ASHRAE 170 ACH Calculations

ASHRAE 170, ACH, Healthcare Ventilation, Laboratory, Lab, Hospital

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

ASHRAE Standard 170 Ventilation of Health Care Facilities provides design parameters for spaces with various functions found in healthcare and laboratory projects. The design parameters are defined as air changes per hour (ACH) and determine the outdoor air, supply air, or exhaust air requirement for a given space function.

To have a room following the ASHRAE 170 ACH calculation method, the Vent Calculation Procedure of the Room Template must be set to ASHRAE 170 (ACH). Once selected there are 88 default Occupancy Categories to choose from. These categories provide the default values for air change rates from ASHRAE Standard 170 - 2017. In addition there is a Custom option that can be used to define a project specific category.

There are six inputs available to define the air flows for the room. In the image above inputs 1, 3, and 5 are the max, peak, or occupied air flow requirement. Typically these are the ones required in the standard and are populated when an occupancy category is selected. Inputs 2, 4, and 6 are the minimum, or unoccupied air flow requirements for facilities that are able to turn down during times of less use.

Input 7 above provides control of the volume used for calculating the air flows from the ACH requirements. By adjusting the calculation height directly for the calculation the model geometry can remain simple. If however you like to include the plenums directly this can be done in the drawing.tool following this guide.

Calculations - Room by Room

All calculations of air flow based on the ACH preformed on the ASHRAE 170 tabs of the Ventilation Calculation Tables. The basic formulas are described in this help article. Each calculation of air flow uses the same volume for that given room.

Several inputs can be customized for each room in the Ventilation Calculation Table. The editable calculations are noted with larger text size and include the Height, and the various ACH rates used. Editing any of these fields will results in a Custom icon being added to the row to indicate a change from the template.

Calculation - System Summary

For each system the calculation summary can be opened by selecting the panel on the right side of the screen. This summary includes sums of the area, volume, and all three types of air flow. The overall ACH for the system is also calculated and displayed in this summary.

Calculation - Connection to the Load Model

The air flow rates calculated for each room and the total system can be pushed to the load model for inclusion in the sizing simulations. Currently the max/occupied OA and EA rate for each room and the minimum system OA rate is assigned.


Two native report types for the ASHRAE 170 procedure are available. A letter paper size PDF report and an Excel report.

The PDF report can be exported via the Export PDF Report action at the top of the Ventilation Calculation Table. A preview of the report is display and then users can select Download to save to their local machine. Note, that the PDF report is produced for the Air System current selected in the table. The report includes the same information from the web interface, including the system summary.

The Excel report is accessed via the Export Spreadsheets action at the top of the Ventilation Calculation Table. A zip file will be downloaded that includes an Excel file for each system present in the project. The Excel files include the calculations in a formatted table along with the same system level summaries.

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