I saw an intersting presentation at CLOSER in Aachen a few weeks ago where a cloud simulator developed at the University of Bristol was being used to model heat output and energy efficiency. The simulator is called CReST, it is cross platform (so can be used in both Linux and Windows) and is available here:
I haven't tested yet, but the university of Luxembourg developed a "Green Cloud Simulator" : http://greencloud.gforge.uni.lu/install.html. This project is on Linux.
The famous CloudSim of Melbourn (http://www.cloudbus.org/cloudsim/) took into account different element about energy. This project is multi-platform.
To make a choice between this different projects, I think it's depend what you want to do with.
Thanks to all of You for your kind responses. All the answers were really helpful in my study.
In addition to these options, "CloudReports" built on top of CloudSim is also a good cloud simulation tool, which provides GUI interface of CloudSim and is very easy to understand and use.
Now my problem is: I want to implement policies and algorithms in cloud environment and want to measure carbon footprint based on energy efficiency. Unfortunately I am unable to figure it out.