design guide_chilled beams (trox)

7/28/2019 Design Guide_Chilled Beams (TROX)

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Chilled BeamDesign Guide

Trox USA, Inc.4305 Settingdown CircleCummingGeorgiaUSA 30028

Telephone 770-569-1433Facsimile 770-569-1435

www.troxusa.come-mail [email protected]

TB0202


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Introduction to Chilled Beams 3

Passive chilled beams 3Active chilled beams 5

System Application Guidelines 8

Benefits of chilled beams 8Chilled beam applications 9

Multi-service Chilled Beams 11

System Design Guidelines 14

Comfort considerations 14

Air side design 15Water side design 19Control considerations 21Installation and commissioning 24

Chilled Beam Selection 27

Passive beams selection 27Passive beam performance data 28

Active beam selection 31Active beam selection examples 35

Performance Notes 38

Active Beam Performance Data 39

Coil pressure loss data 39DID600 series beams 44

DID620 series beams 50DID300 series beams 56

Chilled Beam Specifications 62

Contents

Notice to Users of this Guide

This Guide is intended for the sole use of professionals involved in the design and specification of TROX chilledbeam systems. Any reproduction of this document in any form is strictly prohibited without the written consent of

TROX USA.

The content herein is a collection of information from TROX and other sources that is assumed to be correct andcurrent at the time of publication. Due to industry and product development, any and all of such content is subjectto change. TROX USA will in no way be held responsible for the application of this information to system design

nor will they be responsible for keeping the information up to date.


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Introduction

Chilled beams have been employed in European HVACsensible cooling only applications for over twenty years.Within the past few years they have become a popularalternative to VAV systems in North America. The

growing interest in chilled beams has been fueled bytheir energy saving potential, ease of use as well astheir minimal space requirements.

Chilled beams were originally developed to supersedethe outputs achieved by passive radiant cooling ceilingsystems. Sensible cooling capacities of chilled ceilingsare limited by the chilled water supply temperature(must be maintained above dew point to preventcondensation from forming on their surfaces) and thetotal surface area available that can be chilled.Obviously, this area is limited as other services(lighting, fire protection, air distribution & extract etc.)limit the degree of employment of the active ceiling

surface such that their maximum space sensible cooling

capacity is very typically less than 25 BTUH per squarefoot of floor area. As this is not sufficient for maintainingcomfort especially in perimeter areas, chilled beamsvery quickly became the preferred solution in so muchas they occupied less space, had fewer connection andmost importantly offered sensible cooling outputs 2 to 3times that of chilled ceilings.

INTRODUCTION TO CHILLED BEAMS

Chilled beams feature finned chilled water heat ex-changer cooling coils, capable of providing up to 1100BTUH of sensible cooling per foot of length and aredesigned to take advantage of the significantly highercooling efficiencies of water. Figure 1 illustrates that a

one inch diameter water pipe can transport the samecooling energy as an 18 inch square air duct. The useof chilled beams can thus dramatically reduce airhandler and ductwork sizes enabling more efficient useof both horizontal and vertical building space.

There are two basic types of chilled beams (see figure

2). Passive chilled beams are simply finned tube heatexchanger coil within a casing that provides primarilyconvective cooling to the space. Passive beams do not

incorporate fans or any other components (ductwork,nozzles, etc.) to affect air movement. Instead they relyon natural buoyancy to recirculate air from the

conditioned space and therefore needs a high free areapassage to allow room air to get above the coil andcooled air to be discharge from below the coil. As theyhave no provisions for supplying primary air to thespace, a separate source must provide spaceventilation and/or humidity control, very typicallycombined with, but not limited to, UFAD. The air sourcecommonly contributes to the sensible cooling of the

space as well as controlling the space latent gains.

Active chilled beams utilize a ducted (primary) air sup-ply to induce secondary (room) air across their integralheat transfer coil where it is reconditioned prior to itsmixing with the primary air stream and subsequent dis-

charge into the space. The primary air supply is typi-cally pretreated to maintain ventilation and humiditycontrol of the space. The heat transfer coil

Figure 1: Cooling Energy TransportEconomies of Air and Water

Figure 2: Basic Beam Types

18 x 18Air Duct

1 diameterWater Pipe

Pass ive Chilled Beam(Exposed Beam Shown)

Active Chilled Beam


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Passive Chilled Beams

provides sensible cooling, it is not used to condense orprovide latent cooling.

Further discussion of the performance, capacities and

design considerations for each type of beam is providedin the following sections of this document.

PASSIVE CHILLED BEAMS

Passive chilled beams are completely decoupled fromthe space air supply and only intended to remove sensi-ble heat from the space. They operate most efficientlywhen used in thermally stratified spaces.

Figure 3. illustrates the operational principle of a pas-

sive beam. Warm air plumes from heat sources risenaturally and create a warm air pool in the upper portionof the space (or ceiling cavity). As this air contacts the

coil surface, the heat is removed which causes it to drop

back into the space due to its negative buoyancyrelative to the air surrounding it. The heat is absorbedlifting the chilled water temperature and is removedfrom the space via the return water circuit. About 85%of the heat removal is by convective means, thereforethe radiant cooling contribution of passive chilled beamsis minimal and typically ignored.

Passive chilled beams are capable of removing 200 to

650 BTUH of sensible heat per linear foot of lengthdepending upon their width and the temperature

difference between their entering air and chilled watermean temperature. The output of the chilled beam isusually limited to ensure that the velocity of the air

dropping out of the beam face and back into theoccupied zone does not create drafts.

It should also be noted that the air descending from apassive beam necks rather like slow running water outof a faucet. This slow discharge can be effected byother air currents around it and should passive beamsbe installed side by side, the two airstreams will join and

combine resulting in a higher velocity in the occupiedspace. Air discharge across the face of the beamshould be avoided as this can reduce the cooling outputby inhibiting the flow of warm air into the heat ex-

changer coil.

Passive Chilled Beam Variations

Passive chilled beams may be located above or belowthe ceiling plane. When used with a suspended ceilingsystem recessedbeams, TROX TCB-RB, are located afew inches above the ceiling and finished to minimizetheir visibility from below. Figure 4. illustrates such arecessed beam application.

Recessed beams are concealed above the hung ceilingand should also include a separation skirt (TCB-RB-Skirt) which assures that the cooled air does not shortcircuit back to the warm air stream feeding the beam.

Recessed beams (TROX series TCB) may be eitheruncapped (standard) or capped (more commonlyknown as shrouded) (see figure 5). Capped orshrouded beams have a sheet metal casing whichmaintains separation between the beam and the ceilingair cavity which is often used for the space return airpassage. This also provides acoustical separation be-tween adjacent spaces.

Passive beams mounted flush with or below the ceilingsurface are referred to as exposed beams. Most ex-posed beams (e.g., TROX TCB-EB and PKV series) arefurnished within cabinets designed to enhance the ar-chitectural features of the space as well as assure thenecessary air passages for the beam.

Figure 3: Passive Beam Operation

Figure 4: Recessed Beam Installation

Separation Skirt

Figure 5: Capped Passive Beam


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Active Chilled Beams

TROX Passive Chilled Beams

TROX USA offers 2 ranges of passive chilled beam asthe core engine behind the variants.

TCBU series beams offer a full range of 1 & 2 rowrecessed and exposed passive beams.

PKVU series beams are 1 row passive beamswith or without exposed cabinets.

Figure 6 illustrates an exposed passive beam in whosecabinet other space services (lighting, smoke and

occupancy detectors, etc.) have been integrated. Suchintegrated beams are referred to as integrated ormulti-service chilled beams (MSCB). As with recessed

beams, it is generally recommended that the crosssectional free area of the passage into an exposedchilled beam be equal to at least one its width. For more

information on these beams see pages 11-13.

ACTIVE CHILLED BEAMS

In addition to chilled water coil(s), active chilled beamsincorporate ducted air connections to receive pretreatedsupply air from a central air handling unit. This air isinjected through a series of nozzles within the beam toentrain room air. Figure 7 illustrates an active beam thatinduces room air through a high free area section withinits face and through the integral heat transfer coil whereit is reconditioned in response to a space thermostat

demand. The reconditioned air then mixes with theducted (primary) air and is discharged into the space bymeans of linear slots located along the outside edges of

the beam.

Active beams mounted above the occupied zone

maintain a sufficient discharge velocity to maintain afully mixed room air distribution. As such, they employ adilution ventilation strategy to manage the level of

airborne gaseous and particulate contaminants. Certainvariants of active beams (see discussion below) may bemounted in low sidewall or floor level applications as

well. In these cases, displacement ventilation and con-ditioning will be used to produce a thermally stratifiedroom environment.

Active chilled beams typically operate at a constant airvolume flow rate, producing a variable temperaturedischarge to the space determined by the recirculatedair heat extraction. As the water circuit can generallyextract 50 to 70% of the space sensible heat genera-tion, the ducted airflow rate can often be reduced ac-cordingly, resulting in reduced air handling requirementsas well as significantly smaller supply (and ex-haust/return) ductwork and risers.

Active chilled beams can provide sensible cooling ratesas high as 1100 BTUH per linear foot, depending ontheir induction capabilities, coil circuitry, and chilled

water supply temperature. Later in this guide, you willsee that careful selection of the beam must be made toensure that high terminal velocities are avoided to main-

tain comfort, a beam is not just a method of providingcooling, but also a terminal discharge device that has tobe selected to suit the location, space and how the

space is being utilized.

