Add a Component to Calculate Air Films in Constructions

[ayezioro]

Hi, I think the R and U outputs of both components are inverted. I would also add units to the R output hint/

One misspell in the callFromEPConstrLibrary output. Should be EPWindowMaterilAs (Missing A). -A.

[ayezioro]

Will add that this happens in some materials for the EPConstruction. I checked a window and it is wrong, but checked a wall and it is ok (one of each).

[mostaphaRoudsari]

Hi Abraham, There is a great chance that I am making a mistake here but here is my test and it shows the U-Value as expected for both cases

[ayezioro]

Well, my comment is based on the values i see for U and R in the component. I just took the output values and then applied U=1/R Higher Resistance, lower Conductance. Obvious. So i took an insulation material to be sure this must be true. See picture. No way the U be higher than R, which is the case. I'm not familiar wit the numbers in US (IP units) but from the picture i'm also suspecting that the values are also inverted between IP and SI. There is supposed to be a relation between the material name and the U or R values? What is this 0.43 in the name of the insulation? Makes any sense? -A.

[chriswmackey]

@ayezioro , for a very thin material, I would expect there to be a very high heat flow across it and thus a very high U-Value. I checked the values and comments and it turns out that the thickness of that material is only half of a mm so I think that those values make sense.

[ayezioro]

One more thing, I'm not quiet about calculating U for individual materials. U in general relates to the thermal conductivity of an element composed of a number of layers. It is defined as 1/R, where R takes into consideration both air layers (internal and external), otherwise is called r (small r). Do you take this into consideration for the construction calculation?

[ayezioro]

Maybe you are right Chris, Tried another insulation and the results make more sense.

[chriswmackey]

@ayezioro , the U-Values and R-Values that you see there do not take into account the air films on either side of the material. This is because E+ has a way of calculating the resistance of these air films depending on the geometry of the surface the construction is applied to and things like outdoor/indoor wind speed. We could add in some default air film but this would be a bit misleading from what E+ will actually use.

[ayezioro]

You are great Chris, I think this can be important to have since this is a value you expect to achieve. And since this output is only for information user (me) will like to know the whole package value. In my work i have a pretty good correlation to E+ calculated results so i know i'm fine. If you like/want i can look for the air films i'm using for different cases (wall, roof, floor). As for this whole issue, i'll define materials and constructions i'm used to and then i will report. BTW, who will use a half milimeter insulation. Crazy!!

[chriswmackey]

@ayezioro , I can see value in adding a component that can take any R-Value or U-Value and add in the effects of air films depending on an input of surface type (wall, roof, floor, interior wall, ground floor, etc). If you get the rough coefficients for these, I can draw up the component or you could since this one seems like it would be a breeze for you after the bio chart :)

The OpenStudio library is filled with some weird stuff. Maybe they meant to have a material for a layer of paint and just called it insulation to save time.

[ayezioro]

I can try to add the values. I'm sure you will do in 1 minute. In any case here they are (as one of our standards here in Israel defines them): Wall: 0.16 (0.12 + 0.04) Roof: 0.16 (0.12 + 0.04) Exposed floor: 0.21 (0.17 + 0.04) Interior wall: 0.24 (0.12 + 0.12)element types are hard to conclude from this standard. But i believe those include most of the cases. Ground you don't have the external air film. If only the internal is to be taken into account it is 0.17. Also there is floor over non acclimatized space (0.29) and roof under non aclimatized space (0.24).

Other

[ayezioro]

Good news, Checked constructions that i know and the results are OK. The only thing is that the U/R values provided don't include the air layers. So, for now, in order to get the correct values i do the operation externally. Just in case i dare, Chris, It will be more difficult for me to add the air layers in the way you are calculating U. I'm used to calculate r and R first. In this way i know the resistance of those layers as a "given" value. After i have R i get U. You are calculating U first, and in this case the influence of the air changes and is relative to the section of the wall. But assuming this is solvable, any suggestion how to differentiate in the calculation floors/walls/etc? BTW, i've found a more updated version of our standard. The numbers i wrote above change a bit: External Wall: 0.17 (0.13 + 0.04) Roof: 0.14 (0.10 + 0.04) Exposed floor: 0.21 (0.17 + 0.04) Interior wall: 0.26 (0.13 + 0.13) Have this for the above: https://www.dropbox.com/s/xu0ru4vn0qrtxmz/HB_IS_Materials.gh?dl=0

[chriswmackey]

I took your researched knowledge, Abraham, and put it all into a component to account for air films. The new component is on the github and I have added an updated version of your gh file here:

https://www.dropbox.com/s/28l8zee6yd9e3at/HB_IS_Materials_CWM.gh?dl=0

[ayezioro]

This is good! Simple and elegant. In the future, hope i can get there, this should be embedded in the main components. Thanks, -A.

[mostaphaRoudsari]

This is a great addition. Thank you both.

[ayezioro]

Hi guys, Please take a look on this and let me what do you think: https://www.dropbox.com/s/q70y6eee019nc91/DecomposeEPConstructionWithAirFilm.gh?dl=0 Probably not the best coding but it works ... The truth is that the code is ok, since i copied Chris's, but the paste maybe can be improved.

[mostaphaRoudsari]

Hi Abraham. Thank you for implementing the code. I personally think that we should keep the components separate. Based on my experience when people talk about U-Values and or R-Values for materials/constructions it is considered for the material itself and without the air resistance. I can see how it can be really confusing for people to get the values with air resistance from the component.

[ayezioro]

Hi Mostapha, Don't want to re-open this issue but i have a question: Really? :-) I can understand what you say, but i can't agree this is the correct view. I'm not sure when in the US they have R requirements (they have?), or U, they consider the air film or not. But ... here you have to. Also, when receiving the E+ results you get the U value, including this layers of air. For me this is more confusing, but ... OK. Thanks, -A.

[chriswmackey]

@ayezioro , I have to agree with Mostapha on this one. The manufacturers tend to give the R-Values and U-Values in terms of just the material. Otherwise, they could choose an orientation of the material and an air speed that maximizes the R-value of the air films, which could really be misleading and get you to buy a product that has a much lower R-value than what you expected. That said, I know that a lot of the ASHRAE building code requirements for minimum amounts of insulation have you calculate the R-value with the air films. So they are both important but, given that people will be inputting R-values and U-values that they get from manufacturers, I think that it is safer to stick with this output as the default and have the air films calculated separately in another component (if people need to prove stuff for code requirements). Also, I checked and ASHRAE seems to have some different means of calculating these air film R-values than the numbers that you sent me and I may include these numbers in the component later. In any case, all of these methods of calculating air films are different than that actually used by E+, which looks at the exact angle of orientation of each surface and other things like the wind speed at that hour so I think it's just safer to keep this component separate from the "pure" E+ component since our methods for air film calculation clearly have some biases towards certain building codes.

[ayezioro]

Ok. There is something in what you wrote. So, closed it is.