desiccant dehumidification wheel desiccant dehumidification wheel

DESICCANT DEHUMIDIFICATION WHEEL

NovelAire TechnologiesDesiccant Dehumidification WheelDesiccant DehumidificationThe NovelAire Technologies Desiccant Dehumidification Wheelis designed to provide maximum moisture removal with a minimumpressure drop for those applications where humidity controlis required. A desiccant dehumidification wheel provides theHVAC system designer another tool to control humidity effectivelyand efficiently particularly in the low humidity ranges.NovelAire Technologies offers a complete line of both high performancesilica gel (WSG) and molecular sieve (LT3) desiccantwheels to meet all outlet humidity requirements.➣➣➣➣➣Improved indoor air qualityPrecise humidity controlBoth silica gel (WSG) and molecular sieve(LT3) desiccantwheels availableUtilizes all types of regeneration energyVery low dewpoints achievableDesiccant CoolingThe availability of waste heat from distributed generation projectsalong with the increased ventilation standards for improvedIAQ, is revitalizing the desiccant cooling industry. With wasteheat, desiccant cooling systems become extremely efficient whileproviding the additional benefit of independent temperature andhumidity control.The ASHRAE Standard 62-1989 (Ventilation for AcceptableIndoor Air Quality), describes a recommended target ratio ofmakeup air to return air for a variety of applications and buildingtypes. Building codes in the U.S. and abroad are becomingincreasingly more comprehensive in addressing ventilationrequirements. NovelAire’s line of actively regenerated desiccantwheels combined with sensible only wheels, heat pipes, DXcoils, and/or indirect evaporative cooling provide the designengineer with many options to deal with the high latent loadsassociated with increased ventilation requirements.The NovelAire desiccant wheels are used extensively in the wellknownindustrial markets for corrosion protection and humiditycontrol for many industrial processes. Commercial applicationsinclude refrigerated warehouses, ice rinks, schools, supermarketsand hospitals. A residential and light commercial market isdeveloping where small gas fired or hot water regenerated desiccantequipment is used for centralized humidity control. Theability to control home humidity in the 50% RH range improvescomfort, saves energy with higher set point temperatures, andprevents the formation of mold and mildew--a potential problemthat is of increasing importance to the homeowner.FRESH AIR95°F / 118 gr/lbEXHAUST AIROUTDOOR AIR95°F / 118 gr/lbSUPPLY AIR91°F / 60 gr/lbA typical twin wheel system: a desiccantwheel for dehumidification, and a sensiblewheel for heat exchange.

Desiccant TypesNovelAire offers both a high performance Silica Gel (WSG) desiccantand specialty Molecular Sieve (LT3) desiccant to meet thedehumidification needs of most applications. The differences inthe desiccant properties are more clearly defined by their respectivestatic adsorption isotherm curves, a measure of the desiccant’sability to adsorb moisture under constant static conditions.The isotherm curve for the WSG desiccant is more linear andrises to a high capacity at higher relative humidity. Conversely,the LT3 curve exhibits high desiccant capacities at lower relativehumidity and flattens out as %RH increases. Therefore, theWSG desiccant wheels are recommended when the inlet %RH ishigh (>60%) and the primary goal is the removal of the largestquantity of moisture with the most efficient use of the heat input.If the inlet %RH is low (60%) and whenefficient removal of moisture is required.LT3 wheels preferred with low inlet %RH ( 75%.➣➣➣➣Tough, non-brittle media- resists damage.Wheel is completely water washable.High temperature resistant media for use with regenerationtemperatures up to 350°F.Used with direct or indirect fired gas, electric heat, steam,and hot water regeneration.Cassettes➣➣➣➣➣Heavy duty galvanized steel construction with removableside panels.Wheels are center supported, using a fixed shaft and internalmaintenance-free bearings on smaller cassettes. Largercassettes use a rotating shaft with external pillow block orflanged bearings.NovelAire’s unique adjustable, full contact silicon bulb sealdesign prevents air leakage for differential pressures of up to8" wc.Drive system includes a heavy duty gear motor with chaindrive and tensioner that eliminates wheel slippage.Cassette orientation available in a 75/25 or a 50/50 split.Note: Detailed wheel and cassette specifications, as well assoftware selection programs, are available for downloadat www.novelaire.com

