Dear All,

I am curious how many systems or fan systems most of you usually create when
you model baseline systems?

I am particularly interested because under point G3.1.2.10 - Exhaust Air
Energy Recovery, one only has to apply an energy recovery device if a single
fan system is larger than 5000 cfm. I have not seen anywhere (please direct
me if there is indeed prescriptions for this in an ASHRAE publication)
guidelines for how many fan systems one has to model in a baseline building?
It seems that if I have a building with let's say 15000 cfm supply air, I am
free to model this building's baseline system with either 2 or 4 fan
systems? Then, if I model this building with 4 fan systems (each system
sized equally at 3750 cfm), I would not have to use energy recovery in the
baseline building, while if I choose to model the baseline with 2 fan
systems (each sized equally at 7500 cfm), then I must use energy recovery.

I would also appreciate input on a typical size of a fan system. If I have a
building that has a supply design air flow requirement of 100,000 cfm, how
many fan systems would typically be modeled? I am not too familiar with HVAC
design, and I tried looking for clues at manufacturers' websites but only
Carrier indicated an upper threshold of about 150 tons for their coils. Does
anyone have an experience with a typical airflow for a very hot climate over
a 150 ton coil? I am looking at System 8 for my baseline building, and I
imagine that for a large building (35 stories), several coils will be
installed. I am using Trace to do the energy model, and for some reason, the
more systems I model the higher the energy usage, keeping everything else
constant. Therefore I am interested in modeling several fan systems, if that
is common design practice.

Lastly, I would like to confirm that the design of the baseline system
beyond what is stipulated in Appendix G should comply with common practice?
In particular, numbers and sizes of systems does not seem to be much
discussed in Appendix G. Please let me know if you share my approach in
applying common design practices to size and locate equipment beyond
Appendix G prescriptions.

I appreciate any feedback you might have on these issues.

Faithfully yours,

*Ulrik Welle-Strand Horn *