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Shallow Geothermal Systems (SGS) are widely used to provide low-cost heating and cooling of residential and commercial buildings. SGS can be an economically-viable solution even for commercial buildings, where controlled temperature is fundamental for the production processes. To assess the thermal resistance of the soil and the performance of a SGS, Thermal Response Tests (TRT) must be performed. TRT machines are today designed mainly for short term monitoring, for relatively deep SGS (up to 200 m) and for being used by expert operators. Lightweight, low-cost machines for both fast and long term, reliable and unattended TRT for very Shallow Geothermal Systems (vSGS) are not available today. This paper describes the design of a micro-TRT machine (mTRT) for vSGS, which is gaining interest in the civil engineering, environmental, energy and food chain sectors. The paper describes the features of the wireless monitoring system, the design choices to achieve the required accuracy and the software developed for adding remote control capability. Experimental validation in a real test field demonstrates the quality of measurements collected for analysing the TRT data.

Shallow Geothermal Systems (SGS) are widely used to provide low-cost heating and cooling of residential and commercial buildings. SGS can be an economically-viable solution even for commercial buildings, where controlled temperature is fundamental for the production processes. To assess the thermal resistance of the soil and the performance of a SGS, Thermal Response Tests (TRT) must be performed. TRT machines are today designed mainly for short term monitoring, for relatively deep SGS (up to 200 m) and for being used by expert operators. Lightweight, low-cost machines for both fast and long term, reliable and unattended TRT for very Shallow Geothermal Systems (vSGS) are not available today. This paper describes the design of a micro-TRT machine (mTRT) for vSGS, which is gaining interest in the civil engineering, environmental, energy and food chain sectors. The paper describes the features of the wireless monitoring system, the design choices to achieve the required accuracy and the software developed for adding remote control capability. Experimental validation in a real test field demonstrates the quality of measurements collected for analysing the TRT data.

Nordhaus (1973) has in his seminal contribution addressed two emerging questions in the field of energy economics. First, how do current market prices of natural resources reflect true scarcity fro...

Nordhaus (1973) has in his seminal contribution addressed two emerging questions in the field of energy economics. First, how do current market prices of natural resources reflect true scarcity fro...

Abstract Water transport control is the major issue of direct methanol fuel cell. High water flow rates through the fuel cell imply extra water feeding at the anode and flooding at the cathode. In the present work, water transport and flooding in the direct methanol fuel cell are investigated through both experimental and modeling analyses and an interpretation of such phenomena is proposed. The model is validated on the experimental data of two different fuel cells in an extensive range of operating conditions. The analysis elucidates that water transport through the cathode diffusion layer is determined by vapor diffusion, slightly affected by current density, and by liquid water permeation proportional to current density, that occurs when liquid pressure in the electrode exceeds a threshold value. To simulate the effects of cathode diffusion layer flooding two mechanisms must be considered simultaneously: superficial pore obstruction, proportional to liquid water concentration in cathode channel, and bulk pore obstruction, proportional to liquid water permeation. The modeling analysis proposes the correlations to reproduce the effects of cathode flooding and permits to discuss the onset and magnitude of such phenomenon and the influence of micro-porous layer.

Abstract Water transport control is the major issue of direct methanol fuel cell. High water flow rates through the fuel cell imply extra water feeding at the anode and flooding at the cathode. In the present work, water transport and flooding in the direct methanol fuel cell are investigated through both experimental and modeling analyses and an interpretation of such phenomena is proposed. The model is validated on the experimental data of two different fuel cells in an extensive range of operating conditions. The analysis elucidates that water transport through the cathode diffusion layer is determined by vapor diffusion, slightly affected by current density, and by liquid water permeation proportional to current density, that occurs when liquid pressure in the electrode exceeds a threshold value. To simulate the effects of cathode diffusion layer flooding two mechanisms must be considered simultaneously: superficial pore obstruction, proportional to liquid water concentration in cathode channel, and bulk pore obstruction, proportional to liquid water permeation. The modeling analysis proposes the correlations to reproduce the effects of cathode flooding and permits to discuss the onset and magnitude of such phenomenon and the influence of micro-porous layer.

Nanosecond-level transient electromagnetic disturbance (TED), including very fast transient overvoltage caused by operation of disconnectors, high-altitude electromagnetic pulse, and many other fast transients may interfere or even damage the electrical equipment. As one of the main overvoltage protective equipment, the protective performance of metal-oxide surge arresters (MOAs) under nanosecond-level TED should be investigated and then compared with that under microsecond-level TED, especially the lightning impulse. Based on a testing platform containing a 400-kV pulse generator with adjustable rise time from 5 to 100 ns, the behaviors of nonlinearity, fast impulse response, and converting impedances of three types of 10-kV MOAs under TED with different rise time were explored experimentally in this article. The peak residual voltages of 10-kV MOAs under TED with the rise time of 5 ns at 5 kA are 50.2–60.7% higher than those under the lightning impulse. The rise time of TED has significant influence on the peak voltage and impedance converting behaviors of MOAs. A circuit model of 10-kV MOAs under nanosecond-level TED is built and validated by experimental results, which can be applied in insulation coordination and design of protective devices against TED.

Nanosecond-level transient electromagnetic disturbance (TED), including very fast transient overvoltage caused by operation of disconnectors, high-altitude electromagnetic pulse, and many other fast transients may interfere or even damage the electrical equipment. As one of the main overvoltage protective equipment, the protective performance of metal-oxide surge arresters (MOAs) under nanosecond-level TED should be investigated and then compared with that under microsecond-level TED, especially the lightning impulse. Based on a testing platform containing a 400-kV pulse generator with adjustable rise time from 5 to 100 ns, the behaviors of nonlinearity, fast impulse response, and converting impedances of three types of 10-kV MOAs under TED with different rise time were explored experimentally in this article. The peak residual voltages of 10-kV MOAs under TED with the rise time of 5 ns at 5 kA are 50.2–60.7% higher than those under the lightning impulse. The rise time of TED has significant influence on the peak voltage and impedance converting behaviors of MOAs. A circuit model of 10-kV MOAs under nanosecond-level TED is built and validated by experimental results, which can be applied in insulation coordination and design of protective devices against TED.