Designing HVAC systems involves many considerations such as building type, layout, orientation, and heating/cooling requirements. Here are some key steps involved in designing an HVAC system:

1. Load calculation: This involves calculating the heating and cooling loads for each room or area of the building. The load calculation takes into account factors such as climate, building orientation, occupancy, lighting, and appliances.
2. System selection: Based on the load calculation, the appropriate HVAC system type is selected. The most common types are split systems, packaged systems, and variable refrigerant flow systems.
3. Ductwork design: The design of the ductwork is important to ensure that the HVAC system can deliver the required amount of air to each room. The ductwork design takes into account factors such as air velocity, pressure drop, and noise level.
4. Equipment selection: Once the system type and ductwork design are determined, the appropriate HVAC equipment is selected. This includes items such as the furnace or air handler, air conditioner or heat pump, and ductless mini-split units.
5. System layout: The layout of the HVAC system is then designed, including the location of the equipment and ductwork. This takes into account factors such as ease of installation, access for maintenance, and space constraints.
6. Controls and automation: Finally, the system is designed with appropriate controls and automation to ensure that it operates efficiently and meets the heating and cooling needs of the building.

Overall, designing an HVAC system requires a deep understanding of the building, its occupants, and their needs. By carefully considering these factors, an HVAC technician can design a system that is efficient, effective, and comfortable for everyone inside.