Flexible HVAC Zoning for Conference Centers

Overview

Conference centers require HVAC systems capable of adapting to constantly changing space configurations. Operable partitions transform single large rooms into multiple smaller spaces or combine small rooms into larger venues, demanding sophisticated zoning strategies that maintain comfort and efficiency across all configurations.

The fundamental challenge involves reconciling static mechanical systems with dynamic space utilization patterns while preventing cross-contamination of thermal conditions between adjacent zones.

Operable Partition Integration

HVAC systems must coordinate with operable wall systems to prevent air pressure differentials that impede partition operation or create uncomfortable drafts when walls are in motion.

Pressure Differential Management

Maintain pressure differential across operable partitions below 0.02 in. w.g. when walls are in motion. Install pressure sensors on both sides of partition locations to trigger airflow balancing sequences before partition movement begins.

Coordinate with building automation systems to receive partition status signals. When partition movement is initiated, the HVAC system should:

1. Reduce supply airflow to both zones by 30-50%
2. Modulate return/exhaust dampers to equalize pressure
3. Suspend heating/cooling to prevent equipment cycling
4. Resume normal operation 2-3 minutes after partition reaches final position

Acoustic Considerations

Seal all ductwork penetrations through partition ceiling pockets with acoustic barriers rated to match the Sound Transmission Class (STC) of the partition system. Typical conference partitions achieve STC 45-55, requiring corresponding duct seal details.

Install sound attenuators in branch ducts serving flexible spaces within 10 feet of diffuser connections to minimize noise transmission between zones when partitions are closed.

Zone Reconfiguration Strategies

Design mechanical systems to serve the maximum anticipated number of zone combinations while minimizing redundant equipment.

Base Configuration Matrix

Zone Load Calculation

Calculate cooling loads for each possible configuration using the maximum coincident load rather than summing individual zone peaks:

$$Q_{combined} = Q_{envelope} + Q_{occupants} + Q_{lighting} + Q_{equipment}$$

where occupant load varies by configuration:

$$Q_{occupants} = N \times SHG \times CLF$$

For a combined 600-person hall with sensible heat gain (SHG) of 250 Btu/h per person and cooling load factor (CLF) of 0.90:

$$Q_{occupants} = 600 \times 250 \times 0.90 = 135,000 \text{ Btu/h}$$

When divided into six zones, calculate diversity factor:

$$DF = \frac{\sum Q_{individual}}{\sum Q_{simultaneous}}$$

Typical conference diversity factors range from 0.75 to 0.85, allowing system downsizing from the sum of individual zone peaks.

Variable Air Volume System Design

VAV systems provide optimal flexibility for conference spaces through independent zone control and load tracking capability.

VAV Terminal Configuration

Install one VAV terminal per smallest anticipated zone. For a ballroom dividable into six sections, install six VAV boxes even when the space operates as a single room. This configuration enables any combination of zone arrangements.

Locate VAV terminals to serve balanced areas when partitions are in any position. Avoid configurations where one terminal serves portions of two independent zones separated by a closed partition.

Minimum Airflow Considerations

Set VAV minimum airflow to satisfy ventilation requirements for maximum occupancy of the smallest zone configuration:

$$CFM_{min} = \frac{V_{oz} \times A}{E}$$

where $V_{oz}$ is outdoor air ventilation rate per unit area, $A$ is zone area, and $E$ is zone air distribution effectiveness (typically 1.0 for overhead distribution).

For a 1,000 ft² zone with 0.06 cfm/ft² plus 5 cfm per person at 100 occupants:

$$CFM_{min} = (0.06 \times 1000) + (5 \times 100) = 560 \text{ cfm}$$

Size VAV boxes for maximum cooling load with 20°F supply-to-room temperature differential to allow turndown capability:

$$CFM_{max} = \frac{Q_{cooling} \times 12,000}{1.08 \times \Delta T}$$

For 6 tons cooling load:

$$CFM_{max} = \frac{6 \times 12,000}{1.08 \times 20} = 3,333 \text{ cfm}$$

This provides a turndown ratio of approximately 6:1, adequate for most conference applications.

