Assuming you're talking about the Building Regulations and Approved Document L, there are specific exemptions you may wish to look at which might apply to certain parts, but not necessarily all, of your facility.

But wasted energy is wasted energy whether it's generated on-site or imported and generally facility owners will find it useful to keep tabs on it; as a designer of similar (but different) type of facility an appropriate level of detail is not normally that onerous. Otherwise you'd have no visibility of heaters left on max temperature in unpopulated areas when they should be on frost setting etc.

...And, perhaps even because they are in the business of generating electricity, I do find this data is reviewed and acted upon.

Hi and thanks for your reply,

the point you raise is actually one of my doubts... What could be considered an appropriate level of detail?

F.e. if I have various areas of the plant and for each of them I meter all mechanical systems together and all small power&lighting together, would it be ok? I can't find any clear and unambiguous instruction for this.

Bindu,

Electrical sub-metering involves installing meters within a building to monitor electricity consumption in specific areas or equipment. These meters track usage more accurately than a single main meter, enabling precise billing and identification of energy-saving opportunities.

By distributing metering points strategically, sub-metering provides insights into energy consumption patterns, facilitating targeted efficiency measures. It allows for fair cost allocation among tenants or departments, promotes billing transparency, and aids in maintenance by quickly identifying anomalies. Ultimately, sub-metering enhances both cost management and sustainability efforts within buildings and properties.

To enable separation, split load metered boards can be installed, allowing distinct metering for lighting and power usage. Mechanical plant often integrates with Building Management Systems (BMS) for metering and control. The level of detail required is outlined in Approved Document L, advising on energy efficiency standards and regulations.