Open Letter To ASHRAE and ACCA, Better HVAC Air Ducts In Our Homes

 The following is a re-posting of a Google Docs document that will be subject to constant correction and update from reader comments.

https://docs.google.com/document/d/1o3j4ayBkhDhq8U9HVDwYujwKQCOQLpANUYvNFKFWfco/edit?usp=sharing

Better HVAC Air Ducts In Our Homes

The following message is sent to the Duct Design leadership at ACCA and to ASHRAE Ducts Design Committee colleagues, TC 5.2.

From my PhD-level work forty to fifty years ago, with hydraulics of pressurized water nuclear power generators, I have an understanding of HVAC duct design with direct application of Bernoulli Principle.  This understanding contradicts ACCA Manual D design of residential HVAC ducts, where there is no usage even of the word Bernoulli. By ACCA methods, nothing is seen as wrong in silly long too-small ducts that sprout Medusa-like from beloved D-boxes and assorted Supply Trunks. Absent Bernoulli math, air is somehow transported as if it were no-energy toothpaste. Static pressures change and diminish for reasons little-known, not controllable. Manual D pros say: Just squeeze enough at the blower,to push the needed flow. Flow violence and attendant inefficiencies are only a noise problem.  Ignorance is revealed in non-scientific phrases total static pressure and total external static pressure.

With Bernoulli energy balances, we have spectral local values of static pressure and kinetic head, additive to  total pressure..Energy losses attendant to poor design are more-usefully computed, than measured. Better than computing penalties, use common sense to avoid them. Let the controlling flow resistance in any path be at the register discharge to ambient. Find folly always in trying to fix a mess with use of dampers. Resize any register and its approaching duct, to deal with complaints.

Please see a best demonstration of my duct construction and  analysis methods in one home:

Duct Hydraulic Analysis, Koempel

Koempel Job Photo Album

Blog Post An Attic Ladder Installed Diagonal to Attic Floor Framing

Blog Post Flawed Measurement Of R-Value With A Certainteed InsulSafe4 Gage

I have several similar achievements to share:

Chamberlain-Mann Crawl Space Ducts Hydraulic Analysis

Chamberlain-Mann Crawl Space Job Photos

Waters HVAC Ducts Plan

Waters Attics All Photos

Duct Hydraulic Analysis, Leet Rental

Blog Post, Leet Rental Crawl Space

Leet Rental CS Overhaul

Leet Home Better Furnace Ducts

HVAC Ducts Hydraulic Analysis_Meyer

Job Album, Meyer Attic

Find more duct redesign from found cheap industry expectations. Employ shop-built fittings, often lined with insulation. No leaky, inefficient on-the-job hacks to just make connections. Ducts are buried as much as possible, never placed carelessly, obstructing access.

Blog Post: Best Placement of an In-Attic Gas Furnace, Among Roof Trusses

Blog Post: More Furnace Plena and Flex Duct Quality Work

Blog Post: Following ACEEE Blog, Furnace Fans As Energy Hog

Blog Post: Better In-Attic Furnace Ducting

Blog Post: Steel Ducts Heat Capacity, Forced Hot Air Heat

My insight in all of this is with confidence from my work in the nuclear power industry where a key achievement was in the reversal of a management decision that the cost of reactor pressure vessels should be reduced by making the inlet and outlet nozzle forgings abrupt, sharp-edged, no chamfering. A million dollar scale-model flow test under my direction proved that flow is then with damaging violence. Such silliness.

Please see that these contributions are extraordinary. All measures taken for energy efficiency are affordable. The wonderful sheet metal shop that enables my work shall wish for more customers like me. At present the cleverness I offer to customers has insufficient demand.

ACCA Manual D does not offer scientific best methods. Together ASHRAE and ACCA must offer better guidance. I want to help.

