Officials at the 14,000-sq-ft Georgia Department of Corrections (GDOC) minimum-security Bainbridge Probation Substance Abuse Treatment Center recently tested an hvac IAQ design. The project was done under the guidance of GDOC's Danny Brown, director of engineering and construction, with James (Bill) Knox, project manager.
Bainbridge is part of GDOC Commissioner, James Wetherington's ongoing quest to upgrade the state's correctional facility system. Instead of using conventional DX rooftop air conditioners, the design by mechanical/electrical/plumbing consulting engineer firm Jordan & Skala Engineers Inc., Norcross, GA, uses packaged outdoor air dehumidifiers by Dectron Internationale of Roswell, GA, to supply cooled or heated dehumidified air. The four Dry-O-Tron DK-30 units and accompanying outdoor condensers satisfy outdoor air requirements by dehumidifying southeast Georgia's hot and humid air by using compressor hot gas for reheat when desired.
Current American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) standards are 20 cfm/person of outdoor air at correctional facilities. This has made cooling public buildings problematic for consulting engineers, especially in highly humid regions. Relying solely on traditional split systems or rooftop units to reduce humidity can be inefficient and sometimes unattainable on hot and humid summer days.
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, housing up to 25 inmates, have few windows for security reasons. "Because correctional facilities have so few windows, there's no solar effect, which would normally increase the room sensible heat ratio," said Craig Gradick, P.E., project engineer, Jordan & Skala. "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 room draws 52% outdoor air and 48% return air, says the manufacturer. This results in 3.8 air changes per hour. Each unit is controlled by a room thermostat and humidistat by Honeywell.
NO ESCAPE
While the mechanical contracting portion of the project was routine, Dodge Heating & Air Conditioning Inc., Eastman, GA, did have to fabricate "escape-proof" ductwork. The 30-yr-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's manager of plan and specifications.
Gradick's specification of the hot gas reheat option on each Dectron unit will save the GDOC operating expenses. Each unit's hot gas reheat coil uses energy from the refrigeration cycle and does not rely on an added heat source for reheat when in the dehumidification mode. Each unit cools the air to a dry 48 degrees F dew point and then uses hot gas reheat to warm the supply air to aroom set point of 75 degrees F with 38% relative humidity. Hot gas bypass provides cooling capacity reduction on off-peak design days.
Gradick maintains a neutral building pressure by relieving the outdoor air through fans in each day room's bathroom, which is sized for 2 scfm. Bainbridge also has 2,500 sq ft of office space and a guard tower supplied by Carrier air conditioning units.
By specifying split-system packaged make-up air dehumidifiers, architect firm Ingram Parris Group, Valdosta, GA, received an aesthetic benefit from the standpoint that the roof's sight lines remain clear of equipment clutter.
Instead, the equipment is hidden away in a 1,000-sq-ft mechanical room that also has a 450,000-Btu Bryan Steam Corp. flex-tube boiler and two Taco 3/4-hp pumps. The boiler and pump combination supply hot water to factory-installed coils in the Dry-O-Tron units when heat is needed in winter months.
Publication date: 12/03/2001
