If you are going to have AC, might as well be a heat pump. They are very efficient with some caveats. The BTU output is typically matched to the house size for AC to prevent re-evaporation or short run times. This produces long very long run times in winter to the extent that most home setups reach a balance point around 15-18F where the losses in the house exceed the BTU output and you get 100% run. In Maryland (Where I live) this rarely happens and heat pumps typically keep the house at whatever temp you set the thermostat at without calling for "backup" below the balance point. In the event the heat pump can not keep up (18F for my setup), backup is called. For me, that is electric, which is wicked expensive. In the north, I'd expect the backup system is something other than electric, probably natural gas. Usually when non-electric backup is used, there is an outdoor thermostat that can be set to just swap over the heat pump to the backup (not run both at same time). This is pretty convenient and you can set it at something nice like 25F or so and minimize long run times and maximize your furnace "backup". Heat pumps have an outdoor unit that gets colder than the ambient air in winter (heat) mode. This will cause frost on the outdoor unit. In humid areas (coastal) this frost can be excessive. Most units have a "Defrost Cycle" to get rid of the frost. The way this works is by automatically running the AC (and turning off the outdoor fan) for a few minutes every hour to move heat from the house to the outdoor coils and melt the ice. Some use a sensor to do this rather than a timer. Either way, when it happens, it blows cold air through the house, which many people totally hate. The backup heat is used to minimize the chill, but most people notice it (Dusty Chalks "Heat Suck!"). I'm a heat pump fan, but I'm not sure I would be in Chicago unless I had a good backup.
In Maryland, the typical way we do Geothermal is to drill auxiliary wells into the shallow aquifer here. It's cheaper and more efficient than a horizontal trench system.
