Numerical investigation on a low energy-consumption heating method for recirculating aquaponic systems

Abstract

In a recirculating aquaponic system (RAS), the heating method based on an electric heater requires considerable amounts of electrical energy to maintain the water temperature for optimal warm-water fish growth conditions. Minimizing electrical energy consumption in the RAS is a great challenge. To solve this problem, a novel heating method that uses a combination of helically coiled heat exchangers (HCHEs) and a thermal energy storage (TES) unit is proposed to replace the electric heater. Several studies on heating and cooling systems with HCHEs and TES tanks have been conducted, but their integration in RASs is very rare. In this study, the thermal energy of the water in an RAS was the research objective. A computational fluid dynamics approach was adopted for transient analysis and inspection of the HCHE model considering eight cases with four temperature levels, 55, 60, 70, and 80 °C, and three mass flow rates, 0.166, 0.249, and 0.332 kg/s. The results showed that the HCHE was compatible with the regular heat sources of the TES unit (including solar collectors and heat pump systems). The temperature distribution of the water in the fish tank, from 26.75 to 30 °C, was suitable for maintaining the health of warm-water fish. To heat 3.4 m3 of the fish tank water from 24.5 to 28 °C, case 6 (where the temperature and mass flow rate of hot water were 70 °C and 0.332 kg/s, respectively) obtained the best results during a period of 26 min, usable heat transfer rate of 31.8 kW, and thermal efficiency of 76.1%. On the contrary, the results for case 1 (where the temperature and mass flow rate of hot water were 60 °C and 0.166 kg/s, respectively) were 70 min, 11.8 kW, and 57.5%, respectively.