Calculating Minimum Damper Positions with Demand Control Ventilation (DCV)
This process determines how DCV systems can reduce outdoor air requirements and calculates the resulting minimum damper positions for each zone.
Overview
The calculation accounts for DCV reductions based on building use type and the percentage of area served by DCV controls. Different building types (office, retail, school, multifamily) have different potential for outdoor air reduction based on empirical data.
For a detailed view of these calculations, please explore the Excel file attached at the bottom of this page.
System Factors by Building Type
| Use Type | Base OA Rate (CFM/ft²) | System Efficiency | Diversity Factor | Ventilation Opt. Factor | MDP Multiplier |
|---|---|---|---|---|---|
| School | 0.47 | 0.65 | 1.0 | 0.0 | 1.2 |
| Office | 0.09 | 0.75 | 0.966 | 0.22 | 1.5 |
| Retail | 0.23 | 0.75 | 1.0 | 0.0 | 1.5 |
| Hotel | 0.06 | 0.75 | 1.0 | 0.0 | 1.5 |
| Multifamily | 0.06 | 0.75 | 1.0 | 0.0 | 1.5 |
Process Steps
1. Input Required Data
Enter zone information including use type, area, DCV control percentages (on/off and CO2), and design flow rates.
2. Calculate DCV Reduction Potential by Use Type
- Calculate total DCV percentage: CO2 control % + (On/Off control % ÷ 3)
- Example: 25% CO2 + (30% On/Off ÷ 3) = 25% + 10% = 35% total DCV
- Determine total DCV-controlled area and total area for each use type
- Calculate the percentage of area for each use type under DCV control
- Apply empirical reduction equations based on use type:
- School: 0.7136x⁴ - 1.5165x³ + 0.7753x² + 0.2676x
- Office: -0.4168x⁴ + 1.0092x³ - 0.8489x² + 0.4053x
- Retail: -0.5895x⁴ + 1.1925x³ - 0.848x² + 0.4623x
- Multifamily: -0.6379x⁴ + 1.3565x³ - 1.0712x² + 0.5882x
- (where x = percent DCV controlled)
3. Apply Reductions to Individual Zones
- Calculate base outdoor air requirements using standard rates. See the table below. (e.g., 0.09 CFM/ft² for office, 0.23 CFM/ft² for retail)
- Determine each zone's share of the total DCV reduction based on its DCV-controlled area
- Subtract the reduction from base outdoor air requirements
- Outdoor Air w/DCV = (1-DCV adjustment) x Outdoor Air Base
- Outdoor Air w/DCV = (1-DCV adjustment) x Outdoor Air Base
4. Account for System Factors
- Apply building-type specific factors to adjust the reduced outdoor air requirements:
- System Ventilation Efficiency (Ev): Accounts for system mixing and distribution effectiveness
- Diversity Factor: Accounts for non-simultaneous peak occupancy across zones
- Ventilation Optimization Factor: Additional reduction for advanced control strategies
- Final Outdoor Air = Outdoor Air w/DCV x Ev x Diversity Factor * (1-Ventilation Optimization Factor)
5. Calculate Minimum Damper Position (MDP)
Divide the final adjusted outdoor air requirement by the zone design flow rate, then apply the building-type specific MDP multiplier to determine the minimum damper setting.
- MDP = Final Outdoor Air / Zone Design Flow Rate x MDP Multiplier
