LBL-35445
`
`New Technologies for Residential HVAC Ducts
`Burke Treidler and Mark Modera
`Energy and Environment Division
`Lawrence Berkeley National Laboratory
`Berkeley, CA 94720
`
`February 1995
`
`Executive Summary
`There are many problems with residential duct systems as they are currently installed. It has been
`shown that they lose significant amounts of energy through leakage and conduction to their
`surroundings (Cummings et al. 1990, Davis 1993, Modera et al., 1991, Modera 1993, Modera and
`Jump 1995, Parker 1989, Parker 1993, Proctor et al. 1992, Treidler and Modera 1994). For electrical
`utilities this is of particular concern because the effects of this leakage and conduction are more
`pronounced during periods of peak electrical demand.
`
`Unfortunately, the problems with duct systems are not widely recognized within the
`construction industry and there are no strong economic incentives to solve them. Duct system
`performance is not evaluated and HVAC contractors overcome duct system shortcomings by installing
`oversized equipment. Currently, most duct systems are installed with minimal insulation and by
`methods that give little thought to insuring proper sealing.
`The lack of incentives for improved duct system performance has repressed innovation. With
`the exception of insulated plastic wireflex duct, residential duct systems are essentially unchanged
`since the 1920’s. ucts with higher levels of insulation have recently become available bu duct fittings
`have seen no change. Fittings are uninsulated, have a large potential for leakage, and are difficult to
`install in a manner which will insure no leaks.
`This report summarizes the potential for new technologies for ducts, duct fittings, and insulation.
`It begins with a review of what technology is currently in use or available and found that the only
`inexpensive ducts in production are insulated wireflex ducts, sheet metal ducts, fiberglass board ducts,
`and uninsulated plastic ducts. For duct fittings, the market was found to be dominated by sheet metal
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`fittings with some use of ductboard. Fittings that snap together were found for use with steel ducts but
`are too expensive for a residential setting. An uninsulated sheet metal duct which uses a rubber gasket
`was also found. Two companies are trying to develop plastic fittings, but their designs don’t consider
`improving the method of attachment to wireflex duct.
`A survey was conducted of California HVAC contractors to determine what methods they
`currently use, how concerned they are with sealing duct connections, and what fractions of their
`expenses go to duct materials and installation. It was found that insulated wireflex ducts and sheet
`metal fittings are used in almost all residential installations in California. Fiber board and sheet metal
`are used equally for plenums. It was found that there are basic misunderstandings about sealing duct
`connections. For example, gaskets were placed on registers in such a way that they would not prevent
`the register leaking air into the wall cavity. The use of duct tape to attach flexible duct was also a
`common practice even though it is common for duct tape to fall off after some time. The cost portion
`of the survey showed that HVAC equipment, duct materials, and duct installation are approximately
`equal parts of the contractors’ costs.
`Ideas are presented for new duct technologies that are foolproof to install, sufficiently insulated,
`and not prone to leakage. For ducts, the Gas Filled Panel (GFP) technology of Griffith et al. (1992) was
`FP ducts were developed and their qualities for manufacturing, ease of installation, compressibility,
`etc. were evaluated. A model was then made of the most promising design. Ideas for plenum fittings,
`attaching registers to boots, and attaching ducts to fittings were created and evaluated for their potential
`advantages. Several of the ideas for fittings are applicable to existing wireflex ducts and sheet metal
`fittings.
`In order to be accepted, new designs would have to pass code requirements. The most difficult
`code requirement to pass economically is fire spread and smoke generation tests. The plastics currently
`used in buildings for windows and wall panels will not pass the stricter smoke generation criteria for
`duct materials.
`Finally, we evaluated the major hurdle for acceptance of new technologies, economics. Analysis
`of initial costs for the GFP technology shows that it is more expensive than existing technology even
`before considering steps necessary to pass fire regulations. However, new fitting designs appear to be
`competitive with other options for improving ducts and offer simple payback times of no more than 6
`years.
