Geothermal heat exchanger is an essential part of a total geothermal heating system, just as important as the heat pump. Learn how earth thermal energy is delivered to the heat pump using geothermal heat exchanger coils, loops, etc. Geothermal heat exchanger is usually made of PVC shell and flexi-metal base, and is filled with special anti-freeze liquid which. A water pump circulates the heat exchanger liquid through the loops, delivering constant thermal energy from the ground and increasing the efficiency of the geothermal heat pumps.
Geothermal Heat Exchanger
There are two major types of geothermal ground heat exchangers: horizontal and vertical. Horizontal ground heat exchanger means that the pipes are buried in the ground in trenches. There can be single or multiple layers of pipe in the trench, depending on their depths, or the pipe can be buried forming so-called slinky. In cases of multiple layers or slinky we have to keep in mind to allow enough soil between layers or otherwise pipes can interfere in terms of thermal conductivity reducing overall system performance. Vertical ground heat exchanger means that pipes are buried in one or more vertical boreholes that can be 100-500 feet deep.
The choice of whether to use vertical or horizontal heat exchanger depends on available land area, local soil characteristics and drilling costs. For residential applications horizontal systems are usually used. Vertical systems are used in large commercial applications or where land area is limited. In some cases it can be the only choice. In any way the selection between vertical or horizontal geothermal ground heat exchanger should be done after the cost study has been made. The cost study should be performed by the certified contractor. The contractor should also pick out the geothermal equipment which they have experience and are comfortable working with.
The geothermal ground heat exchanger can also be either series or parallel. In series ground heat exchanger system fluid cam only flow in one path and in parallel there can be more low paths in the circuit. There is a list of advantages and disadvantages of each system, and the choice depends on what are you aiming for.
Series system advantages:
1. single flow path and pipe size – meaning that the flow path is well defined which makes removing of the trapped air much easier
2. slightly higher performance – since series system requires larger size pipes there is a better thermal conductivity per square foot of pipe
Series system disadvantages:
1. larger pipe size requires larger volume of antifreeze
2. larger size pipes are usually more expensive
3. increased installation cost
4. limited piping lengths due to the pressure drop characteristics
Parallel system advantages:
1. lower pipe cost because of the smaller diameter
2. lower volume of antifreeze is required
3. lower installation cost
Parallel system disadvantages:
1. special attention is required to assure air removal
2. flow balancing between each parallel path to result in equal lengths loops.
There are major components in geothermal ground heat exchangers:
Supply and return headers –
Supply and return headers are the antifreeze supply and return lines from the geothermal heat pump to the ground loops (ground heat exchanger). They carry out the total system flow of the heat pump system. Headers are constructed from the large diameter pipes to minimize antifreeze flow pressure drop down the length of the pipe run.
Loops are the pipes extended from the header down to the borehole or to the trench, returned in the same trench or borehole and joined together to the return header.
Reverse return –
Reverse return is a piping arrangement that allows each loop of a parallel system to have the same inlet and outlet pressure. It is used to cancel out the effects of the pressure drop along the header lines.
U-bend is a 180 degree fitting is a loop type heat exchanger used at the bottom of a borehole or at the end of the trench to return the antifreeze.
Geothermal Heat Pump – the ground source heat exchanger and the heat pump need each other to operate, as one will be useless without the other.
Geothermal heating and cooling system is comprised of heat exchanger, heat pump and distribution system – air ducts or radiant heating pipes.