[Bldg-sim] [Equest-users] Ground/Water reflectance

Wed Dec 8 08:36:47 PST 2010

Thanks for sharing Alex =).

Regarding that concern I voiced between visible and other wavelengths... I dug a little and found a resource supporting the notion.  See the color chart near the bottom of the following link that plots water absorption coefficients against the electromagnetic wavelength spectrum - visible light is absorbed by water much less than other wavelength ranges.  http://www.lsbu.ac.uk/water/vibrat.html

Again, I brought this up for two purposes:  To suggest a reason why the DOE2 help files list an albedo of 0.05 for the ocean (unqualified with a frequency range like "visible light," 'albedo' generally refers to the full electromagnetic spectrum), and as a reason to caution that a majority of the sun's energy which might otherwise produce a solar heat gain on a building envelope may fall outside the visible range, and thus would be subtracted out of what's reflected to your building if you're talking about a body of water.  Again, I'm no physicist but I know enough to suggest caution.

If you're modeling daylighting controls, the lake could certainly be modeled as a surface with a reflectance in the 90%+ range at low incident angles (sunrise/sunset), but if you're trying to account for additional envelope thermal loads reflected from a lake, I think your albedo figure should never fall in that range (unless, again, the lake is covered with snow), and that figure further might not vary appreciably with the incident angle... 

***

Calculating seasonal sun angles for a specific latitude/longitude as a separate topic can be a tricky business - but there a number of free and for-cost tools that do all the legwork for you.  

Here's one example of a free, simplistic tool to get angles at a specific time/location:  http://solardat.uoregon.edu/SolarPositionCalculator.html

A tangent tip: you can right-click anywhere in google maps and select "what's here" from the context menu to get the exact latitude and longitude for your location.

~Nick

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

From: Alex Krickx [mailto:akrickx at seriousmaterials.com] 
Sent: Tuesday, December 07, 2010 9:08 PM
To: Nick Caton
Subject: RE: [Equest-users] Ground/Water reflectance

Hi Nick,

Thanks for the in depth response (as always!).

I'm working off of this website: http://www.atmosphere.mpg.de/enid/3rv.html 

Which shows how reflectance of water changes with the sun's angle.

The late afternoon sun (in winter) could have reflectance of as much as 35%... It looks like late afternoon in summer just doesn't have that high of sun angles which I found surprising.

I'm still trying to get my head around the whole thing, but figured I'd share the link with you.

In my readings I didn't see where it said that water would absorb infrared while reflecting visible wavelengths. Working with glass and Low-E coatings, I have some idea of how different wavelengths interact differently with different materials (but I'm also not an astrophysicist). In any case, it's been interesting reading people's viewpoints on this one. 

Cheers,

Alex 

From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: Tuesday, December 07, 2010 12:23 PM
To: Alex Krickx; Bishop, Bill; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Ground/Water reflectance

Hey Alex,

I hate to muddy the waters further, but I'm pretty sure the visible light spectrum (a small band of the sun's energy) does not behave identically to the rest of the electromagnetic spectrum regarding how much energy is reflected for a given incidence angle on water...  

To voice my concern another way:  sunlight bounced from a lake in the morning/evening may well effectively double the amount of visible light energy incident on a building façade for a certain hour, but this would likely not result in a corresponding doubled thermal solar load - energy at frequencies above/below the visible light spectrum may be more prone to simply dive into the lake...

I understand the term 'albedo' in the context of collected weather data / energy modeling generally refers to the full spectrum of the sun's energy (light inclusive), and you might trip yourself up by assuming terrestrial surface albedo is the same thing as surface reflectivity, for light.  

(good catch-up reading with examples:  http://en.wikipedia.org/wiki/Albedo)

Water bodies do have a really low albedo - not because they do not reflect light, but mostly because they suck up the rest of the electromagnetic spectrum really well.  If on the other hand your lake freezes and is covered with snow during the winter, I'd expect the sun's full spectrum of energy to bounce much more effectively to your cozy lakehouse =). 

PS:  I am no astro-physicist, nor am I a meteorologist... I'm only throwing out some cautions/thoughts from what I've picked up here and there on the topic...

~Nick

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

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 Alex Krickx
Sent: Tuesday, December 07, 2010 1:13 PM
To: Bishop, Bill; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Ground/Water reflectance

So changing it to 0.05 to try to account for the reflectance of the water, would actually decrease the reflected solar heat... 

Hmmm. I'll play with some different values in eQUEST and see how much ground reflectance impacts consumption, and keep in mind the 0.05 value.

Thanks for everyone's quick and thoughtful responses. 

Cheers,

Alex

From: Bishop, Bill [mailto:wbishop at pathfinder-ea.com] 
Sent: Tuesday, December 07, 2010 11:08 AM
To: Alex Krickx; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Ground/Water reflectance

Alex,

The default ground reflectance is 0.20. You have to enter a different value for it to appear in the inp file.

Bill

________________________________

From: Fleming, Joe [mailto:joe.fleming at tlc-eng.com] 
Sent: Tuesday, December 07, 2010 2:03 PM
To: Alex Krickx; Bishop, Bill; John Aulbach; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Ground/Water reflectance

The albedo of an ocean should probably equal that of a lake on an average basis throughout the day (not a peak hourly basis).  The radiation reflected by water is very low when the incident wave is perpendicular to the surface of the water, and it approaches 100% as the angle of incidence approaches 90 degrees (morning and evening).  As the waves move through the water the incident angle of each zone of water will vary from 0-90 degrees on a constant basis and the reflectance should roughly average out to equal that of a still body of water.  

