ASHRAE Journal - June 2009 - 44

Lessons Learned at MacDill Air Force Base • In high ceiling areas, locate HVAC devices such as VAV boxes and fan coil units in lower, more accessible and maintainable overhead locations. • Increase amount of flow and ducting of supply air out to underfloor spaces. • Determine better AHU underfloor pressure sensing and control methodologies. • Consider increased window treatments to retard solar effects. • Improve quality and quantity of commissioning from inspection and testing items. • Coordinate more specifics on protocol interoperability technologies with building automation systems and graphic front-end. • Determine and specify specific time schedules of operations, setpoints, alarm limits, and trending requirements for all HVAC&R control points. • Improve understanding of who receives BAS alarms and what is done when alarms are received. • Coordinate and identify BAS system duties, trending and alarms with respect to fire alarm and life safety. • Coordinate and specify duties of multiple PCs on site, and what software (for all integrated devices and systems) is included for operations and monitoring. • Integrate fiberoptic cabling systems with BAS requirements. • Provide more direction on the BAS on types and complexity of graphics, as well as control/monitoring points desired for display. A small noise was generated by the modulating of the floor box basket (open and close) as its motors turned its threaded shaft. The supply air temperatures of the AHUs serving the UFAD systems were approximately 52°F to 60°F (11°C to 15.5°C), as they left the AHU supply duct. But as they went into the open plenum of the underfloor spaces, within 25 ft (7 m) of the AHU mechanical equipment room, the underfloor supply plenum temperatures rose 3°F to 5°F (1°C to 3°C); and after 25 to 50 ft (7 m to 14 m), supply plenum temperatures rose 5°F to 10°F (3°C to 5°C) in some areas. This represents a 7% to 20% increase in temperature from its supply temperature value to the temperature delivered to the space, also known as a thermal decay factor. During commissioning, the AHU VFD pressure control was performed with sensing underfloor pressure relative to the mechanical room. This was approximately a 0.03 in. w.g. (7.5 Pa) (negative) difference from relative to space pressure. Many low readings of volumetric flow at the floor grilles occurred. Since the underfloor relative to the occupied space operating pressure setpoint was 0.05 in. w.g. (12.4 Pa), this 0.03 in. w.g. (7.5 Pa) difference was significant and the sensing tubes for the 44 ASHRAE Journal • Locate moisture-sensing devices underfloor in more accessible and maintainable locations. • Coordinate chiller and boiler plant equipment and layouts so that any combination of pumps, towers, chillers or boilers are interchangeable with each other’s operations. • Specify better start-up procedures for water-using equipment and water treatment processes. • Provide definite dedicated power sources (from electrical design) for BAS control devices in the underfloor areas. • Provide interconnecting disconnect status wiring and monitoring with variable frequency drive for motors. • Better identify common areas, such as corridors and open entrance areas, where nonadjustable temperature control setpoint devices (thermostats) can be designated. • Better coordinate AHU locations and clearances to structural members to avoid access interference. • Improve condensate piping installation details and routing to floor drains. • Protect critical areas of the building with DX airconditioning equipment in case of chilled water failures. • Program as many critical alarm points into the BAS and make written alarm response procedures. • Formalize and execute a comprehensive daily inspection, maintenance and operational plan as part of the occupancy process. four static pressure sensors per floor were relocated to read and control pressure relative to the underfloor and space pressure. The static pressure setpoint was decreased 20% when the average room temperatures reached their cooling and heating setpoints. Before occupancy and before plug loads were active, temperature tests were made: in the cooling mode in the four corner interior zones (open workspace architecture with partitions) and exterior zones (near windows with blinds and not in direct sunshine), and on the second and third floors to measure stratification of space temperature occurring at differing heights above the floor (the probe used has an accuracy ±0.54°F [0.3°C]). The temperature was tested at 2 ft, 5 ft, and 7 ft (0.6 m, 1.5 m, and 2.1 m) above the floor. The temperature rose as height above the floor increased. Using the 5 ft (1.5 m) mark as the baseline, readings indicated that the temperature was slightly lower below, and slightly higher above, the baseline (but not significantly different). For example, we measured the interior zones: –0.1°F to 0.3°F (0.05°C to 0.16°C) at the 2 ft (0.6m) level; plus 0.1°F to 0.3°F (0.05°C to 0.16°C) at the 7 ft (2.1 m) level. Exterior zones were –0.1°F to 0.3°F (0.05°C to 0.16°C), at the 2 ft (0.6 m) ashrae.org June 2009

ASHRAE Journal - June 2009

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