T. Kusunoki1* and M. Udagawa1

1Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo, 163-8677, JAPAN
Corresponding Author, dd08002@ns. kogakuin. ac. jp

Abstract

As the performance of solar hot water heating system is strongly influenced by heat load, this study is focused on the followings.

1) Usually the simulation of the solar hot water heating system is carried out with 1 hour time increment. However, the domestic hot water demand varies in very short time. In this study, the simulation was carried out for considering the suitable simulation time increments in solar hot water heating systems. As a result, it was found that 10 minutes is the suitable time increment for the simulation of the solar hot water heating system.

2) Using the time increment of 10 minutes, the simulation for 42 combinations of collector tilt angle and azimuth for five cities in Japan was carried out. As a result, it was found that the difference in the performance of solar hot water heating systems was within 15% from the best performance with the combination of the tilt angle from10 to 60 degrees and azimuth within 45 degrees from the south in Tokyo. The similar results were obtained for the combination of the tilt angle and azimuth in other four cities. The simulation result showed that the solar contribution for DHW heating load in Sapporo, Morioka, Sendai, Tokyo and Kagoshima were 44 %, 46 %, 51 %, 57 % and 66 %, respectively. The difference is caused by the DHW heating load which is strongly influenced by the city water temperature.

Keywords: Solar DHW System, Simulation Time Increments, Tilt Angle, Azimuth

1. Introduction

More than 35% of the purchased energy consumption is used for domestic hot water (DHW) heating in the Japanese housing sector. Therefore, it is important to reduce the energy consumption used for the hot water heating. Reduction of the energy consumption by solar DHW heating system is expected in the housing sector.

Solar DHW heating systems are affected by the DHW use profile as well as the solar radiation on collector. As the DHW use varies in very short time, the simulation of the solar DHW heating systems needs to consider for suitable time increments in the simulation. In this study, the time increment in the simulation of the solar DHW heating systems to reflect the detailed hot water use profile was examined first.

The overall solar system performance was also studied to find the allowable collector tilt angle and azimuth in designing the solar DHW heating system. In addition, the total performance of the solar DHW system is compared for five cities in Japan.