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Ventilation Calculation Tool

VRP, ASHRAE 62.1, ASHRAE 170, Outdoor Air, Fresh Air, ACH, CFM

Patrick Chopson avatar
Written by Patrick Chopson
Updated over a week ago

Ventilation is the V in HVAC and one of the core features of modern buildings that keeps occupants comfortable, health, and happy.

the process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity, or temperature within the space

Calculating the ventilation requirements is an important part of every mechanical design now possible via our platform! Here are the key features of the tool along with links to further details on specific calculations, connection to the mechanical load model and more.

  • Perform calculations per ASHRAE Standard 62.1 - 2019 Ventilation Rate Procedure

    • Includes Single Zone, Multi Zone, DOAS, and exhaust only rooms and systems

  • Perform calculations per ASHRAE Standard 170 based on ACH

    • Includes all systems types, healthcare and laboratory use types

  • Export PDF reports for all calculations

  • Export Excel spreadsheets of all calculations

  • Control load model inputs for outside air, supply air, and exhaust air

Ventilation Rate Procedure

The ASHRAE Standard 62.1 Ventilation Rate Procedure is a prescriptive method which determines the outdoor air intake rates based on use type, occupancy level, and floor area. The procedure results in both room level and system level outdoor air rates. On the platform there is are unique calculation tables for Single-Zone, Multi-Zone, DOAS and Exhaust Only rooms. This allows for easy inspection and adjustments to individual inputs of the calculation

ASHRAE 170 ACH Procedure

Healthcare and laboratory spaces typically refer to an ACH requirement which determines the air flow based on the room volume. ASHRAE Standard 170 includes requirements for US based healthcare facilities along with some types of labs. The calculation table for this procedure includes an optional height input which controls the calculation volume.

Navigating around Ventilation Calculations

All calculations can be found in the fourth icon of the navigation bar. Export options can be found across the top of the page.

Type of calculation can be selected in the first menu bar. Note that only calculations present in your project will be active.

The second row of options will be all the systems present in your project. Selecting any of these will bring up the ventilation calculations.

Note: rooms not assigned to an Air Systems will go into an 'unassigned' section showing a simplified ventilation calculation

The calculation summary panel can be found on the right side of the screen. Select the arrow to expand to close. Depending on the calculation type this panel displays the system flow information or a summary of the rooms not yet assigned.

Many of the calculations include a lot of steps, don't forget to scroll to see the entire calculation!

Connection to Load Model

To connect the detailed ventilation calculation to the Load Model simply toggle on Use in Load Model. This will flag all ventilation calculations to be used and send information into the simulation run. Values can be observed on the Air System page as well.

Note: If ventilation calculations are not enabled, the default methods within OpenStudio are used. These include the ASHRAE 62.1 - 2007 method and more limited ability to control the critical zone etc.

Existing templates created before v4.0

All existing templates prior to the v4.0 update have been mapped to the new input options for Air Flow Rates. Values such as OA Flow per Person and Exhaust CFM/ft2 will remain the same. The occupancy category for these templates is set as Custom.

Learn more about each calculation in one of these help articles!

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