Temperature modeling of a land-based aquaculture system for the production of Gracilaria pacifica: Possible system modifications to conserve heat and extend the growing season

• A heat transfer model predicted Gracilaria pacifica system temperatures.
• A literature review indicated an ideal growing temperature of 21 °C.
• Using a cover raised system temperature by 2.80 °C during the winter months.
• A simple cover is not adequate to raise system temperatures to 21 °C.

Temperature control is a major cost for numerous aquaculture systems. Solar thermal engineering techniques can be used to identify inexpensive methods for conserving and capturing heat. Gracilaria pacifica, also known as the culinary ingredient ogo, is currently grown in land-based tanks at a site in Goleta, CA where influent sea water temperatures infrequently reach the 21–28 °C range that provides for optimal growth. The major objective of this study was to explore various designs of a G. pacifica tank culture system that maintain optimal water temperature year round to maximize growth. A model was constructed and calibrated by comparing results to a one-third scale pilot system operated in Davis, CA. For model calibration the most sensitive parameter such as cover optical properties were adjusted first and less sensitive parameters were adjusted later. The pilot system consisted of six tanks, three insulated with foam and a clear polyethylene cover (experimental), and three uninsulated and uncovered (controls). The model had weather data inputs including air temperature, humidity, wind speed, and solar radiation. The model was then compared to a full-scale system operated in Santa Barbara during the winter. The experimental pilot system was 4.93 °C warmer than the control pilot system under optimal weather conditions. The full-scale experimental system was 2.80 °C warmer than the control system under non-ideal conditions. The model demonstrated predictive accuracy under most weather conditions. Furthermore the model is robust enough to accept estimated values for many inputs and still produce accurate results, this suggests a simpler model may be feasible. A polyethylene cover and insulation are not sufficient in general for raising the water temperature to the optimum range during the winter; they may be during other times of the year when more solar energy is available, thereby extending the growing season.