HVAC for Convention Center Meeting Rooms

Convention center meeting rooms present unique HVAC challenges due to rapid occupancy fluctuations, high-density audiovisual equipment loads, and the need for individual thermal comfort in spaces that frequently reconfigure. These rooms—ranging from 10-person breakout spaces to 100-person divisible conference halls—require responsive systems that balance energy efficiency with occupant comfort during highly variable use patterns.

Ventilation Requirements and CO2-Based Control

ASHRAE 62.1 specifies minimum ventilation rates for meeting rooms based on occupant density and floor area. The standard prescribes:

$$V_{bz} = R_p \times P_z + R_a \times A_z$$

Where:

• $V_{bz}$ = breathing zone outdoor airflow rate (cfm)
• $R_p$ = people outdoor air rate (5 cfm/person for conference rooms)
• $P_z$ = zone population
• $R_a$ = area outdoor air rate (0.06 cfm/ft²)
• $A_z$ = zone floor area (ft²)

For a 1,200 ft² divisible meeting room designed for 60 occupants, the minimum outdoor airflow calculates to:

$$V_{bz} = 5 \times 60 + 0.06 \times 1200 = 300 + 72 = 372 \text{ cfm}$$

CO2-based demand control ventilation (DCV) offers substantial energy savings by modulating outdoor air based on actual occupancy. The relationship between occupancy, CO2 generation, and steady-state concentration follows:

$$C_{ss} = C_{oa} + \frac{N \times G}{V_{oa} \times 60}$$

Where:

• $C_{ss}$ = steady-state CO2 concentration (ppm)
• $C_{oa}$ = outdoor air CO2 concentration (~400 ppm)
• $N$ = number of occupants
• $G$ = CO2 generation rate per person (~0.3 cfm at sedentary activity)
• $V_{oa}$ = outdoor air ventilation rate (cfm)

Setting a control setpoint of 1,000 ppm allows the system to reduce outdoor air during low occupancy periods while maintaining code compliance and air quality.

Thermal Load Dynamics and Response Time

Meeting rooms experience step-function load changes as occupants enter for scheduled sessions. The sensible heat gain from occupants follows:

$$q_{sensible} = N \times SHG$$

For sedentary adults in a 72°F space, $SHG$ = 245 BTU/hr per person. A room transitioning from empty to 40 occupants generates an instantaneous 9,800 BTU/hr sensible load increase.

The thermal time constant of the conditioned space determines how quickly temperature rises without adequate HVAC response:

$$\tau = \frac{m \times c_p}{\dot{Q}_{cooling}}$$

Where:

• $\tau$ = time constant (hours)
• $m$ = thermal mass (lbm of air + furnishings)
• $c_p$ = specific heat (0.24 BTU/lbm·°F for air)
• $\dot{Q}_{cooling}$ = cooling capacity (BTU/hr)

Meeting rooms with light construction and minimal thermal mass may exhibit time constants of 15-30 minutes, requiring rapid HVAC response to prevent temperature drift exceeding 2°F during occupancy transitions.

Audiovisual Equipment Heat Loads

Modern meeting rooms contain significant electronic loads from projection systems, displays, computing equipment, and videoconferencing infrastructure. These loads exhibit distinct thermal characteristics:

The high radiant component from projection equipment creates elevated mean radiant temperature (MRT), which affects thermal comfort independently of air temperature:

$$PMV = f(T_{air}, T_{radiant}, RH, v_{air}, M_{met}, I_{clo})$$

Where PMV (Predicted Mean Vote) accounts for both air and radiant temperatures. A 5°F increase in MRT from projection equipment requires approximately 2-3°F reduction in air temperature to maintain equivalent comfort.

System Design Strategies

graph TD
    A[Meeting Room HVAC System] --> B[Zone-Level VAV Terminal]
    B --> C[DDC Controller]
    C --> D[Temperature Sensor]
    C --> E[CO2 Sensor]
    C --> F[Occupancy Sensor]

    D --> G{Temperature Deviation}
    E --> H{CO2 > Setpoint}
    F --> I{Rapid Occupancy Change}

    G -->|>2°F| J[Increase Airflow]
    H -->|Yes| K[Increase OA Damper]
    I -->|Detected| L[Boost Mode]

    J --> M[VAV Damper Modulation]
    K --> N[AHU OA Control]
    L --> M
    L --> N

    M --> O[Supply Air Delivery]
    N --> O

    O --> P[Space Conditioning]
    P --> Q[Return Air Path]
    Q --> R[Ceiling Plenum]
    R --> S[Behind AV Racks]
    S --> T[Return Grilles]

VAV terminal sizing must accommodate both peak loads and maintain minimum airflow for ventilation. The peak cooling airflow calculates as:

$$\dot{V}{peak} = \frac{q{sensible}}{1.08 \times \Delta T}$$

For a room with 15,000 BTU/hr peak sensible load and 20°F temperature differential:

$$\dot{V}_{peak} = \frac{15,000}{1.08 \times 20} = 694 \text{ cfm}$$

The terminal must also deliver minimum ventilation at turndown ratio, requiring careful selection to avoid excessive discharge velocities during heating or low-load conditions.

Individual Room Control and Zoning

Each meeting room requires independent temperature control to accommodate:

• Variable occupant density (10-100 persons)
• Diverse thermal preferences across simultaneous meetings
• Operable wall configurations that combine/divide spaces

Zoning strategies include:

1. One VAV box per room - Provides complete independence but increases cost and coordination complexity
2. Shared VAV with zone dampers - Economical for smaller breakout rooms with similar load profiles
3. Series fan-powered terminals - Maintains air circulation during low outdoor air periods, improving comfort response

Control sequences must incorporate occupancy-based setback with rapid recovery capabilities. Unoccupied setpoints of 78°F cooling / 65°F heating reduce energy consumption while allowing 30-minute pre-occupancy boost cycles to establish comfort conditions before scheduled events.

Return Air Configuration

Strategic return air placement prevents short-circuiting and ensures effective removal of heat from concentrated sources:

• Low sidewall returns - Capture stratified warm air from occupants and projection equipment
• Ceiling plenum returns behind AV racks - Direct removal of high-density equipment loads
• Minimum 10 ft separation from supply diffusers to prevent mixing losses

Transfer grilles in operable walls must provide minimum 1 in² per cfm for pressure equalization when rooms combine, preventing door slamming and comfort complaints.

Performance Metrics

System effectiveness for meeting room HVAC centers on:

Meeting these targets requires integrated controls, properly sized equipment, and commissioning that validates performance across the full range of occupancy scenarios typical in convention center operations.