In this research, the impact of solar thermal water heaters on the electric water heating load curve in a residential distribution circuit is analyzed with realistic hot water draw profiles. For this purpose, the electric and solar thermal water heater models are developed in MATLAB and validated with results from GridLAB-D and TRNSYS respectively. The solar thermal water heater model is developed for two types of collectors namely the flat plate and evacuated glass tube collector. Simulations are performed with the climate data from two cities - Madison, WI and Tampa, FL - which belong to two very different climate zones in the United States. Minute-by-minute electric energy consumptions in all three configurations of water heaters are modeled for a single water heater as well as a residential distribution circuit with 100 water heaters for daily as well as monthly time frames. The research findings include: The electric energy saving potential of a solar thermal water heater powered by auxiliary electric element is in the range of 40-80% as compared to an all-electric water heater depending on the site conditions such as ambient temperature, sunshine and wind speed. The simulation results indicate that the energy saving potential of a solar thermal water heater is in the range of 40-70% during winter and 60-80% during summer. Solar thermal water heaters aid in reducing the peak demand for electric water heating in a distribution feeder during sunshine hours when ambient temperatures are higher. The simulation results indicate that the peak reduction potential of solar thermal water heaters in a residential distribution feeder is in the range of 25-40% during winter and 40-60% during summer. The evacuated glass tube collectors save an additional 7-10% electric energy compared to the flat plate collectors with one glass pane during winter and around 10-15% during summer. The additional savings result from the capability of glass tube collectors to absorb ground reflected radiation and diffuse as well as direct beam radiation for a wider range of incidence angles. Also, the evacuated glass tube structure helps in reducing wind convective losses. From the simulations performed for Madison, WI and Tampa, FL, it is observed that Tampa, FL experiences more energy savings in winter than Madison, WI, while the energy savings are almost the same in summer. This is due to the fact that Tampa, FL has warmer winters with higher ambient temperatures and longer sunshine hours during the day compared to Madison, WI while the summer temperatures and sunshine hours are almost the same for the two cities. As expected, the simulation results prove the fact that lowering the hot water temperature set point will result in the reduction of electricity consumption. For a temperature reduction from 120 deg. F to 110 deg. F, electric water heaters save about 25-35% electric energy whereas solar thermal water heaters save about 30-40% auxiliary electric energy for the same temperature reduction. For the flat plate collectors, glass panes play an important role in auxiliary electric energy consumption. Flat plate collectors with two glass panes save about 10-15% auxiliary electric energy compared to those with no glass panes and about 3-5% energy saving compared to collectors with one glass pane. This is because there are reduced wind convective losses with glass panes. However, there are also transmittance losses from glass panes and there are upper limits on how many glass panes can be used. Results and findings from this research provide valuable insight into the benefits of solar thermal water heaters in a residential distribution feeder, which include the energy savings and peak demand reduction. / Master of Science

Este trabalho propõe um método com objetivo de avaliar a eficiência energética de aquecedores de água residenciais de acumulação elétricos. Os aquecedores foram submetidos a um ciclo de operação simulando uma condição de uso para o cálculo da eficiência. Este ciclo de duração de um dia é composto pelas fases: produção de água quente, reaquecimento e manutenção da temperatura interna. O método foi aplicado no programa experimental e permitiu a identificação de diversos parâmetros referentes ao funcionamento dos aquecedores, tais como: perda passiva por 24 horas, produção de água quente, tempo de reaquecimento, variação da temperatura interna da água e a sua eficiência energética. / This work proposes a method with objective of evaluating the energy efficiency of electrical residential storage water heaters. The heaters were submitted to an operation cycle simulating a use condition for the calculation of the efficiency. This cycle with duration of one day is composed by the phases: hot water withdrawal, temperature recovery and standby thermal loss. The method was applied in the experimental program and it allowed the identification of several parameters regarding the operation of such heaters as: standby thermal loss per 24 hours, hot water rate output, reheating time, cyclic variation of the temperature and its energy efficiency.

Este trabalho propõe um método com objetivo de avaliar a eficiência energética de aquecedores de água residenciais de acumulação elétricos. Os aquecedores foram submetidos a um ciclo de operação simulando uma condição de uso para o cálculo da eficiência. Este ciclo de duração de um dia é composto pelas fases: produção de água quente, reaquecimento e manutenção da temperatura interna. O método foi aplicado no programa experimental e permitiu a identificação de diversos parâmetros referentes ao funcionamento dos aquecedores, tais como: perda passiva por 24 horas, produção de água quente, tempo de reaquecimento, variação da temperatura interna da água e a sua eficiência energética. / This work proposes a method with objective of evaluating the energy efficiency of electrical residential storage water heaters. The heaters were submitted to an operation cycle simulating a use condition for the calculation of the efficiency. This cycle with duration of one day is composed by the phases: hot water withdrawal, temperature recovery and standby thermal loss. The method was applied in the experimental program and it allowed the identification of several parameters regarding the operation of such heaters as: standby thermal loss per 24 hours, hot water rate output, reheating time, cyclic variation of the temperature and its energy efficiency.