News
The following is an excerpt from a study conducted by the Energy Conservation Assistance Program at the University of South Florida:
"On June 12th thru 18th 2001, a survey was conducted at a facility located in Lakeland Florida in accordance with the State of Florida Energy Office / ENERGY CONSERVATION ASSISTANCE PROGRAMS Designation: ECAP-CUL-1-99 Test Method for Comparing Utility Loads in Standard Constructed Buildings. The objective of this procedure is to determine the impact of the "As Built Conditions and As Installed Components / Equipment" on the utility loads in occupied residential, commercial and government buildings. The focus of this procedure is to provide a comparison to known standards for all parties interested in using passive energy devices to displaced conventional utility loads. This procedure addresses the energy consumption properties of the equipment and structural envelope tested and has no relationship to structural, electrical or fire code requirements.
- Our survey
indicated that the Total, Roofing System, Solar Heat Loads on the structure
tested were being significantly reduced by 27% during day light hours, by the
use of your ENERGY HOME-SHIELD Radiant Barrier System as a Energy Conservation
Measure (ECM).
-This is being accomplished with no negative effect on the existing buildings
Architectural Aesthetics or water tight integrity, and is also reducing Solar
Gain related air conditioning cost.
Our survey data indicates that your, as installed, ENERGY HOME-SHIELD Radiant
Barrier System consisted of ;
-1,000 Square Feet of Installed Material. · Was Rejecting 15.6 BTU per Square
Foot per Hour of thermal load.
- On the facility surveyed this is the equivalent of 1.43 Tons of Air
Conditioning Load per hour.
As installed, at the time of this survey, the ENERGY HOME-SHIELD Radiant Barrier
System installed by Energy Home Shield, P.O. Box 6244 Lakeland Florida
33807-6244, would qualify as an Effective Energy Conservation Measure in
accordance with the criterion set by the State of Florida Energy Office / ECAP
Program.
The system, as installed, reduced;
The above was
accomplished by Rejecting 27% of the Solar Heat Gain that had been being
Absorbed into the Attic System prior to the installation of the product.
On behalf of the United States Department of Energy, The State of Florida Energy
Office and the United States Environmental Protection Agency, let me thank you
for your efforts in assisting others to Conserve Energy and for considering your
Energy Conservation Assistance Program and the University of South Florida's
SBDC as an ally. This report is meant to be an educational guide to familiarize
you with the performance of your chosen Energy Conservation Measure and should
not be construed as an endorsement of any product or service by name or specific
design. Once again let me thank you for giving us the opportunity to use your
facility as a field test site. The data collected is a valuable asset to our
program in building a comprehensive profiling of actual energy related loads
that occur in occupied / operational buildings. This type of data is critical to
other Engineers facing decision making tasks, where published measurement and
verification data is not yet available or inaccurate. Please feel free to
contact our offices if we can be of any assistance in helping you meet your
future conservation goals."
Download the full report in PDF Format (1.2 MB)
We have known the TRUTH for 18 + years,
NOW it’s time
for YOU to KNOW THE TRUTH
The
following is an excerpt from Metal Building
Review, March 1982, which discusses the unique benefits of using
reflective foil insulation over using fiberglass in the metal building market:
From
an installer's point of view, foil insulation is a much better material than
fiberglass for use in metal buildings - no holes to drill in trusses., wires to
string, no problems insuring the crews arrive ahead of time to run insulation
over tops of trusses before the roof is laid down. no itchy mess under clothing,
and, best of all, no need for bulky protective wear during hot weather.
An owner or builder has ever better reasons
to consider foil insulation
superior to fiberglass than just the
installer's convenience:
Foil, installed, costs fifteen to eighteen percent less than
fiberglass of comparable R value; foil performs the primary task of insulating a
building more efficiently; foil meets fire safety standards better than
fiberglass; and foil can look better after installation than clumps of
fiberglass batting suspended overhead.
Insulation's
basic job to help maintain a set temperature level inside the building despite
extreme variations of temperature outside.
Since metal structures conduct heat well, insulation is a particularly
important component in conserving energy and sustaining a comfort level for
workers or temperature-sensitive materials inside. Quality foil insulation,
installed properly, meets this task far more reliably than fiberglass.
These
are sweeping claims for foil insulation that only a short time ago couldn't have
been seriously made. It took major
developments in the design and fabrication of foil isolation to make the product
really usable. Now, foil should be
getting a close, second look.
There are two reasons for foils performance advantages: first, fiberglass
installation procedures tend to defeat the very properties that make fiberglass
an effective insulator; and second, condensation of moisture, common to metal
structures in particular; substantially reduces fiberglass's ability to
interrupt the conducting of heat.
Fiberglass
works as an insulating material by creating air spaces within its bulk.
If the batting is compressed, the fiberglass becomes a conductor instead
of an insulator.
