Ventilation Systems

Overview

Engineering reference data for Ventilation Systems 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

Duct Sizing Methods

Two primary methods for sizing air ducts are the Equal Friction Method and the Velocity Reduction Method.

• Equal Friction Method: This straightforward approach sizes all duct sections to maintain a constant pressure loss per unit length (e.g., inches of water per 100 ft). It's easy to use and results in a system where the fan must overcome predictable friction losses.
• Velocity Reduction Method: This method sizes ducts by starting with a higher air velocity near the fan and gradually reducing the velocity in branches further away. This can help balance pressure drops but requires more careful planning.

Air Filters: Key Metrics

Air filter performance is commonly evaluated by two metrics:

• Arrestance: A measure of a filter's ability to capture large, visible particles like lint and dust. A higher arrestance percentage indicates better performance.
• Efficiency: A measure of a filter's ability to capture smaller, often invisible particles (e.g., pollen, mold spores). Efficiency is typically rated using standard tests (like ASHRAE or MERV).

Relevant Standards and Organizations

• ASHRAE: The American Society of Heating, Refrigerating and Air-Conditioning Engineers develops widely adopted standards for indoor air quality, ventilation, and system design.
• Clean Room Standards: For controlled environments, cleanliness is defined by standards such as *Federal Standard 209 and *ISO Standard 14644, which specify maximum allowable particle counts per unit volume for different classes.

References

• Original Source