TAB Journal Spring 2014 - (Page 11)

Environmental Considerations of the Southwest Michael Ziegler, TBE, TAB Technology, Inc. T he Southwestern United States is not as dry as people may believe. In the wintertime, dew points range from less than 10°F to 50°F. In the summertime the region is subject to summer monsoons, with dew points from 50°F to 70°F plus. Moisture comes from the south courtesy of the Bermuda High pressure that is over the mid-north Atlantic Ocean. This Bermuda High is what ushers the weather that causes hurricanes from the west coast of Africa to the Caribbean, the southeastern United States, and across the Gulf of Mexico. It's the moisture from Mexico that gives the Desert Southwest its summer weather dew points. Out-of-state design professionals will design to a 30-day dew point average, meaning that 15 days are below the average, with 15 days above. It's these 15 days above the 30-day average where troubles can arise. The following are some examples of issues that have been encountered from this lack of familiarity with regional weather patterns. CASE STUDY The director of the hospital's physical plant department called in technicians to troubleshoot the cooling issues with the air handler. Tests conducted included traversing the unit for airflow, taking dry bulb and wet bulb temperatures of the air entering and leaving the cooling coil, measuring cooling coil pressure drops for water flow determination and obtaining chilled water temperatures. The unit was delivering the proper airflow and the BTU transfers of the air to the water were essentially the same. Upon plotting the data on a psychrometric chart, all points were above the design engineer's scheduled data. When the engineer's data was also plotted on the psychrometric chart, it was observed that the cooling was a straight line with no latent cooling taken into TAB Journal Spring 2014 account. The horizontal cooling line followed a dew point that was well below the actual dew points that we were experiencing during the summer, by about 15°F. After reviewing the data, a report was issued and a larger cooling coil that would fit the actual characteristics for summer weather patterns in the Southwestern region was recommended. The hospital contacted a local design professional who agreed with the recommendations and the coil was installed. Fortunately, the piping to the air handler was large enough to handle the approximately 30% increase in required water flow. Two days after the work and testing of the coil performance was completed, the director of the physical plant department reported that the tower was finally under control. 2 There was a nationally known semi-conductor plant that was having issues with keeping the relative humidity in their main assembly area within the specified range for the product during the summer, particularly after a thunderstorm had moved through as the main assembly rooftop unit was 60% outside air. After testing, it was discovered that after CASE STUDY 1 A hospital in the Phoenix metropolitan area had an issue with their main tower air handler not maintaining a proper comfort level during the summer monsoon season. They installed aboveceiling package AC units in an attempt to cool critical areas, but the heat rejection above the ceiling also included the compressor heat and it exasperated the cooling issues of the air handler for the rest of the main tower. 11

Table of Contents for the Digital Edition of TAB Journal Spring 2014

Indirectly Determining Air Volume
Calibration and Balancing of Phoenix Valves in Laboratories
The Trouble with Canned Specs
Environmental Considerations of the Southwest
Airflow Measuring Station Considerations
Putting the Proper "SPIN" on Things
Chasing the Air

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