For a lake, in the late afternoon, the reflectance will increase from 0.05 to 0.1 or 0.2.   Later in the evening it will reach closer to 0.8 or 0.9, but at this time the radiation intensity from the sun drops off significantly.

To model the lake on one side is a challenge, your peak loads may not change but your annual consumption may.   If eQuest uses the gnd reflectance values as a multiplier of solar radiation, it may be worth running a few iterations with different values of gnd reflectance to see the results.

Joe Fleming

E.I., LEED AP BD+C, BEMP

Mechanical Engineer I

TLC Engineering for Architecture
Your 2030 Challenge Partner

800 Fairway Drive, Suite 250

Deerfield Beach, FL 33441-1816

phone: 

954-418-9096

fax: 

954-418-9296

direct: 

954-418-4591

website: 

www.tlc-engineers.com

  <http://www.tlc-engineers.com/> 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Alex Krickx
Sent: Tuesday, December 07, 2010 1:28 PM
To: Bishop, Bill; John Aulbach; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Ground/Water reflectance

Thanks Bill and John for your responses. 

I guess I would expect that the ocean would be a bit more "turbid" (seems appropriate) - but what about for buildings facing a lake or harbor where the water is calmer? Perhaps the additional reflected solar gain is negligible, but my gut tells me that is not the case. 

This project is a retrofit and they talked of having intense heat along the facades facing the water. Perhaps it's more due to the tinted single-pane glass that gets hot (?) but my initial thought was the water is the culprit.

Is it possible to create a 2d shape in the ground plane south of the building, and apply the reflectance to that, or do I need to apply it to the whole ground?

I looked through a previous project and didn't see the term "GND-REFLECTANCE" anywhere in the inp or pd2 files. Is the default to have a ground-reflectance of 0? If so, I guess I'll run one case with 0, and one with 0.05... although I doubt there will be much difference between the two.

Thanks again - any other thoughts on this are much appreciated.

Kind regards,

Alex Krickx

Alex Krickx

Building Energy Specialist

1250 Elko Dr, Sunnyvale, CA 94089

(t) 408.541.8124

Warning: The information contained in this e-mail may be privileged attorney-client communications or attorney work product and/or proprietary and confidential.  If the reader of this message is not the intended recipient then you have received it in error and any review, distribution or copying of this message is prohibited and you are to notify us immediately by reply e-mail and delete the original message immediately.

From: Bishop, Bill [mailto:wbishop at pathfinder-ea.com] 
Sent: Tuesday, December 07, 2010 7:20 AM
To: John Aulbach; Alex Krickx; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Ground/Water reflectance

Alex,

Exterior surfaces have a "Ground reflectance" property - GND-REFLECTANCE, accessible through the Daylighting - Shading - Other tab of the exterior surface. Reading the DOE-2 Help description, the reflectance value for "ocean" is 0.05, implying that most solar radiation is absorbed, not reflected. I'm guessing that the visual glare we perceive does not increase the solar load as much as we would think. Sea monsters do not seem to have been considered by the DOE-2 team.

Regards,

Bill

William Bishop, PE, BEMP, LEED® AP | Pathfinder Engineers & Architects LLP

Mechanical Engineer

 134 South Fitzhugh Street             Rochester, NY 14608
T: (585) 325-6004 Ext. 114            F: (585) 325-6005

wbishop at pathfinder-ea.com           www.pathfinder-ea.com <http://www.pathfinder-ea.com/> 

P   Sustainability - the forest AND the trees. P  

________________________________

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John Aulbach
Sent: Monday, December 06, 2010 8:35 PM
To: Alex Krickx; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Ground/Water reflectance

Alex:

I wonder if the turbidity (word ??) of the water will actually not make a difference. Any harbor will have boats, wind effects, and an occasional sea monster disturbing the "glass" water.

Only in paintings ???

John R. Aulbach, PE, CEM

Senior Energy Engineer

________________________________

Partner Energy

1990 E. Grand Avenue, El Segundo, CA 90245
W: 888-826-1216, X254| D: 310-765-7295 | F: 310-817-2745

www.ptrenergy.com <http://www.ptrenergy.com/>  | jaulbach at ptrenergy.com <mailto:%7C%20jaulbach at ptrenergy.com> 

________________________________

From: Alex Krickx <akrickx at seriousmaterials.com>
To: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Sent: Mon, December 6, 2010 5:11:24 PM
Subject: [Equest-users] Ground/Water reflectance

Hello everyone,

I've got a building that is located at the edge of a harbor with the water directly to the south of it. How do I model a reflective surface on the ground that represents the harbor? I feel this is key to include, as this reflectivity will send additional heat through the windows. I looked through the archives but didn't see anything related to ground reflectivity.

If anyone knows how to create reflective objects and/or an appropriate value of reflectivity for water in eQUEST, that would be most helpful.

Thanks in advance!

Regards,

Alex Krickx

Alex Krickx

Building Energy Specialist

1250 Elko Dr, Sunnyvale, CA 94089

(t) 408.541.8124

Warning: The information contained in this e-mail may be privileged attorney-client communications or attorney work product and/or proprietary and confidential.  If the reader of this message is not the intended recipient then you have received it in error and any review, distribution or copying of this message is prohibited and you are to notify us immediately by reply e-mail and delete the original message immediately.

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