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

What is the maximum ach (infiltration) for office buildings?

asked 2016-12-02 04:58:09 -0500

poppo92 gravatar image

updated 2017-08-28 09:25:07 -0500

I would like to know the maximum ACH to set the infiltration of an office building. I knew that 0,51 is a good parameter. Anyway if I increase this parameter to about 2-2,5 during the night in order to decrease the temperature, is this reasonable, or is there a maximum parameter?

edit retag flag offensive close merge delete

2 Answers

Sort by ยป oldest newest most voted
5

answered 2016-12-02 14:25:12 -0500

When you specify an ACH, specify which pressure you are using. Building pressurization tests are typically done at 50 Pa for residential buildings, and 75 Pa for commercial buildings. Actual infiltration occurs at natural pressure differences, which is closer to around 4Pa. The design rate in EnergyPlus/OpenStudio is flow at typical design conditions which is the ACHnat/ACH4 number. 2-2.5 ACH is reasonable for ACH50, but really high for ACHnat/ACH4 for an office building. ACHnat will be about ~5x smaller.

I recommend using the CFM/ft2 enclosure area option instead of ACH. If you specify ACH, you can have interior zones with high infiltration rate, even though they don't have any exterior wall.

Here are typical CFM50/ft2 (CFM/ft2 at 50Pa) values:

source:Building Science Corporation image description

Assuming a design pressure difference of 4 Pa and a flow exponent of 0.65, you can convert CFM50/ft2 values to CFM4/ft2 values by multiplying by (4^0.65)/(50^0.65) = 0.194.

NIST has data on this for different buildings types, etc.

edit flag offensive delete link more
2

answered 2016-12-03 08:05:49 -0500

updated 2016-12-03 08:13:32 -0500

Are you doing this to try to simulate opening doors and windows at night to provide natural ventilation?

If you are using EnergyPlus, the better way to do this is to use the air flow network and open windows.

Check out the AirflowNetwork_MultiZone_SmallOffice examples in the EnergyPlus examples directory that uses forced ventilation during the day and natural ventilation in the evening.

The info and links to NIST data in @mdahlhausen's answer is really good, so do make use of it even if you use the air flow network and simulate open doors/windows.

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

4 followers

Stats

Asked: 2016-12-02 04:58:09 -0500

Seen: 3,065 times

Last updated: Dec 03 '16