Chilled Beam- Engineering_Guide

7/30/2019 Chilled Beam- Engineering_Guide

1/48

Please refer to the Price Engineers HVAC Handbook

for more information on Active & Passive Beams

S E C T I O N L

Engineering GuideActive & Passive Beams


2/48

All Metric dimensions ( ) are soft conversion. Copyright Price Industries Limited 2011.Imperial dimensions are converted to metric and rounded to the nearest millimeter.L-2

Return to product page

Introduction

Active & Passive Beams

Engineering Guide

Like radiant heating and cooling systems,active and passive beam systems use wateras well as air to transport energy throughoutthe building. Like radiant and coolingsystems, they oer savings in energy, spaceand maintenance costs. Unlike radiantheating and cooling systems, however,these technologies deliver the majorityo their cooling and heating throughconvection, oten leading to a ully mixedenvironment. This section introduces activeand passive beam systems and their designconsiderations, and addresses the uniquerequirements o some o the most commonapplications.

Management o heat loads can generally

be classied into two dierent types: all-

air systems or hybrid systems. All-airsystems have been the most prominentin North America during the 20th centuryand have been in use since the advent oair conditioning. These systems use air toservice both the ventilation requirementas well as the building cooling loads. Ingeneral, these systems have a central airhandling unit that delivers enough coolor warm air to satisy the building load.Diusers mounted in the zone deliver thisair in such a way as to promote comortand evenly distribute the air. In many cases,the amount o air required to cool or warmthe space or the fuctuations o loads makedesigning in accordance to these principles

dicult.

Hybrid systems combine an air-sideventilation system and a hydronic (or water-side) system.The air-side system is designedto meet all o the ventilation requirementsor the building as well as satisy the latentloads. It is typically a 100% outside airsystem and because the primary unctiono the supply air system is ventilation anddehumidication as opposed to sensiblecooling it can be supplied at higher supplyair temperatures than is typical o traditionalmixing air distribution systems. The water-side system is designed to meet the balanceo the sensible cooling and heating loads.These loads are handled by water-basedproducts, such as active and passive beams,

which transer heat to the zone by induction.
http://www.price-hvac.com/Catalog/Section_L/CatalogData.aspxhttp://www.price-hvac.com/Catalog/Section_L/CatalogData.aspx


3/48

Copyright Price Industries Limited 2011. All Metric dimensions ( ) are soft conversion .Imperial dimensions are converted to metric and rounded to the nearest millimeter. L-3


Active & Passive BeamsEngineering Guide

Concepts and Benefts

Active and passive beam systems providean eective method or providing heatingor cooling to a space while promoting ahigh level o occupant comort and energyeciency. There are two distinct systemdesign philosophies that are consideredwhen applying hydronic heating and/orcooling:

Hydronic heating or cooling where thehydronic systems are integrated with theprimary ventilation system. These are activebeam systems (Figure 1).

Hybrid heating or cooling systems wherewater-based devices are used in conjunctionwith a scaled-down ventilation system, andmanage the bulk o the sensible coolingload. These systems generally use passivebeams (Figure 2).

Hydronic systems have been successullyused in several applications havingdramatically dierent characteristics. Someexamples o areas where active and passivebeam systems have been applied include:

GreenBuildings

PostSecondaryEducationalFacilities

LoadDrivenLaboratories

K-12Schools

OfceBuildings

Cafeterias

TelevisionStudios

Benefts o Air-Water SystemsThere are many benets to heating andcooling using active or passive beams.Advantages o water-based heating andcooling systems over other mechanicalsystems include:

Energyandsystemefciency

Reducedsystemhorsepower

Improvedindoorenvironmentalquality

Improvedindoorairquality

Increasedthermalcomfort

Reducedmechanicalfootprint

Lowermaintenancecosts

Improvedsystemhygiene

Active or passive beam systems are a good

choice where: Thermal comfort is a major design

consideration

Areaswithhighsensibleloadsexist/arepresent

Areasrequiring a high indoorair quality(100% outdoor air system) exist/are present

Energyconservationisdesired

Energy Efciency

The heat transer capacity o water allows ora reduction in the energy used to transport anequivalent amount o heat as an all-air system(Stetiu, 1998). These reductions can be oundprimarily through reduced an energy.

Figure 1: Air fow diagram o a typical linearactive beam in cooling

Figure 2:Air fow diagram o a passivechilled in cooling

Figure 3: Active beams installedin an oce

Figure 4: Passive beams behinda perorated ceiling

Nozzles

Plenum

Primary Air

Room Air

Coil

Room Air

Primary Air

The higher chilled water supply (CHWS)temperatures used with active and passivebeam systems, typically around 58 F[14.5 C], provide many opportunities or areduction in energy use, including increasedwater-side economizer use. This increasedCHWS temperature also allows or morewet-side economizer hours than would bepossible with other systems where CHWStemperaturesaretypically~45F[7C].

Indoor Air Quality

Depending on the application, undermaximum load, only ~15 to 40% o thecooling air fow in a typical space is outdoorair required by code to satisy the ventilation

requirements. The balance o the supplyair fow is recirculated air which, when nottreated, can transport pollutants through thebuilding. Active and passive beam systemstranser heat directly to/rom the zone andare oten used with a 100% outdoor airsystem that exhausts polluted air directlyto the outside, reducing the opportunityforVOCsandillnesstotravelbetweenairdistribution zones.

Noise

Active and passive beam systems do notusually have an powered devices near thezone. This typically results in lower zone

noise levels than what is achieved with allair systems. In situations where passivebeams are used in conjunction with aquiet air system, such as displacemenventilation, the opportunities or noisereduction increase urther.

Reduced Mechanical Footprint

The increased cooling capacity o wateallows the transport system to be reducedin size. Generally, it is not unusual to beable to replace ~60 t [6 m] o air shat witha 6 in. [150 mm] water riser, increasing theamount o foor space available or use olease. Due to the simplicity o the systems(i.e. reduction in the number o moving parts

and the elimination o zone lters, drainpans, condensate pumps and mechanicacomponents), there tends to be less spacerequired in the interstitial space to supporthe HVAC system.

Lower Maintenance Costs

With no terminal unit or an coil lters omotors to replace, a simple periodic coicleaning is all that is required in order tomaintain the product.


4/48




When to use Beam Systems

ApplicationTotal Air

Volume (Typ.)Ventilation Requirement

(Typ.)Air-Side

Load Fraction

Ofce 1 cm/t2 [5 L/s m2] 0.15 cm/t2 [0.75L/sm2] 0.15

School 1.5 cm/t2 [7.5L/sm2] 0.5 cm/t2 [2.5 L/s m2] 0.33

Lobby 2 cm/t2 [10 L/s m2] 1 cm/t2 [5 L/s m2] 0.5

Patient Room 6 ach 2 ach 0.33

Load-driven Lab 20 ach 6 ach 0.3

Hygienic System

With the elimination o the majority olters and drain pans, there is a reducedrisk o mold or bacteria growth in the entiremechanical system.

Active and passive beam systems are well-suited to some applications and less so toothers. As a result, each application mustbe reviewed or potential benets as wellas the suitability o these types o systems.Oneconsiderationwhichcanassistinthedecision to employ hydronic systems asopposed to an all-air system is the air-sideload raction, or the percentage o the totalair supply which must be delivered to the

zone to satisy code and dehumidicationrequirements. Table 1 shows the loadraction or several spaces. In the table thebest applications or hydronic systems arethose with the lowest air-side load ractionas they are the ones that will benet the mostrom the eciencies o hydronic systems.Another actor which should be examinedis the sensible heat ratio or the percentageo the cooling load which is sensible asopposed to latent. The latent loads must besatised with an air system and oer somesensible cooling at the same time due tothe temperature o dehumidied air. I thetotal sensible cooling load is signicantlyhigher than the capacity o the air suppliedto satisy the latent loads, a beam system

might be a good choice.Commercial Ofce Buildings

In an oce building, active and passivebeam systems provide several benets. Thelower supply air volume o the air handlingsystem provides signicant energy savings.In addition, the smaller inrastructurerequired to move this lower air fow allowsor small plenum spaces, translating intoshorter foor-to-foor construction or higherceilings. The lower supply air volume andelimination o ans at or near the spaceoers a signicant reduction in generatednoise. The lower air fow oten translatesto reheat requirements being reduced. Inthe case o 100% outside air systems, the

lighting load captured in the return plenumis exhausted rom the building, lowering theoverall cooling load.

