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The following text is from a currently inactive and unfunded research project. We think that duct losses are very significant and that some entity ought to undertake further research in the area. To date we have not been able to pursuade the CEC to fund it in the public interest.

 

 

Profitable Residential HVAC Duct Sealing
Project Narrative

1 Project Goal

The goal of this project is to determine the feasibility of producing an economically attractive residential HVAC duct sealing process.

2 Project Objectives  - Detailed Discussion of Objectives and Solutions

The technical objective of this project is to develop and test duct sealant materials and a process that can be applied by a below average competency HVAC technician or duct cleaner using ordinary tools.  The intent of the research design is to create a procedure that will become part of his normal business practice.

Summary of Objectives:

We plan to explore a method of sealing ducts using blow-in sealant material, delivering it cost effectively to the leaks so that it will remain stable in the leaks in a benign way.  Our research path will have four distinct degrees of freedom:

  •   Filler materials (we will use both “fluff” and “balloon/bubbles” filler matrices as a starting set).
  •   Bonding agents (expected to be water activated powders).
  • Application sequence and number of cycles (filler/mist/filler; or mist/filler/mist, etc).
  • Sequence of different types/sizes of filler materials.

These options will be explored rigorously, with the aim developing of a cost effective, easy-to-use commercial product useable by HVAC and duct cleaning technicians, with minimal or no additional training.

What:  Method to be pursued

To accomplish this, we will develop a non-toxic, non-allergenic, easily cleanable sealing process and filler material, which can be blown down heterogeneous ducts.  The filler material will lodge itself in any cracks and holes encountered and seal them by clogging.  The blown-in filler clogging mass will be fixed with a vapor, which will harden the material into the duct crack or hole.  Once the first application is allowed to harden, a second or third filler/fixative cycle may be used.  In the latter cycles flame- and biologic-suppressant chemicals may be applied to suppress mold and bacteria growth on the fluff [1] .

Significant consultation will be done with existing companies and materials experts making “instant bubbles”(see Attachment I), “foam latex”, ”canned string” and similar products for applicability.  This may generate one or more trips to visit with manufacturers of related products.

Materials

The materials to be used as “filler” can be classified into three distinct groups:

  • Group I materials: Cellulose dust will be used, with a water activated surface finish glue as a “sticker”.  Fire suppression post-fixative will be required.
  • Group II materials. Polystyrene dust, with an alcohol-activated finish adhesive as a sticker.  We will start by investigating very lightweight polystyrene and iso-cynate based beads, that are impregnated with helium in the field just prior to use, so that they are neutrally buoyant in air for a brief period until the helium diffuses out (about 1 minute).
    The beads can be delivered to the duct in a container that charges them with helium.  Helium is observed to be resident in expanded closed cell polystyrene for a few minutes.  Its outgassing and conductive coating will be used to suppress the known electrostatic cling problem of Polystyrene/Polycynene beads.
  • Group III materials.  Very small bubble/balloons, with a powdered water/casein based glue, will be applied as a very fine mist.  Attachment I to this proposal shows a commercial bubble product that produces bubbles which feel and act like soft, lightweight, small ping pong balls.  For this material research path, we will start with similar materials, and attempt to use a helium bubble generator to make the bubbles neutrally buoyant in air.  The idea is to produce sealing “balloons in a can”.  These bubbles will be filled with helium, and a “sticker” surface treatment will be applied as the small balloons are injected into the ducts.

Application Techniques:

The Float and Seal Approach

The eventual application procedure will be similar for the three materials.  The design goal will be to use equipment that is simple and profitable for the HVAC technician to use.  During application, the supply ducts will be sealed where they enter the living areas.  The normal supply fan will be partially blocked or “plugged into” a variable speed drive box, allowing the technician to use the existing house air distribution fan for driving the system.  This has multiple benefits:

  • It uses existing equipment familiar to the technician
  • Little training is required, because fan pressure, fans, fan fuses and fan controls are all part of a technician’s normal work.
  • Air flow/pressure can be varied over a wide range, to accommodate large and small houses with no equipment change.
  • Blowback of materials to the fan area is suppressed.

