Thermal Analysis by elements - Changing insolation thickness has no effect

[talk2rene]

Hello,

I am using Revit 2022 to do a thermal analysis of a simple rectangular structure that results in a zone-load summary (cooling/heating). NB I am fairly new to Revit.

However when I change the insulation thickness of the external wall from 300 mm (R=6.5 (m2K)/W, U=0.15 W/(m2K)) to 600 mm (R=15.3 (m2K)/W, U=0.06 W/(m2K)) the Delayed Sensible Energy associated with the wall does not change at all for Heating and just 1W for Cooling.

Nevertheless, with such an increase in insulation thickness I was expecting to see a jump in the wall's Delayed Sensible Energy value... (see my questions at the end)

I am using "Use Building Elements" as the Energy Setting mode which to my understanding will allow the analysis to use the thermal material properties of the model elements (rather than fixed numbers from material tables). 

The wall is made up of a typical set of inner, centre, and outer layers (poplar board, membrane, insulation, OSB, membrane, insulation, rain-screen)

Before doing an Analysis I delete the Analytical model and re-generate a new one because of the changes I made in the thickness of the insulation material. 

I have defined 1 room which encompasses the entire interior space of the model. The room boundaries are touching the first interior layer of the wall as well as the floor and ceiling. My understanding is that the room is solely used to calculate the volume of the space. 

Each wall, floor, and ceiling element has its "Room Bounding" set to true. 

I have attached an image of the corresponding Analytical Space.

Hence a few questions...

1) Is it reasonable to expect a bigger jump in the wall's Delayed Sensible Energy value (due to insulation thickness increase)?

2) Is it right to assume that "Use Building Elements" mode will use the thermal properties of model elements like wall, floor, ceiling (rather than pre-set material values)?

3) I tried the "space/zone" mode (added a non-default zone + 1 space) but then I didn't see any change in the wall's energy value which made me conclude that pre-set material parameters were used rather than the material parameters of the model elements. Is this the correct assumption?

4) The fact that the room is merely touching the inner side of the wall... is that sufficient for doing the analysis or should the room know about the wall thickness and its composition? If so... how? 

Any thoughts or pointers would be very welcome! 

Many thanks, -Rene

[iainsavage]

I haven't read your full post but bizzarely the default insulation materials provided by Autodesk do not contain any thermal properties and you have to edit the material and add a thermal asset to it before you will notice any effect from the insulation.

[talk2rene]

Thanks for your reply! I just had a look at the thermal properties of the insulated material (Rockwool) and it seems that the thermal properties are set ok (See screenshot below). That explains also why I see a change in the R and U values of the wall. But unfortunately the change in thickness of the insulation layer is not reflected in the analysis results.  Perhaps an obscure analysis setting or an extra step that is needed?

Thanks again though! -Rene 

[talk2rene]

Just a few more screenshots

Wall (thermal) properties

Basic Thermal Analysis properties

Advanced Thermal Analysis properties

[iainsavage · Accepted solution]

I think you need to tick the Detailed Elements box in the advanced energy settings.

This post might be of some use although the analysis methods have moved on since the post was written but it seemed then that Detailed Elements had no effect for the old heating & cooling loads tool but did have an effect on energy (now systems) analysis.

[iainsavage · Accepted solution]

If your subscription covers it this tutorial might be of use:

https://www.autodesk.com/certification/learn/course/revit-system-analysis-mechanical-design-professi...

I've attached the module notes for the material thermal properties part.

[talk2rene · Accepted solution]

It seems to work now... On the Analysis ribbon there is a section called "Energy Optimization" which contains a button called "Energy Settings". The latter brings up the "Energy Settings" panel.

Make sure that the mode is set to "Use Building Elements". Then click on "Edit other options"

On the "Advanced Energy Settings" scroll all the way to the bottom and check the "Detailed Elements" option to 'true'.

So with those settings I ran the thermal Revit analysis again for different insulation thicknesses and this time it gave different 'Delayed Sensible Energy' for the associated wall. 

So to answer my own questions in my first post

1) yes it is reasonable to see a jump in the wall's Delayed Sensible Energy value when changing insulation thicknesses

2) In addition to "Use Building Elements" one also need to toggle the "Detailed Elements" on the 'Energy Settings" panel

3) I am not sure at this point whether the "Use Zone/Area" mode will use the Elements' thermal values or only pre-set thermal parameter values!!

4) It seems that it is sufficient that the "room" boundaries just touch the inner surfaces of the wall, floor, and ceiling elements. NB Make sure that the "Room Bounding" property attribute on each touching element is toggled on.

Lastly, at this point I can't judge whether the "Zone Load" values for heating and cooling are correct. I have seen posts from around 2015 that questioned the validity of those values. Things may have improved! However this post is merely about the effect of a wall (or floor/ceiling) insulation thickness (or other material parameters) on the load values for heating and cooling.

NB I am sure this is all in the official Revit docs somewhere 🙂

[talk2rene]

I just noticed your response which seems to confirm my latest findings... thanks for your time and help!

[talk2rene]

And that answers my question about the documentation. Many thanks for those pointers, much appreciated!