Autodesk Ecotect 2011 installation, unfortunately, doesn't support silent installation method from a command line. However, if you need to install it silently, you can try the following workflow:
setup.exe /silent /suppressmsgboxes /nocancel
copy "licpath.lic" "C:\Program Files (x86)\Autodesk\Ecotect Analysis 2011"
reg delete HKLM\SOFTWARE\Wow6432Node\Autodesk\Ecotect /f
reg add "HKLM\SOFTWARE\Wow6432Node\Autodesk\Ecotect\2011\AdLM" /v "Type" /t REG_DWORD /d 1 /f
reg add "HKLM\SOFTWARE\Wow6432Node\Autodesk\Ecotect\2011\AdLM" /v "ACADType" /t REG_DWORD /d 3 /f
Thanks to Brian Fleury for sharing this tip with the community.