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`1.0 Introduction
`Residential HVAC duct systems in California perform inadequately. Research has shown that
`installed duct systems have significant losses to their surroundings through both leakage and
`conduction (Cummings et al. 1990, Davis 1993, Modera et al., 1991, Modera 1993, Modera and Jump
`1995, Parker 1989, Parker 1993, Proctor et al. 1992, Treidler and Modera 1994). For example,
`Modera et al. (1991) found that conduction losses averaged 23% of furnace output in California’s
`mild climate. It was also found that the leakage of ducts was approximately 1 cm2 of effective leakage
`area per m2 of floor area. For a typical house with 140 m2 (1500 ft2) of floor area, this means the
`leakage in the duct system is equivalent to that from a 13 cm (5.25 inch) diameter hole.
`
`The performance of duct systems is of particular interest to electrical utilities because research
`has shown that energy losses from ducts are disproportionately higher on days of peak electrical
`demand. Peak electrical demand in California occurs in the late afternoon on weekdays during heat
`waves. This is when cooling demand is high from commercial customers and more residential
`customers are using their air conditioners in the afternoon. On these days, duct performance is very
`low because most ducts are located in attics. Attics are at their highest temperatures and ducts therefore
`lose more energy to them by conduction. Also, the air sucked in by leaks in return ducts is hotter and
`increases the air temperature entering the cooling coil.
`From a technical standpoint, the dismal performance of duct systems is a simple problem to
`correct. New connection methods, using snap-together fittings, would insure that installed ducts have
`negligible leakage. Increased levels of insulation would decrease conduction losses. However, this has
`not happened because residential HVAC contracting is a very competitive business where the only
`incentive is to keep first costs low. There are no standards for duct performance and consumers do not
`typically realize how poor duct system performance affects them. So HVAC contractors have tended
`to install poor duct systems and overcome their problems by oversizing the air conditioner. Since the
`consumer only considers air conditioner size, the oversizing convinces them they are getting a better
`system.
`Because of the lack of incentives for improvement, ducts and duct fittings show few signs of
`innovation. Insulated wireflex duct is the one exception. It has lower labor and material costs than its
`competitors and has become the most commonly used duct in California. A glance at catalogues for
`HVAC fittings shows they are still made of sheet metal, just as they have been since the 1920’s. We
`found residential duct fittings available in the United States which use gaskets or snap fittings to ensure
`a leak proof connection. One Swedish duct system was found which uses rubber gaskets to seal
`connections, but no consideration was given to insulation.
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`This project was divided into five primary tasks. First, we made a survey of existing and planned
`products for ducts and fittings. This included looking at products used in other applications as well as
`those being produced by duct manufacturers. To complement this review of existing products we
`conducted a phone survey of HVAC contractors to determine their methods of installation, costs, and
`materials used. We also asked about their opinions on some potential new duct technologies. Since
`little innovation had been found in either survey we worked on developing potential new designs for
`ducts and fittings. The ducts were assumed to be made of plastic and to compress more for shipping
`than curren products (i.e. flexduct), while the fittings were assumed to be of insulated plastic. The goal
`was a system which was sufficiently insulated, leakproof, and foolproof to install. Finally we
`considered the economic and code requirements which would have to be met by any new technologies.
`
`2.0 Survey of Existing Technologies
`To determine the range of existing technologies for ducts and fittings we used several methods. The
`Thomas Register was searched for duct products which emphasized ease of installation. The HVAC
`contractors who participated in our survey were asked if they used any unusual or exceptional
`products. Finally, contacts from industry and in the research community were asked about any
`products they had learned about.
`
`Table 1 lists the insulation products we found while Table 2 lists the duct types we found. In both
`tables, names of some manufacturers are given. The list of manufacturers for insulated plastic wireflex
`ducts, sheet metal ducts, foam insulation, and glass fiber insulation are not complete. These products
`are made by many companies.
`
`Survey of Duct and Insulation Products
`2.1
`Glass fiber insulated plastic wireflex ducts dominates the market in California. In many ways, it fits
`our requirements for new ducts. It has low material costs and is easier to install than its competeitors.
`No fittings are needed to go around corners because the duct bends and no time is spent on insulation
`because wireflex is insulated. In addition, wireflex compresses so well that all of the ducts for a
`typical house can be carried at once by one or two workers.
