How many types of systems are there?
The majority of loops utilized in residential buildings are installed horizontally or vertically in the ground or are immersed in a pond or lake. Most of the times the fluid circulates through the loops in a closed circuit but open systems can be used if the local conditions allow it. Each type of system has its own advantages and disadvantages.
Horizontal closed loop
This configuration is the least expensive and can be implemented when the owned surface is adequately large and the terrain allows easy ditch digging. The process consists of parallel digging of ditches at a depth of 90-180 cm beneath the ground, followed by the installation of plastic pipes inside the ditches and the subsequent filling of the ditches with soil, without damaging the pipes. The fluid circulates through the pipes in a closed circuit. A closed horizontal circuit needs to have 120-180 m in length for every ton of refrigeration, meaning 35 to 52 m for 1 kW. The pipes can be coiled up in winding shape in order for the ditches to be shorter and thus the area affected by the digging will be smaller as well. However, in this case a bigger quantity of pipes will be necessary. The horizontal loops are easier to install while the building is in construction, but they can also be installed after the completion of the building with a minimum of discomfort for the tenants.
Vertical closed loop
This type of loop is ideal for the buildings that have very little space available for a yard or garden, and where horizontal loops would not fit in, when the terrain is stony close to the surface or where the client wishes to inflict minimal damage to the lawn. The constructors perform vertical boreholes at a depth of 45 to 135 m. Each borehole contains a single loop with a “U” shaped terminal section (at the base of the borehole). After the pipe is introduced in the vertical borehole the borehole is filled with earth or with a special formula of cement. Each vertical loop is then connected to a horizontal loop which is also installed underground. The horizontal loop conducts the fluid to a junction of the geoexchange system. The installation of the vertical loops is generally more costly but requires a smaller quantity of pipes in comparison to the horizontal loops.
Closed loop submerged in the water of a lake
If the building is situated in the vicinity of a lake or pond, setting the loops in the water is the cheapest solution. The fluid circulates through polyethylene pipes identical to the ones that are usually buried underground. In order for an optimal heat exchange capacity to be available, Geoexchange experts recommend using submerged loops only if the water level does not go below 180-240 cm throughout the year. A variation of the submerged closed loop appeared recently. Instead of the pipe loops the variation uses a metallic heat exchanger vertically submerged beneath the freezing point of the water and no lower than 50 cm above the bottom of the lake.
This configuration is the most efficient if water can be found in significant quantity in the soil. The open loop system is the cheapest and easiest to install. In this type of system the water coming from a borehole that reached the phreatic layer is pumped in the building where it gives up heat to a GSHP. After leaving the premises, the water is pumped back in the phreatic layer through a second borehole, the return borehole. The return borehole is drilled at an adequate distance from the first one. The local authorities must be consulted in advance if the open loop system is chosen. In most cases a given number of water boreholes can serve communities and thus the open loop will need a buffering reservoir with a capacity proportional to the existing phreatic layers’ flux. The vertical water boreholes have an 18 cm diameter and a depth of up to 450 m and can be used as extraction and return boreholes in the same time. In this case, the water that is extracted from the bottom of the borehole is then circulated towards the GSHP’s heat exchanger and afterwards is forwarded to the higher section of the water column. Usually, the borehole provides drinking water as well. However, in order for the system to work properly, the water coming in the system needs to flow at a relatively high speed and in sufficient quantity. If the water temperature increases or decreases too much in the borehole the water in the return borehole can be purged from the system with the purpose of allowing the phreatic layer to restore optimal temperature level. The return conditions vary depending on the location but they are usually not very restrictive due to the fact that the quantities are relatively small in comparison with the volume of the phreatic layer. During the geoexchange process the water is not contaminated chemically or biologically.