According to ASHRAE 90.

For the small commercial building described, the applicable requirement is whole-building energy-use monitoring for each energy source at least monthly. This establishes a basic record of electricity, natural gas, district energy, fuel oil, or other energy supplied to the building. Fifteen-minute electricity monitoring represents a much more granular interval and is not the stated minimum for this building-size condition. End-use submetering separately measures categories such as lighting, HVAC, plug loads, and service water heating and is generally associated with more extensive monitoring provisions rather than the basic small-building requirement presented here. Monthly whole-building data enables owners to benchmark performance, identify abnormal changes, compare actual use with forecasts, and support ongoing energy-management activities. Therefore, Option C correctly describes the required monitoring level.

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