Water source (geothermal) heat pump systems are a tried and proven method for reduction of HVAC system operational costs of up to 35% in some instances. Water source heat pump systems implement a well-field to draw heat from the earth in the winter and reject heat to the earth in the summer. Efficient compressors, variable speed compressors and larger heat exchangers all contribute to heat pump efficiency. Liquid-to-water heat pumps (also called water-to-water) are hydronic systems that use water to carry heating or cooling through the building. Systems such as radiant under floor heating and baseboard radiators use a liquid-to-water heat pump. These heat pumps are preferred for pool heating or domestic hot water pre-heat. Heat pumps can only heat water to about 50 °C (122 °F) efficiently, whereas a boiler normally reaches 65–95 °C (149–203 °F). Legacy radiators designed for these higher temperatures may have to be doubled in numbers when retrofitting a home. A hot water tank will still be needed to raise water temperatures above the heat pump's maximum, but pre-heating will save 25-50% of hot water costs.

Of course there is additional up-front cost. This cost is substantial and ends up being a deterrent for many projects that would be great candidates for geothermal (residential, office buildings, schools). Local well-drilling companies approximate additional up-front costs at approximately $1,400 per well (hole) at 150’ deep. At approximately one well per ton of cooling, a 15,000 square foot office building would be looking at upfront well-drilling costs of $61,600 alone… These large upfront costs make payback analysis tougher to justify.
Luckily in addition to grant money, government tax credits and rebates make water source heat pump systems more affordable for both residential and commercial consumers and can change payback calculations significantly. Up to 30% of the cost of the well-field makes a big difference and will hopefully help this technology grow to become even more of a mainstream staple.

Direct Exchange
The direct exchange (DX) system is a series of copper tubes buried in trenches 4 to 6 feet below ground level or in deep vertical boreholes. Refrigerant gas is then fed through these so buried copper tubes creating a direct heat exchange between the temperature of the ground and the heat transfer medium, which in this case is the refrigerant gas (as you can see this eliminates the water-to-refrigerant heat exchanger and the electric water pump too). Because of this direct exchange feature these systems can operate at lesser costs than water source systems. DX should also be less expensive and complex to install as it requires no water well drilling or plumbing costs. As copper is a more efficient heat transfer medium than PVC pipe as found in water source, trenching costs are less due to less ground mass being required by DX. As with water source heat exchangers a leak in the system requires reinstallation of the entire heat exchange field. A common concern about Direct Exchange (DX) geothermal systems is that the copper tubing may corrode and leak refrigerant into the soil creating an environmental hazard. Before installing the loop, the dealer or contractor should do a soil test to determine the acidity of the soil and if measures are required to protect against acidity. Manufacturer's recommend that soils be checked for high concentrations of acids, chlorides, hydrogen sulfide, sulfates or ammonia; these are to be avoided because of the potential for corrosion. To determine whether or not this is an issue, soil samples can be taken at a depth of 3 feet where the manifold pit would be placed.
DX systems, like water-source systems, can also be used to heat water in the house for use in radiant heat applications and for domestic hot water, as well as for cooling applications.

