[Bldg-sim] ASHRAE 90.1 Definition of "Conditioned" - The PRM Reportfor LEED EAc1 and Appendix G Energy Model

James V. Dirkes II P.E. jvd2pe at tds.net
Mon Jan 12 07:36:08 PST 2009


Dear Ulrik,
 
Regarding "conditioned space":
 
"Conditioned space" seems pretty straightforward to me.  If, for example,
the cooling system for a 10,000 sq.ft. space has 10 tons cooling capacity,
then the capacity is 12Btu/hr/ft2 (10tons x 12,000 Btu/hr/ton / 10,000 ft2)
This exceeds the ASHRAE threshold of 5 Btu/h/ft2, so it's "conditioned".  If
the cooling system was only 4 tons, it would not be "conditioned" (only 4.8
Btu/hr/ft2).
 
The definition depends only indirectly on "U" values and wall areas.  For
any given construction, you choose to provide an air conditioning system or
not.  You can also choose to cool a lot or a little.  Each choice affects
whether you end up with an air conditioning system greater than 5 Btu/hr/ft2
or not.
 
Heating works the same way, except the threshold varies by climate zone.
 

The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

 

 

  _____  

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Ulrik
Welle-Strand Horn
Sent: Saturday, January 10, 2009 9:47 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] ASHRAE 90.1 Definition of "Conditioned" - The PRM
Reportfor LEED EAc1 and Appendix G Energy Model


Dear All,

I would like to know if and how you consider ASHRAE's definition of
conditioned space on page 13 of the 2004 version.

Specifically, I am interested to know if you abide by this definition when
listing the conditioned vs unconditioned area? The definition seems really
specific to me, explaining how the system serving a conditioned area must
have a certain capacity per square foot of building area served. It even
goes on to explain how for some spaces one must consider the sum of the
products of various U-factors and wall areas. To me, it does not seem like
one can eyeball all these comparisons and definitions and therefore one has
to go ahead and measure the capacities of systems and compare them with the
area they serve, as well as do computations for rooms that might be
indirectly conditioned.

The PRM report for LEED requires you to list unconditioned and conditioned
areas separately. Do any of you actually go through the calculations to find
out if each single space in your project complies with the definitions put
forward in the 90.1 document? It seems to me like more effort than what it's
worth. I don't recall ever using this classification of unconditioned vs
conditioned anywhere else in the LEED certification process. Especially, I
don't recall ever having to use this definition to do the PRM model itself
under Appendix G. Has anyone come across another place than the PRM report
where the efforts of classifying their spaces accoring to the 90.1
definition above has been rewarded? Please also let me know if any one of
you have ever experienced trouble getting your project LEED certified
because of lack of compliance with this definition.

Lastly, the definition explicitly states that "Crawlspaces, attics, and
parking garages with natural or mechanical ventilation are not considered
enclosed spaces." Do most of you usually leave out car parks from the PRM
area report? I am working on a building where about 60% of the floor area is
parking space, meaning the sum total in my Space Summary will be much less
than stated otherwise in the documents submitted to USGBC. I know that they
are looking for all the total areas to be pretty consistent, and that some
people experience problems when thes total areas don't match up. Has anyone
ever dealt with this issue? If so, how did you deal with it?

I appreciate any response you may have to any or all of my questions.

Sincerely yours,


Ulrik Welle-Strand Horn 
Sustainability Engineer


Silpa Inc.
s i m p l e  .  s c i e n t i f i c  .  s u s t a i n a b l e

AMERICAS | MIDDLE EAST | ASIA
www.silpainc.com <http://www.silpainc.com/> 


India: +91.90080.96083

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