Research Shows Duct System
Performance Has Significant Impact
On Home Energy Costs
Several research studies have taken a close and practical look at duct systems in homes. The results
are astounding. They show duct leakage and location of supply and return outlets have a much
greater impact on overall home energy usage than previously thought. The magnitude of the observed leakage from an un-insulated system when the air handling unit is turned on may double or triple the home infiltration rate and increase space conditioning costs by an estimated 10% to 12%. With field data from well over 1000 houses in different regions of the country, these tests demonstrate that duct
leakage is a major cause of energy loss. Pressure imbalances in the house produced by leakage, duct location and forced air distribution systems, can also cause secondary problems such as increased radon and moisture entry through foundations, plus possible back drafting of combustion appliances.
Other studies show that duct leakage can reduce the efficiency of a heat pump by more than 25%.
Fig. 1 – Duct Noise Attenuation Loss (dB/L)
Octave Band Frequency (Hz.)
Description 125 250 500 1000 2000 4000
Bare Sheet Metal* .1 .1 .1 .1 .1 .1
No perceived noise reduction
Wrapped Sheet Metal* .2 .2 .2 .2 .2 .2
No perceived noise reduction
Lined Sheet Metal* .2 .5 1.4 3.0 2.4 1.9
(1” thick)**
Significant perceived noise reduction
Fiber Glass Air Duct .4 1.4 3.3 3.9 5.0 3.7
(1” thick)***
Very significant reduction.
Perceived noise reduced to less
than 1⁄2 original level.
* Ver. I.L., 1978 ASHRAE Transactions Vol 84. Part 1, p.122
** ASHRAE HVAC Applications Handbook, 1999, Ch.
*** Noise Control Manual, O.C. 6th Edition, 1986
NAIMA North American Insulation
Manufacturers Association
A COMPARISON OF
AIR DUCT SYSTEMS
ENERGY SAVINGS
AND ACOUSTICAL
PERFORMANCE
Proven–In–Use
Since 1956, fiber glass duct systems have saved energy and power costs while delivering quiet comfort-conditioned air.
Fiber Glass Air Handling Systems
and the Indoor Environment
As interest in health and the environment has increased, so has American’s interest in the issue of indoor
air quality. When fiber glass air handling products are installed and maintained according to specifications, they can improve the overall quality of the indoor environment through the efficiency of their thermal and acoustical properties and their ability to reduce condensation. When IAQ problems are traced to the air handling system, the typical culprit is poor or inadequate ventilation and system maintenance – and not the type of ducts in the system. HVAC system operation and maintenance is being given increased attention as the need to improve indoor air quality continues.
If cleaning of the HVAC air distribution ducts becomes necessary, NAIMA’s publication entitled
Cleaning Fibrous Glass Insulated Air Duct Systems may be consulted for guidance. The guide provides general, recommended practices for the inspection, opening, cleaning, and closing of air ducts using fiber glass insulation. The guide also includes pre-cleaning and post-cleaning system inspection lists along with information on performance criteria such as fire classifications, air velocity ratings, leakage prevention, temperature allowances and reinforcement recommendations.
Air Erosion
Fiber glass duct board and duct liner products do not exhibit long term fiber erosion. Tests for erosion have
been conducted in accordance with the industry recognized UL 181 Standard, “Factory-Made Air Ducts and Connectors.”
Results of these tests, in addition to other independent studies, indicate that after initial start-up and blow
down, levels of airborne glass fiber found in buildings with fiber glass duct systems were no greater than the amount of fiber glass found in the outside air.
PUB. NO. AH109 5/00
Members of NAIMA’s
Air Handling Committee are:
CertainTeed Corporation
Johns Manville Corportation
Knauf Fiber Glass
Owens-Corning Fiberglas Corporation
44 Canal Center Plaza
Phone: 703/684-0084
Fax: 703/684-0427
E-mail: insulation@naima.org
Website: http://www.naima.org
Fiber Glass Duct Systems Compliance with
National Codes and Standards Making Bodies
n National Fire Prevention Assoc. (NFPA 90A & 90B)
n Building Officials Conference of America
n International Conference of Building Officials
(ICBO)
n Southern Building Code Congress (SBCC)
n Federal Housing Authority
“Minimum Property Standards”
n General Services Administration,
Conditioning Specifications”
n Corps of Engineers
“Air Conditioning Guide Specifications”
n Department of Army Guide Specifications –
Family Housing
n Department of Defense Guide Specifications –
Family Housing
n Department of Navy Guide Specifications –
Family Housing
Fiters Laboratories.
For a complete compliance list, refer to the back page.
For over 30 years, fiber glass duct systems have been handling air reliably and quietly in commercial and residential buildings throughout the country.
With a rigid fiber glass duct system, air is delivered to the registers quietly at design temperatures. Equipment and fan noise is absorbed and there are no banging and popping sounds typically associated with the contraction and expansion of metal ducts. It also helps reduce noise that can be transmitted through the duct system from room to room. (See Figure 1.)
