And, using your detailed interval data, it's usually pretty easy to make reasonable estimates of how much energy is being wasted at different times. For example, if you've identified that a lot of energy is being wasted by equipment left on over the weekends, you can:
Use your interval data to calculate how much energy (in kWh) is being used each weekend.
Estimate the proportion of that energy that is being wasted (by equipment that should be switched off).
Using the figures from a and b, calculate an estimate of the total kWh that are wasted each weekend.
Alternatively, if you have no idea of the proportion of energy that is being wasted by equipment left on unnecessarily, you could:
Walk the building one evening to ensure that everything that should be switched off is switched off.
Look back at the data for that evening to see how many kW were being used after you switched everything off.
Subtract the target kW figure (ii) from the typical kW figure for weekends to estimate the potential savings in kW (power).
Multiply the kW savings by the number of hours over the weekend to get the total potential kWh energy savings for a weekend.
Also, most buildings have open to them a variety of equipment- or building-fabric-related energy-saving opportunities, most of which require a more significant capital investment. You are probably aware of many of these, such as upgrading insulation or replacing lighting equipment, but good places to look for ideas include the Carbon Trust and Energy Star websites.
Although your detailed meter data won't necessarily help you to find these equipment- or building-fabric-related opportunites (e.g. it won't tell you that a more efficient type of lighting equipment exists), it will be useful for helping you to quantify the potential savings that each opportunity could bring. It's much more reliable to base your savings estimates on real metered data than on rules of thumb alone. And it's critically important to quantify the expected savings for any opportunity that you are considering investing a lot of time or money into – it's the only way you can figure out how to hone in on the biggest, easiest energy savings first.