With the ductwork nearly in place in one of the new elementary schools in Tucson, workers make adjustments to fittings and hangers supporting the duct, lined with CertainTeed ToughGard duct liner with Enhanced Surface.
Mechanical consultant O.J. Clayton thinks that putting students in a classroom where the temperature is 85 degrees F and the humidity is nearly 90% cannot possibly be conducive to learning. “The kids sit there sweating and they find it hard to concentrate and learn in an environment like that,” he said.

It seems that the State of Arizona has come around to his way of thinking. Recently, the state’s School Facilities Board, which governs all building improvements at state schools, established minimum facilities guidelines for all schools in Arizona. Any school that is measured against the new guidelines and exceeds them will eventually be converted from the commonly used evaporative cooling systems to air conditioning systems.

In the coming year, the Tucson Unified School District (TUSD) is receiving nearly $72 million in state building improvement funding, much of which is being used to help convert a sizeable number of schools to air conditioning. The exact number at this time is not known. What is known by experts like Clayton, principal and owner of Clayton Engineering and Consulting in Tucson, is that air conditioning will eventually become the standard cooling system in most Tucson schools.

“And with so many schools going to year-round schooling and public interest growing in improving students’ learning environments, it’s inevitable that all qualifying schools will be making the changeover,” he said.

The conversion that is taking place will not only mean the installation of new equipment, but also the need for new air distribution systems comprising smaller ductwork, lined with fiberglass insulation to attenuate sound and improve thermal efficiency. In contrast, evaporative cooling ducts, because they deliver moisture-laden air, cannot be lined with insulation.

The move from evaporative cooling systems to air conditioning systems in many Tucson schools has necessitated the installation of lined sheet metal ductwork for the first time. The liner is used to attenuate sound and improve thermal efficiency.


In Clayton’s estimate, about 50% of mechanically cooled buildings in the Tucson area employ evaporative cooling. As the name implies, evaporative cooling works by evaporating water into the airstream. Air is passed through wetted cooling media, most commonly an aspen pad, which is made of wood fibers packed together loosely to allow air to pass through. Water cascades down the pad as a blower pulls air through it.

The effectiveness of an evaporative cooling system depends on the amount of moisture that is already in the air. So, the lower the humidity is in the existing air, the cooler the air from the evaporative cooling system feels on the skin.

There are several advantages to evaporative cooling systems that have kept them in use in certain climates since the 1940s. The first and foremost is cost, both in terms of equipment and operation. The second is effectiveness in regions where the air is dry year-round.

The trouble is that, in areas like Tucson, there is a monsoon season from late spring through early fall, which brings in very humid air. The air already has so much moisture in it that it cannot absorb any more from the evaporative cooling system. The cooling effect on the skin from evaporative cooling is thus cancelled out when the air is extremely humid.

“Sometimes, with an evaporative cooling system, you cannot get the room temperature below 84 or 85 degrees,” Clayton said. “That can get very uncomfortable both for the students and the teachers.”

According to the state’s School Facilities Board, a maximum classroom temperature of 82 degrees is included in the guidelines. If the district can prove that its evaporatively cooled schools cannot meet this temperature limit, especially during the high humidity period associated with monsoons, the district may get the funding necessary to provide air conditioning to those schools.

According to the TUSD’s public information department, the district has asked a registered mechanical engineer to determine the expected theoretical performance of each school’s cooling system during periods of high dewpoint. This can be done even when the monsoon season is over, by using mathematical calculations.

A worker in Qualified Mechanical Contractors' fabrication shop sprays adhesive on the back of the duct liner before applying it to the sheet metal duct.


Naturally, this movement to air conditioning systems has kept local mechanical contractors extremely busy. They have been working on the conversion to air conditioning in approximately 40-plus schools in the district, as well as the installation of air conditioning systems in new schools under construction.

Qualified Mechanical Contractors Inc., the second largest mechanical firm in Tucson and one of the largest in the state of Arizona, has been handling much of the work, including the HVAC systems in two schools opening this school year: Laura Nobles Banks Elementary School and Henry “Hank” Oyama Elementary School. Qualified Mechanical is working with general contractor Richard E. Lambert Construction.

The family-owned plumbing and HVAC business, under the direction of Nick and Santiago Nieto, has specialized in the educational market since it was established in 1985, having completed more than 50 projects at the University of Arizona and projects for not only TUSD, but also Tanque Verde, Amphi, Sunnyside, and other school districts.

In the two new elementary schools mentioned above, Qualified Mechanical specified the use of CertainTeed ToughGard™ duct liner with Enhanced Surface within the air distribution systems. Each school used approximately 11,000 square feet of the 1-inch-thick, 1-1/2-pound density, moisture-repellent fiberglass duct liner.

According to Nick Nieto, it is the only duct liner he uses in his 4,500-square-foot shop because of its consistency and the low dust level generated during fabrication. The shop did close to 450,000 pounds of sheet metal fabrication in 2001. Qualified Mechanical is supplied by SPS Supply Inc., headquartered in Tucson, which is part of the Watsco Group.

And with concerns about indoor air quality at the forefront, Nieto is looking ahead by choosing a duct liner with a high-performance airstream surface that is resistant to tearing, puncturing, and surface wear during installation and cleaning.

“I’m here for the long run and know that air quality issues will be coming up,” he said. “The moisture-resistant enhanced surface upgrade is another safeguard to preserving the integrity of the insulation, especially during our humid monsoon season.” Clayton agreed, adding that Tucson area humidity levels have been rising in recent years.


Students in the TUSD schools will benefit from the conversion to air conditioning for another reason: quieter classrooms. “With evaporative cooling, air movement must be very high, so you have a problem with loud air rush noise,” Clayton explained. “In my opinion, this is another obstacle to our students learning in the classroom.” In fact, the U.S. General Accounting Office found that duct system noise in our nation’s schools is a frequent complaint of school administrators.

With the changeover to air conditioning systems with insulated ductwork, Clayton believes systems will operate much more quietly, with air movement at a lower velocity and the ToughGard with Enhanced Surface further keeping acoustical levels down to their lowest practical levels.

“I see air conditioning as the future in most schools here,” said Clayton. “There’s still a reluctance to moving away from the more common evaporative cooling systems, though. I was asked by a church to design an evaporative cooling system for their new building, but refused because I felt that the system was not conducive to the congregants getting the most out of church services. They still went ahead and put in evaporative cooling, but came back to us in about three or four years, asking us to put air conditioning in.”

For more information, contact O.J. Clayton, Clayton Engineering and Consulting, at 520-323-9110; Nick Nieto, Qualified Mechanical Contractors Inc., at 520-624-8988; Tom Newton, CertainTeed Corporation, at 610-341-7739.

Sidebar: Key Players — Tucson Schools Applications

Mechanical contractor:Qualified Mechanical Contractors Inc., Tucson, AZ

Mechanical consultant: Clayton Engineering and Consulting, Tucson, AZ

Architect: Hanson Group Architects Inc., Tucson, AZ

General contractor: Richard E. Lambert Construction, Tucson, AZ

HVAC distributor: SPS Supply, part of the Watsco Group, Tucson, AZ

HVAC insulation mfr.: CertainTeed Corporation, Valley Forge, PA

Publication date: 10/21/2002