Page 182 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

160 Cha pte r F o u r

recovery of potential energy losses by various methods, such as water preheating
from waste streams, and the use of some natural sources, such as daylighting.
For the purposes of the calculations presented in the following section, all these
as just listed are included in the determination of the annual PDEM costs. If the
energy model used cannot adequately include some of these recovery savings,
then these can be calculated separately by using the ECM method and then
incorporated into the PDEM.
• The savings from on-site renewable energy sources that produce power are
calculated separately and are referred to as the renewable energy cost (REC). They
are defined in greater detail in EAc2. The anticipated annual costs of off-site energy
usage as represented by the PDEM can be offset by the on-site renewable energy
source cost savings (REC). The on-site renewable energy usage values (RECs) can
be subtracted from the PDEM as if the power they provide to the project were free.
As in the PDEM calculations, the actual capital costs of the REC are not included.
The REC savings are virtual savings based on the typical off-site utility rates.
• The baseline building is different from the proposed building in many ways.
The LEED-NC 2.2 and 2009 Reference Guides list many of these differences in
detail. Some of them include the following:
1. The proposed design is modeled with the actual building orientation on the
lot. The baseline design is the average of this orientation and the other three
orthogonal orientations.
2. Many building schedules, such as lighting or occupancy schedules,
can differ between the two models if the differences can be defended.
(See Chap. 8 for more information on schedules with respect to design
and construction.)
3. The baseline building is based on a specific assembly for floors, walls, and
roofs as outlined in App. G of the standard.
4. The total exterior wall area occupied by vertical fenestrations in the base
building must be the same percent of the total exterior wall area as in the
design case, unless the design case percentage is greater than 40 percent
and then the base building is restricted to 40 percent.
5. The vertical fenestrations in the baseline case are distributed uniformly on
all sides in version 2.2, but distributed in the same proportion as the design
in version 2009. In version 2009, the baseline case has these fenestrations
flush to the outer wall without any shading features.
6. The baseline building can be based on a different HVAC system, but again,
this variation must be defensible.
7. In version 2009, roof surfaces are modeled with a solar reflectivity of 0.30 in
the base case.
8. In version 2009, projects with natural ventilation may be able to include
these savings in the design, but will be evaluated on a case-by-case basis.
9. Combined heat and power (CHP) systems capture waste heat from
electricity for heating. ASHRAE 90.1 2007 App. G with the performance
rating method does not address how to incorporate the benefits of district
CHP systems into the design model and additional insight into how these
energy savings can be realized for the EAc1 Option 1 calculations is available
in the LEED 2009 Reference Guide.
10. In version 2009, the baseline case does not take credit for automatic lighting
controls.