Thermal Break or lact there of... is there a way to detect the impact via modeling?

The BC Hydro Thermal Bridging Guide may be useful. Based on my energy modeling experience for whole building simulation (eQUEST) it would not be particularly useful in evaluating design options for thermal bridging.  There may be other programs that are.  https://www.bchydro.com/content/dam/BCHydro/customer-portal/documents/power-smart/builders-developers/building-envelope-thermal-bridging-guide-1.1.pdf

Seonhee, Others probably know better, but my understanding is that thermal bridging (and poor envelopes in general) create comfort issues that are not represented well in the commercial energy modeling world. If the occupant or facility owner responds to comfort issues by increasing the heating set point and/or decreasing the cooling set point, then a significant amount of additional energy is used in building operation. Most energy modeling software does not accurately consider thermal comfort near poorly performing/lightweight exterior walls/windows/thermal bridges, meaning that the Aqua tower would not easily be accurately modeled for comfort or energy performance. Passive House workflows, however, do include thermal bridging modeling, and even include 1d and 2d thermal bridging for points and lines of thermal bridging instead of just an average wall (decremented per BC Hydro report and other studies) U value. Some of us in Seattle gathered last Friday to discuss why commercial energy modeling recommendations differ significantly from Passive House recommendation – in other words, why does PHPP suggest infiltration or envelope improvements have a more significant effect on energy use than commercial energy modeling would for the same variations? The draft notes from this group are still being circulated (I intend to send them to this group once they are complete), but the short answer seems to be that commercial energy modeling (eQuest, Energy+, etc.) does not dynamically vary the set point* based on thermal comfort near exterior walls, where operative temperature (and comfort) is very different from air temperature. One could probably trick software into doing this. At the meeting, which included several of the best modelers in Seattle, it was stated that no commercial energy modeling software inherently accounts for this. This is a fundamental reason why often the energy modeling results we see from energy modeling consultants suggests that envelope U-value improvements are a relatively minor part of energy efficiency. Conversely, if we have an improved envelope, we should be able to argue that the set points can be widened, saving a great deal of energy as well as – more importantly – reducing first cost due to decreased mechanical system sizing. *PHPP does not dynamically vary the set point, but the envelopes required for PH projects are good enough that thermal comfort is not as significantly impacted by being near an exterior wall. -Kjell ................................................................. Kjell Anderson AIA, LEED AP Associate Director of Sustainable Design LMN 801 Second Avenue, Suite 501 Seattle, WA 98104 T 206 682 3460 lmnarchitects.com<%20lmnarchitects.com%20> From:

Kjell, Like it. We often use energy model compares apple to orange (in comfort) and claim one is more energy efficient, looking at the actual thermostat set points and energy use of exterior zones suggest occupants are compensating MRT by using cooler air in summer and hotter in winter than what we modeled

Seonhee, Yes, you can use an energy model to understand the impact on energy and potentially comfort. To account for comfort impacts, you have to make sure are using an energy modeling program that determines radiant temperatures like EnergyPlus, as opposed to one that does not, like eQuest. However, the energy model will not determine the difference in R-value between having a thermal break or not, so the analysis is only as good as your understanding of the thermal performance of your detail. There are a couple ways you can try to determine the difference in R-value with and without the thermal break. The best option, I think, is to run a heat flow simulation with a program like THERM of the detail. All things considered, it’s a fairly simple tool to use. If you are using Rhino, you can now use Honeybee to avoid having to using the terrible drawing interface in THERM. (THERM’s engineering calculations are great, but the drawing interface leave a lot to be desired. If you have a fairly standard detail you can use something like the Passive House workflow that Kjell mentioned to calculate by hand the impact, or find a detail similar to yours in either the Morrison Hershfield report or Payette’s thermal bridging report (shameless plug) to try to estimate the difference in thermal performance. Hope that helps, Andrea Andrea Love , AIA, LEED Fellow Principal and Director of Building Science | Phone: 617-895-1025 From:

We have used the THERM model developed by Lawrence Berkeley Labs. https://windows.lbl.gov/software/therm I don’t think we used it to compare to other energy models but we did do comparisons forward and steel framing and for different exterior insulations over. The differences between steel and wood without the exterior insulation were striking. Larry Strain, FAIA LEED AP S I E G E L & S T R A I N A r c h i t e c t s

We had a hard time getting folks to dive into the THERM native drawing format, but now that it can be brought into Honeybee we are getting more traction internally. It is the same LBNL engine but the front end is tied in now to a tool we’re using for other purposes as well, and it allows for more ease of iteration. F

Hello Kim, The use of Therm gets one to an “effective” heat transfer coefficient for Exterior Wall. Rest of the Building Physics lies with:: 1. Simulating heat exchanger geometry appropriately. A concrete balcony should be accounted for as a heat exchanger with 3 surfaces (perimeter edges, upper surface, lower surface). 2. Accounting for high winds at high altitudes which will further affect heat transfer coefficient during certain times in Winter. Happy simulations! Kapil Upadhyaya, BEMP, Fitwel Ambassador, LEED AP Senior Associate Kirksey | Architecture 6909 Portwest Drive | Houston Texas 77024 | www.kirksey.com o 713 426 7508 | kapilu@kirksey.com Houston + Austin Fro