Because some of the sealing material (whether balloons or fluff) will escape, some will remain in the ducts, and some will enter the living spaces both during the sealing process and later when it is released inside the duct, the selected filler material must be non-allergenic, non-toxic, non-staining, and easy to clean up.  Easy cleaning is necessary due to the nature of how the eventual product will be used, and is part of the reason that current products are not being used.  Some of the sealant will blow out of the leaks before they are sealed, and as commonly happens, some will flow into rooms when the room seals fall off during use.  This is not an infrequent occurrence with present methods, so easy cleaning is a requirement of the fluff material design.  At the same time, the filler must bond to itself and the cracks in a cohesive mass that will plug the leak.  To effect this, we will provide and test various water based surface chemistries that, when moistened with a light mist, will bond the mass.

The three core material paths:

  • non-woven natural fabric dust,
  • artificial polymer tufts infused with helium, and
  • small sticky helium balloons/bubbles variants.

These starting materials will be designed to be airborne and to plug leaks.  Our research path will exercise these materials as a starting point over a range of size (and possiblyHe gas) mixtures, to see how they must be treated and modified to produce a viable economic product.  We will allow for changes in materials and material aggregate sizes, as the tests indicate, to see what new properties are needed to make them effective.  Changes will always be towards efficacy, economy, ease of use, and the idea that we are designing a product to best fit the HVAC technician’s or duct cleaner’s toolkit.

We will test the above-mentioned materials and processes under Phase I in a series of test chambers at the Davis Collaborative lab.  From our experience with duct sealing, the basic test set-up is straightforward – cleaning is not.

Description of the Test Duct Races:

“Race I” is a fan-driven duct, with pressure and flow gauges, and a socket end capable of taking a set of interchangeable “standard” leaky ducts.  The race has pressure gauges and a long straight section for flow measurements, as well as allowing the simulation of a long duct length to the leak.  Identical “Standard” metal sections are used for testing leaks, with a standard set of holes and cracks.  This allows for accurate repeatable comparison of different materials.  The test ducts are metal, so cleaning and standardized filth can be added each time.

“Race II” also a fan driven duct, but open for testing a wide array of materials.  In this field test set-up, we will try to seal all duct types and ad hoc mixtures of flex-duct, fiberglass duct, and metal, so we can look at how different materials interact with the different sealants and processes.  We will be focusing on materials used in California construction that are primarily engineered for cooling as opposed to heating dusts for the north-eastern US.

The facility allows for testing both clean and dirty ducts.  This test facility will be constructed so that tests can be repeated with different pressures, fluff materials, and surface bonding agents, and with different degrees of cleanliness in different types of cracks. 

In the Race I standard ducts, with a large number of punches and replaceable duct pieces, this testing is standardized and is repeatable when clean.  We will measure flow and pressure as the sealant is applied.  The sealing effectiveness will be judged in several ways:

  • Sealing effectiveness:  the change in flow for a given pressure
  • Ability to bridge different shaped standardized leakage gaps
  • Response to dirty surfaces
  • Response to a calibrated shock (hitting) of the duct to judge adhesion.
  • East of application and clean-up [2]
  • Time of application
  • Ease of cleaning duct after application as well as
  • Robustness to physical duct expansion and contraction (elasticity)

2 Energy Problem Targeted: Leaky HVAC Ducts

In the United States, HVAC air ducts are a major source of leakage of both cold air from air conditioning and hot air from heating.  Typically, 20% of the energy in a home HVAC system is lost to duct leakage.  Indications are that the problem is similar, or more severe, in commercial establishments. 

There is only one commercial solution for resealing ducts in residences.  Unfortunately, it is too expensive for use in most cases, and exists primarily as the result of utility subsidy or legislative programs.

3.a  Impact on Energy Problem

Adoption of duct sealing as a standard marketable service by the HVAC service industry and/or the duct cleaning industry will dramatically reduce air duct losses and save large amounts of energy all over California.  There is also a health issue, because the duct leakage we are referring to is on the supply side of the delivery system.  With leaks on this side, the house becomes depressurized.  The depressurized house sucks air in from garages, moldy walls and cracks, down gas flues, and other locations.  Leaks on the return side have a differential effect depending on which air is drawn into the leak.  The duct sealing technology addressed here is for the supply side, where almost all of the hidden leakage occurs.

If we could cut leakage by half on average by sealing ducts tightly, we should be able to save about 10 % of the energy used in California for heating and cooling residences.  The sealing would be done to a much higher standard than 10%, but we must average the effect over time.

