The DC Compressor Refrigerator: The Real Scoop

Danfoss Compressor RefrigeratorIf you’re planning to buy a factory built truck camper, one of the most important decisions that you’ll have to make is which type of refrigerator to have installed in it. During the construction of my Northstar Laredo truck camper, I had the choice of installing either a Dometic CR-1110 Danfoss compressor refrigerator or a standard Dometic three-way ammonia absorption refrigerator. Living in the sun drenched southwest, this was a fairly easy decision for me—the Danfoss compressor fridge was the only way to go. For you, however, the choice might not be so easy. The purpose of this article is to provide a little history about the Danfoss compressor refrigerator, how it works, and the pros and cons of owning one.

It wasn’t that long ago when the ammonia absorption refrigerator was the only choice for an RV. Unlike the Danfoss compressor refrigerator or the refrigerator found in your home, the ammonia absorption refrigerator neither uses a compressor, nor does it have any moving parts. It works through a process called absorption. Basically, the ammonia absorption refrigerator uses heat to operate. The source of this heat comes from either a propane flame or from electricity (110 volt AC or 12 volt DC). This heat starts a chemical reaction and the process of evaporation and condensation causes the refrigerator to cool. This time-tested process generally works well for RV owners, but for overlanders and boondocking enthusiasts, running the refrigerator on propane was and still is the only viable, long-term mode of operation. This is because an absorption refrigerator operating on 12 volts DC will consume anywhere between 8 and 23 amps an hour, an overly excessive amount that would run an RV battery down in a single day.

All that changed with the development of the Danfoss compressor refrigerator. As the name implies, the key component that makes this type of refrigerator possible is the Danfoss BD35F compressor. Invented in 1998 and manufactured in Denmark, the Danfoss BD35F is a brush-less, variable speed, hermetically sealed compressor. Key features of this revolutionary compressor include rapid cooling, a low amp draw, and a whisper quiet operation. Nearly all AC/DC compressor refrigerators being produced today for the RV and marine industries use the Danfoss compressor with the BD35F and BD50F (a larger version of the BD35F) being the most popular models. Danfoss was recently bought out by the German company, Secop, but Secop still maintains the Danfoss manufacturing operation in Denmark. The name Danfoss is a bit of a household word in the Marine/RV industry which is why many still refer to this compressor as a Danfoss. Neither Danfoss nor Secop make refrigerators.

danfoss_bd35f-2
The Danfoss/Secop BD35F refrigerator compressor

At this point, you may be wondering what a refrigerator compressor does. What’s its purpose? The refrigerator compressor basically does two things: it raises the pressure of the refrigerant vapor used in the refrigerator and helps to maintain the vapor’s flow rate. Unfortunately, the process of compressing gas and raising pressure requires a lot of energy. This is why refrigerators that employ vapor compression refrigeration technology typically use a lot of electricity. All that changed with the arrival of the Danfoss BD35F compressor. This special compressor is able to accomplish both of these tasks and use far less power than its predecessors.

So what are the pros of the Danfoss compressor refrigerator? Well, we’ve just mentioned the biggest–it consumes far less amperage than conventional RV refrigerators. Exactly how much depends on several factors including the refrigerator’s temperature setting, the ambient temperature, the available voltage, how well the unit is insulated, and whether the refrigerator is working to get the temperature cold at start-up or working to maintain the operating temperature. The Danfoss compressor works in what are called duty cycles, the hourly period when the compressor is actually on and working. These cycles can run as high as 100 percent of the time at start-up and when the temperatures outside are 100 degrees or higher during the day or 0 percent at night when the refrigerator door isn’t being opened and closed a lot and when ambient temperatures are below freezing. Though, typically, duty cycles of 30 to 50 percent during the day are the norm as the refrigerator works to maintain its operating temperature.

So what are the numbers? How much amperage does the DC compressor refrigerator typically consume running on 12 volts DC? According to the Secop website, the maximum current draw of the Danfoss BD35F compressor is 4 amps. The literature that came with my Dometic CR-1110 lists a maximum current draw of 5.9 amps DC. According to a Dometic representative, the disparity between the two figures is due to the other components in the refrigerator that require power to operate as well like the condenser fan and light. Typically, I’ve found that the Dometic CR-1110 doesn’t require that much current to operate. With ambient temperatures in the upper 70s and at a temperature setting of 4.5 (1 lowest 7 highest), the refrigerator typically consumes about 30 watts or 2.5 amps DC per hour. As you can see, these numbers are far less than what you would see with a standard three-way ammonia absorption refrigerator operating on 12 volts DC.

Dometic CR-1110 Danfoss Compressor Refrigerator
Interior view of the Dometic CR-1110 Danfoss compressor refrigerator.
Dometic CR-1110 Danfoss Compressor Refrigerator
Closeup of the light and temperature control unit of the Dometic CR-1110.

