Direct Exchange Ground Source Heat Pump
A direct exchange ground source heat pump is more commonly known as a direct exchange geothermal heat pump. The geothermal heat pump was the original version of these items and is really the oldest known kind of ground source heat pump in existence.
The direct exchange geothermal heat pump is not only the earliest version of these devices they are also the very simplest version of these devices. The ground coupling for these units is formed in a single loop that circulates refrigerant by it. This single loop is in direct contact with ground. The refrigerant leaves out of the warm pump and travels by the single loop. It extracts heat from the ground as it circulates by that portion of the loop and when it returns to the heat pump it is warmer.
These types of ground source heat pumps are referred to as direct exchange because of the way the refrigerant exchanges heat with the ground without another fluid being involved in the move. These units are frequently referred to as ground coupled pumps and must not be confused with the water source heat pumps.
What makes These Units Different?
The majority of systems that you see today have two loops instead of one. The loop that has the refrigerant inside it is generally contained in the cabinet of the appliance while a loop that has water running by it circulates under the ground surface.
The water loop is generally made up of a high density polyethylene piping. The water inside this piping is not just water, but is a combination of water and antifreeze. Sometimes instead of antifreeze the system will use methanol and water or denatured alcohol and water to circulate by this second loop.
This secondary loop will be buried well below the frost line on the ground. The ground is only affected by a frost up to a certain thoroughness and if you place the piping too close to the top of the ground you will have it at a level that could nevertheless be potentially affected by a frost. Placing the piping at the proper thoroughness to avoid frost and halting temperatures will allow you to avoid problems with your piping halting and rupturing.
Because there is a possible danger that these pipes could one day become ruptured and leak the fluid that is in them out the types of antifreeze that can be used in them are limited. In most countries the use of monopropylene glycol is allowed because this is the kind of antifreeze that has the least possible to be a danger if it is leaked out.
There are also versions of these systems that have the pipes running vertically because of a without of space surrounding the structure. You have to have an adequate amount of space in which to place the underground piping for these systems to work efficiently. When you do not have such space obtainable then you have to have your piping installed vertically so that you can acquire enough area to properly make the appliance work efficiently.