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What simulation software is best suited for modeling cantilevered balcony ?

asked 2020-01-06 23:56:01 -0500

CentralHeater's avatar

updated 2020-01-07 17:27:53 -0500


I need to study the insulation of a 2 story house built in early the 1970s in Western Europe which has a cubic shape of 10m x 15m x 6m (height).

I am focusing on the cantilevered balcony which is an extension of the intermediate floor (1st floor) made of approximately 30 cm concrete slab. The balcony is 1m50 wide and 14 m long. So it represents a pretty good fin!

I already tried eQuest' "slab penetrates walls" option within DD Wizard mode (as advised somewhere on the forum) but the results are only qualitative since the simulated slab does not extend onto the balcony. So I guess the simulated heating losses in winter due to this "fin-balcony" will be far less than the actual losses.

I also tried BeOpt but there was no way to add a balcony or I couldn't find it. Maybe as a workaround I could define a intermediate floor only made of a 2 foot slab (it is not possible to input a value less than 2 feet which is ~60cm), although the balcony would be approximately twice as thick as the actual balcony. By the way will the simulated losses also be twice as the actual ones?

Eventually I tried OpenStudio and started to draw the 3D model of the house with balcony under Sketchup using OpenStudio plugin. However as soon as I clicked on "project loose geometry" the exterior balcony disappeared and only the interior slab up to the walls remained as if the balcony was cut off.

Consequently now I wonder if it is even possible to model a cantilevered balcony, and if so which (free) simulation software I should use and how I should model the cantilevered balcony ?

Any help appreciated,

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2 Answers

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answered 2020-05-05 10:07:57 -0500

updated 2020-05-05 10:14:17 -0500

Keep in mind that heat transfer in most BEM software is 1-dimentional, i.e. a balcony fin will only transfer heat in the direction of its surface normal (vertically in this case).

@dradair's suggestion of Therm is a good one. It could be used to calculate the assembly's U-factor, which could be used in a whole-building model.

An easier option is to use the values from the Building Envelope Thermal Bridging Guide (Morrison Hershfield, 2019) to derate the thermal performance of the assembly in your whole-building model.

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didnt know of that reference (or i i did I'd forgotten) - good deal!

dradair's avatar dradair  ( 2020-05-05 11:46:18 -0500 )edit

Also, click the thermal-bridgetag to see other questions and answers...

MatthewSteen's avatar MatthewSteen  ( 2020-05-05 12:00:56 -0500 )edit

Thanks @MatthewSteen for you advices ! I'll have a look at the guide it looks very interesting.

CentralHeater's avatar CentralHeater  ( 2020-05-06 12:49:17 -0500 )edit

(a year late) The TBD measure described here provides an easy way to factor-in cantilevered balconies. TBD will automatically (a) recognize an OSM shading surface "aligned" with a floor slab (i.e. sharing a common surface edge) as a "balcony", (b) apply a corresponding balcony PSI value (e.g., 0.2 or 0.5 or 1.0 W/K per m), and (c) consequently derate "linked" wall surface constructions (as per ISO/BETBG as cited by @MatthewSteen).

Denis Bourgeois's avatar Denis Bourgeois  ( 2021-04-23 04:05:19 -0500 )edit

answered 2020-05-05 08:51:57 -0500

It may depends on the answer you're seeking. If looking to assess energy loss/consumption due to the balcony, the eQuest or E+ or Openstudio can do it. However - it will be a manual process to define the geometry & relationships of this.

A step prior to any of the above is that the thermal performance needs to be quantified. How good or bad is the thermal bridging? In that case, I'd recommend THERM from LBNL. It does 2D heat Transfer calculations and should be able to help you determine the performance of this assemble. These results can then be used in the simulations above to compare/evaluate annual energy gain/loss/use.

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I hadn't heard of THERM. There seems to be a pretty comprehensive documentation, so it looks better suited for my needs than Energy2D. Thanks a lot! Along with @MatthewSteen's tip I will be correctly "equipped" to achieve my goal.

CentralHeater's avatar CentralHeater  ( 2020-05-06 12:55:30 -0500 )edit

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Asked: 2020-01-06 23:56:01 -0500

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Last updated: May 05 '20