Unique dehumidifier retrofit saves school $400,000 in construction costs
A unique indoor pool HVAC system at Adlai E. Stevenson High School in Lincolnshire, IL, helped to save big money in construction costs. The innovative approach added to the suburban Chicago school district’s progressive green mission and also promises a value-engineered resolution to the HVAC industry’s impending mechanical room dehumidifier replacement challenges.
The school’s huge 40,000-sq-ft natatorium, one of only four 100-meter Olympic-sized pools in Illinois, was faced with replacing two aging HVAC dehumidifiers requiring tens of thousands of dollars annually in maintenance costs the last few years. Installed when the natatorium was built in 1996, the removal of the two 15-ft recovery dehumidifiers would require upwards of $400,000 in construction costs to tear open a wall or roof for their removal, according to Mark Michelini, CPA, assistant superintendent for business at School District 125.
Instead, the school district’s longtime building automation and energy services contractor, Siemens Industry Inc., and Michelini conceived the idea of leaving the units in place, gutting them, and commissioning dehumidifier manufacturer Seresco USA to factory-build entirely new 64- and 40-ton dehumidifier components, coils, piping inlet/outlet receptacles, and control packages that would fit inside the original manufacturer’s steel shell configurations.
The technique was also approved by Stevenson’s on-site building services contractor, Sodexo; Bruce Svec, sales engineer at manufacturer’s representative Imbert Corp.; and architect consultant firm Cannon Design. The school district signed a performance contract with SII to guarantee solving the dehumidifier replacement challenge at a specified payback and cost.
Most of the challenge rested on Seresco USA, however, which sent its Vice President of Production, Jonathan Theriault, to assure the critical measuring accuracy of the shells, components, various piping connections, and positions of inlets/outlets and the 25,000- and 15,000-cfm blowers, the latter of which were retained to value-engineering project costs. Matching the evaporator coils was the most difficult challenge, according to Theriault.
Factory engineers then designed the entire configuration and provided the installing contractor, Team Mechanical-EMCOR Services, with 3-D, computer-modeled blueprints to simplify on-site assembly and installation. The new partially-assembled internal component packages arrived as a compressor/refrigeration circuit skid, separate fully-dipped enamel corrosion-proof evaporator, reheat and hot water coils, Command Center/electrical control panels, and dry coolers to minimize onsite assembly.
“All dehumidifier manufacturers have a similar physical airflow sequence consisting of an evaporator coil, reheat coils, compressor module/refrigeration circuit and fans, but fitting equipment into another manufacturer’s configuration and making it easy for the contractor to install was a custom- engineering feat,” said Svec, who helped coordinate the project between SII and Seresco.
Instead of a conventional 100% refrigerant dehumidifier, SII chose two NP-Series Protocol models, which together substitute nearly 1,200 lbs of the original systems’ refrigerant with environmentally-friendly glycol that is PVC-piped to rooftop dry coolers 60 ft away for heat rejection. The units do use a substantially reduced charge of approximately 400 lbs of refrigerant R-410A, which doesn’t have ozone-depleting chemicals such as chlorine.
Michelini estimated the school could have postponed the dehumidifier retrofit another five years; however, the refrigerant R-22-based units were developing leaks regularly and increasing maintenance costs. Since R-22’s chemical makeup includes chlorine, a major leak and total refrigerant loss of either unit would have damaged the environment. Furthermore, replenishing a total charge of R-22 refrigerant would cost a minimum of $20,000 just in refrigerant because its prices are skyrocketing as the U.S. Environmental Protection Agency (EPA) continues an HCFC production phase-out that culminates with a complete ban in 2020.
The strategy of reducing potential environmentally-damaging refrigerants enhances the school district’s aggressive green mission, which typically includes annual carbon footprint reductions aimed at cutting energy use by 3% to 5% annually.
The 833,000-sq-ft school’s ongoing progressive sustainability efforts, such as high-efficiency pumps, condensing boilers, and various lighting and plumbing upgrades, for example, have led to the district’s LEED gold certification.
“Reducing refrigerant and chemical use in our building is part of our sustainability mission,” said Michelini.
Besides refrigerant reduction, the new dehumidifiers also save 15% to 20% more energy than their predecessors via scroll compressors, direct drive fans, and other comparably higher-efficiency components. Besides sustaining a 50% rh, the units use energy recovery to heat the pool water to 80°F, and maintain an 82°F space temperature.
Another key to the project’s success was no downtime during the three-month retrofit. One unit operated continually while the other was retrofitted. Thus the pool remained operational and open during its typical 16-hr days.
Michelini suspects the original dehumidifiers may have unknowingly experienced slowly degrading inefficiencies in between annual routine service checkups. The new dehumidifiers won’t run inefficiently because they are each outfitted with a Command Center and Ethernet connection that relays more than 100 operating parameters to Seresco’s factory engineers for daily review via Seresco’s proprietary web-based WebSentry. An operating inefficiency can be pinpointed and corrected the day it occurs, rather than discovered months later during a service call. Authorized personnel from the school district or Siemens can also access the dehumidifiers via WebSentry 24/7 with a PC or a smart phone to review operating conditions or e-mailed alarms. The Command Center independently operates the dehumidifiers, but also reports monitoring data to Siemens’ Apogee building automation system. The extensive information includes operational data log histories that factory engineers use to assist local contractors troubleshoot and repair service issues.
Although there were no ductwork modifications and new dehumidifiers have a similar refrigeration capacity, Michelini said there’s a noticeable difference between the old and new technology in terms of air comfort, especially during meets with in the 240-seat spectator section.