[Equest-users] External wall area for simulation
Bishop, Bill
wbishop at pathfinder-ea.com
Tue Mar 1 11:04:29 PST 2011
[If you are not interested in one-dimensional heat transfer through
insulated pipes - delete this message and attachment.]
Dan,
I looked this up after Michael's message. Heat transfer from an
insulated pipe occurs by conduction through the insulation (which you
described below) and convection with the surrounding air (and through
radiation from the insulation surface, which can usually be neglected).
For small diameter tubes or wires, and for small convection
coefficients, it is possible for a small amount of insulation to
increase heat transfer. Once the insulation reaches a critical
thickness, any additional insulation decreases the heat loss. The
attached example is from "Fundamentals of Heat and Mass Transfer, Fourth
Edition" by Frank Incropera and David DeWitt. Note that the example
mentions that, "In a plane wall the area perpendicular to the direction
of heat flow is constant and there is no critical insulation thickness
(the total resistance always increases with increasing insulation
thickness)."
Regards,
Bill
William Bishop, PE, BEMP, LEED(r) 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 Daniel
Knapp
Sent: Tuesday, March 01, 2011 1:25 PM
To: Michael Hardy
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] External wall area for simulation
Since the area of the outside surface of the insulation scales with the
thickness of the insulation (surface area = 2*Pi*L*radius), I don't see
how it is possible to increase the heat loss by adding insulation to a
pipe. The formula for radial heat flow from the inside to the outside
of a cylinder is given by Q = [2*Pi*k*L (T_i - T_o)] / [Ln(r_o/r_i)],
where k is the thermal conductivity, L is the length of the cylinder,
T_i is the inside temperature, T_o is the outside temperature, r_o is
the outside radius, r_o is the interior radius. As the thickness of the
cylinder increases (that is, as r_o increases) the radial heat flow will
decrease as 1/Log(r_o).
Cheers,
Dan
-
Daniel Knapp, PhD, LEED(r) AP O+M
danielk at arborus.ca
Arborus Consulting
Energy Strategies for the Built Environment
www.arborus.ca
76 Chamberlain Avenue
Ottawa, ON, K1S 1V9
Phone: (613) 234-7178 ext. 113
Fax: (613) 234-0740
On 2011-03-01, at 10:47 AM, Michael Hardy wrote:
As Nick previously mentioned, you may need to use different areas for
different aspects of the project (lighting, PV, energy, ventilation,
etc.) For the energy modeling portion, you should probably talk to your
project design engineer as the building construction you describe is a
bit unusual.
Going back to the fundamental heat flow equations that simulations use,
the heat flow calculation is based on some area and includes outside
and inside air films, wall assembly construction, material properties,
heat transfer path, etc. For your specific building, the thermal
properties of the wall material may not offset the additional wall areas
due to the thickness of the wall. In a normal size building, the wall
area of the corners is usually small in comparison to the total wall
area so the corner details become negligible. Since you've said the
building area changes by 4% when you include the wall thickness, you are
correct to raise the question. I think the question needs to go back to
the design engineer who is familiar with your specific building
construction.
In a very simple example, when specifying insulation for piping, it is
actually possible to increase the heat-loss by adding too much
insulation because of the increase in surface area relative to the
insulation thickness. I know your building is not a pipe (and probably
not round) but this simple example just goes to show how important it is
to understand the limitations of the equations being used and not assume
that what is negligible for 8-12" thick wall construction, is also
negligible for 24" thick wall construction.
Regards,
Michael Hardy, PE, F.NSPE
Sr. Mechanical Engineer
Black Oak Engineering, Inc.
Cell 503.314.5244
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Praveen
Jain
Sent: Tuesday, March 01, 2011 4:44 AM
To: Nick Caton
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] External wall area for simulation
Thanks Nick for good explanation.
Actually in my project we are using almost 2ft wide external walls to
get the effect of thermal mass. if I consider external wall area in
eQUEST model my area deviation is almost 4% and mismatch in conditioned
area is more than this. So project energy consumption would be more and
also not able to match TR for the project.
Actually we are also planning to go for 2.5% renewable energy credit, if
I consider external wall than PV cost would be more.
Can I exclude external wall area for eQUEST modeling ?
--
With Thanks and Regards
Praveen
On Mon, Feb 28, 2011 at 10:02 PM, Nick Caton <ncaton at smithboucher.com>
wrote:
Hi Praveen,
I've copied below a discussion from some time back outlining my general
practice for "where to draw the line" when it comes to envelope/wall
boundaries. This may be generally useful and seems to answer at least
part of your inquiry.
When I'm doing electrical and/or HVAC design alongside the model, my
area takeoffs for each inevitably will match up, because I hate doing
the same work twice.
I use the outermost surfaces when defining my building footprint and
midpoints for all internal partitions for all calcs. Space-by-space LPD
calcs in a strict reading do not require the space areas to be measured
to the outermost surface of an exterior wall (they do say to use the
midpoint of interior partitions, as of 90.1-2007). I'd feel comfortable
saying the extra square-footage "handicap" I'm imposing on myself as a
lighting designer is an insignificant fraction in 99.9% of cases when
determining baseline LPD...
