A new 14,000-sq.-ft. Bainbridge Probation Substance Abuse Treatment Center, a minimum security lockup for the Georgia Department of Corrections, was built here with IAQ and moisture guidelines in mind.
Instead of using conventional DX rooftop air conditioners, the innovative design by consulting engineer Jordan & Skala Engineers, Norcross, uses packaged outdoor air dehumidifiers by Dectron Internationale, Roswell, to supply cooled or heated dehumidified air. Four “Dry-O-Tron” DK-30 units and accompanying outdoor condensers satisfy outdoor air requirements by efficiently dehumidifying southeast Georgia’s notoriously hot and humid air and using compressor hot gas for reheat when needed.
Current ASHRAE standards of 20 cfm/person of outdoor air for correctional facilities, has made cooling public buildings difficult, especially in highly humid regions. Relying solely on traditional split systems or rooftop units to reduce humidity is both inefficient and sometimes unattainable on hot, humid summer days. The sensible heat ratio of a conventional ac system is at best 0.70 versus the 0.48 required to delivery ideal conditions on this project.
The human element and the building envelope design add to the moisture load as well. Each of the four 2,500-sq.-ft. barrack-style day rooms at Bainbridge, which houses up to 25 inmates, have few windows for security reasons.
“Because correctional facilities have so few windows, there is no solar effect, which would normally increase the room sensible heat ratio,” said Craig Gradick, PE, project manager. “When you combine outdoor humidity with the indoor moisture produced by inmates 24 hours per day in a single room with few windows, controlling humidity can be a prominent problem. Conventional air conditioning will satisfy temperature set points (sensible load) prematurely without running long enough to bring humidity (latent load) to comfortable levels.”
In order to supply 20 cfm/person of outdoor air, Gradick’s air distribution design of 1,850 cfm per day draws 52% outdoor air and 48% return air. This results in 3.8 changes per hour. Each unit in controlled by a Honeywell room thermostat and humidistat.
While the mechanical contracting portion of the project was routine, Dodge Heating & Air Conditioning Inc., Eastman, did have to fabricate “escape-proof” ductwork. The 30-year-old firm welded steel bars in ducts to block an inmate’s passage. An extra measure of security involved one-way screws in the supply registers that can only be removed by cutting them out, according to Deborah Davis, Dodge manager of plans and specifications.