Low energy consumption hvac systems for green buildings using chilled beam technology


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Low energy consumption hvac systems for green buildings using chilled beam technology

  1. 1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME316LOW ENERGY CONSUMPTION HVAC SYSTEMS FOR GREENBUILDINGS USING CHILLED BEAM TECHNOLOGYSyed Moazzam AliTechnical Director,Taiba Engineering ConsultantsDr.Balu Naik BanothProfessor JNTUHABSTRACT:The movement toward sustainable building designs is being driven largely byenvironmentally-sensitive building owners and/or their prospective tenants. There are also heightenedconcerns about assuring a proper indoor environment at all times and conditions for the buildingoccupants. In addition to providing temperature control, a fully effective HVAC system must alsoaddress many other indoor environmental issues that affect occupant comfort, productivity and healthsuch as ventilation air, air distribution, humidity control, noise levels, etc.As these owners and their consultants weigh their HVAC system alternatives, they often findthat chilled beam systems are the ideal "green" solution for many buildings. There is also a persuasiveoverall comfort and economic argument for the use of active chilled beam systems over other of themore conventional systems choices. While relatively new in India, chilled beam systems are provenand are successfully being used in Europe since a decade.The chilled beam system promotes excellent thermal comfort, energy conservation and efficient useof space due to the high heat capacity of water used as heat transfer medium. It is an energy efficientHVAC technology which works on dry cooling principle.Chilled beams system would be examined which would show energy conservation and haspotential to save 30-40% HVAC energy consumption to a conventional Air conditioned Buildingcase. The simulation results would be encouraging, and they would confirm the advantage of theapplication of these Chilled beams system cooling strategies.1.0 INTRODUCTIONChilled beam systems are used mostly in the nonresidential buildings. These are commercialbuildings, offices, hotels, banks, universities, schools and hospitals. Typical applications are cellularand open plans offices, hotel rooms, hospital wards, retail shops, bank halls etcChilled beam systems are primarily used for cooling, heating and ventilating spaces, wheregood indoor environmental quality and individual space control are appreciated. These systems areINTERNATIONAL JOURNAL OF ADVANCED RESEARCH INENGINEERING AND TECHNOLOGY (IJARET)ISSN 0976 - 6480 (Print)ISSN 0976 - 6499 (Online)Volume 4, Issue 3, April 2013, pp. 316-324© IAEME: www.iaeme.com/ijaret.aspJournal Impact Factor (2013): 5.8376 (Calculated by GISI)www.jifactor.comIJARET© I A E M E
  2. 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME317dedicated outdoor air systems meant to be applied primarily in spaces where internal humidity loadsare moderate.2.0 OVERVIEW OF CHILLED BEAMS“A cooled element or cooling coil situated in, above or under a ceiling which coolsconvectively using natural or induced air flows. The cooling medium is usually water.”There are two basic types of chilled beams: active and passive.2.1 Active chilled beams (ACB) uses a pre-cooled (and dehumidified) primary air using chilled waterin a quantity needed to meet the room latent load and ensure good air quality for the occupied area.The cooled and dehumidified primary air absorbs the space latent load; ensuring the chilled beam coiloperating without condensation. The chilled beam then cools or heats the induced air to meet the roomsensible load and react to the room thermostat requirements.Active chilled beams operate using the induction process. During induction, the primary airdischarges under pressure through nozzles located within the device. This high velocity incomingprimary air creates a negative pressure in the inlet portion of the beam thereby inducing room airthrough the beam coil where it mixes with the cold primary air. This mixed air is then dischargedthrough the outlet slot of the beam into the room, resulting in a total airflow quantity 3 to 4 timesgreater than the primary airflow. We refer to this ratio of total air to primary air as the induction ratio.“A convector with integrated air supply where primary air, induced air or primary air plusinduced air passing through the cooling coils. The cooling medium in the coil is water.”2.2 Passive chilled beams (PCB) work using natural convection. Air cooled by the coil inside thebeam becomes denser than the surrounding room air and therefore flows downward into the room.The difference in density combined with the height of the beam induces room air down through thebeam coil. Thus passive beams mainly provide a downward airflow in the room. This downward flowinduces air from the room upward to the ceiling level and then through the beam coil. Unlike an activechilled beam, the passive chilled beam delivers treated primary ventilation air directly to the spaceand not through the chilled beam. Nevertheless, like the active chilled beam, this ventilation air mustbe sufficiently dehumidified to meet the entire latent room load. To avoid drafts in spaces with lowceilings do not locate passive beams above workstations with sedentary occupants. Both remixing anddisplacement terminal devices provide good comfort in the room in combination with passive beams.