Sirichai Thepa

Field investigation of night radiation cooling under tropical climate

This paper discusses the feasibility of cooling by using night radiation under Thailand’s hot and humid climate. Four types of roof radiators were made by using common construction materials. They were examined under three sky conditions: clear, cloudy and rainy, respectively. Investigation was done, mainly, based on the temperature of different surfaces of a roof radiator. The experimental results showed that the depression of different surface temperatures is in the range of 1–6°C below ambient temperature under clear and cloudy skies. Under rainy skies, the temperature of different surfaces of roof radiators and ambient air was fairly close. Apart from sky conditions, the factors which affect the night radiation cooling are the thermal emissivity of materials and water condensation on the radiator surface area. Finally, this first study indicated that cooling by using night radiation is feasible mainly during tropical winter season.

Assessment of photovoltaic pumping systems in Thailand - one decade experience

By mid 1999 nearly 1000 rural villages in Thailand have been installed with photovoltaic water pumping units. The cumulative wattage is close to 1 MWp. Over 80% are in the Northeast. We conducted a survey between 1995 and 1998 on 489 units, representing over 80% of the units installed then in that region. Interviews were conducted with 360 water users from 18 villages. The results indicate that 45% of the units have been damaged and broken down. Important sources of damages are motor/pump units (35%) and inverters (19%). Inappropriate siting, lack of adequate preparation of villagers and follow-ups by respective agencies are major factors contributing to the untimely damages and breakdown.

Field study using the ground as a heat sink for the condensing unit of an air conditioner in Thailand

This paper reports on an investigation of the feasibility of using earth to absorb the heat normally rejected into the atmosphere by the condensing unit of a conventional air conditioner. To this end, a copper tube of about 67 m in length was buried at a depth of 1 m underground, where the temperature was constant at about 27°C year round. The copper coil of an air type condenser is about 22 m long. For the buried condenser, the R-22 refrigerant requirement was 5.8 kg as compared with 1.2 kg for the air condenser system. It was found that with this modified condensing unit, the coefficient of performance (COP) was much higher than that of a conventional one: it varied between 7.1 (daytime) and 8.1 (nighttime), compared to 2.8 and 3.1, respectively. The ground temperature near the buried copper coil did not increase, thus demonstrating the ability of the soil to dissipate the absorbed heat into the ground. Consequently, there is a high potential for contributing to environmental protection by using the ground as a heat sink. The elimination of the condensing fan is an additional advantage of the buried condenser system.

A microcontroller based islanding detection for grid connected inverter

This paper presents the development of a microcontroller based islanding detection for grid connected inverter with very simple under/over voltage and under/over frequency islanding detection algorithms. The system based on a microcontroller from Microchip Technology Inc. PIC family. A PIC microcontroller searches the under/over voltage and under/over frequency from utility grid and processed the value of voltage and frequency for turned on-off relay between grid connected inverter and utility grid.

CPLD-based islanding detection for mini grid connected inverter in renewable energy

This paper presents the development of a CPLD-based islanding detection for mini grid connected inverter in renewable energy with very simple under/over voltage and under/over frequency islanding detection algorithms. The system was implemented on a single XC9572 complex programmable logic device (CPLD) chip using schematic based and VHDL based synthesis model The CPLD monitor the under/over voltage and under/over frequency of utility grid and processed the value of voltage and frequency for turned on-off relay between mini grid connected inverter and utility grid.

Improving indoor conditions of a Thai-style mushroom house by means of an evaporative cooler and continuous ventilation

The paper discusses the effect of an evaporative cooling process and continuous ventilation for improving the indoor conditions of a conventional Thai-style mushroom house. A numerical model describing the behaviour of the Thai-style mushroom house model was developed. It was validated by comparing its output with that of the experiment of a small model of a mushroom house. It was found that the combination of evaporative cooling and continuous ventilation reduced the temperature and increased the relative humidity of air inside a mushroom house that is suitable for growing Lentinus.

Multi-Layered TiO2 Films towards Enhancement of Escherichia coli Inactivation

Crystalline TiO2 has shown its great photocatalytic properties in bacterial inactivation. This work presents a design fabrication of low-cost, layered TiO2 films assembled reactors and a study of their performance for a better understanding to elucidate the photocatalytic effect on inactivation of E. coli in water. The ability to reduce the number of bacteria in water samples for the layered TiO2 composing reactors has been investigated as a function of time, while varying the parameters of light sources, initial concentration of bacteria, and ratios of TiO2 film area and volume of water. Herein, the layered TiO2 films have been fabricated on the glass plates by thermal spray coating prior to screen printing, allowing a good adhesion of the films. Surface topology and crystallographic phase of TiO2 for the screen-printed active layer have been characterized, resulting in the ratio of anatase:rutile being 80:20. Under exposure to sunlight and a given condition employed in this study, the optimized film area:water volume of 1:2.62 has shown a significant ability to reduce the E. coli cells in water samples. The ratio of surface area of photocatalytic active base to volume of water medium is believed to play a predominant role facilitating the cells inactivation. The kinetic rate of inactivation and its behavior are also described in terms of adsorption of reaction species at different contact times.

FPGA-based islanding detection for grid connected inverter

This paper presents the development of a FPGA based islanding detection for grid connected inverter with simple under/over voltage and under/over frequency islanding detection algorithms. The design is based on the Xilinx chip XC4005E field programmable gate array (FPGA). The FPGA is used for all system logic function. This allows software development, testing, implementation and modification of logic circuitry without hardware modification. The FPGA monitor the under/over voltage and under/over frequency of utility grid and processed the value of voltage and frequency for turned on-off relay between grid connected inverter and utility grid. The results are provided to demonstrate the effectiveness of the design.

Comparison between FPGA-Based and dsPIC-Based islanding detection for grid connected inverter in a photovoltaic system

This paper presents the comparison between FPGA-based and dsPIC-based islanding detection for grid connected inverter in photovoltaic (PV) system with under/over voltage and under/over frequency islanding detection algorithms. The comparison is based on the XC4005E field programmable gate array (FPGA) and the dsPIC30F2010 high-performance digital signal controller. The prototypes of the FPGA and the dsPIC are monitor the grid voltage and grid frequency at the point of common coupling (PCC) between the grid connected inverter, the local load and the distribution transformer and processed the value of voltage and frequency for turned off the relay between the grid connected inverter and the utility grid. The results of study, the prototypes can turn off the relay when the voltage is change under 200 V or over 240 V and frequency is change under 48 Hz or over 52 Hz. The FPGA-based is turn off the relay faster than the dsPIC-based but the cost of design and implement is higher.

Experimental Study of Heat Transfer in Soil to Inhibit Microbial Growth Using the Underground Release of Hot Water and a Hydraulic Head Method

ABSTRACT This research aimed to study the effectiveness of heat transfer in soil using the underground release of hot water with a hydraulic head. Pressure heads of 1.0, 1.5 and 2.0 m were utilized for underground release with a nozzle to investigate heat transfer in soil necessary to inhibit microbial growth through underground hot water release using a pressure head of liquid. The nozzle was made of stainless steel pipe (SUS304). The proposed system was designed to inhibit microbes of Ralstonia solanacearum with a hot water volume flow of 300, 400 and 500 ml min−1, while temperature was kept constant at 70 ºC. The hot water released underground provided higher soil temperature with shorter working time. The research found that the number of layers and diameter of drilled holes had a significant effect on soil temperature distributed at various depth levels (y-plan), resulting in enhanced performance (100%) for the inhibition of microbes in an x-plan radius of 15 cm for a shorter time of 20–30 min with one nozzle.