How Your Kegerator Cools Your Beer
To understand your kegerator cooling operation it is better to think of it as removing heat from the air inside the box rather than cooling the air inside the box.
In fact, all residential refrigerators work on the same principal for cooling. They’re designed to remove heat not add cold.
In this system there is a refrigerant gas that is alternately cycled from highly compressed to low pressure absorbing and losing heat during each cycle.
In order to do this your kegerator will have:
A Metering Device (Capillary Tube)
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The compressor is the motor of the cooling system. In most kegerators it's normally at the bottom in the back. It's black and about the size of a football. The compressor runs whenever the kegerator thermostat calls for cooling. It is normally very quiet. When running, it is compressing a refrigerant that is in a low-pressure gaseous state to a high-pressure liquid. This sets the stage for the heat removal process to begin.
The condenser is a series of tubes with fins attached to them, similar to a radiator. It's always somewhere on the outside of the kegerator. It may be:
A large black grid mounted to the back of the kegerator
Folded and placed under the kegerator
Coiled up and placed near the compressor
Integrated in the liner of the kegerator
The most common condenser set-up is in the back of the kegerator where it looks like a cage covering the back of the unit. If the condenser isn't a big grid on the back of the kegerator, it will always have a cooling fan to draw room air over the tubes and fins to dissipate the heat from the tubes and fins. This is the case with the under counter style models that do not require space between the unit and walls and cabinetry.
The refrigerant gas flows through the tubes of the condenser. As this occurs, the refrigerant gives off heat. The heat is conducted away from the tubes by the fins. This is similar to how the radiator in your car works.
The metering device in most kegerators is a capillary tube, a tiny copper tube. The capillary tube is attached from the end of the condenser to the beginning of the evaporator.
The capillary tube controls the pressure and flow of the refrigerant as it enters the evaporator. Once the liquid refrigerant has traveled the length of the condenser, it is forced through the capillary tube by the action of the compressor thereby pressurizing the refrigerant. This prepares the refrigerant for injection into the evaporator.
The evaporator is always located on the inside of the kegerator, usually at the back, mounted vertically.
When the liquid refrigerant comes out of the small capillary tube, it’s injected into the larger tubes of the evaporator causing a pressure drop. This pressure drop allows the refrigerant to expand back into a gaseous state. This change of state from liquid to gas absorbs heat.
The gaseous refrigerant travels through the evaporator tubes, back out of the kegerator, through the condenser and down to the compressor to begin the circulation process again.
Because the evaporator is absorbing heat, it is very cold to the touch. The coldness causes any humidity in the air to freeze on the evaporator as ice or frost requiring either manual or automatic defrosting.
In a commercial kegerator the evaporator is housed inside a compartment at the top of the box. A fan or fans pulls the cold air inside the compartment and circulates it around the box. The fans also provide a circulation device to push cold air up into the draft tower via a hose. This keeps the beer in the beer line and shank cold. Most store bought kegerators do not have this air circulation apparatus.
All kegerators have a thermostat to maintain the proper temperature. When the kegerator reaches the set temperature, the thermostat interrupts the electricity flow to the compressor, which stops the cycling of the refrigerant gas and that stops the heat removal (cooling).
Along with the thermostat is a sensor that resides inside the cabinet. The sensor delivers temperature information to the thermostat’s switch.
On some models the thermostat is located inside the cabinet. In others it is located outside, usually in the back of the unit.
Learn More About Keeping Your Beer Cold