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Energos and R-Values

Kevin C

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Can someone please help me with the data input requirements for Energos. More specifically what the R-Value is and how do I relate it to the U-Value of a construction.

Example: I have a project where the wall makeup is 140mm timber kit using 120mm 0.022 rigid board (thermal conductivity in W/mK) reflective membranes and a standard Low-E service zone internally finished internally with 2 layers 12.mm plasterboard and externally there is an existing sandstone wall with a 70mm cavity. This gives a U-Value of 0.19 W/m2K (Watts per square metre per degree Kelvin), the equivalent R-Value for that construction is 5.304 m2K/W.

This makes no sense whatsoever in the Energos calculations, as R-Values for the equivalent constructions in the database are similar to the U-value (but not the same).

Is there a units or conversion problem? - Ie. The building is being constructed in metric (SI units) and does Energos work in imperial?? If so there is a serious problem wth the software engine.

Or have I just got it completely skewed.

I have attached the wall U-Value calculation for information

Please help.

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R-Value is the thermal resistance of the construction, units are m2K/W , also shown as the R layer in your BRE sheet.

To get from R to U-Value : U= 1/R (W/m2K) , both are in metric already.

ie. (U= 1/5.304 = 0.188 rounded up to 0.19 W/m2K.

I believe Energos is linked to passive house PHPP calculations methods, which measure from the outside of the building envelope instead - still waiting on a video tutorial from vector works to understand better!

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I fully understand how to get from a U-Value to an R-Value, that is not the issue.

The problem is that in Energos the R-values for equivalent constructions is of the magnitude of 0.17 (check the pre-populated values for some of the generic wall constructions), which would using the formula U = 1/R, give a U-value of 5.88 which is the same as a polythene sheet!! This is obviously wrong.

I have done some more digging and found that in the US the R value unit is h.ft.ºF/Btu.

How are we meant to use a system that cannot calculate values in metric. Also means that there must be a 'fiddle' in the software to export to PHPP - as that system is fully metric.

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Guest Wes Gardner

Hi All,

If you find LAMBDA values that are incorrect, please file a bug report to let us know. Both "R" and "U" should be correctly calculated from Lambda (being the constant) based on the thickness of the material (being the variable) in both SI and Imperial units. If you find errors, please report.

Additionally, if you find the overall value for the wall style to be incorrect, please let us know.

Thank you


Edited by Wes Gardner
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Hi Wes,

Thanks for that. However, that only works when the individual component values are being entered into the system and does not allow for thermal bridging to be calculated (this would normally be carried out by other specialist energy software -which I have and am certified to use, for U-values, SAP Calculations and linear thermal modelling)

Example: Modern timber frame wall, as per the specification in my post contains specialist membranes and low emissivity service voids and cavities to enhance the overall U-Value of the structure. The insulation and service void are both bridged by the timber studs.


Timber studs - 140mm thick infilled with 120mm PIR board (lambda 0.022) and and a 20mm thick low-e service void (declared R-value of 0.655) both of these components are bridged by the 38x140mm CLS timber studs at 600mm Centres. Convention states that 25% bridging is applied to the insulation and service void to account for the timber studs. - Entering the lambda value of each component only works if you can also add the bridging fraction (and the bridging element resistance).

Breather membrane on the OSB facing the cavity (min. 50mm thick) - again a high performance reflective membrane with a declared R-Value of 0.655 (Protect TF200 thermo in this case)

The external leaf in this case is an existing sandstone external wall, but could be anything as its just a rain screen

The internal plasterboard (in this case) is double sheeted due to the fire resistance requirements of a flatted property.

As you can see, although the software is smart, unless it has an approved U-value calculator built in (for each country that uses the software) I would not trust it to give an accurate value in terms of thermal efficiency.

I need to be able to select a wall and know that the U-Value is correct or be able enter in an overall U-Value for the structure. If I need to convert it to an overall R-Value, so be it - its not difficult to do.

