Whole house dehumidifiers are what your A/C does. There are some thermostats that allow you to run the a/c as a dehumidifier (the 3m Filtrete 3m-80 does this and some more), besides using it as a heat pump, by measuring the humidity in the house. As for Geothermal, it works the same as a heat pump. Instead of a outside unit, the piping from the inside unit runs into the ground either vertical, in trenches, or under water if in a climate that you do not get a complete lake or pond freeze.