Designing HVAC systems for government buildings covers a spread of occupancies that range from office spaces to laboratories, detention facilities, high security areas, data centers, and military bases. Long life is one common requirement of design. However, over the life of a building, its systems will need to be revised and often modernized. Many existing building are visually historic in nature, and that historic appearance must be maintained. Other buildings must be also expandable either vertically or horizontally.
Guidelines and Standards
Most governmental agencies have developed a design guideline or manual of standards for their facilities. The purpose of these documents is to aid the design team to stay on a common course of system design throughout the agency. The published materials are utilized to define systems and lists of equipment that have a history of success in meeting the client’s goals of comfort, dependability, and economy of operation. The downside of this approach is that newer technologies are not often considered. The good news is that in today’s world, high LEED® ratings are now a new design goal.
Old Historic Buildings
The look of modern HVAC systems must blend in with the old historic appearance of the space. The first change is often the conversion from steam heat in the radiators and built-up AHUs to a hot water system. Hot water is piped to existing cast iron radiators with the addition of either all new piping or at least new piping, for the replacement of the old return condensate piping which is too small for the return piping. The old built-up units are replaced with new modular factory-built AHUs that feature hot-water heating coils, improved efficiency filter banks, either chilled water or DX cooling coils, variable-speed motor/fan systems, and a DDC system that can be adjusted and monitored from a central location.
HVAC systems in historic buildings often began just as heating/ventilation systems. When air conditioning became a need, the existing distribution ductwork was modified by adding a cooling source (chilled water or DX coils) and insulating the ductwork to prevent condensation. To maintain the old look most of the terminal air outlets were changed to bronze-colored grilles. The use of the bronze-colored outlets and return grilles should be maintained in any modernization projects.
Reducing Energy Usage and Increasing Comfort
Dual-duct systems and multi-zone systems lowered fan hp by the variable volume concept. Hot water hydronic systems further reduced energy by introducing variable flow pumping systems. The use of variable-speed controllers on the fan and pump motors did reduce energy usage. When DDC was added to the chillers, chilled water pump hp reduction was also possible. This variable pumping flow through the chillers also has reduced the number of systems using the primary/secondary design concept. Variable primary pumping systems use less pumping hp.
A constant volume reheat system can be economically modified by removing the zone reheat coils, sealing up the existing ductwork above the ceiling to reduce the duct leakage, and then joining the ends of the zones into a loop-type supply system. Then new VAV zone units are connected to the modified existing cooling loop to offer more comfort at the use of less energy. A perimeter heating system of heating is either added or modified to condition the building’s perimeter zones.
Ventilation Security
To improve the durability of piped and ducted HVAC systems, seismic supports are recommended as standard in facilities that consider homeland security as a design goal. The outdoor air louver location was noted as the easy way for a chemical introduction into the air system. Dummy outdoor air louvers have been installed to create uncertainty as to the true outdoor air path into the facility. Chemical powder protection filters have been installed in high-security facilities.
All new buildings locate the intake louvers in places that make unauthorized access difficult. The intake dampers are also low-leakage types, connected to an emergency shutdown control/alarm system. The alarm system is also connected to gas sensors in the outdoor air intakes.
Laboratories
State health and agriculture departments have extensive laboratories. A modern laboratory ductwork layout should be designed for changes that occur often in this field. The ductwork should have capacity flexibility in both the supply and return duct mains. The lab hood exhaust should be variable flow. The general laboratory working space also has a general exhaust to control the IAQ. Heat recovery is possible from the general exhaust stream. Coordination from a general team leader is required to prevent over design requests from various departments.
The basic principle for designing modern HVAC systems in old buildings is to be able to blend the modern system types into the historic old look of the building. This process does take thought and market analysis as to what is available. The system selected should have been successful in providing comfort conditions at reasonable first and continuing operational costs. A life-cycle cost analysis should be included in the proposed design options. New systems contain many controls that need to be monitored and adjusted to obtain the planned for energy savings, however in the real world, the controls are usually “dumbed down” to the abilities of the operators. This results in energy saving design funds being wasted.
Economic energy usage and wise reuse of construction materials is the environmental design goal in today’s world. The current model building codes (international and uniform) also guide the design team down this path. The goal of green facilities and gathering of LEED points for government projects is only becoming more important as a design goal in today’s engineering environment. HVAC is the key factor to achieving these goals and LEED points.