Compressor refrigerator

Reading time 6 minutes

Updated - June 21, 2024

The compressor refrigerator in the motorhome not only cools better, especially at higher outside temperatures, it also consumes - significantly - less energy, at less than a tenth.

Compressor refrigerators that can run on 12 V DC are offered by well-known manufacturers for motorhomes at prices that can even exceed 2,000 euros.

This raises the question: can't it be cheaper?

Not just a question of price

People rarely think about using a conventional domestic built-in refrigerator. People are too focused on the accessory suppliers from the motorhome and camping industry. But it's worth thinking outside the box.

If you compare the power consumption of the standard compressor units on the market in the 150 liter capacity class with 12 V DC for motorhomes, you will find that the daily or annual consumption is 180 ... 210 kWh/a.

A high-quality, yet standard household refrigerator consumes from 80 kWh/a, and 141 kWh/a for a fridge-freezer combination.
The acquisition costs are significantly lower than those of their more power-hungry colleagues from the motorhome sector.

But will it fit through the motorhome door? Because this aspect is often the end of the pious wish.

If this is the case, the compressor refrigerator is not yet doomed, as the absorber can also be installed very inexpensively. convert …

230 V AC operation without shore power

This raises the question of how to operate a 230 V AC cooling appliance with 12 V DC. First of all, a powerful battery is required, not less than for a 12 V DC appliance, but rather more, given the higher consumption requirements of 12 V DC appliances.

The more economical 230 V AC appliance therefore needs an inverter that generates and supplies the required 230 V AC from the 12 V DC.

The inverter does not perform its service without reward. The wage corresponds to the losses, which are defined by the so-called efficiency. The efficiency is usually around 93 %, i.e. the reward for the inverter's work is 7 %.
The real annual consumption of a cooling appliance with 80 kWh/a is therefore 7 % higher with inverter operation, namely 85.6 kWh/a or 151 kWh/a in real terms, corresponding to 141 kWh/a nominal consumption.

In the worst-case scenario, this is still a good 20 % below the lowest consumption of 180 kWh/a or a third less at 210 kWh/a in comparison, apart from the savings on the purchase costs of well over 50 %.

A very good quality inverter with 800 VA output (560 W continuous load at 40 °C) from Victron, the Phoenix Inverter 12/800, if it is not already part of the equipment, costs less than 200 euros and offers plenty of reserves for other consumers in addition to supplying the cooling unit.

Dimensions

The dimensions of the built-in appliances, particularly in terms of width, are the only obstacle, as household appliances with a width of 54.5 cm are generally around 2 cm wider than their 12 V DC counterparts, which are only 52.5 cm slimmer.

The height of the usual fridge-freezer combinations in motorhomes ranges from approx. 124.5 cm to 150.0 cm, the depth ranges from approx. 55.0 ... 60.5 cm. Ultimately, the definitive installation dimensions must determine the final permissible dimensions in each individual case. It may be possible to gain space in the width, provided that filling panels can be removed.

Unfortunately, the brand manufacturers of domestic refrigerators have fixed on the more or less standardized installation width of 56 cm.

Only less well-known manufacturers also supply appliances with a width of e.g. 54 cm and a usable capacity of 181 liters, such as Wiggo WFR-BUR123E (146 kWh/a) and WOLKENSTEIN WKS190.4 EB (182 kWh/a).
With a width of 54.5 cm and a usable capacity of 183 liters, the Privileg PRFI 336 (161 kWh/a), with 187 liters usable capacity of the Bauknecht KSI 12GF2 (177 kWh/a), the Bauknecht KSI 12GF3 (141 kWh/a), and the TELEFUNKEN EKG123S187E (150 kWh/a) is already very close to the original motorhome appliances.

As a purely built-in refrigerator, the Siemens KI41FADD0 iQ700 with a usable capacity of 187 liters and a width of 54.5 cm at 80 kWh/a consumption; that's just 9 W/h!

Spoilt for choice

If the dimensions are acceptable, then - according to the current state of knowledge - as a pure refrigerator the Siemens KI41FADD0 iQ700as a fridge-freezer combination of the Bauknecht KSI 12GF3 make the race.

Before ordering, the existing refrigerator should be disconnected from the internal gas supply, the DC and AC power supply and dismantled if shore power is available, in order to gain an impression of the possible maximum dimensions.
Once the dimensions have been determined and provided that the door dimensions of the motorhome allow the width of the new refrigerator, the refrigerator can be reconnected to its place and the power supply until the household refrigerator arrives and is replaced with the existing one.

Removing the old device

Absorption refrigerators must be hermetically sealed off from the interior in order to reliably prevent the ingress of exhaust gases. This is why they are usually installed very tightly and firmly in their niche. It therefore takes considerable effort to coax them out of their installation location.

First remove the freezer compartment and refrigerator door. Then remove the screw covers on the left and right sides of the side panels in order to remove the screw connections to the side panels.
At the Dometic RMD 10.5 There is one screw on the left and right of the front side panels in the freezer compartment and two more screws on the left and right in the refrigerator area.

