[Bldg-sim] Modeling a Green Roof

[Drury B Crawley]

This is described in the Engineering Reference (
http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringreference.pdf)
beginning on page 133 of the PDF (page number 89).

It depends on the moisture of the soil, plant cover, air temperature,
rainfall, etc.

On Tue, Jul 13, 2010 at 11:21 AM, Chris Jones <cj at enersave.ca> wrote:

> I am wondering how EnergyPlus handles the effect of saturated soil in
> insulation value; especially in winter when the damp/wet soil would be
> frozen.  I am interested mostly in heating loads.
>
>
> At 07:26 PM 6/26/2010, Drury B Crawley wrote:
>
> From the EnergyPlus Input-Output Reference, the fields describing the green
> roof top layer include:
>  Height of Plants {m}
> Leaf Area Index {dimensionless}
> Leaf Reflectivity {dimensionless}
> Leaf Emissivity
> Minimum Stomatal Resistance (s/m)
>
> (this is on page 183 of the IORef PDF (page number 144):
> http://apps1.eere.energy.gov/buildings/energyplus/pdfs/inputoutputreference.pdf)
>
>
> The Engineering Reference describes the equations beginning on page 114 of
> the PDF (page number 90):
>
> http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringreference.pdf
>
>
>
> On Fri, Jun 25, 2010 at 10:41 AM, Nick Caton <ncaton at smithboucher.com >
> wrote:
>
>
> Open question:
>
>
>
> I’ve ascribed to the “tack an R / thermal mass value onto a new  layer”
> approach in the past… but would appreciate a more nuanced approach if it
> could be done quickly enough.
>
>
>
> I’m curious:  Does EnergyPlus or any other option/model out there account
> the variable shading effects of the foliage on the roof construction, as a
> user might define it?  I’ve speculated this element could be handled
> relatively simply in eQuest using a geometrically adjacent shading surface
> with an annual fractional schedule, but eQuest (to my experience) doesn’t
> have a clean approach to account for the varying thermal mass and insulative
> properties of soil that varies in moisture over time…
>
>
>
> ~Nick
>
>
>
>
>
> NICK CATON, E.I.T.
>
> PROJECT ENGINEER
>
> 25501 west valley parkway
>
> olathe ks 66061
>
> direct 913 344.0036
>
> fax 913 345.0617
>
> Check out our new web-site @ www.smithboucher.com
>
>
>
> From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org<bldg-sim-bounces at lists.onebuilding.org>]
> On Behalf Of Drury B Crawley
> Sent: Friday, June 25, 2010 9:25 AM
> To: bldg-sim at lists.onebuilding.org
> Subject: [Bldg-sim] Modeling a Green Roof
>
>
>
> EnergyPlus has a model for green roofs built in -- based on experimental
> measurements and experience of researchers at Portland State University,
> Prof David Sailor:  http://web.cecs.pdx.edu/~sailor/
>
>
>
>
> ---------- Forwarded message ----------
> From: Jeremy Poling < jpoling at epsteinglobal.com>
> Date: Fri, Jun 25, 2010 at 10:04 AM
> Subject: Re: [Bldg-sim] Modeling a Green Roof
> To: Jason.Boehning at ricegardner.com, bldg-sim at lists.onebuilding.org
>
>
>
> Penn State University ( http://horticulture.psu.edu/cms/greenroofcenter/)
> and Michigan State University ( http://www.hrt.msu.edu/greenroof/) both
> have significant research programs on green roofs.  I would recommend
> looking at the results of the Penn State study on energy transfer in Green
> Roofs (http://etda.libraries.psu.edu/theses/approved/WorldWideFiles/ETD-4616/Thesis_Paulo_Tabares_revised.pdf).  In general, green roofs handle energy through the insulating effects of
> soil, the cooling effects of evapotranspiration in the plants, and water
> flows within the green roof assembly.  This means that a calculated R-value
> will be different depending on the amount of plant material participating in
> evapotranspiration, the wetness of the soil, and whether the roof is
> intensive or extensive.  A straight R-value approach is very simplified and
> should be used with the understanding that model results are much less
> likely to be accurate.  The Penn State study gives a review of published
> literature showing extensive green roofs have R-values between 1.8 and 4.8
> while intensive green roofs have R-values between 5 and 20.
>
>
>
> In general, the average R-value of soil is 0.25 per inch, so for a 12” soil
> depth the R-value of the soil would be R-3 excluding assumptions on soil
> wetness and evapotranspiration.  We typically go conservative and just model
> the R-value of the additional soil since you would need a TRNSYS or MatLab
> model to take into account the other energy benefits of a green roof.
>
>
>
> JEREMY R. POLING, PE, LEED AP
> Associate Vice President,
>
> Senior Sustainability Analyst
> Strategic Services
> Site Solutions | Operations | Sustainability
>
> EPSTEIN
>
> Epstein is a firm believer in sustainability. We ask that you please
> consider the environment before printing this e-mail.
>
>
>
> From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org<bldg-sim-bounces at lists.onebuilding.org>]
> On Behalf Of Fareed Syed
> Sent: Friday, June 25, 2010 8:05 AM
> To: Jason Boehning; bldg-sim at lists.onebuilding.org
> Subject: Re: [Bldg-sim] Modeling a Green Roof
>
>
>
> I heard from our director of sustainability to use R-5 for a typical green
> roof. It was confirmed by few senior architects.
>
>
>
> Thanks,
>
>
>
> Fareed
>
>
>
> From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org<bldg-sim-bounces at lists.onebuilding.org>]
> On Behalf Of Jason Boehning
> Sent: Friday, June 25, 2010 8:46 AM
> To: bldg-sim at lists.onebuilding.org
> Subject: [Bldg-sim] Modeling a Green Roof
>
>
>
> Howdy!
>
>
>
> Has anyone modeled a green roof? I have a standard roof with 12 inches of
> soil and grass. I have been searching the web for thermal properties such as
> U values, thermal absorptivity and so on. Are there any good references to
> find these values or does anyone have tips to model a green roof? I
> appreciate your help.
>
>
>
>
>
> Jason Boehning, EIT
>
> Mechanical Engineer
>
> Error! Filename not specified.
>
> 6161 Savoy, Suite 1212
>
> Houston, Texas  77036
>
>
>
>  v.  713.482.2322
>
>  f.   713.482.2314
>
>  e. Jason.Boehning at ricegardner.com
>
>
>
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> Chris Jones
> 14 Oneida Avenue
> Toronto, ON M5J 2E3.
> Tel.  416-203-7465
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>
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