[Bldg-sim] Thermal bridges

[David Reddy]

The 90.1 user's manual briefly touches on modeling uninsulated and minor 
uninsulated assemblies; here are some snipets from the section that 
describes modeling for PRM:

/All uninsulated assemblies shall be explicitly modeled. Examples 
include projecting balconies, perimeter edges of intermediate floor 
slabs, concrete floor beams over parking garages.//All//
//uninsulated assemblies shall be separately modeled using a separate 
description of each of these assemblies within the energy simulation 
model, or the area-weighted average U-factor based on separate 
calculation of the U-factor for each of these assemblies. The latter 
approach may only be used for assemblies with similar thermal mass/
...
/Provided that these assemblies are insulated, the method allows any 
envelope assembly that covers less than 5% of the total area of a given 
assembly type (e.g., exterior walls or roofs) to be added to an adjacent 
assembly of the same type with the same orientation and the same thermal 
properties. This is not intended, however to allow framing members in 
walls to be ignored  just because they have an area less than 5%./

There are some graphics that help illustrate the recommendations.

- David


On 11/26/2012 3:35 PM, Christian Cianfrone wrote:
>
> LEED is no more specific than ASHRAE 90.1, which is not very specific 
> on thermal bridges other than those occurring in the assembly (studs, 
> cladding attachments, etc).  It is not specific about thermal bridges 
> such as slabs, shelf angles, parapets, etc.
>
> Aside from LEED, standard linear transmittance values are available 
> for common North American details, as per ASHRAE 1365-RP.  Our company 
> authored the report, which can be found here:
>
> http://www.morrisonhershfield.com/ashrae1365research/Pages/Insights-Publications.aspx
>
> *Christian Cianfrone, M.A.Sc., P.Eng., LEED*^® *AP BD+C*
>
> Principal, Building Energy Specialist
>
> ccianfrone at morrisonhershfield.com <mailto:email at morrisonhershfield.com>
>
> Description: Description: Description: logo4email4 
> <http://www.morrisonhershfield.com/Pages/default.aspx>
>
> Suite 310, 4321 Still Creek Drive  |  Burnaby, BC  V5C 6S7
> Dir: 604 454 9305 x1052319  |  Cell: 604 376 1315  |  Fax: 604 454 0403
>
> _morrisonhershfield.com/sustainability___
>
> *From:*bldg-sim-bounces at lists.onebuilding.org 
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of 
> *Goulouti Kyriaki
> *Sent:* Monday, November 26, 2012 1:03 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] Thermal bridges
>
> Dear all,
>
> I am a student from Switzerland, studying building physics and I would 
> like to ask you how LEED takes into account the thermal bridges.
>
> Are there specific values for the linear thermal transmittance, like 
> Passivhaus?
>
> I would really appreciate if somebody can answer to my question.
>
> I would like to thank you in advance,
>
> Best regards,
>
> Kyriaki Goulouti
>
>
>
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