Active Passive Beams Engineering Guide - Price Industries

Active & Passive BeamsEngineering GuideWhen to use Beam SystemsHygienic SystemWith the elimination of the majority offilters and drain pans, there is a reducedrisk of mold or bacteria growth in the entiremechanical system.SchoolsSchools are another application that canbenefit greatly from active and passive beamsystems. Similar to office buildings, thebenefits of a lower supply air volume to thespace are lower fan power, shorter plenumheight, reduced reheat requirements andlower noise levels (often a critical designparameter of schools).Active and passive beam systems are wellsuited to some applications and less so toothers. As a result, each application mustbe reviewed for potential benefits as wellas the suitability of these types of systems.One consideration which can assist in thedecision to employ hydronic systems asopposed to an all-air system is the air-sideload fraction, or the percentage of the totalair supply which must be delivered to thezone to satisfy code and dehumidificationrequirements. Table 1 shows the loadfraction for several spaces. In the table thebest applications for hydronic systems arethose with the lowest air-side load fractionas they are the ones that will benefit the mostfrom the efficiencies of hydronic systems.Another factor which should be examinedis the sensible heat ratio or the percentageof the cooling load which is sensible asopposed to latent. The latent loads must besatisfied with an air system and offer somesensible cooling at the same time due tothe temperature of dehumidified air. If thetotal sensible cooling load is significantlyhigher than the capacity of the air suppliedto satisfy the latent loads, a beam systemmight be a good choice.Hospital Patient RoomsHospitals are unique applications in thatthe supply air volume required by localcodes for each space is often greater thanthe requirement of the cooling and heatingload. In some jurisdictions, local coderequires these higher air-change rates forall-air systems only. In these cases, thetotal air-change rate required is reduced ifsupplemental heating or cooling is used.This allows for a significant reductionin system air volume and yields energysavings and other benefits.Furthermore, because these systems aregenerally constant air volume with thepotential to reduce the primary air-changerates, reheat and the cooling energydiscarded as part of the reheat process isa significant energy savings opportunity.Depending on the application, a 100%outside air system may be used. Thesesystems utilize no return air and thereforeno mixing of return air between patientrooms occurs, potentially lowering the riskof hospital associated infections.ENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSCommercial Office BuildingsIn an office building, active and passivebeam systems provide several benefits. Thelower supply air volume of the air handlingsystem provides significant energy savings.In addition, the smaller infrastructurerequired to move this lower air flow allowsfor small plenum spaces, translating intoshorter floor-to-floor construction or higherceilings. The lower supply air volume andelimination of fans at or near the spaceoffers a significant reduction in generatednoise. The lower air flow often translatesto reheat requirements being reduced. Inthe case of 100% outside air systems, thelighting load captured in the return plenumis exhausted from the building, lowering theoverall cooling load.LaboratoriesIn load driven laboratories where the supplyair rate is driven by the internal gains (suchas refrigerators, testing equipment, etc.)as opposed to the exhaust requirements,active and passive beam systems canoffer significant energy savings. In theseenvironments it is not unusual to requirea large air-change rate in order to satisfythe load, although significantly less maybe required by code (ASHRAE, 2008; CSA,2010).In these applications, the difference betweenthe supply air volume required to managethe sensible loads and that required tomeet the fume hood air flow requirementsprovides opportunity for energy savingsthrough the application of active and passivebeams. These savings are typically due tothe reduction in fan power as well as theenergy associated with treating the outsideair, which, in the case of a load driven lab,may be significant.Hotels / DormsHotels, motels, dormitories and similar typebuildings can also benefit from active andpassive beam systems. Fan power savingsoften come from the elimination of fancoil units located in the occupied space.The energy savings associated with these“local” fans is similar in magnitude to thatof larger air handling systems. It also allowsfor the elimination of the electrical servicerequired for the installation of fan coil units,as well as a reduction in the maintenanceof the drain and filter systems. The removalof these fans from the occupied space alsoprovides lower noise levels, which can be asignificant benefit in sleep areas.LimitationsThere are several areas in a building wherehumidity can be difficult to control, suchas lobby areas and locations of egress.These areas may see a significant shortterm humidity load if the entrances are notisolated in some way (revolving doors orvestibules). In these areas, a choice of acomplimentary technology such as fan coilunits or displacement ventilation is ideal.Other applications may have high airflow/ventilation requirements, such as anexhaust driven lab. The majority of thebenefit provided by the hydronic system islinked to the reduction in supply air flow.As such, these applications may not seesufficient benefit to justify the addition ofthe hydronic circulation systems, makingthem not likely to be a good candidate forthis technology.Total AirVolume (Typ.)Ventilation Requirement(Typ.)Air-SideLoad FractionOffice1 cfm/ft2 [5 L/s m2]0.15 cfm/ft2 [0.75 L/s m2]0.15School1.5 cfm/ft [7.5 L/s m ]0.5 cfm/ft [2.5 L/s m ]0.33Lobby2 cfm/ft2 [10 L/s m2]1 cfm/ft2 [5 L/s m2]0.5Patient Room6 ach2 ach0.33Load-driven Lab20 ach6 ach0.3Application2222Table 1: Typical load fractions for several spaces in the United StatesL-4All Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter. Copyright Price Industries Limited 2011.

