2.2.7 Combining HVAC Zones

Under specific conditions, different HVAC zones may be combined into a single thermal block to reduce user input and to simplify the computer description of the building. Zone multipliers may also be used to achieve similar simplification, when this is a feature of the software. Provided all of the following conditions are met, different HVAC zones may be combined to create a single thermal block (or identical thermal blocks to which multipliers are applied):

• No more than ten different HVAC zones are included in any one thermal block.
• All the HVAC zones have similar space conditioning requirements.
• All of the zones are served by the same HVAC system or by the same kind of HVAC system. Perimeter baseboards, unit heaters or fan powered boxes (vs. straight boxes) should not be considered the “same kind” of HVAC system as zones without these features.
• All zones have similar minimum airflows (cfm/ft²) and if any have separate exhaust, this is met generally by transfer air from the HVAC zones in the thermal block.