`But wireflex is not an ideal product. At insulation levels higher than 23 m2·°C/W
`(R-4 hr·ft2·°F/Btu) it does not compress as easily. Ducts insulated to 23 m2·°C/W will compress by a
`factor of 10 in length while ducts with twice as much insulation will compress by a factor of 7. The
`boxes for ducts insulated to 46 m2·°C/W (R-8 hr·ft2·°F/Btu) are 170% of the size used for R-4 insulated
`ducts. More importantly, no one has produced a foolproof method of easily attaching wireflex to
`fittings. All of the current methods, while simple to do in an open area, are potentially very difficult in
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`an attic or crawlspace. This can lead to mistakes in installation by workers who are pressed for time.
`Other problems with wireflex are that its outer liner tears easily and the insulation can compress where
`the duct is supported. Finally, it is unclear how durable the plastics in insulated wireflex duct are. One
`contractor in the telephone survey described in Section 3.0 claimed that a significant portion of his
`business was replacing wireflex where the inner liner had disintegrated.
`Among the technologies we found for ducts and duct insulation, there are three new technologies
`which have not been fully developed as potential alternatives for fiberglass insulation: gas filled panels
`(GFPs) for both ducts and insulation, the Haines system for ducts, and the “Ultimate R” for duct
`insulation. The other products listed have already benefitted from economies of scale and are not
`competitive with fiberglass insulation and wireflex ducts.
`The Haines System for ducts would use a duct very similar to wireflex but with a foam as the
`insulation. Consequently, it offers little advantage over flex duct and would not change the
`performance of duct systems. The Ultimate R is a system of cardboard forms which are placed over
`duct systems which lay on joists in the attic. Cellulose is then sprayed over the duct to achieve an R-
`value of up to 39 (hr·ft2·°F/Btu) with little effort. It is of interest how much savings will result from
`such a high insulation level but the technology is only of use where there is adequate space, a rare
`situation in California houses.
`GFP’s are the one new technology we found for ducts which could offer significant advantages
`over existing products and be used in all situations. Their advantages are: they can be designed as ducts
`rather than add on insulations, can be made to compress completely for shipping and can achieve a
`higher insulation level for a given thickness. If new building codes require higher levels of insulation,
`the additional compressibility of GFPs and the higher specific R-value could be of value for squeezing
`ducts into existing spaces. The questions which must be answered about GFP ducts are: how much
`higher performance would be obtained, how much would this higher performance cost, and how will
`safety and performance requirements be met?
`
`Survey of Duct Fitting Products
`2.2
`Table 3 shows the types of fittings which we found in the marketplace or in development. There are
`two companies which are trying to produce plastic fittings that attach to insulated wireflex duct. In
`both cases, wireflex duct would still be attached to the new fittings just as it is presently attached to
`sheet metal fittings. The advantages of the fittings are: insulation is incorporated into their design,
`they are less likely to be bent or torn and they can’t leak along seams like sheet metal fittings. One of
`the plastic fittings, Flexmate, is designed to easily be mounted to joists. This could reduce the number
`of supports needed for the ductwork.
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`TABLE 1. Existing duct insulation products found by surveying suppliers, contractors, the Thomas Register,
`and building science researchers.
`
`Manufacturer
`
`Description
`
`Accessible Products
`Company
`Foster Products
`Corporation
`
`Manville
`CertainTeed
`CertainTeed
`
`precut foam for pipes
`and fittings. Tapes on.
`PVC covers for insula-
`tion on bends in pipes.
`Tapes on.
`fiberglass pipe insula-
`tion
`fiberglass duct wrap
`
`Insulation
`Type
`
`Special fit-
`tings for
`pipes
`
`fiberglass
`duct insu-
`lation
`loose-fill
`insulation
`
`gas filled
`panels
`
`the ultimate “R”
`
`LBL Windows
`Groupa design
`
`Reflectix™, Inc.
`
`blown in cellulose insu-
`lation held in place by
`cardboard forms.
`made of reflective foil
`and plastic baffles using
`techniques from the
`food-processing indus-
`try.
`aluminum
`bubble plastic used for
`coated
`shipping which has
`bubble
`been coated with alumi-
`plastic
`num
`acurrently being licensed for refrigeration applications
`
`R-Value
`(°F·ft2·h/BTU)
`
`Contractor
`Cost ($/ft2)
`
`4
`
`1-8
`
`5 per inch.
