Download The area weighted average maximum SHGC for all glazed

Proposed Modification to the Florida Building Code
Modification #:
Name:
Address:
E-mail:
Phone:
Fax:
Code:
Section #:
Section 553.73, Fla Stat
Garrett A. Stone
BBRS
1025 Thomas Jefferson St., NW
Eighth Floor, West
Washington, DC 20007
[email protected]
202-342-0800
202-342-0807
Florida Building Code, Building
13-601.1.A
Text of Modification [additions underlined; deletions stricken]:
13-601.1.A Prescriptive requirements specific to Method A.
Windows shall meet the air infiltration requirements in Section 606.1 The area weighted
average maximum SHGC for all glazed fenestration products (windows, doors and
skylights) shall be 0.50.
Fiscal Impact Statement [Provide documentation of the costs and benefits of the
proposed modifications to the code for each of the following entities. Cost data
should be accompanied by a list of assumptions and supporting documentation.
Explain expected benefits.]:
A.
Impact to local entity relative to enforcement of code:
There should be virtually no impact on local code enforcement since it is
necessary to determine window areas and SHGCs (whether labeled or default
values) for code compliance already. This proposal would merely require that an
area-weighted average of such SHGCs be calculated by the builder and
determined to be equal or less than 0.50. This calculation can and should be
incorporated in the software and on the forms for compliance.
B.
Impact to building and property owners relative to cost of compliance with
code:
This proposal does not increase (or decrease) the overall baseline home energy
points required by the code. In fact, this maximum SHGC level (0.50) is 25% higher
than the baseline SHGC level of 0.40. However, this requirement will ensure that
windows with excessive solar gain are not used extensively throughout the home,
which will increase occupant comfort, reduce the size and cost of air conditioning
units, and potentially save energy. Owners will also be benefited by the
installation of more efficient windows versus other trade-off options since
windows have longer average useful lives than other efficiency measures (like
HVAC equipment). While it is possible that under some circumstances the first
cost of such windows could be greater than some other option that might be
Official Form 9B-3.047-2004
565339566
selected to meet the code requirements (although this is unlikely since the
reduced cost of HVAC due to smaller size alone should offset any increased cost),
no other option would provide the offsetting long-term benefits of this measure as
identified above.
C.
Impact to industry relative to cost of compliance with code:
This proposal will slightly reduce the builder’s flexibility in choosing options for
code compliance. However, this proposal still leaves reasonable flexibility since:
(a) the maximum SHGC level (0.50) is 25% higher than the baseline SHGC level of
0.40 and (b) the weighted average will allow a wide choice of windows and design
flexibility so long as the glazing collectively meets the 0.50 SHGC maximum. This
proposal does not increase (or decrease) the overall baseline home energy points
required by the code. While it is possible that under some circumstances the
builder’s cost of windows to meet this requirement could be greater than some
other option that might be selected to meet the code requirements, the reduced
costs from the commensurate reduction in the size of HVAC units permitted by
lower SHGC windows should more than offset any increased cost. Moreover, the
additional benefits of energy efficient windows addressed above more than justify
this restriction. Finally, reducing or eliminating poorly performing windows from
production and inventories will result in reduced costs to suppliers and increased
economies of scale in producing more efficient products, benefits likely to be
passed along to builders due to competition.
Rationale [Provide an explanation of why you would like this Proposed
Modification to the Florida Building Code.]:
This proposal is intended to establish a prescriptive provision that requires
collectively, on a weighted-average basis, that glazed fenestration (windows,
doors and skylights) meet a maximum 0.50 SHGC. The purpose of this provision
is to ensure that windows, glazed doors and skylights installed in homes
incorporate reasonable solar protection. The need for reasonable solar protection
in windows is already recognized in the overall baseline (0.40 SHGC), but this
prescriptive provision will ensure that poorly-performing windows are not
installed extensively throughout a home under the performance path.
The code already establishes prescriptive requirements for window air infiltration.
This proposal builds on that requirement, recognizing that in Florida, solar gain
protection is actually even more important than air infiltration.
This proposal will also make the code consistent with the national model code.
This provision is already included in the 2004 IECC and will be included in the 2006
IECC.
