Browsing by Author "Cloete, Andrew Hector"
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- ItemA domestic electric water heater application for Smart Grid.(Stellenbosch : Stellenbosch University, 2017-03) Cloete, Andrew Hector; Booysen, M. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Domestic electric water heaters (EWHs) are some of the largest consumers of electricity in the residential sector. EWHs are also responsible for high demand peaks, which add additional strain to the electrical grid. Currently, redistributors manage EWHs countrywide by using ripple control to remotely switch EWHs. However, ripple control is a unidirectional system that switches EWHs in bulk and subsequently cannot take individual customers into consideration. Peak demand management of electricity supply often disregards the comfort level of EWH users. This study presents advancements on two separate, but complementary, components that are necessary in a system in order to address both aspects, i.e. demand-side management as well as comfort levels. The components include a bidirectional communication system and computationally efficient EWH model. The former has the ability to connect a large number of EWH for monitoring and control. The latter is an accurate prediction tool to assess the EWH state in order to assist in its switch control. For the purpose of this research, two communication systems were developed for existing EWH monitoring that are equipped with cellular modems. The first system complies with the recent specifications released for machine-to-machine (M2M) communication known as SmartM2M. The second system uses popular web technologies and employs the lightweight MQTT application layer protocol. Both systems functioned as designed. It was found that the SmartM2M standards, although effective, lacks adoption at this point in time which made application development cumbersome. MQTT was employed by using community developed software for both client and server side, and proved highly effective. The cellular modem interface (known as the extended AT command set) proved challenging, as it is an obscure, vendor dependent interface with little community support. A communication software stack was developed that systematically interfaces with the modem. The communication software stack proved highly effective, enabling the MQTT protocol, the dialling of network service codes and remote firmware updates. A rigorous laboratory experiment was developed to validate the accuracy of computationally effcient EWH models proposed in a previous study. The experiment entailed performing automatic, consistent and precise water draw-off and heating, while periodically measuring several metrics. Eight datasets of 9- day experimental data was generated and used to compare with corresponding simulated results using the EWH nodal models. Overall, the models showed good accuracy in predicting input energy, energy efficiency and water draw-off temperature. Under scheduled heating control (as opposed to "always on"), increased model accuracy was observed in all three aforementioned categories. The experimental data was also used to show that the energy savings possible by implementing a heating schedule is approximately 6%, given the same effective output energy as when an "always on" heating schedule is applied.