I've a feeling there's something building regs wise for being able to monitor consumption separately for "lighting" and "power" that usually drives split metering in commercial premises over a certain size, I'd check on the details though.

   - Andy.

I checked APDL and it states the following:

Energy submetering systems should be installed in new buildings, or when fixed building services
are provided or extended in an existing building, and should meet all of the following requirements.

a. The various end-use categories, such as heating, lighting and cooling, should be submetered in
such a way that at least 90% of the annual energy consumption of each fuel can be assigned to
an end-use. Detailed guidance on how to achieve this is given in CIBSE’s TM39.

"Fixed building service in an existing building" - some services remain in place some new. The way I read that is if tenant load doesn't make up 90% landlord needs to be sub-metered too? 

I checked APDL and it states the following:

Energy submetering systems should be installed in new buildings, or when fixed building services
are provided or extended in an existing building, and should meet all of the following requirements.

a. The various end-use categories, such as heating, lighting and cooling, should be submetered in
such a way that at least 90% of the annual energy consumption of each fuel can be assigned to
an end-use. Detailed guidance on how to achieve this is given in CIBSE’s TM39.

"Fixed building service in an existing building" - some services remain in place some new. The way I read that is if tenant load doesn't make up 90% landlord needs to be sub-metered too?