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Ventilation

HVAKR calculates outdoor air requirements per ASHRAE Standard 62.1 - Ventilation for Acceptable Indoor Air Quality. This ensures adequate fresh air for occupant health and comfort.

ASHRAE 62.1 Method

Section titled “ASHRAE 62.1 Method”

The Ventilation Rate Procedure calculates outdoor air based on:

  • Occupancy (people-based component)
  • Floor area (area-based component)
  • Zone air distribution effectiveness

Breathing Zone Outdoor Air

Section titled “Breathing Zone Outdoor Air”

The outdoor airflow required at the breathing zone:

People Component (Rp)

Section titled “People Component (Rp)”

Outdoor air per person from ASHRAE 62.1 Table 6.2.2.1:

  • Office space: 5 CFM/person
  • Conference room: 5 CFM/person
  • Classroom: 10 CFM/person
  • Gym: 20 CFM/person

Area Component (Ra)

Section titled “Area Component (Ra)”

Outdoor air per unit floor area:

  • Office space: 0.06 CFM/ft²
  • Conference room: 0.06 CFM/ft²
  • Classroom: 0.12 CFM/ft²
  • Retail: 0.12 CFM/ft²

Breathing Zone Calculation

Section titled “Breathing Zone Calculation”
Vbz = Rp × Pz + Ra × Az

Where:

  • Vbz = Breathing zone outdoor airflow
  • Pz = Zone population (design occupancy)
  • Az = Zone floor area

Zone Outdoor Air

Section titled “Zone Outdoor Air”

Adjust for air distribution effectiveness:

Zone Air Distribution Effectiveness (Ez)

Section titled “Zone Air Distribution Effectiveness (Ez)”

How effectively outdoor air reaches the breathing zone:

  • Ceiling supply, ceiling return: Ez = 1.0
  • Ceiling supply, floor return: Ez = 1.0
  • Floor supply, ceiling return: Ez = 1.2 (improved)
  • Floor supply, floor return: Ez = 1.0

Zone Outdoor Airflow

Section titled “Zone Outdoor Airflow”
Voz = Vbz / Ez

System Outdoor Air

Section titled “System Outdoor Air”

For multi-zone systems, calculate system outdoor air:

Zone Outdoor Air Fraction

Section titled “Zone Outdoor Air Fraction”

The ratio of outdoor air to supply air for each zone:

Zp = Voz / Vpz

Where Vpz is the zone primary airflow.

System Ventilation Efficiency (Ev)

Section titled “System Ventilation Efficiency (Ev)”

Accounts for multi-zone system inefficiency:

  • Single-zone systems: Ev = 1.0
  • Multi-zone systems: Ev varies (typically 0.6-0.9)
  • Critical zone determines system OA

System Outdoor Airflow

Section titled “System Outdoor Airflow”
Vot = Σ(Voz) / Ev

VAV System Considerations

Section titled “VAV System Considerations”

For VAV systems, ventilation varies with airflow:

Minimum Airflow

Section titled “Minimum Airflow”

Zones must maintain minimum airflow for ventilation:

  • At minimum, outdoor air fraction increases
  • May require outdoor air reset

Critical Zone

Section titled “Critical Zone”

The zone requiring the highest outdoor air fraction:

  • Determines system outdoor air rate
  • Changes as zone loads vary

Exhaust Air Requirements

Section titled “Exhaust Air Requirements”

Some spaces require exhaust per 62.1:

Exhaust Rates

Section titled “Exhaust Rates”

From Table 6.5:

  • Restrooms: 50-70 CFM per fixture
  • Kitchens: Varies by equipment
  • Laboratories: Per hood requirements

Transfer Air

Section titled “Transfer Air”

Exhaust can be satisfied by:

  • Direct outdoor air
  • Transfer air from adjacent spaces
  • Combination

Results Display

Section titled “Results Display”

Zone Ventilation Summary

Section titled “Zone Ventilation Summary”

For each zone:

  • Breathing zone outdoor air (Vbz)
  • Zone outdoor air (Voz)
  • Zone outdoor air fraction (Zp)

System Ventilation Summary

Section titled “System Ventilation Summary”

For each system:

  • Total outdoor air (Vot)
  • System ventilation efficiency (Ev)
  • Critical zone identification

Compliance Verification

Section titled “Compliance Verification”

Verify ASHRAE 62.1 compliance:

  1. Check that all spaces have appropriate space types
  2. Verify occupancy matches design intent
  3. Confirm zone OA fractions are achievable
  4. Review system-level OA requirements