Final answer:
Enthalpy is the measure of heat content in Btu per pound of air, representing the total heat content of a system at constant pressure. It is different from entropy, specific heat, and humidity ratio. Option B is correct.
Step-by-step explanation:
The measure of heat content in Btu per pound of air is referred to as the enthalpy of the air. Enthalpy (B) is a thermodynamic property that represents the total heat content of a system. It is the sum of the internal energy of the system and the product of its pressure and volume (when pressure is held constant).
This is different from entropy (C), specific heat (D), and humidity ratio (A). The total change in entropy, in this context, would be the measure of the amount of energy that has become unavailable to do work as a result of heat transfer, assuming an average indoor and outdoor temperature.
The value of specific heat (b) is a measure of how much energy is required to raise the temperature of a given mass of a substance by a specific temperature increment and is essential for calculating the heat transfer rate (Q/t).