TRACE LEED ENERGY MODEL-Modeling Water Cooled Unitary Systems With Single Outside Air System and Cooling Tower
Hi All,
I am working on a LEED Energy model for a 8 floor Office Building. The
Baseline System type I have is Type 8 -VAV with PFP boxes / Chilled
Water-cooling, Electric Heating.
Now, the proposed building has Water cooling unitary units with a single
Outside Air unit. The outside air is supplied to mechanical room on each
floor through a ducted shaft with each floor having its own VAV box to
control the OA. Also, there is one single cooling tower that is used as a
Heat rejection equipment. I am doing this model in TRACE, so all the trace
experts are welcomed to answer this as well.
1. Since i have a Dedicated Outside Air Unit, I should model the outside
air fan for the baseline as well and allow it be sized based on PRM method
? Now, TRACE does not allow me to create a overall Air side system type
Outside air unit and thus i have to basically provide a Optional
Ventilation fan on each unit (i guess this is limitation but i cant think
of other way) for the Baseline. Also, TRACE only allows 90.1 Fan power
adjustment to Primary fan (Supply fan) so i will not be able to take any
credit for fan power adjustment on Outside air fan for using better filters.
Similarly, for proposed building i have to model the Optional Ventilation
Fan but this would be based on my actual selection. The selection i have is
for Dedicated Outside Air fan. Is it safe to assume the proposed outside
air fan power in "KW/CFM" from the actual selection for the energy
consumption?
2. Similar to point 1, TRACE does not allow to create a single plant as a
heat rejection equipment for all the Indoor units. Thus, based on my
selection for cooling tower , condenser water pump, is it safe to simulate
the proposed building with cooling tower and pump for each water cooled
unitary system with the same KW/TON and Watts/GPM respectively?
Finally, if i can do the above mentioned things in simulation, does anyone
else have any experience with this kind of situation for the LEED model? I
can explain everything in Narrative (that these are limitations of Modeling
software) , however acceptance is based on who is reviewing this.
Any thoughts, suggestions are greatly appreciated.
--
Thanks
Sincerely,
Amit Bhansali, LEED Green Associate, M.S. , EIT
Nov 29, 2012
OK so very simple, untrain your brain for a second, and listen...to some light jazz for a second. OK with me? Starting with your DOAS, your system selection for your proposed design should be the final htg/clg device/s. Trace has an optional dedicated outdoor air unit built within the Main system on a separate tab. So for instance, let's say you have individual fan coils (4-pipe) at each office zone that are connected to the DOAS air handler...the System is not a Single-Zone, but maybe "Fan Coil" then go to the Dedicated OA tab for setting the AHU discharge temps (should be neutral as to not put a ±load on the FCU's). Your main fans are the individual fan coil units, the optional fan is the AHU (incl. return or exhaust fan with this). The exhaust fan listed is for your rooms that have direct exhaust (bathrooms, showers, janitors closets, etc...
Just like a geothermal system, you're correct. You cannot have 2 sources of heat rejection. You can hook up multiple chillers to one tower. You will have to use your best engineering judgement to quantify for totals and loading/unloading.
I'm sure I didn't answer all of your questions, but hopefully I helped with the initial assessment of your proposed/baseline models and how they relate to Trace. Again, don't look at it from the AHU, but from the end user within the space, cause that is ultimately who we want to make comfortable.
Be Sustainable -- Never let today use up tomorrow!.