9.5 Mechanical Systems
This section focuses on technical requirements for the mechanical engineering systems which should be provided in buildings designed to serve the U.S. Courts. Specific requirements are presented for all special or unique spaces used by the U.S. Courts and Court-related agencies, including spaces designed to accommodate the U.S. Marshal Service.
Federal Court facilities should be designed to take advantage of integrated systems and controls to provide better building performance through energy conservation, economy of operations, maintenance and flexibility for changes. Opportunities for system integration need to be evaluated throughout the design process.
U.S. Courts facilities require a variety of space types, each with its own set of specific requirements. In addition, Court functions require flexibility in the time of operation and control of dedicated HVAC systems.
System Selection and Design
HVAC Specific Design Criteria Requirements
- Outdoor winter temperature equal to ASHRAE 1% design dry bulb and coincident wet bulb.
- Outdoor summer temperatures equal to ASHRAE 99% design dry bulb/97.5% wet bulb.
- Indoor air: Courtrooms – 22°C (74°F)/50% RH (at summer conditions and occupancy) - 22°C (74°F)/20-35% RH (at winter conditions and occupancy).
- If provided, the smoke purge system in the courtroom should be activated manually.
- All openings carrying piping through the slab or through partitions must be sealed with appropriate fire resistive/smoke resistive material. All air ducts leading to and from sensitive spaces must be acoustically treated with 2 inches (50 mm) of duct lining for a distance of at least 12 feet (3700 mm) from the diffuser or return air intake.
- HVAC systems shall be designed to provide optimum flexibility in scheduling the use of courtrooms and chamber areas.
The selection of the HVAC systems, equipment, and source of energy will be in accordance with the guidelines and procedures established in Chapter 5. Life Cycle Cost (LCC) analyses will be conducted to ensure selection of the most cost-effective alternative environmental considerations. The HVAC system should also be designed to provide 23.4°C (74°F) in judge’s chambers, courtrooms and trial jury suites on average. The courtroom HVAC system will be designed so that courtroom thermostats can be reset from the building automation system to precool the courtrooms to 21.1°C (70°F) prior to scheduled occupancy. Jury deliberation rooms, judges’ chamber suites, and courtrooms are to be placed on the same system with separate zones having related thermostats and the design should account for variation in occupancy load. Humidification must be provided as specified in Chapter 5. Mechanical systems will provide 5.7 cubic meters (20 cubic feet) per minute as a minimum per person in all occupiable areas of U.S. Court facilities.
The HVAC systems shall be zoned in such a manner that the requirements of the special areas can be satisfied by efficient use of the systems and equipment. To allow flexible and efficient use of the HVAC systems for “after hours activity”, and to satisfy specific requirements in a U.S. Court facility, the central plant equipment (chillers, boilers, cooling towers, pumps, AHUs, etc.) will be designed using redundant equipment of various sizes to satisfy the requirements of differing number and sizes of zones. (The goal is to service no more than two courtrooms per each air handling unit.) Piping systems should consider arrangements to permit changing courtroom HVAC systems from primary to secondary chilled water for off hours. The design shall allow sub metering of utilities and equipment to permit the facility manager to allocate cost of operation beyond standard hours of operation.
Temperature and Systems Control. The HVAC system serving judge’s chambers, courtrooms, and trial jury suites should provide an average temperature of 23.4° (74°F). The courtroom system zone will be designed to allow thermostats to be reset from the building automation system to pre-cool to 21.1°C (70°F) prior to scheduled occupancy.
Air Distribution. The diffusers serving the spectator areas must be sized to serve the allowable seating capacity plus 25%, to accommodate for extra seating. The diffusers need to be selected to meet minimum ventilation requirements at no loads, with no appreciable increase in system noise during load changes.
Provide six (6) air changes per hour for rooms with ceiling height up to 4.6 meters (15 feet); and eight (8) air changes per hour for rooms with a ceiling height greater than 4.6 meters (15 feet). Systems should be designed to meet these requirements when spaces are fully occupied, unless otherwise noted.
The maximum percentage of recirculated air should not exceed 85%.
If the courtroom is served by a fan system dedicated to more than one courtroom, then the return air from each courtroom and its associated areas must be ducted directly to the unit.
Return air from the chamber suites will be ducted directly toward the return air shaft for a minimum distance of fifteen (15) feet. (Treat ductwork to meet the acoustical design criteria.)
System Description and Control. Trial jury suites should be served from the same system as the associated courtrooms. (A separate thermostat for each trial jury room is desirable.)