Active & Passive BeamsEngineering GuidePassive BeamsPassive BeamsPassive beams use a heat exchanger–usually a coil–to change the temperature ofthe adjacent transferring heat and create adifference in density with the ambient air.The density difference creates air movementacross the heat exchanger, transferring heatfrom the heat exchanger to the air.Passive beams are available in models thateither integrate into standard suspendedceiling systems or are suspended freelyfrom the ceiling. They are also commonlyinstalled behind perforated metal ceilingsfor a uniform architectural appearance. Aperforated metal ceiling helps reduce draftunder the beam, however, a minimum freearea of 50% is often required to ensure thecapacity of the beam is not reduced. Passivebeams installed behind a metal perforatedceiling can be seen in Figure 7.ComponentsThe basic components of passive beamsinclude a heat exchanger, comprising ofextruded aluminum fins and copper tubing,commonly termed the ‘coil’, and a frame orshroud. These components are illustratedin Figure 8.LocationPassive beams are ideally suited to aisleways or perimeters of large spaces suchas offices, lobbies, conference centers,libraries, or any other space that requiresperimeter or additional cooling. Air flowfrom a passive beam is straight down sothey are not typically placed above where anoccupant will be stationed for an extendedperiod of time. While the velocity from apassive beam is low, there is the opportunityfor some people in this condition to beuncomfortable. Copyright Price Industries Limited 2011.Figure 5: Room air flow pattern of a passive beam in coolingRoom AirCoilPrimary AirFigure 6: Air flow diagram of a passivebeam in coolingFigure 7: Passive beams installed behinda metal perforated ceilingCoilFrame/ShroudFaceFigure 8: Components of a typical passive chilled beamAll Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter.L-5ENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSPassive beams condition a space usingnatural convection and are primarily usedfor handling the sensible cooling load of aspace. They are water-only products, andrequire a separate air system for ventilationair and to remove the latent load. Aswarm air in the room rises, it comes intocontact with the heat exchanger and flowsdownward 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

Active & Passive BeamsEngineering GuideActive BeamsActive BeamsActive beams use the ventilation systemto increase the output of the coil, and tohandle both latent and sensible loads of aspace. Unlike radiant panels and chilledsails, which rely primarily on thermalradiation to condition a space, active beamsheat or cool a space through inductionand forced convection. An active beamaccepts dry air from the system through apressurized plenum. This primary supplyair is then forced 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 theheating/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 flowdiagram of a linear active beam in coolingand heating modes can be seen in Figure 10,and Figure 11 respectively.Figure 9: Room air flow pattern of a typical linear active beam in coolingPlenumComponentsENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSThe basic components of active beamsinclude a heat exchanger with aluminumfins and copper tubing, commonly termedthe ‘coil,’ a plenum box with at least onesupply inlet, internal nozzles, a visible face,and a frame. Although the configurations ofactive beams differ, all general componentsremain the same. These components areillustrated in Figures 12.ApplicationsActive beams can be used in offices,meeting rooms, schools, laboratories,hospitals, data centers, airports, any ‘green’building application, and large areas such aslobbies, conference facilities, lecture hallsor cafeterias.NozzlesPrimary AirPrimary AirNozzlesRoom AirRoom AirFigure 10: Air flow diagram of a typicallinear active beam in coolingFigure 11:Air flow diagram of a typicallinear active beam in heatingTwo basic types of active beams are:Plenum Linear Active Beams Modular Active BeamsMountingBracketLinear Active Beams2 Way DischargeLinear active beams with two-sideddischarge are designed to either integrateinto standard suspended ceiling systemsor be suspended freely in an ‘exposed’application. These beams have two linearair slots that run the length of the beam,one on either side.Primary Air InletOperable Face to allowaccess to the coilCoilFigure 12: Components of a typical linear active beamL-6All Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter. Copyright Price Industries Limited 2011.

