[Bldg-sim] Claiming Energy Savings for Natural Ventilation

[Marcus Sheffer]

To the larger energy modeling community:

 

The USGBC is seeking input and information related to the modeling of naturally ventilated and naturally conditioned buildings. 

 

The currently accepted LEED methodology for claiming natural ventilation/conditioning savings has the following requirements. It is fully explained in the Advanced Energy Modeling Guide for LEED Technical Manual, Appendix D.1.

-              The software must be able to directly model natural ventilation (EnergyPlus, IES-VE, etc.)

-              Perform a comparative thermal comfort model to demonstrate similar comfort levels comparing mechanical to natural ventilation.

-              Compare mechanical to natural ventilation only during met load hours. During unmet load hours it compares like systems (mechanical to mechanical or natural to natural).

 

The goal is to be able to offer project teams a simpler, sanctioned energy modeling methodology(s) to enable projects to claim energy savings related to natural ventilation/conditioning. The methodology should enable the use of all commonly used modeling software (DOE2, Trace, HAP, etc.) for estimating these energy savings. It should also likely enable projects to expand the acceptable thermal comfort comparison so projects can claim some savings for adaptive thermal comfort strategies.

 

We are differentiating between naturally ventilated, a la ASHRAE 62.1, and naturally conditioned or naturally cooled projects. Some thoughts on both are included below.

 

Naturally ventilated: 

A modeling protocol could be developed which makes project teams aware that credit is available for fan savings in naturally ventilated spaces. The fans in the Proposed HVAC system would be allowed to cycle since outdoor air is supplied by natural ventilation, while the Baseline HVAC system would supply the outdoor air mechanically and therefore require continuous fan operation during regularly occupied periods. The volume of outdoor air should remain identical and in both cases would still introduce an identical load on the system, but the method of delivery would be different.

 

Naturally conditioned: 

The modeling protocol should be more straightforward than the existing protocol.  As required by ASHRAE 90.1-2010 Appendix G Table G3.1-1Proposed (a), the proposed case should reflect the building design, however, different temperature and humidity control setpoints could be allowed between the proposed and baseline case . Appropriate methodologies could include work arounds for specific software that produce conservative estimates of savings. The protocol should also address regularly occupied spaces which are not fully enclosed (typically in warmer climates). In order to develop a viable modeling protocol some additional modifications to the baseline requirements may also be necessary for various climates and situations. The baseline thermal comfort settings could reflect the project’s locations as the normal, acceptable conditions will vary in different cultures.

 

We are in the process of gathering information and suggestions on how best to accomplish these goals. We are seeking existing modeling protocols that have already been published (such as for utility incentive programs or other research) and your good ideas for how to address these issues. Please send links and ideas to my attention. Thanks.

 

131011_LFA_seal_final.jpgColor.jpgMarcus Sheffer

7group logo 2011 small.tif 

 

 

1200 E Camping Area Rd, Wellsville, PA 17365

717.292.2636   ☼   717.495.5324 c

 <http://www.sevengroup.com/> http://www.sevengroup.com

 

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