“The cooled element or cooling coil fixed in, above or under a ceiling fitted with a coolingcoil mainly convectively using natural airflows. The cooling medium is usually water” Chilled Beamsoffer a quiet indoor air free from draught. In a typical Chilled beam, the air is cooled by means ofsupplying chilled water and the supply of air flow rate is dimensioned to meet the indoor air qualityrequirements.2.3 Advantages of chilled beam systems over conventional designsChilled beam systems are suitable for use in high sensible cooling load applications or whereindividual temperature control is required. Compared with a system where the cooling duty issupplied entirely by air (all-air systems), a chilled beam system reduces the fan power requirementsand space needed for air- handling plant equipment and ducting.TABLE - 1S.No SYSTEM Energy Noise Output (w/m²)1 FCU (Fan Coil Unit) Medium / High Medium 100-2002 VAV (Variable Air Volume) Low/Medium Low/Medium 100-2003 VRF (Variable Refrigerant Volume) Medium / High Medium 150-2004 Chilled Beam Low Low 100-300
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME3182.4 Chilled beam systems have the following advantages:Fan Energy Savings: In general the design intent is for the central system to circulate only theamount of air needed for ventilation and latent load purposes, with the active chilled beams providingthe additional air movement and sensible cooling and/or heating required through the induced roomair and secondary water coil. In this manner the amount of primary air circulated by the central systemis dramatically reduced (often 60-70% less than conventional "all air" systems).Essentially active chilled beams transfer a large portion of the cooling and heating loads from the lessefficient air distribution system (fans and ductwork) to the more efficient water distribution system(pumps and piping).The net result of this shift in loads with active chilled beam systems is lower energyconsumption and operating costs. Fans are the largest consumer of energy in most commercialbuildings. With active chilled beam systems the fan energy is dramatically reduced due to therelatively small amount and low pressure of the primary air being circulated by the central system.Chiller Energy Savings: While the size of the chiller in an active chilled beam system wouldnormally be the same as that needed in a conventional "all air" system, its effective hours of operation(or loading) could be significantly less if the system employs a water-side economizer to serve theActive Chilled Beams. This is due to the relatively warmer secondary water temperatures (typically56 — 58 °F) used by the Active Chilled Beams which allows the cooling load to be satisfied for morehours using the water-side economizer.Also, if separate chillers are serving the central air handlers and the active chilled beams, theCOP of the chiller serving the Active Chilled Beams would also be much higher due to the relativelywarmer water temperatures used by the Active Chilled Beams.Heating Energy Savings: As the Active Chilled Beams normally provide sufficient heatingcapacities at relatively moderate hot water temperatures (110 – 130 °F) there is also an opportunity tomaximize the efficiency of condensing boilers through the relatively low water temperatures beingreturned to the boilers. With the relatively low water temperatures required, using geothermal heatpumps to satisfy the heating loads is also practical.Excellent Indoor Air Quality and Odour ControlThe full ventilation air requirements are delivered to the zones at all times and at all loadconditions.Superior Humidity Control: Humidity control at all sensible load conditions are also assured as theconstant volume primary air is delivered with the proper moisture content to satisfy the latent loads.Excellent Air Movement and Uniform Air Temperatures: Improved comfort through excellent airmovement and uniform air temperatures throughout the room, with little concern about potentialdrafts and dumping at part load conditions. As the airflow and resulting air movement is constant atall load conditions and the induced room air is typically 3-4 times the amount of primary air, thetemperature of the mixed air being continuously discharged into the room is generally more moderatethan with conventional systems.Other factors positively affecting the overall building costs when using active chilled beamsystems include:There are no electrical line power connections to the active chilled beams which cansignificantly reduce electrical wiring installation costs. In some cases this can result in reducing theoverall electrical infrastructure in the building due to greatly reduced fan power requirements.
