The City of San Luis Obispo in California selected a cogeneration system to provide electricity and heat for its aquatics center. The San Luis Obispo (SLO) Swim Center is the city’s only public aquatics facility, and it provides valued services year-round. It features an outdoor 50-meter by 25-yard Main Pool with temperature controls keeping the water between 78 and 82 degrees. A Therapy/Tot Pool is maintained at 88 degrees with depths ranging from 1 to 4 feet. These pools serve the community by being available for public swimming, therapy sessions, daily lap swimming, and various exercise, jazzer‐bubbles, and private and public swim lessons. The facility is also used by the local swim club, the high school, and the annual SLO Triathlon. The Public Works Department administers maintenance for the pools, bathhouses, and grounds.
“With the proper maintenance, the system has proven to be reliable. In addition to lower utility costs to power the facility, we have seen a large reduction in boiler operation during the spring, summer, and fall months through the use of the heat exchanger to heat the pool water during colder months. The decreased boiler run times have increased utility savings, prolonged equipment life, and led to fewer break downs.” – Greg Cruce, Facility Maintenance, City of San Luis Obispo
The cogeneration project is load following, which adjusts as the facility’s energy demand fluctuates. As electricity is produced by the microturbine, the exhaust is routed to a Cain Industries heat exchanger. The maximum exhaust heat content from the microturbine is 541,000 Btu/hr. whereas the the heat exchanger can recapture up to 400,000 Btu/hr, or 70% of the exhaust energy, into useful pool water heating. Overall system efficiency is around 70%.
The system runs 24/7/365. It is set up to load-follow the facility demand to maximize efficiency and financial return. The system has proven to be very reliable and with regular maintenance has experienced few extended downtimes.
Depending on the ambient and pool temperature (80-degree set point), the heat exchanger modulates natural gas consumption. If the pool water is at or above the desired temperature, 100% of the exhaust heat will be sent to atmosphere. The heat exchanger has the capabilities to modulate 0‐100%.
The main pool has two 1.5 million Btu/hr boilers. During the spring and fall months, the boiler run time is reduced drastically by using the cogeneration waste heat. In the summer months, which consist of cool nights on California’s central coast, the boiler almost never runs.
PROJECT: 60-kW CHP System
LOCATION: San Luis Obispo, CA
MARKET SECTOR: Government Recreation Facility
FACILITY SIZE: A 600,000‐gallon Olympic‐sized pool, a 35,000‐gallon therapy pool, 6,000 sq. feet of bathhouse on a 2‐acre lot.
FACILITY PEAK LOAD: 80 kW
EQUIPMENT: 60‐kW Capstone C60 microturbine, Cain Industries heat exchanger
FUEL: Natural gas
USE OF THERMAL ENERGY: Pool water heating
CHP TOTAL EFFICIENCY: About 70%
TOTAL PROJECT COST: $367,795 before 30% SGIP incentive on eligible project costs
ANNUAL ENERGY SAVINGS: ~$35,000
PAYBACK: 7 years
CHP IN OPERATION SINCE: 2005
REASONS FOR CHP:
- Energy savings
- “Free” pool heating
- Lower electrical demand required from grid
- Taking advantage of lower natural gas prices