Hot Water System Pumps New Life Into Civic Center
All city and county administrative offices as well as the county courts and jail are located within the complex. Over 700 people work in the buildings Monday through Friday, and the complex has over 2,500 visitors each day, not including over 275 prisoners in the jail.
In the summer of 2000, a comprehensive energy and operating cost study conducted at the complex identified several areas needing improvement. Steve Utley, general manager of the building authority, says the building's boilers were never all that effective, and with the cost of natural gas these days, a change was necessary. "The building has been in operation for 32 years, and even when it was constructed, the three main boilers that serve the building were installed at about 60% efficiency," he said.
An Energy Savings Performance Contract (ESPC) was chosen as the wisest strategy. After a competitive selection process, Energy Systems Group, LLC (ESG, Evansville, IN) was selected to design, finance, and construct the project.
Out With The Old
Since the existing dual duct AHUs operated at constant volume, the fans continuously operated at the same speed. ESG installed vav conversion kits on each of the dual duct boxes. This kit is expected to reduce the amount of airflow to the space being served once the thermostat is satisfied. In addition to the vav retrofit kits, ESG also installed new vfd's on supply and exhaust fan motors that are greater than 5 hp.
The new technology will allow the vfd's to be installed on older motors, which in the past would not have been compatible with vfd's. However, it is important to note that there is a possibility that older motors could be burned out by the vfd's. Due to the abundance of replacement motors already purchased for the complex, ESG felt that this was a risk worth assuming.
Duct static pressure is monitored at the farthest point from the AHU. The vfd's either slow down or increase the motor speed to maintain a constant pressure at that point.
Under ControlThe existing controls consisted of old pneumatic and newer ddc. The pneumatic system took care of the majority of the facility and had limited operating capabilities. Several pneumatic system components had not worked correctly for many years. The ddc system monitored and controlled the chilled water plant, the condenser water system, and several points for the induction unit two-pipe system.
ESG installed a new ddc control system for the new hot water boiler plant and on the AHUs. The new ddc system controls and monitors points on the existing ddc system serves. Pneumatic actuators were reused and new valves were pneumatically actuated. Dual duct boxes are controlled by a pneumatic thermostat, as are the terminal units.
During unoccupied mode or night setback, the outside air intake dampers will close and a zone thermostat will take control of the unit. The zone thermostat control temperature will be set at something less than normal operating temperatures. For example, if normal heating conditions are set at 71 degrees F, the night setback thermostat will let the temperature drift back to 55 degrees before calling for heat. The situation is similar for cooling mode. The new zone thermostat setpoints will be adjustable. During occupied mode, the fans will operate continuously, in unoccupied mode, they will engage only when required by the night setback thermostat.
Steaming Up SavingsThe existing steam system consisted of three boilers and one flextube boiler. The flextube boiler operated year-round, providing steam to hot deck coils and terminal equipment. Winter operation required one of the three boilers to be operated in conjunction with the flextube boiler, and on rare occasions a second boiler had to be brought on-line.
ESG replaced the existing steam system with a new hot water heating system. It demolished the existing three boilers and removed steam and condensate lines from the boiler room. The flextube boiler was converted from steam to hot water operation and will be used as an emergency backup boiler.
Five new 2-MBtuh AERCO condensing boilers with 88% efficiency ratings at normal operating conditions were installed. Because additional boilers may be required for potential remodeling projects (such as the jail), ESG made provisions for supplementary boilers by installing additional hydronic headers with the flanged ends bolted shut and sized the pumps to accommodate two additional boilers. Two new 16-in. stainless steel breachings were installed beside the breaching for the flextube boiler. The new breachings will penetrate three floors and be terminated on the roof.
ESG installed new hot water supply and return lines to the existing steam equipment. Existing steam supply lines could have been be used as the new hot water return lines. However, investigation revealed that installing new return lines at a higher up-front cost would be preferred to avoid potential "headaches down the road." The new piping has new control valves, isolation valves, balancing valves, strainers, and thermometers, etc. The existing steam and chilled water lines serving the court building were dug up and removed, and new hot and chilled water lines were installed in their place, using up-to-date engineering practices for proper burial protection.
The existing steam and hot water coils were replaced with new hot water coils. The new coil tubes are oriented horizontally instead of vertically like the existing steam units. Steam and condensate lines were abated and demolished only to the point in which they are out of the way for installation of the new hot water line.
All of which should is expected to produce substantial savings at the center. Building engineer Howard Steen reports that kWh savings are already up 10%, and that the center is spending 10% less on gas than it was a year ago. Added Utley, "The guaranteed energy contract made the project very appealing, and we knew we could increase our efficiency by 25 % to 35%, so those two things clinched the deal for this project." ES