[bldg-sim] Modeling buildings with natural ventilation for Appendix G

[Mike Tillou]

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 at gard.com [mailto:bldg-sim at gard.com] On Behalf Of
Ramana Koti
	Sent: Monday, December 18, 2006 4:53 PM
	To: bldg-sim at gard.com
	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
	
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