When you're building a camper van, you have lots of choices for recreational vehicle (RV) appliances, and one of the most important is the RV refrigerator. Most mass-market North American RVs still use the older 3-way (propane/AC/DC) absorption refrigerators, as most have propane tanks and spend lots of time plugged into shore power at RV parks and campgrounds.

If your RV camping style doesn't involve being plugged in, you'll probably want a more efficient refrigerator, and that's where a vapor-compression (compressor) refrigerator excels. Compressor fridges typically use a third of the electrical power compared to the typical 3-way RV refrigerator running on battery power, and don't require any body penetrations like a 3-way fridge does. Absorption refrigerators also require that the RV be almost perfectly level to operate, compressor refrigerators can be used at up to a 30-degree angle with no problems. Older RV absorption fridges are also implicated in thousands of RV fires and explosions every year, which have led to class-action lawsuits against manufacturers like Dometic and Norcold.

The two most electrically-efficient sealed compressors in RV refrigerators currently are the Danfoss/Secop BD-series sealed rotary compressors (used in Nova Kool, some Dometic & Norcold, ARB, Whynter, TruckFridge, Vitrifrigo, IsoTherm, etc.) and the Sawafuji "swing" piston-style compressors (used in Engel fridges, among others).

Danfoss/Secop BD-Series Compressors

Danfoss was originally a Danish company that added sealed compressors to its product lineup in the 1950s. By the time the BD-series sealed compressors were developed in 1977, Danfoss had already produced over 100 million compressors (the compressor group became Secop in 2010). Secop is headquartered in Flensburg, Germany, and has factories in Slovakia, Austria and China.


Unlike most of Danfoss' earlier compressor designs which were intended for stationary operation with grid-provided AC power, the "battery-driven" (BD)-series compressors were a new series expressly developed for mobile use: they had to work well with 12/24VDC power sources typical of automotive/marine electrical systems (and be flexible enough to adapt to AC power as well) and stand up to the shocks and vibrations of mobile use. These compressors have three main components:

  • Compressor - Single-cylinder piston-driven compressor assembly mounted above the motor. The compressor has a crankshaft that pushes a piston in and out of a cylinder to compress the refrigerant vapor. 
  • Motor - The compressor is rotated by a polyphase motor with three windings and no brushes, meaning it's an electronically-commutated (brushless DC), variable-speed device. The motor is designed to operate in, and be cooled by, the R-134a refrigerant. The compressor and motor assembly are integrated within the sealed casing, mounted on four springs to control vibration, and the sealed casing itself is mounted on large rubber feet for further vibration dampening.  
  • Electronic controller - Besides the compressor, the electronic controller is connected via a three-pin connector. The controller and its accompanying power supply control the speed and run-time of the compressor, responding to the conditions detected by the thermostat (Nova Kools use a mechanical thermostat).
Cutaway View of Danfoss/Secop BD-Series Compressor

    As of 2020, the latest generations of Secop BD-series sealed compressors (in use since around 2000) used in AC/DC refrigerators are mostly the BD-35F, BD-50F, BD-80F, and now the new "micro" BD-1.4F compressor. While the compressor/motor assembly has changed very little in the last 20 years, the software/firmware in the electronic controllers has been continuously improved. Some Danfoss controllers can now record details on event history of any failure, which can be remotely accessed using Danfoss Tool4Cool software and a Danfoss Bluetooth gateway, if the controller is equipped with one.

    Nova Kool: Company and Design Philosophy

    Nova Kool was founded in 1976 in Vancouver, Canada, and that is still the location of their office, factory and support group (in April 2018, they were acquired by Thetford North America, but still operate independently). From their start, they have been building AC/DC marine and RV refrigerators using the BD-series Danfoss/Secop compressors, compressors that today are a byword for reliability and long life.

    Nova Kool R4500 RV Refrigerator Installed in Camper Van

    Bucking the trend among some other manufacturers to produce ever more complex designs with ever-larger motors and complicated electronics, Nova Kool refrigerators are designed for mechanical simplicity: the less mechanical complexity, the more reliable the device. Another design goal (with help from Nova Kool's YouTube channel) is to make almost any service or repair easily done in the field, an attribute very much appreciated by Nova Kool's devoted users in the marine and RV worlds, who spend most of their time off-grid.

    Nova Kool R5810 RV Refrigerator

    Nova Kool's design philosophy is to balance the components in the refrigerator for maximum efficiency. Compressor capacity is matched to the size of the condenser coil outside the fridge and the cold plates inside it. Compressors are sized with maximum electrical efficiency and thus the most frugal power use in mind (like the "micro" BD1.4F compressor used in some newer Nova Kools like the RFU7300D) - reviewers have consistently noted that Nova Kool's refrigerator designs often have the lowest power usage when compared to competitors.

