Consulting-Specifying Engineer - January 2009 - (Page 51) Case Study applications, but the heat energy required to regenerate the desiccant was not costeffective. The exhibit also featured both sound effects and interactive options, which caused noise control problems. Ultimately, the system would also need to deliver 20,000 cfm of conditioned outdoor air to a limited exhibit space. “An exhibit decision dropped a section of the floor just adjacent to the mechanical room that forced some redesign to get the SEMCO unit into the available space. The comfort has been ideal with no report of any noise issues,” said Bill Vanderbilt, facilities director for the museum. Primera selected a Pinnacle Primary Ventilation and Energy Recovery System from SEMCO to solve the problems. The Pinnacle’s passive dehumidification wheel uses a desiccant material that is optimized to remove moisture from a saturated airstream without an active regeneration source. The wheel also uses a cooling coil, heating coil, total energy recovery wheel, and a humidifier for wintertime operation. The Pinnacle system precools and dehumidifies outdoor air during the cooling season and preheats and humidifies the outdoor air during the heating season. The system responds to variations in temperature and humidity by modulating the rotational speed of the passive dehumidification wheel, and adjusting the energy input to the cooling coil. The rotational speed control may be adjusted to control the level of temperature and moisture exchanged by the passive dehumidification wheel. The chilled water coil is sequenced on when the space requires cooling and when the chillers are in operation, from May through October. The heating coil is used only during wintertime operation to boost the supply air temperature. The heat wheels provide approximately three-fourths of the heat required for wintertime operation. In an effort to maximize efficiency but still maintain fresh air, the system Total energy wheel Passive dehumidification wheel Heating coil -3 4.1 28 19 97 53 75 53 Return air 20,000 cfm Exhaust air 23,073 cfm Outdoor air 23,073 cfm Supply air 20,000 cfm -10 .5 Dry bulb temperature in °F 20 15 20 15 90 49 Absolute humidity in gr/lb Cooling coil (off) This peak heating diagram demonstrates how the system works during the cold months in Chicago. Source: SEMCO Total energy wheel Passive dehumidification wheel Heating coil (off) 89 89 66 70 75 53 Return air 20,000 cfm Exhaust air 23,073 cfm Outdoor air 23,073 cfm Supply air 20,000 cfm 94 94 Dry bulb temperature in °F 72 75 54 61 65 43 Absolute humidity in gr/lb Cooling coil (off) This latent-cooling diagram represents how the Primera system cools the area around the submarine during the hottest parts of the year. Source: SEMCO operates with 100% outdoor air during operating hours, if the air can be used for cooling. When outdoor weather is extreme, the system uses just enough outdoor air to maintain proper ventilation. When the museum is closed, the system operates on 50% outside air. The end result is a system that works in harmony with the museum’s central chilled water system without any of the energy penalties associated with conditioning 100% outside air in an area with diverse climate conditions. Equally important, the U-505 shows no signs of aging and should continue to educate future generations. Primera’s completed design modeling demonstrated how the SEMCO system would provide annual energy savings of more than $150K over a conventional system that uses the overcooling and reheat function. Information provided by SEMCO. Consulting-Specifying Engineer • JANUARY 2009 51
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