Quality At A Lower Cost
Rigid fiber glass duct systems are more economical to install, than insulated sheet metal – and they save more energy dollars.
Figure 2 below shows that a rigid fiber glass duct system can save up to four times more energy than bare
sheet metal without sealed joints – 1.2 times more than sealed and lined sheet metal. The same chart shows that a 1² thick fiber glass duct system is thermally equivalent to sealed metal ducts wrapped with 11⁄2² of duct wrap insulation (which is typically compressed 25% as it is installed).
Unsealed metal ducts leak air at the joints where the duct sections are joined together and at the longitudinal joint. Studies show that as much as 30% of conditioned air can be lost at the unsealed joints. Un-insulated sheet metal leaks energy in other ways, too. Heat is lost by radiating through the un-insulated metal. And during cooling periods, the ducts can sweat and drip water. Metal duct joints must
be sealed and the duct insulated. If not sealed, the leakage can be so great that it may make the insulation ineffective.
The Solution
Fortunately, there is one solution to many of the problems reported with unsealed and un-insulated sheet metal – a rigid fiber glass duct system. A properly installed rigid fiber glass duct system has sealed joints. The system combines superior thermal performance and acoustical insulating properties in a single product with a damage-resistant surface.
Fiber glass duct systems are designed for use in indoor commercial and residential heating, ventilating, and air conditioning duct systems operating at air velocities to 2,400 FPM and at static pressures to 2² W.G. (Contact NAIMA member companies for specific limitations.) Fiber glass duct systems meet national and local codes recognized by most standards-making bodies. They are approved for use by key governmental agencies, and are
Fig. 2 – Air Duct Performance
& Cost Comparison
Leakage2(CFM) 216 27 27 27 27
Total Energy Loss3 (BTU/Hr) 20,882 15,915 6,028 5,416 5,129
Energy Cost4 ($/Sq. Ft) 4.70 3.59 1.36 1.22 1.16
Installed Cost5 ($/Sq. Ft.) 4.42 5.08 7.57 7.59 4.12
Payback Period (Days) Baseline 339 555 533
Energy Savings Tips
ReplyDeleteHere's what is most important:
1. Proper window orientation. Windows should be maximized on north and south and minimized on east and particularly on the west and northwest. For instance, if a large fixed window will face west in a plan (nice view etc.), it is vital that it receive an effective awning, very wide overhang or porch or other treatment to reduce solar gain.
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2. Window Shading. Design building so windows are naturally shaded by porches, awnings, shutters, trellises. A wide porch is preferred on the south side of the home. This
reduces cost while preserving daylight and adding a very useful area to the home where shaded outdoor activities can occur. At least 3 ft overhangs should be provided around the perimeter of the building and 4 ft is preferable. First floor windows on two story buildings should receive particular attention. Un-shaded windows should have windows with a maximum shading coefficient of 0.6 installed. Spectrally selective types are preferred, but expensive (>$10/ft2 installed). Trees can be very effective and increase home value as they grow.
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3. Light colored surfaces. Recommended for all of building exterior (this has a large impact on annual cooling; it is low cost since materials and colors are discretionary and color has little impact on cost). R-19 insulation is adequate in hot climates if the roof is white. Best white roof will be a pitched metal galvalum type which will maintain its reflectance and space cooling by 10% over other options. If a white roof is not specified then adequate attic ventilation (gable/ridge and soffit) should be provided with at least R-30 ceiling insulation and a truss mounted radiant barrier system (RBS).
Although they do not provide the performance advantage of a true white roof, light colored shingles (light gray or white) are still preferred although an RBS, added insulation, and good attic ventilation is recommended. Knee-wall insulation in cathedral ceilings should be carefully attached (standard practice falls off of vertical sections). (Attic fans)
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Why Should Ducts in Commercial Buildings Be Sealed?
ReplyDeleteDuct sealing in commercial buildings cost-effectively saves energy, improves air and thermal distribution (comfort and ventilation), and reduces cross contamination between different zones in the building (i.e., smoking vs. non-smoking, bio-aerosols, localized indoor air pollutants).
How Much Energy Does the Sealing Process Save?
Energy savings are different for light commercial vs. large commercial buildings and obviously depend upon the initial duct leakage level. The Carrier-Aeroseal Energy Savings Excel spreadsheet can be used to estimate the savings for both types of buildings. For ducts above an insulated ceiling in a light commercial building, energy savings should be 10–30% of HVAC energy use, and peak electricity-demand reduction is generally a higher percentage. In a large commercial office building with a VAV system, energy savings and demand reduction should be 20–40% of fan-system energy use and 5–10% of cooling energy use. As a rough estimate, excluding any of the non-energy benefits of duct sealing, simple payback times typically range from 1 to 4 years, and return on investment between 30% and 70%.