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[bldg-sim] Green Roofs

I finally got around to reading this interesting paper. It is too bad that someone didn't check the energy simulation results more closely. In Table 1, Part 6, the total for the fourth row is incorrect.
I am wondering about the assumed R-30 value for the "green roof" average insulation value over the entire year. If you examine the winter heat flux diagrams, there difference in total flux for heating days is quite small between the reference and green roofs. I think that assuming an R-30 heating insulation value is too optimistic.
In terms of heating, cooling, and heat island effects, and $cost how would the green roof compare with an R-30 conventional roof with a low-emissivity finish? 


At 11:53 28/02/2005, Ferguson, Alex wrote:

The Institute of Research and Construction (IRC, part of the National
Research Council of Canada) has conducted a fair amount of research in this
area. Much of this work, including hydrology modelling, experimental
investigations and Visual DOE simulations, is summarized in the following
report:

http://irc.nrc-cnrc.gc.ca/fulltext/nrcc46737/

...
Alex Ferguson
CANMET Energy Technology Centre
Natural Resources Canada
P:+1 613 995 3294
F:+1 613 996 9909
Alex.Ferguson@xxxxxxxxxxx




-----Original Message-----
From: postman@xxxxxxxx [mailto:postman@xxxxxxxx]On Behalf Of Brian Thornton
Sent: Monday, February 28, 2005 11:40
To: BLDG-SIM@xxxxxxxx
Subject: [BLDG-SIM] Green Roofs



One issue with Green Roofs that has come up, is analyzing potential energy
savings benefits from evaporation, and plant evapo-transpiration.  There is
at least one program out there that apparently addresses this.

1)       Are there opinions on whether these effects generate credible
supportable energy savings from typical green roof installations?

2)       Does anyone know of a standard methodology that could be
incorporated in a broad energy simulation such as eQuest?

3)       Has anyone received approval from USGBC or a utility incentive
program to claim energy savings from these effects, and if so what kind of
documentation was used?

Thanks-Brian Thornton

Thornton Energy Consulting
p. 503-231-6600 f. 503-231-3555
thorntonenergy@xxxxxxxxxxx




From: postman@xxxxxxxx [mailto:postman@xxxxxxxx] On Behalf Of Nikhil Kapur
Sent: Tuesday, February 22, 2005 2:40 PM
To: BLDG-SIM@xxxxxxxx
Subject: [BLDG-SIM] Green Roofs

Hi  Dan,

You can use a reflectance of 0.70 or greater i.e. absorptance of 0.3 or less
for the roof. Also the effect of the U-value of the roof construction will
change so you will have to set a multiplier for the u-vlaue of the roof.
This can be referenced in the ASHRAE 90.1 - 1999 Users manual in the
Building Envelope section - page 5-20 table 5-E which gives the Roof
U-factor multipliers for the various climate zones.

Regards,

Nikhil



Dan Sobrinski <sobrinski@xxxxxxxxxxxx> wrote:
Hi,

I am looking for some advice on modeling a green roofin Equest.
Specifically, what should I set Surface Roughnessand Ext. Color
(absort)too?  Are there any other parameters that need to be modified to
simulate a vegetated roofing system?

Thanks in advance

Dan Sobrinski, CEM, LEED AP
Associate Engineer
Econergy International Corporation
3825 Iris Avenue, Suite 350
Boulder, CO  80301
303-473-9007  voice
303-473-9060  fax
sobrinski@xxxxxxxxxxxx



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