`
`-
`
`-
`
`-
`
`5-11
`
`0.16-0.32
`
`up to 38
`
`4-9 per inch
`
`-
`
`-
`
`4.7 per inch
`
`0.51 for 1”
`
`The basic conclusion for duct fittings is that little has changed since the 1920’s. The only
`common fittings which aren’t sheet metal are plenums and tees constructed of glass fiber board. Even
`these fittings have the ducts attached to them using sheet metal fittings.
`None of the duct fittings we found seems to have given much attention to sealing the leaks which
`are known to exist in fittings. This is true even for the “innovations” we found. For example, the Haines
`system has a register face which just slides on the register boot with no gasket for sealing. There is
`considerable room for improvement in fitting performance with simple improvements such as placing
`gaskets in existing fittings.
`
`3.0 HVAC Contractor Survey
`We conducted a telephone survey of HVAC contractors for several reasons. We wanted to determine
`how ducts are installed and how much contractors know about leaks in duct systems. We also wanted
`to confirm what types of materials are used. Most importantly, we wanted to see how contractors’
`costs break down between labor and materials. Finally, we wanted to assess reactions from HVAC
`contractors to our ideas for new technologies.
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`TABLE 2. Existing duct types found from by surveying suppliers, contractors, the Thomas Register, and building
`science researchers.
`
`Contractor Costa
`[$/ft.]
`
`R-Value
`[°F·ft2·h/BTU] Description
`
`Duct Type
`
`Manufacturer
`
`sheet metal
`solid plastic
`foam-like plastic
`
`Leslie Locke
`General Plastics
`Haines System
`
`uninsulated
`
`$1.57
`$1.43
`
`-
`
`$0.80-$2.00
`
`light gauge galvanized steel
`plastic for placing under slabs
`extruded foam -like material
`(w/vapor lining)
`flexible duct, surrounded by
`fiberglass insulation with an
`outer cover
`ducts made of rigid fiberglass
`board with a facing usually
`made of aluminum
`
`4
`
`4-8
`
`4.3
`
`insulated flexible
`
`fiberboard
`
`J.P. Lamborn
`CertainTeed
`Dumas-Jaffner
`CertainTeed
`$1.44b
`Owens/Corning
`afor 8 inch diameter duct or 4 in by 12 in rectangular duct, as appropriate
`b$0.54/ft2 for 1” thick
`
`The population used for the survey was found through the Business to Business Yellow Pages
`for all regions of California. Out of 46 contractors called, 10 were available to take the survey. Five of
`the contractors were from Los Angeles County and five were from Northern California. Of the persons
`contacted, 6 were executives or owners.
`Table 4 lists the type of business done by the contractors surveyed. Two of the contractors
`surveyed installed 1500 and 4000 systems each. All of the averages presented in the survey are
`weighted by the number of systems installed. So the averages are dominated by the two largest
`contractors with the other eight contractors determining the range of the responses.
`
`TABLE 3. Existing fitting types found from by surveying suppliers, contractors, the Thomas Register, and building
`science researchers.
`
`Type
`
`Manufacturer
`
`Product
`
`costa
`
`Description
`
`standard sheet
`metal
`special sheet
`metal ducts and
`fittings
`
`Leslie Locke
`
`-
`
`Veloduct
`
`Veloduct
`
`$5.49 (6” round to
`10”x4” register boot)
`-
`
`Nordfab, Inc.
`
`Nordfab
`
`-
`
`solid plastic
`
`General Plastics
`
`-
`
`foam-like plastic
`
`Flex-Mate Prod-
`ucts, Inc.