Active chilled beams can be used for heating as well,provided the faade heat losses are moderate.

Active Chilled Beam Variations

Active chil led beams come in a number of lengths and

widths allowing their use in exposed mounting orintegration into suspended ceiling systems, (their weightrequires they be independently supported). They can befurnished with a variety of nozzle types that affect theinduction rate of room air. Their discharge pattern canbe supplied as either one or two way while some beamsallow modification of their discharge characteristicsonce installed. Finally, some variants are available withcondensate trays designed to collect a limited amountof unexpected condensation.

Figure 6: Exposed Beam Installation

Primary air

supply

Suspended

ceiling

Figure 7: Active Chilled Beam Operation


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Figure 8: TROX Ceiling Mounted Active Chilled Beams

DID620 series beams are a low profile beam designed to allowintegration into standard 24 inch wide ceiling grids. They are ideal forapplications with limited ceiling plenum spaces.

DID600 series beams are also designed to allow their integration intostandard 24 inch wide acoustical ceiling grids. Though slightly tallerthan the DID620, their construction allows easy modification tospecific customer requirements.

DID300 series beams have a nominal face width of 12 inches andutilize two vertical chilled water coils. As such they can be furnished

with condensate trays to catch any moisture that might haveunexpectedly formed on the coil surfaces during periods of unusualoperation.

DID604 series beams are designed for four-way discharge patternswhich may be suitable for location certain room sizes.


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Figure 9: Other TROX Air-Water Products


BID series beams condition perimeter areas in UFAD applications.Conditioned air is delivered by a dedicated perimeter area airhandling unit. This relieves the UFAD system of the responsibility ofproviding sensible cooling and heating to the perimeter, resulting insubstantially reduced building airflow requirements.

DID-E series beams are designed for high sidewall mounting inhotels and other domiciliary applications.

QLCI series beams are integrated into low sidewall mounted cabinets andto discharge conditioned air to the space in a displacement fashion. Theyare most commonly used for classroom HVAC as they offer significant airquality and acoustical advantages. In fact, they are the only availableterminal capable of maintaining classroom sound pressure levels compliantwith ANSI Standard S12.60.


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Benefits of Chilled Beams

CHILLED BEAM SYSTEM APPLICATIONGUIDELINES

Chilled beams (both passive and active) posses certaininherent advantages over all-air systems. Thesebenefits can be divided into the three categories asfollows:

First cost benefits of chilled beam systems

Chilled beams afford the designer an opportunity toreplace large supply and return air ductwork with smallchilled water pipes. This results in significant savings interms of plenum space and increases usable floorspace.

Chilled beams can be mounted in ceilingspaces as small as 8 to 10 (vertical) inches

while all-air systems typically require 2 to 2.5times that. This vertical space savings can beused to either increase the space ceiling

height or reduce the slab spacing and thus theoverall building height requirements.

The low plenum requirements of chilled beamsystems make them ideal choices for retrofit ofbuildings that have previously used sidewallmounted equipment such as induction units,fan coils and other unitary terminals.

Chilled beams contribute to horizontal spacesavings as their significantly lower supply

airflow rates result in smaller supply and re-turn/exhaust air risers. The capacity of the air

handling units providing conditioned air to thechilled beam system is also reduced, resultingin considerably smaller equipment room footprints.

LEEDTM also requires that certified buildingsbe purged for a period of time beforeoccupancy in order to remove airbornecontaminants related to the construction proc-ess. The significantly reduced airflow require-ment of chilled beam systems reduces the fanenergy required to accomplish this task.

Operational cost benefits of chilled beam systems

The energy costs of operating chilled beam systems areconsiderably lower than that of all-air systems. This islargely due to the following:

Reduced supply air flow rates result in lowerfan energy consumption.

Operational efficiencies of pumps areintrinsically higher than fans, leading to muchlower cooling and heating energy transportcosts.

Higher chilled water temperatures used bychilled beams may allow chiller efficiencies tobe increased by as much as 35%.

Chilled beam systems offer attractive waterside economizer. Unlike the case with air sideeconomizers, these free cooling opportunities

are not as restrictive in climates that are alsohumid.

Maintenance costs are considerably lowerthan all-air systems. Chilled beams do notincorporate any moving parts (fans, motors,damper actuators, etc.) or complicated controldevices. Most chilled beams do not require

filters (and thus regular filter changes) orcondensate trays.As their coils operate dry,regular cleaning and disinfection of

condensate trays is not necessary. Normal

maintenance history suggests that the coils bevacuumed every five years (more frequently inapplications such as hospital patient roomswhere linens are regularly changed). Figure10 compares the lifetime maintenance andreplacement costs for active chilled beams tofan coil units (FCU), based on an expectedFCU lifetime of 20 years. It assumes thateach beam or FCU serves a perimeter floorarea of 150 square feet.

Active Chilled

BeamFan Coil Unit

Filter Changes:

NAFrequency: Twice Yearly

Cos t per Change: $30. 00

$0.00Cost over Lifetime (20 Years): $1,200.00

Clean Coil and Condensate System:

Every four YearsFrequency: Twice Yearly

$30.00Cos t per E vent: $30. 00

$150.00Cost Over Lifet ime: $1,200.00

Fan Motor Replacement:

NAFrequency: Once during life

Cos t per Event: $400.00

$0.00Cost Over Li fet im e: $400 .00

$150.00Life Cycle (20 years) maintenance cost: $2,800.00

Source: REHVA Chilled Beam Application Guidebook (2004)

Figure 10: Life Cycle Maintenance CostsActive Chilled Beams versus Fan Coils


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Applications

Comfort and IAQ benefits of chilled beam systems

Properly designed chilled beam systems generallyresult in enhanced thermal comfort and indoor air

quality compared to all-air systems.

Active chilled beams generally deliver a

constant air volume flow rate to the room. Assuch, variations in room air motion and cold airdumping that are inherent to variable volumeall-air systems are minimized.

The constant air volume delivery of primary airto the active chilled beam helps assure thatthe design space ventilation rates and relative

humidity levels are closely maintained.

Chilled beam application criteria

Although the advantages of using chilled beams arenumerous, there are restrictions and qualifications thatshould be considered when determining their suitabilityto a specific application. Chilled beams are suitable foruse where the following conditions exist:

Mounting less than 20 feet. Ceiling heightsmay be greater, but the beam should generallynot be mounted more than 20 feet above thefloor.

The tightness of the building envelope isadequate to prevent excessive moisture

transfer. Space moisture gains due tooccupancy and/or processes are moderate.

Space humidity levels can be consistentlymaintained such that the space dew pointtemperature remains below the temperature ofthe chilled water supply.

Passive beams should not be used in areaswhere considerable or widely variable airvelocities are expected.

Passive beams should only be consideredwhen an adequate entry and discharge areacan be assured.

Passive Chilled beams can not be used toheat.

Applications best served by chilled beams

Chilled beams are ideal for applications with high spacesensible cooling loads, relative to the space ventilationand latent cooling requirements. These applicationsinclude, but are not limited to:

1) Brokerage trading areas

Trading areas consists of desks where asingle trader typically has access to multiple

computer terminals and monitors. This highequipment density results in space sensiblecooling requirements considerably higher than

conventional interior spaces while the ventila-tion and latent cooling requirements are es-sentially the same. Active chilled beams re-move 60 to 70% of the sensible heat bymeans of their water circuit, reducing theducted airflow requirement proportionally.

2) Broadcast and recording studios

Broadcast and recording studios typicallyhave high sensible heat ratios due to their

large electronic equipment and lighting loads.

In addition, space acoustics and room airvelocity control are critical in these spaces.Passive chilled beams are silent and capableof removing large amounts of sensible heat,enabling the use of a low velocity supply airdischarge.

3) Heat driven laboratory spaces

Designers often classify laboratories according

to their required supply airflow rate. Inlaboratories that are densely populated byfume hoods, the make up air requirement is

typically 12 air changes per hour or more.These laboratory spaces are classified as air

driven. Laboratories whose make up airrequirement is less than that are typicallyconsidered heat driven. This category includesmost biological, pharmaceutical, electronicand forensic laboratories. The ventilation re-quirement in these laboratories is commonly 6to 8 air changes per hour, however, the proc-esses and equipment in the laboratory canoften result in sensible heat gains that require18 to 22 air changes with an all-air system. Tomake matters worse, recirculation of airexhausted from these laboratories is notallowed if their activities involve the use ofgases or chemicals.

Active chilled beams remove the majority (60to 70%) of the sensible heat by means of theirchilled water coil, enabling ducted airflow ratesto be reduced accordingly. Not only is thespace more efficiently conditioned, but theventilation (cooing and heating) load at the airhandler is substantially reduced as far lessoutdoor air is required.


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Applications

4) High outdoor air percentage applications

Applications such as patient rooms in hospitals

typically demand higher ventilation rates aswell as accurate control of those rates. Chilledbeam systems are ideal for these applications

as their hydronic sensible cooling regulates thespace temperature while allowing a constantvolume delivery of supply and ventilation air tothe space. Displacement chilled beams suchas the TROX QLCI also offer opportunities forimproved contaminant removal efficiencies,reducing the likelihood of communicablediseases spreading to health care staff

members.

