#1613 CBECC-Com Issue - HVAC Results (2/20/2016)

[Nikhil Kapur]

2/20/2016 User - I am having some difficulty with a very simple model. The project is going into an existing space with some changes to lighting and envelope. The HVAC system is existing to remain. The HVAC system is comprised of 3 existing to remain fairly small roof top units, which have SEER 13 Dx heating and electric heating.

With the above information, the project is going for ‘Existing Alteration’ compliance; with New/Altered on the envelope & lighting systems as appropriate and ‘Existing’ for all HVAC components.

There are a couple issue when running a compliance simulation.
• The first and largest is that I am losing, with the cooling energy usage verses the baseline. Per the NACM I was under the assumption that both the baseline and proposed models should have the same exact HVAC system [Section 1.6.2 Table 1]. Is this correct? OR is there a different input path required to achieve this end goal.
o While these models should respond differently with baseline Envelope and Lighting systems, even modifications to the building envelope to make it far exceed code do not have an impact.
o The model has less than 40% WWR.

• Secondly, one of the units potentially has an economizer on it [to be field confirmed]. If an economizer is added to RTU-2 in the model, a warning is issued that the systems needs DDC to zone controls because its required on multizone system with an economizer. This is a single zone system. Please confirm how this should be handled. Currently, I just added DDC to zone in the model, which does not reflect reality/plans.
o Also worth nothing, that an economizer make the performance of the cooling system worse, but that hasn’t been fully tested.

[Nikhil Kapur]

2/22/2016 NK -

1. The Standard and Proposed systems in your model are modeled the same as existing. You can check the 165-0266 - Bkstore - ab - HVACSecondary.csv & 165-0266 - Bkstore - ap - HVACSecondary.csv files and the systems modeled is the same in both ( as your existing system). I also did a quick check on the IDF (E+) files – below is the snapshot of the baseline and proposed DX cooling coils:

So attached is a model that is configured to Baseline = Standard (so everything is existing). I then took the changes (alterations from your model and ran them individually to see where the penalty was happening). Attached is the spreadsheet with the individual runs. It appears the Roof alteration has the biggest penalty so we would suggest looking at the roof construction and in particular the reflectance/absorptance. Not sure if you have a cool roof on the project as part of this alteration.

            Analysis:           
                    Pass /  Compliance

Start Date & Time Filename (saved to) Run Title Weather Station Analysis Type Elapsed Time Fail Margin
2016-Feb-20 23:52:57 165-0266 - Bkstore_nk Standard=Proposed SAN-DIEGO-MONTGOMER_722903 Title24Compliance 0:23 PASS --
2016-Feb-20 23:54:06 165-0266 - Bkstore_nk Proposed Shading Surface = New SAN-DIEGO-MONTGOMER_722903 Title24Compliance 0:24 PASS 0.6
2016-Feb-20 23:57:08 165-0266 - Bkstore_nk Proposed Windows=New SAN-DIEGO-MONTGOMER_722903 Title24Compliance 0:24 FAIL -1.8
2016-Feb-21 00:02:16 165-0266 - Bkstore_nk Proposed Roof - Altered SAN-DIEGO-MONTGOMER_722903 Title24Compliance 0:23 FAIL -14.7
2016-Feb-21 00:04:22 165-0266 - Bkstore_nk Proposed Interior Wall - New SAN-DIEGO-MONTGOMER_722903 Title24Compliance 0:24 PASS --
2016-Feb-21 00:07:21 165-0266 - Bkstore_nk Proposed slab - Altered SAN-DIEGO-MONTGOMER_722903 Title24Compliance 0:24 PASS --

1. The economizer issue is something that could be a bug (which we will know more once the development team has reviewed). But in order to bypass the error message you would need to do the DDC to zone as you did and since the system is existing it would be modeled the same in the Standard case. The other alternative would be to not model it as you the system right now.

2. Regarding the economizer making the cooling performance/results worse – we would need to investigate it (we haven’t had any issues come in regarding this – though will need to go through our list in detail). Could you please send us a separate issue/files if you do run into it.

[Nikhil Kapur]

2/22/2016 User - Thanks for your help on this. I continued to test on this model as well, and noted a similar result that the roof is a major issue.

On this front, since it is an existing building, it is unknown if the Landlord has any documentation to specifics or if a CRRC rating was obtained for the original building. We have photographs and site observations that the roof is white, not a dark color as is the assumption for models without a CRRC ID. Is there any precedent for how to document an ETR roof which [potentially] pre-date [or missing] a CRRC rating?

[Nikhil Kapur]

Define/publish vintage data for default constructions

[Nikhil Kapur]

Closing old CBECC 2016 issue.