  4. 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME319Very Low Noise Levelsa) Decouples ventilation load from room sensible + latent loads resulting in better temperaturecontrol and fan energy savings.b) Typical supply air temperature is 64-66 °F exiting the chilled beam maximizing occupantcomfort. Conventional systems deliver cold air at 55 °F with the potential of creating drafts ifpoor mixing occursc) Reduced plenum space required (units are ~12” tall), good for retrofit applicationsd) Some units incorporate fluorescent lighting fixtures and fire sprinkler heads.e) Some units offer directional air flow pattern control, optimizing comfort and preventing draftsf) Water moves energy through the building and is much more effective than air approximately600 x heat transfer capacity (6oF vs 20oF ∆T), But Still little quantity of ventilation air isneeded.g) Chilled beams provide benefits in life cycle costs: Low maintenance cost, Good energyefficiency.h) Free cooling possible in cold and temperate climatei) Chilled beams system is a hygienic systemj) No filters to be changed or cleaning of drain pans for condensatek) Easy cleaning of coils and surfaces, only once in every 5 yearsl) Chilled beams operate with a dry cooling coilm) No condensate collection systemn) Primary air should be dehumidified in the air handling unit2.5 Increased energy efficiency:Water-based systems transfer energy more efficiently than air-based systems. Bytransferring the heating and/or cooling load to water based system, energy requirements andoperational costs may be significantly reduced.Reduced mechanical footprint: Water distribution systems are a fraction of the size of airdistribution systems, reducing the ceiling space needed for the HVAC system and increasing availablefloor space.Lower maintenance costs: These systems are simple and efficient, with Low maintenance costs.Increased thermal comfort: These systems are very quiet and require significantly reduced airvolumes, leading to a reduced risk of drafts.Improved indoor air quality: These systems do not require air to be recirculated throughout thebuilding to achieve heating or cooling, and are typically coupled with 100% outside air systemsLow energy consumption (passive beams in particular)Superior Comfort & Performance (passive beams in particular)Quiet, draft-free and thermally stable environmentPart-radiation, part-convection heat transfer is more comfortable than all convection air systemSelf-adaptable output, Resistant to tampering and de-commissioningHealthOnce-through, no-recycling air system, No ‘sick-building-syndrome’, Humidity controlBuilding design efficiencySmall plant rooms and risers, Small ceiling spaceWhen the active chilled beams are sized at the typical inlet static pressures of 0.5" w.c. or less, verylow noise levels are achieved as the new technology nozzles are whisper quiet and there is no terminalunit fan or motor in or near the occupied spaces.
