Cooling Load - Infiltration




Infiltration is described as outside air that leaks into a building structure. These leaks could be through the building construction or through entry doors. Infiltration heat gains are found by the following equations. These equations are discussed more in the Psychrometrics Section.

The first equation is the total heat gains using enthalpy. In this equation, the volumetric flow rate of the infiltration or ventilation air must be known. This value is converted and multiplied by the difference in enthalpy between the outdoor air conditions and the indoor air conditions.

Heat Transfer Infiltration for the Mechanical PE Exam

The following two equation split the total heat gain into the sensible and latent heat loads.

Sensible Heat Gains are calculated by multiplying the CFM of the infiltrated air by the difference in the temperatures of the indoor and outdoor air.

Heat Transfer Infiltration for the Mechanical PE Exam

Latent Heat Gains are calculated by multiplying the CFM of infiltrated air by the difference in the humidity ratio of the indoor air and the outdoor air.

Heat Transfer Infiltration for the Mechanical PE Exam

It is important to note that these loads are not seen directly by the cooling coil. These are indirect loads that occur in each air conditioned space. Ventilation air is seen directly at the coil and thus this air must be cooled down to the supply air distribution temperature which is much lower than the room condition air.

Heat Transfer Infiltration for the Mechanical PE Exam