Inevitably, areas summed for all spaces in a building between
architects, HVAC, and lighting designers will not match - that's a fact
of life and in my book that's okay, so long as nobody is way off. Model
reviewers will inevitably/reliably gripe when the numbers don't match
exactly, and it's usually an easy thing to either fix or explain after
the fact. If you to try to make everyone use the same numbers from the
DD/CD design phases, you've chosen a losing battle. For my part in the
role of the project's energy modeler, I'm satisfied to allow my fellow
designers do their own calcs, and just ensure nobody is way off along
the way... quibbles over small differences in the final tallies, if they
come up, are easy to reconcile.
~Nick
Error! Filename not specified.
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 <http://www.smithboucher.com/>
From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of Praveen Jain
Sent: Monday, February 28, 2011 3:37 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] External wall area for simulation
Dear All
While modeling in eQUEST should we include external wall area or not?
While creating single line diagram I exclude external wall and draw sld
on inner of external wall to match conditioned area.
But for lighting power density calculation ASHRAE 90.1 user manual
suggest to including external wall area.
We are getting mismatch in area calculation for all HVAC, Lighting and
Architectural design sides.
Can anyone suggest what correct way of modeling in eQUEST ?
--
With Thanks and Regards,
Praveen K. Jain
Roorkee
From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Wednesday, August 04, 2010 1:20 PM
To: John Aulbach; Nijenmanting, F.C.; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] area of (internal) partitions
Filique,
This sounds a lot like a question I brought up when I was getting
started with eQuest and energy modeling in general: What is "standard
practice" regarding where the inter-zonal and footprint boundaries are
defined, relative to actual wall thicknesses? The quick answer is that
there aren't any hard/fast answers to this. It was a good discussion
and is probably archived in [bldg-sim] if anyone cares to dig around...
In short:
1. eQuest areas correspond to the polygons used to define the
floor areas/building footprint. These polygons are defined by the
shapes defined or traced from a CAD file in the wizards. I'm pretty
sure (someone correct me if I'm wrong) the floor area taken up by
internal partitions (which have thickness) on the floor slab is NOT
subtracted from the total area, so if you double the thickness of your
internal partitions you will not see a change reflected in space areas.
This is normally not a big deal in the context of thermal modeled
behavior, but if you have many unusually thick partitions (1ft or more
deep), you might want to either account for them by modeling them as
unconditioned zones between spaces.
2. Regarding "best practice," here's a set of general guidelines
that would apply to various loads & modeling software packages (beyond
eQuest), prioritizing the interest of modeling with thermal accuracy:
a. Define interior partitions using the midpoint between the two
surfaces. This is generally not terribly critical - I will take small
liberties on this to reduce the number of vertices and simply actual
internal zones.
b. Define the building footprint areas using the outermost surface.
This is more important as you want to accurately model the actual amount
of surface area subject to exterior loads.
c. Define top of each zone (in the z-axis) using the top surface
elevation the respective floor or roof construction.
3. On a related note, this ties into the general advice to not use
energy modeling programs with the intent to create perfect 3D
representations of your buildings. If you need a pretty picture, they
make 3D modeling software for that purpose. When it comes to building
geometries, simplicity is a virtue, and ASHRAE will even back you up on
that one (re: 90.1 User's Manual). Avoiding overly-accurate building
geometries lets you spend more time modeling the more critical building
elements of a building's energy behavior (loads/systems/schedules/etc).
Best wishes,
~Nick
Error! Filename not specified.
NICK CATON, E.I.T.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
Check out our new web-site @ www.smithboucher.com
<http://www.smithboucher.com/>
From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of John Aulbach
Sent: Wednesday, August 04, 2010 12:15 PM
To: Nijenmanting, F.C.; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] area of (internal) partitions
Filique:
Can you rephrase your question, please? I don't understand how doubling
the size of your internal partitions decreases your floor area. The
eQuest floor areas are (to my undestandinding), from the outside of
outside walls to the "outside" of any internal partitions IN THE SPACE
THAT PARTITION RESIDES. You can have only one internal wall separating
two adjacent spaces.
Others may comment.
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: "Nijenmanting, F.C." <F.C.Nijenmanting at student.tue.nl>
To: "equest-users at lists.onebuilding.org" <
equest-users at lists.onebuilding.org>
Sent: Wed, August 4, 2010 12:15:19 AM
Subject: [Equest-users] area of (internal) partitions
Hello all,
I have a question about the area which is calculated by equest.
Does it take into account the width of internal partitions?
In reality, if I would double the size of my internal walls, my actual
floor area decreases.
But I could not find differences in the floor area calculated by Equest
if I change the thickness of my walls.
A similar question accounts for the external partitions. For drawing the
ground plan, should I therefore take the internal boundary, external
boundary or middle line?
Kind regards,
Filique
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--
with regards,
Praveen K. Jain
Roorkee
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