U.S. Army

Sierra Army Depot - Herlong, CA

EXECUTIVE SUMMARY [Continue to full document]

The United States Army Construction Engineering Research Laboratory (CERL) is implementing a project to demonstrate natural gas engine driven air compressors (NGEDAC) at army industrial facilities. This report documents the results of a compressed air survey conducted at the Sierra Army Depot (SIAD) to: (1) determine the suitability of SIAD as a host site for an NGEDAC demonstration and (2) identify compressed air system cost reduction/energy saving opportunities. Since a detailed compressed air system survey had recently been performed at SIAD addressing the cost reduction/energy saving opportunities, the focus of the work was on the NGEDAC suitability assessment. Science Applications International Corporation (SAIC), under contract to CERL, provided technical assistance in carrying out the survey, which was conducted on April 19, 2001.

The compressed air survey focused on the feasibility of installing a 125 hp, 600 scfm natural gas engine driven air compressor as a direct replacement for the existing electric motor driven air compressor of the same capacity. The existing unit is housed in building 210 but serves as the central compressed air source for two other buildings (208 and 209). Adequate space exists within this building for the NGEDAC. Natural gas is available and heat recovery for space heating appears promising.

The principal benefits of the NGEDAC unit for SIAD include:

• Net savings in operating costs
• Hedge against power disruptions – operates on natural gas, not electricity.
• Added capacity/redundancy for the compressed air system

The table below summarizes the energy performance and operating cost savings. The net annual operating cost savings are estimated to be $16,373.

¹ Electricity Costs: $.145/kWh average – includes demand @$7/kW and energy charges @.105/kWh (2/6/01 rate). Natural Gas Costs: $7.28/MBtu (Average for April 2000 – March 2001)

² Based on (.22/.8) *heat value of natural gas into the engine, where .22 is the fraction of recoverable heat and .8 is assumed efficiency of heating or process water boiler displaced.

The survey indicated that other opportunities for reducing energy and operating costs associated with the compressed air system, that had been identified previously have not yet all been implemented (Lin, et al, Compressed Air System Survey at Sierra Army Depot, ERED/CERL TR –00-37, November 2000). These six opportunities (other than the NGEDAC) included:

• Repair Compressed Air Leaks
• Change the Air Compressor Control to Low Demand Mode
• Disconnect the Air Receiver from the Oil/Water Separator
• Duct Outside Air into the Air Compressor Room
• Install Sensor-Type Valves on the Purifier Pre-Filters
• Replace the Timer-Type Drain Valves with Sensor-Type Valves

Collectively, these six opportunities represented an annual cost savings of $15,541 in electricity costs, an energy savings of 181,409 kWh, and a demand reduction of 49.9 kW. Given the recent price increases in electricity, these savings opportunities are now worth more than $25,000, and should be increasingly attractive to SIAD.