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME320Chilled Beam system typical Design considerations for the chilled water and primary aira) Assume spaces with normal ceiling heights (9-10 ft), apply chilled beams in with coolingloads of 25-30 Btu/ft² of floor area. This capacity limitation is primarily due to the maximumpossible air velocity in the space. Cooling Capacity to avoid draughts in the occupied zone:Active chilled beams is typically 250 W/m (max 350 w/m), Passive chilled beams is 150 W/m(max250w/m), Cooling demand in the space typically less than 80W/floor-Sq.m (Max 120W/floor-Sq.m) and Heating demand less than 40 W/floor-m2.b) Chilled beams uses warmer chilled water from the secondary side of the cooling plant (orfrom mixing of primary and secondary water) at an inlet temperature from 57-61 °F toprevent condensation from occurring on the beam coil. This equates to a primary supply airtemperature of approximately 65 °F.c) Special humidity (condensation) sensors should be installed on the chilled beam coil thatclose the water control valve if the RH gets to 90% on the incoming chilled water pipe.Alternatively, use an atmospheric RH sensor in combination with an air temperature sensor toreset the supply water temperature upward closer to 60 °F during conditions whencondensation might occur.d) It is important for the DOAS system to adequately dehumidify the primary ventilation airsuch that it can absorb all of the latent loads in the zone. The DOAS leaving air temperature(LAT) should be in the 44-55 °F dry bulb range with approximately 44-45 °F dew point (DP)to ensure there is no condensation on the beam coil. The lower end of the ranges should beused when the zone latent loads are higher, such as conference rooms, school classrooms, etc.while the higher end of the range may be used in applications with low zone latent loads.e) Chilled beams offer a simple design process with superior final efficiency. Designing withchilled beams is very similar to conventional system design. Chilled beams available in theU.S. generally have a 3:1 induction (room air to ventilation, or primary, air) ratio, are capableof 100 to 200 CFM of primary air per 6 ft of beam, and provide from 4,000 Btuh to 8,000Btuh of sensible cooling per 6 ft of beam. Airflow, cooling, and sound performance varyconsiderably by manufacturer.f) Chilled beams should be installed and placed correctly in the space. In general the ChilledBeam Width ranges from 0.3m to 0.6m, and lengths range from 0.6m to 3.0m.g) Active Chilled Beams recirculate room air through a unit-mounted coil, driven by ventilationair (primary air) with mixing ratios as high as 6:1 (discharge air to primary air). They haverelatively shallow depth with clearance requirements generally less than 0.3m.Figure 1 – Positioning of Chilled Beams2.7 Problems with Chilled Beam Air ConditioningActive chilled beams should not be considered a silver bullet in terms of addressing highsensible cooling requirements in all spaces. Certain spaces are well suited to chilled beam use, andothers are not appropriate for this technology.
  6. 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME321Areas that may not be suitable for active chilled beams may include, but are not limited to:Large vestibules/atriums, latent load is difficult to control and could be addressed via other designstrategies, High latent cooling requirements: kitchens, pools, locker •rooms, spas, gymnasiums, etc.Cost: Slightly higher than conventional VAV system, mainly due to novelty factorLimited experience: Risk factor and potential litigationsVested interests: Contractors protecting investment in sheet metal shops, Consultants not rewardedfor additional engineering and development.Technical: Duct leakage: unsuitable technologies cannot air-condition glasshouse with chilled beams:need efficient building envelopes, Noise from valves, Creative energy absorbed in energy modellingand ticking off rating system charts.3.0 Design procedure:Selection of thermal environment load: Room air temperature (summer/winter)Selection of the indoor air quality level and air flow