What does the First Law of Thermodynamics state?

The First Law of Thermodynamics, often expressed as the principle of conservation of energy, asserts that energy cannot be created or destroyed in an isolated system. This means that the total energy within a closed system remains constant, although it can change forms—such as from kinetic to potential energy, or from thermal energy to mechanical work. The implication of this law is critical in understanding energy transfers and transformations in various systems, including building performance and energy efficiency.

For instance, in residential energy assessments, understanding that energy remains a constant quantity can help professionals evaluate how energy is transferred through heating and cooling systems, insulation, and air leakage. This foundational principle supports the concept that while we may use or lose energy in different ways, the total amount of energy involved in a system’s processes remains unchanged, thus guiding effective energy management strategies.