HHB Engineers selected for Maxwell AFB Central Plant Upgrade

HHB Engineers has been selected to design a major upgrade to the Central Chilled Water Plant at Maxwell AFB, outside Montgomery, AL. The upgrade to include replacement of 5 of the 6 chillers, currently 800-tons each with greater capacity chillers.  Cooling towers to be upgraded and chiller pumps to be replaced.  The building was constructed with all chillers located on a mezzanine level, and boilers located at grade.  The boilers have been removed, and one chiller has been installed at grade.  This project will install all the new chillers at grade level, utilizing mezzanine space for the chilled water pumps.  Project construction to be phased as the plant must continue to provide chilled water to the base throughout construction.

Initial construction cost estimate is between $3M-$5M.

HHB has a 30 year history of work at the Maxwell central plant.  HH&B has been involved in all phases of design to convert a circa 1960 central energy plant to its current configuration today. The plant was constructed in 1954 for the USAF Air War College as an all steam utility plant: steam turbine pumps, chillers and boiler ID fans. Chillers used Murray non-condensing steam turbines and required a  600-hp industrial type 125-psig water tube boiler. Excess steam was piped through a condenser using the cooling towers as a heat sink. Starting in 1985, the USAF initiated a multi-year plan to upgrade the plant and improve the overall system efficiency.

The “chilled water” work consisted of replacement of the 4000 tons of steam driven refrigeration with 4800 tons of electric driven chillers, de-coupling of the plant chilled water piping from the underground distribution loop, replacement of several miles of underground distribution piping, providing a new plant control system, and revising the condenser water system to a variable flow type.  Included as part of the work was the re-configuration of the 4800 ton cooling tower piping to a gravity collection and pumping system, the addition of an 800 ton field erected cooling tower cell to the existing bank of cooling towers, and the installation of pump service crane facility.

HHB involvement included the following:

  • Replacement of five 600-ton steam/absorption chillers with 800-ton electric drive chillers. This significantly reduced the steam requirement for the plant, requiring only two of the 5 boilers to satisfy winter load.
  • Replacement of all chiller and condenser pump with electric drive.
  • Conversion of the plant from constant flow to primary/secondary variable flow.
  • Hydraulic modeling of the 1.5 mile long chilled water distribution system. This allowed the USAF to upgrade portions of the chilled water distribution system to address flow shortages.
  • Upgrades and repairs to boiler water tubes and burner refractory. Upgrade of boiler burners and control. Induced draft burners were replaced with register type forced draft burners. (Note, these boiler have since been removed)
  • Upgrade to plant electrical power supply and interior distribution. With the addition of new electric drive equipment, the electrical power was upgraded
  • HHB has been responsible for over $20 million of mechanical upgrades to this plant.
  • Design completed in 2014 (PNQS-13-6160) included improvement of the condenser and chilled water control.  Project included condenser water flow, variable speed drives on cooling towers, upgraded DDC controls, and control of the chilled water leaving temperature.

HHB Engineers has experience with other central utility plants other than at Maxwell AFB, view our portfolio for more information.