Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
Ask Your Question
2

ASHRAE 62.1 - Ventilation Rate Procedure - Reported Average Outdoor Air Fraction

asked 2017-01-25 14:49:43 -0600

I have a model with several VAV systems and have been working on setting them up so the ventilation (outdoor air) is done via the ASHRAE 62.1 ventilation rate procedure. I am comparing the results from the Standard 62.1 Summary report created by EnergyPlus and comparing them to a manual calculation.

My manual calculation is identical to system ventilation requirement for heating, I have however noticed some differences for the cooling.

My manual calculation gives the following average outdoor air fractions (Xs) for cooling:

  • VAV_1: 0.107
  • VAV_2: 0.090
  • VAV_3: 0.091
  • VAV_5: 0.490

Here's a snippet of the report generated by EnergyPlus:

62.1Report

ASHRAE 62.1, definees Xs as $Xs =\frac{Vou}{Vps}$

For the cooling report, Xs doesn't seem to be calculated according to the previous formula for VAV_1, VAV_3 and VAV_5 but is for VAV_2. How can that be?

edit retag flag offensive close merge delete

Comments

Can you provide a test file, either to the help desk or my email address?

rraustad gravatar image rraustad  ( 2017-01-25 15:41:06 -0600 )edit

@rraustad Thank you but it was actually an input error on my part. I had inadvertently set the Minimum Zone Ventilation Efficiency of the DesignSpecification:ZoneAirDistribution to 1 early on while doing some tests. I now get the right result for Xs, and the results of my manual calculation align with the EnergyPlus report so it's all good! I'm however not sure why this error resulted in those values for Xs since it doesn't depend on Ev (or Evz) but on Vps and Vou which if I am not mistaken don't depend on Ev (or Evz) either.

Jeremy gravatar image Jeremy  ( 2017-01-25 17:11:45 -0600 )edit

1 Answer

Sort by ยป oldest newest most voted
2

answered 2017-01-25 17:02:32 -0600

I had inadvertently set the Minimum Zone Ventilation Efficiency of the DesignSpecification:ZoneAirDistribution to 1. I now get the same results as my manual calculations.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

 

Question Tools

3 followers

Stats

Asked: 2017-01-25 14:49:43 -0600

Seen: 263 times

Last updated: Jan 25 '17