What is it about?
In this work, the authors develop and evaluate a hybrid solar-geothermal absorption air-conditioning system (AACS) using NaOH-H₂O as the working fluid, aiming to reduce costs and environmental impact compared to traditional systems. The main idea is to use a combination of two renewable systems nearest to the geothermal wells.
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Why is it important?
This research presents a hybrid solar-geothermal absorption air-conditioning system (AACS) utilizing sodium hydroxide-water (NaOH-H2O) as a cost-effective alternative to traditional absorption air conditioning systems, leveraging low-enthalpy geothermal heat from shallow wells (50-55 m deep) in Baja California Sur, Mexico, coupled with parabolic trough collectors (PTC) to achieve the required thermal input. Numerical heat transfer simulations demonstrated that maximum convective heat transfer coefficients and temperatures (51.0 to 56.2°C) occur at fluid velocities close to 5.0 m/s and depths near 40 m, enabling geothermal preheating of water from ambient to 63°C before solar enhancement. Experimental evaluations of the PTC field, using water as the working fluid, yielded average storage tank temperatures from 92.9 °C to 93.8°C. Under design conditions—generator at 90°C, condenser and absorber at 35°C (natural convection), and evaporator at 10°C—the system's coefficient of performance (COP) was calculated as 0.71, offering a sustainable solution for cooling loads up to 7.05 kW while reducing operational costs and CO2 emissions compared to fossil fuel-based systems.
Perspectives
Future challenges for hybrid solar-geothermal absorption air-conditioning systems using NaOH-H2O include enhancing system scalability beyond small cooling loads like 7.05 kW to meet larger commercial demands, improving the coefficient of performance (COP) from 0.71 through advanced heat exchanger designs and optimized fluid dynamics to compete with conventional systems, and addressing the corrosiveness of NaOH-H2O, which necessitates durable, corrosion-resistant materials to prevent long-term degradation and maintenance issues. High initial capital costs for parabolic trough collectors, shallow geothermal wells, and integration components remain a barrier, requiring economic incentives and standardized methodologies to shorten payback periods often exceeding 5-12 years without subsidies. Technical complexities such as managing solar variability, geothermal resource depletion over time due to soil hydrology and moisture variations, and ensuring consistent performance in diverse climates pose ongoing hurdles, particularly in regions without ideal geothermal gradients or solar irradiance. Additionally, limited public awareness, site-specific limitations, and the need for policy frameworks to support hybrid renewable integration could hinder widespread adoption. Emerging advancements in membrane technology and thermochemical storage offer potential solutions, but they require further validation for cooling applications.
Professor Rosenberg J Romero
Universidad Autonoma del Estado de Morelos
Read the Original
This page is a summary of: Hybrid Solar-Geothermal Energy Absorption Air-Conditioning System Operating with NaOH-H2O—Las Tres Vírgenes (Baja California Sur), “La Reforma” Case, Energies, May 2018, MDPI AG,
DOI: 10.3390/en11051268.
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