There are many advantages of geothermal heat, but the main one is that there is no boiler or furnace needed to burn fuel.
As you are aware, all the systems you talk about have totally different characteristics and operation, therefore they require different knowledge, training and skills for each of the appliances and there systems.
Individuals earn their BPI certification as a way to show that they have the knowledge and skills of determining gas & oil appliance safety Inspection, heating system replacement and new Installations, along with furnaces and forced air distribution.
With the AC/HP Certification Individuals are tested on new and replacement air conditioning system sizing to ensure that no larger than 115% (or the next nearest size available from the manufacturer) of total load at design conditions. And that new and replacement heat pump systems must be sized no larger than 125% (or next nearest size available from the manufacturer) of total load at design conditions.
Also, all refrigerant must be handled and stored in compliance with EPA Section 608 standards at all times, including charging, recovery, reclamation, storage, and transportation requirements.
Only EPA certified technicians may install or service small residential (smaller than 5 ton capacity) central air conditioning or heat pump equipment
BPI certifications also enhance ones knowledge base with the understanding of the house as a system, Building Science Principles.