Following the ban on chloroflurocarbons (CFCs) and hydrochlorofluorocarbons(HCFCs), substances used as substitute refrigerants such as fluorocarbons (FCs) and hydroflourocarbons(HFCs) have also come under criticism. They are currently subject to prohibition discussions on account of their harmful effect on the climate. In 1997, FCs and HFCs were included in the Kyoto Protocol Convention on Climate Change. In 2006, the EU adopted a Regulation on fluorinated greenhouse gases, which makes stipulations regarding the use of FCs and HFCs with the intention of reducing their emissions. The provisions do not affect climate-neutral natural refrigerants. Ammonia (R717) has been used in industrial refrigeration plants for more than 130 years and is deemed to be environment-friendly, economical, and energy-efficient. The natural refrigerant carbon dioxide (R744) has a similarly long tradition in refrigeration technology. Natural refrigerants such as ammonia, carbon dioxide and non-halogenated hydrocarbons preserve the ozone layer and have no (ammonia) or only a low (carbon dioxide, hydrocarbons) global warming potential. As of July 1, 1992 it is illegal to release refrigerants into the atmosphere (intentional or accidental) because they can cause severe damage to the ozone layer. When CFCs are removed they should be recycled to clean out any contaminants and return it to a usable condition. Refrigerants should never be mixed together. Some CFCs must be managed as hazardous waste even if recycled and special precautions are required for their transport, depending on the legislation of the country's government. The fluids used in closed loops may be designed to be biodegradable and non-toxic, but the refrigerant used in the heat pump cabinet and in direct exchange loops was, until recently, chlorodifluoromethane, which is an ozone depleting substance. Although harmless while contained, leaks and improper end-of-life disposal contribute to enlarging the ozone hole. This refrigerant is being phased out in favor of ozone-friendly R410A for new construction, but R-410A systems require service personnel to use different tools, equipment, safety standards and techniques.

Here is a the solution that I prefer:

GeoColumn™ - The Hybrid Geothermal Heat Exchanger
In response to the disadvantages and shortcomings of both of the water source geothermal systems as well as conventional direct exchange geothermal systems GeoEnergy Enterprises, LLC (GEE) has developed the advanced hybrid GeoColumn geothermal direct exchange heat exchanger system.
The GeoColumn system is a self-contained “off-the-shelf” ground source heat exchanger that eliminates the required engineering of the heat exchanger apparatus and field thus dramatically reducing the cost and complexity of “going geothermal”. As a result of the GeoColumn’s unique design and operation the GeoColumn heat exchanger has been awarded a US Patent.

The GeoColumn
The GeoColumn patent covers a sub-terrain heat exchanger consisting of a containment device containing a standing column of fluid which is 100% water (unlike certain other geothermal systems no antifreeze is required) and a refrigerant-to-water heat exchanger. The refrigerant gas exchanges heat with the water column, which, depending on the mode of operation, causes the water to either rise or fall within the containment by natural convection effect. Heat is then exchanged through the wall of the containment with the earth’s mass.

The GeoColumn heat exchanger unit is 28 inches in diameter by 20 feet long, per ton of conditioning required, and installs within a borehole that is 23 feet deep. This compares to 450 to 900 square feet of land surface area, per ton of conditioning, for horizontal loop systems or to the 100 to over 1500 foot boreholes or wells, per ton of conditioning, typically required for vertical plane geothermal heat exchanger systems.

The GeoColumn is pre-engineered to your region and soils and using a componentized heat exchanger such as the GeoColumn greatly reduces the expense and complexity of field design. The GeoColumn can be quickly installed with utility pole type digger-derrick drilling equipment or with caisson type pressure drill rig equipment. This consequently enables the GeoColumn to be installed in much less time that other systems and thus reduces the drilling expense which is often a cost barrier to the use of geothermal HVAC.

The small footprint of the GeoColumn is ideal for all types of installations, new and retro fit, but is especially suited for geothermal usage in areas of limited ground areas, such as in urban or suburban areas. GeoColumns can be placed below sidewalks, driveways, lawn and garden areas or, in new construction, even underneath the foundation!

GEE's GeoColumn heat exchanger units are coupled to GEE indoor components (a compressor section, air handler, etc.) to provide heated and cooled air and hot water and it may also be used for hydronic heating systems as well. These GeoColumn based systems provide many advantages over conventional fluid based geothermal equipment since it generally requires a smaller land area to install and eliminate the use of pumps and fluid-to-refrigerant heat exchangers. This alone may provide cost savings of 35% to 50% or more over other conventional geothermal equipment’s installation. GEE’s systems are also much easy for any competent HVAC dealer to install than a conventional water source geothermal unit since it does not require the use of engineers, plastic pipe welders, plumbing professionals and/or well drillers/trench excavators for installation. In the event of a field failure as the top of the GeoColumn is only 3 feet below the surface any necessary repairs can easily be made in the field.