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Item Voltage and wire standards for domestic DC distribution systems(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Ariyarathne, Y.S.S.,; Jayatissa, N.W.K.; De Silva, D.S.M.Home micro-grid concepts have gained interest in the modern world due to the increased distributed generations with renewable energy sources. The present "DC-AC-DC" route from distributed generations to DC loads via inverters may not be rational from the viewpoint of system simplicity and energy efficiency. Considering the increasing prevalence of DC home appliances, establishing reasonable DC distribution standards for domestic buildings is significant. In this study, the Wattage of household electric appliances and the time duration they are being used were collected. The monthly power consumption of each appliance category was calculated. According to the results, the average monthly electricity demand of a Sri Lankan family is 111 kWh. Only eight equipment categories consume nearly 90% of domestic power. Those are refrigerators (22%), lights (16%), fans (16%), rice cookers (14%), TV (8%), irons (7%), washing machines (4%) and water pumps (3%). When considering the average maximum power demand, the most commonly available appliances have less than 1 kW maximum power demand. By considering the power requirements, to minimize the loss, and keep the system's safety at the maximum level, the midpoint grounding system with main wires at +60 VDC and -60 VDC is proposed. Using this topology, 120 V line to line potential difference can be archived with keeping the ground to line voltage within safety extra-low voltage limit as proposed by the European telecom standards. Following the IEE wiring standards, three commonly available wire sizes (2.5 𝑚𝑚2 , 4 𝑚𝑚2 , 6 𝑚𝑚2 ) were selected to analyze the suitability for the system's sub circuits. Voltage drop, power loss, short circuit current, and insulation resistance were considered to select the maximum allowable current for each wire size in a sub-circuit. Since the wire length for a sub-circuit of a domestic distribution system is usually less than 10 m, the voltage drops and the power losses are too small and negligible. The insulation resistance of each wire was tested against high voltages. All the wires show infinite resistance (more than 1 𝑇Ω) up to 2500 V. The most critical factor in wire selection is the short circuit current. According to the results, for a high power sub-circuit that require power up to 2400 W, wire size of 6 𝑚𝑚2 can be used with 20 A circuit breaker. For sub circuits with power requirement less than 1800 W, 4 𝑚𝑚2 wires can be used with a 15 A circuit breaker. And for low power sub-circuits, 2.5 𝑚𝑚2 wire can be used with 10 A circuit breaker to supply power up to 1200 W. Further studies must be carried out to determine the power/voltage losses and increase the whole distribution system's efficiency under these conditions.Item Energy efficient hybrid water heating system(2016) Piyumal, P.L.A.K.; Nagahapitiya, N.W.H.G.B.; Jayatissa, N.W.K.; de Silva, D.S.M.As the world’s energy resources are diminishing, we need to find greener solutions through renewable energy sources that can generate electricity for heating, lighting homes and for a variety of commercial and industrial uses. Among many types of renewable energy resources, such as wind and solar energy, are constantly replenished and will never run out. At present we are experiencing an electrical energy shortage in Sri Lanka. However, we are still wasting so much of electrical energy in spite of the above crisis. The University of Kelaniya has many cafeterias. The cafeteria attached to the Gymnasium is the largest food and refreshments supplier in the university. The main refreshment for the students is hot tea. Hence, every day, every hour, the canteen has to produce a large number of cups of tea by using considerable amount of electrical energy for boiling water. Hence, the purpose of this project is to minimize the electricity consumption in the boiler using freely available sunlight. Initially, the project was focused to power the boiler using a photovoltaic array. Even though this method was straight forward, investigations have shown that this method was not financially viable. Hence, the next approach was to utilize solar thermal energy to heat the make-up water to the boiler which is significantly cheaper to implement than the previous. Fresh water is circulating through the heat exchanger unit placed on the top of the roof of the cafeteria. Heated water is fed to the boiler as make-up water. Although the heating system is unable to produce boiling water. It is capable of producing nearly half of the energy requirement for boiling the water. A temperature sensor was placed to measure the boiler temperature and the output of the sensor is fed to the heating element to maintain the boiler temperature at 373 K. According to the observation it is clear that make-up water temperature in the morning is 332 K which is little lower than the temperature of make-up water in the afternoon which is 342 K due to overnight cooling of the storage tank. Therefore, morning electricity consumption of the boiler is little larger than the evening. The average daily hot water consumption for making tea is approximately 78 liters in the morning and 88 liters in the afternoon. According to the calculations, it can be shown that the hybrid system is capable of saving 50% of electrical energy of the boiler. It can be concluded that the total energy provided by the solar heating system or the saving of the system is around 2450 kWh per annum.Item Lesson 19: Introduction to Pumps(Research Services Centre, Faculty of Science, University of Kelaniya, 2015) Jayatissa, N.W.K.Item Lesson 15: Programmable Logic Controllers(Research Services Centre, Faculty of Science, University of Kelaniya, 2015) Jayatissa, N.W.K.Item Lesson 14: Introduction to Microcontroller(Research Services Centre, Faculty of Science, University of Kelaniya, 2015) Jayatissa, N.W.K.Item An inexpensive universal serial bus interfaced home automation system(IET Sri Lanka Network-19th Annual conference, 2012) Wijesundera, R.P.; Abeyratne, M.D.G.M.; Kalupahana, I.U.; Buddhika, W.A.P.; Kumara, S.D.; Jayatissa, N.W.K.; Harambearachchi, J.C.; Kalingamudali, S.R.D.Item Investigating the thermal efficiency of commercially available thermo-foils in Sri Lanka(Journal of Science of the University of Kelaniya Sri Lanka, 2011) Maduranga, A.D.; Sumathipala, H.H.; Jayatissa, N.W.K.The thermo-foil is an insulation material which can be used to insulate roofs of residential buildings which causes less energy to accomplish a comfortable temperature inside the building. It?s becoming popular in Sri Lankan building construction sector. In this research, an investigation of the efficiency of the thermo-foils is done for commonly used brands. The important thermal properties are analyzed for thermo-foils with a thickness of 3mm, 5mm and 8mm and it is tested using a miniature building model for the further evaluation of the efficiency. It was observed that the aluminium layer of the thermo-foil could reflect most of the radiation back and the polyethylene foam layer could keep a temperature gradient of a few degrees. A temperature drop of 1.6 to 2.8 degrees was noted. The results obtained were discussed with an analysis of the thermal insulation properties. A heat transfer model for a residential building was also proposed.