Use HPXML Zones in energy modeling

[shorowit]

Residential software tools generally describe buildings in two ways:

1. Some describe the fraction of the building's heating/cooling load served by individual HVAC systems (which may be approximated by the fraction of conditioned floor area served or the fraction of total HVAC capacity)
2. Some describe zones in a building, each of which is served by a single (?) HVAC system

Now that we support HPXML zones & spaces for design load (HVAC sizing) calculations, we could consider also using them in the energy model, in which case the heating/cooling fractions would not be used. While handling surfaces would be reasonably straightforward, other aspects (e.g., infiltration, ventilation, internal gains, etc.) would be more involved.

Note: If we did this, we would not revert to allowing an HVAC system to serve multiple conditioned zones (e.g., above-grade and below-grade zones, both served by a furnace), we moved away from that for good reasons. An HVAC system would only serve a single conditioned zone.