Hi All,
Was hoping you all could check my thinking regarding how to model the following.
The project is a LEED NCv3/2009 energy model. The project is a large warehouse with some support spaces (offices, toilets, lunch room, security etc). It is located in Medellin, Columbia. Medellin has a very mild climate. It is apparently common for buildings in this location to not be provided with heating or cooling. In keeping with that, most spaces on this project will not be heated or cooled and satisfy the ASHRAE 90.1-2007 definition for UNconditioned spaces. (A few of the UNconditioned spaces even have permanently open, fixed louvers and could potentially meet the ASHRAE 90.1-2007 definition for unenclosed spaces).
Appendix G, Table G3.1, 1. Design Model, item b. states: All CONDITIONED spaces in the proposed design shall be simulated as being both heated and cooled even if no heating or cooling system is to be installed.......
My Modeling Plan:
Since the above statement is for CONDITIONED spaces, my plan is to model the UNconditioned spaces as neither heated nor cooled in both the proposed and baseline models. I intend to only model the lighting and process energy in these spaces. For the few cooled spaces on the project, I intend to model both heating and cooling in both the proposed and baseline models even though the spaces will actually only have cooling.
Potential Issues:
The only point of confusion or difficulty I see with my plan is that Table G3.1, 4. Schedules, Exception a, and 10. HVAC Systems could potentially create the impression that every space has to be simulated as heated and cooled. However, with further careful reading, it seems to me that the intent of sections 4 & 6 is to provide details for but not change the scope of section 1 which establishes the extent of spaces that have to be modeled as heated and cooled.
Natural Ventilation Credit?
Also, am I missing an opportunity here to get credit for natural ventilation in these spaces? Although, does providing someone with say an operable window really count as a natural ventilation system? That doesn't seem quite right to me in terms of getting LEED credit for energy savings. While the spaces have been designed to satisfy the natural ventilation requirements with respect to ASHRAE 62/LEED IEQ purposes, they haven't been "engineered" for natural ventilation from a comfort standpoint.
I would appreciate feedback regarding the correctness my thinking and modeling plan above.
Thank you for reading this far. Thanks in advance for your feedback.
Julia
Julia,
In response to your natural ventilation issue: The user manual for
ASHRAE 90.1 states "The proposed building default cooling system does
not exclude natural ventilation from consideration. It just means that
the proposed building is modeled as a "hybrid system" where cooling is
provided by natural ventilation when conditions are acceptable and by
the default mechanical cooling system when natural ventilation is
inadequate to provide thermal comfort." From this, I would imagine that
you should model your regularly occupied spaces as conditioned with this
so-called hybrid system, rather than unconditioned, as i understand from
your modeling plan. (by regularly occupied spaces, I mean offices and
conference rooms are conditioned and storage is NOT conditioned)
Technically, if your spaces are "sufficiently" ventilated naturally,
there would be little to no hours in which the mechanical half of the
hybrid system turns on.
If you are using equest, you might need to supplement your model with
separate comfort analyses of the naturally ventilated spaces and then
work in those results in the form of schedules.
-Linda
Linda Lam