Schools

Schools are another application that canbenet greatly rom active and passive beamsystems. Similar to oce buildings, thebenets o a lower supply air volume to thespace are lower an power, shorter plenumheight, reduced reheat requirements andlower noise levels (oten a critical designparameter o schools).

Hospital Patient Rooms

Hospitals are unique applications in thatthe supply air volume required by localcodes or each space is oten greater thanthe requirement o the cooling and heatingload. In some jurisdictions, local code

requires these higher air-change rates orall-air systems only. In these cases, thetotal air-change rate required is reduced isupplemental heating or cooling is used.This allows or a signiicant reductionin system air volume and yields energysavings and other benets.

Furthermore, because thesesystemsaregenerally constant air volume with thepotential to reduce the primary air-changerates, reheat and the cooling energydiscarded as part o the reheat process isa signicant energy savings opportunity.Depending on the application, a 100%outside air system may be used. Thesesystems utilize no return air and thereoreno mixing o return air between patientrooms occurs, potentially lowering the risko hospital associated inections.

Laboratories

In load driven laboratories where the supplyair rate is driven by the internal gains (suchas rerigerators, testing equipment, etc.)as opposed to the exhaust requirements,active and passive beam systems canoer signicant energy savings. In theseenvironments it is not unusual to requirea large air-change rate in order to satisythe load, although signicantly less maybe required by code (ASHRAE, 2008; CSA,2010).

Table 1: Typical load ractions or several spaces in the United States

In these applications, the dierence betweenthe supply air volume required to managethe sensible loads and that required tomeet the ume hood air fow requirementsprovides opportunity or energy savingsthrough the application o active and passivebeams. These savings are typically due tothe reduction in an power as well as theenergy associated with treating the outsideair, which, in the case o a load driven lab,may be signicant.

Hotels / Dorms

Hotels, motels, dormitories and similar typebuildings can also benet rom active andpassivebeamsystems.Fanpowersavingsoten come rom the elimination o ancoil units located in the occupied space.The energy savings associated with theselocal ans is similar in magnitude to thato larger air handling systems. It also allowsor the elimination o the electrical servicerequired or the installation o an coil units,as well as a reduction in the maintenanceo the drain and lter systems. The removalo these ans rom the occupied space alsoprovides lower noise levels, which can be asignicant benet in sleep areas.

Limitations

There are several areas in a building wherehumidity can be dicult to control, suchas lobby areas and locations o egress.These areas may see a signicant short

term humidity load i the entrances are notisolated in some way (revolving doors orvestibules). In these areas, a choice o acomplimentary technology such as an coilunits or displacement ventilation is ideal.

Other applications may have high airfow/ventilation requirements, such as anexhaust driven lab. The majority o thebenet provided by the hydronic system islinked to the reduction in supply air fow.As such, these applications may not seesucient benet to justiy the addition othe hydronic circulation systems, makingthem not likely to be a good candidate orthis technology.


5/48




Passive Beams

Passive Beams

Passive beams use a heat exchangerusually a coilto change the temperature othe adjacent transerring heat and create adierence in density with the ambient air.The density dierence creates air movementacross the heat exchanger, transerring heatrom the heat exchanger to the air.

Passive beams condition a space usingnatural convection and are primarily usedor handling the sensible cooling load o aspace. They are water-only products, andrequire a separate air system or ventilationair and to remove the latent load. Aswarm air in the room rises, it comes intocontact with the heat exchanger and fowsdownward through the cool coils back intothe space, as seen in Figure 5. In heatingmode, passive beams are generally notused, though in some special instancesthey would condition the space primarilyby thermal radiation.

Product Description

Passive beams are available in models thateither integrate into standard suspendedceiling systems or are suspended reelyrom the ceiling. They are also commonlyinstalled behind perorated metal ceilingsor a uniorm architectural appearance. Aperorated metal ceiling helps reduce dratunder the beam, however, a minimum reearea o 50% is oten required to ensure the

capacity o the beam is not reduced. Passivebeams installed behind a metal peroratedceiling can be seen in Figure 7.

Components

The basic components o passive beamsinclude a heat exchanger, comprising oextruded aluminum ns and copper tubing,commonly termed the coil, and a rame orshroud. These components are illustratedin Figure 8.

Location

Passive beams are ideally suited to aisleways or perimeters o large spaces suchas oices, lobbies, conerence centers,libraries, or any other space that requiresperimeter or additional cooling. Air fowrom a passive beam is straight down sothey are not typically placed above where anoccupant will be stationed or an extendedperiod o time. While the velocity rom apassive beam is low, there is the opportunityor some people in this condition to beuncomortable.

Figure 6: Air fow diagram o a passivebeam in cooling

Figure 5: Room air fow pattern o a passive beam in cooling

Coil

Room Air

Primary Air

Figure 7: Passive beams installed behinda metal perorated ceiling

Face

Figure 8: Components o a typical passive chilled beam

Frame/Shroud

Coil


6/48




Figure 10: Air fow diagram o a typicallinear active beam in cooling

Figure 11: Air fow diagram o a typicallinear active beam in heating

Active Beams

Plenum

Mounting

Bracket

Primary Air Inlet

Hinged Face to allow

access to the coil

Coil

Figure 12: Components o a typical linear active beam

Figure 9: Room air fow pattern o a typical linear active beam in cooling

Active Beams

Active beams use the ventilation systemto increase the output o the coil, and tohandle both latent and sensible loads o aspace. Unlike radiant panels and chilledsails, which rely primarily on thermalradiation to condition a space, active beamsheat or cool a space through inductionand orced convection. An active beamaccepts dry air rom the system through apressurized plenum. This primary supplyair is then orced through nozzles in orderto create a high velocity air pattern in thearea adjacent to the coil. This high velocitycauses a reduction in the local staticpressure, inducing room air through the

heating/cooling coil. The induced air thenmixes with the primary supply air and isdischarged back into the space via slotsalong the beam (Figure 9). A typical air fowdiagram o a linear active beam in coolingand heating modes can be seen inFigure 10,and Figure 11 respectively.

Components

The basic components o active beamsinclude a heat exchanger with aluminumns and copper tubing, commonly termedthe coil, a plenum box with at least onesupply inlet, internal nozzles, a visible ace,and a rame. Although the congurations oactive beams dier, all general componentsremain the same. These components are

illustrated in Figures 12.Applications

Active beams can be used in oices,meeting rooms, schools, laboratories,hospitals, data centers, airports, any greenbuilding application, and large areas such aslobbies, conerence acilities, lecture hallsor caeterias.

Two basic types o active beams are:

LinearActiveBeams

ModularActiveBeams

Linear Active Beams

2 Way Discharge

Linear active beams with two-sideddischarge are designed to either integrateinto standard suspended ceiling systemsor be suspended reely in an exposedapplication. These beams have two linearair slots that run the length o the beam,one on either side.

NozzlesPrimary Air

Room Air

Nozzles

Plenum

Primary Air

Room Air


7/48




Primary Air

Room Air

Primary Air

Room Air

Active Beams

Figure 13: Air fow diagram o a linearactive beam in cooling with 1 way discharge Figure 14: Air fow diagram o a lineaactive beam in heating with 1 way discharge

Figure 15: Room air fow pattern o a typical linear active beam in cooling

Figure 16: Air fow diagram o amodular beam in cooling

Figure 17: Air fow diagram o amodular beam in heating

1 Way Discharge

Linear active beams with single-sided airdischarge are designed to either integrateinto standard suspended ceiling systemsor be suspended reely in an exposedapplication. These beams have only onedischarge air slot that runs along one sideo the beam.

The general air fow o linear active beamswith 1 way air distribution in cooling andheating are seen inFigures 13andFigure 14.Figure 15 illustrates the room air fow o atypical 1 way active beam.