Multiple Thermostat Strategy

Each potential zone configuration requires independent temperature control while preventing conflicting signals when zones are combined.

Thermostat Placement

Install one thermostat per smallest zone configuration at partition wall locations. Mount thermostats 48 inches above finished floor on interior walls away from exterior glazing, supply diffusers, and return grilles.

Control Logic for Combined Zones

When partitions are open and zones combine, implement average temperature control:

$$T_{control} = \frac{\sum_{i=1}^{n} T_{zone,i}}{n}$$

Alternatively, use the warmest zone temperature during cooling mode and coldest zone temperature during heating mode to ensure all occupants remain comfortable:

• Cooling mode: $T_{control} = \max(T_{zone,1}, T_{zone,2}, …, T_{zone,n})$
• Heating mode: $T_{control} = \min(T_{zone,1}, T_{zone,2}, …, T_{zone,n})$

Lock out individual zone thermostats when partitions are fully open to prevent occupant adjustments that conflict with master control strategy.

Control Sequences for Room Combinations

Sophisticated control sequences maintain comfort during transition periods and steady-state operation across all configurations.

Partition Status Integration

Interface building automation system with partition control panels to receive real-time position feedback. Typical integration points include:

• Partition fully retracted (zones combined)
• Partition in motion
• Partition fully extended (zones separated)
• Partition position percentage (0-100%)

Transition Sequence

When partitions transition from combined to separated configuration:

1. Pre-separation (T-5 minutes): Increase supply airflow to 100% in all zones to pre-condition spaces
2. During separation (T=0): Reduce airflow by 40% to minimize pressure differential and air turbulence
3. Post-separation (T+3 minutes): Transfer control from combined master to individual zone thermostats
4. Stabilization (T+3 to T+15 minutes): Gradually restore normal VAV control as each zone establishes independent setpoint

Combined Operation Sequence

When operating as a single combined space:

1. Designate one thermostat as master controller
2. Monitor all zone temperatures for deviation exceeding 3°F from master
3. If deviation occurs, modulate individual VAV boxes to rebalance airflow
4. Maintain minimum ventilation air to all zones based on total occupancy

Balancing for Different Configurations

Test and balance procedures must verify acceptable performance in all anticipated configurations.

Configuration-Specific TAB

Balancing Methodology

Balance each configuration sequentially starting with the combined arrangement:

1. Set all partitions to fully retracted position
2. Establish design airflow for combined operation
3. Verify pressure differential between zones <0.01 in. w.g.
4. Deploy one partition section
5. Rebalance affected zones to maintain design airflow
6. Repeat for each partition until all zones are separated
7. Verify minimum airflow setpoints in each zone meet ventilation requirements

Record VAV box damper positions for each configuration to establish baseline performance and identify potential mechanical conflicts where damper position ranges overlap between configurations.

graph TB
    subgraph "Flexible Conference Center HVAC System"
        AHU[Air Handling Unit<br/>20,000 CFM]

        subgraph "Main Distribution"
            MD[Main Duct<br/>24x36 in]
        end

        subgraph "Zone A Controls"
            VAV1[VAV Box 1<br/>3,333 CFM<br/>Min: 560 CFM]
            T1[Thermostat A]
            D1[Diffusers A]
        end

        subgraph "Zone B Controls"
            VAV2[VAV Box 2<br/>3,333 CFM<br/>Min: 560 CFM]
            T2[Thermostat B]
            D2[Diffusers B]
        end

        subgraph "Zone C Controls"
            VAV3[VAV Box 3<br/>3,333 CFM<br/>Min: 560 CFM]
            T3[Thermostat C]
            D3[Diffusers C]
        end

