CBECC Support - Gold Coast

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Please find attached a CBECC v3b-beta model that we have had previous issues 
with (SupportModel.rar).

The reason for using v3b-beta was to fix the baseline unmet load hours issue.

The queries I have are:

1.       I believe that the baseline model (ab) is using the incorrect system 
and would like clarification as to why it is not using System 3 
(SupportModel.rar)

The model attached is a single story, non-residential, less than 25,00 ft2 with 
only one room (B126_Bays) that has a cooling load greater than 75,000 Btu/h 
according to the zb model. I would envision that System 3 would be used in the 
baseline in accordance with Table 5 – HVAC System Map of the 2013 
NonResidential ACM reference. 
(http://www.energy.ca.gov/title24/2013standards/implementation/documents/2013_no
nres_ACM_reference/2012-10-26_2013_Nonres_ACM_Refernce_manual.pdf)

2.       In my model (SupportModel.rar), I have set all my air systems to use 
DDCToZone and DualMaximum control. However when I look in the “ap - 
HVACSecondarySizing.csv”, it states that all VAVReheatBox are using 
SingleMaximum. When I look in CBECC at my VAVReheatBoxs, that are set to 
DualMaximum and are not user editable. Is this a bug in the CSV file and 
energyplus model, or just in the CSV file? Looking in the “ap.xml” also 
show SingleMaximum.

3.       I did a test to see how much TDV was attributed to the exhaust fans I 
had set in a number of my zones. I simulated with the fans in place 
(SupportModel.rar), then removed them and simulated again 
(ExhaustFansRemoved.rar). By comparing the two results I thought that this 
would inform me of the TDV of the exhaust fans. However there was no change in 
the proposed model TDV and the standard model TDV Indoor fans increased by over 
50% (14.4 to 22.1). Can you explain why it increased the standard TDV and why 
it had no effect on the proposed model please.

Can you please include both Colin Rees (cc’d in this email) and myself in any 
replies.

Could you also provide us with an estimated response time.

Original issue reported on code.google.com by f.le...@gmail.com on 20 Feb 2015 at 5:51

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David, Do you have time to take a look at this?  If not, let me know and I can 
review.

Original comment by rhedr...@archenergy.com on 23 Feb 2015 at 5:07

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I can take a look at this today.
David

Original comment by da...@360-analytics.com on 23 Feb 2015 at 7:23

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Response to queries 1 & 2)

1) The NACM link provided to an old version of the NACM. The most current 
version I found on the CEC website indicates the current threshold for a 
baseline PSZ system is <10,000 ft2. 
http://www.energy.ca.gov/title24/2013standards/index.html
Roger, please check with John or Nikhil to make sure there is not a more 
current version that the user should reference.

2) DualMaximum VAV box control is only available for VAVReheatBox terminal with 
hot water coils. As indicated in a Warning posted to the log file, the control 
scheme is automatically revised to DualMaximum for the compliance simulation.

I'm still reviewing the two models associated with item 3).

Original comment by da...@360-analytics.com on 24 Feb 2015 at 3:33

• Changed state: Discussion

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Response to query 3):

The difference (or lack there of) in energy use noted between the two models 
(with and without an exhaust system) is due to the modeled exhaust AirSystem 
'Exhaust' not having the required AirSeg and Fan objects defined, which 
resulted in 0 fan power for the exhaust systems. A model that includes a fix 
for this has been uploaded to the Issues folder with the name 
'942_SupportModel_16Feb15_Fixed.cibd'. It should be noted that the increase in 
baseline fan power observed with the 'NoExhaust' model is due to the fact the 
baseline relief fan flow is non-zero once the building exhaust is flows are 
removed.

Rules to check for this and related issues have been committed @ r3097. 

Also noted in my review is two of the AirSystems had no OACtrl object defined 
despite the system have >0 ventilation air flow. Rules to check for this have 
been added, and the uploaded 'Fixed' model includes these objects. This change 
results in the simulated model having OA flow simulated, and in final testing 
of this model with OA simulated, one of the systems has insufficient heating 
capacity to ensure ThrlZn 'Zn B126_Bays' has <150 htg UMLHs.

Original comment by da...@360-analytics.com on 24 Feb 2015 at 7:16

• Changed state: Fixed

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Sent responses above to user along with fixed model.

Original comment by rhedr...@archenergy.com on 24 Feb 2015 at 5:05

• Changed state: DoneVerified

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I mentioned in my r3097 commit comment, but forgot to mention here: There was a 
bug in assignment of availability schedules for the exhaust systems in thermal 
zones.  I have fixed this in the current trunk version of v3b, but it is not 
present in the public beta release of v3b.  

Here is the error:

Error:  Table look-up failed: SpaceFunctionGroups:AvailSchRef( 
FuncGroup='UNDEFINED' )  |  ERROR:  Table row match not found evaluating rule: 
Set SIZING_PROPOSED ThrmlZn:ExhAvailSchRef  
(63:'HVACSecondary-ScheduleGroups.rule' line 885)

The result of this bug is that exhaust fans that are specified for some 
ThrmlZn:Type = 'Unconditioned' spaces will run continuously rather than track 
the availability schedule of other systems in the building, and therefore, a 
bit more fan energy than expected.

Original comment by da...@360-analytics.com on 24 Feb 2015 at 5:18