Trace 700 vs 3D+ for load calculations

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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:

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]

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 Fong, PE

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Curtis Fong's picture
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Hi Curtis and list
Over the last 20+ years we have done most of our loads in Trace 700 and are aware of the need to migrate. We answered a survey that implied Trane was considering modifying the sunset timeline but we have not read or heard anything lately. We have started a modest comparison and are trying to be systematic and a bit rigorous about it. In our study, internal loads and low mass wall/roof/window conductivity have seemed reasonably comparable. We are looking more at infiltration, solar gains, and ground coupled heat transfer. We have not gotten to testing high mass scenarios. Yes the differences have us wondering if we 1) trust that 3D is more accurate and we keep our standard safety factors OR 2) devise workarounds and/or different safety factors OR 3) find another software package. We have not used 3D output for a live project and we have not communicated with Trane about this. I would be open to a conversation next week or later.

Paul Riemer, PE, LEED AP BD+C
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One interesting question would be to know whether anyone has done rigorous
analysis on whether buildings constructed using RTS calculations are
oversized and by how much.

I expect this would be a really useful exercise in growing your confidence
in the suitability of new calculations.

On Mon, Feb 28, 2022 at 9:03 PM Paul Riemer via Bldg-sim <


*Andrew Corney* ? PE, M.CIBSE, M.ASHRAE
Product Director - PreDesign & Sefaira

Trimble - Architecture & Design Division
andrew_corney at

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The closest thing I have seen is ASHRAE research project RP-942, which compares the results of HB and RTS as referenced on page 18.32 of the 2021 ASHRAE Fundamentals Handbook. RP-1117 is always good because they used physical measurements.

Realistically, RTS was created as a simplified version of the true HB method, so if one should be trusted it is the base methodology I would think.

Cory Duggin, PE, LEED AP BD+C, BEMP
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Tell me more about RP-1117, that sounds really interesting. ?

Adding some thoughts from the draft email started a couple of hours ago and not sent yet:

Glenn is on TC 4.1, what are his thoughts from the committee? There might be some seminars

IBPSA-USA might also be a good group to host a forum or discussion panel.

Anyway ? the push for Heat Balance Method has been an initiative for over 20 years going back to research on the 1117 project when I was in grad school ? to make the load calculation more accurate. You are welcome to use any safety factors that you need but one of the drivers from the TC originally was that the load calc should be accurate, and then the engineer would use their judgement as opposed to a load calculation method that included an overestimate and then the engineer added their own safety factor, and then systems across the country get installed with excess capacity and can?t turndown, etc.

So absolutely yes you should re-think your approach to the safety factors, but the intention was also to give the engineers confidence in using a smaller load.

Looking at the two charts below the outlier would appear to be Trace 700.


David S. Eldridge, Jr., P.E., BEMP, BEAP, HBDP, GGF/A
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