I have a questions about the modeling of Parking Garages for ASHRAE 90.1 Appendix G energy model
As I was looking up the definition of a conditioned and semi-heated space in Section 3 of ASHRAE 90.1 I noticed that under the definition of an "unconditioned space" it states that "Crawlspaces, attics, and parking garages with natural or mechanical ventilation are not considered enclosed spaces." In addition the definition of "ventilation" is "the process of supplying or removing air by natural or mechanical means to or from any space. Such air is not required to have been conditioned." Since the air is not required to be conditioned then the air can or cannot be conditioned, does that mean that any parking garage conditioned or unconditioned is not considered an enclosed space? If that is true then how do you model a parking garage since all spaces are defined as being enclosed?
Richard Auffermann
These definitions came up during review of one of my recent LEED
projects. For future reference, 90.1 questions may be seen by a group
more keen to respond if you post to the [bldg-rate] list.
I've got a definite position if you'd like to hear:
1. As you point out, per the definition of "unconditioned space,"
parking garages are "...not considered enclosed spaces." Whether in
design it's actually conditioned or not has no bearing on this
statement.
2. All of the definitions for space classifications, and indeed the
definition for "space," start with "an enclosed space..." Therefore no
parking garage can be considered "conditioned" or "semiheated," or even
as a "space."
3. This also means by extension (re: section 5.1.2): There are no
envelope requirements for parking garages, as they are not "spaces" of
any classification.
If you reject this approach and instead assert a parking garage can be a
"conditioned space," you'd be forced down a path of assigning identical
heating/cooling systems to parking garage spaces in both proposed and
baseline models, per Table G3.1.1.b, regardless of whether it's actually
conditioned or not. Things might get hairy if you're only heating or
only cooling (I believe the other would need to match the baseline
serving the rest of the floor/building, as may apply). I'd only suggest
that requiring heating/cooling of parking garages in all climates seems
odd for an energy efficiency standard - you'd have to explain that one
to me ;).
If you do have heating and/or cooling for a parking garage design, I'd
personally stick with points #1/#2 above and simply model such energies
as a process load alongside any mechanical ventilation systems,
identical in both models.
I personally use eQuest, and prefer to model parking garages as simply
as a series of building shades with a series of process/lighting loads
attached directly to the meter.
All this is my take on the situation. I think it's pretty defensible,
but there may have been CIR's I'm unaware of to the contrary - not that
precedent matters anymore...
Hope that helps you and others,
NICK CATON, E.I.T.
While parking garages may not be considered "spaces" per ASHRAE, I think
lighting should still be modeled differently for baseline and proposed
per Appendix G, and not considered a process load. "Lighting power for
parking garages and building facades shall be modeled" per Table G3.1,
and baseline lighting is determined per Section 9.2, where values for
parking garage lighting power appear in both the Building Area and
Space-by-Space Tables. You could attach these (different) lighting loads
directly to a meter, as Nick suggests, if you don't model the parking
garage as a space in the model.
William Bishop, PE, BEMP, LEED(r) AP
I would also add that, while lighting loads could be modeled differently
in the baseline and proposed models, ventilation fans should be modeled
identically. One exception to that would be if proposed fan motors
exceed minimum motor efficiencies in Table 10.8. Another possible
exception might be if ventilation fans were equipped with VFDs and
automatically controlled by carbon monoxide sensors, but you'd have to
prove your savings through an Exceptional Calculation Method.
Clark Denson, PE, CEM, LEED AP
A semi-related question on parking garages.
If the parking garage is part of a high rise, does the surface area count towards the overall window to wall ratio calculation?
Please advise,
Fred Betz PhD., LEED AP