In relation to the overall reported 'R-Values' for the generic wall constructions in the software - they are all US (imperial) R values, even when the project is being designed in metric, so are all wrong, or rather the software has not converted them to metric.

Example, all of the timber frame walls have a pre-determined R-Value of 0.17, I calculated "nbl_Ext_Blk-Cavity-CBPBrd-TmbrFrmInsul-MtlFrm-GypPlstrbrd" and the R-Value is 5.184 which generated a U-Value of 0.20

I do have one question in relation to the default timber frame wall styles though (specifically the UK ones). Who on earth decided on the standard constructions. No-one uses particleboard in a timber frame - you won't get an agreement certificate for it! and no structural engineer will sign it off, because they are nothing like what is built as standard practice (or have ever been) - from my experience at least.

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  • 3 months later...

i'm still waiting for the energos manual (how far is it?), but i can't see the flow resistance added (approaching and departing energy - 0.17 m2 k/w, and 0.04 m2 k/w, respectively). is it integrated in the calculations?

or am i missing something?


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  • 5 years later...

I think this is an appropriate thread to add this to:


@Wes Gardner Is there a way to access the "Manual R-Value" entered in Wall Styles (Insertion tab) via Data Tags and Worksheets?  I'm trying to edit a VW default Wall tag to report the manually entered R-Value and I'm failing miserably.  I'm just starting out with the Data Manager, Custom Records, etc, so I'm assuming this is user error.  I do not need the Energos calculations, but I do need to tag wall R-values of my thermal envelope on plan & section permit drawings.  I have a basic understanding of Data Tags and the need to set dynamic text, but finding the right data to connect to is a problem.  I have tried searching on https://developer.vectorworks.net/ but haven't had any luck.  I tried using #WS_OBJRVALUE# but the number does not match the manually entered value (entered 21, tag shows 0.97 which I'm guessing is the Energos calculated value).


My fallback would be to create a Custom Record to attach to the walls, but that would require setting R-values per wall instance, rather than by Wall Style, and remembering to attach the record every time I create a new wall type.


Edited by E|FA
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  • Vectorworks, Inc Employee

Hello @E|FA,


I was able to get #WS_OBJRVALUE# to read the correct R-Value of an object, even if it is overridden manually. I have a attached a file that has a working data tag. This file also has R Values and U Values mapped to a custom record. Doors, Windows, and Walls all have their R- and U-Values mapped in the Data Manager, so even though it is in a custom record, the value is coming from the object and the record is automatically attached to the correct objects.

The Greyhound.vwx


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For what it's worth I just tried + the data tag works with #WS_OBJECTDATA('RValue')# as well.


If you add a Manual R-Value to an existing styled wall you need to ensure that 'Replace Energos data' is enabled in the 'Wall Replacement' dialog in order for existing wall instances to reflect the change.


@sbarrett could you explain a bit more what you did with the data mapping? I am vaguely aware of the data manager + keep meaning to look into it properly but never seem to get round to it. This looks like a good introduction. I am not interested in IFC particularly but I like the way you have got the wall objects having the Thermal Values Record automatically attached to them + the U/R value info being available in the OIP. Is this something you'd have to set up from scratch again each time you start a new project or is there a way to save it for reuse? I'm sure there are useful things I could do with this if you pointed me in the right direction...


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2 hours ago, Tom W. said:

ensure that 'Replace Energos data' is enabled in the 'Wall Replacement' dialog in order for existing wall instances to reflect the change.

That was the problem.  


@sbarrett Thanks for the R-Value tag, and the greyhound.vwx file.  I'm in the middle of watching the recording of the Design Summit webinar you gave, and was going to get in touch to ask for the file. 

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  • Vectorworks, Inc Employee

@E|FA in order to reset the default mappings,  go to the settings dropdown in the top left corner of the Data Manager and choose Vectorworks Defaults. This will reset all of the mappings that you have done. Unfortunately, there isn't an easy way to partially undo your mappings. If this works then great, but if you are still having issues, you can send me the file and I will look it over.

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