Ventilation Efficiency

Overview

Engineering reference data for Ventilation Efficiency in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Variables

Symbol	Description	Unit
$Q$	Heat transfer	W
$\dot{m}$	Mass flow rate	kg/s
$c_p$	Specific heat of air	J/(kg·K)
$\Delta T$	Temperature difference	K

Ventilation Principles

Displacement Ventilation Characteristics

This principle leverages natural convection to separate the occupied zone from the pollutant/heat layer:

• Heat and pollutants are transferred out of the residence zone (near the floor).
• Heat from ceiling-mounted lights has limited influence on temperatures in the occupied zone.
• The cooling effect of supply air is limited to a few degrees below the residence zone temperature.
• Pollution concentration in the residence zone remains limited.

Supply Conditions: Supply air is typically colder than the average air in the residence zone. The evacuated air near the ceiling is warmer than the average room air.

References

• Original Source