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

Wed Jan 14 10:55:39 PST 2009

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 
  To: James Geers ; 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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