[Equest-users] Green Roof - eQuest style

Sami, Vikram Vikram.Sami at perkinswill.com
Fri Mar 2 13:13:19 PST 2012
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So I have a 2 part question for the group:


1.       Has anyone compared the results before and after adding a green roof (assuming similar insulation levels in both - because you have to have insulation in a green roof) in eQUEST and in DB/E+? Also - has anyone compared the delta that you get in eQUEST with the Delta that you get in E+?

2.       If so - did you see a significant difference? My guess is no - but I am willing to be convinced. For a well-insulated roof - especially in a building more than a couple of stories, your thermal load through the roof is probably not what's breaking the bank (residential users might be different - I am assuming people who are running Energyplus & eQUEST models aren't doing this for a small house, but a larger building).

3.        As far as I know - the positive effect of green roof constriction is mainly for the lower surface temperature in the summer (the soil material - especially when its wet - is pretty conductive. It does provide thermal mass, but that's less effective outside your insulation). Furthermore - green roofs often use drought resistant plants that resist drought by not evapotranspiring in hot dry months - so you lose some of the benefit there.

Are we obsessing about getting pinpoint accuracy on the answer when the more pertinent question might be - does it really matter & by how much?

Apologies for stirring the pot, but its Friday afternoon and I can hear the beer bottles clinking.

Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com<http://www.perkinswill.com/>
Perkins+Will.  Ideas + buildings that honor the broader goals of society


From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Design Builder USA
Sent: Friday, March 02, 2012 3:10 PM
To: Nick Caton
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Green Roof - eQuest style

As I am an Equest user for appropriate projects, an Energy Plus user for projects that can not be done well in eQuest, and as a representative of Design builder my advise is to use Design builder, (free for a month) to develop your Green Roof project. You will find that design builder has a Green Roof feature built in and that it is not much harder then eQuest.  You can export your project from Design Builder to Energy Plus, in a fashion similar to how you might start with the wizards in eQuest then move on to the detailed mode at the tail end of the project.

Then you can benchmark whatever work around(s) you decide to use in eQuest with the Design Builder/Energy Plus results, or can just use the Design Builder/Energy Plus simulation for your project.

There has been a lot of work put into the Green roof simulation tools of Energy Plus/Design Builder, and I think that using work around in eQuest simply for fear of the unknown land of Energy Plus should not deter you from the prospect, as Design Builder has simplified Energy Plus down to a comparable ease of use to that of eQuest.

Below is the documentation from Design Builder on modeling a Green Roof for your review..








Green Roof

Green roof tab Materials<http://www.designbuilder.co.uk/helpv3/Content/Materials.htm> Dialog



Green roofs can be modelled in DesignBuilder by creating a roof construction using a Green roof material as the outer layer. The green roof can receive water during the simulation from an irrigation system<http://www.designbuilder.co.uk/helpv3/Content/_Site_details.htm#Roof> and/or from site precipitation<http://www.designbuilder.co.uk/helpv3/Content/_Site_details.htm#Site> (defined separately from the hourly weather data). The initial properties of the soil layer are defined on the Green roof tab of the Materials dialog.



Green walls can also be modelled though in this case the irrigation must be treated differently to roofs as walls will not naturally trap much precipitation.



Note that specifying a green roof material as the material for a component block will not work - these only use materials for their reflective properties.


[cid:~WRD000.jpg]Background<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

Use of green roofs (aka ecoroofs or vegetated roofs) is becoming increasingly common for both new and retrofit buildings. There is widespread recognition and a growing literature of measured data that suggest green roofs can reduce building energy consumption. The EnergyPlus Green Roof capability can assist developers and architects in assessing the likely magnitude of energy savings associated with various implementation options (e.g., soil type/depth, irrigation options, plant type). It provides a quantitative and physically-based building energy simulation tool that represents the effects of green roof constructions and facilitates more rapid spread of green roof technologies and make it possible to account for green roof benefits in state energy codes and related energy efficiency standards such as LEED.



