technical feature Figure 3A Summer. Recovery with dual wheels/air-handling system: neutral air. Lab Exhaust (45,000 cfm) 3°F Increase from Friction & Duct Heat Gain (62/57.5°F) Neutral Air H 65°F C Typical VAV Box Supplemental Cooling CB (Provides Minimal Reheat FCU As Required) MEP Spaces * Wheel Enthalpy Wheel Room Supply (75,000 cfm) (65°F – 75°F) Wheel 57°F/47°F Sensible Wheel Room Exhaust (30,000 cfm) (40%) 55°F/54.5°F 79°F/69°F 23.5 Btu/lb 33.5 Btu/lb AHU/ ERU 75°/62.5°F 28.4 Btu/lb Hazardous Exhaust C C General Exhaust (90°F) Off P C 43°F Outside Air 92°F/76°F (39.5 Btu/lb) Three-Way Diverting Valve (typ) 58°F Chiller CT HX energy recovery effectiveness at enthalpy Wheel 39.5 Btu/lb — 33.5 Btu/lb = 54% 39.5 Btu/lb — 28.4 Btu/lb Water Economizer for Shoulder Season *80,250 cfm with additional purge due to two wheels vs. one in traditional design. Figure 3B Winter. Recovery with dual wheel/air-handling system: neutral air. Lab Exhaust (45,000 cfm) Hazardous Exhaust P/C Provides Preheat as Required And Frost Protection for Wheel 3°F Increase from Friction 55°F & Duct Heat Gain 58°F C Supplemental Cooling Typical VAV Box CB (Provides Final Heating FCU As Required) MEP Spaces Off 55°F C 50°F 60°F (40°F — 20°F) (Wheel) + (55°F — 40°F) (C/C) =50% 70°F Room — 0°F Outside Air General Exhaust (21°F) 20°F P 0°F C Two Recovery Devices Operating CT energy recovery effectiveness C 40°F Wheel Enthalpy H 70°F Wheel Sensible Room Supply (75,000 cfm) (58°F – 70°F AHU/ERU (70°F) Room Exhaust (30,000 cfm) (40%) Outside Air 0°F Three-Way Diverting Valve (typ) Chiller HX Modified recovery efficiency (40°F — 20°F) (Wheel) + (55°F — 40°F) (C/C) =50% 70°F Supply — 0°F Outside Air Chilled Water Coil Recovery Mode (1,200 MBH) Examples www.info.hotims.com/44636-19 24 ASHRAE JouRnAl ashrae.org The first energy recovery method using wheels is illustrated in Figure 1. As seen in this figure, hazardous Septem ber 2013 Water Economizer for Shoulder Season exhaust is handled with a separate system with fans located on the roof of the building. In this example the hazardous exhaust from each