Gas Refrigerator Absorption System

Gas Refrigerator Absorption System

We have put together a simple comprehensive explanation of how a gas powered absorption refrigerator works. First let’s understand what the name Absorption Refrigerator means. The Absorption System or more commonly referred to as the Cooling Unit is a completely sealed system consisting of a maze of steel pipes usually located at the rear of the refrigerator box. The main purpose of this unit is to ABSORB heat from inside of the refrigerator box. This absorption of heat will turn the air inside of the box to cold temperatures Just like removing the heat of the sun and the air turns to cold.

The Absorption System is filled through a valve at the factory with a mixture of water, ammonia, sodium chromate, and pressurized with hydrogen. Water and ammonia are the primary active ingredients. Sodium chromate is an anti-corrosion compound that counter acts the highly corrosive ammonia. The solution mixture percentage is a highly guarded secret at each factory as the slightest change to the amounts of any ingredient will dramatically change how efficient the system operates.

In order to activate this mixture to do the job of absorption, it must be boiled by a heat source. The Gas Refrigerators use either a propane gas powered flame or a natural gas powered flame. Another not so commonly used fuel is kerosene. Kerosene does not burn clean and creates a high maintenance situation. The propane or natural gas flame will burn at a rate of 1700 to 1900 BTU per hour depending on the manufacture specifications. This flame heats the boiler section of the Absorption Unit. The boiler is located at the lowest point of the unit. The heat will boil the mixture and the mixture will perk up to the top of the boiler. Similar to how a coffee maker will perk. At this point the mixture is in an ammonia vapor state. The vapor rises to the highest point of the absorption unit where it then condenses down to pure ammonia liquid. At this pure ammonia liquid state, the absorption process begins. Here is where gravity takes over and the pure ammonia liquid falls downward following the zig zag direction of the absorber pipes through the freezer compartment.

The pure ammonia liquid absorbs the warm air from the freezer first, it then flows to the refrigerator compartment and does the same. If the freezer has not absorbed to near maximum and cooled down considerably then the pure ammonia liquid gets “used up” in the freezer compartment and none gets down to the fridge. This is why the upper freezer compartment will chill first, and then the lower fridge compartment will chill after the freezer is cold.

Once the gas freezer and gas fridge compartments are chilled down completely, the thermostat switches to a low flame which is about 50% of the high flame. On this low flame circuit, the mixture will continue to boil and circulate through the system at a slower rate. We call this idling. When the thermostat senses the refrigerator warming to a temperature above the user setting of the thermostat dial, then the circuit will switch back to a high flame and speed up the cooling process.

The thermostat sensor (capillary tube) is usually located in the gas refrigerator compartment. Any adjustments made to the thermostat will affect the refrigerator compartment first. If the fridge is cooled to the desired temperature then the freezer will be at a freezing temperature.

After the spent ammonia exits the fridge compartment it will remix with the water and start the process all over again. The Absorption process takes 1 hour to complete the first cycle. From start up at room temperature, no change in the freezer compartment will be observed until after the first hour.