I am modeling a new building applying for LEED certification and want to make sure I'm using the right Appendix G baseline HVAC system configuration. The proposed design has three gas/electric rooftop packaged HVAC units, each with VVT dampers for subzoning, 6 to 12 subzones per system, all zones are defined at the stage of design development we're at. I believe I need Appendix G system type 3, gas/electric single zone units for my baseline, but do I use the same three HVAC unit configuration and assign the same eQUEST spaces/zones to the corresponding systems, or do I use a separate HVAC system for each space/zone? Thanks in advance for any replies.
Rick Routh
Dear Mr. Rick Routh,
You will have to assign one system type 3 to every zone in your building.
System type 3, as you point out, are single zone units, meaning they can
only respond to one thermostat input. However, in ASHRAE 90.1 User's Manual,
2004 on page G-23 they say that "the baseline building HVAC system is a
rooftop packaged system serving each thermal zone (or thermal block)." This
allows you to group similar zones in your proposed building together, and
you can assign your System type 3 to each block instead, speeding up the
calculations for your model. However, your thermal blocks must be specified
identically in your proposed and baseline building. Example G-H on page G-27
in the same User's Manual highlights this point.
For information on thermal blocks and how they are modeled in your proposed
building, refer to ASHRAE 90.1 (the standard, not the user's manual), p 173,
table G3.1 - 7.
I hope this clarifies your question, if not, feel free to contact me.
Sincerely yours,
*Ulrik Welle-Strand Horn *