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Transmittance schedule for trees

asked 2017-04-18 12:33:00 -0600

updated 2017-04-26 14:04:02 -0600

Has anyone got some references on transmittance schedules that could be used to model deciduous trees?

In E+ I mean to use Shading:Site:Detailed, in particular the field Transmittance Schedule Name, but this question is software-agnostic.

(Bonus point if you can find one in Europe)

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answered 2017-04-18 12:41:02 -0600

I found this study which is based on McPherson et al 1985 apparently. It assumes 75% Apr-Oct and 25% Jan-Mar / Nov-Dec.

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That seems like reasonable starting point, there will always be uncertainty related to the type of tree, how it is maintained, and how old it is for the simulation year. Also the size one chooses to model it, it isn't always clear what the shading surface should look like, in some cases I modeled three intersecting octagons on x,y, and z. They were large trees close to the building so horizontal or vertical surface by itself didn't seem right.

David Goldwasser gravatar image David Goldwasser  ( 2017-04-18 13:14:01 -0600 )edit

There's an updated version in 1995 (published 1997) from McPherson, they use 0.7 summer and 0.175 winter.

Julien Marrec gravatar image Julien Marrec  ( 2017-04-19 08:59:38 -0600 )edit

Hi Julien, can you please give us the complete reference of the updated version that you mentioned? there are any new one maybe?

NCB gravatar image NCB  ( 2019-05-09 06:28:25 -0600 )edit

Another question, isn't should have higher values of transmittance the deciduous trees in winter, and not the opposite? i understand that from https://bigladdersoftware.com/epx/doc..., where ... for deciduous trees that have a higher transmittance in winter than in summer...

NCB gravatar image NCB  ( 2019-05-09 06:50:39 -0600 )edit

The study talks about a tree shading factor, which would be the opposite of the transmittance. The study I linked to has a few references to McPherson, the one that matters is called "Simulating tree shadow patterns for building energy analysis", and you will find a 1998 study called "Simulation of tree shade impacts on residential energy use for space conditioning in Sacramento" (cf here) that mentions the 0.7 summer and 0.175 winter factors I put above. McPherson appears to have published a bunch of studies after that too

Julien Marrec gravatar image Julien Marrec  ( 2019-05-13 06:02:38 -0600 )edit

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Asked: 2017-04-18 12:33:00 -0600

Seen: 381 times

Last updated: Apr 18 '17