Retrotec Blower Door - Manual (Page 59)

Page 59 of 87
©Retrotec Inc. 2015
Appendix A: Calculate Airflow Manually
When testing without a computer, or when testing very large or leaky buildings, it may be necessary to calculate the
airflow manually.
Note: Manual calculations are really only appropriate for Single Reading Tests. It is possible to do a Multi-Reading Test
manually and attempt to plot out the results on log-log graph paper, but it is not recommended.
To calculate airflow
1. Record the Door Fan Range Configuration.
2. Adjust the fan speed to achieve the desired Room Pressure.
3. Record the Fan Pressure (Channel B on the DM-2, lower two gauges on the analog gauge clip).
If using a computer program:
4. Record the indoor and outdoor temperature.
5. Record the airflow direction.
6. Input the induced Room Pressure and the Fan Pressure into the software, and calculate the results.
If calculating manually:
7. When pressurizing (flow towards operator), subtract the Room Pressure from the Fan Pressure to determine
the true Fan Pressure.
8. Using the Manual Flow Tables listed in the DM-2 Operation Manual, locate the true Fan Pressure in the left
column and read the airflow under the appropriate Range Configuration column.
Manually calculated flows may vary from the more accurate computer output for several reasons:
The Fan Pressure is corrected for Room Pressure which is not known so is approximated to equal Fan Pressure.
The computer corrects each input for gauge error.
The computer may add a fan correction factor K4.
In spite of these reasons, manually calculated results will typically be within 2% of the computer result.
When using multiple fans, never add Fan Pressures, they aren't additive. Determine airflows in CFM separately and add
the flows together to determine total airflow.
The Manual Flow Tables are listed in the DM-2 Operation Manual and DM32 Operation Manual.