’s ventilation ports are unobstructed, and that hot air can flow freely away from the unit.

Heat will follow the path of least resistance, this includes the door / lid seal that’s designed to be compressed.

Solution: Always keep your fridge’s lid properly latched.

Frequently opening and closing your fridge will increase the number of compressor cycles, as well as how much energy is consumed over 24-hours.

Solution: Try to think ahead in terms of what you need from your fridge, and keep the lid opening to a minimum.

Click here to browse the full range of National Luna fridges