DALLAS, TX — Indoor air quality (IAQ) is a hot topic in school environments. Many schools rely on dehumidification units to facilitate proper IAQ and comply with American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) standards.

Parkhill Junior High in Dallas was no exception. The approximately 650 students and faculty members complained about the “musty smell” and high humidity in the 40 classrooms. There was also the problem of uneven climate control throughout the single-story, 111,000-square-foot building.

“We were getting a lot of complaints about air quality in the school,” said Scott Porter, Richardson Independent School District (RISD) HVAC maintenance manager. “We were not meeting ASHRAE standards. Some classrooms were freezing cold and others were hot and humid. There were a lot of problems.”


A lot of the climate and IAQ problems were due to the 25-year-old, worn-out units, which were installed when the school was first constructed. The single-zone rooftop units had no dehumidification system or device. They needed replacing. RISD decided to evaluate using a humidity control unit.

“Most of the air quality complaints revolved around the building being too cold or too clammy from too much humidity,” said Porter. “The solution we considered was new rooftop units with a dehumidification device. We needed outside air introduced to the building, while at the same time we needed to stop the humidity and irregular indoor climates altogether.”

The RISD maintenance staff viewed a Humiditrol option demonstration on the L Series® packaged units. “I … brought my portable Humiditrol unit on a trailer for them to see,” said Chris Murray, Lennox commercial territory manager.

The system is said to be able to provide dehumidification on demand without a call for cooling from a space thermostat. “The humidity sensor can initiate the unit’s operation irrespective of the occupied temperature,” states Lennox.

The Richardson Independent School District purchased 47 L Series units with the Humiditrol option for the school.


Allied Mechanical, a contractor in Richardson, TX, installed the 47 units in August 2001. Tonnage for the replacement units was increased, since today’s classrooms differ from the classrooms of 25 years ago.

“Today, classrooms have about five to six more students in them, and they also have at least eight computers in each classroom,” said Porter. “We had to increase the tonnage for more cooling and to bring in more outside air.”

RISD wanted to increase the 5-ton units to 6-ton units, but at the time, the Humiditrol option was only available on the 5-ton unit. The next available size was the 7.5-ton high-efficiency unit. Since this tonnage size was in a larger cabinet that didn’t easily facilitate an adapter curb, the curbs were replaced on the roof.

In the beginning, thermostats were installed to maintain the new HVAC system, but eventually, an energy management system from Andover Controls (Andover, MA) replaced the temporary thermostats.

“The energy management system controls humidity, and we’re able to program it with our specifications,” said Porter. “We have subcontrollers in each individual unit with one main controller in the building. This controller basically allows us to regulate correct temperature, and if we get temperature complaints, we can go to the one panel to determine the problem.”


Parkhill Junior High has already noticed changes. The school’s mechanical system is now meeting ASHRAE standards, maintaining even temperatures throughout the building, and achieving humidity removal goals.

“We have noticed a tremendous difference in the school’s climate,” said Porter. “There is also uniform climate throughout the building in each classroom, and no humidity problems, which is great.

“We’re very pleased with these units,” he continued. “We’re anticipating energy savings. Even though we’ve increased our unit tonnage, our temperatures are more even throughout the building, and we won’t have to overcompensate in some areas to cool humid or hot areas anymore.”

Publication date: 08/12/2002