What is the cheapest way to save energy?
This is actually a tricky question as it massively depends on your business, how you're using energy and what you consider "cheap".
Usually, the cheapest way to save energy in an existing building is to get better visibility of your energy consumption data. This is normally done through computer-based monitoring tools and using this information to identify times of unexpected energy use.
Implementing this is surprisingly easy to do and the problems are typically traced back to occupant behaviour or building control systems being wrongly set. Both of these types of issue are cheap to resolve and can lead to substantial energy consumption reductions.