Section 3.1.2 - HVAC System Map

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What 90.1 PRM Section(s) are relevant to this issue?
Section 3.1.2 - HVAC System Map, Table 1

Questions:

1) The floor area and number of stories used to determine a baseline system 
type, according to the 2007 UM, apprears to the follow this logic if the 
predominant occupancy if NonRes:

NonResCondFlrArea = TotCondFlrArea - ResCondFlrArea

You then use NonResCondFlrArea and its predominant heating fuel source to 
determine the baseline system type per the map.  

Assuming this is correct, should the HtgOnly system area and/or any other 
process/exception areas be subtracted from the NonResCondFlrArea to determine 
the baseline system type?  For example:

NonResCondFlrArea = TotCondFlrArea - ResCondFlrArea - HtgOnlyFlrArea

2) The user manual also suggests that the number of stories used in the system 
map table is based on the occupancy of the story.  For mixed occupancy stories, 
should the story classification based on the predominant occupancy conditioned 
area, or always include any story that has >0 nonresidential space? 

3) Are all conditioned stories, above- and below-grade included in the system 
map count?

4) In either case stated above, if the story has any amount of conditioned 
floor space, is it included in the count?  For example, a below- or above-grade 
parking garage with just elevator lobbies/stairwells at each floor, where the 
floor is predominantly unconditioned.

Proposed resolution:

1) For T24 NACM, I subtracted out the HtgOnly area to determine the area for 
the table, but left process other system exception space area in calculation.  
The thought being that a 1 story, 50000ft2 htg only warehouse with 5000ft of 
office should not be pushed into the System 5 level, rather should be System 3. 
 Recommend the same here.

2) T24 NACM does not distinguish between Res/NonRes stories, just total 
above-grade stories. Since UM does distinguishes, recommend using the 
predominance rule.

3/4) Both above and below-grade, any story with conditioned floor area is 
included. 

For building stories, I am assuming this is a user input, since the 
BuildingStory count in the model may not be the correct indicator. I ask the 
questions here so that I can provide some direction in the HELP documentation.

Original issue reported on code.google.com by da...@360-analytics.com on 18 Sep 2014 at 5:32

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Roger, I believe your proposed resolution is mostly on the right track. Copying 
Mike's response to this issue below-

1.Yes, I think it makes sense to subtract out the heated only storage area in 
the calculation. This is discussed in the 2010 User's Manual. 

I think the calculation of Non-Res or Res conditioned floor area should only 
subtract out the area of spaces qualifying for a different system type from 
Table G3.1.1A. 

Predominant Condition Floor Area = Total Area – Area qualifying for 
additional system type in Table G3.1.1A. 
So;
NonResCondFlrAreaFosFuelHt = TotCondFlrArea – ResCondFlrArea (if greater than 
20,000 sqft) -  NonResCondFlrAreaElectHt (if greater than 20,000 sqft) – 
HtOnlyStorage (any area)

2.  If a mixed res/non res building does not have enough of area of each 
(greater than 20,000 sqft) to qualify for additional system type per 3.1.1 
exception A, all floors should be counted as the predominant type. If a mixed 
res/non res building has enough area of each (greater than 20,000 sqft) to 
qualify for both res and non res systems per 3.1.1 exception A, than a mixed 
use floor should be counted in both. So a five story building with 2 floors 
res, 2 non-res, and one mixed could have three floors res and 3 floors non-res. 

3.  Both above and below grade floors should be counted. This is actually 
clarified in an addendum to 2013 that is out for public review right now. 

4.  A floor with any conditioned area should be counted as a floor. 

Original comment by supriya....@pnnl.gov on 18 Sep 2014 at 10:21

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One clarification on the example for item 2) provided in Comment #1.  If this 
is a traditional mixed-use building with dwelling unit entries from an interior 
corridor, wouldn't the 5 story building example be 5 stories non-res, 3 stories 
res?

Original comment by da...@360-analytics.com on 1 Oct 2014 at 9:23

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David,
In example 2, if the mixed use floor has enough area of each residential and 
non-residential space types then it would be counted in both.
in the example stated above, 2 floors are use type residential, 2 
non-residential and one mixed use which has area >20,000 sq.ft for both, hence 
is counted towards both, i.e. 3 floors residential and 3 floors non-residential.
The example I can think of where a building would be 5 stories, with 5 floors 
non-res and 3 res- If 2 floors are non-res (i.e. predominant use type is 
non-res) and 3 floors have area >20,000 sq.ft for both non-res and res then 
what you've stated would be true.

Mike, could you also confirm my interpretation

Original comment by supriya....@pnnl.gov on 1 Oct 2014 at 10:23

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David and I discussed this on a call. We decided on the following steps for 
defining the baseline system type-

1. First determine the predominant use type (residential vs non res vs mixed 
use for each floor)
2. Taking an example of a building with a floor, predominant use type non-res,
NonResCondFlrArea = TotCondFlrArea – ResCondFlrArea (if greater than 20,000 
sqft) – HtOnlyStorage (any area)

NonResCondFlrAreaFosFuelHt = TotCondFlrArea – NonResCondFlrAreaElectHt (if 
greater than 20,000 sqft)

Original comment by supriya....@pnnl.gov on 1 Oct 2014 at 11:22

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I think you are correct. I had not considered that. 

Original comment by bikerose...@gmail.com on 2 Oct 2014 at 12:43

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In David's example, the rules have determined that the building qualifies for 
two system types. I think the issue is what systems would be used for the 
corridors in the predominantly residential floors. I think they use 
non-residential systems. Possible the main system, but more likely they qualify 
for the additional packaged single zone exception due to differences in 
schedules or loads. 

Original comment by bikerose...@gmail.com on 2 Oct 2014 at 1:11