5) Perimeter treatment for UFAD systems

As conditioned air passes through the openfloor plenum in UFAD systems, it picks up heattransferred through the structural slab from thereturn plenum of the floor below. The amountof heat transfer that is likely to occur is veryhard to predict as many factors influence it.However, the resultant temperature rise in theconditioned air can often lead to dischargetemperatures 4 to 5F higher than thoseencountered in interior zones nearer the point

of entry into the supply air plenum. Suchhigher temperatures contribute to perimeterzone airflow requirements that are typically 35

to 40% higher than that of conventional(ducted) all-air systems.

Passive chilled beams such as the TROX TCBseries provide effective and reliable cooling ofperimeter spaces in UFAD applications. Figure11 illustrates such an application where thepassive beam is mounted above the acousticalceiling and adjacent to the blind box above anexterior window. Floor diffusers fed directlyfrom the pressurized supply plenum continueto provide space ventilation and humiditycontrol. Heating cannot be effectivelyaccomplished by passive beams, so anunderfloor finned tube heating system orradiant panel heating system typicallycompliments the chilled beams.

Use of passive beams for perimeter areasensible cooling can reduce overall supplyairflow rates in UFAD systems by as much as50%. This also results in a) smaller airhandling units and ductwork, smaller supplyand return air risers, c) reduced maintenancerequirements and occupier disruption, d)improved space acoustics and air quality.

Chilled beams are also an excellent choice where the

vertical height of the ceiling cavity is limi te d. Th es einclude applications involving:

1) Building height restrictions

Building codes may restrict the overall heightof buildings in certain locales. This commonlypromotes the use of tighter slab spacing whichreduces the depth of the ceiling cavity. Passivechilled beams can often be fit betweenstructural beams in these applications. Activechilled beam systems can easily be designedto require 10 inches or less clearance whenintegrated into the ceiling grid system.

2) Retrofits involving reduced slab spacing

Many buildings that are candidates for HVACsystem retrofits utilize packaged terminal units(induction units, vertical fan coil units, etc.)that are installed below the ceiling level. Assuch, many of these structures have ceilingcavities with limited depth. Chilled beams areideal for such retrofits.

a

Finned Tube

Heating Coil

Passive

Chilled Beam

Return Air

Grille

Swirl Type

Floor Diffuser

Blind Box

Figure 11: Passive Chilled Beams forPerimeter Treatment in a UFAD System


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Multi-Service Chilled Beams

Multi-service (or integrated) chilled beams incorporateother space services into the linear enclosures associ-ated with the chilled beams. This allows fitting of theselected services to the beams within the factory and

delivery of elements that house all of these services tothe job site in a just -in-time fashion. Upon arrival,these devices are hung, attached in a linear fashion and

modular connections facilitate the installation of thevarious service systems.

Figure 12 below illustrates an active multi-service beamand the services that can be easily integrated with it.The core of this device is a DID302 active chilled beamwhich incorporates a primary air duct (and plenum) achilled water coil as well as inlet (perforated face) and

discharge (linear slot) air passages. The outer frame ofthe device is designed to provide mounting surfacesand provisions for other services which are installed at

the factory prior to shipment to the job site. Some of the

services that can be integrated include:

1. Lighting fixtures and controls2. Speakers3. Occupancy sensors4. Smoke detectors

In addition, the outer frame is often customized to pro-vide a visual appeal that is consistent with the architec-ture of the space in which it is mounted.

Multi-service chilled beams can be provided as eitheractive or passive versions. In cases where passivebeams are used, a separate air distribution system must

be provided. Oftentimes this air supply utilizes the cavitybeneath a raised access flooring system as a supplyplenum and is referred to as Underfloor Air Distribution.

The service fixtures provided with multi-service beamsare usually provided by others and issued tom the fac-tory for mounting and connection where possible. Uponcompletion, the beams are shipped to the job site for

mounting and final connection.

Lighting provided with these beams may be direct, indi-

rect or both. In all cases, the lighting system designer

should be consulted to assure that the beam design andplacement also provides sufficient space lighting. Fireprotection designers should also be consulted in orderto assure that the placement of the beams does notconflict with that of the fire sprinklers.

Figure 12: Multi-service Chilled Beams


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Multi-service Chilled Beam Designs

Figures 13 and 14 below illustrate passive and activemulti-service beam installations.

Note that the photograph in figure 13 includes a swirltype diffuser mounted in the floor near the window. This

diffuser supplies conditioned air for the ventilation anddehumidification of the space. The beams include alinear bar grille for the room air discharge and arecurved to conform to the curvature of the ceiling. Bothdirect and indirect lighting is provided.

Figure 14 illustrates an active beam version where thefacial slots have been relocated such that they are not

visible and are integrated into the top of the beam, dis-charging supply air across the surface of the exposedslab. Again lighting is both direct and indirect in the

case of these beams.

The photographs in these figures do not show a ser-vices corridor that runs perpendicular to the beams to-ward the interior of the space. This corridor is approxi-mately the depth of the beams themselves and housesthe main ductwork, piping and other services that feedthe beams. These corridors may also house the returnair passage in case where the slab is exposed. As arule of thumb, about thirty (30) linear feet of beams maybe connected to each run leaving the service corridor.

Most multi-service beams are provided for exposed slabapplications but other versions can be provided to inte-

grate with acoustical ceiling grids.

The Case for Multi-service Beams

Multi-service chilled beams offer numerous advantagesover conventional service delivery systems, notably:

1. As the services are integrated into the beams in thefactory, quality control can be much better main-

tained than with field mounted services. Factorymounting involves the provision of proper fixturesto do the work and facilitates difficult piping andvalve connection. This also allows the final pipingto be leak tested after the components are assem-bled.

2. Factory mounting of the space services reducesthe amount of required trade coordination on the

job site.3. All of the space services mounted in the common

housing can be easily accessed for final connection

and commissioning as well as future maintenance.

4. The design of the housing involves the project ar-chitects as well as the engineering consultants anddrives early coordination efforts as opposed to lastminute panics.

5. The above advantages can result in significantreductions in the time required to construct thebuilding.

The construction time reduction has made multi-servicebeams very popular in the Europe, especially the United

Kingdom. Cases where the building construction timehas been reduced by 25 to 30 percent have been welldocumented in a number of publications. Construction

schedule reductions of ten to fifteen percent result in

Figure 13: Passive Multi-service Beams Figure 14: Active Multi-service Beams


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significant cost savings. In particular, fixed site costscan be retired much earlier. These fixed site costsinclude but are not limited to:

1. Communication and utilities services2. Sanitation services3. Equipment rentals4. Insurance costs

On a job with a two year construction schedule, thesefixed costs (which contribute nothing to the value ofthe project) typically amount to 12 to 14% of the valueof the construction itself. Terminating the projectsooner allows these costs to be cut proportionally.

The use of multi-service beams can also allow theelimination of the acoustical ceiling system and, onnew construction projects, may afford the use of

lesser slab spacing. This may reduce the structurecosts as well or may allow more floors to be housedwithin in a similar structure height (see next section).

Finally, earlier completion allows the building owner tobegin realizing revenue faster. The combination ofthese financial impacts typically offsets the cost differ-ence between the multi-service approach and that ofconventional HVAC and space services delivery.

Building Height Requirements

Multi-service beams may also afford opportunities for

reduced building height and/or facilitate the retrofit ofbuildings with limited slab spacing. The integration ofspace services in the beam often eliminates the needfor an acoustical ceiling and allows the beams to bependant mounted directly to the structural slab.

Figure 15 below illustrates the slab spacing require-ments of a VAV system with fan powered terminalsversus an exposed mounted multi-service activechilled beam. The ductwork in the VAV system ismust be located such it remains below the horizontalstructural supports. It also must be supported severalinches above the ceiling grid to allow the installationof light fixtures and sprinkler systems. In order to pro-vide a floor to ceiling height of nine (9) feet, the slab

spacing is typically thirteen (13) feet.

Multi-service beams which are mounted to the slaballow the provision of a ten (10) foot distance from thefloor to the overhead slab while maintaining an 8.5foot clearance under the beams when used with a10.5 foot slab spacing. This savings essentially allowsthe addition twenty percent more floors in a buildingwhen multi-service beams are used instead of a VAVsystem.

Suspended ceiling

13'-0"9'-0"

VAV with Fan Terminals

Light fixture

10'-0" 8'-6"

Multiservice Chilled Beams

10'-6"

Figure 15: Slab Spacing Reduction with Multi-service Beams


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Comfort Considerations

CHILLED BEAM SYSTEM DESIGNGUIDELINES

The HVAC system is responsible for three importanttasks that help assure occupant comfort and a healthyindoor environment:

1) Removal of the space sensible heat gains.2) Delivery of a prescribed volume flow rate of

outdoor air to properly ventilate the space.

3) Sufficient dehumidification to offset the spacelatent heat gains.

As the water circuit in chilled beams is designed only toassist in achieving the sensible cooling objective, the air

supply to the space must be properly maintained toaccomplish the ventilation and dehumidification goals.

In order to achieve efficient chilled beam systemoperation, certain considerations should be factored intothe development of the system design and operational

objectives. The following sections identify and brieflydiscuss such considerations that apply to the design,selection and specification of the equipment thatsupplies and controls the chilled beams.

General design objectives. Air-side design goals and considerations. Water-side design goals and considerations.

Control and operational considerations.

The following sections discuss design decisions that

affect the sizing and selection of the air and watersystem equipment and accessories.