Active & Passive BeamsEngineering GuideActive Beams1 Way DischargeLinear active beams with single-sided airdischarge are designed to either integrateinto standard suspended ceiling systemsor be suspended freely in an ‘exposed’application. These beams have only onedischarge air slot that runs along one sideof the beam.Primary AirPrimary AirThe general air flow of linear active beamswith 1 way air distribution in cooling andheating are seen in Figures 13 and Figure 14.Figure 15 illustrates the room air flow of atypical 1 way active beam.PRODUCT TIPLinear active beams with 1 wayair distribution are best suited forplacement along a façade or wall.In applications where 1 way beamsare used with 2 way beams, asymmetric face may be selected forthe 1 way unit to ensure a consistentappearance from the room.Room AirRoom AirFigure 13: Air flow diagram of a linearactive beam in cooling with 1 way dischargeBeamFigure 14: Air flow diagram of a linearactive beam in heating with 1 way dischargeReturnModular active beams combine fresh airventilation, hydronic heating and cooling,and four-sided air flow. They are typicallyavailable in modular sizes, 2 ft x 2 ft [600 mmx 600 mm], and 2 ft x 4 ft [600 mm x 1200mm], and are available in models eitherdesigned to integrate into standard ceilingtiles or suspend freely from the ceiling.The typical air flow pattern of a modularbeam in cooling and heating is illustratedin Figure 16 and Figure 17. Often, thesemodular beams can be customized toindividually modulate the air flow from eachside of the unit. For example, one side of theunit can be blanked off to create a modularbeam with three-sided air flow.Figure 15: Room air flow pattern of a typical linear active beam in coolingPrimary AirPrimary AirPlenumNozzlesNozzlesPRODUCT TIPActive beams are typically availablein a 2 pipe or 4 pipe configuration.Beams with 2 pipe configurationshave one supply and one returnpipe for each unit, which servesfor either/both heating and coolingpurposes. Beams with 4 pipeconfigurations have two supplyand two return pipes for each unit,comprising separate loops forcooling and heating. Copyright Price Industries Limited 2011.Room AirFigure 16: Air flow diagram of amodular beam in coolingRoom AirFigure 17: Air flow diagram of amodular beam in heatingAll Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter.L-7ENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSModular Active Beams

Active & Passive BeamsEngineering GuidePassive Beam Selection and Design ProcedureENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSThe performance of a passive beam isdependent on several factors: Water flow rate Mean water temperature andsurrounding air temperature Shroud height Free area of the air paths (internal andexternal to the beam) Location and applicationThe water flow rate in the coil affects twoperformance factors: the heat transferbetween the water and the coil, whichis dependent on whether the flow islaminar (poor) or turbulent (good); and themean water temperature, or the averagetemperature, in the coil. The higher the flowrate, the closer the discharge temperaturewill be to the inlet, thereby changing theaverage water temperature in the coil.Figure 18 shows the effect of the flowrate, indicated by Reynolds number, onthe capacity of a typical passive beam. Asindicated on the chart, increasing the flowrate into the transitional and turbulentranges (Re 2300, shaded in the graph)causes an increase in the output of thebeam.The water flow rate is largely dependenton the pressure drop and return watertemperatures that are acceptable to thedesigner. In most cases, the water flowrate should be selected to be fully turbulentunder design conditions.The difference between the mean watertemperature, t̅ w, defined as:and the surrounding (coil inlet) airtemperature is one of the primary driversof the beam performance. The larger thisdifference is, the higher the convective heattransfer potential. Conversely, a lowertemperature difference will reduce theamount of potential energy exchange, andthereby capacity. As a result, it is desirablefrom a capacity standpoint to select entrywater temperatures as low as possible,L-8Room Temperature74 F to 78 F in summer, 68 F to 72 F in winterWater Temperatures, Cooling55 F to 58 F EWT, 5 F to 8 F TDesign Sound Levels 40 NCCooling CapacityUp to 500 Btu/hftVentilation Requirement0.1 to 0.5 cfm/ft2 floor areaSIRoom Temperature23 C to 25 C in summer, 20 C to 22 C in winterWater Temperatures, Cooling13 C to 15 C EWT, 3 K to 5 K TDesign Sound Levels 40 NCCooling CapacityUp to 500 W/mVentilation Requirement0.5 to 2.5 L/s m2 floor areaTable 2: Design Values for passive beam systems10090Capacity, %Product Selection and Location –Passive 0012000Figure 18: Passive beam capacity vs. water flow120024tw - troom ,K6810100Capacity, %Passive beam systems will vary inperformance, configuration and layoutdepending on the application. There are,however, some characteristics that arecommon for most systems. Furthermore,the performance of passive beams is largelydependent on a common set of factors.This section will discuss how factorssuch as chilled water temperature affectthe performance and layout of passivebeams. Table 2 shows common designcharacteristics for passive beam systems.8060402000510tw - troom , F1520Figure 19: Passive beam capacity vs. difference between mean water and room airtemperatureAll Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter. Copyright Price Industries Limited 2011.

