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Ventilation Rate Procedure (VRP) Outdoor Airflow Calculation
Ventilation Rate Procedure (VRP) Outdoor Airflow Calculation

VRP, ASHRAE 62.1, Ventilation, Outdoor Air

Christopher Riddell avatar
Written by Christopher Riddell
Updated over a week ago

When the Ventilation Rate Procedure (VRP) option is selected for Ventilation Calculation Type input, the following set of equations from ASHRAE Standard 62.1 are used to calculate the total outdoor airflow (Voz).

First, the breathing zone outdoor airflow (Vbz) is calculated.

The Vbz is based on people-related sources, and area-related sources. The equation for the calculation of Vbz is as follows:

Vbz = Rp * Pz + Ra * Az


Rp (Unit: CFM/person or L/s/person) = Outdoor airflow rate required per person as determined from ASHRAE Standard 62.1 Table

Pz = Number of people in the ventilation zone during use. cove.tool calculates this number based on the occupant density and the floor area of the project.

Ra (Unit: CFM/ft2 or L/s/m2) = Outdoor airflow rate required per unit area as determined from ASHRAE Standard Table

Az (Unit: ft2 or m2) = Net occupied floor area of the ventilation zone.

Next, the total outdoor airflow (Voz) is calculated by the following equation:

Voz = Vbz/Ez


Vbz = breathing zone outdoor airflow

Ez = zone air distribution effectiveness

User control,

Both the Rp and Ra are automated for the Baseline energy model based on the building type, location, and energy code. However, if required users can adjust these values via the People Outdoor Air Rate and Area Outdoor Air Rate inputs on the Building Systems Tab of the inputs.

To learn more about the implemented values of Ez for different systems types, check out this article.

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