Designing for occupant thermal comfort

The maintenance of a high level of occupant thermalcomfort is the primary objective of most chilled beamapplications. ANSI/ASHRAE Standard 55-2004 ThermalEnvironmental Conditions for Human Occupancy 2identifies key factors that contribute to thermal comfortand defines environmental conditions that are likely toproduce such. The Standard generally states that dur-ing cooling operation, the space (operative) dry bulbtemperature should be maintained between 68 and77F and the space dew point temperature should notexceed 60.5F. If the space operative temperature is75F, this maximum dew point temperature corresponds

to a relative humidity of 60%.

The standard also defines the occupied zone as theportion of the bounded by the floor and the head level ofthe predominant stationary space occupants (42 inchesif seated, 72 if standing) and no closer than 3 feet fromoutside walls/windows or 1 foot from internal walls. It isgenerally accepted that velocities within the occupiedzone should not exceed 50 to 60 feet per minute.

Designing for acceptable space acoustical levels

The space acoustical requirements are usually dictatedby its intended use. The 2007 ASHRAE Handbook

(Applications)3 prescribes design guidance (includingrecommended space acoustical levels) for various typesof facilities and their use.

AIR SIDE DESIGN CONSIDERATIONS

Room and primary air design considerations

When chilled beam systems are being contemplated,

the relationship between the room design conditionsand the primary air requirements should be closelyevaluated.

As previously stated, the chilled water circuit withinchilled beams is capable of considerably higher

sensible heat removal efficiencies than doesconditioned air supplied to the space. As such, it isadvantageous to remove as much sensible heat aspossible by means of the chilled water circuit. In theory,this practice would allow the supply airflow rate to thespace to be reduced proportionally and result in bothenergy savings and reduced HVAC services spacerequirements. However, the airflow supply to the spaceis also the sole source of space ventilation and dehu-midification so consideration of these functions is im-perative in the design of chilled beam systems. Theprimary (conditioned) airflow rate to the beam must besufficient to provide space humidity control, ventilationand supplement the chilled water circuit in satisfying thespace sensible heat gains. The space primary airflow

rate must be the maximum of that needed to adequatelyaccomplish all of those individual tasks.

Space ventilation requirements are usually based onthe number of space occupants and the floor area inwhich they reside. ASHRAE Standard 62-2004provides guidance in the calculation of theserequirements. Some spaces (laboratories, healthcarefacilities, etc.) may require higher ventilation rates dueto processes they support. Identification of the re-quired space ventilation rate should be the first step in

the design process.

a


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Airside Design Consideration

In order to maintain specified room humidity levels, theprimary airflow must remove moisture (latent) heat atthe rate at which it is generated. The supply airflow raterequired to do this is determined by the equation:

CFMLATENT = qLATENT / 4840 x (WROOM - WSUPPLY)

where, qLATENT is the space latent heat gain and WROOMand WSUPPLY is the humidity ratio (LBS H2O per LB Dry

Air) of the room and supply air, respectively.

When chilled beam systems are used, the chilled watersensible heat extraction rate allows reduction of designsupply airflow rates by 50 to 60% over conventional all-air systems. Reductions of this magnitude may, how-

ever, compromise space ventilation and dehumidifica-tion. When chilled beams are used in applicationswhere a) the design outdoor dew point temperature is

above 50F and b) preconditioning outdoor air to a dew

point temperature below that (50F) is not feasible,careful consideration should be given to the determina-tion of design room air humidity levels.

Figure 16 illustrates relationships between the primaryair supply and the space design conditions for a typicalinterior space. This figure uses the specified room rela-tive humidity and the primary air dew point tempera-ture to establish a factor (FLATENT) that relates the pri-mary airflow requirement to maintain the desired room

relative humidity as a ratio of the space ventilation re-quirement. It assumes a ventilation rate of 20 CFM perperson.

The primary airflow rate required to accomplish the

desired space ventilation and dehumidification can becalculated as:

CFMLATENT = FLATENT x CFMVENT

Note that maintenance of 50% relative humidity withprimary air supplied at a 52F dew point temperaturewill require that the primary airflow rate for the requiredspace dehumidification be some 2.3 times the spaceventilation rate. If the design relative humidity of thespace were 55% (well within ASHRAE recommenda-tions), the primary airflow requirement could be halved.

Alternatively, the primary air could be conditioned to a48F dew point in order to maintain 50% relative humid-ity with a similar primary airflow rate. As the beams aregenerally operated at a constant volume flow rate, theroom relative humidity levels will remain constant duringoccupied periods.

Perimeter airflow requirements in chilled beam systemsare generally driven by space sensible heat gains,therefore, space relative humidity levels in those areaswill typically remain lower than in interior spaces.

In summary, designing for slightly higher relativehumidity levels can result in significant reductionsin space primary airflow requirements!

A

Primary Air Dewpoint Termperature, F

48 49 50 51 52 53 54 551.0

2.0

3.0

4.0

LatentAirflowFactor,FLATE

NT

1.5

2.5

3.5

4.5

56

Space Relative

Humidity

Optimized Design

Range

50%

51%

52%

53%

54%

55%

56%

57%

Figure 16: Pschrometric relationshipBetween Space and Primary Airflow


16/68

16

Airside Design Considerations

Room air distribution in passive beam applications

As passive beams rely only upon natural forces torecirculate the air to and from the space, it is critical thatexcessive restrictions in the air passages to and fromthe beams be avoided. As such, passive beams utilizevery wide fin spacing (typically 3 to 4 fins per inch) asopposed to conventional cooling coils. Researchindicates that the performance of these beams can alsobe significantly compromised if an adequate entry anddischarge path is not maintained.

It is generally recommended that the return and dis-charge passage of air through the ceiling perforated tilebe equal to 2 times the width of the coil, normally split50-50, down the long sides of the beam. Figure 17 illus-trates the recommended entry and discharge area rela-

tionships for recessed passive beams mounted above aceiling tile with a 50% free area. The free area of theperforated ceiling has a direct result on performance ofthe beam., as the free are decreases, the output alsodecreases. The free area of the tile should not be lowerthan 28%, however, no increase in output is gainedbeyond 50% free area. When passive beams aremounted very near a perimeter wall or window, the re-quired return air passage may be reduced as the warmair entering the beam has more momentum (contactTROX USA for further application assistance). Exposedbeams must also be located such that the entering airpassage requirements are observed.

Passive chilled beams operate most efficiently in astratified or partially stratified room environment. Assuch, displacement ventilation or underfloor air

distribution (UFAD) outlets with limited verticalprojection (throw to a terminal velocity of 50 FPM is nomore than 40% of the mounting height of the beams).For design purposes, the beam entering air temperatureshould be assumed 2F warmer than that at the controllevel of the room under the described installation andoperating conditions.

When passive beams are mounted adjacent to anoutside window (and the room is thermally stratified),

the momentum of the warm air rising along theperimeter surface will likely result in entering airtemperatures 4 to 6F warmer than the room controltemperature, dependent on the surface temperature ofthe faade.

Ceiling or high sidewall outlets can be used (with alesser heat transfer efficiency) provided their horizontalthrow to 50 FPM does not extend to within four feet ofthe passive beam.

In order to maintain a high level of thermal comfort,passive beams should be located such that the veloci-ties of the falling cool air do not cause discomfort. As ageneral rule, the velocity at the head level of a station-

ary occupant should not exceed 50 FPM. Figure 18illustrates typical velocities directly below passivebeams as a function of the sensible cooling theyprovide.

B

W = 2.0 x B

Min. 0.33 x B

Separation Skirt

Minimum

20% Free

Area Panel

Figure 17: Entry Area Requirements for

Passive Chilled Beams

Figure 18: Velocities Below Passive Beams

0

20

40

60

Loca

lVe

loc

ity,

FPM

10

30

50

70

Average local velocity

3 feet be low passive

beam


17/68

17


Space temperature control in passive beam systems isaccomplished by varying the amount of sensible heatremoved by the chilled water. The chilled water supplyto several beams within a single zone is generally

controlled by a single chilled water valve. Although thezone may consist of multiple spaces, a certain degreeof temperature compensation for each space will be

affected by the passive beam itself. As the coolingrequirement of the space is reduced, the temperature ofthe air entering the beam will also be reduced. This willresult in less heat transfer to the water circuit and alower return water temperature.

Passive chilled beams cannot be used for heating as itsairflow would be reversed. They are typically applied

with some type of separate heating system such as lowlevel finned tube heaters. Radiant (ceiling or wallmounted) heating panels can also be used depending

on the faade heat losses expected.

Thermal comfort considerations with active beams

While the primary (conditioned) airflow rate for activechilled beams can be greatly reduced, their inductionratios (2 to 6 CFM of room air per CFM primary air)result in discharge airflow rates that are slightly higherthan those of conventional all-air systems. As such,attention should be exercised in the beam placement toavoid drafty conditions and maximize occupant thermal

comfort. Figure 19 predicts maximum occupied zonevelocities for various combinations of primary airflowrates and active beam spacing. This nomograph

suggests local velocities which will maintain acceptablelevels of occupant comfort per ASHRAE.

As the room air distribution provided by activebeams is identical to that provided by ceiling slotdiffusers, their selection for (total) discharge airflowrates greater than 40 CFM per linear foot of slot isnot recommended when high levels of occupantthermal comfort are required!

