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rooms in service, the team is able to keep the hospital fully functional during the replacement process. Space constraints — particularly the size of the opening necessary to bring units into the building — are often a significant challenge. Other important space considerations are the necessity for access space in and around the units for maintenance and service, as well as clearances for control valve access, access doors, electrical panels and coil pulls. Weight limits are also an issue, with some units requiring alteration to weigh less than the 5,000-pound limit imposed by a tower crane and others requiring a 550-ton crane. Although a variety of AHU systems can be used, the project team has found that Fanwall Technology — designed using multiple high-efficiency fan arrays — provides a variety of benefits in a rapid replacement scenario: > The modular units fit through most standard-width doorways and are more easily moved and manipulated into tight spaces. > The unit is smaller than similar capacity conventional units. Its efficiency allows for increasing capacity to provide more comfort air when replacing units in multipleunit configurations. > The unit size allows for greater capacity and redundancy in a smaller space. To ensure uninterrupted service, the fans are set up as N+1, providing a redundant fan in the rare occurrence of a fan failure. The ease of maintenance inherent An internal compartment of an air-handling unit featuring Fanwall Technology array on the right and a bank of filters on the left. New unit being placed in a tight space with minimal overhead clearance. in the Fanwall design allows a maintenance person using standard tools to quickly and efficiently replace a nonfunctional fan. In addition, the systems can operate at a higher airflow rate and static pressure with a reduction in fan horsepower, resulting in lower operating costs. Noise and vibration levels are also substantially reduced, creating a safer and more comfortable maintenance environment. Of the 12 AHU replacements completed to date using this method at Moses Cone Hospital, the longest took 48 hours and the shortest 36 hours. The hospital remained fully functional with patient, visitor and staff comfort maintained throughout the process. Scott Duckworth has more than 20 years of experience in the construction industry. As vice president and division manager of Brasfield & Gorrie, he is responsible for the overall operations of the firm's Raleigh, N.C. office. 58 Medical Construction & Design | January/February 2013 www.mcdmag.com