There appears to be a bug in Rhino plugin where the U-factor does not change between metric and imperial units.
Snips that describe issue are below. Should value listed in name of material represent the U factor or U value? As you can see the value called out in name does not match listed U value or U factor. It looks like the metric value is carried over to the IP side.
If I want to create glazing with target U factor, should I override U factor value with target IP value, for example, U=1.2? Or should I enter the metric equivalent until bug is corrected?
Would it be possible to expose the interior and exterior film coefficients and maybe COG vs frame performance that are being used to calculate the Ufactor? That would provide transparency.
An example from IES, they call U factor (inclusive of film coefficients) the “net U value”. I’d expect in Pollination the glazing assembly U factor should match the value called out in the name. In snip below this is “U=0.5”.
The exterior coefficient is a constant 23 W/m2-K, which comes from an assumption of an outdoor wind speed around 6.7 m/s. However, the interior coefficient is a function of the inside emissivity of the construction, following this formula here:
If we want to just put a note in the Rhino plugin that the R/U Values/Factors follow the ISO 10292 standard as well as NFRC 100-2010, I’d be fine with that.
I just wanted to say that showing the film coefficient resistance is a really good idea for an App that I have in mind that would enable you to test out individual window constructions under various different conditions and would look a lot like the IES window there. But this might be a little overkill for the table of all the different materials or constructions, which already has a lot of information in it and is really meant for a high-level comparison. Maybe we’ll put this into the plugin eventually.
Picking up on this thread,
I am a bit confused as to why the specs don’t correspond to the name of the material:
U 1.3 while UFactor appears at 7.38. The difference shouldn’t be this large.
Furthermore, is there a way in RhinoPlugin to create my a material with a specific U value and SHGC ? The only way I see is to specify explicitly the construction materials until the specs match, but it’s trial and error and not so convenient.
I went to check Metric or Imperial and 2 things remain. here is a video to show what I mean :
the information box at the bottom does not update the text as I switch from Metric to Imperial.
the Metric and Imperial units are inverted.
U Value in Metric should be 1.3 W/m2·K
U value in Imperial should be 7.38 Btu/h·ft2·F
I wouldn’t know the cascade of consequences this has on the tool itself, which one is being actually considered.
The bottom information box only shows the definition of the selected material above and they are all defined in metric (except the name). Switching the “display units” won’t affect the material definition, and the imperial value is calculated based on the matric value.
I know these are confusing, but those materials are defined by NREL if I am not mistaken (@chriswmackey please correct me). So they use imperial value in the materials name but kept all property values in metric. Hope this helps.
I’m just confirming that you are correct here, @mingbo .
The IDs (or EnergyPlus names) of those constructions come originally from the US Dept of Energy Commercial Reference Buildings. Back when they originally made those sample models as a standard for other energy modelers, they put in all of their biases towards the IP system when they were naming them. Long story short, they are just IDs and the actual properties of the objects are visible in the nice tabular UI that @mingbo built, which is responsive to the SI/IP switch. Maybe at, some point, they will update the IDs to include both the SI and IP values but, knowing how slow the US is to update its units of measurement, I would not hold my breath.
the Metric and Imperial units are inverted.