PRODUCT TIPLinear active beams with 1 wayair distribution are best suited orplacement along a aade or wall.In applications where 1 way beamsare used with 2 way beams, asymmetric ace may be selected orthe 1 way unit to ensure a consistentappearance rom the room.

PRODUCT TIP

Active beams are typically availablein a 2 pipe or 4 pipe conguration.Beams with 2 pipe congurationshave one supply and one returnpipe or each unit, which servesor either/both heating and coolingpurposes. Beams with 4 pipecongurations have two supplyand two return pipes or each unit,comprising separate loops orcooling and heating.

Modular Active Beams

Modular active beams combine resh airventilation, hydronic heating and cooling,and our-sided air fow. They are typicallyavailable in modular sizes, 2 t x 2 t [600 mm

x 600 mm], and 2 t x 4 t [600 mm x 1200mm], and are available in models eitherdesigned to integrate into standard ceilingtiles or suspend reely rom the ceiling.

The typical air fow pattern o a modularbeam in cooling and heating is illustratedin Figure 16 and Figure 17.Often,thesemodular beams can be customized toindividually modulate the air fow rom eachsideoftheunit.Forexample,onesideoftheunit can be blanked o to create a modularbeam with three-sided air fow.

Beam Return

Room Air

Nozzles

Primary Air

Room Air

Nozzles

Plenum

Primary Air


8/48




Passive beam systems will vary inperormance, coniguration and layoutdepending on the application. There are,however, some characteristics that arecommonformostsystems.Furthermore,the perormance o passive beams is largelydependent on a common set o actors.This section will discuss how actorssuch as chilled water temperature aectthe perormance and layout o passivebeams. Table 2 shows common designcharacteristics or passive beam systems.

Product Selection and Location Passive Beams

Perormance

The perormance o a passive beam isdependent on several actors:

Waterowrate

Meanwatertemperatureandsurrounding air temperature

Shroudheight

Freeareaoftheairpaths(internalandexternal to the beam)

Location and application

The water fow rate in the coil aects twoperormance actors: the heat transerbetween the water and the coil, whichis dependent on whether the low islaminar (poor) or turbulent (good); and themean water temperature, or the averagetemperature, in the coil. The higher the fow

rate, the closer the discharge temperaturewill be to the inlet, thereby changing theaverage water temperature in the coil.Figure 18 shows the eect o the fowrate, indicated by Reynolds number, onthe capacity o a typical passive beam. Asindicated on the chart, increasing the fowrate into the transitional and turbulentranges (Re > 2300, shaded in the graph)causes an increase in the output o thebeam.

The water fow rate is largely dependenton the pressure drop and return watertemperatures that are acceptable to thedesigner. In most cases, the water fowrate should be selected to be ully turbulentunder design conditions.

The dierence between the mean watertemperature,tw, dened as:

and the surrounding (coil inlet) airtemperature is one o the primary driverso the beam perormance. The larger thisdierence is, the higher the convective heattranser potential. Conversely, a lowertemperature dierence will reduce theamount o potential energy exchange, andthereby capacity. As a result, it is desirablerom a capacity standpoint to select entrywater temperatures as low as possible,

Passive Beam Selection and Design Procedure

Table 2: Design Values or passive beam systems

IP

Room Temperature 74Fto78Finsummer,68Fto72Finwinter

Water Temperatures, Cooling 55Fto58FEWT,5Fto8F T

Design Sound Levels < 40 NC

Cooling Capacity Up to 500 Btu/ht

Ventilation Requirement 0.1 to 0.5 cm/t2 foor area

SI

Room Temperature 23 C to 25 C in summer, 20 C to 22 C in winter

Water Temperatures, Cooling 13Cto15CEWT,3Kto5K T


Cooling Capacity Up to 500 W/mVentilation Requirement 0.5 to 2.5 L/s m2 foor area

Figure 18: Passive beam capacity vs. water fow

40

0 2000 4000 6000 8000 10000 12000

50

60

70

80

90

100

Capacity,

%

Re

Figure 19: Passive beam capacity vs. dierence between mean water and room airtemperature

0

0 5 10 15 20

0 2 4 6 8 10

20

40

60

80

100

120

Capacity,%

tw - troom ,F

tw - troom ,K


9/48




while maintaining it above the dew pointin the room to ensure sensible cooling only.

In some instances, it might be advantageousto the designer to use higher watertemperatures, where it makes sense roman equipment standpoint. This may alsooer some control simplication where theoutput o the beam is determined by theload in the room:

Astheloadincreases,theairtemperaturerises and increases the dierencebetween it and tw, thereby increasingbeam perormance.

Astheloaddecreases,theairtemperaturealls and reduces the cooling capacity o

the beam.A passive beam uses buoyancy orces andthe stack eect to drive air through thecoil. The stack eect is a phenomenonthat can be used to increase the rate ocirculation through the coil by increasingthe momentum o the alling air. As theair surrounding the coil ns decreases intemperature, it becomes more dense thanthe surrounding air, causing it to all downinto the zone below. Figure 20 shows across section o a passive beam and how theshroud, or skirt, o the beam separates thecool air rom the surrounding air, allowing itto gain momentum and draw an increasingvolume o air into the coil rom above.

The taller this stack is, the more air is drawnthrough the coil, increasing the coolingpotential o the beam. As the volume oair is increased, the velocity o the air allingbelow the beam is also increased. It is notuncommon to adjust the height o the stackin order to adjust the capacity and velocitiesin order to suit application requirements.

Figure 21 shows the increase in capacitywhen the stack height is changed rom 6 in.[150 mm] to 12 in. [300 mm] vs. the dierencebetween troom and tw. The graph indicatesthat the increase in capacity rom the largershroud reduces as the overall capacity othe beam increases. A practical lowerlimit where the mean water temperature is18F[10K]belowtheroomtemperature

translates to a capacity increase o 25% withthe taller stack.

Because the air fow through the beam isdriven by buoyancy orces, any restrictionto the air paths will impact the perormanceo the beam. Figure 22 shows the variousactors that aect perormance, including:

Facedesignofthebeamwhenexposed

Perforatedceilingbelowthebeamwhennot exposed

Gapbetweenthebeamandtheslab

Restrictionsofthe returnairpathwhenthe ceiling is closed (either return grillesor perorated ceiling tiles)

Figure 20: Passive beam air fow pattern

Figure 21: Passive beam capacity vs. temperature dierence


1

0 5 10 15 20

0.0 2.0 4.0 6.0 8.0 10.0

1.1

1.2

1.3

1.4

1.5

1.6

Capac

ity12in.

[300mm]Shroud

Capac

ity6in.

[150mm]Shroud

tw - troom,F

tw - troom, K

Figure 22:Factorsthataffectperformanceo passive beams

Figure 23: A passive beam installed abovea perorated ceiling

Slab Clearance

Face TypeReturn Air Path

Slab Clearance

Coil

Shroud/

Stack

Room Air


10/48




The design o the ace material may restrictair alling through the ace. I the beam isinstalled behind a perorated ceiling, asshown in Figure 23, the air alling belowthe beam will hit the ceiling, spread out,and all into the zone below over a largerarea. As long as there is enough ree areain the ceiling to allow the air to all through(as well as rise through in order to eedthe beam with warm air), there should notbe a reduction in the capacity o the unit.Use o a perorated ceiling is also a goodway to reduce velocities below the beam,i required.

The distance between the top o the beamand the structure can reduce the air fow

and capacity o the passive beam i it is toonarrow. Figure 24 shows the impact o thegap between the beam and the slab in termso the beam width (gap/width).

In most cases, a clearance o 20 to 25% othe beam width is recommended. Theseproducts are generally selected to be 18in. [450 mm] or less in width, which wouldrequire a gap up to 4.5 in. [115 mm].

There are other actors that aectperormance, including the application,choice o ventilation system, and location.It is possible to increase the capacity o thepassive beam through induction. I a highvelocity is located near a passive beam, itmay pull air through the coil at a higher rate

than the natural convection would alone, asindicated in Figure 25. It is also possibleto trap thermal plumes at the buildingenvelope and orce this air though a passivebeam, as shown in Figure 26.