The vL velocities shown in figure 19 are those predictedwithin 2 inches of the window or wall surface duringcooling operation. It is recommended that beams whichare configured for both heating and cooling of perimeterspaces be selected such that vL (selected for coolingoperation) is between 120 and 150 FPM in order toassure that the warm air is adequately projected downthe perimeter surface. Velocities taken 6 inches awayfrom the surface can be expected to be about half thosevalues.

Heating in chilled beam applications

Ceiling or high sidewall mounted passive chilled beamsexert no motive force on their discharge airflow, andcannot be used for overhead heating. Heating must beprovided by a separate source, either the primary airsupply or a separate heating system (finned tube,radiant panel, etc.).

Active beams can be for heat in moderate climates. Hotwater can either be delivered to each perimeter areabeam or to a hot water heating coil in the duct supply-ing a number of beams within the same thermal control

zone. The use of a zone hot water heating coil feeingmultiple chilled beams is a generally more economicoption than piping each chilled beam for heating as it

may save considerable labor and piping material costs.If active chilled beams are used for heating, the follow-ing recommendations should be observed:

Chilled beam discharge temperatures shouldbe maintained within 15F of the roomtemperature.

Velocities at the mid-level of outside walls and

windows should be maintained within theregion indicated in figure 19.

Unoccupied periods demanding heating via the chilled

beams or primary air system will require that the AHUremain operational.

Variable air volume operation using active beams

Although normally operated as constant air volumedelivery devices, active chilled beams can also be usedas variable air volume (VAV) devices. VAV operationmay be advantageous when space occupancy and/orventilation demands vary widely. Recommendations for

the control of chilled beams in VAV applications can befound in the control section of this document.


18/68

18

Distance A/2 or X (feet)

Cooling mode velocity exceeds recommended

level for high occupant comfort levels.

LocalVelocityVH1

,FPM

63 4 5

H - H1 (feet)

40 FPM

30 FPM

6 5 4

H - H1 (feet)

6 8 10 12 144

30 CFM/LF

35 CFM/LF

40 CFM/LF

3

BEAM

TOTAL

AIRFLOW

RATE (PER

LINEAR

FOOT OF

SLOT)

Velocities VH1 VL2 and VL6 are based on a

15F tem perature differential between

the room and the supply airstream.

Local

Velocity VL6 ,

FPM

H - H1

AX

VH1VL2 orVL6

2" for VL2

6" for VL6

0.5 QSUPPLY0.5 QSUPPLY 0.5 QSUPPLY

H - H1 Cooling

H/2 Heating

25 CFM/LF

20 CFM/LF

50 FPM

35 FPM

45 FPM

55 FPM

60 FPM

70 FPM

80 FPM

70 FPM

60 FPM

50 FPM

90 FPM

100 FPM

Type C Nozzle: QTOTAL = 3.2 x QPRIMARY

Type B Nozzle: QTOTAL = 4.2 x QPRIMARY

Type A Nozzle: QTOTAL = 5.3 x QPRIMARY

Type G Nozzle: QTOTAL = 3.7 x QPRIMARY

Type M Nozzle: QTOTAL = 4.8 x QPRIMARY

6 5 4

H/2

80 FPM

60 FPM

120 FPM

90 FPM

70 FPM

100 FPM

110 FPM

50 FPM

CoolingCooling Heating

Local

Velocity VL2 ,

FPM

Velocities (VL2) within recommended levels foroverhead heating applications.


Figure 19: Local Velocity Predictions for TROX Active Chilled Beams

NOTES:

1. VL2 values in chart are measured 2" from wall in a heating mode. For adequate heating performance, VL2 value at mid-level height of the wall should be atleast 50 FPM.

2. VL6 values in chart are measured 6" from wall in a cooling mode. VL6 values the top of the occupied zone should be limited to about 75 FPM.3. VH1 values in chart are measured at the top of the occupied zone directly below the point of collision of two opposing air streams (cooling mode). For opti-

mum thermal comfort, VH1 values should not exceed 50 FPM.

2 for VL26 for VL6


19/68

19

Water Side Design Considerations

WATER SIDE DESIGN CONSIDERATIONS

Once the room air conditions have been established,the water side design objectives and requirements can

be identified. Certain factors must be considered inarriving at the chilled water system design. Thefollowing sections discuss these.

Chilled water supply source

There are several possible sources of adequatelyconditioned chilled water for the supply of chilled beamsystems. Among these are several sources discussedbelow:

Return water from AHU chilled water coil Dedicated chilled water supply system District chilled water supply Geothermal wells

When air handling units associated with chilled beamsystems utilize chilled water evaporator coils, theirreturn water can often be used to remove heat from thechilled beam circuit. Figure 20 illustrates a chilled waterloop whose heat is extracted through a heat exchangerto the AHU return water loop. The chilled water supplyis a closed loop which includes a bypass by whichreturn water can be bypassed around the heatexchanger to maintain the desired chilled water supply

temperature to the beams. Figure 21 illustrates a chilledbeam system where the beams are supplied by a dedi-cated chiller. The chilled water loop allows the chiller to

operate at a higher efficiency due to the higher returnwater temperatures associated with the chilled beam

system. The chillers COP can often be increased by 25to 30% by doing so.

In some cases, water from district chilled water suppliesor geothermal wells may replace the return water fromthe AHU and serve as the primary loop in the heatexchanger shown in figure 20.

Chilled water supply and return temperatures

The most important decision regarding the chilled watersystem involves the specification of a chilled watersupply temperature. In order to prevent condensationfrom forming on the beams, the chilled water supplytemperature must be sufficiently maintained. TheREHVA Chilled Beam Applications Guidebook

1

suggests that condensation will first occur on the supplypiping entering the beam. As such, it is very importantto insulate the chilled water supply piping to the beams.Reference 4suggests that condensation will not likelyform when the active chilled water supply temperatureis maintained no lower than 3F below the room air dewpoint and at least 1F above the space dew pointtemperature in the case of passive beams.

TROX USA recommends that the chilled water sup-ply temperature for passive chilled beams is at least1Fabove the maximum room dew point that can becontrolled to whilst active beams are kept at orabove the room dew point as an operational safetymargin. In general, most beams installed to date havea supply temperature 1.5F or more above room dewpoint.

The return water temperature leaving chilled beams isat least 3F higher than the chilled water supply. Assuch, the chilled water return piping does not normallyneed to be insulated.

T

Supply Temperature

Controller

Chilled Water

Pump

3-wayModuating

Valve

Return Water Bypass

Primary Chilled

Water Supply

Secondary

(Tempered) Chilled

Water Supply to

Beams

HEAT EXCHANGER

Secondary

Chilled Water

Return

Primary Chilled

Water Return

T

Supply Temperature

Controller

Chilled Water

Pump

3-way

Moduating

Valve

Return Water Bypass

Secondary

Chilled Water

Return

Storage

Vessel

DedicatedChiller

Secondary

(Tempered) Chilled

Water Supply to

Beams

Figure 20: Shared or Tempered ChilledWater Supply Circuit

Figure 21: Dedicated Chilled Water Circuit


20/68

20

Water Side Design Considerations

Hot water supply and return temperatures

Active chilled beams can be used for perimeter heatingand cooling in mild climates. It is recommended that the

hot water supply be maintained at a temperature thatwill result in a beam discharge temperature no morethan15F warmer than the ambient room temperature.

Water flow rates

There are factors that affect the minimum and maximumwater flow rates within the chilled beam system.Maximum flow rates are limited by the pressure losswithin the beam. Minimum flow rates are based on themaintenance of turbulent flow to assure proper heat

transfer. The following recommendations apply to thechilled water system design:

Water head loss through the beams should be

limited to 10 feet H2O or less.Pressures exceeding 10 feet H2O at the water con-trol valve may cause noise when the valve beginsopening.The 2005 ASHRAE Handbook (Fundamentals)

5

limits water flow rates in pipes that are two (2)inches in diameter or less to that which results inmaximum velocities of 4 FPS.Chilled beam water flow rates below 0.15 GPMmay result in non-turbulent flow. Selection below

this flow rate should not be made as the coil per-formance cannot be assured.

Water treatment recommendations

As most of the elements within the chilled (and hot)water piping systems are typically copper or brass, it isimportant that the water circuit is treated to assure thatthere are no corrosive elements in the water. The watercircuits feeding the chilled beams should also be treatedwith a sodium nitrite and biocide solutions to preventbacterial growth. Glycol should not be added exceptwhere absolutely necessary as it changes the specificcapacity of the chilled water and its effect on the chilledbeam performance must be estimated and accountedfor. Prior to start up and commissioning, all chilled andhot water piping should be flushed for contaminants.


21/68

21

Control Strategies

CHILLED BEAM CONTROL CONSIDERATIONS

This section discusses the control of both the air and

the water supply in chilled beam systems. It alsopresents and discusses strategies for condensationprevention.

Temperature control and zoning with chilled beams

Room temperature control is primarily accomplished byvarying the water flow rate or its supply temperature tothe chilled beam coils in response to a zone thermostatsignal. Modulation of the chilled water flow rate typicallyproduces a 7 to 8F swing in the beams supply airtemperature, which affects a 50 - 60% turndown in thebeams sensible cooling rate. This is usually suffi-cient for the control of interior spaces (except confer-ence areas) where sensible loads do not tend to varysignificantly. If additional reduction of the space cooling

is required, the primary air supply to the beam can bereduced. In any case, modulation of the chilled waterflow rate or temperature should be the primary meansfor controlling room temperature as it has little or noeffect on space ventilation and/or dehumidification. Onlyafter the chilled water flow has been discontinuedshould the primary airflow rate be reduced.