Increasing the mass of fiberglass
insulation doesn't compensate, because its effectiveness diminishes as the mass
increases. Fiberglass, as a
material, is a relatively good conductor, yet by use of air spaces, slows the
transfer of heat-but a substantial thickness of fiberglass will transmit heat
through the material itself
This
is a partial explanation of why ratings tests on fiberglass rarely match ratings
produced after the product is installed in a field location and tested again.
The
original rating supplied by the manufacturer is based upon a test of one inch
thickness, then extrapolated for three, four, or five inches thickness of the
material. However, as explained
above, piling on the fiberglass adds very little additional insulating value, so
the extrapolation method is invalid, and the R value from the manufacturer is
exaggerated. Additional R values
are tested at a moderate temperature. As
temperature changes, the values change by geometric proportions.
To complete the review of fiberglass insulation efficiency problems when used inside metal structures, consider the effect of moisture condensation. Condensation causes an R value loss quite suddenly. An R 13 insulation with only 1-1/2 percent moisture content drops to R 8.3."
Radiant
Barriers...
A
New Strategy for Fighting the Summer Heat
A radiant barrier system, used with traditional energy conservation strategies, could help you reduce your home's cooling bill. A radiant barrier basically is a layer of aluminum foil that reflects thermal radiation without transferring heat to other materials in your home.
Heat Gain
A building gains heat in three ways: conduction, convection, and radiation. Conduction is the transfer of heat directly through a solid material and on to another material with which it is in contact. Convection is the transfer of heat by air movement in which lighter warm air rises and heavier cold air sinks. Radiation is the transfer of heat from one object to another through space.
Radiant heat gain is not affected by most traditional conservation strategies. For example, insulation in walls and ceilings primarily restricts conductive heat gain, and double-glazed windows restrict both conducive and convective heat gain. On the other hand, a radiant barrier system can restrict the thermal radiation entering a building and thereby decrease the building's cooling load.
Radiant Barrier Systems
A radiant barrier system is composed of an airspace with one or more of its boundaries acting as a radiant barrier. A radiant barrier is a material that restricts the transfer of thermal radiation by reflecting the radiation that strikes it and by preventing the radiation of heat to other surfaces.
Aluminum foil is a good radiant barrier. Although aluminum foil is a good conductor it is highly reflective and absorbs very little of the thermal radiation that strikes it. So if it is placed between materials that are attempting to transfer heat by radiation (rather than conduction) and if it is separated from these materials by an airspace, the foil effectively eliminates the normal radiant heat exchange across the airspace.
Roof Systems
The attic of a Texas house offers excellent potential for the use of a radiant barrier system. First because the roof is the surface most exposed to solar radiation, and second, because most of the solar gain absorbed by the roof is transmitted down to the attic floor by radiation. Because the attic airspace separates the hot roof surface from the ceiling, no heat will move down by conduction. Because heated air rises, no heat will move down by convection from the hot roof to the ceiling.
If you place a radiant barrier (layer of foil) in the airspace between the hot roof deck and the cooler attic floor (insulation), you can eliminate almost all radiant heat transfer. Studies at the Florida Solar Energy Center (FSEC) indicate that, under peak daytime conditions, total heat transfer down through attics can be reduced by more than 40 percent through the use of a radiant barrier system. The temperature of attic insulation also is reduced significantly. During the period of peak daytime temperatures (noon to 2:00 p.m.) the temperature at the top of the attic insulation was about 10 degrees cooler beneath the roof with the radiant barrier system than beneath the roof without the system.
Heat
transferred upward through attics (winter heat loss) will not be affected as
much because a greater part of total upward heat transfer occurs by convection.
That is why radiant barriers in roof systems are a more effective cooling
rather than healing strategy, and why they may be a great benefit to Texas
homeowners. FSEC studies show that
in a typical Florida home, a radiant barrier roof could cut annual cooling loads
by 4 to 8 percent and peak cooling loads by 9 percent, depending on the level of
attic ventilation.
Guidelines
Based on the results of full-scale tests conducted at the FSEC Passive Cooling Laboratory, the FSEC has developed climate guidelines for the use of radiant barriers. Attic or roof radiant barrier systems are likely to be effective where there are 3000 or fewer annual heating degree days and 2000 or more annual cooling degree days (both measured at a base temperature of 65 degrees F). This area includes all of Texas except the Panhandle (figure 1). Radiant barriers are most effective on homes and smaller buildings that receive most of their cooling load from the outside conditions, rather than on larger buildings that receive most of their cooling load from inside the building.
Placement
Most types of roofs already contain some kind of attic or airspace that can accommodate an effective radiant barrier system. In new construction, it should be easy to install radiant barrier systems regardless of roof pitch. Figure 2 shows three possible generic locations for radiant barriers in attics. When first installed there will be no significant difference in the effectiveness of these locations. But in time, location 3 will suffer because of dust accumulation, which decreases performance. Dust is not as likely to collect on the underside of the radiant barriers at locations 1 or 2.
