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5.7.2.3 Cooling SAT for interior zones of 60F is uncommon for single-zone systems #857

Open GoogleCodeExporter opened 9 years ago

GoogleCodeExporter commented 9 years ago 
What NACM Section(s) are relevant to this issue?

5.7.2.3 Cooling Supply Air Temperature

Explanation of issue:

First, CBECC-Com is implementing this rule correctly, per the current ACM. 
However, I believe the rule should be modified slightly as discussed below, in 
the ACM, to reflect standard practice.

The ACM defines the Cooling Supply Air Temperature (design SAT setpoint) as the 
space temperature minus 20F for perimeter zones, and the space temperature 
minus 15F for interior zones. This requirement was put in primarily for VAV 
multizone systems: if the SAT were 55F for the interior zone, since it always 
receives a significant cooling load, the SAT could not be reset upwards as 
often as perimeter zone loads decrease, since the system would always have to 
make 55F air to serve the interior zone.

This problem does not exist when using single zone DX (SZAC, or PSZ) systems, 
but the interior zone SAT setpoint is still 60F. These systems are usually not 
designed with airflow rates needed to make 55F under all conditions. Energy 
impacts vary, but benefits from integrated economizer use could offset 
increased fan energy with the higher design SAT setpoint.

Proposed resolution:

Consider setting the standard design SAT cooling setpoint at 55F for all 
single-zone systems.

Consider the change for v3b.

Original issue reported on code.google.com by JohnJArent on 20 Nov 2014 at 9:33

GoogleCodeExporter commented 9 years ago 
Rules to reflect this change merged to trunk @ r2970. 

Includes update to user default to have the same logic as the baseline.

NOTE: The change to the user default has impacts on models that use default 
rules for specifying the Air/ZnSys:ClgDsgnSupAirTemp. This includes sensitivity 
test models. Regression testing of the streamlined sensitivity test models 
indicates the change is small (<0.5% TDV), with the exception of the the 
following models where the TDV change was in the range of 1-5%:

0512815
0512916
5130006

Original comment by da...@360-analytics.com on 25 Jan 2015 at 10:12