The perormance o the beam undernon-standard conditions, such as thosedescribed above, can be dicult to estimate.Forexample,theplumecomingupfromthe aade may be so strong, and the inletto the plenum so narrow, that the plumecomes across the ace o the beam. Thiswould disturb the air movement throughthe coil, dramatically reducing the capacityo the beam. In these instances, it is bestto conduct a building mockup or usesimulation sotware to understand how the

various parameters aect each other.

40

0.07 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23 0 .25

50

60

70

80

90

100

Capacity,

%

Gap / Beam Width

Figure 24:The impact on the capacity o the gap between a passive beam and buildingstructure

Figure 26: Capturing the plume at the perimeter may increase passive beam perormance

Window

Room Air

Primary Air

Ceiling

Figure 25: Inducing air through the passive beam with increased velocity across the ace

Passive Beam

Slot Diffuser

Induced Air

Primary Air



11/48




Figure 27: Expected velocities below an 18 in. wide passive beam

0.0

100 150 200 250 300 350

96 146 196 246 296

10.0

20.0

30.0

40.0

50.0

0.3

0.25

0.2

0.15

0.1

0.05

0

60.0

Velocity,

fpm

Velocity,

m/s

Passive Beam Capacity, W/m

Passive Beam Capacity, Btu/hft

Avg. + 2

Average

Avg. 2

Selection and Location

Due to the air cascade below the passivebeam, it is common to locate the beamabove aisles or along walls. Dependingon the capacity and the expected velocitybelow the beam, the air may pose a risko drat to occupants who are regularlylocated beneath them. Figure 27 showsthe velocity below an 18 in. [450 mm] widepassive beam vs. beam capacity.

In most cases, it is desirable to maintain thevelocity in the occupied zone below 50 pm[0.25 m/s], though this value will depend onthetemperatureoftheair.FromFigure 27,the average velocity (the solid line) rangesfrom35fpm[0.175m/s]to50fpm[0.25m/s],operating between 150 Btu/ht [145 W/m]and 300 Btu/ht [290 W/m].

The installation height is not a critical actorbecause the plumes will make their waydown into the occupied zone. Even witha displacement ventilation system wherethere may be thermal plumes rising romthe occupants and heat sources, thesetend to slide past each other as opposedto mixing.

Selection o passive beams is airlystraightorward. Manuacturers generallyprovide data or standard product that hascapacity vs. fow rate or standard valuestw - troom. In most cases, it is preerable to usesotware because it allows greater control o

the design parameters and more selectionoptions. It is important to consider both thecapacity as well as the velocity beneath thebeam. This usually means selecting longer,narrower beams which typically causelower velocities below them or applicationswhere they are located above stationaryoccupants.



12/48




Design Procedure Passive Beams

1. Determine the ventilation requirement

Theventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todetermine the minimum resh air fow rate:

H1

2. Determine the required supply dew-point temperature to remove the latent load

H2

I the required humidity ratio is not practical, recalculate the supply air volume required with the desired humidity ratio.

3. Determine the supply air volume

The supply air volume is the maximum volume required by code or ventilation and the volume required or controlling the latent load:

H3

4. Determine the sensible cooling capacity o the supply air

IP H4

SI H4

5. Determine the sensible cooling required rom the water side

H5

6. Select a beam or series o beams

Select a beam or series o beams that will provide the appropriate amount o cooling using an appropriate entry water temperature.

7. Locate the beams to minimize drat as well as piping length


13/48




Example 1 - Small Ofce Passive Beams Selection (IP)

Consider a small oce with a southern exposure. The space is designed or two occupants, a computer with LCD monitor, T8 forescenlighting,andhasatemperatureset-pointof75F.Theroomis10ftwide,12ftlong,and9ftfromoortoceiling.

12 ft

9 ft10 ft

SMALL OFFICE

Window

Space Considerations

Oneoftheprimaryconsiderationswhenusinganactiveorpassivebeamsystemishumiditycontrol.Aspreviouslydiscussed,itisimportant to consider both the ventilation requirements and the latent load when designing the air-side o the system. ASHRAE Standard62.1-2010 stipulates the ventilation requirements, but these are oten not sucient to control humidity without specialized equipment.

The assumptions made or this example are as ollows:

Load/personis250Btu/hsensibleand155Btu/hlatent

Lightingloadinthespaceis6.875Btu/hft

Computerloadis300Btu/h(CPUandLCDMonitor)

Totalskinloadis1450Btu/h

Specicheatanddensityoftheairare0.24Btu/lbFand0.075lb/ftrespectively

Designconditionsare75F,with50%relativehumidity

Designdewpoint=55F

Determine:

a) The ventilation requirement.

b) The suitable air and water supply temperatures.

c) A suitable passive beam to meet the cooling requirement.

d) A practical layout or the space.

Design Considerations

Occupants 2

Set-Point 75F

FloorArea 120 t

Exterior Wall 108 t

Volume 1080ft

qoz 800 Btu/h

ql 825 Btu/h

qex 1450 Btu/h

qT 3075Btu/h


14/48





Solution:

a) Determine the ventilation requirement

Theventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminethe minimum resh air fow rate or a typical oce space:

b) Determine the required supply dew-point temperature to remove the latent load

FromequationH2:

Using the ventilation rate:

Atthedesignconditions(75F,50%RH),thehumidityratiois65gr/lb,requiringadifferenceinhumidityratiobetweenthesupplyandroom air o:

Fromthegurebelow,thedewpointcorrespondingtothehumidityratiois40F,whichistoocoolforstandardequipment.

Evaluating the humidity ratio at several temperatures:

Humidity Ratio

Dew Point lb/lb gr/lb

40 0.00543 38

45 0.0065 46

50 0.0075 53

55 0.0095 67

0.0095

0.0065

0.0075

0.0054

0.000

0.002

0.004

0.010

0.012

0.014

0.016

0.018

0.020

0.022

0.024

0.026

0.028

0.030

35 40

12.5

13.0

13.5 10%

20%

30%

40%50%

60%

70%8

0%90%

14.0

14.5

15.0

45 50 55 7560 65 70 80 85 90 95 100 105 110 115 120

65

Dry Bulb Temperature, F

Enth

alpy

-Btu/

lbofD

ryAir

HumidityRatio,lbw/lbDA

70

75

80

85

15

20

25

30

35

40

45

50

60 65

Volume - ft3/lb of Dry Air

Saturation Temperature,F

Relative Humidity

40

45

50

55

60

35


15/48





Evaluatingthehumidityratioatseveraltemperaturesshowninthetableledtotheselectionofadewpointof50Finordertouselessexpensive equipment while also minimizing the supply air volume required to control humidity. The required air volume to satisy thelatent load is:

The supply air volume to the oce is the maximum volume required by code or ventilation and the volume required or controllingthe latent load:

Determine the sensible cooling capacity o the supply air

Using equation H4:

Determine the sensible cooling required rom the water side

Assumingachilledwatersupplytemperature2F abovethedesigndewpointinordertoavoidcondensationprovidesamaximumtemperaturedifferencebetweentheMWTandTroomof75F-57F=18F.Usingselectionsoftwaretogenerateasuitableselectionprovides the ollowing perormance:

Perormance

Capacity 2049 Btu/h

Length 72in.

Width 24 in.

Water fow rate 1.01 gpm

Water pressure drop 4.9 thd

It is practical to locate passive beams along a wall where occupants are not regularly located. In this case, the area beside the desk isa good choice.

Person

SMALL OFFICE

Passive Beam


16/48




Example 1 - Small Ofce Passive Beams Selection (SI)

Consider a small oce with a southern exposure. The space is designed or two occupants, a computer with LCD monitor, T8 forescentlighting, and has a design temperature set-point o 24 C. The room is 3 m wide, 4 m long, and 3 m rom foor to ceiling.

3 m

4 m

3 m

SMALL OFFICE

Window


Oneoftheprimaryconsiderationswhenusinganactiveorpassivebeamsystemishumiditycontrol.Aspreviouslydiscussed,itisimportant to consider both the ventilation requirements and the latent load when designing the air side o the system. ASHRAE Standard62.1-2010 stipulates the ventilation requirements, but these are oten not sucient to control humidity without specialized equipment.

