Flexible Space Design for Exhibition Halls

Engineering Challenge

Exhibition halls present a unique thermal design problem: the same physical space must accommodate vastly different layouts, occupant densities, and heat loads depending on event configuration. A 100,000 ft² hall may host a sparse trade show with 50 booths one week and a dense consumer expo with 500 booths the next. The HVAC system must deliver consistent thermal comfort across all configurations without permanent ductwork constraining floor layouts.

Thermal Load Variability

The fundamental challenge stems from the wide range of heat generation scenarios:

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

Where each component varies by orders of magnitude:

The total cooling load can swing from 35 Btu/hr·ft² to 95 Btu/hr·ft², requiring HVAC systems sized for peak conditions while maintaining acceptable performance at partial loads.

High-Bay Air Distribution Strategies

Traditional ceiling-mounted diffusers in exhibition halls face two competing requirements:

1. Throw distance: Air must project 40-60 ft horizontally before dropping to occupied zones
2. Temperature differential: Supply air temperature depression ($\Delta T$) affects throw and comfort

The relationship between throw and temperature differential follows:

$$L = K \cdot \sqrt{\frac{Q}{v_{terminal}}}$$

Where:

• $L$ = throw distance (ft)
• $K$ = diffuser constant (dimensionless)
• $Q$ = airflow rate (cfm)
• $v_{terminal}$ = terminal velocity at occupied zone (fpm)

For high-bay applications (25-40 ft ceiling height), specify high-induction linear diffusers with throw ratios of 3.5-4.5. Supply air temperature should be 8-12°F below space temperature to maintain adequate throw without causing drafts at floor level.

Stratification Management

Vertical temperature gradients in high-bay spaces follow:

$$\frac{dT}{dz} = \frac{Q_{internal}}{A \cdot \rho \cdot c_p \cdot ACH \cdot h}$$

Where:

• $dT/dz$ = temperature gradient (°F/ft)
• $A$ = floor area (ft²)
• $h$ = ceiling height (ft)
• $ACH$ = air changes per hour

Without destratification, temperature differentials of 15-25°F between floor and ceiling are common. Implement ceiling fans operating at 50-100 fpm or continuous air curtains along perimeter walls to limit gradients to 5-8°F.

Floor-Level Supply Systems

Floor-level air distribution eliminates throw distance constraints and provides direct conditioning at occupied zones. Two primary configurations exist:

Underfloor Air Distribution (UFAD)

Raised access flooring (12-24 inches) serves as a pressurized plenum. Supply air enters at 63-68°F and exits through floor diffusers at booth locations. Key design parameters:

• Plenum pressure: 0.05-0.15 in. w.g.
• Supply airflow: 0.8-1.2 cfm/ft²
• Diffuser spacing: 6-10 ft on center
• Discharge velocity: 50-150 fpm

Advantages:

• Reconfigurable diffuser placement
• Reduced fan energy (lower static pressure)
• Natural stratification assists cooling
• Direct ventilation to breathing zone

Challenges:

• Higher installation cost ($15-25/ft² premium)
• Plenum cleaning and maintenance access
• Cable management conflicts with airflow paths

Floor-Mounted Duct Systems

Modular duct sections installed on finished flooring connect to perimeter air handling units. Common in retrofit applications or temporary installations.

graph TD
    A[Perimeter AHU] -->|Primary Trunk| B[Floor-Level Distribution Manifold]
    B -->|Flexible Duct Sections| C[Booth Zone 1]
    B -->|Flexible Duct Sections| D[Booth Zone 2]
    B -->|Flexible Duct Sections| E[Booth Zone 3]
    C -->|Low-Velocity Diffusers| F[Occupied Zone Supply]
    D -->|Low-Velocity Diffusers| F
    E -->|Low-Velocity Diffusers| F
    F -->|Buoyancy + Mixing| G[Return Air Path]
    G -->|Ceiling Return Grilles| A

Modular Utility Distribution

Exhibition booths require flexible connections for:

• Electrical power (120V, 208V, 480V)
• Compressed air (90-125 psi)
• Data/telecommunications
• Chilled water (for large exhibit cooling loads)