Phillip Norman <pjnorman@gmail.com>

1764 Bonniebrae Drive

Lake Oswego, Oregon 97034

503-255-4350

My Customer Meyer:

Please visualize the defect of D-box work imagined as no-cost squeezing of toothpaste. The discharge of a blower over a plenum area is quite directional. Noisy turbulent eddies form if flow does not remain guided in consistent direction. In a D-box, the orderly kinetic energy fan-generated,  is not converted in efficient buildup of static pressure to drive lateral flows through the resistive and leaky sharp-edged hacks. Chaos has a cost. energy-wasting large eddies uselessly elevate the blower head.

Here see guided concentrating flow continue, steadily, quietly  and with best-possible efficiency. Flow is quite turbulent, but with very small energy-blasting  eddies. Regardless of frenzied froth, flow wants to be guided, and absent guidance behaves wildly and noisily. All needed turns must be efficient, at lowest-economical velocity.

Where flow may divide in wyes, each path to register discharge may be individually summed in a Bernoulli balancing analysis. Where the dominant resistance is at each register, register velocities will be equal as obvious good design. The ONLY place to throttle flow is in a register. Control the service to a room in the sizing of its register and approaching duct. Keep duct sizes as large as possible except in a consistent final length, say of six feet, at each register.

Here see effort to reduce steel-duct swung thermal mass by insulative coating that does matter..

Let the planned flows be charted for analysis, in diagrams such as this for the plenum above:

Here is the completed ductwork at the furnace:

None of this simple common sense is the Medusa-teaching of ACCA Manual D.

The convenient found storage space in this beautiful attic now super-insulated, is quite valuable.

At 11/16/2024 I am inspired by yet-another project eliminating a leaky, thoughtless hack-in D-box, to address this topic:

loss coefficient for unguided turn through an abrupt sharp take-off. I know this is costly of energy and produces chaotic, noisy turbulence. I find a loss coefficient as high as 1.8, probably greater than the total of all other losses in a path. An ASHRAE Handbook Table 10.5 of 1981 is presented in a mark-up at the University of Texas, Austin.

Now, make that take-off ragged. Say, like this:

Projecting tabs and leakage burn energy.

Support a campaign to eliminate construction with D-boxes. 

Here is the shop-built replacement supply ducts top-box of this furnace:

10/29/2024

Let developed flow remain guided and silent. Here nine home registers are geographically collected to four equal outlet paths. Nothing in ACCA Manual D recommends this. This 21" square 12" tall and with 9" outlets might become a common standard supply box. Flow progresses through sequences of wyes, always maximizing pipe size such that the discharge register is the main flow resistance. Want the total loss coefficient in each path at final duct velocity, to be little more than 2. It is easy to do.

Lessons Learned With A Year-2009 Fakro Fire-Rated Attic Ladder, Much-Improved

To assess achievements in any job, it is helpful to note starting conditions that had been coped-with for many years,

My 17' Little-Giant-like aluminum ladder in stepladder mode, reached this high to a ceiling 114.5" above the concrete floor.

A 3/8" plywood flimsy skirt about the "hole" was 16" high, far taller than surrounding R19 loose-fill insulation. Somehow from the top step of a step ladder, one had to place weight upon the wobbly skirt, to hurdle over tripping electric power cables and to land on a single 24" path to the furnace platform. Furnace filter changes and more demanded safe access.

All of the landing area is over house heated space and should have remained R38, undisturbed. R38, at R2.2 per inch, demands 18" insulation depth, not achieved anywhere. If insulation over 10% of heated space is only R8 and the remainder were actually R38, the effective R-value is as 1/(Reff + 3) = .1/11 + .9/41. Reff = 29. If the remainder is only R25, Reff is 21. In Metro Portland Oregon at Fall 2023, there is a $1.25 per sq ft rebate of cost paid for added attic floor insulation. Installation specifications: Existing insulation must be R-18 or less. Must insulate to R-38 or greater or the fill accessible cavity.

I would do further math to prove qualification at <R18, where space with no insulation, under the furnace and in general near roof eaves amply brings down the average.

