Future Ducting

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2nd Edition

The Future In Air Distribution


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The cold air diffuser line isanother Thermal Coreexclusive. Unlike conven-

tional systems that handle 55degree air supply, the cold airdiffuser allows 40 degree orlower air to be distributedwithout the use of mixingboxes. The high inductionratio ensures comfort ismaintained and air qualitycriteria are met. Usersdiscover the benefits of coldair systems through lowerinitial system installation andconstruction costs. This is

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Drury College proved to be an elent testing ground for Thermal Ccold air diffusers since the structoffered a variety of room configtions. At left, the 30 foot ceilingatrium posed no problem for the efficiency of the diffusers.


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Thermal Core Cold-Air Diffusers

Thermal Core technology was de-veloped by applying the latest sci-entific knowledge of air jet behav-ior. The team responsible for itsdevelopment utilized data providedby the worlds leading air distribu-tion scientists. Computerized math-

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sible. Thermal-imaging was used tostudy the exact air distribution en-velope, the interaction of the pri-mary air stream with room ambientair, and resultant thermal gradients.An array of highly sensitive air flowand temperature sensors were in-

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Vena Contracta is formed pulling room air back into the jet nozzle and mixing it with the primary supply air streaminduction accomplished through the nozzle and within 4 1/2 inches of the diffuser outlet has a ratio of 2.35:1. Thimeans that for every CFM of supply air 2.35 CFM is introduced to the room. Induction continues throughout itsthrow due to the high mass and velocity of the individual circular jets. These two principles account for the veryoverall induction ratio. The diagram illustrates induction of room air into the supply jets exiting a Thermdiffuser. Room air adjacent to the supply jets is entrained into the stream, expanding the jet and transferring heatWithin a few inches from the diffuser, the temperature of the supply air has increased to the extent that dumpingcold air into the living space does not occur.

diffusers, when appsuggested guideline acedures. Deviation application procedgrade the performafuser, but degradatipredicted.

Thermal Core Research and Development


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Room temperatures and humidity levels were variedfrom 35 oF to 95 oF and 25% RH to 90% RH. A coldglass curtain wall mock-up was provided in the labo-

ratory to determine heating performance. This wall wastested down to -20 oF. Finally all thermal core diffus-ers were submitted to Energistics Laboratory, a divisionof Cerami and Associates for complete independenttesting. (See end note.)

The following tests were conducted:

Air flow, air throw, and air drop

Sound power and NC level development

Air pressure drop

Induction ratio determination

Air distribution performance (ADPI) tests

Cold curtain wall heating test

Complete cataloging of performance data for eachdiffuser

Condensation test in a warm and humid room withcold primary air (i.e. room - 95% DB, 90% RH;primary supply air - 35% DB

These tests concluded that the Thermal Core high

induction diffuser accomplishes a superiosion performance index and provides thebenefits:

Superior indoor air quality

Superior heating performance from ovdistribution, even in northern climates

Complete air mixing which providesperature gradients throughout the smore importantly, the elimination ofcuiting of the primary supply air to tair system. This increases the ventfectiveness factor and optimizes theness of outdoor ventilation air in achceptable indoor air quality.

The primary cold air stream wil

(dump) into the occupied zone, ethrottled back to zero flow rate.

Condensation problems often enduring initial pulldown in humid arecold-air distribution systems, are el

The thermal core line of high induction d

probably the most researched, studied, air distribution product of our time.

End Note:

Independent laboratory testing confirmed or prevailed over the initial testing which was performed in the Titus Labin Richardson, TX. All performance data and performance claims are based on the final testing in Energistics, a divCerami & Associates Inc., independent laboratory.


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Principles of Cold-Air Distribution

Air EntrainmentMathematical modeling and laboratory tests have proven that the application of five scientific principnecessary to accomplish optimum ambient air entrainment.

1. The injected airstream must have adequate velocity and mass to provide sufficient momentum to cadesired circulation, entrainment, and mixing of ambient air.

2. The ratio of peripheral surface area to cross-sectional area must be high to provide maximum contbetween the two air masses.

3. The ratio of the longitudinal dimension to cross-sectional area of the nozzle should be 3:1 or greateestablishes nonturbulant, linear flow within the nozzle, which prevents diffusion of the airjet when it the nozzle, thereby allowing the airjet to continue its circular form for some distance into the conditroom. A Vena-Contracta is established setting up an induction effect back into the nozzles.

4. Adequate space must be provided around the perimeter of each air shaft to allow maximum contathe injected airstream with the ambient air.

5. The jetstream must be projected at a specific angle away from the surface it is flowing across, creanegative pressure region between the high velocity jet and that surface. The low pressure region crmust be of sufficient depth and intensity so as to cause ambient air to flow into it, thus enhancing amair entrainment.

Thermal Core diffusers embody all five of these principles to a higher degree than has previouslybeen possible.

InductionDue to the innovative design of Thermal Core diffusers, induction ratios are much higher than thpreviously. Conventional diffusers offer induction ratios from 4:1 to 10:1. Thermal Core difinduction ratio from 200 to 400 percent. The induction ratio is cataloged for each diffuser at various arates so its performance can be easily ascertained. (See Diffuser Specifications.)