Figure
1.
Climatic
region recommendations for use of radiant barriers Figure
2. Typical
attic section with three possible locations for a
radiant barrier.
Location 2 is best for two reasons. First it can easily have two radiant barrier surfaces (top and bottom). Second-and more important-it offers the potential for separately ventilating the space between the radiant barrier and hot roof deck and the attic space itself. This results in an attic air temperature somewhat closer to the conditioned space temperature in both winter and summer. As with location 3 dust may collect on the top of location 2, but a radiant barrier surface facing downward will perform as well as one facing upward. Therefore, for reasons of dust accumulation use location 1 or 2 and depend on the downside for radiation control.
In
new construction, there is an alternative, which offers the advantages of
location 2 while providing the construction ease of location 1. This technique
places the radiant barrier on top of the roof rafters (or trusses) before the
roof decking is applied. It is
installed so that it droops 1 1/2 to 2 inches below the upper surface of the
roof structure. When the roof
decking is applied, an airspace separates it from the radiant barrier in a way
similar to that of location 2. This airspace also can be vented separately from
the attic. As with location 2 the
most reflective radiant barrier surface should face downward toward the attic
airspace.
Economics show that more than one radiant barrier in an attic is not cost effective. The first barrier surface eliminates about 95 percent of the radiant heat transfer across the attic. Adding more layers can affect only 95 percent of the remaining 5 percent.
Tightness
It
is not necessary to form airtight seals with radiant barriers; radiant energy
travels in a straight line through the air but is not transported by the air. In fact, if you choose location 3 (figure 2), you should use
a perforated foil product that will allow the free passage of vapor out of the
Insulation during winter This may also apply to location I in some cases because
the barrier is in contact with the roof decking.
Location 2 should not have moisture condensation problems because h has
an airspace on both sides of the radiant barrier.
Radiant barriers can reduce energy consumption and / or improve comfort in many buildings. But the radiant barrier strategy and construction technique will have to meet individual building needs.
Conclusions
Summer
heat gain can be driven by forces different from those that cause winter heat
loss. In southern climates, radiant barriers offer significant potential for
impeding solar-driven heat gains in buildings.
Their effectiveness depends on their location in the building structure,
direction of heat flow, building type, and occupant needs.
Widespread use of radiant barriers in overheated climates will prove
their potential for energy conservation in small buildings.
Information
for this article was taken from “Radiant energy transfer and radiant barrier
systems in buildings “ (FSEC-ON-6-84) and “Designing and installing radiant
barrier systems” (FSEC-ON-7-84), by Philip Fairey.
Both items were published as part of the Florida Solar Energy Center
Design Note series.
ROOF TEMPERATURES WITH RADIANT BARRIER FOIL APPLIED TO RAFTERS
INTRODUCTION
This test was
conducted in order to address the modest concern over the question that; “ if
the hot suns’ radiant energy is absorbed and conducted through the roof,
radiated through the air space to the radiant barrier foil insulation, which has
been stapled to the rafters, reflected back through the air space, and then
re-absorbed and conducted back through the roof ;” Would the roof temperature
rise appreciably enough to cause damage to the asphalt shingles ?
TEST
A modular roof
was constructed in a conventional manner, using 2 “ x 4 “ rafters, plywood
and reddish brown asphalt shingles. Radiant Barrier Foil Insulation was stapled
to the bottom of one section 24” wide by 48 “ long; and omitted in the
adjacent section. Two model 2v342 infared ( 2 tube 900 watt ) electrical heaters
were placed 6 “ perpendicular to the face of the “ roof “ at each section.
The roof “ tar “ started to” run “ in both sections. The heaters were
then placed 10 “ perpendicular as above with the same results. The heaters
were then placed 15 “ perpendicular and two thermometers were taped to each
section of the roof. ( one each side ). The results of this test are recorded
below.
TEST
RESULTS ON EFFECTS OF RADIANT BARRIER FOIL INSULATION ON ROOF TEMPERATURES
Note: All Temperatures are 0
F
* Outside shop
door was open influencing the temperature of the section without the radiant
barrier foil insulation. The door was shut at 10: 15 A.M.
** A
6 “ ( R-19 ) paper backed strip of FIBERGLASS Insulation was placed between
the 2 “ x 4 “ studs for the remainder of the testing period.
CONCLUSION
Installing
Aluminum Foil Radiant Barrier Insulation on roof rafters DOES NOT
increase roof temperatures. Placing FIBERGLASS Insulation between the rafters
next to the roof deck INCREASES the roof temperatures by approximately 16 0
F under the conditions tested.