1. EDMC, “Handbook of Japan’s and world energy and economic statistics”, The Institute of Energy Economics, Japan, 2017.
2. Sunpot co., ltd, http://www.sunpot.co.jp/products8.php
3. Zeneral Heat Pump Industry co. ltd., http://www.zeneral.co.jp/pdf/catalog_zpx.pdf
4. Kobe Steel, Ltd., http://www.kobelco. co.jp/p109/english/link02.htm#rotating.