The two plugs for the 12 V DC and 230 V power supplies must be disconnected at the rear.

The stopcock for the gas supply to the refrigerator must be closed and secured against unintentional opening!
After disconnecting the gas connection screw fitting on the back of the refrigerator and fitting a dummy plug (tighten the screw fitting firmly!), a person can push from the outside while the bottom of the freezer compartment is shaken and pulled vigorously on the inside until the refrigerator can be moved from its original position.

It is helpful to line the floor, including the entrance and step area, with cardboard (e.g. from the outer packaging of the new refrigerator) to protect the floor from damage when transporting the new appliance out and lifting it in.

Installation of the new appliance

Installation is much quicker and easier, especially as only the side screw connections and the rear 230 V AC connection need to be made.

Before connecting to the power supply, the compressor should be allowed to rest for a while to collect the coolant that may have wandered around in the system during the various tilted positions.

Conversion

The conversion is the alternative to simply replacing the absorber with a compressor refrigerator. In this case, the existing refrigerator remains in place. Only for the removal of the absorber and installation of the compressor technology is the refrigerator temporarily removed from its housing, if necessary, in order to gain full rear access.

DANFOSS compressors and evaporators, e.g. from ISOTHERM or VITRIFRIGO, are available in various performance levels and dimensions, both for 12 / 24 V DC or 230 V AC operation.
The average consumption of the compressors (BD35F* / BD50F) as a replacement for the Dometic 10.5 with 124 l refrigerator capacity is around 108 W/d*, or 39.4 kWh/a*, depending on the model and usable capacity of the refrigerator/freezer.
This minimum consumption beats any household compressor refrigerator with around 92 kW/a, or the only 61 liter Dometic CombiCool RF60 with 2.64 kWh/d, corresponding to 963.6 kWh/a.

The power consumption is therefore extremely moderate even with moderate sunshine and a relatively low PV yield, making it a real alternative to the power-hungry absorber!

In terms of price, the compressors range from around 525 to 800 euros, depending on their performance, and are therefore in a similar price segment to good domestic refrigerators.

Once you have found the right appliance (in terms of the usable capacity of the fridge and freezer compartments), there is nothing standing in the way of the conversion.

Expansion of absorber technology

After shutting off the associated shut-off valve and disconnecting the gas supply line, the plug connectors of the power supply lines are disconnected (12 V DC and 230 V AC).

This is followed by the removal of the evaporator(s) in the refrigerator/freezer compartment, including absorber piping, gas/e-heating and ignition electronics.

The power supply for the LED lighting is disconnected from the control electronics and later connected to the on-board voltage accordingly.

Installation of compressor technology

The quick-release couplings of the refrigerant lines are fed through the openings created at the rear of the refrigerator/freezer. They ensure a simple, disconnectable connection between the compressor and the evaporators without loss of refrigerant.
The mechanical thermostat is fitted to the evaporator if temperature control via SmartHome is not required. The capillary tube for temperature measurement must not be kinked or crushed. Its length represents the maximum distance of the thermostat controller from the installation location.

The compressors vary in width, the height and depth are pleasingly small and therefore generally suitable for any installation situation behind the refrigerator, directly behind the lower ventilation flap. Low-vibration installation and acoustic insulation, if required, ensure quiet operation.

After connecting the thermostat cables and the power supply, the compressor can be put into operation.

Contrary to my expectations and habits with household appliances, the compressor works silently(!). If you stand directly in front of the compressor, you can hear the fan whirring very quietly, but it is absolutely silent inside.
The silent operation of the compressor leads to the assumption that the compressor is not working. However, the slight heat development on the cooling grid and the clear cooling on the evaporator are evidence of perfect functioning.

If, contrary to expectations, a fault should occur, in 99.9% of cases the electronics are the originator. The electronics box can be easily replaced by removing the power supply and thermostat connections, loosening a screw and disconnecting a three-pin plug connection (the three-phase connection of the compressor itself).
To date, the number of defective compressors in a decade can be counted on one hand.

The internal refrigerator lighting receives its 12 V supply voltage via a gray cable with two wires. The white wire is connected to plus, the brown wire to minus.

insulation

After removing the absorber technology, the insulation of the bare rear wall of the cooling unit, including the feed-through for the temperature sensor / thermostat sensor and LED power supply, can be restored with several layers of 10 mm and 25 mm self-adhesive Armaflex AF, alternating in width and height.

You can also take the opportunity to insulate cavities in the refrigerator housing of the motorhome with Armaflex AF. This also reduces the energy consumption of the compressor.

Notice

All electrical installation work must be carried out by qualified personnel in compliance with applicable regulations. When working on electrical installations, they must always be kept safely disconnected from the power supply!
To inform uninvolved third parties, appropriate information signs must be attached to the shutdown devices during the work.

ps If you need personal support in the implementation for a fee, you are welcome to Ticketing make!
I will be happy to convert your existing refrigerator. The work is usually completed within one working day, provided all the materials are available.