The assumptions made or the example are as ollows:

Load/personis75Wsensibleand55Wlatent

Lightingloadinthespaceis25W/m

Computerloadis90W(CPUandLCDMonitor)

Totalskinloadis405W

Specicheatanddensityoftheairare1.007kJ/kgkand1.3kg/m3respectively

Designconditionsare24C,with50%relativehumidity

Designdewpoint=13C

Determine:

a) The ventilation requirement.

b) The suitable air and water supply temperatures.

c) A suitable passive beam to meet the cooling requirement.

d) A practical layout or the space.


Occupants 2

Set-Point 24 C

FloorArea 12 m

Exterior Wall 12 m

Volume 36m

qoz 240 W

ql 300 W

qex 405 W

qT 945 W


17/48




Solution:

a) Determine the ventilation requirement


b) Determine the required supply dew-point temperature to remove the latent load

FromequationH2:

Using the ventilation rate:

At the design conditions (24 C, 50% RH), the humidity ratio is 9.5 g/kg, requiring a dierence in humidity ratio between the supply androom air o:

Fromthegurebelow,thedewpointcorrespondingtothehumidityratiois5C,whichistoocoolforstandardequipment.

Evaluating the humidity ratio at several temperatures:

Humidity Ratio

Dew Point g/kg

5 5.57.5 6.75

10 8

12.5 9.25


Dry-Bulb Temperature, C

Enthalpy

-kJ/k

gof

Dry

Air

30

25

20

15

10

0

50454035302520150

0

45

40

35

30

25

20

15

50

55

60

65

70

75

85

90

95

100

105

105

110 115 120 125

Volume - m3/kg of Dry Air

Saturation Temperature,C

Relative Humidity

H

umidityRatio,gw/kgDA

30

10

5

15

20

0.78

0.80

0.82

0.84

0.86

0.90

0.92

0.94

0.96

10%

20%

30%

40%

50%

60%

70%8

0%90%

25

9.25

8

6.75

5.5

10 12.5 245 7.5


18/48




Evaluating the humidity ratio at several temperatures shown in the table led to the selection o a dew point o 10 C in order to use lessexpensive equipment while also minimizing the supply air volume required to control humidity. The required air volume to satisy thelatent load is:


Determine the sensible cooling capacity o the supply airUsing equation H4:

Determine the sensible cooling required rom the water side

Assumingachilledwatersupplytemperature1Kabovethedesigndewpointinordertoavoidcondensationprovidesamaximumtemperature dierence between the tw and troomof24C14C=10K.Usingselectionsoftwaretogenerateasuitableselectionprovidesthe ollowing perormance:

PerormanceCapacity 567W

Length 1800 mm

Width 600 mm

Water fow rate 230 L/h

Water pressure drop 14.6 kPa

It is practical to locate passive beams along a wall where occupants are not regularly located. In this case, the area beside the desk isa good choice.


Person

SMALL OFFICE

Passive Beam


19/48




Active beam systems will vary inperormance, coniguration and layoutdepending on the application. There are,however, some characteristics that arecommonformostsystems.Furthermore,the perormance o active beams is largelydependent on a common set o actors.This section will discuss how actors suchas supply air volume and chilled watertemperature aect the perormance andlayout o active beams. Table 3 showscommon design characteristics or activebeam systems.

Product Selection and Location Active Beams

Perormance

The perormance o an active beam isdependent on several actors:

Activebeamconguration

Coilcircuitry

Primaryairow(plenumpressure)

Waterow

As discussed previously, there are severalcongurations o active beams. The mostcommon is the linear type, which is availablein both 1 way and 2 way air patterns. A thirdtype is modular and typically has a 4 waydischarge.

Active beams are appropriate or heatingand cooling. The coil circuitry has a largeeect on the beam perormance. I the beam

is to be used or cooling and heating, it wouldusually have a 4 pipe coil. A 4 pipe coil sharesns between two separate circuits. I thebeam is used or either cooling or heatingonly, the beam may make use o the entirecoil with a single circuit, thereby allowingadditional heat transer rom the water tothe air. The primary driver o active beamcapacity is the plenum pressure. Figure 30and Figure 31 show the air path o linearand modular beams in cooling.

As discussed, it is the primary air that inducesthe room air through the coil, the rate owhich is determined by the nozzle size andthe plenum pressure. A good measure orthe overall perormance o an active beamis known as the transer eciency. This isthe ratio o total heat transerred by the coilper unit volume o primary air:

Typical values or transer eciency vary byapplication type but in general, the higherthe eciency, the more energy savings areavailable or a given system. The transereciency is largely dependent on the air-side load raction and the sensible heat ratio.

Active Beam Selection and Design Procedure

IP

Room Temperature 74Fto78Finsummer,68Fto72Finwinter

Water Temperature, Cooling 55Fto58FEWT,5Fto8F T


Cooling Capacity Up to 1000 Btu/ht

Water Temperature, Heating 110Fto130FEWT,10Fto20F T

Heating Capacity Up to 1500 Btu/ht

Ventilation Requirement 0.1 to 0.5 cm/t2 foor area

Ventilation Capability 5 to 30 cm/t

Primary Air Supply Temperature 50Fto65F

Inlet Static Pressure 0.2 in. w.g. to 1.0 in. w.g. external

SI

Room Temperature 23 C to 25 C in summer, 20 C to 22 C in winter

Water Temperature, Cooling 13Cto15CEWT,3Kto5K TDesign Sound Levels < 40 NC

Cooling Capacity Up to 1000 W/m

Water Temperature, Heating 60Cto70CEWT,5Kto12K

Heating Capacity Up to 1500 W/m

Ventilation Requirement 0.5 to 2.5 L/s m2 foor area

Ventilation Capability 7to40L/sm2

Primary Air Supply Temperature 10 C to 18 C

Inlet Static Pressure 50 Pa to 250 Pa external

Table 3: Design values or active beam systems

Figure 28: Linear type active beam Figure 29: Modular type active beam

Figure 30: Air fow diagram o a typicallinear active beam in cooling

Nozzles

Plenum

Primary Air

Room Air

Figure 31: Air fow diagram o a modulabeam in cooling

Room Air

Nozzles

Plenum

Primary Air


20/48





The higher the sensible load raction is, thesmaller the beam nozzle can be, resultingin a higher induction ratio, dened as theratio o the induced mass air fow to that othe primary air:

The selection o smaller nozzles also resultsin higher plenum pressures or a xedprimary air fow rate. Larger nozzles willhave a lower induction ratio but allow moreprimary air to be supplied, though at a lowertranser eciency, as shown in Figure 32.

Figure 33shows the water-side perormanceo a typical beam vs. air fow. The curvescorrespond with various nozzle sizesincreasing in diameter rom let to right. Thelength o the curves is dened by standardoperating pressures. It is noted romthe graphs that the capacity o the beamincreases as more air is supplied, thoughnot in a linear ashion.

Figure 34 shows how the increase incapacity is dependent on the air volume.As shown in the gure, as the nozzle sizeincreases to provide a ve-old increaseinairvolume,onlya175%increaseinthewater-side capacity is realized, while thetranser eciency has reduced by 65%.

The water fow rate in the coil aects twoperormance actors:

The heat transer between the water andthe coil which is dependent on whether thefow is laminar (poor) or turbulent (good).

The mean water temperature, or the averagetemperature in the coil. The higher the fowrate, the closer the discharge temperaturewill be to that o the inlet, assuming nochange in heat transer, thereby changingthe average water temperature in the coil.

Figure 32: Transer eciency is reduced by increasing nozzle size

TransferEfficiency

Smaller Nozzle Larger Nozzle

Figure 33: Capacity o a typical active beam vs. primary air fow

Figure 34: Capacity vs. air volume

0

0

0 10 20 30 40 50 60 70

10 20 30 40 50

400

200

600

800

1000

1200

1400

0

200

400

600

800

1000

1200

Ca

pacity,Btu/hft

C

apacity,W/m

Air Flow, cfm/ft

Air Flow, L /sm

0

100 200 300 400 500 600

100

120

140

160

180

20

40

60

80

200 Capacity Increase

Transfer Efficiency

IncreaseinWater-SideCapacity

,%

Increase in Air Volume, %


21/48




Figure 35 shows the eect o the waterfow rate, indicated by Reynolds number,on the capacity o a typical active beam.As indicated on the chart, increasing thefow rate into the transitional and turbulentranges (Re > 2300, shown in blue on thegraph) causes an increase in the output othe beam.