Design Considerations and Control StrategiesControl of moisture levels in spaces or process air streams isgenerally accomplished by either regulating reactivation heator bypassing a portion of the air around the dehumidificationwheel. The response time, energy efficiency, and dewpointbandwidth determine what level of control is required. Thedegree of control varies from the simplest form of on/offcontrol to maintain a space condition, to the most comprehensivewhich would include wheel bypass dampers (andperhaps face dampers) plus reactivation heat modulated tocontrol an exit exhaust air temperature.Humidity sensors vary in type, principle of operation, accuracy,and precision, and need to be chosen to suit the controlrequirements. Placement of sensors in well-mixed airstreams is critical to performance monitoring.Reactivation heaters should be equipped with suitable safetydevices and interlocks to prevent overheating the wheel.The maximum operating temperature is 350°F. Separatehigh temperature cutouts should be provided if this temperaturecould be exceeded during operation. Reactivation airflowshould be maintained and proven anytime reactivationheat is energized.Software Selection ProgramFor a more comprehensive analysis of performance, NovelAire offers a model selection software program available fordownload at www.novelaire.com. The program models the performance of a wide array of input parameters to ensure theproper selection of desiccant wheel size and type.NovelAire Desiccant Wheel Simulation Software

Wheel PerformanceNovelAire desiccant wheels are designed to operate witheither a 25% area for reactivation and 75% area for process(25/75 split), or with 50% area for reactivation and 50% forprocess (50/50 split). Generally, the 25/75 split is used forindustrial dehumidification, low dewpoint and compact desiccantcooling applications. The 50/50 split is more often usedfor commercial cooling applications, or application where lowtemperature waste heat is available for reactivation.NovelAire desiccant wheels are designed to be reactivatedwith either electric resistance, (indirect) steam, (indirect) hotwater, or direct (or indirect) fired natural (or propane) gas.Additionally, solar or waste heat sources may be utilized.NovelAire desiccant wheels are designed for regenerationtemperatures up to a maximum temperature of 350°F.In addition to the regeneration temperature and cassette zoning,several other factors influence the performance of thedesiccant wheel. Process and regeneration inlet humidityand temperature, regeneration to process flow ratio, facevelocity, and wheel rotational speed all has an impact onperformance. The following curves show the relationshipbetween some of these parameters on performance for theWSG desiccant wheel.600 sfpm, Regen Ratio = 0.33, Tr=284F120160WSG WheelPerformance600 sfpmR/P ratio .33Tr= 284°FOutlet Moisture, gr/lb100806040200140120100806040Outlet Temperature,FGrains Out, 95 FGrains Out, 75 FGrains Out, 55 FTout, 95 FTout, 75 FTout, 55 F0 50 100 150 200Inlet Moisture, gr/lb400 sfpm, Regen Ratio = 1.0, Tr=190F120160WSG WheelPerformance400 sfpmR/P ratio 1.0Tr= 190°FOutlet Moisture, gr/lb100806040201401201008060Outlet Temperature FGrains Out, 95 FGrains Out, 75 FGrains Out, 55 FTout, 95 FTout, 75 FTout, 55 F0400 50 100 150 200Inlet Moisture, gr/lb

Engineering DetailWSGLT3NovelAireModel No.High Performance Silica Gel DesiccantMolecular Sieve DesiccantFlowRate(scfm)75/25FlowRate(scfm)50/50WheelDiameter(mm)WheelDepth(mm)CassetteHeight/WidthA(inches)CassetteDepthB(inches)Approx.Total Wt.(pounds)DriveMotor(Hp)2502001502502002111.5901/8037050035037020024121101/8044070050044020026121201/80550100075055020029121501/807702000150077020036122201/809653500250096520043132901/80107045003000107020048133301/80122060004000122020054134101/40152585006000152520069147901/40173011000750017302007715.510201/61940140001000019402008515.513701/6219018000125002190200961717301/62438225001600024382001061720001/627432800020000274320012218.2527401/630503500025000305020013418.2533901/6Note: NovelAire desiccant wheels are offered in a standard depth of 200 mm. Optional 50mm, 100mm, 150mm and400mm depths are available in some sizes. Please consult the factory for depth options and dimensional tolerances.The information contained in this brochure is believed to beaccurate by NovelAire Technologies, but is not warranted.10132 Mammoth AvenueBaton Rouge, LA 70814-4420Phone: (800) 762-1320 or(225) 924-0427Fax: (225) 930-0340Website: www.novelaire.comRevision 2/1/04