There is a whole type of refrigerators (both car and household) called absorption refrigerators. Absorption is the process of absorbing refrigerant vapor that has been formed in the evaporator by a solid or liquid absorber (in our case, the absorber is water). The refrigerant in absorption refrigerators is ammonia. In other words, ammonia vapors are absorbed by water and form a ammonia-water solution. The evaporator itself is located inside the refrigerator compartment, and the refrigeration unit is located on the back of the refrigerator. Natural gas in this refrigerator serves only to heat the ammonia-water solution in the generator (boiler) to the boiling point. Ammonia boiling point (tkip −33.35 ° C) is significantly below the boiling point of water and in the process of evaporating the solution from the boiler, concentrated ammonia vapors with a small amount of water exit to the condenser.
Highly concentrated liquid ammonia from a condenser enters the evaporator, where it boils at a negative temperature, cooling the evaporator plates. In this way, the cooling and freezing compartment inside the refrigerator is cooled.
A weak solution from the boiler flows into the absorber, where it is cooled by the environment before the start of the absorption temperature. Ammonia vapor coming out of the evaporator is also fed to the absorber in the opposite direction to the cooled, weakly concentrated solution. In the absorber, the process of absorption (absorption) of ammonia vapors by a weak solution occurs. In this case, a certain amount of heat is released, which is discharged into the environment through the ventilation grilles in the camper's wall behind the refrigerator.
By the way, in the winter season, these grilles can be closed with special plugs or simply sealed with tape and thus not only blocking the flow of cold air into the motorhome, but also gaining help for your Truma.
The concentrated ammonia solution formed in the absorber is fed by a heat pump into a generator (boiler). The circulation of ammonium water solution occurs continuously, while the boiler and the heat pump are heated. Thus, in absorption chillers, the role of the suction part of a mechanical compressor is performed by the absorber, and the pressure part by the heat pump.
So let's summarize. The refrigeration unit consists of several main parts:
Generator (boiler). Produces ammonia vapor and raises a weak solution to the height of the drain in the absorber.
Capacitor. Condenses ammonia vapors, making the vapor highly concentrated.
Heater. Produces heating ammonium water solution in the generator.
Absorber. Where ammonia vapors are absorbed by water (absorption).
Evaporator. Evaporates liquid ammonia with heat dissipation.
All elements are connected to each other by seamless pipes by means of gas welding.
The absorber heater can work both from electricity and from any kind of combustible fuel: gasoline, gas or at the worst of firewood (in Africa even refrigerators powered by the heat of the sun are used!). The essence does not change. It is important that the water-ammonia solution is heated (and it is not important with what) and circulated in the refrigeration unit. Constant evaporation of ammonia from the solution and its subsequent dissolution in water provides heat removal from the refrigeration chamber, namely, the direct purpose of the refrigerator is to cool your products!
Refrigerators installed in mobile homes can operate on propane (natural gas) or electricity, with a voltage of 12V / 220V.