[Equest-users] Scale modeling

[Stefano Moret]

Dear Nick,

Thanks for your suggestions, I totally agree with your points, and I'm conscious of the issues about the "generic guidelines". I'm still surprised by some unexpected results in my models though: I'll work on my models to try to understand the reasons leading to results which are different from the measured ones.

Thanks, Stefano

From: Nick Caton [mailto:ncaton at smithboucher.com]
Sent: Monday, April 09, 2012 3:57 PM
To: Karen Walkerman; Stefano Moret
Cc: equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Scale modeling

...I see my response is arriving too late to the conversation but here are some further thoughts that might help Stefano and others:

I have some parallel experience from which I can build/add to Karen's suggestions.

I have performed studies with similar structure as Karen is suggesting (creating and adding "building blocks" to evaluate building massing options).  However, for Stefano's purposes I would caution to carefully take stock of what questions you are trying to answer and whether an energy model is really the way to go about finding those answers.

Using an energy model to develop generic guidelines with "arbitrary" buildings/spaces for something inherently site/climate/building-geometry-specific  (such as "ideal window wall ratio" or "ideal window properties") is actually a terribly complex endeavor, as I'm sure you are appreciating.  You can ultimately come up with a set of guidelines/spreadsheets/principles to use, but applying such developed guidelines to an actual project for decision-making will always be fraught with accuracy disclaimers  (perhaps that is not the ultimate goal - I'm only throwing this out for consideration).

Guidelines built around generic conditions are indeed useful and have their place (ASHRAE's advanced energy design guides are worth reviewing if you're at the outset of trying to find such results), but should only be relied upon in the context of "I don't want to invest in a site-specific study and the increased accuracy / differing suggestions that may produce."  Evaluating how well any study applies to the project-at-hand is something to always keep in mind.

To cut myself off:  I think my response drafted so far is falling away from Stefano's original question as he's more recently clarifying it, but I'm ultimately driving towards furthering Karen's first line:  Build project-specific models where you need a project-specific answer.

To Stefano's issue of scaling - I am nodding my head vigorously as you're observing how spaces modeled in isolation do not always additively represent a group of spaces modeled together.  It's possible for that to happen under certain circumstances, but the variables in play do not normally scale linearly between an isolated space and a whole building  (consider the ratio of envelope surface area to conditioned volume, for one instance).  A big part of "big picture" modeling differences when compared to "the smaller parts" is the tempering of various loads across spaces and the way that has energy saving effects on HVAC systems in particular .

I would not spend too much time deliberating on such (expected) differences, and would emphasize focusing on the results of isolated or "whole building" models as appropriate to the purpose of your study =).

~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> [mailto:equest-users-bounces at lists.onebuilding.org]<mailto:[mailto:equest-users-bounces at lists.onebuilding.org]> On Behalf Of Karen Walkerman
Sent: Monday, April 09, 2012 4:18 PM
To: Stefano Moret
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Scale modeling

The short answer is that every building is different, and there is no "typical" model that will fit them all.

As you mentioned, the ratio between lighting/cooling/heating changes depending on the size of the building.  I'm willing to guess that this is because the core zones that have very little need for heat get much larger in relation to the perimeter zones.  Also, the building energy needs will change depending on orientation and global location.

I would suggest that you take a slightly different approach - try to come up with values that are representative for different types of spaces.  You might do say:

1.  A perimeter office space with XX% glazing (run for North, East, South and West exposures)
2.  A core office space with no skylights
3.  A core office space with XX% of roof area as skylights
4.  A core manufacturing space???
5,6,7....

Run each model in the applicable climate.  Then, if you have an office building that is 70% core and 30% perimeter space, you'll have a better understanding of the building.  This is still a very rough approximation, but should get you farther than trying to model one "typical" building.

--
Karen


On Mon, Apr 9, 2012 at 4:57 PM, Stefano Moret <smoret at ucdavis.edu<mailto:smoret at ucdavis.edu>> wrote:
Dear all,

I've recently played around quite a bit with E-quest to simulate the effect of dynamic fenestration on building energy consumption.
For these simulations I've been using a very simple office model with a skylight on the top as a test-bed for my calculations (with default system for HVAC and daylighting controls with dimming for lights) but, observing the values I'm obtaining in output, I see that the values I obtain for lighting, cooling and heating consumption make sense relatively, i.e. if compared to themselves in different conditions, but are sometimes of totally different order of magnitude if compared to each other (lighting/cooling loads are often much higher than heating, by orders of magnitude), especially when scaling up the model to bigger sizes. This way, it's very difficult to see the effect of a variable change on the total energy consumption.

I know the model I'm using is very idealized, but is there any variable that I can act on in order to obtain a model which has energy consumption values more similar to a real building? For example, is there a "suggested" size of the building that gives better results? Or maybe simulating a single room in a large building gives more realistic results than the single room alone?
My point is that I would like to have a model whose results in scale might be consistent when applied to bigger buildings.

Thanks for your hints and suggestions,
Stefano

--

Stefano Moret
California Lighting Technology Center<http://cltc.ucdavis.edu/>
University of California, Davis
633 Pena Drive
Davis, CA 95618
530-747-3846<tel:530-747-3846>
smoret at ucdavis.edu<mailto:smoret at ad3.ucdavis.edu>


_______________________________________________
Equest-users mailing list
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20120409/75bd19d4/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 1459 bytes
Desc: image001.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20120409/75bd19d4/attachment-0002.jpg>