`Haines Systemb
`
`fiberglass board
`
`-
`
`Flex-Mate
`
`-
`
`-
`
`$7.48 (6” round to
`12”x4” register boot)
`currently prototyping
`
`$5.66 (6” round to
`12”x4” register boot)
`-
`
`light gauge aluminum or galva-
`nized steel
`special O-ring fittings for easy
`installation
`quick release latches for ducts
`with raised lips at their ends
`fittings for placement under
`slabs
`Special insulated plastic fittings
`to attach to flexduct
`snap-on plastic fittings and
`boots. Fitting insulation is plastic
`usually for plenums, sometimes
`for wyes
`
`ato contractor
`bAustralian product, not certified in United States
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`3.1 Material used
`Table 5 lists the types of ducts, plenums, and fittings used by the contractors. As expected, insulated
`wire flex duct is the most commonly used duct type. For plenums, sheet metal and glass fiber board
`constructions are both common. The insulation levels on the plenums ranged from 12 m2·K/W (R-2
`hr·ft2·°F/Btu) to 36 m2·K/W (R-6 hr·ft2·°F/Btu). For plenum fittings, no alternatives to sheet metal
`fittings were used. The sheet metal tab collar, which has a high potential for leakage, is most
`commonly used, although it is not used in a majority of installations.
`
`Installation methods
`3.2
`One of the more interesting parts of the survey was the contractors’ responses about their installation
`methods. These are summarized in Table 6. For attaching wireflex ducts, most of the contractors use
`tape only. They all used tape on both the inner and outer liners. However, the Air Diffusion Council
`(ADC) standard for flexible duct installation specifies that a strap should also be used on the inner
`liner. (ADC, 1991)
`
`Highlights of the responses include:
`• When connecting registers, most of the contractors applied gaskets on the faces of the register. This does not
`prevent the damaging leakage around the edge of the register boot and into the wall containing the boot An
`illustration of the leakage path is shown in Figure 1.
`• Only 2 of the contractors used sealant on the plenum fitting. The others either did nothing or used tape,
`which can fall off.
`• Six of the ten contractors used wall or floor cavities as ducts. Two of the six tried to seal the cavity with dry-
`wall. Another contractor applied insulation on the sheet metal pan used to seal the cavity. Four of the six
`contractors used methods which did not attempt to prevent leakage and conduction losses.
`
`System cost estimates
`3.3
`We had the contractors estimate the breakdown of costs involved with installing a complete system in
`a standard new house. The house was assumed to be one story with slab on grade construction. The
`equipment and ducts were in the attic. Table 7 summarizes the contractors’ responses. The most
`important point in the data is that the heating/cooling equipment, duct materials, and duct installation
`labor costs are all large parts of the contractors’ cost. The contractors estimates of these costs only
`add up to 74% of the total system cost. The remaining 26% includes installing the equipment,
`administrative costs, etc.
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`3.4 Reaction of contractors to our ideas
`The final section of the survey asked the contractors for their responses to our new ideas for ducts and
`fittings. They were first asked if they would consider a new type of plastic duct which was packed in
`a compressed form if R-8 insulation were required. Most of them expressed interest in gas filled panel
`ducts but only if there was no increase in price over glass fiber insulated wireflex. They did not
`consider the additional compressibility of the duct to be very useful. The contractors were also asked
`if they would consider using self-sealing snap-together insulated plastic fittings if they were required
`to avoid leak testing duct systems. Again the response was that they would be interested only if there
`was little or no increase in price. Several of the contractors implied that they would only use new
`products if they were required by code and all other contractors were using them.
`
`In an attempt to find out about any new products for ducts or fittings, we asked the contractors
`whether there were any exceptional new products they used. Most said no and the others listed well
`known products like wireflex ducts, glass fiber board, and improved duct tapes. We also asked them
`what they felt was the part of duct systems which could be improved most. Instead of concentrating on
`easier to install technologies, 3 of them said they needed more room to work. Other responses included
`returning to sheet metal ducts and protecting ducts from mechanical damage. No one mentioned
`energy conservation concerns with leaky and insufficiently insulated ducts.
`Several conclusions may be drawn from the HVAC contractors survey:
`• HVAC contractors compete on bids for projects and are very concerned with low cost. This concern with
`low cost is not offset at all by concerns about performance.
`• There is not much awareness of problems with the performance of duct systems or how to solve them.
`• There is some fear of new technologies. Individual contractors don’t feel comfortable using different meth-
`ods than their competitors.
`• Duct installation labor is a large fraction of the cost of an HVAC system, so technologies which save instal-
`lation time will appeal to installers. However, they think wireflex is easy to install and will have to be con-
`vinced of the need for snap-fit connectors.
