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Background

Green Mountain Coffee Roasters (GMCR), a gourmet coffee roaster and packager, located in Waterbury, Vermont, had experienced several power disturbances a month, ranging in duration from less than a second to hours. Because the coffee roasting process cannot be interrupted, the outages had caused significant product loss.

Problem

GMCR needed a reliable backup power supply to prevent further loss. They contracted Northern Power Systems, who worked in conjunction with Niagara Mohawk Energy, to custom engineer and install the system. Since their process control devices could be disrupted by as little as a 20 cycle dropout, truly continuous power was required. Safety was also a priority, because the roasting process has an exothermic stage and can be a fire hazard if the machinery shuts down. Northern addressed GMCR’s needs through installing two grid-connected power sources that reduce utility power costs during peak use periods (peak-shaving) and provides highly reliable backup power. The system also incorporates the cost-saving function of heat recovery for potable hot water and space heating.

The combined heat and power system consists of one 95kW and one 280kW propane-fueled Waukesha Enginator®, providing 208 Volt 3 Phase power to critical load panels, which are also served by the utility. The genset operates full time during coffee production. In the event of an outage or anomaly as short as two cycles, the utility-side circuit breakers open and the critical electrical loads are seamlessly sustained by the generator.

Solution

Northern installed and programmed digital engine control and microprocessor-based utility-grade relay to provide system control and safety functions. The intelligence of the GMCR system is provided by Northern’s Engine Control System, which utilizes a programmable Generator Power Control (GPC). The custom-designed control system provides the optimal mix of power from the on-site generators and the utility grid. A Local Operator Interface provides control of equipment, and a display of electrical parameters, equipment status, and system alarms.

Waste heat from the Enginator water jacket is sent to super-insulated tanks that preheat wash water for processing and other building uses. An air/water heat exchanger on the engine exhaust preheats water in the building’s hydronic space heating system.

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