Fig.1. shows the system diagram of the solar DHW heating system [5]. The solar collector is a flat plate type with selective absorption surface and one glass pane.

The total collector area is 6 m2 and the storage tank volume is 300 litters. The effectiveness of the built in heat exchanger in the tank is assumed to be 30 %. The input electric power of the motor of the collector circulation pump is 35 W. The auxiliary boiler efficiency is assumed to be 76.2 %.

2. Simulation method

The simulation tool EESLISM [6] was used. Usually, the time increment of one hour is used in the simulation. However, smaller time increment was examined in this study. Table1. shows the simulation cases examined in this study. The time increments used to examine are Case 1: 1 hour, Case 2: 10 minutes and Case 3: 1 minute.

The standard weather data prepared as the Expanded AMeDAS Weather Data [7] and the supplied city water temperature data prepared by the Solar System Development Association were used in this simulation.