    Nova Kool RV refrigerators come in one- and two-door styles, both in upright and side-by-side configurations, and ranging from small ones like the R1200 1.2 cu ft model to large versions like the RFU9000 9 cu ft model (see the most popular Nova Kool fridges in the Campervan HQ store). They come with either a DC-only power module or an AC/DC power module (a single power cord auto-senses available voltage). Nowadays, Nova Kool RV refrigerators are used in many big-name RV conversions like the Nova Kool RFU7300D in the Winnebago Travato (shown in the below video), among others. 


    Features of Nova Kool Refrigerators

    Nova Kool refrigerators have some unique features not found in many other RV refrigerators:

    • Very low electrical usage: Nova Kool refrigerators combine a small BD-35F Danfoss compressor with good insulation in the box (you can also add insulation around the Nova Kool to improve performance, as this technical note describes) and the ability to run the compressor at very low speeds, if desired. How little power do they use? Here's some stats - assuming a 38F temperature inside the refrigerator, and a 75F degree day (ambient outside temperature), and running on 12VDC power. The "running amperage" is the max power draw of the compressor at any given time, while the average amp/hr usage takes into account the duty cycle of the compressor. At the tested temperature conditions, the "duty cycle" (the portion out of a 24-hour day that the compressor is running) is not 100%:
    • Model Running Amperage 
       Avg Amps/Hr
      R3100 2.2A 1.2A
      Max. ambient temp 55C/131F, compressor stops if over 100C/212F.
      Keep in mind the other variables for power use:
      1. The more the fridge is opened and closed, the more power is used.
      2. The hotter the day, the higher the duty cycle will be.
      3. The compressors require specified ventilation (min 60 sq inches for single-door), less ventilation will result in more power use.
    • Variable-speed compressor - Nova Kool refrigerators come from the factory with the compressor speed set to 2500 rpm. However, the compressor speed is user-adjustable, via a resistor in the control module. The compressor has 4 possible speeds: 2000 rpm, 2500 rpm, 3000 rpm and 3500 rpm. With the compressor at the lowest setting, the fridge will use the least power, but also cool the slowest. With the compressor at the highest speed, the fridge will use the most power, but it will cool the fastest, very useful on days with high temperatures.
    • Onboard LED diagnostics - Both the DC and AC/DC electronic controllers have the ability to display a number of different diagnostic fault codes to help you troubleshoot any issues (see this article for a list and descriptions of the codes).
    • Chine hugger option for boats - This option moves the compressor from the bottom rear of the fridge to near the top, and also may change the shape and size of the condenser coil. The chine hugger option is designed to make the refrigerator's shape more closely match the curve of the hull, reducing wasted space. Boat users may also want the optional AC/DC control module if there may be a situation where 12/24VDC power is not available. If your boat is wired so shore power comes through an inverter/charger and the charger has an AC output to your fridge, you can run AC power straight to the Nova Kool.
    • Field-replaceable parts - Every Nova Kool comes with a list of parts (like the R3800 parts list shown below), many of which can be replaced in the field. This means that Nova Kool refrigerators are easy to repair if necessary, even if you don't have access to a refrigeration technician or a full suite of refrigeration tools.
    • Nova Kool R3800 RV Refrigerator Parts List

      In short, there are quite a few reasons why Nova Kool refrigerators have a well-earned reputation for being some of the best compressor refrigerators for an RV or boat. Whether you're putting a new refrigerator in a DIY camper van build or thinking of replacing an older inefficient refrigerator, it's worth considering a Nova Kool refrigerator.

      Other Nova Kool Refrigerator-Related Articles

      "Pros and Cons of the Danfoss Compressor Refrigerator", Truck Camper Adventure magazine, April 2016.

      "Danfoss/Secop Compressor Fault Codes Explained", Coastal Climate Control blog.

      "Eliminating Radio Interference From Fridge Compressors", Practical Sailor magazine, Apr 2017.

      "Direct Current Compressors", Danfoss Service and Support case study, Jun 2010.

      "Investigating Absorption Refrigerator Fires (Part 1)", Fire & Arson Investigator magazine, Apr 2008.

      "Investigating Absorption Refrigerator Fires (Part 2)"Fire & Arson Investigator magazine, Jul 2008.


    Bd-35f compressorBd-50f compressorBd-80f compressorBd1.4f compressorDanfoss compressorNova kool rv refrigeratorSecop compressor
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