• Geothermal systems are primary systems that produce heating and cooling by using water.

Why Water?

• In actuality water stores a lot of heat.  In fact, few naturally occurring substances have a higher specific heat then water.  In comparison to air, there is 3472 more heat stored in one cubic foot of water (7-1/2 Gallons) then in one cubic foot of air.  This is because water has a specific heat of 1 BTU/lb while air’s specific heat is 0.018 BTU/ft³.  While this may be numerical hard to comprehend, the comparison below speaks for itself; the bigger cube represents 3472 ft³ air while the smaller block represents 1 ft³ of water

• There is more then just a higher specific heat that makes water a good substance to use.  Water’s heat characteristics make it superior then air.  This is because conduction is more rapid, efficient, and complete in comparison to convection.  A comparative example is that an air-source heat pump extracting heat from 60^o air is approximately equal in performance to that of a ground-water heat pump extracting heat from water at freezing.

Loops

• Geothermal systems can work in two different ways.  These ways are also known as “loops”.  There are two kinds of loops that a geothermal system can be implicated in.  These are Open Loops and Closed Loops.  These will be discussed below.

Open Loops

• An open loop is a loops established between a designated discharge area and water source.  The water is collected and pumped to the ground water heat pump then discharged to a separate location or back to its original source.  In this loop configuration, the piping is open at bother ends and the water is only utilized once.  You would most likely see these loops where wells, lakes, ponds, etc, are present.  In situations where ponds and lakes are present the discharge water is returned to the source.  Some advantages of using these loops are higher equipment performance due to the fact that the water is used only once and then discharged.  There are however, two major disadvantages.  The first one is the fact that the quality of the water needs to be treated to remove corrosive and abrasive substances.  The second disadvantage is that the cost of pumping water is generally higher then those associated with a closed loop.

Closed Loops

• A closed loop has both ends of the piping closed.  This causes the water to reticulate eliminating the need to new water to be introduced to the loop.  Heat transfer occurs thru the walls of the piping to or from the source.  The source can be ground, ground water, or surface water.  As the heat is extracted from the water in the loop, the temperature falls and the heat from the source flows toward the loop.  In this loop systems water quality is not an issue.  However, system efficiencies are somewhat lower, but given the lower pumping costs associated with this method, economics generally favor this approach.  The initial cost is generally high and consideration in weather a client has a well or other source needs to be taken into account.  There are many types of closed loops systems that can be used including vertical loop and horizontal loop.

Slinky Loops

• This loop was developed by the IGSHPA generates a compromise between performance and installation cost.  While this system is not as efficient as sized vertical ground loops, it represents an improvement in the horizontal loop configurations and has a cheaper initial cost.  Typical quantities of pipe range from 700’ to 1000’ per ton of unit capacity, which is a massive amount.  The Slinky design utilizes 1000’ of pipe in an 80’ trench per ton of unit capacity. 

Typical Uses

• Today this is accessible to many people in many places.  Although there are a lot of positives that this system has, it has a couple of drawbacks.  If a lot of people converted their current HVAC system to geothermal, there might be a large, unforeseen, environmental effect.  The system might warm the ground and although has minimal effect on the environment as a whole, if everyone used it there might be a change in ground temperature that would effect the environment.  This system can be used for private residences and for larger scale buildings.  It might not be economical or probable to use this system in a larger building such as a high-rise.

Parameters

• Temperature ranges can vary based on the users inputted parameters.  Location might limit the max temperatures that can be reached, for example, if you wanted to heat a house built on a sheet of ice in Antarctica, it wouldn’t be able to reach the temperature that a geothermal heated house in California.  Despite these extremes, geothermal units have a typical temperature range of 40-105^o in typical soils (which are about 55 ^o).  The humidity can also be controlled by the user.  It is easy for the heat pump associated with the geothermal system to maintain a relative humidity of 50% since outside air humidity is negligible.