[Bldg-sim] Trace 700 vs 3D+ for load calculations

[Curtis Fong]

Hello Trace users!

As you probably know, Trane is phasing out Trace 700. This is the last year that you can renew your annual license, and after your license expires sometime in 2023, there will be very limited opportunity to edit and run existing models. The replacement is the heavily hyped Trace 3D+, which uses EnergyPlus as the simulation engine. From a load calculation perspective, this is a very big deal. Trace 700 is one of the industry's leading load calculation tools and is arguably the basis for the standard of care for HVAC equipment sizing. Load calculations in E+ are based on the heat balance method, which is a fundamentally different approach from the radiant time series that is commonly used for cooling loads in Trace 700. Having a 3D view in the tool is, for sure, a step forward and the heat balance method is a more rigorous approach, but applying that to real equipment sizing is not trivial. The workflow will be different and the load results will also be different, generally lower in 3D+. The load calc results with the 3D+ approach will be sensitive to some inputs that are not particularly critical in Trace 700 so care will be required as designers switch over to this new tool. But yet Trane has provided very little guidance on the differences between the software tools, calculation methods, and resulting peak loads. Really only this: https://tranecds.custhelp.com/app/answers/detail/a_id/454/~/comparison-of-trace-700-and-trace-3d-plus

One potential data point is to compare the published Std 140 results for 700 vs 3D+. Below are the peak sensible cooling results for the high mass building, 700 at left in pink, and 3D+ at right in pink. High mass would be the most challenging comparison, where there is more time delay heat transfer with the HB method - but these are tremendously different peak loads (3D+ predicts a ~30% lower peak for case 900). Are you ready to hang your PE license on that result at right? I don't know enough about Std 140 to know whether this is reflective of an apples to apples comparison between load calculation results between the two tools but it seems to match my general expectation.


[cid:image001.png at 01D82A23.3DF83BD0]
https://www.trane.com/content/dam/Trane/Commercial/software/trace-3d-plus/T3DP_V3-01-25_final_lowres.pdf
https://tranecds.custhelp.com/ci/fattach/get/266924/0/filename/STANDARD+140-2014+OUTPUT+FORM+-+Modeling+Notes.pdf

So my questions:

  1.  Has anyone already switched to using 3D+ for load calculations?
  2.  Has anyone done a careful comparison between the two tools and/or developed any guidance on workflow differences that you would be willing to share to avoid duplicating effort? (it would obviously be better and more practical for Trane to do this since they are forcing the switch, instead of expecting their users to each do it on their own)
  3.  Do you have concerns about using load calculations from 3D+ for equipment sizing, and have you expressed those to Trane? Perhaps if there was enough industry concern over the risk of under- or mis-sized equipment, they might consider maintaining Trace 700 to avoid having users simply switch to using Carrier HAP.

Thanks for reading!

Curtis

Curtis Fong, PE
Associate

taylor|engineers
1080 Marina Village Parkway, Suite 501, Alameda CA 94501
(510) 747-9660 direct, (510) 749-9135 office
(510) 749-9136 fax, (510) 290-1368

cfong at taylorengineers.com<mailto:cfong at taylorengineers.com>
www.taylorengineers.com<http://www.taylorengineers.com/>


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