Ventilation per ASHRAE 62.1

Methodology 

This document describes the methodology for calculating minimum ventilation rates according to ASHRAE Standard 62.1 "Ventilation for Acceptable Indoor Air Quality." The standard establishes minimum ventilation rates for commercial and institutional buildings based on occupancy category.

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Calculation Methodology

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1. Data Source

The calculations are based on tables from ASHRAE Standard 62.1, specifically:

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• Table 6-1: Minimum Ventilation Rates in Breathing Zone

• Table 6-2: Minimum Exhaust Rates

 

Source: ASHRAE Standard 62.1, "Ventilation for Acceptable Indoor Air Quality"

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2. Input Parameters

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For each occupancy category, the following parameters are specified:

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Table 6-1 Parameters:

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• People Outdoor Air Rate (Rp): Ventilation rate per person

  • Units: cfm/person or L/s·person

• Area Outdoor Air Rate (Ra): Ventilation rate per unit floor area

  • Units: cfm/ft² or L/s·m²

• Default Occupant Density: Expected number of occupants per unit area

  • Units: #/1000 ft² or #/100 m²

• Air Class: Classification level (1-4)

 

Table 6-2 Parameters:

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• Exhaust Rate: Minimum exhaust ventilation rate

  • Units: cfm/unit, cfm/ft², L/s·unit, or L/s·m²

• Notes: Special conditions or requirements (A-H)

• Air Class: Classification level (1-4)

 

3. Calculation Formulas

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Breathing Zone Outdoor Airflow (Vbz)

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The minimum outdoor airflow required in the breathing zone is calculated as:

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Vbz = Rp × Pz + Ra × Az

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Where:

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• Vbz = Breathing zone outdoor airflow (cfm or L/s)

• Rp = People outdoor air rate (cfm/person or L/s·person)

• Pz = Zone population (number of people)

• Ra = Area outdoor air rate (cfm/ft² or L/s·m²)

• Az = Zone floor area (ft² or m²)

 

Exhaust Airflow (Ve)

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The minimum exhaust rate depends on the occupancy category and may be expressed per unit, per area, or both.

 

 

4. Worked Examples

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Example 1: Retail-Pet Shops (Animal Areas)

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Given Data (from Table 6-1):

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• Occupancy Category: Retail-Pet shops (animal areas)

• Rp = 7.5 cfm/person

• Ra = 0.18 cfm/ft²

• Default Occupant Density = 10 #/1000 ft²

• Air Class = 2

 

Scenario: Calculate ventilation for a 2,000 ft² pet shop area

 

Step 1: Determine zone population

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• Pz = (2,000 ft² × 10 people/1000 ft²) = 20 people

 

Step 2: Calculate breathing zone outdoor airflow

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• Vbz = (7.5 cfm/person × 20 people) + (0.18 cfm/ft² × 2,000 ft²)

• Vbz = 150 cfm + 360 cfm

• Vbz = 510 cfm

 

Exhaust Requirements (from Table 6-2):

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• Exhaust Rate = 0.9 cfm/ft² or 4.5 L/s·m²

• For 2,000 ft²: Ve = 0.9 cfm/ft² × 2,000 ft² = 1,800 cfm

• Air Class = 2

 

Example 2: Soiled Laundry Storage Rooms

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Given Data (from Table 6-2):

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• Occupancy Category: Soiled laundry storage rooms

• Exhaust Rate = 1 cfm/ft² or 5 L/s·m²

• Notes: F (See other applicable standards for exhaust rate)

• Air Class = 3

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Scenario: Calculate exhaust for a 500 ft² soiled laundry storage room

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Calculation:

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• Ve = 1 cfm/ft² × 500 ft²

• Ve = 500 cfm

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Special Considerations:

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• Note F applies: See other applicable standards for exhaust rate

• Air Class 3 indicates moderate contamination potential

 

5. Special Notes and Conditions

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The ASHRAE 62.1 tables include important notes that modify requirements:

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Note A: Stands where engines are run shall have exhaust systems that directly connect to the engine exhaust and prevent escape of fumes.

Note B: Where combustion equipment is intended to be used on the playing surface, additional dilution ventilation, source control, or both shall be provided.

Note C: Exhaust shall not be required where two or more sides compose walls that are at least 50% open to the outside.

Note D: Rate is per water closet, urinal, or both. Provide the higher rate where periods of heavy use are expected to occur. The lower rate shall be permitted to be used otherwise.

Note E: Rate is for a toilet room intended to be occupied by one person at a time. For continuous system operation during hours of use, the lower rate shall be permitted to be used. Otherwise the higher rate shall be used.

Note F: See other applicable standards for exhaust rate.

Note G: For continuous system operation, the lower rate shall be permitted to be used. Otherwise the higher rate shall be used.

Note H: Exhaust air that has been cleaned to meet Class 1 criteria from Section 5.18.1 shall be permitted to be recirculated. Rate is per showerhead.

 

6. Air Classification System

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The Air Class designation (1-4) indicates the level of air quality and potential contaminant concentration, with:

• Class 1: Lowest contamination potential

• Class 2: Low-moderate contamination

• Class 3: Moderate contamination

• Class 4: Highest contamination potential

 

7. Unit Conversions

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Volumetric Flow Rate:

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• 1 cfm = 0.4719 L/s

• 1 L/s = 2.119 cfm

 

Area:

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• 1 ft² = 0.0929 m²

• 1 m² = 10.764 ft²

 

8. Important Considerations

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1. Actual vs. Default Occupancy: The default occupant density values are provided for reference. Actual occupancy should be used when known.

2. Combined Requirements: Some spaces require both supply ventilation (Table 6-1) and exhaust ventilation (Table 6-2).

3. System Operation: Many rates have provisions for continuous vs. intermittent operation, with lower rates permitted during continuous operation.

4. Additional Standards: Some occupancy categories reference other applicable standards that may impose additional requirements.

5. Breathing Zone: Rates in Table 6-1 are for the breathing zone and may need adjustment for system-level calculations based on ventilation effectiveness.

 

References

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American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). ANSI/ASHRAE Standard 62.1: Ventilation for Acceptable Indoor Air Quality. Atlanta, GA: ASHRAE.

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This is intended for educational and reference purposes. Always consult the complete ASHRAE Standard 62.1 and applicable local codes for design and compliance purposes.