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Background

The Propane Education & Research Council and the Gas Technology Institute field-tested an 810-kilowatt propane-fueled combined heat and power system at the Kauai Marriott Resort and Beach Club. The field test provides the propane and lodging industries with needed data on the in-service performance of propane-fueled engine technology for continuous use in commercial combined heat and power and distributed generation applications.

The Team

Project partners include the Gas Technology Institute (teaming with The Gas Company through the National Accounts Energy Alliance), PERC, and the Kauai Marriott Resort and Beach Club. The resort provided electricity, air conditioning, and hot water for guest use and hotel operations using two new 450-ton electric chillers for air conditioning, two 20-year-old 140-ton heat pumps for hot water and supplemental cooling, and two diesel-fired steam boilers for laundry and kitchen use.

The New System

The new building cooling, heating, and power system replaces the aging 140-ton heat pumps with two 405-kilowatt Caterpillar 3412LE generator sets, a heat recovery system, and a 244-ton absorption chiller. The system is integrated with the resort’s existing diesel-fired boilers (which now provide steam for laundry use and supplemental domestic hot water heating) and 450-ton electric chillers. To preserve the resort’s electric rate structure, the system is sized to allow the resort to purchase electricity from the grid and use on-site generation only as a supplement to meet at least 50 percent of the resort’s daily electric load.

How It Works

The generator sets efficiently combust propane fuel to generate electricity, which is fed into a facility system that can provide power to the entire campus. Heat exchangers capture waste heat produced by the generators and transfer it to the resort’s swimming pool, domestic hot water system, and absorption chiller. Any unrecovered waste heat is dumped to a 600-ton cooling tower. The hot water system uses the captured heat to heat water for domestic uses (such as bathing, showering, and washing dishes). The absorption chiller uses the captured heat to provide chilled water for a portion of the resort’s air conditioning. Switchgear and a utility transformer connect the system to the electrical grid. A web-accessible data monitoring program measures the system’s overall mechanical and economic performance, collecting data at 15-minute intervals from approximately 50 instruments.

Estimated Payback

The system could have

a payback
period of just
6.3 years

Several factors limited savings from operation during the demonstration, including record-low electricity rates, unusually high propane prices, and technical issues that prevented the system from realizing the maximum savings from pool heating and absorption cooling. Low electricity rates were especially problematic because a majority of the savings from operation are derived from the cost of utility-provided electricity that is displaced by on-site generation. As a result, the payback period, calculated based on performance during the demonstration, totals approximately 20 years. Under more realistic circumstances (a price of 30 cents per kilowatt hour of electricity and a price of $2.30 per gallon of propane), the system can realize a much shorter payback period—6.3 years.

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