  The insulation space under the furnace platform is 10 1/4". I will build framing in new safe passage to the furnace that again is 10 1/4" tall. I want no trip-edges. Where the found loose-fill so-readily collapses to 3 1/2" depth, new insulation should be in the form of tough and resilient R25 fiberglass batts 24" x 48" parallel to the trusses, for total then of almost R38. Very importantly in this, all space with no insulation, must be filled. This might demand temporary jacking of the furnace off of the messy flooring, two heavily-nailed layers of 7/16" OSB.

The new, level plywood floor is non-tripping, although 19/32" plywood does flex some.

Get on now to the core purpose of this post, considering lessons learned with a unique attic ladder.

A fire-rated ladder must not be compromised by a gap about the ladder frame, only concealed by wood trim. This framing is trimless as seen in the full-scale drawing that follows.

Limit arm upper pivots are 5/16" x 2 1/2" lag screws embedded strongly in the ladder rough frame (well-strengthened truss bottom elements).

See that the ladder frame is tight against the perfectly-square rough frame. No shims. No gaps. With removal of a few screws, the ladder is fully removable, not bonded in place. At some future time, the ladder might be in the way of furnace replacement or removal.

The clear no-snags ladder opening with a 22" frame width will pass large bags of insulation now-needed. Know that no large garage like this could have other than 24" on-center framing. With truss framing, this is the best-possible accessibility. Be very grateful to have this last-of-its' -kind-on-Earth, wonderful attic ladder.

The deployed ladder steps are quite rigid, The two rails meet the floor equally with soft, gripping leveler legs.

The invoiced ladder cost is $419, now a bargain where inflation has doubled costs of weatherization since 2009.

See that the upper section of the ladder is highly customized. To have the Top Step I now demand for customer safety, I blocked the little step section, raised above the door, in a sturdy birch-plywood frame. The springs to-be-added can't be strong enough to have the heavier assembly slam-close as is foolishly and firmly a Fakro fire-rating feature. Fakro then will not offer a door latch that would reduce demands upon the springs.

I have been tasked then with invention of the latch, using good Central-European hardware purchased from one-time ladder manufacturer Calvert USA, in 2011. Calvert USA built excellent ladders in Maryland until 2016, including fire-rated ladders  that did not cost extra.

This is the currently-offered Fakro LWF 54" ladder shown with 30" frame width. 

$805 at Home Depot. A large fraction of this cost is in individual FedEx or UPS shipments from an Illinois warehouse.

See much-steeper 66° fixed angle, and large springs obstructing the opening. The door linkage is at a tripping-point, no down-stability, ready to lift and slam with a nudge. The needed pretty handle is absurdly placed, with barely enough clearance for finger-grips.

Pay attention to a successful further evolution in nature of a tenting rest.

A screw protruding from the left stile engages the tenting rest slot. Stability of the tent is dependent on having the tent center of gravity well behind the tent pivot, the center of the step section hinge at left in this photo. Imagine a tenting rest serving any attic ladder, perhaps that  drawn-on (darker) below the leveler leg here.

Study the dangerous factory-default deployment of this ladder at door angle 66°.

The better as-built installation is almost perfectly as drawn in the project bid. All installers of attic ladders should have such facility in planning. Surely architects demand this. Why should anyone want a ladder for its thoughtless cheapness?

Learn to follow the example of Swedish MidMade ladders in the location of lower pulls for the 

balancing springs.

Want the upper and lower pivots of limit arms to be at the same elevation, as low as possible. See multiple drilled-in positions for lower pivots upon the door face. Each one-inch shift from the 60° position set, brings the door steeper by approximately 2°. Choose least-steep as the factory default.

Please know that I have successfully installed Fakro fire rated ladders of current production, with 60° default, springs resident on the door and pretty-good slam closure. I have wished these ladders could have door latches for more-firm sealing. Here is the installation of Fakro LWF 25/54 Model 869719, costing $770 in May 2022, and costing $855 in November 2023. Surely the customer now with the LWF 22/54 of 2009, has  gotten a better deal.

