cool return air without the use of mechanical cooling. The effective performance of this system is dependent on precise control of the outdoor, return and exhaust air dampers as well as adequate mixing of outdoor and return air in the mixing plenum. Air flow through the system is balanced using manual volume dampers. These are located at the beginning of each zone branch line upstream of the heating coil and at each supply and return diffuser. Access panels at each location are provided for manual balancing. Periodic system balancing is necessary to maintain even pressure and conditioned air distribution in the library. Over the 40 years since installation, the HVAC system-- including the controls--has received irregular maintenance. Inoperable damper actuator motors are evidence of a need for routine system inspection. As well, periodic thermostat calibration and zone damper balancing have not been performed. Pneumatic control systems have a life span of 25-30 The air supply system which includes the compressor, drier, filters and regulators becomes contaminated with oil, water and dirt and causes fouling of the field devices over time. While the system is still functional, its performance is not optimal at present and is nearing or beyond its useful service life. In order to continue the use of the pneumatic system and operate it at optimal performance, all field devices should be inspected , tested and recalibrated. The continued use of this control system would require replacement of any actuators, valves, damper motors or thermostats that are not functioning. The pneumatic lines and fittings should be inspected for leaks and blockages. Also, the damper positions and linkage condition should be inspected to insure that positions match desired setpoints. Conversion to a direct digital control (DDC) system would provide significant energy savings and offer greater control over the HVAC setpoints, proportional or integral gains, minimum on and off times, high or low limits, night-flush cycles and tighter control of the economizer cycle.DDC would also allow for integration of demand-controlled ventilation (DCV). DCV uses CO2 sensors to modulate the outdoor air damper to meet minimum ventilation requirements based on occupancy, thus reducing the energy used to heat or cool excess outdoor air. Another advantage of DDC would be to incorporate humidity control using the cooling coil. Humidistats could be placed in zones with the highest levels of humidity. If
cool return air without the use of mechanical cooling. The effective performance of this system is dependent on precise control of the outdoor, return and exhaust air dampers as well as adequate mixing of outdoor and return air in the mixing plenum. Air flow through the system is balanced using manual volume dampers. These are located at the beginning of each zone branch line upstream of the heating coil and at each supply and return diffuser. Access panels at each location are provided for manual balancing. Periodic system balancing is necessary to maintain even pressure and conditioned air distribution in the library. Over the 40 years since installation, the HVAC system-- including the controls--has received irregular maintenance. Inoperable damper actuator motors are evidence of a need for routine system inspection. As well, periodic thermostat calibration and zone damper balancing have not been performed. Pneumatic control systems have a life span of 25-30 The air supply system which includes the compressor, drier, filters and regulators becomes contaminated with oil, water and dirt and causes fouling of the field devices over time. While the system is still functional, its performance is not optimal at present and is nearing or beyond its useful service life. In order to continue the use of the pneumatic system and operate it at optimal performance, all field devices should be inspected , tested and recalibrated. The continued use of this control system would require replacement of any actuators, valves, damper motors or thermostats that are not functioning. The pneumatic lines and fittings should be inspected for leaks and blockages. Also, the damper positions and linkage condition should be inspected to insure that positions match desired setpoints. Conversion to a direct digital control (DDC) system would provide significant energy savings and offer greater control over the HVAC setpoints, proportional or integral gains, minimum on and off times, high or low limits, night-flush cycles and tighter control of the economizer cycle.DDC would also allow for integration of demand-controlled ventilation (DCV). DCV uses CO2 sensors to modulate the outdoor air damper to meet minimum ventilation requirements based on occupancy, thus reducing the energy used to heat or cool excess outdoor air. Another advantage of DDC would be to incorporate humidity control using the cooling coil. Humidistats could be placed in zones with the highest levels of humidity. If