[BLDG-SIM] Natural Ventilation in LEED

Peter Alspach peter.alspach at arup.com
Fri Mar 30 09:47:24 PDT 2007


Marcus,
 
I think that this approach to documenting natural ventilation within the
bounds of Appendix G is the correct one. 
 
However, there are a couple things I'd like to note for future
consideration:
 
1. If the proposed building can stay within the unmet load hours limits
without a fictitious mechanical cooling system, that should be
acceptable, provided that budget and proposed models have identical
thermostat setpoints, etc. 
 
2. As the USGBC considers project carbon savings and benchmarking of
buildings versus target finder, I would encourage a broader view on
natural ventilation and other strategies and the modeling process. In my
opinion, for this type of comparison the building should be modeled
exactly as it is to be built and operated - i.e. don't include
fictitious mechanical systems that are not installed or other such
deviations from the as-built condition. We already run this type of
model for owners so they can see what they are really going to expect
for energy savings and indoor conditions and I suspect that others do
the same.
 
Thanks for the good news.
 
Peter Alspach, P.E.
Associate
Arup
403 Columbia St., Suite 220
Seattle, WA 98104
T: 206-493-2226
C: 206-816-4902
F: 206-749-0665
E: peter.alspach at arup.com

________________________________

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Marcus
Sheffer
Sent: Friday, March 30, 2007 6:45 AM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Natural Ventilation in LEED[Filed 30 Mar 2007 09:36]


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, sheffer at sevengroup.com <mailto:sheffer at sevengroup.com> 
www.sevengroup.com
 
 

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