Air Distribution. Air distribution systems in the jury facilities must provide separate temperature control and a high degree of acoustical isolation, particularly in the grand jury and trial jury rooms. Return air from the rooms must be ducted directly back to the exhaust air riser. Ductwork will be treated to meet the acoustical deliberation room design criteria.
Air Changes . In the Assembly Room, Deliberation Room, and toilet rooms, the system must provide 10 air changes per hour (ACH) with 80-85% return.
Refer to USMS-RSSPSSM for all detention requirements.
and U.S. Courthouse, Worcester, MA
Since U.S. Court facilities should be expected to have a long useful life, new construction and renovation projects need to be planned to provide adequate mechanical and electrical capability to the site and building(s) to support future additions. It is particularly important to design the systems for specialized areas of the building (lobby, food service, mechanical rooms, electrical rooms) to support the anticipated 30-year needs of the occupants. This can be accomplished by building additional space for future growth of the HVAC systems during initial construction and temporarily allocating it to building or tenant storage. HVAC designers shall locate equipment adjacent to the building perimeter wall that will abut future expansion for orderly tie into new system components.
The HVAC system design for the Courtroom, Judge’s Chamber Suite, and the Jury Deliberation Room, which comprise a single “court set”, shall be designed to allow the HVAC system to operate after hours.
The design shall include winter humidification for “special” designated areas in the building. Special controls for winter dehumidification will not be included since modern HVAC systems are designed to keep relative humidity within acceptable ranges.
Acoustic performance should be a major consideration regarding the selection of HVAC equipment. Systems serving the courtrooms and auxiliary spaces should be designed with sound attenuation to provide consistent and acceptable sound levels. This is particularly critical in design of court facilities that require extensive use of sound and A/V equipment for recording and presentations.
To control noise during all modes of operation and for all load conditions, the HVAC system should be provided with one or more of the following:
- Sound traps and acoustic lining in the duct work;
- Low-velocity, low static-pressure fan systems;
- Special low-noise diffusers; and
- Sound traps.
If air is returned by the ceiling plenum, special attention should be given to the location of any partitions extending to the floor structure above and to the acoustical treatment of the required penetration of these partitions for return air.
HVAC equipment including air-handling units (AHUs) and variable air volume (VAV) boxes will not be located in close proximity to courtrooms, jury rooms, and chambers. The minimum distance should be 7.6 meters (25 feet) between AHU and courtrooms. (Refer to Chapter 5, Theaters and Auditoriums, for criteria regarding maximum duct velocity.) General system design needs to provide appropriate treatment of mechanical supply/return ducts to minimize sound and voice transfer from courtroom, chambers, jury deliberation spaces, witness rooms to surrounding areas.
Noise criterion (NC), defines the limits that the octave band spectrum of noise source must not exceed, should range from 25-30 in U.S. Court facilities. For sound level maintenance, the courtroom needs to be served by constant volume air supply. The system must also support variable outside air requirements and variable cooling loads. Air ducts serving the trial jury and grand jury suites must be lined with 2 inches (50 mm) of acoustical absorption material for a length of at least 12 feet (3700 mm) from the diffuser or return air intake.
Mechanical System Diffusers, Vents
Mechanical system diffusers and grills in public and staff areas will need to be secure from tampering, particularly in areas which provide some degree of seclusion and privacy (restrooms, attorney-client visitation rooms, etc.) Maximum-security detention-type grilles, secured with tamper proof fasteners, shall be provided at all areas accessible to prisoners. (Refer to USMS-RSSPSSM for more information.)
Changes in Building Envelope to Meet Energy Guidelines
Due to the energy load requirements of court facilities, designers should use the alternative design processes of ASHRAE 90.1R to meet Federal energy guidelines for overall building energy usage. Increases in building envelope energy resistance should be used to compensate for higher than average load requirements resulting from court functions. Total building energy usage should be established according to calculations using mandatory design standards contained in Chapter 5. To demonstrate the same total energy usage, a new calculation will be done incorporating factors for energy reduction strategies to offset increased lighting, cooling and heating energy loads.
Information Technology System Loads
Information technology systems are not the largest source of heat within the office spaces but may be the largest sources in particular areas. Information technology systems will be the most uncertain source of heat flows during design phases, therefore the HVAC system should be planned with capacity and control to accommodate the need for constant temperature and humidity environments 24 hours a day, where systems hardware could be placed.
The design of the HVAC systems must take into consideration provisions for separate units for critical areas such as computer rooms, USMS control room, elevator machine rooms, etc., which generate additional heat loads. (The HVAC design for these areas should have redundancy and also be connected to the emergency power system.)