[Bldg-sim] R-50 attic insulation

[Abaza Hussein]

Some of DOE recommendations is using R-50 in the attic ( above the ceiling). If the HVAC ducts are also in the attic, is it true that this might result in condensation on the ducts espicially in moderate to hot climates? is there any literature on this or any practical experience.
Any help is really appreciated.
H. Abaza

----- Original Message -----
From: "Kendra Tupper" <ktupper at rmi.org>
To: "Michael I Rosenberg" <michael.rosenberg at pnl.gov>
Cc: bldg-sim at lists.onebuilding.org
Sent: Monday, October 26, 2009 9:49:10 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Bldg-sim] Ashrae 90.1 - Unmet hours


I agree that Nick's interpretation is correct, but this is my biggest frustration with 90.1. For multi-zone buildings, the limit should be on the sum of "non-concident" unmet load hours for each zone. For standard energy modeling output reports, you can determine the total annual unmet hours for each zone, but you don't know which hours of the year they occur. 

In Jim's example, what if each of the 300 zones had 1 unmet load hour that all occurred during the same hour of the year? Or better yet, what if you had 300 zones with 30 hours of unmet loads (all at the same hours)? By the 90.1 reasoning, you would have 9000 unmet load hours (greater than the number of hours in a year!). 

I have thought about requesting a change to 90.1, but if the standard were to require people to determine the sum of non-coincident unmet load hours for each zone, it would put a large burden on the energy modeler to develop hourly output reports for each zone and hand calculate this. It seems like we're stuck with what we have until the energy modeling programs can produce an output report that describes the sum of non-coincident unmet load hours. 

Kendra Tupper, PE, LEED AP 
Senior Consultant 
Built Environment Team 

Rocky Mountain Institute  |  T  303-567-8641 |  F  303-245-7213  |   www.rmi.org 



On Mon, Oct 26, 2009 at 6:38 PM, Rosenberg, Michael I < michael.rosenberg at pnl.gov > wrote: 






Nick, 

  

Your interpretation is the correct one. According to the definitions in Standard 90.1. 

unmet load hour: an hour in which one or more zones is outside of the thermostat setpoint range. 

  

  

Mike 


__________________________ 

Michael Rosenberg 
Senior Commercial Buildings Energy Analyst 
ENERGY & ENVIRONMENT DIRECTORATE 

Pacific Northwest National Laboratory 
2032 Todd Street 
Eugene, OR 97405 
(541) 844-1960 
michael.rosenberg at pnl.gov 
www.pnl.gov 



From: bldg-sim-bounces at lists.onebuilding.org [mailto: bldg-sim-bounces at lists.onebuilding.org ] On Behalf Of Nick Caton 
Sent: Monday, October 26, 2009 5:33 PM 
To: Crockett, Jim; bldg-sim at lists.onebuilding.org 
Subject: Re: [Bldg-sim] Ashrae 90.1 - Unmet hours 




  

Jim, 

  

That’s actually a really good question that I was afraid to ask when I first encountered it – kudos to you!  I’ve currently resolved to follow what others seemed to be doing within and outside of my office:  Sum up all unmet hours for cooling and heating between the zones just as you describe.   In your example, I’d agree that the unmet hours of your 301 zone building total 301. 

  

I do agree that this doesn’t seem intuitively to be the intent of the standard, however between what is suggested within 90.1, the LEED handbook, and the LEED credit templates – I honestly can’t see any clear indication either way on which is the appropriate interpretation.  

  

I think the appropriate metric for ensuring appropriately sized systems should be something like: “hours of the modeled year in which at least one zone has an unmet cooling/heating load,”  but I think that was avoided by all concerned parties because it’s too wordy! 

  

My acting interpretation, again referencing your example, is that all systems of your 301 zone example affecting the zones with unmet cooling/heating hours should have their heating/cooling/overall sizing capacity ratios increased incrementally until the design hours fall below 300 (and/or within 50 of the sum from the other model, depending on your situation). 

  

Afraid I’m only really adding to the discussion here without providing a solid answer.  Would like to echo the desire to see anyone’s experiences that would help us know the “right” way to interpret this (in my case, specifically in the context of a LEED submittal). 

  


cid:489575314 at 22072009-0ABB

  

NICK CATON, E.I.T. 

PROJECT ENGINEER 

25501 west valley parkway 

olathe ks 66061 

direct 913 344.0036 

fax 913 345.0617 

Check out our new web-site @ www.smithboucher.com 

  



From: bldg-sim-bounces at lists.onebuilding.org [mailto: bldg-sim-bounces at lists.onebuilding.org ] On Behalf Of Crockett, Jim 
Sent: Monday, October 26, 2009 4:27 PM 
To: bldg-sim at lists.onebuilding.org 
Subject: [Bldg-sim] Ashrae 90.1 - Unmet hours 

  

Ashrae 90.1 (2004) Appendix G3.1.2.2 requires a baseline building to have less than 300 unmet hours.  What exactly does this mean? 

  

To illustrate my question:  assume you have a building with 301 zones, and each zone has 1 unmet hour per year.  This gives you a total of 301 unmet hours, and requires you to increase your baseline equipment capacity.  But you could argue that, on average, the building has only 1 unmet hour per year. 

  

Have any of you run into this?  Is it addressed in an addendum somewhere, etc? 

  

Any help is appreciated.  Thanks, 

  

  

  

Jim Crockett, P.E. 

  

Senior Project Engineer 

Energy & Carbon Management 

Nexant, Inc. 

4021 S. 700 E., Suite 250 

Salt Lake City, Utah 84107 

  

(801) 639-5603 - phone 

(801) 266-4786 - fax 

  
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