The water fow rate is largely dependenton the pressure drop and return watertemperature that are acceptable to thedesigner. In most cases, the water fowrate should be selected to be ully turbulentunder design conditions.

The dierence between the mean watertemperature and the room air temperatureis one o the primary drivers o the beamperormance. The larger this dierenceis, the higher the convective heat transerpotential, as shown inFigure 36.Conversely,a lower temperature dierence will reducethe amount o exchange, and therebycapacity. As a result, it is desirable roma capacity standpoint to select an entrywater temperature as low as possible, whilemaintaining it above the dew point in theroom to ensure sensible-only cooling.

In some instances, it might be advantageousto have higher supply and return watertemperatures, where it makes sense roman equipment standpoint. This may alsooer some control simplication where the

output o the beam is determined by theload in the room:

As the load increases, the air temperaturerises and increases the dierence betweenit and t w, thereby increasing beamperormance.

As the load decreases, the air temperaturealls and reduces the cooling capacity o thebeam.


Figure 35: Active beam capacity vs. water fow

40

0 2000 4000 6000 8000 10000 12000

50

60

70

80

90

100

Capacity,

%

Re

Figure 36: Active beam capacity vs. dierence between the mean water and room airtemperatures

0

0 5 10 15 20

0 2 4 6 8 10

20

40

60

80

100

120

Capacity,

%

tw - troom ,F

tw - troom , K


22/48




Design Procedure Active Beams

1. Determine the ventilation requirement

Theventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminethe minimum resh air fow rate:

H1

2. Determine the required supply dew-point temperature to remove the latent load

H2

I the required humidity ratio is not practical, recalculate the supply air volume required with the desired humidity ratio.

3. Determine the supply air volume

The supply air volume is the maximum volume required by code or ventilation and the volume required or controlling the latent load:

H3

4. Determine the sensible cooling capacity o the supply air

IP H4

SI H4

5. Determine the sensible cooling required rom the water side

H5

6. Select a beam or series o beams

Select a beam or series o beams that will provide the appropriate amount o cooling and heating using appropriate entry watertemperatures and throw distances.

7. Review that the primary air calculation in (3) is still appropriate

H6

8. Lay out the beams in such a way that the comort in the space is maximized


23/48L-23



Copyright Price Industries Limited 2011. All Metric dimensions ( ) are sot conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter.

Example 2 - Small Ofce Active Beam Selection (IP)

12 ft

9 ft10 ft

SMALL OFFICE

Window

ConsiderthesmallofcepresentedinExample1-SmallOfcePassiveBeamSelection.


Occupants 2

Set-Point 75F

FloorArea 120 t

Exterior Wall 108 t

Volume 1080ft

qoz 800 Btu/h

ql 825 Btu/h

qex 1450 Btu/h

qT 3075Btu/h

Qs 38 cm

ts 50F

tCHWS 57F

Determine

a) A suitable active beam to meet the cooling requirement.

b) A practical layout or the space.

Solution

Fromexample1-SmallOfcePassiveBeamSelection.

Perormance

Total Capacity 3075Btu/h

Air fow Required or Dehumidication 38 cm

Supply Air Temperature 50F

CHWS Temperature 57F


24/48




Using selection sotware to select beams with these parameters provides several possible solutions:

Example 2 - Small Ofce Active Beam Selection (IP)

Parameter Option 1 (ACBL) Option 2 (ACBL) Option 3 (ACBM)

Total Capacity 3074Btu/h 3076Btu/h 3077Btu/h

Length 72in. 48 in. 48 in.

Width 24 in. 24 in. 24 in.

Air fow 35 cm 40 cm 40 cm

Throw @ 50 pm 10 t 13 t 10 t

Air Pressure Drop 0.75in. 0.42 in. 0.56 in.

Transer Eciency 88 Btu/h cm 77Btu/hcfm 77Btu/hcfm

WaterFlowRate 0.41 gpm 1.2 gpm 0.61 gpm

Water Pressure Drop 0.63 t hd 3.1 t hd 1.26 t hd

NC 15 18 17

The rst option meets the capacity requirements though has slightly lower air fow than that required to handle the latent loads; it isalso the most ecient option. The second and third options both meet the capacity and air fow requirements.

Revisiting the air volume required:

Fortheprivateofce,eitherselection(2)or(3)isappropriate.Themodularunithastheadvantageoflowerthrowandwouldresultinlower occupied zone velocities. The linear unit can be selected with an integrated return grille, increasing the overall length o the beamwhile allowing the return to appear to be a part o the beam. Both o these layouts are shown below:

Section ViewPlan View

Person

Person

2 wayBeam

IntegratedReturn

Return

SMALL OFFICE

Person

SMALL OFFICE

Person

ModularBeam

Window

Window


25/48




Example 2 - Small Ofce Active Beam Selection (SI)

12 ft

9 ft10 ft

SMALL OFFICE

Window

ConsiderthesmallofcepresentedinExample1-SmallOfcePassiveBeamSelection.


Occupants 2

Set-Point 24 C

FloorArea 12 m

Exterior Wall 12 m

Volume 36m

qoz 240 W

ql 300 W

qex 405 W

qT 945 W

Qs 22.5 L/s

ts 10 C

tCHWS 14 C

Determine

a) A suitable active beam to meet the cooling requirement.

b) A practical layout or the space.

Solution

Fromexample1-SmallOfcePassiveBeamSelection.

Perormance

Total Capacity 945 WAir fow Required or Dehumidication 22.5 L/s

Supply Air Temperature 10 C

CHWS Temperature 14 C


26/48




Using selection sotware to select beams with these parameters provides several possible solutions:

Example 2 - Small Ofce Active Beam Selection (SI)


Total Capacity 945 W 946 W 952 W

Length 1.8 m 1.2 m 1.2 m

Width 0.6 m 0.6 m 0.6 m

Air fow 16.5 L/s 22.5 L/s 22.5 L/s

Throw @ 50 pm 3.9 m 3.7m 3 m

Air Pressure Drop 187Pa 107Pa 100 Pa

Transer Eciency 48 Ws/L 25 Ws/L 25 Ws/L

WaterFlowRate 93 L/h 216 L/h 148 L/h

Water Pressure Drop 1.88 kPa 8.07kPa 4.18 kPaNC 15 21 17

The rst option meets the capacity requirements though has slightly lower air fow than that required to handle the latent loads; it isalso the most ecient option. The second and third options both meet the capacity and air fow requirements.

Revisiting the air volume required:

Fortheprivateofce,eitherselection(2)or(3)isappropriate.Themodularunithastheadvantageoflowerthrowandwouldresultinlower occupied zone velocities. The linear unit can be selected with an integrated return grille, increasing the overall length o the beamwhile allowing the return to appear to be a part o the beam. Both o these layouts are shown below:

Section ViewPlan View

Person

Person

2 wayBeam

IntegratedReturn

Return

SMALL OFFICE

Person

SMALL OFFICE

Person

ModularBeam

Window

Window


27/48




In active beam selection, there is oten atrade-o required between the primary airvolume and the beam length. When thetotal capacity o the beam is consideredthere is an increase in the capacity with anincrease in the primary air volume; though,as indicated in Figure 37, this is largely dueto the increased capacity o the primary airand only slightly due to an increase in theperormance o the cooling coil. The overalleect o an increase in primary air volumeis invariably a reduction in the transereciency o the beam; thereore, care mustbe taken when increasing the air volume pastwhat is required to satisy the ventilationrequirements and latent loads.

