[Bldg-sim] simulation program for green roof

Joe Huang yjhuang at whiteboxtechnologies.com
Fri Sep 26 12:47:20 PDT 2014

Reposted with better subject line.

On 9/26/2014 11:24 AM, Joe Huang wrote:
> Thanks for providing this link to the paper, which I've read with interest.  However, 
> I'm puzzled because  my primary concern with respect to modeling green roofs is whether 
> and how evapotranspiration has been handled and, unless I missed it in my quick read, I 
> don't see that mentioned in the paper.
> In brief, evapotranspiration is the process by which vegetation sheds excessive heat 
> gain through transpiration, a process akin to sweating in animals for the same reason. 
>  When I had worked with the Urban Heat Island Group at LBNL (before the group got 
> formalized), my main interest was the effect of vegetation on counteracting the urban 
> heat island, and very quickly I got enmeshed with evapotranspiration models both at the 
> individual tree level (too detailed) or at the macro urban level (which I ended up 
> applying in this 1987 paper 
> (http://journals.ametsoc.org/doi/abs/10.1175/1520-0450%281987%29026%3C1103%3ATPOVIR%3E2.0.CO%3B2 
> ).
> In another project that I was then doing on modeling foundation heat flows, I worked 
> with another researcher at the Univ. of Minnesota who had a foundation model including 
> the heat balance of the surrounding soil, who told me that he could get any ground 
> surface temperature he wanted simply by playing around with the evapotranspiration rate 
>  (which is really just the conversion of incoming solar radiation to latent heat).
> Since a green roof is basically a shallow slice of ground with vegetation, wouldn't it 
> make sense to add evapotranspiration to the model (if it doesn't handle it already) 
> before looking for other explanations why measured and modeled results differ?  In my 
> view, attributing these differences to the urban heat island effect is unsatisfying for 
> these reasons: (1) it doesn't explain the cause and effect (although i would suspect 
> that it's precisely the latent cooling of evapotranspiration), (2) it confounds a 
> building-level strategy with a neighborhood-level phenomenon, i.e., you can be in an 
> urban heat island (or oasis) without a green roof, as well as having a green roof 
> somewhere with no urban heat island, (3) I am skeptical that a single green roof would 
> have an appreciable effect on reducing the air temperature above the roof, unless the 
> air is completely still (see 
> http://heatisland.lbl.gov/publications/effects-roof-reflectance-air-temperat ).
> Joe
> White Box Technologies, Inc.
> 346 Rheem Blvd., Suite 205A
> Moraga CA 94556
> yjhuang at whiteboxtechnologies.com  <mailto:yjhuang at whiteboxtechnologies.com>
> http://weather.whiteboxtechnologies.com  for simulation-ready weather data
> (o) (925)388-0265
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> On 9/26/2014 5:45 AM, Jones, Christopher wrote:
>> Link to the paper referred to below:
>> http://www.ibpsa.org/proceedings/BS2011/P_1927.pdf
>> *Christopher Jones**,***P.Eng./
>> /Tel: 416.644.4226 • Toll Free: 1.888.425.7255 x 527
>> *From:*Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of 
>> *hamnmegs at ozemail.com.au <mailto:hamnmegs at ozemail.com.au>
>> *Sent:* Friday, September 26, 2014 4:28 AM
>> *To:* Fred Betz; shahryar habibi; bldg-sim at lists.onebuilding.org 
>> <mailto:bldg-sim at lists.onebuilding.org>
>> *Subject:* Re: [Bldg-sim] simulation program for green roof
>> But do all of these programs account fro the impact on the roof micro climate? None to 
>> my knowledge do. When you get a large roof surface the above roof air temperature bias 
>> can be 2-5DegC between a cool roof (or green roof) and more historical roof (higher 
>> absoprtance). These second order effects become essential to account for if you have 
>> mechanical equipmnt on the roof as ventilation air and condesning temperatures are 
>> impacted. We have been doing some research into this area in Australia. Think about the 
>> urban heat island effect at a micro scale, becomes very important with big box retail, 
>> shopping centres, industrial facilities, airports, maybe hospitals etc. for shopping 
>> centres in Australia with AHUs on the roof, E+, DOE-2.2 and IES only account for 20-25% 
>> of the cool roof benefits via th first order effects. The second order effects due to 
>> the micro climate bias are 3-4 times what is accounetd for within these programs ...
>> We haven't been able to get software developers to bring attention to this so if others 
>> can shake the tree it would be good as the workarounds while possible are quite 
>> involved with a high degree of uncertainty. There is a paper I wrote for IBPSA BS 2011 
>> I can forward when I get back from leave in a few weeks for those interested.
>> Graham Carter
>>     ----- Original Message -----
>>     *From: *
>>     "Fred Betz" <fbetz at aeieng.com <mailto:fbetz at aeieng.com>>
>>     *To: *
>>     "shahryar habibi" <shahryar_habibi at yahoo.com <mailto:shahryar_habibi at yahoo.com>>,
>>     "bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>"
>>     <bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>>
>>     *Cc: *
>>     *Sent: *
>>     Thu, 25 Sep 2014 20:23:22 +0000
>>     *Subject: *
>>     Re: [Bldg-sim] simulation program for green roof
>>     EnergyPlus has a model for green roofs
>>     I’m not sure it handles acoustics, but it will simulate energy and water.
>>     *Fred Betz***PhD., LEED AP ®BD&C
>>     Senior Sustainable
>>     Systems Analyst
>>     5802 Research Park Blvd. | Madison, WI  53719
>>     P: 608.236.1175 | F: 608.238.2614
>>     fbetz at aeieng.com <mailto:fbetz at aeieng.com>  | *www.aeieng.com <http://www.aeieng.com/>*
>>     *From:*shahryar habibi [mailto:shahryar_habibi at yahoo.com]
>>     *Sent:* Thursday, September 25, 2014 9:00 AM
>>     *To:* bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>
>>     *Subject:* [Bldg-sim] simulation program for green roof
>>      Dear Colleagues,
>>     Would you tell me, please, which simulation program can simulate performance of
>>     green roofs.I would be grateful if you
>>     could kindly guide me by offering any information . I am planning to simulate
>>     performance of one the building in terms of
>>     energy and acoustic through green roof.
>>     Thanks in advance for any help and advice
>>     */Shahryar Habibi/*, architect
>>     PhD candidate in  Architectural Technology
>>     University of Ferrara, Department of Architecture
>>     *
>>     <mailto:francesco.guidi at unife.it>*
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