Feasibility study of low voltage DC house and compatible home appliance design

In this work a low voltage direct current (DC) distribution system for a house or an apartment have been investigated. The feasibility of the low voltage DC systems for a home is investigated by evaluating the advantages and disadvantages with respect to the existing alternating current (AC) system of homes. The goal is to make a energy efficient system that would be able to cope with local electricity generation and storage systems at the end-user level, from DC sources. Data obtained from measurements of power consumption for different household appliances such as refrigerator, microwave oven, rice cooker, dish washer etc. have been used to evaluating the systems. The performance of the 230V AC system and the proposed low voltage DC system is analyzed by considering factors such as losses in the wire, internal loss of the device itself, investment cost for new wiring and energy consumption cost. From the investigation, it can be concluded that the 48 V DC system with optimized cable area is most economical system compared with the 230 V AC system and with a 20 years life time, it will save almost 13000 SEK. In the case of a low voltage DC distribution system, there is a problem with high power loss in the feeder for high power consuming loads. The stove is one of the high power consuming kitchen appliances and it consumes large amount of energy. This project focuses on an efficient stove design for a low DC voltage supply. To decrease the energy consumption of the stove, the idea is to combine it with the refrigerator. The heat extracted from the refrigerator is stored both in the stove, to be used for cooking and in a water tank to be used for other purposes, for example providing hot water to a dishwasher. Two individual thermoelectric modules (TEM) are used for the refrigerator and the stove. A water tank is used in the middle of the refrigerator and the stove unit. Some parts of the extracted heat from the refrigerator, is stored in paraffin inside the stove and the remaining parts of that extracted heat is stored in the water tank by raising its temperature. The calculated efficiency of the refrigerator unit is 54%, the efficiency for heating up the water by storing the extracted heat is 154% and for storing heat in the paraffin is 134%. The stored heat in the water tank has the possibility to supply other devices such as a dishwasher with hot water. This would reduce the peak energy consumption of the dishwasher since it does not need to heat the water by using electricity in this case. The prototype was tested together with a dishwasher that runs on a low DC voltage and the peak power consumption was reduced by supplying hot water from water tank. The overall efficiency of the system was increased by storing the extracted heat from the refrigerator unit in a latent heat storage using paraffin and in a water tank.