rate: Fresh air flow temperature, Infiltrationthrough walls –pressure, temperature, Relative humidity in the space, Primary air cooling coiltemperature, Humidity balanceCalculation of required cooling and heating capacity: Heat loads, Heat losses, Comfort conditions,cooling effect of primary airAdjustment of building design parameters: Decrease electrical load losses by better solar shadingand improved window typeSelection of chilled beam type: Active beam (exposed/integrated), Passive beamSelection of inlet water temperature: Temperature climate, Location of the buildingSelection of water temperature and air water flow rate: Temperature difference, Water flow rateSelection of water temperature and air water flow rate: Specific cooling capacity of beam,Specific primary air flow rateNoise level and system pressure loss calculation: Selection of room controls, Rom air temperatureis controlled by modeling water flow rate, two port valves, and Air flow rateAir and water distribution system: Dehumidification of AHU, 3 port mixing valves in cooling pipeto keep the inlet water temperature in design value, Free cooling equipment’s in chiller3.1 Duct Design and Working Static PressuresIt is generally preferable to consider a low-velocity downstream ducting strategy. The mainducts may be sized as they would normally for offices at 1,200 fpm to 2,400 fpm (6 m/s to 12 m/s).Active chilled beam projects often are installed using round spiral downstream ducting. A good ruleof thumb would be to restrict the branch ducting to less than 600 fpm (3 m/s).Typical operating static pressures range from 0.3 in. w.c. to 1.2 in. w.c. (75 Pa to 300 Pa) atthe pressurization plenum of the beam.At 1 in. w.c. (250 Pa), the acoustic signature of a single active chilled beam in a typical roomcould be as low as 29.5 Dba. Supercharging beam applications by considering working staticpressures between 0.75 in. w.c. to 1 in. w.c. (185 Pa to 250 Pa) is fundamentally a sound approachfrom an optimization perspective in terms of first costs3.2 Beam Placement and Room Air DistributionAverage room air velocity is 30 fpm [0.15m/s]. Air discharge temperature from ACBs rangebetween 64°F to 66°F (18°C to 19°C).3.3 InstallationOperating weight is approximately 15 lb/ft (6.8 kg/m) for 2 ft (600 mm) wide, doubledeflection units. Hanging a beam from the structure is through four adjustable hanging brackets thatcan be fastened to the concrete under floor via threaded rod or aircraft cable.
  7. 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME3223.4 Water-Side ControlChilled water temperatures for ACB loops range between 55°F to 61°F (12.7°C to 16.1°C)although the space design conditions and the minimum ventilation rates dictate that the beams receive59°F to 61°F (15°C to 16.1°C) The separation between the secondary chilled water supplytemperature, and both the dew point of the primary air and dew-point design of the space, is thetechnique used to prevent condensation on the beam-mounted cooling coil3.5 Air-Side ControlDischarge air from the DOAS is used to dehumidify the space. It is often quite common toservice the makeup air unit with 45°F (7.2°C) chilled water. As such, 51°F to 52°F (10.6°C to 11.1°C)dew-point temperatures supplied to the occupied zone are relatively easy to achieve in many areas ofthe country by slightly oversizing the evaporator coils. Coil face velocities less than 400 fpm (2 m/s)increases the coil residence time and lowers the overall fan static pressure to further decrease systemoperating costs. Duct discharge temperature of 54°F to 55°F (12.2°C to 12.7°C).4.0 CASE STUDY ON MODELLING CHILLED BEAM SYSTEM IN HAPLOCATION: HYDERABAD, ANDHRA PRADESH, INDIA.CLIMATE: Tropical ClimateTemperature: 106 °F, Humidity: 80%, Latitude: 17.5°, Longitude: 78.5°Summer Dry Bulb 106 °F,Summer Wet Bulb 78 °F,Winter Dry Bulb 55 °F,Summer Daily Range 14 °FRoom design set point of 75 °F/50% RH (~ 55 °F DP)Cooling coil LAT 55 °F.4.1 Design Considerations:Primary air from DOAS unit enters beam @ 44-55 °FResulting supply air to room @ 64-66 °FChilled beam system is a 4-pipe cooling & heating system with cooling and heating provided in thebeam.Terminal Units are selected as the Equipment Type and 4-pipe Fan Coil as the System Type."Common Ventilation System" is HAPs term for the DOAS unit.The chilled water plant for chilled beam systems needs to operate at two supply watertemperatures. The DOAS needs to receive cold water at a supply temperature like 44 °F in order tocondense sufficient moisture out of the outdoor air stream to handle the space latent load.Figure 2 Active Chilled Beam for the case study. Drawing is prepared using RevitMEP