3.b Benefit to California Electric Market

The direct impacts will be seen during the heating and cooling seasons.  In either case, conditioned air comes from the furnace/evaporator coils into the house.  In winter, the furnace will have to run less often, saving electricity. In summer, where the big impact for the California Electric market is, the impact will be dramatic for houses that have their ducts sealed. If in the summer a house spends 60% of its electricity bill on air conditioning, a 20% reduction would exceed a 10% electric energy savings directly for that consumer, and because marginal losses are very high in the summer, the marginal system savings [3] (including losses) would be over 12% of electric demand savings.  In addition to the energy reduction, with the demand reduction there will be a decrease in price through market elasticity.  As the demand drops, so too does the price, historically rather dramatically in the summer.  What this will be in the future is pure speculation, but it is unlikely that the price elasticity would be less than the marginal electrical loss rate. Thus, the price per kWh decrease will be in the 20% reduction range from a 10% fall in electrical energy, giving about a 28% total cost savings to the aggregate [4] California consumer.

4 State of the Art

4.a Results of Literature Search

Considerable related research has been done at Lawrence Berkeley Laboratory over the past 20 years on ducts and sealing ducts.  LBL reports point out that over 20% of heating and cooling energy is lost due to duct leakage.  These reports are located at: http://www.lbl.gov/Science-Articles/Research-Review/Highlights/1998/EES_duct.html

Their reports document the pervasiveness of the problem. They document their test facilities, and the development of Aeroseal – their licensed commercial duct sealant.  The complete list of all Aeroseal background information is available at this web site

             http://epb1.lbl.gov/aerosol/pub.htm#GP

Some of the key papers are as follows: 

  • Carrie, F.R. and Modera, M.P. (1993) "Particle Deposition in a Two-Dimensional Slot from a Transverse Stream", Lawrence Berkeley Laboratory Report.  Presented at the 12th Annual Meeting, American Association for Aerosol Research, Oak Brook, Illinois, October 1993.
  • Carrie, F.R., and Modera, M.P., (1995) "Reducing the Permeability of Residential Duct Systems", Presented at the 16th AIVC Conference, Palm Springs, CA, September 1995.
  • Modera, M.P., Dickerhoff, D.J., Nilssen, O., Duquette H., and Geyselaers, J. "Residential Field Testing of an Aerosol-Based Technology for Sealing Ductwork." Proceedings of ACEEE Summer Study, Pacific Grove, CA, August 1996,

The LBL duct testing lab has been less active during the past 5 years.  There is considerable research in sealing of ducts, but the research emphasis has been on duct tapes and duct sealant that is hand applied.  This sealant is inappropriate for an aerosol application.

4.b  Comparison of Existing Products

Small residential and small commercial air duct leaks can now be plugged using simple procedures that blow sealants (to be developed in this research) down the ducts until they block a leakage hole.  The process is slow, bulky, requires special equipment, significant training, large capital investment, and a franchise from Carrier.  It is not part of an HVAC technician’s or duct cleaner’s normal service set.

This proposal will examine coarser, lighter sealant materials than are currently used and will explore chemically fix the material into the orifices.  The efficacy of the existing, somewhat similar, technique using very fine particulate “sticky” material” has already been proven in the field by Aeroseal, now a subsidiary of Carrier.  However, the Aeroseal process is seldom cost-effective in existing housing [5] due to the expense, filth, training, slowness of application (which can take several hours) and special computer controlled equipment required.

This research will find a new airborne sealant and sealant technology marketable by the HVAC repair and duct cleaning industries.  To be economically attractive, it must be simple, cost effective, easy to apply, and most importantly, it must be usable by normal HVAC or duct cleaning technicians [6] with little training or required equipment.

5 Feasibility Issues:

Feasibility is determined by market acceptance.  There is little question that some sealants can be blown down ducts to seal them.  The question is whether a product can be developed that will gain widespread market acceptance:  The product characteristics that determine this feasibility include: 

  • Clean enough to not mess up walls and ceilings where it leaks out during use.
  • Easy and economical enough for technicians to use it
  • Quickly effective given limited technician time on site.
  • Fire retardant, mold retardant, inhospitable to bacteria, and non-allergenic.
  • Elastic in order to accommodate duct movement, sticky enough to bond.
  • Light & free enough of electrical charge to blow down the ducts

These are the feasibility issues.  LBL has explored a very narrow set of materials (1), and has come up with a good solution that has met with only limited market acceptance, thus a new product is needed.

6 Proposed Innovations

  • Using a multi step process air system to seal ducts.
  • Using existing furnace fans with speed controllers (small vfd if needed) as blowers so no special equipment is needed.
  • Inducing sealant through a 0.25” pilot hole in a primary distribution plenum.
  • Possibly using “as light as air” gas/solid materials
  • Separately using moisture as an activator of the bonding agent to product composite sealant.