        subgraph "Zone D Controls"
            VAV4[VAV Box 4<br/>3,333 CFM<br/>Min: 560 CFM]
            T4[Thermostat D]
            D4[Diffusers D]
        end

        subgraph "Zone E Controls"
            VAV5[VAV Box 5<br/>3,333 CFM<br/>Min: 560 CFM]
            T5[Thermostat E]
            D5[Diffusers E]
        end

        subgraph "Zone F Controls"
            VAV6[VAV Box 6<br/>3,333 CFM<br/>Min: 560 CFM]
            T6[Thermostat F]
            D6[Diffusers F]
        end

        subgraph "Partition Control Interface"
            PCI[Partition Status Signals]
            PS1[Partition 1: A|B]
            PS2[Partition 2: B|C]
            PS3[Partition 3: C|D]
            PS4[Partition 4: D|E]
            PS5[Partition 5: E|F]
        end

        subgraph "Building Automation"
            BAS[BAS Controller]
            ML[Master Control Logic]
        end

        AHU --> MD
        MD --> VAV1 & VAV2 & VAV3 & VAV4 & VAV5 & VAV6

        VAV1 --> D1
        VAV2 --> D2
        VAV3 --> D3
        VAV4 --> D4
        VAV5 --> D5
        VAV6 --> D6

        T1 -.->|Zone Temp| BAS
        T2 -.->|Zone Temp| BAS
        T3 -.->|Zone Temp| BAS
        T4 -.->|Zone Temp| BAS
        T5 -.->|Zone Temp| BAS
        T6 -.->|Zone Temp| BAS

        PCI --> PS1 & PS2 & PS3 & PS4 & PS5
        PS1 & PS2 & PS3 & PS4 & PS5 -.->|Position Status| BAS

        BAS --> ML
        ML -->|Control Signals| VAV1 & VAV2 & VAV3 & VAV4 & VAV5 & VAV6

        style AHU fill:#e1f5ff
        style BAS fill:#fff4e1
        style ML fill:#ffe1e1
        style PCI fill:#f0e1ff
    end

Airflow Distribution Uniformity

Ensure diffuser layouts provide acceptable distribution regardless of partition configuration.

Maintain diffuser spacing at 15-20 feet on center to provide 3-5 air changes per hour in cooling mode. Specify linear slot diffusers parallel to partition travel paths to minimize airflow pattern disruption when partitions are in intermediate positions.

Calculate throw distance to ensure airflow reaches adjacent zones when partitions are retracted:

$$L = T_{50} \times \sqrt{\frac{CFM}{V_{terminal}}}$$

where $T_{50}$ is throw to 50 fpm terminal velocity (manufacturer data), $CFM$ is diffuser airflow, and $V_{terminal}$ is typically 50 fpm.

For a 500 cfm diffuser with T₅₀ = 20:

$$L = 20 \times \sqrt{\frac{500}{50}} = 63 \text{ feet}$$

This throw distance adequately covers combined zones up to 120 feet in length with diffusers at opposite ends.

Return Air Strategy

Provide return air grilles in each zone with motorized dampers that modulate based on partition position. When zones are combined, open all return dampers to create balanced return airflow patterns. When separated, modulate return dampers to maintain slight negative pressure in each zone relative to adjacent corridors, preventing air migration between closed zones.

Install pressure sensors at return grille locations to verify balanced operation. Target return air velocity of 400-600 fpm through grilles to minimize noise while providing adequate air circulation.

Performance Verification

Commission flexible zoning systems by testing all common configurations under occupied and unoccupied conditions.

Verify temperature uniformity within ±2°F across each zone during occupied periods. Measure air velocity at occupant level (<0.5 fps) to confirm draft-free operation. Test partition operation with HVAC system at full load to ensure pressure differentials remain within acceptable limits.

Document control sequences for each configuration and train facility operators on proper mode selection and override procedures for special events requiring non-standard arrangements.