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[bldg-sim] displacement ventilation again

Title: Message
 
I have a question which might have been proposed to the Bldg. Sim. in the past but I'm not sure. Regarding underfloor air systems, since  DOE2 assumes a well mixed space and cannot model the destratification effect and since the supply air temperature for heating and cooling tends to be much lower/higher than typical conditions, the throttling range tends to be quite high. There is an exception in ASHRAE 90.1 Appendix G that if you have a high throttling range you can try to argue an exception to this but I'm not sure if LEED would accept this. This might be similar to the natural ventilation issue. Would an underfloor air system which has typically 62 F to 64 F SAT with room thermostat settings of 72 to 75 F fall under this exception for LEED since DOE2 cannot mode the distratification effect or do most people try to force the throttling range down to meet LEED/ASHRAE requirements which is what I have done in the past.  I did not see anything in the USGBC Credit Interpretation Rulings regarding this subject. I have heard the next version of eQuest should be able to model underfloor air systems and that Energy Plus does but until then.....
 
Thank you,
 
Renée

Renée Azerbegi, CEM, LEED-AP

ambient energy ? solar & sustainable design solutions

t 303.278.1532 | f 303.278.8533 | c 303.885.2695 | renee@xxxxxxxxxxxxx | ambient-e.com 

 

 


From: bldg-sim@xxxxxxxx [mailto:bldg-sim@xxxxxxxx] On Behalf Of Mike Tillou
Sent: Thursday, December 28, 2006 10:56 AM
To: bldg-sim@xxxxxxxx
Subject: [bldg-sim] Modeling buildings with natural ventilation for Appendix G

There is no specific temperature range called out but Section G3.1.2.2 does limit the number of unmet heating and cooling hours your simulation can have.  The heating and cooling schedules you establish would be the required high / low temperatures you would need to meet. 
 
Again my interpretation of the Exception Calculation methodology is that if I feel the design I am modeling doesn't need to meet G3.1.2.2 then I need to argue the case why.
  
 

Michael Tillou, PE
ETC Group, Inc - Energy Engineering for a Sustainable Future
Ph:413-458-9870

-----Original Message-----
From: bldg-sim@xxxxxxxx [mailto:bldg-sim@xxxxxxxx] On Behalf Of Jon McHugh
Sent: Thursday, December 21, 2006 2:44 PM
To: bldg-sim@xxxxxxxx
Subject: [bldg-sim] Modeling buildings with natural ventilation for Appendix G

Mike,
 
The prescribed range being what?  Is there a schedule of high and low  temperatures that are called out in Appendix G?
 
Thanks,
 
Jon

From: Mike Tillou [mailto:miket@xxxxxxxxxx]
Sent: Thursday, December 21, 2006 11:12 AM
To: Jon McHugh; bldg-sim@xxxxxxxx
Subject: RE: [bldg-sim] Modeling buildings with natural ventilation for Appendix G

I have always gone under the assumption that my results have to meet the criteria for zone temperatures being within the prescribed range.
 
MMT
 

Michael Tillou, PE
ETC Group, Inc - Energy Engineering for a Sustainable Future
Ph:413-458-9870

-----Original Message-----
From: Jon McHugh [mailto:Jon.McHugh@xxxxxxxxx]
Sent: Tuesday, December 19, 2006 1:25 PM
To: Mike Tillou; bldg-sim@xxxxxxxx
Subject: RE: [bldg-sim] Modeling buildings with natural ventilation for Appendix G

Mike,
 
Does this proposed methodology place limits on the number of occupied hours above or below a given temperature/RH?
 
Thanks,
 
Jon McHugh

From: bldg-sim@xxxxxxxx [mailto:bldg-sim@xxxxxxxx] On Behalf Of Mike Tillou
Sent: Tuesday, December 19, 2006 7:18 AM
To: bldg-sim@xxxxxxxx
Subject: [bldg-sim] Modeling buildings with natural ventilation for Appendix G

Ramana,
 
The ASHRAE 90.1 ECB sub-committee is working on a methodology for simulating natural ventilation within the framework of Appendix G but I don't think its finished yet.  In the meantime here is what I would recommend.
 
Appendix G / 90.1 ECB allows you to use an exception calculation method to simulate hybrid systems or unique efficiency measures to demonstrate above-standard performance.  I think this would certainly apply in your case.  
 
Here's what I have done on projects requiring an exception calculation method. 
1. Establish your energy cost budget and your design energy case following the Appendix G guidelines.  
2. Create a second model using the Design Energy Case as the baseline and make the necessary modifications to simulate radiant heating / no cooling via natural ventilation. 
3. Report the energy savings from your exception calculation as a line item at the end of your LEED EA-1 summary table (similar to how renewable energy is reported). 
4.  Include a seperate summary table  for the exception calculation showing the energy end-use breakdown and how you arrived at the cost savings.  Show both the baseline and proposed energy use. 
5. Make sure the savings are reasonable and prudent for the system you are proposing. 
6. Document any changes to the model especially changes to schedules that were necessary to properly simulate your system.
7. Make it easy for someone to review your assumptions and the methodology you used to estimate the savings
 
I hope this helps.  Good luck.
 
Mike
 

Michael Tillou, PE
ETC Group, Inc - Energy Engineering for a Sustainable Future
Ph:413-458-9870

-----Original Message-----
From: bldg-sim@xxxxxxxx [mailto:bldg-sim@xxxxxxxx] On Behalf Of Ramana Koti
Sent: Monday, December 18, 2006 4:53 PM
To: bldg-sim@xxxxxxxx
Subject: [bldg-sim] Modeling buildings with natural ventilation for Appendix G

Dear all,

Is ignoring natural ventilation in both proposed and baseline designs an accepted/fair way of modeling based on Appendix G (ASHRAE 90.1-2004)?

Part of the proposed design has (radiant heating + natural ventilation) with no cooling which was modeled as a radiant slab, no cooling, natural ventilation ignored.

But the Baseline HVAC system based on Appendix G is System 5: Packaged VAV w/Reheat. (Natural ventilation can be modeled based on Air Change method or Sherman Grimsrud method though I do not know how to do it).

I cannot decide how to make the baseline and proposed comparable with respect to Natural Ventilation (in a manner acceptable to LEED review), suggestions will be appreciated.

Thanks,

Ramana Koti, Sustainable Building Analyst
LEED AP

ELEMENTS | a division of berkebile nelson immenschuh mcdowell architects
106 W. 14th Street Suite 200
Kansas City, Missouri 64105

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