· 2dix.com
http://ww2.2dix.com/
· Findebookee
http://findebookee.com/
· The Online Books Page
http://onlinebooks.library.upenn.edu/webbin/book/browse?type=subject&index=32608&key=environmental%20control&c=c
· The eBook Directory
http://www.ebookdirectory.com/
