[Equest-users] Green Roof - eQuest style

[Nick Caton]

Jeremiah,

While dumping eQuest entirely and (re?)starting a project using different software may certainly be a viable solution, I think it's reasonable to assume someone posting a "how do I do this in eQuest" question in forum titled [Equest-users] is probably not looking for such answers first!  I personally understand EnergyPlus is often the tool-of-choice for green-roof specific research, but let's avoid telling a carpenter to throw away his hand saw just because power tools exist ;).

John,

eQuest can certainly *approximate* green roofs, to varying degrees of accuracy.  There were a couple long, informative, and unfortunately disjointed conversations on this exact topic held over the [bldg-sim] list some time ago.  I'm attaching those messages including various attachments and white papers here in a zip file - if you can move these into a folder in outlook or similar you may find it easier to follow the flow of the conversation...

Read up on what's been discussed so far, and I'm certain you'll be able to decide for yourself how comfortable you are using eQuest for your current project ;).

Regards,

~Nick
[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nathan Miller
Sent: Thursday, March 01, 2012 10:18 AM
To: 'CleanTech Analytics'; 'John Aulbach'
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Green Roof - eQuest style

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

From: equest-users-bounces at lists.onebuilding.org<mailto: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<mailto: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<mailto: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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--
Jeremiah D. Crossett
CleanTech Analytics
503-688-8951
www.cleantechanalytics.com<http://www.cleantechanalytics.com>

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