Solar-Energy-System Performance Evaluation, April-August 1982, University of Minnesota Bookstore, Minneapolis, Minnesota.

摘要

The solar system at the University of Minnesota Bookstore provided a total of 5% of the combined space heating and cooling load of 825 million Btu. The solar savings ratio, which accounts for operating energy used to collect solar energy, was 0.02. The fossil energy savings were 154.6 million Btu, equivalent to nine tons of coal, but there was an electrical energy expense of 19.2 million Btu (5620 kwh). The system had a net energy savings of $49.09 based on energy costs of $41.36 per ton of coal and 5.75 cents per kwh. Major energy flows to the heating and cooling subsystems are presented in the Energy Flow Diagram. In terms of solar energy utilization, the space cooling subsystem used 82 million Btu compared to 10.7 million Btu used in the space heating subsystem. The active solar energy system was retrofitted in 1979 on a relatively new earth-sheltered building which houses a bookstore, admissions and records facility. The building is 95% below ground for energy conservation and to preserve open space on the campus. Other energy conservation features are triple glazing on the windows, clerestories for daylighting and passive solar energy collection in winter, and a warm-air heat recovery system on the ventilation air. Due to the energy conservation features, the solar collection subsystem could be downsized and still provide large solar fractions. The solar collector array is comprised of six stationary units of 10 movable reflectors, each about 110 feet long and one foot wide. These glass mirrors concentrate sunlight onto a copper absorber tube receiver. Solar heated water from the storage tank or the collector array and water heated with auxiliary steam via a heat exchanger are delivered to a 147-ton absorption chiller for space cooling or to the heating coils for space heating. (ERA citation 08:035539)