In order to determine i it is necessary toincrease the air volume beyond that which isrequired, several actors should be weighed:

1. Beam Size

With higher capacity per unit length o beamit is possible to reduce the size o the beam,which may reduce the visual impact o theHVAC system. It may also help to t beamsinto spaces with high specic loads, such asa corner oce in a hot climate like Phoenixor Dubai.

2. First Cost

The reduction in overall size o the beamdoes oer some rst cost savings, thoughthese should be compared to the rst costadditions required o the air handling system,

including equipment and ductwork. In mostapplications, these costs are similar and maynot oer the benet sought.

3. Energy

By decreasing the transer eciency (orincreasing the percentage o the loadmanaged by air rather than water), there isusually a reduction in the overall eciency othe system. In most cases, it is more ecientto pump energy through the building withwater than air, and so an increase in the loadmanaged by air may cause an increase in thesystem horsepower.

4. Noise

Active beam noise is largely dependent onprimary air fow, thereore an increase in the

primary air volume to the beam will increasethe noise levels in the space.

5. Control

With additional air supplied to the beam,there is an increased risk o overcoolingthe zone under part-load conditions. Thesesystems are typically constant volume, whichreduces the systems ability to control thezone temperature i the minimum capacityo the beam is increased due to an increasein primary air volume.

Managing Primary Air Volume and Capacity

6. Lie-Cycle Cost

This type o design decision is oten best madewith a lie-cycle cost analysis to determine thecost impact over the lie o the building.

There are applications where an increase inair volume is a reasonable design decision,either due to very large specic loads or highventilation rates, such as in a health careapplication. In situations where the specicload is high, there are some options thatwill allow the system to meet the required

capacity but will also maximize the energyeciency:

1. Select an active beam and a passivebeam together.

This allows the designer to minimize theair and add sensible cooling capacity whererequired. This also signicantly increasesthe transer eiciency o the room bykeeping the air volume as low as possiblewhile increasing the sensible capacity.

2. Employ a variable air volume (VAV)strategy.

Whether or an individual oice or ora larger zone, VAV allows the system tosupply the capacity required under designconditions while allowing the air volume

to be turned down to minimum during o-peak hours. The most ecient congurationwould have the air turn up/down only as thesecond stage o cooling, as shown in thediagram below.

Max. Water Flow

Min. Water Flow

Dead Band

Tset-point

CHW

SFl

owHWSFlow

Max. Air Flow

Air

flow

Airfl

ow

Min. Air Flow

Cool WarmRoom Condition

Figure 37: VAV control sequence


28/48




Example 3 - Small Ofce with High Internal Gains (IP)

Consider the small oce presented in Example 1, though now in a hot climate with an increased solar gain:

12 ft

9 ft10 ft

SMALL OFFICE

Window


Occupants 2

Set-Point 75F

FloorArea 120 t

Exterior Wall 108 t

Volume 1080ft

qoz 800 Btu/h

ql 825 Btu/h

qex 6575Btu/h

qT 8200 Btu/h

Qs 38 cm

ts 50F

tCHWS 57F

Compare

a)AsuitableactivebeamwithconstantairsupplytoonewithVAV,assuming2175Btu/hofenvelopeloadinoff-peakhours.

b) A suitable active beam to a combination o active and passive beams.

Solution

a) Using sotware, select a beam with the ollowing requirements.

Perormance

Total Capacity 8200 Btu/h

AirFlowrequiredforDehumidication 35 cm


CHWS Temperature 57F


29/48





In this case, increasing the supply air volume was required in order to meet the capacity required:

Parameter Peak Load O-Peak Load

Total Capacity 8202 Btu/h 3817Btu/h

Length 96 in. 96 in.

Width 24 in. 24 in.

AirFlow 140 cm 55 cm

Throw 18 t 10 t

Air Pressure Drop 0.88 in. w.g. 0.15 in. w.g.

Transer Eciency 59 Btu/h cm 69 Btu/h cm

WaterFlowRate 1.23 gpm 1.23 gpm

Water Pressure Drop 5.8 t hd 5.8 t hd

NC 32


30/48




Inthisexample,anactivebeamandapassivebeamwereselectedtobethesamesizetosimplifythelayout.Furthermore,thewater-sidepressure drop has been selected to be equivalent to make the piping more straightorward. These beams could be laid out and piped as shown:

Person

SMALL OFFICECHWS

CHWR

Window

P

assiveBeam

A

ctiveBeam


Person

Person

Beam

SMALL OFFICE

Window Max Load

The layout is the same as in example 1. Reviewing the throw pattern at peak load:

b) Using software again, an active beam and passive beam are selected together

Parameter Passive Beam Active Beam Total

Total Capacity 2718Btu/h 5481 Btu/h 8200 Btu/h

Length 96 in. 96 in. -

Width 24 in. 24 in. -

AirFlow 0 55 cm 55 cm

Throw - 15 t -

Air Pressure Drop n/a 1 in. 1 in.

Transer Eciency n/a 100 Btu/h cm 149 Btu/h cmWaterFlowRate 1.29 gpm 1.65 gpm 2.94 gpm

Water Pressure Drop 9.8 t hd 9.9 t hd 9.9 t hd

NC - 20 20


31/48





In this case the air pattern rom the active beam passes over the ace o the passive beam, thereore the concern o velocity below thepassivebeamislargelyeliminated.Furthermore,thistypeofarrangementtendstoincreasetheairvolumethroughthepassivebeam,which would typically result in an increase in perormance.

Comparing the two options:

Parameter Active Beam Active &Passive Beam

Total Capacity 8202 Btu/h 8200 Btu/h

AirFlow 140 cm 55 cm

Throw 18 t 15 t

Air Pressure Drop 0.88 in. 1 in.

Transer Eciency 59 Btu/h cm 149 Btu/h cm

WaterFlowRate 1.23 gpm 2.94 gpm

Water Pressure Drop 5.8 t hd 9.9 t hd

NC 32 20

The dierence between the two is largely in the supply air volume and noise. Selection (1) requires an additional 85 cm, or 250% theamount o air required in the second selection and also has a signicantly higher NC level. This will translate into larger air handlingequipment and ductwork (even or the VAV case), adding cost as well as additional energy to move the air through the building. In someareas, the selection o the system with lower supply air volume translates into signicant energy savings:

This energy savings is or the sensible cooling o the outdoor air only; additional savings would exist in the latent cooling and transporenergy o the additional air volume. There is additional cost in the passive beam, though it may be oset by the increase in equipmenand distribution cost as well as the energy required or the higher air volume case. This will however, depend largely on the applicationand building design.

Annualdegree -hours

Annual ton - hours savedper ofce

Total annual kWh saved perofce

Phoenix 76121 582.33 3654

Atlanta 46253.4 353.84 2220

Minneapolis 25494.8 195.04 1224

Seattle 19345.8 148.00 929

Washington DC 36635.9 280.26 1759


32/48



Hydronic Heating & Cooling SystemsEngineering Guide

Example 3 - Small Ofce with High Internal Gains (SI)

Consider the small oce presented in Example 1, though now in a hot climate with an increased solar gain:


Occupants 2

Set-Point 24 C

FloorArea 12 m

Exterior Wall 12 m

Volume 36m

qoz 240 W

ql 300 W

qex 1860 W

qT 2400 W

Qs 22.5 L/s

ts 10 C

tCHWS 14 C

Compare

a) A suitable active beam with constant air supply to one with VAV, assuming 580 W o envelope load in o-peak hours.

b) A suitable active beam to a combination o active and passive beams.

Solution

a) Using sotware, select a beam with the ollowing requirements.

