As mechanical manager for Leon County Schools in Tallahassee, Fla., Dave Ventry is responsible for maintaining the mechanical and HVAC operations of 50 school campuses in the district. When the district faced the need to meet the Florida version of the ASHRAE 62 ventilation code, which requires the introduction of 15 cfm of outdoor air per person, Ventry sought a district-wide solution for controlling humidity levels while complying with the state of Florida's new fresh air requirements.

The age of the equipment was another reason for the mechanical renovation, as students and teachers were feeling uncomfortable in a number of schools.

To address these issues, the district scheduled five schools for mechanical retrofitting during a five-year span starting in 2002. Roger Walsh, P.E., Walsh Engineering Inc., was selected by the district to work with Ventry to develop a plan for schools within the district, including Killearn Lakes Elementary School.

Challenging Conditions

"The original system at Killearn Lakes was a mechanic's worst nightmare," said Ventry. "Every classroom and administrative office had its own small water-source heat pump unit to cover its HVAC and IAQ needs. You can imagine the maintenance headaches with literally 60 separate units."

Clearly, the first order of business was to create accessible mechanical spaces. Walsh and Ventry devised a plan to construct a mezzanine floor above each of the school's single-story wings. Key to the mechanical solution of achieving the outdoor air code requirement was the need to control the level of humidity being introduced into the buildings.

"If the humidity isn't controlled, you've just opened yourself up to perfect conditions for bacteria and toxic mold," said Walsh.

Walsh worked with engineers from Applied Mechanical Equipment of Jacksonville, Fla., to pre-sent to Ventry the idea of using Desert Aire Q-Pumpsâ„¢ combined with TotalAireâ„¢ 5- to 20-ton dehumidifiers, each equipped with an enthalpy wheel to maximize the sensible and latent heat recovery. Unlike traditional heat pumps, which use a two-element reverse cycle system, Desert Aire's Q-Pump uses a four-element refrigeration system that relies on the dehumidifier's reheat coil for heating, thus eliminating the need for a reversing valve.

"To be honest," Ventry stated, "I was leery when I first looked at the Desert Aire unit with its circuitry, configuration circuits, and recovery wheel. My initial thought was, ‘Gosh, that's complicated,' but when I really looked at it and broke it down, I soon realized it is quite simple. When I say ‘simple,' I mean that it is precise at doing what it's supposed to do and appeals to my common sense."

After becoming comfortable with Desert Aire's approach, Ventry requested detailed technical information from Desert Aire and studied the TotalAire unit's control logic.

"I wanted to make full use of our existing controllers, so I wrote my own software program to make sure our controllers would match the Desert Aire controller requirements," Ventry said.

The Desert Aire system at Killearn Lakes has been in place since October 2002, and Ventry can vouch for its performance. "I'm very pleased. The Desert Aire system has reduced our maintenance costs substantially and has delivered on everything promised."

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Publication date: 08/09/2004