A domestic electric water heater application for Smart Grid.

Thesis (MEng)--Stellenbosch University, 2017.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.AFRIKAANSE OPSOMMING: Suid Afrika se nasionale elektrisiteitsverskaffer, Eskom, swig toenemend onder die land se elektrisiteitaanvraag. Gevolglik word die kragnetwerk teen 'n historiese lae reserwemarge bedryf. Huishoudelike elektriese warmwater verhitters (EWVs) is van die grootse elektrisiteitsverbruikers in die residensiële sektor. EWVs is verantwoordelik vir hoë aanvraag pieke, wat dus bykomende druk op die kragnetwerk plaas. Op die oomblik gebruik herverspreiders rimpeleffekbeheer om EWVs oor 'n afstand te aan of af te skakel. Die geriefsvlakke van EWVs-gebruikers word dikwels laag geprioritiseer in 'n poging om piekaanvraag van kragvoorsiening te bestuur. Hierdie studie bied verbeteringe op twee afsonderlike, maar komplementêre, komponente wat 'n stelsel benodig om beide aspekte aan te spreek, m.a.w. aanvraagbeheer en geriefsvlakke. Die komponente sluit 'n tweerigting kommunikasiestelsel en 'n berekeningse effektiewe EWH model in. Eersgenoemde het die vermoë om 'n groot aantal EWVs te verbind ten einde hulle te monitor en beheer. Laasgenoemde is 'n akkurate voorspellingsinstrument om die EWV-toestand te assesseer ten einde skakelbeheer te help fassilitee. Vir die doel van hierdie navorsing, is twee kommunikasiesstelsels vir bestaande EWVmoniterings hardeware (toegerus met sellulêre modems) ontwikkel. Die eerste stelsel voldoen aan die hedendaagse spesifikasies vir masjien-tot-masjien (M2M) kommunikasie wat bekend staan as "SmartM2M ". Die tweede stelsel gebruik populêre webtegnologieë en benut die liggewig MQTT-toepassingsvlakprotokol. Beide stelsels funksioneer volgens die beplande ontwerpspesifikasies. Daar is gevind dat die SmartM2M standaarde effektief is, maar 'n gebrek aan grootskaalse aanvaarding, het implimentering en toepassing daarvan vermoeilik. The MQTT-protokol is geïmplimenteer deur gemeenskapsgedrewe sagteware vir beide the kliënt- en bedienertoepassing. Implementering van die MQTT-protokol was hoogs doeltreffend. Die sellulêre modem koppelvlak (bekend as die "AT" bevelstel) het vele ontwikkelingsuitdagings gebied aangesien dit 'n onbekende, verkoper-afhanklike koppelvlak is, waavoor daar minimale gemeenskapsondersteuning beskikbaar is. 'n Kommunikasie sagtewarestapel, wat stelselmatig met die modem koppel, is ontwikkel. Hierdie sagtwarestapel was hoogs doeltreffend om die MQTT-protokol te aktiveer, skakeling van netwerkdienskodes te hanteer en die afstands-hegware op te dateer. 'n Nougesette laboratoriumeksperiment is ontwikkel om die akkuraatheid van die berekenings-effektiewe EWV modelle (uit 'n vorige studie) te bevestig. Die eksperiment het outomatiese uitvoering van bestendige, noukeurige wateraftapping en verhitting, met periodiese metings van verskeie parameters, behels. Deur die EWV nodale modelle te gebruik, is agt datastelle (bestaande uit 9-dae experimentele data) gegenereer. Dit was gebruik om eksperimentele data met ooreenstemmende gesimuleerde data te vergelyk. In die geheel, het die modelle goeie akkuraatheid getoon om intree-energie, energiedoeltreffendheid en gemiddelde wateraftrek-temperatuur te voorspel. Onder geskeduleerde verwarmingsbeheer (in teenstelling met "altyd aan" beheer) is verbeterde mode-lakkuraatheid in al drie die bogenoemde kategoriee waargeneem. Die eksperimentele data was ook gebruik om aan te toon dat sowat 6% energiebesparing vir dieselfde uitsetenergie moontlik is (teenoor 'n "altyd aan" skedule) deur 'n verhittingskedule te implimenteer