Ashrae 15 Calculations

What is ASHRAE 15?

ASHRAE Standard 15, "Ventilation for Acceptable Indoor Air Quality," is a widely recognized standard developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). It provides guidelines for determining the ventilation rates required to maintain acceptable indoor air quality in buildings.

The standard is based on the principle that adequate ventilation is essential for removing contaminants, odors, and excess moisture from indoor spaces. It considers factors such as occupancy, building type, and the presence of specific contaminants that may require higher ventilation rates.

Key Concepts

Ventilation Rate

The ventilation rate is the volume of outdoor air supplied to a space per unit of time. It is typically expressed in cubic feet per minute (cfm) or cubic meters per hour (m³/h). The standard provides minimum ventilation rates based on the type of building and its occupancy.

Indoor Air Quality (IAQ)

Indoor Air Quality refers to the condition of the air within and around buildings and structures, which can affect the health, comfort, and productivity of building occupants. The ASHRAE 15 standard aims to ensure that ventilation systems contribute to maintaining acceptable IAQ levels.

Contaminant Sources

Contaminants can come from various sources, including human occupants, building materials, and outdoor air. The standard provides guidelines for determining the ventilation rates required to remove these contaminants effectively.

Calculation Method

The ventilation rate required for a space can be calculated using the following formula:

Where:

• Occupancy is the number of people expected in the space.
• Airflow per Person is the recommended airflow rate per person, typically 15-20 cfm per person.
• Area is the floor area of the space in square feet.
• Airflow per Square Foot is the recommended airflow rate per square foot, typically 0.2-0.4 cfm per square foot.
• Equipment is the number of equipment units in the space.
• Airflow per Equipment Unit is the recommended airflow rate per equipment unit, typically 20-50 cfm per unit.

Example Calculation

Let's calculate the ventilation rate for a small office with the following parameters:

• Occupancy: 10 people
• Airflow per Person: 15 cfm
• Area: 500 square feet
• Airflow per Square Foot: 0.3 cfm
• Equipment: 2 computers
• Airflow per Equipment Unit: 30 cfm

Using the formula:

The calculated ventilation rate for this office is 360 cubic feet per minute (cfm). This ensures that the space is adequately ventilated to maintain acceptable indoor air quality.

Common Applications

ASHRAE Standard 15 is applicable to a wide range of building types, including:

• Offices
• Schools and classrooms
• Hospitals and healthcare facilities
• Retail stores
• Hotels and hospitality venues
• Manufacturing facilities

In each of these building types, the standard helps ensure that ventilation systems are designed to meet the specific needs of the occupants and the building's purpose.