7 Primary Tasks

Task 1. Administration and Reporting

  • Task 1.0 Kick-off and contract adjustments as/if directed by DOE.
  • Task 1.1 Adjustment of schedule to match funding release.
  • Task 1.2 Set up accounting and invoicing procedures as directed.
  • Task 1.3 Monthly reporting as needed by DOE.
    • Task 1.3.a - Monthly progress reports will be supplied as requested
    • Task 1.3.b - A Final Report will be made in accordance with requirements.

Task II Material Review and Collection

The current plan is to start with three different material types, and to use a series of dry surface bonding agents.  In Task II we will exhaustively look at our selected materials and discuss these with people in the textile, industrial hygiene, and HVAC industry to explore the issues of fire, mold, bacterial growth, short term stability, longer term durability, deterioration under thermal cycling, and other selection issues.

Task III Set-Up and calibrate

In this task, we will construct the test ducts and plenums, and connect them to our pressure and flow instruments.  We will review materials and test bench calibration.  The Davis Collaborative has the equipment necessary for testing clean and dirty ducts with pressure and flow gauges.  The Data Acquisition System (DAS) system will be upgraded and automated for these tests.  Because it is expected that there will be many hundreds of minor variations in procedures, sealant types, coatings, and treatment sequences, the DAS will be complemented and integrated by a significant data logging and data management system.

Task IV  Testing

  • Task IV a  - “The Primary Races”.
    There will be at least two different duct testing set-ups, using duct board, flexduct, and steel.  Primary testing will be done on what is called “Race I & II”.  These races will have a series of identical blind sections with small orifices cut in them.  These standardized metal leakage slots and holes will be the same in multiple replaceable sections.  This is necessary for standardization, and because the replaceable sections with the standard holes will get “gummed up” and need to be carefully cleaned out between tests.  Extensive cleaning and repeated measures is required for quantitative testing.
  • Task IVb  - “The Field Test” – in Race III”
    When we have narrowed the field to a few working material/process combinations, we will try them on other common duct materials.  All that is established with Races I & II (with the standard steel leak orifices) is which materials/bonding agents/process work on sheet metal, with different types of dirt.  Gaps in duct board, whether faced or not, are quite different in that the breaches are larger due to poor joint mating and failed tape.  Likewise, gaps, tears, rodent holes and punctures are equally different in very thin walled flexing plastic flexduct.

8  Market Connection

This research is driven by observing that the market is not responding to a particular product for a set of reasons.  We are addressing those reasons through research.  We are knowledgeable about them because we have interviewed many HVAC contractors who are familiar with the Aeroseal product, and are HVAC contractors ourselves.

In terms of manufacturing the product after product development, it would have to be shown to be safe on numerous counts, and tested in the field with independent HVAC contractors.  This would be a follow-on process, unrelated to this research.



Footnotes

[1] Currently, many ducts contain inflammable dust and lint which in tight houses are often moist due to AC condensate and are thus prime mold and bacteria breeding locations.  To the extent that this technology reduces air exchanges with the outside air, the HVAC will increasingly become a breeding ground for pathogens.  To compensate for house tightness,  other ventilation will have to be provided.  This does not diminish the value of sealing the supply ducts, and this is the most conditioned air.  If other air exchange is needed it should be of un conditioned air being exchanged with dry cool outside air. 

[2] Electrostatic charges are the bane of polystyrene type beads.  Part of this research will be to minimize this problem.  Our surface treatments will address this issue.

[3] Assuming an average summer loss is about 10% (weighted by AC load), this makes the marginal losses close to 20%.  The reduction here must get credit at the marginal rate.

[4] The savings are divided as follows.  The house owner gets the 10% savings, and has to share the remainder with all other electricity consumers.  However, if all other California consumers had their ducts sealed, it would reduce aggregate demand and all would receive the 28% aggregate energy savings.

[5] Dykstra and Co. was one of the first to be granted a Carrier Aeroseal franchise.  Franchisees paid $10,000-$39,000 for the franchise fee, with $16,000 to $24,000 for equipment. Price can vary depending on what equipment is bought.  Training takes three to four days at the contractor's facility. (Source: Carrier Promotion Material).

[6] The residential HVAC industry is partially populated by technicians with minimal education and training, who are challenged by lengthy computer based hi-tech solutions.

 
 
 
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