Pros and Cons of the Danfoss BD35F DC Compressor Refrigerator

If you’re planning to buy a truck camper from the factory, one of the most important decisions you’ll have to make is which type of refrigerator to have installed in it. During the construction of our camper, we had the choice of installing either a Dometic CR-1110 Danfoss compressor refrigerator or the standard Dometic three-way absorption refrigerator. Living in the sun drenched southwest, this was a fairly easy decision for us—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 DC 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 RV owners. 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 archaic process of refrigeration works well, but, as we will explain later, it also has its limitations in certain RV applications. The 12 volt DC mode found in the standard three-way refrigerator can address some of these limitations, but this mode can also 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 release of the Danfoss compressor refrigerator in 1998. As the name implies, the key component that makes this type of refrigerator possible is the Danfoss BD35F compressor. 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 in 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.

At this point, you may be wondering what this 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 compressor is able to accomplish both of these tasks and use far less power than its predecessors, which is why it’s so special.

So what are the pros of the Danfoss DC compressor refrigerator? Well, we’ve just mentioned the biggest—it consumes far less amperage than conventional RV refrigerators. Exactly how much amperage 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 at start-up in warm weather or 0 percent at night when the refrigerator door isn’t being opened and when ambient temperatures are below freezing. Such extremes are rare though. Typically, duty cycles of 30 to 50 percent during daylight hours are the norm as the refrigerator works to maintain its operating temperature.

So what are the operating numbers? How much amperage does the DC compressor refrigerator typically consume? According to the Secop website, the maximum current draw of the Danfoss BD35F compressor is 4 amps. The literature that came with our 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 like the condenser fan and light. Typically, we’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 amp hours DC. 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.

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, 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. Not only that, but 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. This also means 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 DC compressor refrigerator requires only minimal ventilation. The Dometic CR-1110 in our camper doesn’t need an external fan to run efficiently in hot weather like the ammonia absorption refrigerators found in our previous RVs.

Those are the pros, now lets look at the cons. There’s really only one. Although the Danfoss DC compressor 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 amp hours 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, we’ve found that having a 340 watt solar power system and a 220 amp hour battery bank is more than large enough to run our compressor refrigerator and meet all of our other electrical needs. However, 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 older Dometic CR-1110 models this is 7, newer models maximum). 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 (we like to turn down the temperature 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 as much as it is during the day.

As for the installation of the Danfoss DC 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 DC 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 DC 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 ones. 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 DC compressor refrigerator offers.