Duval County Unified Courthouse
New construction; Duval County Unified Courthouse; TLC Engineering for Architecture Inc.
Engineering firm: TLC Engineering for Architecture Inc.
2013 MEP Giants rank: 32
Project: Duval County Unified Courthouse
Address: Jacksonville, Fla., United States
Building type: Office
Project type: New construction
Engineering services: Automation & Controls, Code Compliance, Electrical/Power, Fire & Life Safety, HVAC, Lighting
Project timeline: February 2008 to May 2012
Engineering services budget: $31.35 million
MEP budget: $38.47 million
The project is located in Jacksonville, Fla., a hot and humid climate. Providing humidity control for a public building of this size is a challenge. This was a LEED certified project, requiring the most energy-efficient building systems possible. One challenge the design team faced was all the holding cells had to be maintained at negative pressure individually, both occupied and unoccupied. That required a significant amount of make-up air in order to maintain the building at neutral or positive.
A stacked coil approach was used for humidity control, which reduced the amount of reheat, allowing the passive reheat of the return air to be utilized. Heat recovery was used on two of the three 40,000 cfm make-up air units. A run-around passive reheat loop was used on the make-up air units, utilizing the required heating and pre-heating coils, which enhanced the dehumidification capacity of the make-up air unit chilled water coil by nearly 30%. Raw, by-the-space numbers, to comply with ASHRAE 62.1, required 200,000 cfm of make-up air and integrating the above components into a make-up air strategy reduced that by 80,000 cfm, still complying with ASHRAE 62.1 (saving approximately 530 tons of peak cooling capacity).
Everywhere possible, high-efficiency lighting, demand control ventilation using CO2 sensors, premium efficiency motors, variable-speed pumping, variable-speed air handlers, and variable-speed make-up air units were used. In high-density occupancy spaces, TLC provided preconditioned outside air directly controlled by the CO2 via dual-duct terminal control boxes. Leaving air temperature (LAT) temperature reset and static pressure reset algorithms on each air handler were used for optimization of air handler fan energy. To maintain holding cells at negative pressure individually—both occupied and unoccupied—the solution was to use the exhaust to regulate how much make-up air comes to the cell, and therefore how much temperature controlling air is introduced into the cell. This was integrated into the building ventilation relief system.