  8. 8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME323Figure 3 Active Chilled Beam – Isometric Layout for the case study. Drawing is prepared usingRevitMEPFloor Areas and Window-to-Wall RatiosProposedDesign BaselineTotal Conditioned Floor Area(ft²)1,485 1,485Total Floor Area (ft²) 1,485 1,485Window to Wall Ratio 6 % 6 %Gross Wall Area (ft²) 1,919 1,919Vertical Window Area (ft²) 118 118Performance Rating Table - Performance Rating Method ComplianceEnd UseProcessBaselineBuildingUnitsBaselineBuildingResultsProposedDesignEnergyTypeProposedDesign UnitsProposedBuildingResultsPercentSavingsSpace Heating No Energy kWh 98,127 Electric Energy kWh 8,363 91 %Demand kW 11.7 Demand kW 1.0 92 %Space Cooling No Energy kWh 50,115 Electric Energy kWh 33,661 33 %Demand kW 8.5 Demand kW 6.7 22 %Pumps No Energy kWh 7,768 Electric Energy kWh 8545 -10 %Demand kW 1.0 Demand kW 1.1 -10 %Heat Rejection No Energy kWh 13,719 Electric Energy kWh 10,742 22 %Demand kW 1.6 Demand kW 1.2 22 %Energy TotalsBaseline TotalEnergy Use (kBTU)654,558Proposed Total EnergyUse (kBTU)276,919 58 %Baseline AnnualProcess Energy(kBTU)34,926Proposed AnnualProcess Energy (kBTU)34,926 0 %
  9. 9. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME324Energy Cost and Consumption by Energy Type - Performance Rating Method ComplianceProposed Design Baseline DesignEnergy Type Energy Use Energy UseElectric 80,933 kWh 191,840 kWhSubtotal (ModelOutputs)276,919 kBTU 654,558 kBTUEnergy UseNet Proposed DesignTotal276,919 kBTUPercent Savings Energy Use IntensityEnergyProposedDesign(kBTU/ft²)BaselineDesign(kBTU/ft²)Summary Data 57.7 % 186.47 440.66CONCLUSION:In conclusion, chilled beams are becoming more popular. They provide many operational anddesign advantages, as discussed. By decoupling the ventilation loads from the zone sensible and latentloads, the terminals are designed to handle lower total airflow quantities, thereby using smallerequipment while resulting in uniform air distribution, high air-change rates and uniform temperaturesin the zone with fewer drafts. It is important to account for the zone latent loads in designconsiderations and to ensure proper sizing of the DOAS including the ventilation air loads plus thezone latent loads, while the chilled beams are sized to handle the zone sensible loads only.Although they are not the solution for every space within commercial and institutionalbuildings, the strengths of active chilled beams are becoming a more useful tool to handle challengingspaces in today’s high performance buildings.REFERENCES1) Design Considerations for Active Chilled Beams. By Darren Alexander,P.Eng. And MikeO’RourkeASHRAE Journal, September 20082) REHVA Guidebook No 5, Chilled Beam Application Guidebook Maija Virta (ed.), David Butler,Jonas Gräslund, Jaap Hogeling, Erik Lund Kristiansen, Mika Reinikainen, Gunnar Svensson.3) Sevcon Price Chilled Beam. PTP (Price Training Programs). Hydronic Heating/Cooling Systems4) Engineered Systems January 2011 , (Page 30 ~36) Practical Implementation Of Chilled Beams ForOffices. BY PETER RUMSEY, P.E., FASHRAE, AND JOHN WEALE, P.E., LEED® AP5) Chilled Beams for User Wellbeing and Sustainable Buildings. Halton6) Chilled Beam systems as a new HVAC possibility By, Muzaffar Ali and Vishal Chauhan7) http://www.activechilledbeam.com.8) P.S.Joanna, Jessy Rooby, Angeline Prabhavathy, R.Preetha and C.Sivathanu Pillai, “Behaviour OfReinforced Concrete Beams With 50 Percentage Fly Ash” International Journal Of Civil Engineering& Technology (IJCIET) Volume 4, Issue 2,2013, Issn Print : 0976 – 6308, Issn Online : 0976 - 6316