Thermal control zones for chilled beam applicationsshould be establish in precisely the same manner theyare defined for all air systems. These zones shouldconsist of adjacent spaces whose sensible coolingrequirements are similar, and several beams should becontrolled from a single space thermostat. For example,the beams serving several perimeter spaces with the

same solar exposure can be controlled by a singlethermostat to create a zone of similar size to that whichmight be served by a single fan terminal in an all airsystem. Conference rooms and other areas with widelyvarying occupancy should be controlled separately.

Control of the primary airflow rate

Figure 22 illustrates a TROX model VFL flow limiterwhich can be fitted directly to the inlet side of the activebeam. This limiter is fully self-contained and requires nopower or control connections. It may be field set to

maintain a volume flow rate to the beam. VFL limitersare recommended for use on beams fed by the sameair handling unit supplying VAV terminals. The VFL

compensates for system pressure changes to maintainthe beams design airflow rate.

VFL flow limiters require a minimum of 0.15 inches H 2Odifferential static pressure to operate. This must beadded to the catalogued pressure loss of the beam toarrive at an appropriate inlet static pressure require-ment. For acoustical reasons, the inlet static pressure

should not exceed 1.0 inches H2O. More information onVFL flow limiters may be found in TROX leaflet 5/9.2/EN/3.

Chilled (and hot) water flow control strategies

The most economical way to control the output of thechilled beam is to modulate the water flow rate throughthe coil. This may be accomplished in either of twoways. Figure 23 illustrates a typical piping and hydroniccontrol schematic for a single thermal zone utilizingchilled beams. There are isolation valves within eachzone which allow the chilled beam coils within the zoneto be isolated from the chilled water system. Thisenables beams to be relocated or removed without

disturbing the water flow in other zones. The coils waterflow rate is throttled by a 2-way chilled water valveactuated by the zone thermostat. Most chilled beamsystems utilize floating point valve actuators thatprovide on-off control of the beam water flow. Throttlingthe water flow rate results in variable volume flow

through the main water loop while its supply and returnwater temperatures tend to remain relatively constant.

Figure 24 shows a zone within a chilled beam systemthat is controlled by a 3-way valve. Such a schematicwill allow modulation of the chilled water flow to thebeams within the zone while maintaining a constantvolume flow rate within the main distribution system.Such control may be advantageous in cases where adedicated chiller is used and significant variations in the

water flow rate can result in danger of freezing withinthe chiller itself. Three way valves are also frequentlyused when condensation prevention controls areemployed.

The piping illustrated in figure 23 is reverse-return. Thefirst unit supplied with chilled water is the farthest fromthe main chilled water return. Using reverse-return pip-ing tends to adequately balance the water flow to multi-ple beams within a single zone.

Figure 22: TROX VFL Flow Controller


22/68

22

Control Strategies

Chilled beams within a single thermal zone

Chilled

water

supply

Chilled

water

return

Isolation

valve

2 way

on-off

control

valve

T Zone thermostat

Isolation

valve


Chilled

water

supply

Chilled

water

return

Isolation

valves (2)

3 way

proportional

control

valve

T Zone thermostat

Flow

Measurement

and Balancing

Valves


Chilled

water

supply

Chilled

water

return

Isolation

valves (2)

3 way proportional

control valve

TZone thermostat

Pump

Figure 23: Chilled Beam Zone Control by Means of a Throttling (On/Off) 2 Way Valve

Figure 24: Chilled Beam Zone Control by Means of a Diverting 3 Way Valve

Figure 25: Chilled Beam Zone Control by Water Temperature Modulation


23/68

23

Control Strategies

The chilled beam output may also be controlled bymaintaining the water flow rate constant and modulatingits temperature. In these cases, the water flow ratethroughout both the main and zone circuits remains

constant. This is a more expensive alternative which isgenerally only used where space humidity levels areunpredictable yet condensation must be prevented

without compromising the space thermal conditions.Figure 25 illustrates such a zone using a mixingstrategy where return water is recirculated to raise thechilled water supply temperature to the beams. A pumpmust be supplied within the zone piping circuit toproduce a sufficient head to pump thesupply/recirculated water mixture to the beams.

Condensation prevention strategies

As long as the space dew point temperature can be

maintained within a reasonable (+/- 2F) range and the

chilled water supply temperature is at (or above) thedesign value, there should be no chance of condensa-tion on the surfaces of the chilled beams. The beamsurfaces will never be as cold as the entering chilledwater temperature. In the case of active beams, theconstant room airflow across the coil surface will alsoprovide a drying effect.

Some applications may, however, be subject to periodswhere room humidity conditions drift or rise due to

infiltration or other processes that may add significantunaccounted for moisture to the space. In these cases,the employment of some type of condensation control

strategy may be warranted. There are several methodsof condensation prevention control that include the

following (and combinations of such):

Central monitoring and control

Zonal monitoring with on/off control Zonal monitoring with modulating control

Central dew point monitoring and control involves themeasurement of the outdoor dew point temperature andcontrol of the chilled water supply temperature inrelation to that. This is an effective method of control forrelatively mild climate applications where operablewindows and/or other sources contribute to excessiveinfiltration of outdoor air. The central supply watertemperature can be modulated to remain at (or someamount above) the outdoor air dew point. Figure 26illustrates such a method of condensation control.

An alternative method of condensation prevention is theuse of zonal on/off control signaled by moisture sensorson the zone chilled water connection (see figure 27).When moisture forms on the supply water pipe next tothe zone water valve, the zone water flow is shut offand will not be restored until the moisture has been

evaporated. Conditioning of the space will be limited tothat provided by the primary airflow until acceptablehumidity conditions allow the chilled water flow to beresumed. This is an economic and effective method ofcondensation control in spaces where such conditionsare not expected to occur frequently. The sensor mayalso be used as a signal to increase the flow of primaryair to further dehumidify the space, reducing the timethat the chilled water flow is shut off.

T

R

To Chilled Beam

Zones

Pressure

Regulator

Supply Water

Temperature

Controller

Chilled

Water

Pump

Return Water Bypass

2-way ChilledWater Valve

(one per zone)

Secondary (Tempered) Chilled

Water Supply to Beams

HEATEXCHANGER

Secondary Chilled

Water Return

Outdoor Ai r

Dew Point

Sensor

Chilled

water

supply


Chilled

water

return

Isolation

valve

2 way

on-off

control

valve

T Zone thermostat

Isolation

valve

Moisture Sensor

Figure 27: Throttling Chilled Water Controlwith Moisture Sensor Override

Figure 26: Chilled Water TemperatureReset Based on Outdoor Dew Point


24/68

24

Installation and Commissioning

If the maintenance of local thermal conditions is critical,a zone humidistat may be used to modulate the zonechilled water supply temperature as shown in figure 28.This requires that each zone fitted for such control be

fitted with a pump capable of recirculating return waterinto the supply circuit of the chilled beam.

INSTALLATION AND COMMISSIONING

Mounting considerations

The weight of chilled beams requires that they beseparately supported, independent of any integratedceiling grid or drywall surface. They are usuallysuspended from the structure above by means ofthreaded rods or other sufficiently strong support meansthat allow the beams position to be vertically adjusted.The beams are usually mounted and connected prior tothe installation of the ceiling grid or drywall. TROXchilled beams are furnished with a minimum of four (4)attachment angles whose position can be adjustedalong the beam length to allow the beam to bedropped into the suspended ceiling grid with which it isintegrated. When integrated with a ceiling grid systemor drywall, it is recommended that the beams besuspended from linear channels (such as uni-strut) thatrun perpendicular to the beams length, so there issome adjustability in every direction. Figure 29 illus-trates the mounting of active and passive beams.

TROX offers various borders to coordinate DID seriesbeams with three types of acoustical ceiling grids(illustrated in figure 30):


Chilled

water

supply

Chilled

water

return

Isolation

valves

(2)

3 way

proportional

control valve

T

Zone Temperature

and Humidity

Controller

Pump

Temperature

Sensor

Dew Point

Sensor

Figure 28: Condensation Protection UsingTemperature/Humidity Sensing to Modulate

the Zone Chilled Water Temperature

Uni-strut Channels

bolted to structure

above allows

adjustment along

beam width

Beam suspended

from channels by

threaded rods

Factory furnished

mounting brackets

allow adjustment

along beam length

Figure 29: Installation of an Active Beam

9/16"

5/16"

9/16"

1"

Integration with

standard 1" wide(inverted) tee bar grid

Integration with narrow9/16" wide (inverted)

tee bar grid

Integration with narrow

9/16" wide tubular type

grid

Integration into dry wall

ceiling using plasterframe

1"

Figure 30: Integration of Active Beams intoCommon Ceiling System Applications


25/68

25

Installation and Commissioning

When active beams are to be used without an adjacentceiling surface, TROX recommends that an extendedouter surface be furnished which allows formation of aCoanda effect that helps direct the discharge air

horizontally and prevent dumping.

