TAB Journal Spring 2014 - (Page 11)
of the Southwest
Michael Ziegler, TBE, TAB Technology, Inc.
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
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.
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
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.
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
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.
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
TAB Journal Spring 2014