A thermal block is a space or collection of spaces having similar space-conditioning requirements and is the basic thermal unit used in modeling the building. A thermal block can include more than one HVAC zone, but HVAC zones are not split between thermal blocks.
An HVAC zone is a space or collection of spaces having similar space-conditioning requirements, the same heating and cooling setpoint, and is the basic thermal unit (or zone) used in modeling the building. An HVAC zone can include one or more spaces.
A thermal block is a virtual HVAC zone that consists of multiple actual HVAC zones that have similar characteristics. Section 2.3 of this document outlines the rules for defining HVAC zones and thermal blocks and specifies the rules for combining HVAC zones into thermal blocks. Where HVAC zones have been combined into thermal blocks, the descriptors applicable to HVAC zones below also apply to thermal blocks.