Recessed passive chilled beams may also be

integrated with suspension grid systems, but they areusually mounted above the grid and have no directinteraction with it. It is recommended that a separationskirt (see figure 5) be used to separate the two airstreams (warm entering air from cool discharge air) ofthe beam. Exposed passive beams are almost alwayspendant mounted to the structural slab above and usedwithout a false ceiling system.

Air and water connections

Connection of the chilled water (and hot water where

applicable) supplies to chilled beams are theresponsibility of the installing contractor. Chilled beamsmay be furnished with either NPT (threaded) male con-nections or with straight pipe ends appropriate for fieldsoldering. While each coil is factory tested for leakage,it is important that the beams are at no time subjectedto installation or handling that might result in bending orotherwise damaging the pipe connections in any way.

All control, balancing and shutoff valves that may benecessary are also to be provided and installed by oth-

ers. Do not over tighten any threaded connections tothe beams.

All chilled water supply piping should be adequatelyinsulated. Return water piping may be left un-insulated

provided the return water temperature remains abovethe dew point of the spaces over which it passes.

Flexible hoses may be used for chilled beam waterconnections. These hoses may employ either threadedor snap lock connectors. TROX USA offers suchthreaded connectors as an option. These connectorsare 100% tested and marked with individualidentification numbers. In the event of a failure, thebatch within which they were manufactured can bereadily identified and preemptive remediation can beperformed without concern that all hoses on the job aresubject to failure soon. The normal life of flexible hosesexceeds fifteen year but can be affected by (amongother things) swings in their operational temperatureand lack of sufficient water treatment.

The connection of the primary air supply duct to activechilled beams is also the responsibility of the installingcontractor. This connection should include the provisionof at least eight (8) inches of straight sheet metal ductconnected directly to the beams primary air inlet. Nomore than five (5) feet of flexible duct should be used toa

connect the beam to the supply air duct and this flexibleduct should not have any excess bends or radius.

Water treatment

It is imperative that there are no corrosive elements inthe secondary water supply to the beams as there are

brass fittings on the coils and/or connection hoses.Periodic testing of the secondary water circuit on eachfloor should be performed to assure that none of thesecorrosive elements are present.

Prior to connection to the beams and the chiller plant,the water pipes should be thoroughly flushed to removeany impurities that may reside within them. Only after

this purging has occurred should the connections to thecoils and the chiller plant be performed. Additionalinformation regarding system cleaning may be found in

reference 6.

Once filled by the mechanical contractor, the systemshould be dosed with chemicals that prevent bacterialgrowth. Typical additives would be a sodium nitrateinhibitor solution of 1000 parts per million (e.g. Nalcol90) and a biocide solution of 200 parts per million (e.g.Nalcol). Reference 6 provides additional informationregarding water treatment.

System Commissioning

TROX provides each beam with vents that are used topurge air from the water circuit. These vents are locatedon the coils intended return header. Prior tocommissioning any air trapped in the pipe work should

be purged from the water circuit through these vents.

A flow measuring device and suitable balancing valveshould be provided for each beam which will enableadjustment of the chilled water flow rate to each beamwithin the thermal zone to its design value. This isillustrated in figure 24. Where five to six beams areinstalled in a reverse-return piping circuit (per figure 23),there will likely be no need for such measuring devicesand balancing valves.

The primary airflow rate to an active chilled beam canbest be determined by measuring the static pressurewithin the pressurized entry plenum and referring to thecalibration chart provided with the beam. TROXprovides an integral pressure tap (accessible throughthe face of the beam) to which a measuring gauge canbe connected. Do not attempt to read the total dis-charge airflow rate using a hood or any other devicethat adds downstream pressure to the beam as it willreduce the amount of induction and as such give falsereadings.


26/68

26

Maintenance

SYSTEM OPERATION AND MAINTENANCE

There are certain operational requirements that mustobserved when chilled beam systems are employed inhumid climates. In the event the HVAC system isdisabled on nights and/or weekends, the chilled watersupply must remain suspended until the primary airsupply has properly dehumidified the space. It isrecommended that some type of space humiditysensing be used to assure that a proper space dewpoint temperature has been established prior to starting

the delivery of chilled water to the space.

If chilled beams are to be used in traffic or lobby areas,it is important that the space be maintained at a positivepressure in order to minimize the infiltration of outdoorair. In the case of lobby areas, the use of revolvingdoors may be warranted. It is also recommended thatthe beams not be located near any opening doors or

windows in these areas.

Maintenance requirements

Due to their simplicity and lack of moving parts, chilledbeams require little maintenance. In fact, the only

scheduled maintenance with chilled beams involves theperiodic vacuuming of their coil surfaces. Passivebeams generally require that this be done every four to

five years. In the case of active beams, such cleaning isonly required when the face of the unit return sectionshows visible dirt. At this time, the primary air nozzlesshould be visually inspected and any debris or lintremoved. In all cases, it is recommended that good

filtration be maintained within the air handling unit.

REFERENCES

1. REHVA. 2004. Chilled Beam ApplicationGuidebook.

2. ASHRAE. 2004 Thermal environmentalcondit ions for human occupancy.

ANSI/ASHRAE Standard 55-2004.

3. ASHRAE. 2007. ASHRAE Handbook -Applications.

4. Energie. 2001. Climatic ceilings technical note:design calculations.

5. ASHRAE. 2005. ASHRAE Handbook -Fundamentals.

6. BSRIA. 1991. Pre-commission cleaning ofwater systems. BSRIA Application Guide 8/91.

7. ASHRAE. 2004 Ventilation for acceptableindoor air quality. ANSI/ASHRAE Standard62.1-2004.


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Passive Beam Selection

CHILLED BEAM SELECTION

PASSIVE BEAM SELECTION AND LOCATION

Selection and location of passive chilled beams is pri-marily affected by the following parameters:

Required sensible heat removal Allowable chilled water supply temperature Horizontal and vertical space restrictions Occupant thermal comfort considerations Architectural considerations

Chilled water supply and return temperatures

Before a passive beam selection can be made, it isnecessary that an appropriate chilled water supplytemperature be identified. TROX USA recommends thatthe chilled water supply temperature to passive beams

be maintained at least 1F above the space dew pointtemperature in order to assure that condensation doesnot occur.

Return water temperatures will generally be 3 to 6Fhigher than the supply water temperature.

Water flow rate and pressure loss considerations

Water flow velocities in excess of 4 feet per secondshould be avoided in order to prevent unwanted noise.Design water flow rates below 0.25 gallons per minuteare not recommended as laminar flow begins to occurbelow this flow rate and coil performance may bereduced. Passive chilled beams should also be selected

such that their water side head loss does not exceed 10feet of water.

Passive chilled beam performance data

The amount of sensible cooling that can be provided byan active chilled beam is dependent on all of the factorslisted above. Tables 2 and 3 illustrate the performanceof TROX TCB-1 and TCB-2 series passive chilledbeams. The available beam widths are listed in thetable. The water side pressure loss is illustrated for 4, 6,

8 and 10 foot versions of each beam. The sensiblecooling capacity of each beam is expressed in BTUHper linear foot of length for various temperaturedifferentials between entering air and the entering

chilled water supply. This capacity is based on a 6 footbeam length, a discharge free area of 50% and anequal inlet free area. It also assumes that the distancebetween the beam and any obstacle above it is at least40% the width of the beam. Table 4presents correctionfactors for other beam lengths and inlet/dischargeconditions.

Passive beam selection procedures

Selection of passive chilled beams should be performedas follows:

1. Estimate the beam entering air temperature If a fully mixed room air distribution

system is being used, the entering air

temperature will equal the room controltemperature.

If a stratified system is being used, theentering air temperature may be assumedto be 2F warmer than the room controltemperature.

When mounted directly above a perimeterwindow, the entering air temperature canbe assumed to be 6F warmer than theroom temperature.

2. Specify the chilled water supply temperature.

3. Using the temperature difference between theentering air and chilled water, select a beam

whose width and length will remove therequired amount of sensible heat.

4. Identify the required water flow rate andpressure loss for the selected beam.

Passive chilled beam selection examples

EXAMPLE 1:

TCB-1 series passive (recessed type) chilled beams arebeing used to condition an interior office space that is120 feet long by 60 feet wide with a sensible heat gain

12 BTUH per square foot. The space is controlled by athermostat (at the mid-level of the room) for a dry bulb

temperature of 76F and space RH of50%. A thermaldisplacement ventilation system supplies 0.2 CFM persquare foot of pretreated ventilation air at 65F.

SOLUTION:

The total sensible heat gain of the space is 8,640BTUH. The room dew point temperature is 57Ftherefore a chilled water supply temperature of 58F willbe used.

As the displacement ventilation system being used inconjunction with the beams will crate a stratified roomenvironment, the beam entering air temperature (andthe return air temperature leaving the space) may beassumed to be 2F warmer than the room controltemperature, or in this case 78F.

