Several of the most important considerations are:

1. Establishing proper geothermal design criteria, including:
   For ground-coupled systems - ground temperature, type of soil or rock, and moisture content.
   For ground water systems - temperature, quality, and flow rate of well or other water supply.
2. Properly determining the building's cooling, heating, and domestic or service hot water design loads.
   
3. Properly sizing and selecting the heat pump system, using ARI-Certified heat pump models, and properly designing the overall system including duct and air outlet and return components.
   
4. Correctly designing the hydraulic system, including the well pumping system or the ground loop heat exchanger system with pump.
   
5. Properly installing and wiring all the system components. There is no substitute here for a knowledgeable and competent installation contractor!
   
6. Adequately commissioning the system. Which includes:
   a) Cleaning and testing the system,
   b) Placing into initial operation,
   c) Measuring the performance,
   d) Comparing the actual results with the anticipated results, and
   e) Making the final corrections and fixes.
7. Thorough instruction for the owner or operator on how to start, operate, and shut-down the system.

Here is a diagram and description of how a heat pump works.

As you can see by blowing air across the evaporator, you get cool air and by blowing air across the condenser you get warm air.

A fridge is a good example of this.  It cools the inside of the fridge and heats the room all at the same time.

In a heat pump the same coil is both the evaporator and condenser, just the fluid flow is reversed.

In winter, heat is taken from the ground to vaporize the freon which after being compressed transfers heat to the house by condensing

In summer, heat is taken from the house to vaporize the freon which gives up the heat to the ground by condensing.

This is a short explantion,  but covers the basics of heat pump operation.

If you want to learn more and evaporating and condensing go here.
 or here



Hope this helps