Well:

1. You get passive cooling in the summer 2. The greater the temperature difference is the more efficient the pump becomes so they are more efficient even in not so cold weather 3. The maintenance costs of the system are significantly less. You need to clean and replace blower fans. Cleaning has to be done yearly or twice yearly depending on environment. Ground source, you only need to maintain the pump and coolant which needs replacing cca once every 20-30 years.