Ventilation Efficiency
Reference data and engineering information about ventilation efficiency for hvac systems applications.
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Overview
Engineering reference data for Ventilation Efficiency in HVAC systems.
Key Formulas
Sensible Heat
Heat causing temperature change.
Latent Heat
Heat causing moisture change.
COP (Cooling)
Coefficient of performance.
Variables
| Symbol | Description | Unit |
|---|---|---|
| Heat transfer | W | |
| Mass flow rate | kg/s | |
| Specific heat of air | J/(kg·K) | |
| Temperature difference | K |
Ventilation Principles
4 rows
Principle | Description | Suitable For | Key Notes |
|---|---|---|---|
| Short Cut | Supply air is withdrawn before reaching occupied zones. | Generally avoided | Reduces system efficiency significantly. |
| Mixed | High-velocity supply and/or fans create homogeneous air mixture. | Ventilation, cooling, heating | Ensures uniform temperature & pollution concentration. |
| Displacement | Low-velocity supply near floor; heat/pollutants rise to ceiling via convection. | Ventilation, cooling | Not suited for heating. Supply air is cooler than room air. |
| Piston | Air moves as a laminar 'piston' with minimal turbulence. | Special applications | Requires air velocity ≥0.25 m/s to maintain laminar flow. |
Source: engineeringtoolbox.com
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.