Hybrid Solar-Geothermal Energy Absorption Air-Conditioning System Operating with NaOH-H2O—Las Tres Vírgenes (Baja California Sur), “La Reforma” Case

Abstract

Solar and geothermal energies are considered cleaner and more useful energy sources that can be used to avoid the negative environmental impacts caused by burning fossil fuels. Several works have reported airconditioning systems that use solar energy coupled to geothermal renewable energy as a thermal source. In this study, an Absorption AirConditioning System (AACS) used sodium hydroxide-water (NaOH-H 2 O) instead of lithium bromide-water to reduce the cost. Low enthalpy geothermal heat was derived from two shallow wells, 50 and 55 m deep. These wells are of interest due to the thermal recovery (temperature vs. time) of 56.2 • C that was possible at the maximum depth, which can be used for the first stage of the process. These wells were coupled with solar energy as a geothermal energy application for direct uses such as airconditioning systems. We studied the performance of an absorption cooling system operating with a NaOH-H 2 O mixture and using a parabolic trough plant coupled with a low enthalpy geothermal heat system as a hybrid heat source, as an alternative process that can help reduce operating costs and carbon dioxide emissions. The numerical heat transfer results showed the maximum convective heat transfer coefficient, as function of fluid velocity, and maximum temperature for a depth higher than 40 m. The results showed that the highest temperatures occur at low fluid velocities of less than or equal to 5.0 m/s. Under these conditions, reaching temperatures between 51.0 and 56.2 • C in the well was possible, which is required of the geothermal energy for the solar energy process. A water stream was used as the working fluid in the parabolic trough collector field. During the evaluation stage, the average experimental storage tank temperature achieved by the parabolic trough plant was

Thermodynamic Analysis of a Half-Effect Absorption Cooling System Powered by a Low-Enthalpy Geothermal Source

“…The variation in ground temperature is caused by seasonal fluctuations of air temperature on the surface that can reach depths of around 20 m [20,21]. Equation 2is used to describe the transient heat transfer in a semi-infinite solid, where T is temperature ( • C), t is time (s), α is the thermal diffusivity (m 2 /s), and Z is depth (m):…”

“…The shallow thermal perturbation behaves like a sinusoidal wave with time, and, for solving Equation 2, a sinusoidal temperature mathematical model is used [21,22]:…”

“…where γ is the inverse of the damping depth, and P is the period of the oscillation (365 days) in hours. For the numerical heat transfer analysis between well W1 and the U-tube heat exchanger, the convective heat transfer process was evaluated, so for an estimation of the maximum water temperature to the heat exchanger outlet, the following empirical relationship for pipe and tube flow was used [21,23]:…”

“…where Re d and Pr correspond to Reynolds and Prandtl numbers, respectively, and the exponent n is equal to 0.4 for heating and 0.3 for cooling [24]. The thermal properties of water for temperatures between 20 and 100 • C were calculated from the following polynomial regression equations [21]:…”

Enhancement Study of Ice Storage Performance in Circular Tank with Finned Tube

“…As a typical application, the ice storage technique stores cooling capacity through the solidification of water during the valley electricity demand period and releases the cooling capacity by melting the ice during the peak electricity demand period. Peak load shifting of the electrical grid [11,12] can be achieved through ice storage with low cost, which is of significance in maintaining the steady operation of the electrical grid. Hence, extensive efforts have been devoted to the study of ice storage processes.…”