`What these conclusions mean for new duct technologies is that any new products will either have
`to reduce the installers’ costs or be supported by other incentives. Other incentives could be changes
`in code requirements, utility incentive programs, or informed consumer/builder pressure. These
`incentives would allow HVAC contractors to improve the performance of duct systems while still
`assuring their profit margins. We can also conclude, just as we did in the section on existing products,
`that there is a lot of room for improvement on current practices.
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`where most
`contractors
`place gaskets
`
`register face
`
`flooring
`
`register
`boot
`
`air leakage
`path
`
`FIGURE 1.
`
`Schematic illustration of the leakage at duct registers. Most contractors place a gasket between the
`register face and the flooring/wall. This is necessary to eliminate leakage into the room when the
`register is closed, but it does not block the leakage path into the walls or crawlspace.
`
`TABLE 4. Type and amount of business done by HVAC contractors in the survey.
`
`Quantity
`
`Average
`
`Minimum
`
`Maximum
`
`# of systems installed per year
`% of business that is residential HVAC
`% of residential HVAC which is new construction
`average home size
`
`655
`90%
`83%
`214 m2 (2300 ft2)
`
`12
`14%
`0%
`170 m2 (1800 ft2)
`
`4000
`95%
`90%
`325 m2 (3500 ft2)
`
`TABLE 5. Types and amounts of materials used for duct systems by HVAC contractors in the survey.
`
`Quantity
`
`Duct type
`
`Plenum type
`
`Plenum fitting
`
`% of installed
`
`insulated wireflex
`sheet metal
`aluminum flexduct
`sheet metal
`glass fiber board
`sheet metal tab collar
`other sheet metal
`
`94%
`5%
`1%
`42%
`58%
`37%
`63%
`
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`TABLE 6. Results from the survey of ten HVAC contractors for installation methods used to attach
`ducts and fittings.
`
`Task
`
`Method
`
`# of contractors
`using
`
`attaching wireflex to fittingsa
`
`sealing the gaps between the
`plenum fitting and the plenum
`
`6
`duct tape on inner and outer liners
`5
`duct tape on inner and outer liners plus screws
`2
`plastic straps and tape
`5
`tape
`2
`sealant
`1
`screws
`2
`nothing
`5
`gasket on face of register
`4
`nothing
`1
`solid wood headerb
`4
`never
`3
`for return
`1
`only in interior partitions, sealed with drywall
`1
`sheet metal pan w/insulation on outside
`1
`sealed with drywall
`aThe responses sum to more than ten because some contractors used more than one method.
`bOne contractor installed wood blocking to support the boot instead of just nailing to available joists.
`
`sealing the register to its boot
`
`using floor and wall cavities
`as ducts
`
`TABLE 7. Breakdown of estimates of costs for new systems in the survey of HVAC contractors. All costs are customer
`costs.
`
`Costs
`
`$ Amount
`
`Avg.
`
`$2,264
`$3,145
`
`$589
`$1,205
`
`$45
`
`Min
`
`$1,800
`$2,500
`
`$500
`$1,100
`
`$40
`
`Max
`
`$6,000
`$8,500
`
`$1,400
`$2,000
`
`$275
`
`$589
`
`$550
`
`$1,000
`
`$449
`
`$175
`
`$3,000
`
`Percentages
`
`Avg.
`
`NA
`
`26%
`38%
`
`2%
`1%
`
`26%
`19%
`
`20%
`14%
`
`Min
`
`Max
`
`12%
`20%
`
`1%
`1%
`
`16%
`12%
`
`10%
`7%
`
`35%
`44%
`
`8%
`5%
`
`31%
`22%
`
`64%
`42%
`
`Item
`
`system
`
`equipment
`
`control equipment
`
`duct materials
`
`duct installation
`
`furnace
`gas furnace w/
`a.c.
`furnace
`gas furnace w/
`a.c.
`furnace
`gas furnace w/
`a.c.
`furnace
`gas furnace w/
`a.c.
`furnace
`gas furnace w/
`a.c.
`
`New Technologies for Residential HVAC Ducts draft copy: do not quote-7/11/00
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`11 of 30
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`Sleep Number Corp.