Draft-Free OperationThe Thermal Core diffuser is unique in that it projects air away from the ceiling, allowing a low pressutoformforashortdistance Theair streamisthenattractedtowardstheceilingpreventingit fromsinki


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Condensation FormationA successful cold-air distribution system must prevent condensation from forming on the diffusers

under all possible operating conditions. The thermal-core diffuser accomplishes this due to itsunique design. First, all parts of the diffuser are constructed of a self-insulating material. Second,warm ambient room air is induced in such a manner as to impinge on its surfaces. This characteristicwarms the surfaces adequately to prevent condensation. A Vena-Contracta is formed inducing airback into the nozzle which increases the outlet temperature further avoiding condensation formation

Condensation formation can also occur on conventional temperature systems under certain condi-tions. Thermal core diffusers have solved many such conditions in the past.

HeatingThe thermal-core diffusers are well suited to overhead heating systems in very cold climates.Walls with heat losses up to 500 BTUH per linear foot can be heated from an overhead airdistribution system without cold down-drafts affecting the comfort of occupants. The higher

induction rate again provides the circulation and mixing to prevent stagnation, down drafts,and other undesirable conditions from developing. Conventional diffusers simply do not havethe induction capacity to provide a comfortable draft-free environment under these cold adverseconditions.

A cold glass curtain wall was mocked up in a weather chamber at Energistics/Cerami AssociatesInc. Laboratory to ascertain exactly how well the thermal core diffusers would perform underextreme heating situations. The chamber was 20 feet wide, 24 feet long, and 9 feet high. The glasscurtain wall was 20 feet wide and 9 feet tall with a 0.56 U factor. Temperature was -20cold side of the wall and 75 oF on the warm side. The curtain wall heat loss was 478 BTUH pelinear foot. A temperature and air-flow sensor grid was set up in accordance with ADPI standardsThe maximum temperature differences within the occupied zone from head-level to floor level andthroughout the entire space was less than 1.5 oF. All the velocity readings were within the accable range.

ADPI test standards have not been established at this date for heating systems, but if normalADPI standards were applied, the rating would have been 100.

Until now, overhead heating systems could not provide adequate comfort under such adverseconditions. Even dual distribution systems with an overhead cooling system and an underflooheating system have a hard time equaling such performance.


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Cold-Air Distribution Systemsand Indoor Air Quality

Cold-air distribution systems provide improved humidity control enhancingcomfort that occupants perceive.

The buildings are fresher and more comfortable if high induction diffusers aremployed due to superior room-air mixing, greater ventilation effectiveness, animproved circulation rates.

Concentrations of endotoxins (toxic substances secreted by microorganismslower than in conventional systems.

Condensation on cooling-coil fins is up to three times higher than conventionsystems. This virtually turns the cooling-coil into an air washer carrying awamany undesirable impurities, particles, and toxins and flushing them down the

Overall air quality is perceived to be superior. Owners who have used cold-adistribution in conjunction with thermal core high induction diffusers know thaindoor air quality and comfort are improved.

Outdoor Air Introduct ion Rat e andVentilation Effectiveness

ASHRAE Standard 62-1989, Ventilation for Acceptable Indoor Air Quality, states intion 6, Paragraph 6.1.33 that outdoor air introduction rates must be increased if mprovided by the buildings air distribution system is less than 100% effective. Ventieffectiveness will be less than 100% unless complete mixing occurs between the prsupply air and the room ambient air (i.e. short-circuiting to the return air and/exhaust air system) Conventional diffusers typically fall short of complete mixi


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Corrected Outdoor Air VolumeAppendix F of the ASHRAE Standard 62-1989 develops the following equation to dete

correction for outdoor air volume, based on ventilation effectiveness.Corrected outdoor air volume VO c is determined equation:

WhereVO = outdoor air volumeEV = ventilation effectiveness

Ventilation effectiveness is determined by the equation:

WhereS = Percent of non-mixed airR = Recirculating factor (Ratio of recirculating air volume to Supply air volume

ExampleAs an example, consider a classroom occupied by a teacher and 29 students (30 people). Assumrequirement of outdoor air at a rate of 15 CFM/person (450 CFM total), a supply-air volume of CFM, and a supply-air temperature of 40 oF DB. The recirculation factor R is 0.37 [(714 CFCFM)/714 CFM = 0.37]. The following table gives the calculated E V and VO c for ADP100%, 90%, 80%, and 70%.

ConclusionsCondition 1 - air mixing of 100% (i.e. Thermal Core high induction diffuser) requires 4

td i t ti f ASHRAE 62 1989 i d i lit t d d

1 - S

1 - R * S E v =


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The HILT is a high inductionlinear diffuser designed for low

temperature applications. Factory sealed, integral

plenum with internally linedinsulation protects againstcondensation.

Discharge angle of leaving airdesigned to maintain a tight

horizontal pattern even withvarying air volumes. Molded face of diffuser has

smooth curved appearanceto blend into ceiling system.

Diffuser available in 2 and 4ft. lengths.

1 or 2 way opposite blow.

Air Discharge Pattern

The HILT series of low tem-perature diffusers are availablewith one-way or two-wayopposite high induction jets.The number, spacing, and cen-ter of discharge openings inThermal Core were engi-neered and tested to maximizethe diffusers performance in

VAV applications.


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Thermal Core High Induction Linear TStandard Capacity Diffusers

HILTStandard Capacity

24 1-Way Blow

HILTStandard Capac

24 2-Way Blo

HILTStandard Capacity

48 1-Way Blow

HILTStandard Capacit48 2 Way Blow

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