Perormance

Total Capacity 2400 W

AirFlowrequiredforDehumidication 22.5 L/s


CHWS Temperature 14 C

3 m

4 m

3 m

SMALL OFFICE

Window


33/48



Hydronic Heating & Cooling SystemsEngineering Guide


In this case, increasing the supply air volume was required in order to meet the capacity required:

Parameter Peak Load O-Peak Load

Total Capacity 2400 W 1140 W

Length 2.4 m 2.4 m

Width 600 mm 600 mm

AirFlow 66 L/s 26 L/s

Throw 4.9 m 2.4 m

Air Pressure Drop 221 Pa 35 Pa

Transer Eciency 19 W s/L 27Ws/L

WaterFlowRate 218 L/h 218 L/h

Water Pressure Drop 14.6 kPa 14.6 kPa

NC 33


34/48





Inthisexample,anactivebeamandapassivebeamwereselectedtobethesamesizetosimplifythelayout.Furthermore,thewater-side pressure drop has been selected to be equivalent to make the piping more straightorward. These beams could be laid out andpiped as shown:

Person

SMALL OFFICECHWS

CHWR

Window

PassiveBeam

ActiveBeam

The layout is the same as in example 1. Reviewing the throw pattern at peak load:

b) Using software again, an active beam and passive beam are selected together

Parameter Passive Beam Active Beam Total

Total Capacity 811 W 1606 W 2417W

Length 2.4 m 2.4 m -

Width 600 mm 600 mm -

AirFlow 0 26 L/s 26 L/s

Throw - 3.7m 3.7m

Air Pressure Drop n/a 296 Pa 296 PaTranser Eciency n/a 45 Ws/L 76Ws/L

WaterFlowRate 193 L/h 220 L/h 413 L/h

Water Pressure Drop 8.1 kPa 14.9 kPa 14.9 kPa

NC - 21 21

Person

Person

Beam

SMALL OFFICE

Window Max Load


35/48





In this case the air pattern rom the active beam passes over the ace o the passive beam, thereore the concern o velocity below the

passivebeamislargelyeliminated.Furthermore,thistypeofarrangementtendstoincreasetheairvolumethroughthepassivebeam,which would typically result in an increase in perormance.

Comparing the two options:

The dierence between the two is largely in the supply air volume and noise. Selection (1) requires an additional 40 L/s, or 250% theamount o air required in the second selection, and also has a signicantly higher NC level. This will translate into larger air handlingequipment and ductwork (even or the VAV case), adding cost as well as additional energy to move the air through the building. In someareas, the selection o the system with lower supply air volume translates into signicant energy savings:

Parameter Active Beam Active &Passive Beam

Total Capacity 2400 W 2417W

AirFlow 66 L/s 26 L/s

Throw 4.9 m 3.7m

Air Pressure Drop 221 Pa 296 Pa

Transer Eciency 19 Ws/L 76Ws/L

WaterFlowRate 218 L/h 413 L/h

Water Pressure Drop 14.6 kPa 14.9 kPa

NC 33 21

Annualdegree - hours

Total annual kWhsaved per ofce

Phoenix 76121 3654

Atlanta 46253 2220

Minneapolis 25495 1224

Seattle 19346 929

Washington DC 36636 1759

This energy savings is or the sensible cooling o the outdoor air only; additional savings would exist in the latent cooling and transporenergy o the additional air volume. There is additional cost in the passive beam, though it may be oset by the increase in equipmenand distribution cost as well as the energy required or the higher air volume case. This will however, depend largely on the applicationand building design.


36/48




Example 4 - Active Beams in a Computer Lab (IP)

This space is a school computer lab designed or 26 occupants, 26 computers with one LCD monitor each, a projector,threeprinters,T8orescentlighting,andhas atemperatureset-pointof75 Fat 50%RHin thesummer.Theroomis50 ftlong,50 t wide, and has a foor-to-ceiling height o 9 t. The ceiling is exposed, with possible duct connections in the interior o the space.


Someoftheassumptionsmadeforthisspaceareasfollows:

Inltrationisminimal,andisneglectedforthepurposesofthisexample.

Thespecicheatanddensityoftheairforthisexamplewillbe0.24Btu/lbFand0.075lb/ft2respectively. Theairhandlingsystemutilizesenergyrecoverytoprovide65Fat50Fdewpoint.Determinetheventilationrequirement

Design Considerations Total

OccupantLoad 250 Btu/h person 6500 Btu/h

Lighting Load 3 Btu/ht2foor 7500Btu/h

Computer Loads 450 Btu/h person 11700Btu/h

Projector Load 188 Btu/h 188 Btu/h

Printer Loads 444 Btu/h 444 Btu/h

Envelope Load 14.6 Btu/ht2aade 6570Btu/h

Total Load 32902 Btu/h

LatentLoad-OccupantLoad 200 Btu/h person 5200 Btu/h


Determine the required supply dew-point temperature to remove the latent load

Usingahumidityratioofthesupplyairat50Fdewpointandthedesignconditions(75F,50%RH):

Printers Projector

COMPUTER LAB

50ft

50 ft


37/48




The supply air volume to the oce is the maximum o the volume required by code or ventilation and the volume required or controllingthe latent load:

Using sotware to select a beam with the ollowing requirements:

Example 4 - Active Beams in a Computer Lab (IP)

Perormance

Total Capacity 32902 Btu/h

AirFlowRequiredforDehumidication 632 cm


Arrives at the ollowing options:


Total Capacity 32197Btu/h 33044 Btu/h 32933 Btu/h

Quantity 4 6 6

Length 120 in. 96 in. 48 in.

Width 24 in. 24 in. 24 in.

AirFlow 640 cm 780cfm 870cfm

Throw 11 t 17ft -

Air Pressure Drop 0.99 in. 0.76in. 0.83 in.

Transer Eciency 50.3 Btu/h cm 42.4 Btu/h cm 37.9Btu/hcfm

WaterFlowRate 5.96 gpm 6.48 gpm 9.42 gpm

Water Pressure Drop 9.9 t hd 4.6 t hd 0.71fthd

NC 27 30 -

Oftheseoptions,thesecondcombinationofsix8ftlongbeamsisthebestcombinationofcapacity,efciencyandthrow.Withsixbeams, these could be laid out as shown below:

COMPUTER LAB

Printers Projector

CHWS

CHWR

BeamBeam Beam

BeamBeam Beam


38/48




Example 4 - Active Beams in a Computer Lab (SI)

This space is a school computer lab designed or 26 occupants, 26 computers with one LCD monitor each, a projector, 3 printers, T8forescent lighting, and has a temperature set-point o 24 C at 50% RH in the summer. The room is 15 m long, 15 m wide, and has afoor-to-ceiling height o 3 m. The ceiling is exposed, with duct connections possible in the interior o the space.

15m

15 m

Printers Projector

COMPUTER LAB


Some o the assumptions made or this space are as ollows:

Inltrationisminimal,andisneglectedforthepurposesofthisexample.

Thespecicheatanddensityoftheairwillbe1.007kgKand1.3kg/m3respectively. Theairhandlingsystemutilizesenergyrecoverytoprovide18Cat10Cdewpoint.

Design Considerations Total

OccupantLoad 75W/person 1950 W

Lighting Load 25 W/m2foor 5625 W

Computer Loads 130 W/person 3380 W

Projector Load 55 W 55 W

Printer Loads 130 W 130 W

Envelope Load 46 W/m2aade 2070W

Total Load 13210 W

LatentLoads-OccupantLoad 60 W/person 1560 W

Determine the ventilation requirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminethe minimum resh air fow rate or a typical oce space:

Determine the required supply dew-point temperature to remove the latent load.

Using a humidity ratio o the supply air at 10 C dew point and the design conditions (24 C, 50% RH):


39/48





Using sotware, select a beam with the ollowing requirements:

Example 4 - Active Beams in a Computer Lab (SI)

Perormance

Total Capacity 13210 W

AirFlowRequiredforDehumidication 320 L/s


Arrives at the ollowing options:


Total Capacity 13221 W 13216 W 13220 W

Quantity 6 7 8

Length 3000 mm 2400 mm 1200 mm

Width 600 mm 600 mm 600 mm

AirFlow 426 L/s 497L/s 696 L/s

Throw 3.3 m 6 m -

Air Pressure Drop 220 Pa 250 Pa 193 Pa

Transer Eciency 31 W s/L 17Ws/L 19 W s/L

WaterFlowRate 302 L/s 345 L/s 368 L/s

Water Pressure Drop 9.92 kPa 10.32 kPa 9.12 kPa

NC 27 33 -

Oftheseoptions,thesecondcombinationofsix2.4mbeamsisthebestcombinationofcapacity,efciencyandthrow.Withsi

Documents

Chilled Beam- Engineering_Guide