[BLDG-SIM] Natural Ventilation in LEED

[Marcus Sheffer]

FYI a new CIR has been posted on the USGBC web site regarding natural
ventilation systems and LEED projects.  The text is below.  Please consider
this just a starting point and general guidance for projects that are
similar to the one described.  We welcome feedback.
 

3/22/2007 - 
Credit Interpretation Request
Our project consists of two small buildings close to the ocean that will
achieve substantial energy savings by incorporating a natural ventilation
strategy. No mechanical heating or cooling is intended for either building,
with the exception of a small electrical/server room. 

The building is designed with a very narrow and long floor plate situated
perpendicular to prevailing winds in the area. Ventilation openings are
consistent with the requirements of ASHRAE 62.1-2004 Section 6.8. The
project also meets the requirements outlined in the CIBSE Applications
Manual 10: 2005 as referenced in EQc2 for Natural ventilation in
non-domestic buildings. Per Title-24 2005 requirements for natural
ventilation, the sum of operable windows will be greater than 5% of the
floor area of each space that is naturally ventilated. The openings will
also be readily accessible to the occupants of each space at all times.
Outdoor airflow through the openings in regularly occupied spaces will come
directly from the outdoors, not through intermediate spaces such as other
occupied spaces or corridors. Openings include operable windows, through-the
roof ventilators, and vents between interior spaces. Control mechanisms for
the natural ventilation openings are manual. A long, tall hallway situated
perpendicular to the prevailing winds will collect heated air and exhaust it
the outside. The roof over much of the space is sloped allowing air to enter
on the low side and exit on the high side. In all cases, the building is
designed to facilitate cross-ventilation with windows low on the walls for
drawing the air in, and windows and vents high in opposite walls or on the
roof to draw air out. Under ASHRAE 55 definitions, the building spaces are
defined as "naturally conditioned spaces, occupant controlled" where the
thermal conditions of the spaces are regulated primarily by the opening and
closing of windows or vents by the occupants. Since the building will have a
limited number of occupants most of the time, manual control of the windows
and vents has been determined the most appropriate strategy for the building
to allow control over individual thermal comfort. As indicated by ASHRAE
55-2004, section 5.3, the occupants of the space will be engaged in near
sedentary activities with metabolic rates ranging from 1.0 met to 1.3 met.
The mean monthly outdoor temperature for the project is greater than 50 deg.
F, and less than 92.3 deg. F all months of the year, as required under
ASHRAE 55-2004, section 5.3 for naturally ventilated buildings. 

The User's Manual for ASHRAE 90.1-2004 Appendix G states on page G-21: The
proposed building default cooling system does not exclude natural
ventilation from consideration. It just means that the proposed building is
modeled as a hybrid system where cooling is provided by natural ventilation
when conditions are acceptable and by the default mechanical cooling system
when natural ventilation is inadequate to provide thermal comfort. We are
requesting confirmation that the following modeling strategy conforms to the
requirements of ASHRAE 90.1-2004 Appendix G modeling protocol:

1. EnergyPlus will be used to model the building since the EnergyPlus
software has the capability to evaluate energy and comfort parameters tied
to natural ventilation.

2. The Exceptional Calculation Methodology will be applied to calculate the
natural ventilation savings.

3. The Proposed Design model will be developed to reflect the design
parameters for the envelope and lighting. Operable windows will be modeled
as fixed, and vents will not be included in the model. Mechanical systems
will be modeled identically to the default heating, cooling and fan systems
in the Baseline case, except that fans in the proposed case will be modeled
as cycling on and off to meet heating and cooling loads during all hours in
the proposed case, and will operate continuously during occupied hours in
the Baseline Case (per the exception shown in Table G3.1.4).

4. Using the Exceptional Calculation Methodology, The Proposed Design case
will be modified to include natural ventilation for all hours when the
cooling and heating loads can be met. Operable windows and vents will be
modeled as designed. Cooling and heating setpoint temperatures will be
identical to those in the Baseline Case. Schedules will be adjusted to
switch on mechanical cooling during hours when natural ventilation alone
cannot meet the space temperature setpoints. The final model will meet the
ASHRAE G3.1.2.2 requirements stipulating that the Proposed Design cannot
exceed the Baseline Design unmet load hours by more than 50, and that unmet
load hours for the Proposed Design and Baseline Design cannot exceed 300. 

5. (Plan B) If the hybrid system cannot be manipulated to meet the unmet
load hour requirements within the energy model, hourly output data from a
natural ventilation model (having no mechanical cooling) and the Proposed
Design model will be combined in a spreadsheet. Each hour where cooling and
heating setpoints are met in the natural ventilation model, the hourly
results for that model will be used. For all other hours, the hourly results
from the Proposed Design Model will be used.

6. An Exceptional Calculation Methodology narrative provided with the EAc1
submittal will document any schedule adjustments and assumptions that were
made to develop the hybrid system. The savings will also be included as a
separate line item on the EAc1 submittal.

Is our proposed energy modeling strategy for natural ventilation acceptable?

 
 

3/22/2007 - 
Ruling
The project is requesting approval for the method of modeling natural
ventilation as an energy efficiency measure and for taking credit under EA
credit 1. 

Submittals for natural ventilation savings will be evaluated on a case by
case basis. 

The tools and analysis protocol proposed is acceptable for modeling
ventilation savings in this instance. Other analysis tools may also be
appropriate.

To be able to adequately document the process and the results, please be
sure to provide in the LEED submittal the following: 

. A detailed project description 
. Clear identification of the areas that are taking credit for natural
ventilation
. A detailed description or references that document the modeling algorithms
and/or methodology for the natural ventilation portion of the energy model
. All thermostat, fan, infiltration and other appropriate schedules for
naturally ventilated areas

Also, the submitted evaluation must demonstrate that the range of unmet load
hours is similar for both the proposed and baseline building, to ensure that
savings are not claimed for hours outside of the control parameters. In this
case, the project has proposed to meet these peak loads with a hypothetical
cooling system in the proposed building.

The project will also need to clearly demonstrate that the operational
schedule for the natural ventilation system as modeled aligns with
anticipated occupant behavior in terms of scheduled occupancy vs. modeled
operation. For example, the model cannot assume that natural ventilation
will occur when no one is in the building to operate the system.

Because manual control is not addressed by the Appendix G modeling
methodology, the manual control features of this project must be submitted
under the exceptional calculation methodology for case by case review. The
project must be prepared to demonstrate convincingly that a manual control
strategy is appropriate and workable for this project.

Please also be sure to take credit for this measure as a separate item on
the LEED-NC v2.2 Submittal Template.


 
 
Marcus Sheffer - Vice Chair USGBC EA TAG
Energy Opportunities, Inc/a 7group Company
1200 E Camping Area Road, Wellsville, PA  17365
717-292-2636,  <mailto:sheffer at sevengroup.com> sheffer at sevengroup.com
www.sevengroup.com
 
 


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