HVAC through a sufficiency Lens: Reframing comfort and energy demand in buildings

While building HVAC system research has long emphasized energy efficiency, efficiency alone cannot deliver the emission reductions required in the building sector. The sufficiency approach aims to reduce overall energy demand while maintaining thermal comfort, well-being, and equity. This article defines the concept of sufficient HVAC; explores existing and emerging strategies such as adaptive comfort, zoning, and occupancy-based operation, and proposes a set of metrics for evaluating HVAC performance from a sufficiency perspective. The indicators capture energy use, greenhouse gas emissions, ventilation provision, thermal comfort, and spatial selectivity at the occupant level, including energy per occupant-hour, greenhouse gas emissions per occupant-hour, ventilation per occupant-hour, comfort compliance fraction, and average zone area. A published building simulation case is used to illustrate how selected metrics can be computed and how sufficiency-oriented indicators reveal differences in HVAC service delivery beyond conventional efficiency measures.