What are some additional pros of the Danfoss compressor refrigerator? Well, in contrast with the ammonia absorption refrigerator which must be level in order for it to operate efficiently and prevent damage, the Danfoss compressor refrigerator can temporarily operate up to 30 degrees out of level without risk of damage. This is a huge plus for overlanders and boondocking enthusiasts as getting a perfectly level campsite can sometimes be difficult. Another pro is that the Danfoss compressor refrigerator doesn’t require a fossil fuel, like propane, to operate, so when set-up with a capable solar power system, you can run one indefinitely. Another benefit, of course, is that there’s no pilot light. This means you can run a compressor refrigerator while driving without having to worry about the pilot light blowing out and you can run it while fueling up at a gas station without concern of an explosion. Moreover, the Danfoss compressor refrigerator takes only a couple of hours to reach its set operating temperature. Gone are the days of having to turn on your absorption refrigerator the day before your trip to ensure its cold. Last but not least, the Danfoss compressor refrigerator requires only minimal ventilation. My Dometic CR-1110 doesn’t need an external fan to run efficiently in hot weather like the ammonia absorption refrigerators found in my previous RVs.

Those are the pros, now lets look at the cons. There’s really only one. Although the Danfoss compressor type of refrigerator is much more efficient running on 12 volt power than the ammonia absorption type, it still consumes a considerable amount of amperage during a 24 hour day. The consumption rate is typically 60 amp hours a day which breaks down to 2.5 amps or 30 watts per hour. What this means is that your RV will require a minimum of two 12 volt batteries (about 200 amp hours) and a effective way to keep them charged, either a 200 watt solar power system or a generator. Personally, I’ve found that having a 340 watt solar power system and a 220 amp hour battery bank is more than large enough to run my compressor refrigerator and meet all of our other electrical needs, rain or shine. If you boondock for extended periods of time in cold, predominantly overcast areas like the Pacific Northwest then having a generator as a backup to a solar power system or as the primary means of keeping your batteries topped off will probably be needed.

If you own a Danfoss compressor refrigerator, here are a few operating tips. Buy a refrigerator thermometer and place it inside your refrigerator. Doing this will allow you to monitor the refrigerator’s temperature and will allow you to adjust the temperature setting as needed. At start up, turn the temperature knob to the maximum setting (for my Dometic CR-1110 this is 7). This ensures the contents of the refrigerator get cold sooner. Once the refrigerator is operating at the temperature you want, back off the setting a bit (I like to turn down the temperature on my refrigerator to 4.5) to reduce compressor duty cycles. This power saving measure is especially useful during the night when the door isn’t being opened and closed as much as it is during the day.

Dometic CR-1110 Danfoss Compressor Refrigerator
The rear of the Dometic CR-1110 Danfoss compressor refrigerator. Note the lack of cooling fins and the amount of insulation surrounding the unit.

As for the installation of the Danfoss compressor refrigerator, insulation of the area surrounding the refrigerator is key. Most manufacturers recommend at least 2 inches of insulation along the refrigerator compartment bottom, top and sides. Doing this can cut the refrigerator’s duty cycles and power consumption by half. Most RV manufacturers know this is important, but the word hasn’t gotten out to some RV shops that install these unique refrigerators. Some are installed without any insulation, whatsoever. If you’re hiring this work out, it’s important to inspect their work before you pay them. Another issue to be aware of relates to the faulty installation of these refrigerators. Unfortunately, some shops do a poor job. It’s important to remember that this isn’t a problem with the manufacturer, but with the shop that performed the installation. It pays to do some research ahead of time to see if they’re competent installers.

After reading all of the positives of the Danfoss compressor refrigerator, you may be wondering which company makes the best one? That’s hard to say. Top manufacturers include Dometic, Norcold, Vitrifrigo, IsoTherm, and Nova Kool. They all use the Danfoss compressor, so generally speaking, they all offer the same performance and reliability. The quality of construction and the amount of insulation, or lack of it, is where the good units separate themselves from the mediocre. Again, it pays to do some research ahead of time. All manufacturers have detailed spec sheets of their refrigerators online. Take note of amp hour consumption rates and other ratings. Read the product reviews and Internet forums to get a feel for user satisfaction. Whatever your choice, and as long as you have a capable battery charging system, you’ll be sure to enjoy the benefits that the Danfoss compressor refrigerator offers.

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About Mello Mike 305 Articles
Mello Mike is an Arizona native, author, and the founder of Truck Camper Adventure Magazine. He's been RV'ing since 2002, is a truck camper and Jeep enthusiast, and has owned and restored several Airstream travel trailers. He enjoys college football, hiking, travel, off-roading, photography, and fishing. He retired from the U.S. Navy in 2004 as a CWO3 after 24 years and now works as a project manager for a major banking and security firm. He also does some RV consulting and RV inspections on the side.

6 Comments on The DC Compressor Refrigerator: The Real Scoop

  1. Mike, excellent report on your CR-1110 refrigerator. Having gone through the failures of an absorption unit myself and having to throw food out was such a waste. In Dec 2013 I installed a CR-1110 in my own camper and have never regretted it. Mike has allowed me to post a link to my install video in my Lance 815.

    https://youtu.be/haBvZtNh8oo

  2. Mike, that’s a nice clear explanation of both types of fridges. I’ve had an absorption the last 5 years. I had to make a level spot in my yard so I could cool it down before a trip. Looking forward to the compressor in my new-to-me Laredo SC at the end of the month. I’m going to monitor it with a trimetric 2030 and then it’s solar time!

  3. I love the idea of not caring so much about being level, unfortunately it doesn’t sound like it’s feasible without solar. Definitely something I’ll look into if the current fridge dies.

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