`EXHIBIT 2022
`IPR2019-00514
`Page 11
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`

`

`4.0 Potential New Designs and Technologies
`In this section we will consider new designs for ducts and fittings. The economic and building code
`tests for these products are considered in the following two sections.
`
`When considering new approaches to problems, the first step is to determine goals. What
`properties are desirable in a new duct system? Ideally, a system would have:
`• no leaks
`•
`insulation at all points
`•
`low costs for installation and materials
`• durability of the sealing and insulation
`In order to insure that these goals are met, it is necessary that the system:
`•
`require little fabrication on site (to reduce labor costs)
`• have seals made by snapping parts together (to reduce labor costs and be foolproof)
`• have mechanical, rather than adhesive, seals (for durability)
`One vision of a “perfect” system is flexible ducts with universal connectors on their ends that
`snap into fittings and plenums. Excep for mounting register boots to studs or joists and installing the
`heating/cooling equipment, system installation would consist of snapping parts together. If the snap fit
`connection was reversible, then this “perfect” system would also be easy to expand or reconfigure.
`There are many options besides the “perfect” system. These include:
`• Requiring that all fittings be covered by insulation and that wireflex be attached with a nylon strap on the
`inner liner, as specified by the Air Diffusion Council (ADC, 1991). This would eliminate the problem of
`duct tape failing and reduce leakage losses. It would also increase installation time and make technologies
`which offer simpler installation more attractive even with higher material costs.
`• Require that all fittings, including registers and plenum connections, have gaskets which insure a tight seal
`will be made between fittings. This would reduce leakage in a durable and foolproof manner while still
`allowing wireflex duct and fittings very similar to those currently in use.
`• Require that snap-in fittings be used for all connections, including ducts to fittings. This would insure that
`the duct system is connected properly.
`• Require that fittings have an approved method of attaching wireflex duct which is integral to the fittings. An
`example will be shown below.
`
`In the following sections we separately consider new designs for insulation based on GFP technology,
`ducts made of the GFP insulation, and easier-to-install fittings.
`
`Potential designs for new duct insulation
`4.1
`We focused on using gas filled panel (GFP) technology developed in another CIEE project (see
`Griffith et al, 1992). Griffith et al. developed this technology for use as appliance and building
`insulation and consequently chose designs which resulted in a rigid product that did not compress.
`
`12 of 30
`
`7/11/00-draft copy: do not quote New Technologies for Residential HVAC Ducts
`
`Sleep Number Corp.
`EXHIBIT 2022
`IPR2019-00514
`Page 12
`
`

`

`The idea for GFPs was to produce a superior insulation using plastics and existing food packaging
`technology. Heat transfer through the insulation is reduced by eliminating convection and radiation
`heat transfer. Convection is reduced by having small cell sizes. Radiation is reduced by using low
`emissivity coatings on layers between cells.
`
`Our design method was to construct models of the insulation and then critique them for ease of
`manufacturing, compressibility, etc. New models were then made until we had produced several with
`good qualities. Figures 2-7 are drawings of the five most promising designs for duct insulation, which
`we have designated with letters A through E. In Table 8, estimates are presented of the properties, both
`good and bad, of the 5 designs.
`All of the models seem appropriate for use as duct insulation. Design E seems particularly
`appropriate for a compressible duct design because it will open irreversibly when released.
`
`Potential Designs for Ducts
`4.2
`All of the designs for duct insulation in Section 4.1 could be turned into ducts. Designs A-D are
`particularly appropriate to rectangular ducts while design E is appropriate for a circular duct. Since
`round ducts will have lower conduction losses and less material required for a given cross sectional
`area, we elected to construct a model of a round duct using design E. A schematic diagram of the
`model is given in Figure 7. The model was constructed with a thick inner layer of plastic (actually a 2
`liter soft drink bottle). The insulation was made with plastic and the sheet on the outside of the duct
`was metalized polyester. The model could be folded in half and compressed to reduce its volume by a
`factor of 17. Another possible round duct, which could be made continuously in a spiral is shown in
`Figure 8.
`
`For square ducts, any of the insulation designs A through D could be used to produce collapsible
`in