NEC 220.84 (A) (3)

220.84 Multifamily Dwelling
(A) Feeder or Service Load. It shall be permissible to calculate the load of a feeder or service that supplies three or more dwelling units of a multifamily dwelling in accordance with Table 220.84 instead of Part III of this article if all the following conditions are met:
(1) No dwelling unit is supplied by more than one feeder.
(2) Each dwelling unit is equipped with electric cooking equipment.
Exception: When the calculated load for multifamily dwellings without electric cooking in Part III of this article exceeds that calculated under Part IV for the identical load plus electric cooking (based on 8 kW per unit), the lesser of the two loads shall be permitted to be used.
(3) Each dwelling unit is equipped with either electric space heating or air conditioning, or both. Feeders and service conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.61.

Each unit is served by a central VRV electric heat pump system, ie electric heating AND cooling. The heat pump fan coils are served from the guest room unit panels, however the central condensing units are served from the house service. The proposed design (calculations) uses the alternate dwelling unit calculations allowed in NEC 220.84 (A) (3), and not the standard NEC residential load calculations.

The proposed design would include the heating and cooling loads within the calculations, even though they are not connected to the feeder/service being calculated. (le, more conservative).

The proposed design (calculations) seems to meet the intent and language in the code.

The language in the Code says that the dwelling unit must be equipped with electric heating or cooling. All of these units are equipped with electric heating and cooling. The issue at hand is that the majority of this equipment is not connected to the service/feeders being calculated. The proposed design simply includes this heating/cooling load in the calculations. We are proposing to account for the loads that are in the building in the residential service/feeder calculations as well as accounting for them in the house service where they are actually connected. One of the main reasons for not connecting this equipment to the 120/208 volt residential service, and connecting it to the 277/480 volt house service, is a matter of being able to run the equipment at the more efficient voltage of 277/480 volt. From a capacity standpoint, the proposed design accounts for the heating/cooling load that the units are required to be equipped with. The standard residential calculations would increase the calculated load enough that an additional electrical service would be required to serve the guest rooms. From a practical standpoint, these guest rooms or "dwelling units" have VERY low power usage when compared to apartment units. The main reason is that there is very little cooking that is done in these units, but the loads are calculated based on an apartment type usage.