[Bldg-sim] comparing insulated core masonry block with stick built

[Chris Balbach]

Christian:

If you are interested in seeing the detailed annual energy impacts of 
different composite wall constructions in residential buildings, you 
might consider modeling this residence using the TREAT software tool 
(http://www.treatsoftware.com - free 30 day download), which uses the 
SUNREL engine as the basis of 8760 hour whole building energy 
calculations. The SUNREL engine is unique among commercially available 
energy simulation engines in that it incorporates a one-dimensional 
finite difference nodal thermal network model (that's a mouthful) for 
calculating wall conduction losses. In this method, there is no need to 
calculate custom room weighing factors, etc, (needed in DOE2.x) as 
conduction transfer functions are not used.  The SUNREL engine was 
specifically designed to accommodate evaluating modeling the effects of 
conduction in stud/cavity composite types of wall/roof constructions. 
Thermal mass, (thickness, specific heat, density, and conductivity) of 
the composite construction is accounted for in gory detail.

Check out the page 14 of the SUNREL Technical Reference Manual for a 
visual representation of how composite wall constructions are handled in 
TREAT using SUNREL:

http://www.nrel.gov/buildings/sunrel/pdfs/sunrel_tech_ref_30193.pdf

Note that TREAT ships with a standard library of envelope construction 
types, (NOT user definable), but I think you will find they meet your 
needs.

BEWARE - the current release of TREAT (V3.0.27) cannot be user to 
provide a HERS rating, however our next release (targeted spring '08) 
will have this capability again.

Happy Modeling!!

_Chris

Chris Balbach, PE, CEM, LEED AP
Vice President, Research and Development
Performance Systems Development
124 Brindley Street, Suite 4, Ithaca, NY 14850
(607)-327-1647 ph
http://psdconsulting.com




Karen Walkerman wrote:
> REMRate merely takes the UA of the whole house and calculates energy 
> use based on heating degree and cooling degree days.  It also takes 
> into account thermal gain from windows, infiltration and calculates 
> internal energy use (lights, appliances, etc), but does not do a full 
> 24-hr 365 day simulation.
>
> For frame walls with batt insulation, both REMRate and the eQuest 
> Wizard will calculate the overall wall U-value based on their estimate 
> of the ratio of framing material to insulation.  For advanced 
> construction techniques, I usually calculate average U-value the 
> parallel path method.  I then enter this as "continuous" insulation in 
> either REMRate or eQuest, and then other relevant information, such as 
> thermal mass.  eQuest will take into account thermal mass, whereas I 
> don't believe REMRate does.  Sometimes masonry wall manufacturers will 
> claim a higher than actual R-value due to the thermal mass properties 
> of the wall.  This is one case where eQuest will do a better job--, if 
> entered properly.  I don't believe REMRate takes thermal mass into 
> account.
>
> Unfortunately though, eQuest can't be used for HERS ratings, so if 
> that is your final goal, you're stuck with what you have.
>
> Hope this helps,
>
> ~Karen~
>
> On Jan 17, 2008 2:57 PM, Christian Stalberg < 
> cstalberg at southern-energy.com <mailto:cstalberg at southern-energy.com>> 
> wrote:
>
>     I'm doing a modeling comparison in REM/Rate of two identical
>     houses except one has 8" insulated core masonry block walls
>     whereas the second has 4" wood stud insulated walls. Both walls
>     end up having comparable U values. REM/Rate shows negligible
>     difference in energy usage. I am suspicious that REM/Rate does not
>     model the thermal bridging and mass features very well. Would I be
>     better served performing this comparison in DOE-2 or would the
>     results not be that much different?
>
>
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