Temporary HVAC Connections

For exhibits with concentrated heat loads (demonstration equipment, server racks, cooking demonstrations), provide quick-connect utilities at grid locations:

Floor service boxes (typical spacing: 20 ft × 20 ft grid)

• 480V/3-phase power: 60-100A capacity
• Chilled water supply/return: 1-2 inch connections
• Compressed air: 3/4 inch quick-disconnect
• Communication/data: CAT6 or fiber terminations

Booth-level conditioning units Portable or semi-permanent units serving individual exhibits:

$$Q_{booth} = 1.08 \cdot CFM \cdot \Delta T + 0.68 \cdot CFM \cdot \Delta W \cdot h_{fg}$$

Size units for 400-1200 cfm based on booth dimensions (10×10 ft to 20×30 ft). Use water-source heat pumps connected to building chilled/condenser water loops for maximum flexibility.

Zoning and Control Architecture

Divide exhibition floor into 2,000-5,000 ft² zones, each with independent temperature control. Zone boundaries should align with structural bays and utility grid.

flowchart LR
    A[Building Automation System] --> B{Zone Controllers}
    B --> C[Zone 1: Northwest]
    B --> D[Zone 2: North Central]
    B --> E[Zone 3: Northeast]
    B --> F[Zone 4: Southwest]
    B --> G[Zone 5: South Central]
    B --> H[Zone 6: Southeast]

    C --> I[VAV Terminal + Reheat]
    D --> I
    E --> I
    F --> I
    G --> I
    H --> I

    I --> J[Zone Temp Sensors]
    I --> K[Occupancy/CO2 Sensors]
    J --> B
    K --> B

Control Sequence for Variable Density

ASHRAE Standard 62.1 requires ventilation based on occupancy, but exhibition spaces lack fixed occupancy schedules. Implement demand-controlled ventilation using:

1. CO₂-based occupancy estimation: 1 person ≈ 0.3 cfm rise per 100 ppm above ambient
2. Multiple sensor averaging: 1 sensor per 2,500 ft² minimum
3. Gradual setpoint adjustment: 15-minute moving average to prevent hunting

Minimum outdoor air fraction:

$$Y = \frac{V_{ot}}{V_{ot} + V_{recirc}} = \frac{R_p \cdot P_z + R_a \cdot A_z}{CFM_{supply}}$$

Where ASHRAE 62.1 specifies $R_p$ = 5 cfm/person and $R_a$ = 0.06 cfm/ft² for exhibition spaces.

Equipment Staging and Capacity Modulation

Match supply capacity to load variation through:

Multiple smaller air handlers rather than single large units:

• (4) 30-ton units instead of (1) 120-ton unit
• Enables 25% capacity increments
• Redundancy during maintenance

Variable speed drives on all fans:

• Fan power: $P \propto (CFM)^3$
• 50% airflow reduction = 87.5% energy savings
• Minimum speed: 30-40% of design to maintain adequate mixing

Economizer operation: Exhibition halls benefit significantly from free cooling due to high internal loads and large outdoor air requirements per ASHRAE 62.1.

Design Checklist

• Size HVAC for peak occupancy configuration (per fire code maximum)
• Provide utility grid at 20 ft × 20 ft or 30 ft × 30 ft spacing
• Specify high-throw diffusers (throw ratio > 3.5) for ceiling heights above 20 ft
• Include destratification fans for ceiling heights above 25 ft
• Design raised floor plenum for 0.10 in. w.g. or less
• Provide isolation valves for booth-level chilled water at each service box
• Install CO₂ sensors: 1 per 2,500 ft² minimum
• Configure BAS for zone-level scheduling independent of building operation
• Ensure minimum 30% turndown on all air handling equipment
• Specify quick-disconnect fittings compatible with common rental equipment

References

• ASHRAE Standard 62.1-2022: Ventilation for Acceptable Indoor Air Quality
• ASHRAE Handbook—HVAC Applications, Chapter 5: Places of Assembly
• ASHRAE RP-1515: Thermal Environmental Conditions for Human Occupancy