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Energy Recovery in Air Handlers. Delivered by: Jason Richwine 16 April 2012 Columbus, OH. Energy Recovery in Air Handlers Intro. Standards and Definitions Three Popular Technologies Wheels Plates Pipes Summary. Energy Recovery in Air Handlers Standards & Definitions.
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Energy Recovery in Air Handlers Delivered by: Jason Richwine 16 April 2012 Columbus, OH
Energy Recovery in Air HandlersIntro • Standards and Definitions • Three Popular Technologies • Wheels • Plates • Pipes • Summary
Energy Recovery in Air Handlers Standards & Definitions ASHRAE 62.1-2010 • Requires outdoor air (OA) be used for ventilation when it is not polluted • Defines amounts of OA needed for various applications • What’s the problem with ventilating?
Energy Recovery in Air Handlers Standards & Definitions ASHRAE 90.1-2010 • 90.1 defines limits for building energy consumption • ASHRAE plans to develop tools to design net-zero energy buildings (NZEB) by 2020, so NZEBs will be standard by 2030 • How can we have good ventilation and limit energy use?
Energy Recovery in Air Handlers Standards & Definitions ASHRAE 90.1-2010 • Exhaust air (EA) energy recovery is required when: • Many commercial comfort applications don’t require energy recovery (<30% OA) • Energy recovery may still make economic sense • *See Exceptions 6.5.6.1.a – 6.5.6.1.j
Energy Recovery in Air Handlers Standards & Definitions AHRI 1060 • Voluntary Standard • Defines test, rating, and minimum data requirements for published ratings, marking and nameplate data • Helps you compare performance among manufacturers • AHRI Directory provides list of manufacturers that comply • Some manufacturers choose not to participate
Energy Recovery in Air HandlersThree Popular Technologies Solution YC - YORK Custom Air Handlers
Energy Recovery in Air HandlersWheels • What Are They? • Rotating heat exchangers that transfer sensible and latent heat to precondition ventilation air • Material types • Composite (polymer, fiber) • Aluminum • Benefits • High effectiveness • Low pressure drops • Applications • Many commercial applications where isolation of airstreams is not required
Energy Recovery in Air HandlersWheels Desiccant Effectiveness 30%-35% RH is typical for winter-time non-humidified indoor air
Energy Recovery in Air HandlersWheels • Cross-contamination and Purge • Cross-contamination occurs when air leaks past separators and seals, or is carried in the wheel as it rotates from the EA to the OA • We want to limit leakage from EA to OA • A mechanical purge directs OA to the EA section to flush air out the exhaust, limiting cross-contamination • RA that entered wheel prior to the purge section has time to exit wheel on the exhaust side
Energy Recovery in Air HandlersWheels • Blow-thru SupplyBlow-thru Exhaust • Advantage • Minimal leakage when supply and exhaust pressures are similar • Precaution • Design for appropriate pressure differences to manage leakage Blow-thru SupplyDraw-thru Exhaust Advantage Minimal leakage from exhaust to supply Precaution OA can short-circuit to EA wasting fan energy Draw-thru SupplyDraw-thru Exhaust Advantage Minimal leakage when supply and exhaust pressures are similar Precaution Design for appropriate pressure differences to manage leakage Draw-thru SupplyBlow-thru Exhaust Advantage None Precaution Don’t do it. Too much EA will leak into OA.
Energy Recovery in Air HandlersWheels • Frost Control • Frost can form on wheels in the winter when warm moist return air contacts very cold wheel media • Four types of control • On/Off – least expensive and least complicated, but turns the wheel off when you most want to recover heat • Bypass – some OA bypasses wheel. This reduces wheel capacity preventing EA from reaching saturation. Requires good mixing to prevent temperature stratification. • Preheat – install heating coil in RA or OA. Heating RA decreases RA %RH to reduce frost risk, and increases temperature differences to improve wheel performance. • Variable speed control – slowing the wheel reduces heat transfer rate, requires sophisticated controls, and may not work well on certain wheels *See ASHRAE Journal March 2012 page 46 for good article on energy wheel control
Energy Recovery in Air HandlersPlate Heat Exchangers • What is a plate heat exchanger? • Fixed plate heat exchangers transfer sensible and sometimes latent heat • Cross-flow design with airstreams passing at right angles • Keeps air streams segregated under normal conditions • Construction Types • Composite (polymer) • Aluminum
Energy Recovery in Air HandlersPlate Heat Exchangers • Benefits • High transfer efficiencies • Segregated airstreams • No moving parts • No electrical connections • Applications • Commercial and industrial applications where segregation of airstreams is desired – pools, labs, processes, etc. • Do not use when EA contains dangerous contaminants
Energy Recovery in Air HandlersPlate Heat Exchangers • Configurations • Vertical or horizontal orientation • Various blow-thru and draw-thru fan combinations • Bypass arrangements
Energy Recovery in Air HandlersPlate Heat Exchangers • Configurations • Multiple Heat Exchangers • Counter-flow arrangements
Energy Recovery in Air HandlersHeat Pipes • What is a heat pipe? • Refrigerant filled heat exchangers that transfer sensible heat • Hollow cylinders/tubes filled with a refrigerant • How heat pipes work • Heat is absorbed in the evaporating section and boils the liquid refrigerant • Vapor moves to the condensing portion via convection • Heat is released from the condensing part of the pipe and vapor condenses • Liquid returns – by gravity, wick, or pump – to the evaporating section
Energy Recovery in Air HandlersHeat Pipes • Heat Pipes for Dehumidification • Two sections: pre-cooling and reheat • Warm air passes through first section and evaporates refrigerant • Refrigerant vapor moves to the condenser • Pre-cooled air passes through cooling coil which cools it and removes moisture • Over-cooled air passes through condenser and is reheated to comfortable temperature • Refrigerant condenses and flows back to evaporator • Entire process accomplished using minimal additional energy • Result is ability to remove 50% - 100% more moisture than a cooling coil alone
Energy Recovery in Air HandlersHeat Pipes • Energy Recovery of EA to SA • Side by side heat pipes • Fluid moves in a continuous one directional flow through individual three dimension circuits
Energy Recovery in Air HandlersHeat Pipes • Benefits • Phase change provides increased efficiency compared to glycol runaround • No cross-contamination of airstreams • Accommodates air streams located further apart • Applications • Commercial and industrial applications where plates are impractical • When exhaust air contains dangerous orhighly obnoxious contaminants