Active & Passive BeamsEngineering GuidePassive Beam Selection and Design Procedurewhile 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 froman equipment standpoint. This may alsooffer some control simplification where theoutput of the beam is determined by theload in the room:Figure 21 shows the increase in capacitywhen the stack height is changed from 6 in.[150 mm] to 12 in. [300 mm] vs. the differencebetween troom and t̅ w. The graph indicatesthat the increase in capacity from the largershroud reduces as the overall capacity ofthe beam increases. A practical lowerlimit where the mean water temperature is18 F [10 K] below the room temperaturetranslates to a capacity increase of 25% withthe taller stack.Because the air flow through the beam isdriven by buoyancy forces, any restrictionto the air paths will impact the performanceof the beam. Figure 22 shows the variousfactors that affect performance, including: Face design of the beam when exposed Perforated ceiling below the beam whennot exposed Gap between the beam and the slab Restrictions of the return air path whenthe ceiling is closed (either return grillesor perforated ceiling tiles) Copyright Price Industries Limited 2011.Shroud/StackFigure 20: Passive beam air flow pattern1.60.02.04.0tw - troom, K6.08.010.01.51.41.31.21.110510tw - troom, F15ENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSThe taller this stack is, the more air is drawnthrough the coil, increasing the coolingpotential of the beam. As the volume ofair is increased, the velocity of the air fallingbelow the beam is also increased. It is notuncommon to adjust the height of the stackin order to adjust the capacity and velocitiesin order to suit application requirements.CoilCapacity 12 in. [300 mm] ShroudCapacity 6 in. [150 mm] Shroud As the load increases, the air temperaturerises and increases the differencebetween it and tw, thereby increasingbeam performance. As the load decreases, the air temperaturefalls and reduces the cooling capacity ofthe beam.A passive beam uses buoyancy forces andthe “stack” effect to drive air through thecoil. The stack effect is a phenomenonthat can be used to increase the rate ofcirculation through the coil by increasingthe momentum of the falling air. As theair surrounding the coil fins decreases intemperature, it becomes more dense thanthe surrounding air, causing it to fall downinto the zone below. Figure 20 shows across section of a passive beam and how theshroud, or skirt, of the beam separates thecool air from the surrounding air, allowing itto gain momentum and draw an increasingvolume of air into the coil from above.Room Air20Figure 21: Passive beam capacity vs. temperature differenceSlab ClearanceSlab ClearanceReturn Air PathFace TypeFigure 22: Factors that affect performanceof passive beamsFigure 23: A passive beam installed abovea perforated ceilingAll Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter.L-9

Active & Passive BeamsEngineering GuidePassive Beam Selection and Design Procedure10090Capacity, %The design of the face material may restrictair falling through the face. If the beam isinstalled behind a perforated ceiling, asshown in Figure 23, the air falling belowthe beam will hit the ceiling, spread out,and fall into the zone below over a largerarea. As long as there is enough free areain the ceiling to allow the air to fall through(as well as rise through in order to feedthe beam with warm air), there should notbe a reduction in the capacity of the unit.Use of a perforated ceiling is also a goodway to reduce velocities below the beam,if required.ENGINEERING GUIDE - ACTIVE & PASSIVE BEAMSThere are other factors that affectperformance, including the application,choice of ventilation system, and location.It is possible to increase the capacity of thepassive beam through induction. If a highvelocity is located near a passive beam, itmay pull air through the coil at a higher ratethan the natural convection would alone, asindicated in Figure 25. It is also possibleto trap thermal plumes at the buildingenvelope and force this air though a passivebeam, as shown in Figure 26.The performance of the beam undernon-standard conditions, such as thosedescribed above, can be difficult to estimate.For example, the plume coming up fromthe façade may be so strong, and the inletto the plenum so narrow, that the plumecomes across the face of the beam. Thiswould disturb the air movement throughthe coil, dramatically reducing the capacityof the beam. In these instances, it is bestto conduct a building mockup or usesimulation software to understand how thevarious parameters affect each other.706050The distance between the top of the beamand the structure can reduce the air flowand capacity of the passive beam if it is toonarrow. Figure 24 shows the impact of thegap between the beam and the slab in termsof the beam width (gap/width).In most cases, a clearance of 20 to 25% ofthe 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].80400.070.090.110.13 0.15 0.17 0.19Gap / Beam Width0.210.23 0.25Figure 24: The impact on the capacity of the gap between a passive beam and buildingstructureSlot DiffuserInduced AirPassive BeamPrimary AirFigure 25: Inducing air through the passive beam with increased velocity across the faceRoom AirWindowPrimary AirCeilingFigure 26: Capturing the plume at the perimeter may increase passive beam performanceL-10All Metric dimensions ( ) are soft conversion.Imperial dimensions are converted to metric and rounded to the nearest millimeter. Cop

ENGINEERING GUIDE - ACTIVE & PASSIVE BEAMS Introduction Active & Passive Beams Engineering Guide Like radiant heating and cooling systems, active and passive beam systems use water as well as air to transport energy throughout the building. Like radiant and cooling systems, they offer savin