Most of us have heard about the Ton* in connection with Heat Load or capacity of Air-conditioning equipment. The Ton (TR)** in Refrigeration & Air-conditioning is a unit indicating a certain Quantity of Heat. This “Quantity of Heat” is different from temperature which only says how hot the substance is but not how much heat it contains.

The two most common units for stating the heat quantity are the British thermal unit (Btu) and the Calorie (cal).

• The Btu is the quantity of heat needed to raise the temperature of 1lb. of water by 1° Fahrenheit.
• The Calorie is the metric unit of heat quantity. It is the has needed to raise the temperature of 1 gram of water by 1 Celsius.  Since a calorie is a very small measurement, it is practical to use thousand calories as the unit for Air-conditioning and it is expressed as Kilo Calorie (K Cal).
  
  *One Ton Refrigeration was originally conceived to describe the quantity of heat removed to freeze 1 Ton (1 American Short Ton is 2000 pounds) of water at 32 Fahrenheit to ice at the same temperature in 24 hours.
  
  **The Air-conditioning engineer uses the term “Ton Refrigeration” (TR), popularly referred to as ‘Ton’, when associated with refrigeration and Air-conditioning. We will use the term ‘Ton or its abbreviation ‘TR’ in this book.