Typically, packaged rooftop dehumidifiers are specified for such projects. However, rooftop equipment was out of the question because the decades-old pool's "double T," all-concrete roof design could not be opened up for ductwork drops; cutting any reinforcement bars would weaken the structure. No interior mechanical room space was available, and while the Shillington, PA campus was spacious, ducting from an outdoor unit (including a vandalism-proof enclosure for it) was cost prohibitive as well.
The school board relied on the 37-year experience of veteran consulting engineer, Robert Swoyer, Sr., P.E., president of R.A. Swoyer Associates (Reading, PA); mechanical contractor, Shannon A. Smith Mechanical/Electrical (Myerstown, PA); and Dectron Inc., to arrive at a solution that would stay within the retrofit's $400,000 budget while still providing the 13,000-sq-ft pool with its first true dehumidification system.
All In OnePreviously, the natatorium ventilation relied on two air conditioners and two AHUs that basically heated or cooled outside air and exhausted humidity. Indoor air comfort suffered during high humidity summertime temperatures, according to Swoyer. Those units, which were part of a retrofit project prior to modern packaged dehumidifier technology in the early 1980s, were perched in three chases hanging from the ceiling.
Instead of one or two large packaged units that would challenge space provisions, Swoyer's specified six smaller 3,300-cfm Dectron Dry-O-Tron® DS-40 dehumidifiers customized for the existing chases. The dehumidifiers' heat recovery feature heats the pool water to 82°F, all while simultaneously dehumidifying the space, and heating and/or cooling it to 83°.
"Because the previous units did not heat the pool water through heat recovery, the school district stands to save significantly on operating costs while improving IAQ," Swoyer said. New piping with booster pumps was needed to connect the dehumidifiers with the pool's circulation system.
Dealing with the roof and avoiding the severing of any reinforcement bar was a critical issue. After testing the concrete deck for strength and deterioration, a rod and angle iron system was designed to support each unit without damaging the reinforcement bar network. Subsequently, four rods per unit go through the roof and a 1-sq-ft steel plate per rod helps spread the load bearing weight distribution of each unit. Shannon A. Smith Mechanical/Electrical installed the hanging system and drilled all holes after pinpointing critical reinforcement bar points in the roof with original blueprints and a metal detector.
The money saving advantage for Swoyer's choice is the fact little sheet metal work was needed to connect the new dehumidifiers to the natatorium's existing ductwork - six 34-ft long runs of 48-by-16-in. duct that transitions into 48-by-10-in. duct. "The school saved thousands of dollars in time and materials by reusing the existing ductwork versus installing new ductwork," said Swoyer.
More Maintenance, But Increased RedundancyAnother advantage is the redundancy six units offer over one or two units. The disadvantages are few, except for the fact the school district must perform routine maintenance on six units as opposed to one or two. Luckily, the school already owns a lift machine to gain access to the 25-ft-high units. Also addressing accessibility was Swoyer's locating of each unit's HT-800 microprocessor-based monitor/controller located remotely in a secure concrete room below the grandstands. The controllers are interfaced with the school's existing BAS.
Instrumental in the design modifications was Chuck Durback, marketing representative for manufacturer's representative and equipment service firm, Metz Company, who acted as a liaison with Dectron's engineers. One important modification was hinged service access doors that couldn't fall from the units' lofty positions during servicing. Secondly, outside intake plenums were custom-made, with low profiles to accommodate low clearances in the chases.
Outside air of 1,100-cfm per unit is supplied by one outdoor access and delivered to three interior mixing boxes that each supply two units. Readjusted existing relief dampers handle the exhaust.
With the units in the room, Swoyer was careful to specify sound absorbers, which cut operating noise levels during classes and competitions. While many school districts might have razed such an old structure, Swoyer's high-technology retrofit innovation not only saved a worthy old structure, but also saved the school district millions that would have been used for a new building. ES