The green roof model accounts for:



 *   Long wave and short wave radiative exchange within the plant canopy,

 *   Plant canopy effects on convective heat transfer,

 *   Evapotranspiration from the soil and plants, and

 *   Heat conduction (and storage) in the soil layer



The ability to track moisture-dependent thermal properties is not implemented yet due to stability issues in the CTF scheme, but is under development for use with the finite difference solution scheme made available in EnergyPlus starting in version 2. As implemented in EnergyPlus the green roof module allows the user to specify "ecoroof" as the outer layer of a rooftop construction. The user can then specify various aspects of the green roof construction including growing media depth, thermal properties, plant canopy density, plant height, stomatal conductance (ability to transpire moisture), and soil moisture conditions (including irrigation). The model formulation includes the following:



 *   Simplified moisture balance that allows precipitation, irrigation, and moisture transport between two soil layers (top and root zone).

 *   Soil and plant canopy energy balance based on the Army Corps of Engineers' FASST vegetation models (Frankenstein and Koenig), drawing heavily from BATS (Dickenson et al.) and SiB (Sellers et al.).

 *   Soil surface (Tg) and foliage (Tf) temperature equations are solved simultaneously each time step, inverting the CTF to extract heat flux information for the energy balance calculation. The detailed energy balance analysis and resulting equations, being rather complicated, are summarized here. The interested reader is referred to the FASST documentation cited herein for the complete development. The end result is a set of two simultaneous equations for temperature-one for the soil surface and the other for the foliage.
[cid:~WRD000.jpg]Green Roof Model Description<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

As with a traditional roof, the energy balance of an green roof is dominated by radiative forcing from the sun. This solar radiation is balanced by sensible (convection) and latent (evaporative) heat flux from soil and plant surfaces combined with conduction of heat into the soil substrate. This energy balance is illustrated in the diagram below. The variables introduced in this figure are defined in theEnergyPlus Engineering Document<http://www.designbuilder.co.uk/helpv3/Content/EnergyPlus_Documentation.htm>.



[cid:~WRD000.jpg]

The energy balance for a green roof.



The energy budget analysis follows the Fast All Season Soil Strength (FASST) model developed by Frankenstein and Koenig for the US Army Corps of Engineers. FASST was developed, in part, to determine the ability of soils to support manned and unmanned vehicles and personnel movement. In order to accomplish this, however, FASST tracks the energy and moisture balance (including ice and snow) within a vegetated soil. It is a one-dimensional model that draws heavily from other plant canopy models including BATS (Dickinson et al.) and SiB (Sellers et al.). FASST is implemented in EnergyPlus with only a few modifications to adapt it for use with a relatively thin soil layer.

Green roof data
Height of Plants

The average height of plants in the green roof.

Leaf Area Index (LAI)

This is the projected leaf area per unit area of soil surface. It is a dimensionless number between 0.001 and 5.0. The tables below gives some typical values for LAI.



The table below is reproduced from Global Leaf Area Index Data from Field Measurements<http://daac.ornl.gov/VEGETATION/LAI_support_images.html#table>, 1932-2000



[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>



The table below is reproduced from the PhD Thesis of Chen Yu entitled The intervention of plants in the conflicts between buildings and climate - A case study in Singapore<http://scholarbank.nus.edu.sg/handle/10635/15511>
Plant description

Mean Leaf Area Index (LAI)

Picture

"White flowers, spider lily"

3.07

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Pink flowers"

4.95

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Yellow green leaves"

3.75

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Dark green long blades of leaves/grass"

5.82

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Pinkish red flowers"

2.44

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Fern-like"

6.59

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Palm tree-like"

4.41

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"White flowers with yellow center"

3.21

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Small yellow green leaves"

4.08

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Long big leaves"

5.28

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Orange stems and leaves for those which are taller"

2.15

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"No special features"

3.32

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Light green edges with dark green center leave blades"

5.83

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Red yellow tulip like flowers"

3.04

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Large red leaves"

2.33

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

"Dark green leaf blades"

~0

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

Tree

1.69

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>

Palm tree

2.37

[cid:~WRD000.jpg]<http://www.designbuilder.co.uk/helpv3/Content/GreenRoof.htm?SearchType=Stem&Highlight=Green%7Cgreen%7C%7CRoof%7Croofs%7Croof%7CRoofs>




Leaf Reflectivity

The fraction of incident solar radiation that is reflected by the individual leaf surfaces. Solar radiation includes the visible spectrum as well as infrared and ultraviolet wavelengths. Values for this field must be between 0.1 and 0.4.

Leaf Emissivity

This field is the ratio of thermal radiation emitted from leaf surfaces to that emitted by an ideal black body at the same temperature. This parameter is used when calculating the long wavelength radiant exchange at the leaf surfaces. Values for this field must be between 0.8 and 1.0 (with 1.0 representing "black body" conditions).

