Enthalpy is the total energy within a thermodynamic system. Enthalpy is equal to the internal energy of a system plus the product of its pressure and volume. Heat exchangers are examples of enthalpy being transferred from one system to another. Enthalpy is represented by the variable "H" and often seen in computations as "ΔH" meaning the change in enthalpy as a result of an exchange or reaction involving heat or work. The video above is an example of an enthalpy wheel used for heat recovery ventilation (HRV).