This proposal will provide numerous benefits. Occupant comfort during summer
days is a primary consideration, along with electrical peak demand savings
(reduced air conditioner sizing and reduced demands on the power grid at the time
when the system is most strained), reduced environmental impacts associated
Official Form 9B-3.047-2004
565339566
with electric generation, and potential energy savings. None of these issues is
presently accounted for in the performance path, which would allow the use of the
worst-performing glass. As a result, some reasonable limit on glazing SHGC
under the performance method is not only reasonable but absolutely necessary.
The following graph was prepared by Lawrence Berkeley National Laboratory and
posted on the Efficient Window Collaborative website (a non-profit project of the
Alliance to Save Energy), quantifying the probability of discomfort with various
glass products due to unwanted solar heat gain:
This graph clearly indicates that occupant comfort is tied directly to the solar heat
transmitted through windows. For example, for the windows with no solar control
(single and double clear), the probability of discomfort is over 60%, meaning that
more than 6 of 10 people would be uncomfortable in homes incorporating these
windows. On the other hand, both the double tint and double low-E windows,
which will meet the proposed maximum 0.50 SHGC limit, show a slightly more than
20% probability of discomfort. This huge difference in comfort alone justifies the
proposed limitation. Occupant comfort is also critical to energy use, since
overheated occupants are likely to use a thermostat adjustment (decrease the
thermostat and increase cooling energy) to mitigate the impact of unwanted solar
gain, substantially increasing energy use and cost.
A reasonable estimate of reduced peak demand per home from reasonable solar
control is around 1 kW and one ton reduction in cooling capacity. A conservative
estimate of the cost of a ton of cooling capacity is around $500. A reasonable
estimate of the cost of upgrading from clear to solar control windows is less than
$1/square foot of windows. It is readily apparent that the reduced cost of cooling
equipment capacity alone can offset the cost of improved solar control in
windows, not to mention the energy savings and other benefits from the more
efficient windows. Moreover, assuming 100,000 housing starts per year, the
electrical peak demand savings would amount to avoiding a 100 MW power plant
each year.
Please explain how the proposed modification meets the following requirements:
1. Has a reasonable and substantial connection with the health, safety, and
welfare of the general public:
This proposal has a reasonable and substantial connection with the health, safety
Official Form 9B-3.047-2004
565339566
and welfare of the general public because it will ensure that windows with
excessive solar gain are not used extensively throughout the home. As a result,
this modification will increase occupant comfort, reduce HVAC sizes, reduce
electrical peak demand and potentially save energy, which benefits are all
discussed in more detail above.
2.
Strengthens or improves the code, and provides equivalent or better
products, methods, or systems of construction:
This proposal strengthens and improves the code, and provides equivalent or
better products, methods, or systems of construction. Low solar gain windows
are nationally recognized as the best measure to address high solar gain in
southern, cooling-dominated climates. This is reflected by the adoption of this
same requirement in the 2004 IECC. The existing Florida code also recognizes the
appropriateness of this technology by setting the baseline SHGC for windows at
0.40 (well below this weighted-average maximum). By ensuring that windows with
excessive solar gain are not used extensively throughout the home, this proposal
will increase occupant comfort, reduce HVAC sizes, reduce electrical peak
demand and potentially save energy, which benefits are all discussed in more
detail above.
.
3.
Does not discriminate against materials, products, methods, or systems of
construction of demonstrated capabilities:
This proposal does not discriminate against materials, products, methods, or
systems of construction of demonstrated capabilities. This proposal is no
different in concept from the existing prescriptive requirement that windows meet
maximum air infiltration requirements. This proposal will permit substantial room
for use of alternative windows and glazing products by use of a weighted average
and a maximum value 25% above the existing 0.40 SHGC baseline in the code. All
window manufacturers, regardless of frame type, can manufacture windows that
will meet this requirement. By using an objective SHGC standard, this provision
does not require a specific window or glass material type.
4.
Does not degrade the effectiveness of the code:
This proposal will not degrade the effectiveness of the code, but will enhance the
effectiveness of the code. By ensuring that windows with excessive solar gain are
not used extensively throughout the home, this modification will increase
occupant comfort, reduce HVAC sizes, reduce electrical peak demand and
potentially save energy, which benefits are all discussed in more detail above.
Moreover, this provision will make the code more consistent with the national
model code. This provision is included in the 2004 IECC and will be included in the
2006 IECC.
Official Form 9B-3.047-2004
565339566
Section for DCA Only
Committee Action:
Committee Reason:
Commission Action:
Commission Reason:
Official Form 9B-3.047-2004
565339566