Abstract
Conventional vapor compression cooling is a well-established and reliable technology, but consumes a great deal of energy. Therefore, finding less energy-intensive methods of cooling is vital when it comes to conserving energy. One possibility for 'greener' cooling is nocturnal cooling, which provides cooling by dissipating heat to the cooler nighttime environment. Nocturnal cooling is particularly well-suited to climates with low humidity and high diurnal temperature variation, such as California's Central Valley (as well as much of the rest of the Western US). In this project, I built a simple nocturnal chiller using a solar collector, a solar water heater circulating pump, and an insulated tank for storage of chilled water. Temperature data was collected over the course of several nights while the system operated in order to evaluate the performance of the system. Typically, this chiller would cool 6.5 gallons of water by about 25 degrees F (from about 90 degrees F to about 65 degrees F) in about 60 minutes. The value of Fr (a figure of merit for collector plates) averaged around .6-.8 when the temperature of the plate inlet was significantly above ambient, but dropped to around .3 when the inlet temperature approached ambient. The heat flux was very linear in nature, following a line defined by q = 2.0 Delta T (where q is in BTU/hr x ft2, and Delta T is the temperature difference between he plate and air in degrees F). Runs were made at three different flowrates (.5, 1.0, and
1.5GPM). Performance increased with flowrate, but not by much (a few percent with each increase in flowrate). Nocturnal cooling is a viable means of cooling, since it requires no new technology and is simple. But it would require a large collector area, and most likely a large tank for storage. However, with certain modifications, like fan-coils to cool the air by convection or use of photovoltaic panels as radiators, nocturnal cooling might become more feasible. Further study is required for all of these.