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Correctly Using ASHRAE 62.1 or IMC Ventilation Calculations

Wednesday, January 29th, 2014

Calculating the ventilation rates in zones using ASHRAE 62.1 or the International Mechanical Code is a two part process using Design Master HVAC.

1. Set the Calculation Method Correctly

First, you must tell the software which method you are using to calculate the zone ventilation rate.

Use the DM HVAC->Building Definition->Project Information command. Set the Ventilation Calculation Method value.

  • Minimum: No adjustment is made to the ventilation rate in the zones. The ventilation is strictly the sum of the ventilation in the rooms that make up the zone. Select this if you are not using International Mechanical Code or ASHRAE 62.1.
  • 2006 International Mechanical Code: The ventilation rate is calculated based upon 2006 International Mechanical Code. This calculation method is a simplified version of what is specified in ASHRAE 62.1.
  • 2009 International Mechanical Code: The ventilation rate is calculated based upon 2009 International Mechanical Code. This calculation method is exactly the same as the one specified in ASHRAE 62.1.
  • ASHRAE 62.1-2004: The ventilation rate is calculated based upon ASHRAE 62.1-2004.
  • ASHRAE 62.1-2007: The ventilation rate is calculated based upon ASHRAE 62.1-2004. This calculation method is exactly the same as ASHRAE 62.1-2004.
  • ASHRAE 62.1-2010: The ventilation rate is calculated based upon ASHRAE 62.1-2004. This calculation method is exactly the same as ASHRAE 62.1-2004.

The calculation that is performed for the ventilation in a zone is exactly the same in all versions of ASHRAE 62.1 and 2009 IMC. If you are using any of those codes, it does not matter which option you select. They all calculate the same.

2. Set the Ventilation Rates Correctly

Second, you must specify the ventilation rates correctly in each room in the project. The default ventilation rates will not be correct.

Use the DM HVAC->Building Definition->Rooms->Room Project Schedule command. For each room type used in the project, set the correct ventilation rates. These rates will be based upon a table in the code you are using.

A common error is to set the calculation method in the first step, but then not set the ventilation rates correctly in the second step. A major difference between the various versions of the codes is the ventilation rate for each room type. The calculation performed with the ventilation rates is exactly the same. You must manually update the ventilation rates to the correct values, otherwise the values that are used in your project will be wrong.

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