[Bldg-sim] Modeling a Green Roof

Chris Jones cj at enersave.ca
Tue Jul 13 08:21:42 PDT 2010
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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>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>http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringreference.pdf
>
>
>
>On Fri, Jun 25, 2010 at 10:41 AM, Nick Caton 
><<mailto:ncaton at smithboucher.com>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 @ 
><http://www.smithboucher.com/>www.smithboucher.com
>
>
>
>From: 
><mailto:bldg-sim-bounces at lists.onebuilding.org>bldg-sim-bounces at lists.onebuilding.org 
>[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Drury B Crawley
>Sent: Friday, June 25, 2010 9:25 AM
>To: <mailto:bldg-sim at lists.onebuilding.org>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/>http://web.cecs.pdx.edu/~sailor/
>
>
>
>
>---------- Forwarded message ----------
>From: Jeremy Poling 
><<mailto:jpoling at epsteinglobal.com>jpoling at epsteinglobal.com>
>Date: Fri, Jun 25, 2010 at 10:04 AM
>Subject: Re: [Bldg-sim] Modeling a Green Roof
>To: 
><mailto:Jason.Boehning at ricegardner.com>Jason.Boehning at ricegardner.com, 
><mailto:bldg-sim at lists.onebuilding.org>bldg-sim at lists.onebuilding.org
>
>
>
>Penn State University 
>(<http://horticulture.psu.edu/cms/greenroofcenter/>http://horticulture.psu.edu/cms/greenroofcenter/) 
>and Michigan State University 
>(<http://www.hrt.msu.edu/greenroof/>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>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: 
><mailto:bldg-sim-bounces at lists.onebuilding.org>bldg-sim-bounces at lists.onebuilding.org 
>[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Fareed Syed
>Sent: Friday, June 25, 2010 8:05 AM
>To: Jason Boehning; 
><mailto:bldg-sim at lists.onebuilding.org>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: 
><mailto:bldg-sim-bounces at lists.onebuilding.org>bldg-sim-bounces at lists.onebuilding.org 
>[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jason Boehning
>Sent: Friday, June 25, 2010 8:46 AM
>To: <mailto:bldg-sim at lists.onebuilding.org>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. <mailto:Jason.Boehning at ricegardner.com>Jason.Boehning at ricegardner.com
>
>
>
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Chris Jones
14 Oneida Avenue
Toronto, ON M5J 2E3.
Tel.  416-203-7465
Fax. 416-946-1005

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