THERM Intro

[@tundraICE1]

Hi Georg - I read your reply to Oscar. Thank you and thank you for the excellent video! I do not think there is a better intro out there - and super recent too! I am analyzing a wall assembly for condensation potential - dew point. It looks like this: Outside - Vinyl Siding - 3/4" Furring strips (air spaces) - 4" EPS Insulation - Building Paper - 3/4" Plywood - 2x4 studs void of insulation - 1/2" Drywall. 1. Can THERM actually show me condensation probability or dew point? 2. did I understand your reply to oscar correctly that I do not need to detail the furring/airspace/vinyl siding? Start on the EPS surface as exterior winter. 3. Should I bother detailing the WRB (building paper/tyvek). 4. What material do I assign to stud cavities? 5. What's the logic with boundary conditions - when I press the button I get all sorts of adiabatic conditions between studs and plywood or eps and plywood or drywall - everywhere.

[@building-science]

Seems like I missed to reply to this one on time - but just for others who might read this: 1. THERM is thermal conduction software and doesn't know anything about psychrometrics - so in other words, you need to know that stuff. (i.e. which air can get to which colder surface and trigger condensation) 2. Yes, you cannot model ventilated cavities well other than creating fake "materials" that replicate the radiant and convective heat transfer in a conduction model (the ASHRAE Handbook provides some examples for such air spaces for still air) but any resistance that such air layers would provide can be typically ignored as they should be comparatively small in current wall systems. 3. WRBs are so thin that even with a magically low conductivity they wouldn't make a difference. Now that doesn't mean they are not an important function in your wall. In fact, if you don't have an air barrier the conductivity of a fiberglass insulation for example would be much higher than what you put in as your material - the insulation capability would be "blown out" on windy days ... 4. If the cavity is empty (filled with air) you can either use a pseudo-resistance provided in ASHRAE or use the enclosed cavity "material" in THERM. Typically you would fill a cavity with some type of insulation material though. Please note that modeling air cavities goes way beyond what I can cover here and you'd need to read up on this separately. (e.g. windows.lbl.gov/tools/knowledge-base/articles/frame-cavity) 5. Boundary condition replicate radiant and convective heat transfer as conductive properties, since THERM is built on solving the equations for conductive heat transfer in the modeled domain. Many of these questions have been discussed in the user group groups.google.com/g/LBNL-THERM, which would be the better place to ask such questions.

[@annat477]

THANK YOU SO MUCH! AMAZING VIDEO

[@pendenwangchuk123]

Thank you Can I use therm to see how effective an envelope is to reduce the air temperature ?

[@liliu07]

Hello, when I try to set up my drawing size to 36 x 36 inches I get an error requesting a number between 0 and 1. I have no idea whats going on. Can you help me?

[@building-science]

Hi Wiliam - this has been a recent issues also reported by some of my students. I've posted a message on the community discussion board if this is something that's come up for others too. Let's see if the developers may know of that already. groups.google.com/g/LBNL-THERM

[@building-science]

One workaround I found just now is to switch the unit system to SI units, make your changes and then go back to IP if you work in US units.

[@Pasunreve212]

Thank you for the intro and explanation! I've got one more question, that is if there's air cavity in between, will THERM take that into consideration? Or should we ignore that layer in drawing in THERM? Thank you!!

[@building-science]

It depends. If this is a closed off cavity with still air in there, then a simplified cavity model (material) can be used and then take the insulation capacity of air into account. If it is a ventilated cavity like the ones behind a rain screen, you typically ignore the layers exterior to the cavity (e.g. the brick veneer wall) and start with the first layer in contact with the outside air.

[@Pasunreve212]

@@building-science Thank you so much for the explanation! I actually ran into another issue, after creating one detailing for analysis, when I did another detailing for calculation (in a new file), the software showed a pop-up window which says, 'trouble opening the file', and 'calculation failed'. Wondering if you have encountered similar problem before and know the solution?

[@building-science]

@@Pasunreve212 I've seen this before, but it can depend on many factors that I'd have to guess. Did you update in between in versions? Did override one of your libraries? Did you accidently delete something? Such questions can be better answered in the google user group groups.google.com/g/LBNL-THERM. But equally important there, you need to provide more context than just what pops up to receive a useful answer. And updating to the latest version would be a recommendation in any case. There are always bugs that can be addressed in newer versions.

[@Pasunreve212]

@@building-science Thanks for the forum I'll check it out! I didn't update versions in between. Neither did I delete anything I believe. But when I created a new file, I did immediately import the library material and b.c (the ones from the lib file with 'ARCH' in file names), as everytime inside a new file, there's very limited materials available. Would that be the problem, as what you mentioned like a 'override'?

[@Pasunreve212]

Back again with another question In my THERM both 7.7 and 7.8 version, I have constantly been encountering an error stating that 'trouble opening file' whenever i clicked the Analysis botton, does anyone have any idea about the reason and how to fix this issue? Thanks in advance for the help!

[@building-science]

This is again a very generic question, not directly related to the video, which is much better asked in the Google THERM user group groups.google.com/g/lbnl-therm/ - in fact, this answer may actually help: groups.google.com/g/lbnl-therm/c/xcvB5rt5mrc - make sure the THERM is installed with access to a writeable directory such as "C:\Users\Public\LBNL\THERM7.x"

[@Pasunreve212]

@@building-science No it's not related to the video, yet thank you for the info! I'll check the forum.

[@montecrist]

Thank you very much! This is great! I was wondering if you could give me your opinion on a recent problem that I've been encountering with THERM. I want to model a wall assembly that consists of a backup concrete wall, brick face, 4 inches of rockwool insulation, 1 inch rainscreen and sheet metal cladding. 1. What conductance value should I use for the air gap? Would it be the same as the exterior winter? 2. Every time I try to input a conductance value for the sheet metal cladding, I get an error message reading that the thickness is not within the software tolerance. How can I get around this? Thanks again!

[@building-science]

Ok, your setup goes way beyond this starter tutorial and should be covered maybe in a follow up video. But to give you an answer to your immediate question: This really depends ... if you're looking for your wall performance in a cold climate scenario (i.e. heating setting) your rainscreen (not sure what your 1" is made out of) and sheet metal will not contribute (significantly) to your thermal performance. And typically, we'll have an air gap behind the rainscreen for venting out any moisture that could get behind the screen - I guess this is the gap you are referring to? A ventilated cavity is not the same as an air-layer (air cavity) for which we find conductances in the literature. The exterior surface coefficient on the other hand assumes a relatively high wind speed (convective exchange), which is not the same as the one you'd expect behind your rainscreen. So to summarize, once you get outside air "venting" through your airgap, there's no need to model additional layers beyond that as you would give them undue insulation properties. For the surface air film coefficient (the air layer touching the rockwool insulation) you could assume a bit more resistive than the winter coefficient (6 BTUh/sf.F), which assumes 15 mph winds. Something closer to the interior coefficient (for vertical walls this would be 1.46 BTUh/sf.F) would be more meaningful - I'd argue you can put the surface coefficient to 1.5 BTUh/sf.F for a ventilated air cavity behind a rainscreen - but at the same time consider the air therein as "outside" air temperature..

[@itsmrh]

this is awesome! Thank you sir

[@treshanfernando7162]

Appreciate it big time

[@ts.khairolbinkamaruddin6257]

Thanks for the great video.

[@joaomagalhaes1020]

Very helpful, nice video!

[@kanavvij90]

Thanks for this video.

[@jenniferw.3800]

Thank you!!!

[@hubsonik4236]

TY