Minimum Stomatal Resistance

This field represents the resistance of the plants to moisture transport. It has units of s/m. Plants with low values of stomatal resistance will result in higher evapotranspiration rates than plants with high resistance. Values for this field must be in the range of 50.0 to 300.0.

Max volumetric moisture content of the soil layer (saturation)

Maximum volumetric moisture content of the soil depends on the properties of the soil and in particular the porosity.

Min (residual) volumetric moisture content of the soil layer

The minimum possible volumetric moisture content of the soil layer.

Initial volumetric moisture content of the soil layer

The volumetric moisture content of the soil layer at the start of the simulation. The moisture content will be updated during the course of the simulation based on surface evaporation, irrigation and precipitation.

On Fri, Mar 2, 2012 at 8:38 AM, Nick Caton <ncaton at smithboucher.com<mailto:ncaton at smithboucher.com>> wrote:
Karen,

Thank you very much for the feedback.  I personally don't have the cross-platform experience necessary to share such perspective, and it is not my goal to pretend that I do, just trying to keep our community's mutual efforts to help each other constructive =).

As well as I can predict the weather, I see myself adding EnergyPlus to my toolbox sooner or later as well.  UI issues and other items collectively affecting the time-efficiency of EnergyPlus are what I see as the greatest hurdle for myself and others... more easily dismissed if you have the time to burn, but harder to do so where time is a scarcer resource.

In the meantime, myself and others are in the camp of needing to make do with the tools we are able to use with both accuracy and speed.  I do not mean to argue against learning new tools by sharing suggestions/means to approximate.

Thanks again for the input!

~Nick

[cid:image001.jpg at 01CCF88F.608BD3D0]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036<tel:913.344.0036>
fax 913.345.0617<tel:913.345.0617>
www.smithboucher.com<http://www.smithboucher.com>

From: Karen Walkerman [mailto:kwalkerman at gmail.com<mailto:kwalkerman at gmail.com>]
Sent: Friday, March 02, 2012 8:21 AM
To: Nick Caton
Cc: Nathan Miller; CleanTech Analytics; John Aulbach; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>

Subject: Re: [Equest-users] Green Roof - eQuest style

Nick,

I used eQuest intensively for a time and recently moved most of my modeling to EnergyPlus.  In addition to having more capabilities and being more flexible, EnergyPlus gets regular updates and bug fixes.  EnergyPlus is also a total bear, runs slowly compared to eQuest and doesn't have a fully functional user interface.  I wouldn't recommend it to everybody.

eQuest is very good at modeling buildings that use fairly normal constructions with fairly normal HVAC systems.  I have run into problems when modeling water to water heat pumps, central ventilation systems (with heat recovery), high thermal mass buildings, and dessicant wheels, to name a few.  While I've run into problems with EnergyPlus, I've either been able to resolve the issue with help from the EnergyPlus helpdesk, or, when my issue illuminated an underlying problem with source code, a bug fix was incorporated into the next version.

I understand that eQuest/DOE2 is not receiving funding for updates and bug fixes of eQuest.  A few years ago I tried to start a conversation around updates, bug fixes and feature improvements, and also suggested that we in the modeling community fund some of this effort.  There were quite a bit of responses from users to the "modeling wishlist," but few if any responses to the funding idea.

To extend your carpentry analysis, I think that the eQuest community needs to face the fact that the eQuest saw just isn't capable of cutting some of the species of wood coming into the shop these days.

--
Karen
On Thu, Mar 1, 2012 at 7:03 PM, Nick Caton <ncaton at smithboucher.com<mailto:ncaton at smithboucher.com>> wrote:
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:image001.jpg at 01CCF88F.608BD3D0]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036<tel:913.344.0036>
fax 913.345.0617<tel:913.345.0617>
www.smithboucher.com<http://www.smithboucher.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<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<mailto: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<tel:206-285-7100> | D 206-788-4577<tel: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<tel:503-688-8951>
www.cleantechanalytics.com<http://www.cleantechanalytics.com>


This document may contain valuable information proprietary to CleanTech Analytics which is private and confidential. It may not be shared, copied, stored or transmitted in any form without the prior written consent of CleanTech Analytics


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     Jeremiah D. Crossett
Energy Modeling Consultant
        503-688-8951<tel:503-688-8951>
  www.DesignBuilder.com<http://www.DesignBuilder.com>

[cid:~WRD000.jpg]



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