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IESVE Title 24 Adjacent Building Conditions

asked 2015-03-17 20:26:21 -0600

updated 2015-04-13 15:27:47 -0600

All; I am using IES to demonstrate a performance based approach to Title 24 an altered retail facility. The space itself is 1 story below grade and 2 above. The structure is existing and has existing, conditioned buildings on both sides [for all floors] and above. Additionally, there are conditioned spaced to the front and rear of the below grade story. The space types for this below grade area are predominately offices. The HVAC system will be a VAV Reheat with hydronic heat, dual max thermostat. There are two VAV boxes serving zones in the basement/below grade floor. For these basement zones the model is giving an error regarding the a large number of unmet heating hours in the basement. Even after drastically upsizing these boxes [5 and 6x larger both air flow and heat coil capacity], the main fan and the heating system; the error existing with but a small dent in the unmet hours total.

My only thought is that possibly the adjacent buildings are causing some large, phantom heating load to drive this. The adjacent buildings are set up as 'excluded from model square-footage' and as unconditioned. Can anyone confirm this approach or provide some insight into the reason that these two zones would be having such massive heating issues? Is the model letting these adjacent buildings 'float' with outside air temperatures? IS there a way to condition these buildings to reflect what should be minimal heat loss, but not account for the energy to maintain this [since it is not our space and will not be conditioned by our equipment]? Please let me know if I have omitted s/t critical and thanks in advance for the assistance.

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@dradair have you been able to get the T24 module to work? If you have, congrats!

MatthewSteen gravatar image MatthewSteen  ( 2015-03-17 20:56:22 -0600 )edit
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I can appreciate MatthewSteen's comment since it's well known that there are some issues with CBECC-COM and it's module that IES-VE is utilizing. How has the community been approaching performance path compliance for T24? Has anyone out there had any success or is everyone just going prescriptive for the time being?

JO gravatar image JO  ( 2015-03-18 08:35:28 -0600 )edit

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answered 2015-03-26 09:43:14 -0600

Brief update. There are two answers effectively. I contacted IES regarding the adjacent building and how best to handle them. The question I asked on how to best deal with adjacent buildings. The response I received was to create a construction with 'very low U values' for the demising walls; effectively making it adiabatic. Which, with an adjacency to a conditioned space this makes sense. These spaces are classified as 'exclude from square footage' within IES. From what I can tell, this appears to be an approach that works.

The second part is that I have a separate inquiry into IES concerning wall construction layers; part of which deals with material thicknesses. Currently, while building constructions, the material thickness can be adjusted, and IES displays an updated u-value. This is expected, as I'd be more concerned if a change in insulation thickness did not yield a u-value change. The issue discovered through many runs and examination of output files is that while it appears this u-value as an input, the actual simulated u-value is only for the original thickness of the material - which is based on the CBECC-Com approved list of materials. IES must be passing [or only allowed to pass] the material name/designation and not any of the modified parameters [re: thickness]. It is a communication breakdown. I have not seen any IES documentation that explicitly states that this is how materials are handled; but it also does not surprise me with the restrictive nature of the CBECC-Com engine. Even a static text warning that modifications dont matter would suffice, but I digress. The solution here that I have found is to either use a different material OR to use multiple layers of the material needed. So, rather than selecting a single layer of EPS, which comes in at 2", and then modifying the thickness to 4", which does update the displayed u-value; do two layers of the EPS, which add to 4". Note, this is predominately aimed at continuous materials [continuous insulation or thickness of built-up other materials; NOT framed constructions which are handled differently]. This initially impacted my demising walls and basement slab; causing the massive phantom heating load referenced in the question.

I will updated this based on what I hear back from IES on the second issue.

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@dradair your assumption that CBECC-Com does not allow you to edit material properties is correct. In the CBECC-Com GUI, the material properties are read-only. IES probably passes the material ID only, and CBECC-Com looks up the material properties from its own library. There is an FAQ on the CBECC-Com website that backs this up.

aparker gravatar image aparker  ( 2015-04-01 10:05:22 -0600 )edit

Has this been resolved in the latest version of IES?

Austinbonnes gravatar image Austinbonnes  ( 2018-04-12 18:17:29 -0600 )edit

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Asked: 2015-03-17 20:26:21 -0600

Seen: 1,382 times

Last updated: Mar 26 '15