How is one British Thermal Unit (BTU) defined?

One British Thermal Unit (BTU) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. This definition is fundamental to understanding thermal energy and heat transfer in various systems, particularly in heating, ventilation, and air conditioning (HVAC) applications, where precise measurements of energy are crucial for system efficiency and performance.

This definition emphasizes the specific relationship between a unit of heat and a specific mass of water, illustrating how energy is transferred in terms of temperature change. It provides a clear and standardized measurement that can be applied across different thermodynamic calculations and is widely used in the industry. Understanding this measure is essential for anyone working within the refrigeration and air conditioning fields, as it relates directly to the energy consumption and output of heating and cooling systems.

The other options present various heat definitions, but only the first accurately defines a BTU in accordance with industry standards.