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Envelope & Lighting without Mechanical

asked 2016-08-25 13:35:06 -0500

updated 2016-08-26 19:40:27 -0500

I am working on an envelope & lighting only calculation and not modeling the HVAC system (no HVAC system is input). It is my understanding that when I do this, the heating and cooling are then given identical standard and proposed inputs by the software and therefore balance out and don't effect the calculations or the compliance.

What I am finding, is that the calculations show that I am taking a huge penalty for indoor fans (of which none are specified) and penalties for space heating and space cooling. Often, the collective penalties are enough to preclude compliance.

Am I doing something wrong? Why should indoor fans cause such a penalty if I am not modeling mechanical?

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Could you use existing tags and specify the piece of software you are using?

pflaumingo's avatar pflaumingo  ( 2016-08-25 17:14:22 -0500 )edit

In the real world, changes to envelope and lighting systems can be substantially interactive with HVAC enduse energies. You might productively ask yourself: "If I were to remove any differences in fan/heating/cooling, then how am I trying to quantify envelope performance?"

It would be further helpful if you could clarify the code/standard for which you are trying to demonstrate compliance. I suspect for showing envelope and/or lighting prescriptive / "calculated" compliance, you might find the whole exercise much simpler with a purpose-built tool like COMcheck.

Nick Caton's avatar Nick Caton  ( 2016-08-26 09:05:58 -0500 )edit

Thank you for your thoughts. I am using the California CBECC software. Sadly, COMcheck is not approved for use in CA.

CA Title 24 allows us to do the compliance using any two systems (lighting, envelope & HVAC) You are correct - they each affect each other, but in the real world of California <insert joke="" here=""> doing separate calculations is very normal. The software is supposed to allow this.

The problem is that I am taking a huge penalty for fans - despite the fact that there are no fans or HVAC specified.'s avatar  ( 2016-08-26 13:17:28 -0500 )edit

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answered 2016-08-29 02:35:12 -0500

Nick Caton's avatar

I found this exchange which seems to provide some related advice specific to envelope+lighting compliance with CBECC:

I can not claim any practicing expertise with CBECC or recent direct experience with T24, but it does look like auto-sized baseline systems of the same type should be expected. Whether those auto-sized baseline systems applicable to both cases should result in a net penalty I suppose should then depend upon what exactly you're inputting for lighting and envelope, relative to the baseline case.

If the results remain quite unintuitive, perhaps you may find some luck submitting a support ticket here?

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Asked: 2016-08-25 13:35:06 -0500

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Last updated: Aug 29 '16