Jet impingement is considered to be an effective technique to enhance the heat transfer rate, and it finds many applications in the scientific and industrial horizons. The objective of this paper is to summarize heat transfer enhancement through different jet impingement methods and provide a platform for identifying the scope for future work. This study reviews various experimental and numerical studies of jet impingement methods for thermal-hydraulic improvement of heat transfer surfaces. The jet impingement methods considered in the present work include shapes of the target surface, the jet/nozzle–target surface distance, extended jet holes, nanofluids, and the use of phase change materials (PCMs). The present work also includes both single-jet and multiple-jet impingement studies for different industrial applications.

Ground-source heat pumps (GSHPs), despite their high efficiencies, are still not as cost-effective as air-source heat pumps, especially in urban environments, due to the necessity of drilling/excavation. Integrating GSHPs into existing geo-structures, such as underground tunnels, can play a vital role in reducing the overall costs of GSHP systems and promoting their use in cities. Tunnels can be realized through artificial ground freezing (AGF) by using probes for circulating the freezing fluid, which are left in the ground once the tunnel is completed. The novelty of the present work lies in the proposal of a sustainable reuse of AGF probes as ground heat exchangers (GHEs). The idea of converting AGF probes is both sustainable and cost-effective for GSHPs, as it can reduce installation costs by eliminating the drilling/excavation process. A test was performed for the first time in the Piazza Municipio metro station in Naples, Southern Italy, where several AGF probes, initially used for the construction of two tunnels, have then been converted into GHEs. The probes have been connected to a testing device called the energy box. The experiments included testing the heat transfer in the recovered AGF probes through cooling and heating operations. This work presents a numerical simulation of a test that has been validated against experimental results.

Achieving net-zero energy in rural communities requires coordinated optimization of energy demand and renewable supply; however, rural electrification strategies in developing regions frequently adopt generation-centric approaches that overlook thermophysical demand reduction and are costly and unsustainable. This study develops and empirically validates an integrated demand-first framework for Net Zero Energy Villages (NZEVs), defined here as achieving an annual operational energy balance within a standalone microgrid configuration. The applied methodology combines (i) detailed household and community load assessment, (ii) comparative EnergyPlus simulations of seven locally available envelope materials across multiple climatic zones, (iii) pilot-scale experimental validation through indoor thermal performance monitoring, and (iv) photovoltaic (PV) microgrid design and techno-economic optimization using HOMER Pro in four distinct climatic regions of Pakistan. Results demonstrate that optimized Styrofoam insulation reduces annual energy demand by up to 45% while maintaining indoor thermal comfort within 15–25 °C. Experimental measurements confirm simulation accuracy within ±1.5 °C. Demand reduction enables significant downsizing of PV and storage systems, achieving Levelized Costs of Energy between 0.182–0.203 USD/kWh and a minimum Net Present Cost of 38,087 USD in Jacobabad. Across all locations, optimized PV microgrids economically outperform diesel-based alternatives. By coupling thermophysical demand reduction with experimentally validated modeling and microgrid techno-economic sizing, this study advances NZEV design beyond isolated material or PV sizing analyses. Although demonstrated in Pakistan, the proposed framework is transferable to hot-climate, resource-constrained regions seeking cost-effective and climate-resilient rural electrification, directly contributing to UN SDG 7 (Affordable and Clean Energy) and SDG 13 (Climate Action).