A way to integrate thermal bridges in EnergyPlus

grasshopper fairyfly
,
1

Hello.

I’ve been doing a bit of research on similar posts, but I haven’t found anything similar. It’s about linking thermal bridges with EnergyPlus.

There is a software for regulation compliance in Spain that uses EnergyPlus, and since those regulations mandate the study of thermal bridges, this software takes them into account, the following way.

It takes takes the envelope edges, similar to HB Envelope Edges, and it creates a surface underground, the length being the same as the edge’s. The height is the witdth of the wall, because the IDF they generate is like this.

Rhino_9RgoxGVeoc
Rhino_9RgoxGVeoc926×609 58.1 KB

so it doesn’t create redundancies

Then it assigns it a material with the value of the thermal bridge. This could come from FairyFly.

The face it creates has this structure:

BuildingSurface:Detailed,
  Z01_S01_TB32 EF, ! Name
  Wall,            ! Surface Type
  C11_TBW_2278_55U_, ! Construction Name
  Z01_Habitable,   ! Zone Name
  ,                ! Space Name (*)
  Outdoors,        ! Outside Boundary Condition
  ,                ! Outside Boundary Condition Object
  NoSun,           ! Sun Exposure
  NoWind,          ! Wind Exposure
  0.5,             ! View Factor to Ground to Ground
  4,
  0, 0, -12.05,
  0, 0, -12.35,
  22.3 0, -12.35,
  22.3, 0, -12.05;

Construction,
  C11_TBW_2278_55U_, ! Name
  M20_TBW_2278_55U_ (0.6); ! Outside Layer

Material:NoMass,
  M20_TBW_2278_55U_ (0.6), ! Name
  Rough,           ! Roughness (*)
  2.13253,         ! Thermal Resistance {m2-K/W}
  0.65,            ! Thermal Absorptance (*)
  0.6,             ! Solar Absorptance
  0.65;            ! Visible Absorptance (*)`

And it looks like this, geometrically.

Rhino_GSBbD98vNt
Rhino_GSBbD98vNt1858×1224 336 KB

Therefore, with the name it assigns to it, you can easily quanify the effects of that bridge.

What are the current ideas regarding this subject?

2

Have you seen this sample file, @adrisonet ?

It’s not doing any fancy edge analysis over a building (just looking at the effect of studs in walls) but it effectively demonstrates the type of workflow that you described.

3

In the US, ASHRAE has a protocol which they recommend: link. I’m not a big fan of this method though.

I have also heard of some folks using ‘OtherEquipment’ to simulate the energy impact of TBs. In particular this is the method recommend in the ‘Phius REVIVE’ protocol, though it is complex and relies on EMS calculations to determine the total energy demand for each TB during the E+ simulation run.

Personally, I like accounting for the Construction TBs (as opposed the repeating TBs like studs) separately from the assemblies. This makes post-sim evaluation and QA/QC review much easier. I find the ‘Psi-Value’ method to much, much simpler than the ‘blended U-Value’ method - especially on larger projects, or projects with many many TBs (retrofits, etc).

It is too bad that E+ still doesn’t have a nice easy way to build these in. You might take a look at the above and see if they can work for you though.

best,
@edpmay

4

Thanks, @edpmay .

Now that we’re moving away from the more general topic of “how to take the Fairyfly U-Values and plug them into EnergyPlus simulation” and talking philosophy of Psi-value vs. smeared U-Value, have you tried the TBD measure that @brig mentioned here?

I have used it before and it is the way that I would recommend inputting Psi values for a Honeybee EnergyPlus simulation. Basically, @brig 's measure takes your psi values and performs a geometry analysis similar to what the HB Envelope Edges does but on the OpenStudio model instead of the HB model. Then, it derates the U-values of the constructions before sending the model to EnergyPlus for simulation.

If you set up your Honeybee model and run your simulation using this measure, it essentially allows you to use EnergyPlus the way that you want. Your honeybee model can be set up with u-values that follow the repeating TBs like studs. Then, you plug in the psi values of the construction TBs as inputs to the measure.

I know that running a measure is not as elegant as having it implemented natively in E+ but I know a lot of features that eventually get implemented within E+ start as their own separate measures. So, if you find this measure essentially gives the type of simulation results and workflow you want, there may be opportunities in the future to push for porting the functionality of the measure natively to future E+ versions.

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5

FYI, there’s an EnergyPlus enhancement request to directly support linear thermal bridging from surface edges, dating back to 2018. No idea when such a feature could be rolled out (it’s no small task). But I’m assuming (new) ASHRAE 90.1 2022 linear thermal bridging requirements are putting some additional pressure. We provided suggestions here. We continue maintaining TBD in the meantime.

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