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Applying F-Factor Constructions to Ground Floor Perimeter Zones

asked 2015-09-09 14:47:16 -0600

updated 2017-05-08 15:58:06 -0600

I would like to apply f-factor ground floor constructions along the ground floor perimeter zones of a model. Could someone tell me if I need to make an f-factor construction for each perimeter zone, or can I apply the same construction to all the perimeter zones? If I need to make a unique f-factor construction for each perimeter zone, do I input only that zone's area and exposed perimeter in the construction or for the whole floor? I have about 30+ zones on the ground floor and have tried multiple ways to see what works and have not had any luck.

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answered 2016-10-18 15:27:51 -0600

updated 2016-10-18 15:30:45 -0600

Here's a detailed description of how I have been assigning f-factors:

1) In OpenStudio, create enough F-factor Ground Floor Constructions to assign the perimeter floor surfaces to. The best way to do this is create the first one and edit the f-factor field to what all the other ones should be, and put in a place holder for area and perimeter such as 1.0 to make it clear which ones have been edited later. Save and open the Sketchup plugin of the model.

2) Assign all the ground floor perimeter surfaces to the constructions created and change to boundary condition to GroundFCFactorMethod. I like going clockwise around the building so the numbering is easy to come back to later. Save and open the file in OpenStudio while keeping Sketchup open to do takeoffs in.

3) In Sketchup go through the surfaces with f-factors and open the group to click on the surface and get the area in Entity Info. Enter the area into OpenStudio for that construction. Do the same thing for the exposed perimeter of the surface. I do this by control clicking the perimeter lines and typing in the value from entity info into OpenStudio.

4) Repeat for all the F-factor constructions until all of them have been assigned to ground floor perimeter surfaces, have an f-factor value, a unique area, and a unique exposed perimeter.

5) Check that everything looks correct in the space tab under surfaces.

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answered 2016-03-14 16:38:11 -0600

updated 2016-03-14 16:44:12 -0600

I'm assuming you're using OpenStudio, since your other questions on Unmet Hours are on that tool as well (if you are, please add a tag for openstudio). Under the Constructions tab, you can create F-Factor Ground Floor Constructions (reference screen shot below).

image description

F-Factor Ground Floor Constructions in OpenStudio

You'll notice that there are only input fields for F-Factor, Area, and Perimeter Exposed. To be more exact, you should create a new instance of this F-Factor Construction for each perimeter space that has a difference combination of the three input parameters. The only way to apply one instance to your entire model is IF all perimeter spaces have the same values for all three inputs, or you want to simplify this process and assume the same construction for all perimeter spaces.

There have been other questions about F-factor implementation:

HERE is one about how to potentially create F-factor constructions using measures

HERE is one about an error in the ASHRAE table for F-factor values to use according to horizontal insulation

HERE is one about cases with both horizontal and vertical insulation, as well as an external ground heat exchange modeling tool you could use to report F-factors for cases that don't match the ASHRAE Table

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Asked: 2015-09-09 14:47:16 -0600

Seen: 601 times

Last updated: Oct 18 '16