This is a tough question to answer. Let's look first at whether to go open loop or closed loop.
Open loop systems are best applied in situations where the house is, or will be, served by its own water well. A slightly larger well pump is installed to provide for the water required by the heat pump. A major consideration is the disposal of the water. Existing systems have used ponds, lakes, rivers, irrigation ditches, and return (or injection) wells. Surface disposal is obviously the least expensive option; but, even if a disposal well is required, the capital cost is likely to be much less than the cost of a closed loop ground coupling. Water quality is also an important issue. Since the water is used directly in the heat pump, the issue of corrosion and/or scaling can be a problem. If the water is hard (>100 ppm) or contains hydrogen sulphide (rotten egg smell), a closed loop system would be a better choice. If the water is of good quality and the house is to be served by a well for domestic water, serious consideration should be given to the open loop approach. Contractors will often suggest a cupronickel heat exchanger as a way to address water quality problems in open loop systems. It is a rare occasion when this is an effective strategy. Cupronickel is effective for salt water applications. For most of the commonly encountered water quality problems (carbonate scale, iron or hydrogen sulphide), cupronickel construction is of little if any value.
See the costs section of this report for capital costs for the open loop system.
If the system is to be a closed loop design, the choice between vertical and horizontal system is sometimes a difficult one to grapple with. The major advantage of the vertical design is that it places the loop in a much more thermally stable zone. Soil at 100 ft is not subject to the same temperature fluctuations as soil at a 4 or 5 ft depth. As a result, the vertical design offers the potential of supplying the heat pump warmer water in winter and cooler water in summer.
Contractor availability will be the dominant factor in determining which type of ground coupling is used for many projects. In most areas of the country, the availability of contractors is still very limited. As a result, if the local contractors only install horizontal systems, that is what you get.
The thermal advantages of the vertical over the horizontal are less of a factor in moderate climates. The more extreme the climate, either in heating or cooling, the greater the advantage of the vertical system.
See the cost section for a discussion of system costs.