The project has been identified at the Top level of the Building Tree as a Addition Alone. When analyzing this type of project, the HVAC system must either be defined as Existing or New. You cannot select Altered.
If you wish to analyze the HVAC system as being Altered, you must input the entire Existing portion of the building into the building tree. At the top level of the Building Tree, change the Building Type to Existing + Addition/Alteration.
Your other option is to go to the System level of the Building Tree and change the System Type to New or Existing.
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