This IGSHPA Certified Residential Geothermal Designer (CRD) course will help you design geothermal systems for residential and commercial buildings. The buildings can even be quite large.
The Certified GeoExchange Designer (CGD) course is used to design geothermal systems for commercial buildings that have complex energy modeling needs. If the building requires an hourly energy analysis to account for variable schedules, then you need to take the CGD course.
The CRD course uses the bin method to do less complicated energy usage calculations based on weather data. This works great for most buildings.