Explanation
An energy meter must be installed for hot water at the main service point for the project to meet the requirements for Energy and Atmosphere Prerequisite, Building-Level Energy Metering.According to the LEED v4 BD+C Reference Guide, this prerequisite requires that "all energy sources used by the building must be metered or submetered"1. The hot water from the central utility plant is an energy source used by the building, even if it is not directly paid by the office. Therefore, it must be metered at the point where it enters the building. The other options are incorrect because natural gas is not an energy source used by the building in this case, and the flat fee or the ownership of the energy source do not exempt the project from the metering requirement.References: LEED v4 BD+C Reference Guide, Energy and Atmosphere Category, EAp Building-Level Energy Metering, page 569.