[Equest-users] Green Roof - eQuest style

[Nathan Miller]

I suppose there is probably some benefit to a green roof, but I've never
tried to claim credit for it. 

 

At least in Seattle's damp climate, when you would most benefit from the
additional insulation of a green-roof-layer (winter) is the same time of
the year the growth medium will be saturated, and likely provide you with
the least insulative value. In the summer, when you would actually want
the heat to escape, the medium will dry out (unless you are irrigating
it). 

 

Soil has an insulative value of only around R-0.104/in (at least according
to a table in the Seattle Energy Code), so even ignoring moisture levels,
it doesn't seem like there is much benefit there. 

 

I suppose in a heavy cooling climate the reflectivity of the plants might
get you some benefit, as well as the evaportative cooling effect if you
are irrigating. Is that where the credit would be? Is there a thermal mass
benefit?

 

Nathan Miller, PE, LEED AP BD+C

Mechanical Engineer/Senior Energy Analyst

O 206-285-7100 | D 206-788-4577

 <http://www.rushingco.com/> www.rushingco.com

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of CleanTech
Analytics
Sent: Thursday, March 01, 2012 7:08 AM
To: John Aulbach
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Green Roof - eQuest style

 

John,

I advise you to use a more modern software that has the ability to
correctly simulate the effects of a Green Roof rather then some wacky
eQuest work around. Professor David Sailor of Portland State University
developed the Green Roof object for Energy Plus that uses a a finite
difference algorithm and works well. The problem with eQuest/DOE2 is that
it is based on a conduction transfer algorithm, and can not really emulate
the effects of a Green Roof. If you need the easy to use inputs, I suggest
Design Builder to generate the Energy Plus file. 

 

Best of luck, and feel free to ask if you need more about EP/DB..

 

On Thu, Mar 1, 2012 at 6:04 AM, John Aulbach <jra_sac at yahoo.com> wrote:

OK, my fellow Raiders of the Lost BTU..

What would be your advice for developing a green roof in eQuest? I am sure
some of you have gone through the USGBC with hopes of getting this
approved.

I eagerly await your suggestions with thanks.

John Aulbach
Partner Energy


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