Air Conditioner Capacity: Why Do We Measure In Tons?
You have probably heard your air conditioning contractor express the size of your air conditioner in tons. While we usually think of a ton as 2,000 pounds of weight, in the HVAC industry a ton is also a measure of air conditioner capacity. In the days before mechanical refrigeration was invented, people cut ice from ponds and rivers in the winter and stored it for use in summer to cool buildings and keep food fresh. Ice was sold by the ton. When Willis Carrier invented air conditioning, it made sense to express air conditioner capacity in terms that people were familiar with. Carrier and others rated their cooling systems in tons so people could compare them to the cooling effect of melting a ton of ice in one day.
One BTU (British Thermal Unit) is the heat that has to be absorbed by a pound of water for its temperature to increase one degree F. Burning one kitchen match releases about one BTU of heat. In order for a ton of ice to melt in one day, it has to absorb about 12,000 BTUs of heat per hour. So, a one-ton air conditioner removes 12,000 BTUs of heat per hour from the space it is cooling. Air conditioner capacity is measured by manufacturers in their facilities under a standard set of temperature and humidity conditions.
By standardizing the ratings, the nominal or nameplate air conditioner capacity of equipment from different makers can be compared. Your HVAC contractor will calculate load requirements and then use Manual S to modify the actual equipment tonnage specifications required for your home or business facility based on the temperature and humidity conditions we might encounter here in the Delaware area. Your final AC design might call for larger equipment than you might expect based on the load calculations alone.
Please call us at Sobieski Services. with any questions you may have about energy efficiency or your heating and cooling systems. Our goal is to help educate our customers in Delaware, Pennsylvania, Maryland and New Jersey about energy and home comfort issues (specific to HVAC & plumbing systems).
Image Credit: an untrained eye
