Investigation of geothermal energy utilization for thermal regulation of aquaculture raceway

ABSTRACT

Aquaculture raceway temperature has a direct impact on the aquatic specie being reared. In regions that undergo significant seasonal temperature variations, the thermal management of the raceway temperature becomes a challenge, directly impacting the production yield. This study investigates a novel approach to regulate the raceway temperature in a sustainable way by utilizing geothermal energy. A numerical energy model was developed to simulate heat transfer in a geothermal system encompassing both the individual borehole heat exchangers and their thermal interactions. Simulations were conducted for different configurations of the geothermal system over a complete seasonal cycle. Results show that flow rate, number of boreholes and the borehole spacing influence the temperature of the fluid at the raceway inlet. An increase in the number of boreholes provided better thermal regulation but an increase in the flow rate through the boreholes provided less thermal regulation. A borehole spacing of 6 m was found to be appropriate to reduce thermal interference. It was also observed that an increase in the fraction of the fluid passed through the geothermal system enhances the overall thermal regulation, with higher thermal regulation at lower flow rates. Results show that when 100% of the fluid passed through a 64 boreholes geothermal system, the average regulated raceway inlet temperature was 23% higher in winter months and 16% lower in summer months at the flow rate of 21.5 L/s compared to than at 43 L/s.

KEYWORDS:

• Geothermal energy
• aquaculture
• raceway
• energy modeling
• thermal regulation

Nomenclature

$c_p$ specific heat capacity of water [kJ/kg⋅K]

$D$ distance between up-flow and down-flow pipes

$Fo$ Fourier number [INSERT]

$H$ total u-pipe depth [m]

$h_z$ depth of interest [m]

$k$ thermal conductivity [W/mK]

$L_{Pipe}$ total u-pipe length [m]

$l_i$  position of borehole in the × direction [m]

$\dot{m}$ mass flow rate [kg/s]

$N_{BHE}$ number of boreholes []

$\text{mathop qlimits^}$ heating rate per unit length [INSERT]

$R^{\mathrm{\Delta }}$ thermal resistance [INSERT]

${\bar{R}}_i$ dimensionless distance between boreholes []

$r$ radius [m]

$S$ spacing between boreholes [m]

$T$ temperature [°C]

$t$ time [s]

$w_i$ position of borehole in the y direction [m]

$z$ distance along the u-pipe [m]

$\alpha$ thermal diffusivity [m²/s]

${\tau }_i$ reference time [s]

Acknowledgments

Authors would like to acknowledge the support by the Natural Science and Engineering Research Council (NSERC) [RGPIN-2017-04078 and RGPIN-2018-05653] and the Western University.

Additional information

Funding

This work was supported by the Natural Sciences and Engineering Research Council of Canada [RGPIN-2017-04078, RGPIN-2018-05653].