Some building mass-wall heat transfer help? 1

[DRWeig]

Hi Thermo Friends,

(I've also invited the HVAC bunch to join this thread)

I need some guidance. Remember that I'm an EE who had only one semester of thermo, but has learned quite a bit about heat transfer in the process of facility HVAC design and whole-building energy simulation.

I have a building with odd shapes of heavyweight concrete along portions of the exterior walls (see attached). The required method to calculate U-values for such things has been in the ASHRAE 90.1 code for a number of years. However, in the energy modeling business, a well-documented approximation has always been approved. Simple methods such as using an average thickness of concrete and doing a parallel-path calculation have been the norm. After all, so many other variables in the model are only known to a couple of significant digits.

They've never demanded this before, and I have never learned to do it. I'd like to learn, and I'd also like to find a computer program that I can employ once I'm comfortable with it. I may have to hire some help on this particulare project, but I need to become proficient. This will be demanded more and more...

Please suggest me some learning resources and software?

Best to you,

Goober Dave

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[som1973]

Check this.......

http://www.builddesk.co.uk/our+software/builddesk+u

 

[DRWeig]

Thank you som1973. That's not a bad price and it looks very promising. Everything I had found so far dealt almost exclusively with fenestration.



Best to you,

Goober Dave

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[Drazen]

i'm not sure that comprehensive studies are justified for hvac calculations.

even transfer function method, as the one the most detailed, has many assumptions about approximations, and if you chase overly precise U-value, while the rest of thermodynamic model if full of approximations, your final result will hardly be more reliable than the one obtained with "ordinary" methods.

moreover, thermal accumulation and solar radiation hold more significant part of cooling load calculations, while for heating calculations stationary state is one of first assumptions, so if you seek for non-stationary models for heating load calculations, you are mostly leaving hvac field.

 

[DRWeig]

I will agree with that, Drazen. I would never profess to arguing with a seasoned HVAC designer or a thermo whiz.

But if you are constructing a whole-building energy model according to ASHRAE 90.1-2007 Appendix G for LEED certification, you have a very high risk of being told to re-do your model with 2-D analysis of all mass walls. Making changes like that in eQuest / DOE 2.2 for a giant-size, complex building is a costly re-do. Doing what they want on the front end is the most efficient approach. Even worse than a re-do, the reviewers can reject a design credit or a prerequisite if a violating method is discovered on final review.

Since I have 18 different wall sections and a learning curve for the math, the Builddesk-U program is a jewel. I'm working the 30-day free trial, but I'm going to pay for it this week so I can feel right about asking for tech support if something goes awry.

Best to you,

Goober Dave

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