Sensible heat ratio

There are two types of heat gain in the room;

1. room sensible heat gain (RSH)
2. room latent heat gain (RLH)

Therefore, the air (moist air –> the mixture of dry air and water vapor) supplied to a room shall handle two duty.
First, it is cool enough to permit temperature rise up to the room dry bulb temperature –> offset the room sensible heat gain.
Second, it is dry enough to allow a rise up to the room moisture content (or humidity ratio) –> offset the room latent heat gain.

In brief; the supply air to the room must cool enough to offset the room sensible heat gain and dry enough to offset the room latent heat gain. So that, the cold and dry air with a certain airflow rate will be supply to the room to offset room sensible heat and room latent heat.

In order to represent the heat gain characteristic of the room that reflect both sensible and latent heat, the room sensible heat ratio (RSHR) line (or room load line) is drawn on Psychrometric chart in order to specify the HVAC equipment capacity to handle the room load.

See the visual note below of how to draw the RSHR line on the Psychrometric chart.