Heating Supply Air Temperature for System 9 and multizone system coils

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What NACM Section(s) are relevant to this issue?
5.7.2.4

Explanation of issue:
1) The design supply air temperature for HV system is not clearly specified in 
the descriptor Heating Supply Air Temperature or in Tables of 5.7. CBECC-Com 
currently uses 95F and the design Tstat setpoint of 70F, resulting in a 25F dT. 
 This seems low for an HV system.

2) Back in May of last year, Roger and Noah did some testing of the maximum 
Heating Supply Air Temperature (AirSys:ClRstSupHi) used for the baseline 
mulizone systems PVAV and VAV. They found a value above 60F resulted in higher 
baseline energy use. At that time, we settled on using 60F as the maximum 
system supply air temperature during heating. We have not revisited this 
testing since other bugs and translator updates have been made, but it occurred 
to me again when I noted the NACM still indicates the Heating Supply Air 
Temperature 70F. We should add this to the list of items to be reviewed for the 
v3b NACM release.

Proposed resolution:

Please provide any additional information below.

Original issue reported on code.google.com by da...@360-analytics.com on 31 Jan 2015 at 12:30

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1. There is some language in the system description (but not in the ACM rule 
section) that indicates 100F.  I would say that we can set it to 100F, or 105F 
at maximum.  In most cases, even with a 95F setpoint, the delta T will be a bit 
greater if the system is bringing in cold outside air.  In any case we should 
make it more clear in the ACM.

2. If a VAV system serves both interior and exterior zones, it will never be in 
heating except for morning warm-up.  If a VAV system served only exterior 
zones, it could have a bigger impact. Intuitively I don't see why a 60F heating 
setpoint would use less energy than a 70F heating setpoint, if all zones 
require heating, but I am fine with changing it if we feel that's the more 
common option.

Original comment by JohnJArent on 17 Feb 2015 at 8:01

• Changed state: Discussion