Refrigerators and air conditioners are both cooling appliances that operate based on similar principles, but they are measured in different units due to historical and practical reasons. The difference in units is primarily due to the specific applications and industries that developed these appliances independently.
Refrigerators: The cooling capacity of refrigerators is typically measured in terms of "cubic feet" (or "liters" in some regions). This measurement refers to the interior volume or storage capacity of the refrigerator. It tells you how much space is available inside the fridge to store food and beverages. The focus for refrigerators is on the usable storage space, as consumers are more concerned about how much food they can fit inside rather than the cooling capacity in terms of heat removal.
Air Conditioners: The cooling capacity of air conditioners is measured in terms of "BTUs" (British Thermal Units) or "tonnage." BTUs measure the amount of heat an air conditioner can remove from the air in an hour. Tonnage is an older unit that refers to the amount of heat required to melt one ton of ice in 24 hours, which is equivalent to 12,000 BTUs per hour.
The difference in units can be attributed to the historical development and specific needs of these appliances. Refrigerators were developed earlier than modern air conditioners, and their primary focus was on food preservation and storage. As such, measuring them by volume made more sense for consumers who wanted to know how much food they could store.
Air conditioners, on the other hand, were developed to control the temperature and humidity of indoor spaces for comfort and health reasons. The cooling capacity of an air conditioner is crucial in determining its effectiveness in cooling a given room or area, and BTUs provide a practical way to measure and compare this capacity.
While both appliances use similar principles of heat exchange and cooling, the different units used for measurement reflect the specific priorities and applications of refrigerators and air conditioners in their respective industries.