[Equest-users] Effect of reflectivity on building energy consumption

Nick Caton ncaton at smithboucher.com
Mon Oct 1 11:01:13 PDT 2012

Hi Nimesh,

You haven't fully described your goal/purposes for this case study... but here are a few thoughts that might help you and others performing similar case studies:

1.       If you wish to compare 3 alternatives for exterior envelope materials/finishes, representing a wide range of absorptance values, your study may be more accurate to first define those material options (i.e. brick vs. glass vs. aluminum...) and then consider modeling distinct emissivity values for each.  Emissivity is a surface property for eQuest (separate from construction).  Suggested reading attached - check out the different discussions for interior & exterior emissivity for examples.  There's also a large table of Absorptance values for different materials you may find helpful for your present study.

2.       You described your model as a "simple room," suggesting this is a more abstract study & not specific to an actual project.  From experience, selecting a "consumption savings" metric for your results, while perhaps easiest for you initially, can be misleading for such abstract cases and cause you more work in presentation.  If such results are extrapolated or assumed to apply directly to a specific building, with different system or different physical proportions (window/wall/roof area ratios), there's a good chance the results of a study of this nature can mislead.   The general caution here is to consider your audience first (how do they want to interpret/use this information?), and present your results in a fashion that clearly explains what the results do and do not represent.  Choosing to report with a different metric, perhaps specific to envelope load reductions, might make that task easier.

3.       Regarding installed interior lighting: thermal envelope performance and lighting design are two separate topics that require distinct tools/software/approaches to analyze.  If you wish to evaluate the effects of interior finish reflectances (if any) on installed wattage, you are better off engaging a lighting designer or undertaking your own photometric study to produce those results.  eQuest can of course incorporate such results after the fact if desirable.  This particular query is inherently space/project specific however so it may not be appropriate to incorporate into a purposefully abstract study.  In short, for an abstract model that's not intended to be project-specific, you are probably better off holding installed watts constant for lighting.  Otherwise, incorporating the effects on installed watts should involve a separate evaluation to determine what extent the finishes will affect installed watts.  It may be helpful to note eQuest has capacity to model daylight harvesting system behavior for simple space/fenestration configurations provided sufficient inputs (GIGO).  Interior reflectances have a more direct effect on such systems, but that's also a project-specific study unto itself.

Ultimately the model is in the hands of the modeler, and these are your considerations & decisions to make.  I hope this provides some food for thought!

[cid:489575314 at 22072009-0ABB]


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

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nimesh Prajapati
Sent: Saturday, September 29, 2012 8:37 PM
To: 'RobertWichert'; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Effect of reflectivity on building energy consumption

Dear Robert Wichert,

Yes, that is what the results telling and as per common logic we feel that it is ok. But my Question is - Am doing it correctly with my goal? or there is another approach do in eQuest? Or Whether we can have better option with another software?

While modeling the cases I had kept the interior electrical loads - Watts/sqft constant for each case study. But Whether changing absoptivity will affect the interior lighting also?


Nimesh Prajapati

HVAC Design Engineer  & Energy Modeler
(+91 9687133492)
email: nimesh at engineersaid.com<mailto:nimesh at engineersaid.com>
Skype: nimonicsone
P Please consider the environment before printing this e-mail.

From: RobertWichert [mailto:robert at wichert.org]
Sent: Saturday, September 29, 2012 8:22 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Effect of reflectivity on building energy consumption

Dear Nimesh Prajapati,

It looks like your gas consumption went DOWN with increased absorptivity.  This makes sense to me since the building will absorb more solar heat and keep itself warm.

It looks like your electric consumption went UP with increased absorptivity.  This also makes sense since the building heat loads are increased by the additional solar heat.

Am I getting this correct?

Robert Wichert P.Eng. LEED AP BD&C

+1 916 966 9060

FAX +1 916 966 9068

On 9/29/2012 2:37 AM, nimesh.prajapati wrote:
Dear Friends,

I have typical case study and friendly saying I don't know whether I am in correct direction or not, so requesting you to please guide me.

I am trying to analyse effect of reflectivity on building energy consumption. What I had done is as per followings:

1.       For simple room created in eQuest I had kept all other parameters same.

2.       I had taken three case study (Case-01, Case-02, Case-03 ) by changing the parameters as mentioned in the attached sheet. (Changed parameters are marked as blue)

3.       Then I have the output results as attached in the sheet.

4.       Results shows that as absorptivity increases there is saving in cooling but heating have reverse effect.

Can anybody help me out? I am trying on myself and will like to have guidance from you friends.


Nimesh Prajapati

(+91 9687133492)
HVAC Design Engineer & Energy Modeller
[Description: Description:                C:\Users\nimesh.prajapati\Desktop\CADD.jpg]
P Please consider the environment before printing this e-mail


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