The sensible heat removal of the ventilation air can thenbe calculated as follows:

qVENT = 1.09 x CFMVENT x (TRETURN TSUPPLY)= 1.09 x (0.2 x 720) x (78 65)= 2,040 BTUH

a


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Passive Beam Performance

Table 1: TCB-1 Passive Beam (One Row Coil) Cooling Performance Data

4 5 6 8 10 15 16 17 18 19 20 21 22

0.75 0.6 0.6 0.7 0.9 1.1 216 236 257 278 299 319 340 361

1.00 1.0 1.1 1.3 1.6 1.9 243 264 285 305 326 347 367 388

1.25 1.6 1.8 2.0 2.5 2.9 259 280 301 321 342 363 383 404

1.50 2.3 2.5 2.9 3.6 4.2 270 291 301 332 353 374 394 415

1.75 0.4 0.4 0.5 0.6 0.7 278 299 319 340 361 381 402 423

2.00 0.5 0.6 0.6 0.8 1.0 284 304 325 346 366 387 408 428

2.25 0.6 0.7 0.8 1.0 1.2 288 309 329 350 371 391 412 433

2.50 0.8 0.9 1.0 1.2 1.5 292 312 333 354 374 395 416 437

2.75 0.9 1.1 1.2 1.5 1.8 295 315 336 357 377 398 419 439

3.00 1.1 1.3 1.4 1.8 2.1 297 318 338 359 380 400 421 442

0.75 0.4 0.5 0.6 0.7 0.9 211 229 247 264 278 296 315 334

1.00 0.8 0.9 1.0 1.3 1.6 232 249 267 284 299 318 337 355

1.25 1.2 1.4 1.6 2.0 2.4 244 262 279 297 312 331 350 368

1.50 1.7 2.1 2.3 2.8 3.5 252 270 287 305 321 346 359 377

1.75 0.3 0.4 0.4 0.5 0.6 270 276 293 311 327 216 365 383

2.00 0.4 0.5 0.5 0.7 0.8 262 280 298 315 332 351 369 388

2.25 0.5 0.6 0.7 0.8 1.0 266 284 301 319 336 354 373 392

2.50 0.7 0.7 0.8 1.0 1.2 269 286 304 321 339 357 376 395

2.75 0.8 0.9 1.0 1.2 1.5 271 288 306 324 341 360 378 397

3.00 0.9 1.1 1.2 1.5 1.8 273 290 308 325 343 362 380 399

0.75 0.5 0.5 0.6 0.7 0.9 183 197 212 227 241 256 270 285

1.00 0.8 1.0 1.1 1.3 1.6 197 211 226 240 255 270 284 299

1.25 1.3 1.5 1.7 2.1 2.5 205 220 234 249 263 278 293 307

1.50 1.9 2.2 2.4 3.0 3.6 210 225 240 254 269 283 298 313

1.75 0.3 0.3 0.3 0.4 0.5 214 229 244 258 273 287 302 317

2.00 0.3 0.4 0.4 0.5 0.6 217 232 247 261 276 290 305 320

2.25 0.4 0.5 0.5 0.7 0.8 220 234 249 264 278 293 307 322

2.50 0.5 0.6 0.7 0.8 1.0 222 236 251 265 280 295 309 324

2.75 0.6 0.7 0.8 1.0 1.2 223 238 252 267 281 296 311 325

3.00 0.8 0.9 1.0 1.2 1.4 224 239 254 268 283 297 312 327

0.75 0.3 0.3 0.4 0.4 0.5 164 174 185 195 206 217 227 238

1.00 0.5 0.6 0.6 0.8 0.9 172 182 193 204 214 225 235 246

1.25 0.8 0.9 1.0 1.2 1.5 177 187 198 208 219 230 240 251

1.50 1.1 1.3 1.4 1.8 2.1 180 191 201 212 222 233 244 254

1.75 0.2 0.2 0.2 0.3 0.4 182 193 203 214 225 235 246 256

2.00 0.3 0.3 0.3 0.4 0.5 184 195 205 216 226 237 248 258

2.25 0.3 0.4 0.4 0.5 0.6 185 196 207 217 228 238 249 260

2.50 0.4 0.4 0.5 0.6 0.7 186 197 208 218 229 239 250 261

2.75 0.5 0.5 0.6 0.8 0.9 187 198 209 219 230 240 251 262

3.00 0.6 0.6 0.7 0.9 1.1 188 199 209 220 230 241 252 262

Beam Width (B)(inches)

Water Flow Rate(GPM)

PWATER, ft. H2O Sensible Cooling Capacity, (BTUH/LF)

Chilled Beam Length, Ft. TROOM - TCWS

24

20

16

12

NOTES REGARDING PERFORMANCE DATA:

1. Sensible cooling data is based on a six (6) foot long uncapped beam with a 12" stack height (H), a ceiling free area of 50%

and an air passage width (W) twice the beam width (B) per figure 13.

2. For other beam lengths, ceiling free areas and/or air passage widths see table 3 for correction factors.

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4 5 6 8 10 15 16 17 18 19 20 21 22

0.75 1.8 1.3 1.5 1.7 2.1 153 194 236 277 318 360 401 442

1.00 3.2 2.3 2.6 3.1 3.7 242 283 324 366 407 448 490 531

1.25 5.0 3.6 4.1 4.8 5.8 295 336 377 418 460 501 542 584

1.50 7.2 5.2 5.9 6.9 8.3 330 371 412 454 495 536 577 619

1.75 0.8 0.9 1.0 1.2 1.4 354 396 437 478 520 561 602 643

2.00 1.0 1.1 1.3 1.6 1.9 373 415 456 497 539 580 621 662

2.25 1.3 1.4 1.6 2.0 2.4 387 429 470 511 553 594 635 677

2.50 1.6 1.8 2.0 2.5 2.9 399 440 482 523 564 606 647 688

2.75 1.9 2.2 2.4 3.0 3.5 409 450 491 533 574 615 656 698

3.00 2.3 2.6 2.9 3.6 4.2 417 458 499 541 582 623 665 706

0.75 0.9 1.1 1.2 1.5 1.7 169 204 239 273 308 343 378 413

1.00 1.7 1.9 2.2 2.7 3.1 232 266 301 336 371 406 440 475

1.25 2.6 3.0 3.4 4.2 4.8 267 302 337 372 407 441 476 511

1.50 3.8 4.3 4.9 6.0 6.9 292 326 361 396 431 466 500 535

1.75 0.6 0.7 0.8 1.0 1.1 309 343 378 413 448 483 517 552

2.00 0.8 1.0 1.1 1.3 1.4 322 356 391 426 461 496 530 565

2.25 1.0 1.2 1.4 1.7 1.8 332 366 401 436 471 506 540 575

2.50 1.3 1.5 1.7 2.0 2.2 340 375 409 444 479 514 549 583

2.75 1.6 1.8 2.0 2.5 2.7 346 381 416 451 486 520 555 590

3.00 1.9 2.2 2.4 2.9 3.2 352 387 422 456 491 526 561 596

0.75 0.8 0.9 1.0 1.2 1.4 168 195 221 247 274 300 326 352

1.00 1.4 1.5 1.7 2.2 2.5 202 228 254 281 307 333 360 386

1.25 2.1 2.4 2.7 3.4 3.9 222 249 275 301 327 354 380 406

1.50 3.0 3.4 3.9 4.9 5.7 235 262 288 314 341 367 393 419

1.75 0.5 0.6 0.6 0.8 1.0 245 272 298 324 350 377 403 429

2.00 0.7 0.8 0.8 1.1 1.2 252 279 305 331 358 384 410 437

2.25 0.8 1.0 1.1 1.3 1.6 258 284 311 337 363 389 416 442

2.50 1.0 1.2 1.3 1.6 2.0 262 289 315 341 368 394 420 447

2.75 1.2 1.4 1.6 2.0 2.4 266 292 319 345 371 398 424 450

3.00 1.5 1.7 1.9 2.4 2.8 269 296 322 348 375 401 427 453

0.75 0.6 0.7 0.8 1.1 1.3 153 176 198 221 244 266 289 311

1.00 1.1 1.3 1.5 1.9 2.2 177 199 222 245 267 290 312 335

1.25 1.8 2.0 2.3 3.0 3.5 191 214 237 259 282 304 327 350

1.50 2.5 2.9 3.3 4.3 5.0 201 224 246 269 291 314 337 359

1.75 0.4 0.5 0.6 0.7 0.8 208 231 253 276 298 321 344 366

2.00 0.6 0.7 0.7 0.9 1.1 213 236 258 281 303 326 349 371

2.25 0.7 0.8 0.9 1.2 1.3 217 240 262 285 308 330 353 375

2.50 0.9 1.0 1.2 1.4 1.7 220 243 265 288 311 333 356 378

2.75 1.1 1.2 1.4 1.7 2.0 223 245 268 291 313 336 358 381

3.00 1.3 1.5 1.7 2.1 2.4 225 248 270 293 315 338 361 383

Beam Width (B)(inches)

Water Flow Rate(GPM)

PWATER, ft. H2O Sensible Cooling Capacity, (BTUH/LF)

Chilled Beam Length, Ft. TROOM - TCWS

24

20

16

14

NOTES REGARDING PERFORMANCE DATA:

1. Sensible cooling data is based on a six (6) foot long uncapped beam with a 12" stack height (H), a ceiling free area of 50%

2. For other beam lengths, ceiling free areas and/or air passage widths see table 3 for correction factors.

and an air passage width (W) twice the beam width (B) per figure 13.

Table 2: TCB-2 Passive Beam (Two Row Coil) Cooling Performance Data

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Table 3: Correction Factors for Other Beam Configurations

12 * 14 * 16 20 24W = 2.0 x B W = 2.0 x B W = 2.0 x B W = 2.0 x B W = 2.0 x B

30.0% 0.81 0.81 0.81 0.81 0.81

40.0% 0.91 0.91 0.91 0.91 0.91

50

design guide_chilled beams (trox)

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