Sustainable Marine Aquaculture

COMPARISON OF PERFORMANCE AND ECONOMICS OF SOLAR AND PROPANE GREENHOUSE HEATING SYSTEMS

Research Team:
George Buzyna (FSU) - Principle Investigator
Jeffrey Wilcox (FSU)
Nancy Marcus (FSU)

Energy closely follows feed as one of the major variable costs of production in recirculation aquaculture. Maintenance of optimal production temperatures allows farmers to bring crops to market in shorter time, with good feed conversion, with fewer catastrophes, and, ideally, when the market price is highest. Whether this results in greater profits is critically dependent on the cost of energy required. Further expansion of aquatic farming will require production in areas where environmental concerns are greater, water is less abundant, and/or climate is less than optimal for culture of high-value species. Recirculation aquaculture production is one appropriate technology to address these issues. This research attempts to determine whether solar technology can help reduce the cost of maintaining optimal production temperatures.

Two 14.6m x 9m x 4m air-inflated greenhouses each containing an 8500L recirculation system (3.65m x 1m tank, insulated with 5cm Styrofoam, sides and bottom, 60_ drum filter, fluidized bed biofilter, UV sterilization) were constructed. One system is heated to 25°C in winter via low-temperature solar panels (35m2), a 16,000L reservoir, and 73m of 1.25cm PVC pipe as heat exchanger recirculating at 115L/min, and cooled in summer by evaporative cooling of the greenhouse. The conventional system was heated to 25°C with two 1800W immersion heaters and cooled by evaporative cooling of the greenhouse. The conventional greenhouse will be upgraded to heating and cooling by a 2 hp heat pump beginning in September, 2003. Data sets are being collected to develop energy models of both systems (temperature: tanks, reservoir, solar panels, heat exchanger in/out, interior, exterior; flow: tanks, solar panels in/out, heat exchanger in/out; electric demand). Analysis of construction and operational costs, culture tank thermal stability, and predicted useful life of the equipment will be performed to determine whether solar technology has matured sufficiently to be a cost-effective alternative to compressive heating and cooling for maintaining optimal production temperatures in recirculation aquaculture.

Between January and April 2003, the solar system maintained the production system at 25°C +/-10C, with a reservoir temperature of 35°C to 46°C, despite outdoor ambient air temperatures as low as -12°C. The conventional system also maintained production temperatures of 25°C +/-10C. The evaporative cooling system has maintained both of the production systems between 25°C and 28°C through July 2003, despite outdoor ambient air temperatures as high as 37°C and relative humidity in the greenhouse up to 90%. Electric demand to maintain an equal winter thermal profile using resistive heating was 25% greater than in the conventional system.