Typically, precision air conditioning equipment or chiller and air handler combinations with redundant backups are used to cool computer and server rooms. However, Farmer, a vice president of mechanical engineering at the architect/engineering firm Michael Brady Inc., Knoxville, provided Scripps cost savings by using 14 Dry-O-Tron® dehumidifiers manufactured by Dectron Internationale, Roswell, GA, to control the conditions in the technology area.

The dehumidification machinery includes dozens of piping runs that were plumbed by mechanical contractor D.F. Shoffner of Knoxville. “There’s a huge amount of water and refrigeration piping that will impress anyone that enters the room,” said Dennis Pitsenbarger, Shoffner senior project manager.

Those involved with the project said that it might be the first use of dehumidifiers in high-technology rooms. “With Dectron, I saw an opportunity to design something that offered redundant backup with the same unit,” said Farmer. “This allowed me to take advantage of the water-source heat pump loop and reduce equipment costs. I’m still providing the required redundant backup required by the owner and this might change how future computer and server rooms are built and air conditioned.”

COST SAVINGS

The cost savings come in several ways. The use of packaged dehumidifiers consumes the same 4,000 square feet of floor space of the corresponding technical room equipment, but since there is no associated central plant and accompanying mechanical space, about 1,000 square feet is saved. With construction costs averaging $125/square foot, this amounted to a savings of $125,000.

A feature of the redundant heat rejection capabilities of the dehumidifiers allows them to switch from the outdoor condenser to the heat pump loop anytime. During the heating season, the units automatically reject heat into the heat pump loop. The resulting increased loop temperatures improve the effectiveness of all the other heat pumps connected to it. This feature provides heat for the addition’s offices, a tape library, viewing rooms, and cafeteria at annual energy savings of $5,000, according to those who worked on the project.

Space was also saved on the roof. Farmer specified only four custom-manufactured condensers with multiple circuits from Dectron’s Ref-Plus heat transfer division. Because the dehumidifiers have continual cooling modes that supply steady heat to the water-source heat loop, any backup heating, if needed, is be handled by an existing on-site 500,000 Btu boiler by Raypak.

“But my calculations reveal that the boiler probably will never be needed,” said Farmer. “Even on the coldest of days, the contribution of heat from the dehumidifiers allows the heat pumps to handle the entire load.”

Farmer figured that maintaining packaged dehumidifiers rather than chillers could save $10,000 to $15,000 in annual maintenance costs. An in-house staff should be able to handle most service work, he said.

THE HVAC LAYOUT

The layout called for a 265-square-foot mechanical space inside the technology room, but walled off from the five 22-foot-long, 8-foot-high racks of computer equipment. Nestled in between the racks is the mechanical space, which has three Dectron DA5-30 dehumidifiers as well as pre-piping for an additional unit that will come with future expansion. Two units are for current conditions and the third serves as a redundant backup. The mechanical space also includes two DA5-10 dehumidifiers (again with pre-piping) that serve the adjacent broadcast control center and its equipment. Each bank of dehumidifiers is equipped with an on-board humidifier to eliminate static electricity and maintain a 50% relative humidity during the winter.

Above the first floor mechanical room is a 592-square-foot secondary mechanical room that houses six more DA5-30s for the main technical room. Additionally, there’s a hot backup site of corporate IS/IT servers with three more DA5-30 dehumidifiers and piping accommodations for one future add-on.

Farmer also devised an air distribution system to assure the computer equipment is continually bathed in cool air, but doesn’t create air noise that can affect nearby broadcast operations. Over each set of 22-foot-long computer racks is a series of two plenums. An upper supply plenum is connected to a lower distribution plenum via several short ducts. The supply plenum, which has a continuous slot to drop air along the top of the racks, has an equal pressure and self-balancing design. The plenums are integrated into a soffit and end wall system. A cable access area where air is returned to the ceiling plenum separates the racks and wall systems.

Other equipment used on the project included two Taco 7.5 pumps and one Baltimore Aircoil closed circuit cooler. Twenty-seven McQuay heat pumps condition air to offices within the expansion. An existing Alterton building automation system operates the majority of HVAC equipment and systems.

The project also has an uninterruptible power supply (UPS) and a backup diesel-powered generator. In event of a power failure, the inlet UPS provides power to critical systems until the backup generator engages after a 10-second delay.

For more information, contact Dectron at 800-767-2566.

Publication date: 11/18/2002