[Bldg-sim] [Bldg-rate] CO2 sensors and outside airreduction.LEED forschools &ASHRAE 90.1-2004

James V. Dirkes II P.E. jvd2pe at tds.net
Wed Jan 14 13:32:31 PST 2009


Dear Bldg-Sim folk,
 
The insulation issue is one where more is NOT necessarily better, as is
indicated in Mr. Spielvogel's attachment.  For a "standard" building type
such as an office, it won't be too hard to assign an average density of
lighting and plug loads, use the favored HVAC system, and then tinker with
the "R" value to see where "optimum" is found.  Climate does make a
difference, as is also indicated in the article.
 
LEED, for the record, seems to give this interaction between envelope and
internal loads its due because the required energy analysis will  account
for these factors.  To be rigorous, though, you need to use a realistic
level of lighting and plug loads, NOT the connected load!
 
Another factor which I think ASHRAE 90.1 includes is the bridging effect of
many wall constructions.  Wood studs in residential construction, for
example, consume 15%-20% or more of the wall area and have very little
insulation value, degrading the overall average insulation value.  Steel
studs do the same thing in commercial construction.
 

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-rate-bounces at lists.onebuilding.org
[mailto:bldg-rate-bounces at lists.onebuilding.org] On Behalf Of Larry
Spielvogel
Sent: Wednesday, January 14, 2009 1:56 PM
To: Matutinovic, Luka; James Geers; bldg-sim at lists.onebuilding.org
Cc: bldg-rate at lists.onebuilding.org
Subject: Re: [Bldg-rate] [Bldg-sim] CO2 sensors and outside
airreduction.LEED forschools &ASHRAE 90.1-2004


Gentlemen:
 
I disagree about R-values for non-residential buildings.  See the attached
pages from the ASHRAE Handbook of Fundamentals.
 
Eur Ing Int PE Larry Spielvogel, PE, CEng,  FASHRAE, FCIBSE, FSLL
L. G. Spielvogel, Inc.
21506 Valley Forge Circle
King of Prussia, PA 19406-1137
Phone: 610-783-6350; Cell: 215-620-1234
Fax: 610-783-6349; Email: spielvogel at comcast.net

----- Original Message ----- 
From: Matutinovic, Luka <mailto:LMatutinovic at halsall.com>  
To: James Geers <mailto:jgeers at sfa-architects.com>  ;
bldg-sim at lists.onebuilding.org 
Cc: bldg-rate at lists.onebuilding.org 
Sent: Wednesday, January 14, 2009 1:16 PM
Subject: Re: [Bldg-rate] [Bldg-sim] CO2 sensors and outside air
reduction.LEED forschools &ASHRAE 90.1-2004

James,
I disagree with the claim that R-value has little effect. Look at the number
of all-glass buildings in northern climate, and I'll bet they barely meet
LEED or ASHRAE energy pre-reqs.  
 
However, there is definitely a law of diminishing return at work. That is,
after a certain R-value, additional insulation has very little effect. The
curve of R-value vs. energy savings flatlines.  In our case in Toronto, this
happens beyond R-20 walls and R-30 roofs typically.
 
The other thing to keep in mind is the type of building.  Offices are very
much dependant on skin losses, but hospitals for example are dominated by
ventilation loads and envelope losses are almost insignificant by
comparison.
 
As for your question on CO2 control, our experince has shown that you need a
very fine resulution to get any benefit.  That is for a mixed-air system,
you typically need one sensor per box/damper, so that you're not
over-ventilating the rest as you pointed out.  But mixed-air system are bad
anyway so CO2 control is a marginal improvement.  You get the most bang if
you de-couple the ventilation from the heating/cooling by using
compartmental system such as fan-coils or distributed heat-pumps.  Why these
systems aren't more popular in our market is beyond me...
 
 
Luka Matutinovic, B.A.Sc., LEED AP
Halsall Associates Ltd.

  _____  

From: bldg-sim-bounces at lists.onebuilding.org on behalf of James Geers
Sent: Wed 14/01/2009 1:09 PM
To: bldg-sim at lists.onebuilding.org
Cc: bldg-rate at lists.onebuilding.org
Subject: [Bldg-sim] CO2 sensors and outside air reduction. LEED forschools
&ASHRAE 90.1-2004



 

Previous posts have confirmed my suspicions that increasing the R-value of
walls and roofs has little to no effect on energy performance, due to the
outside air requirements.  

 

This raises a few questions:

 

1.   What is the most effective way to use CO2 sensors to dramatically
reduce the outside air requirements?

 

2.	Is it permissible to vary the CFM between the base case and design
case in the ASHRAE 90.1-2004 Appendix G model, and consequently in the LEED
template? 

 

3.	What is the most effective way to use CO2 monitoring in a building
with 40 classrooms and other large spaces.  If one sensor is triggered,
won't the entire zone get fresh air and defeat the energy savings? 

 

4.	If every classroom has a sensor, does any one have experience with
the replaceable / Mail in sensors to assure their accuracy. 

 

5.	If I model this in Equest, do I need a zone for every classroom. 

 

Thank you for any feed back.

 

James F. Geers

Registered Architect

LEED Accredited Professional

 

SFA Architects

300 West Fourth Street

Cincinnati, Ohio 45202

513.721.0600    

513.721.0611 (fax)

 

James F. Geers

Registered Architect

LEED Accredited Professional

 

SFA Architects

300 West Fourth Street

Cincinnati, Ohio 45202

513.721.0600    

513.721.0611 (fax)

 



  _____  




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