Here is the stowed condition, showing spring leverage to pull fully closed. This works! Fakro should care to learn from my innovation, and has not.

Here see a door pull at the door opening end. There is no latch above. The door must self-close. See that installation requires facility with patching of drywall including fill of gaps to the steel edging that perfects frameless installation.

See more elements of the plastic Fakro Pull, as also a latch. I have had two of these from Fakro, not knowing what they are good for. The two long bosses at top in this view would need to be located very precisely by holes drilled in the opening (back) header of the ladder frame.  The mating of the latch halves would be by strong slam, and release by very hard pull. I despair of installing this with sufficient accuracy, and don't trust long-term durability.

The slam closure is better with a smaller ladder 47" frame. Be convinced of invention, with this video of the 47" ladder: https://www.youtube.com/watch?v=YJ4pg_exdvs.  With the easy-reach 47" ladder, there was no interest in tenting.

See a similar YouTube demonstration, year 2012, with a Calvert USA ladder and a ceiling nearly eleven feet up, in a home born as a warehouse of the 1905 Lewis & Clark Centennial Exhibition, in Northwest Portland, Oregon: https://www.youtube.com/watch?v=yBX8seprIO8.

Best fire-rated attic ladders are now wanted from manufacturer MidMade, in Sweden. None are on-offer, where imported by Conservation Technology, in Baltimore , MD. I am engaged in a campaign for change in this:

 https://docs.google.com/document/d/1PNS5irHuzUnGs3juhaudSvQrfubrlL1GkrWgHqdg09I/edit?usp=sharing

An Attic Ladder Installed Diagonal to Attic Floor Framing

 In a very tall attic, let all HVAC ducts be buried under R49 insulation. Here is an example of method to protect all and to provide safety, with a maximum of flooring, safely accessible. Build always for service life of at least sixty years. Such service life adds orders of magnitude to the value of construction. Cheap construction is unaffordable. (Search my Perpetuity Math.)  Build the floor 17” above drywall as dictated by economy in using 16” rips of plywood as webs in a complex box beam structure. Beam lower elements are the found floor joists whatever their dimension. Beam upper elements are typically upright 2x4s of maximum length. There is common practice to be applied in the density of screws or nails bonding webs to the 2x framing, Beam bottoms are room drywall. Beam tops are the plywood flooring, demanded for strength. Let attics be useful, with simple and sturdy lifts that add to user safety.

Such a thick floor was needed where a best attic ladder would be at 45° vs. framing.

Diagonal placement is really quite easy. Here it was wanted in part to allow painless repair of a ceiling fracture in a misstep while installing electronics wiring in the usual attic conditions of darkness and danger. The ceiling cut consumed the broken drywall. The diagonal placement is least obstructive in the hallway, and egress is off the path of work in the attic.

An attic ladder may be simple architectural beauty. This ceiling cut will be almost invisible with the ceiling repainted. The hole is well barricaded, with cautious approach in a step-off well.

Let demand for better, avoid the usual construction with phony insulation really R8, weakly stapled to fragile drywall.

Here is the ladder plan, where a very strong ladder rough box beam frame bears directly on the surrounding walls, and two floor joists, cut, are captured by the ladder frame.

Surrounding flooring ties to the ladder frame, with a walking surface 17" above ceiling drywall. This space is ample to move HVAC ducts to the attic floor, with safe, level, trip-free walking over a large decked area.

Under construction, see found inefficient HVAC ducts that had to be dodged to install the ladder, in August 2016. Construction was then paused to October, when HVAC would not be missed for awhile. For a complete story of this construction, consult the job photo album.

Here are photos of the finished, safe and useful attic.

The found attic access is converted to a storage lift. Near the lift, the 17" floor level is maintained beneficial to coverage of HVAC ducts, but not needed for floor strength,