page_title: Spiral ground heat exchanger
section_title: Ground heat exchanger
hierarchical_section_title: Spiral ground heat exchanger / Introduction / Ground heat exchanger
caption_attribution_description: English: Schematic of series of spiral ground heat exchangers
context_page_description: Using of spiral ground heat exchangers in heat pump applications plays a very important role in supplying heating/cooling demands of the buildings cheaply and sustainable. These-days environmental pollution is one of the main concerns among governments and energy consumption of the buildings has a significant portion in it. One of the efficient ways in supplying heating and cooling demands of the buildings is using potential energy stored in ground which is clean and sustainable. These types of systems are called ground source heat pump systems which are used supplying space heating and cooling demands. The initial cost and efficiency of GSHP systems can be influenced by optimal design of ground heat exchangers.
  One of the most important GHEs that is used these days is spiral GHEs. These types of GHEs are cheaper than others and also have some advantages.
  Many parameters influencing thermal performance of spiral GHEs such as external major diameter of borehole, spacing, distance between each turns of spiral GHEs, etc. When we have a large application area, one spiral GHE is not enough for supplying heating or cooling demands of the building.
context_section_description: Ground heat exchangers use underground soil as a heat source. When water/fluid flows through pipes, heat is transferred from the water to the soil or from soil to the fluid depending on the temperature of fluid and its surrounding temperature. GHEs have some classifications such as deep, shallow, open loop, closed loop etc. Choosing correct types of GHEs is highly depending on geological properties of application area. For instance underground fluid flow or having a lake near application area could be very important advantages. Heat is transferred in the ground by two ways, convection and conduction.
  As it was discussed several types of GHEs such as shallow and deep ones are existed. Deep GHEs are generally U-tube GHEs with common ranges of 50-200 meter. Shallow GHEs are divided to spiral, slinky, pond/lake and snails types. Among different types of shallow GHEs spiral ones show the best performance in the same application unit area which means that more amount of heat can be extracted or injected into the ground. This also means that more space area of the building could be heated or cooled by spiral GHEs. Spiral GHEs are favorable due to their high efficiencies and low initial costs. When spiral GHEs are connected to the heat pump system and total system (GSHP) is integrated to the buildings, heating/cooling demands of that specific residential building could be supplied easily by spiral GHEs. Many researches show that when nine numbers of spiral GHEs are connected to the heat pump system, heating demands of at least 200 square meter space area of a building could be supplied. Based on different parameters of spiral GHEs this value could be changed between 200-800 square meter space area. In Fig. 1 schematic view of series of spiral GHEs are shown.
  Heat transfer rate of GHEs is depending on several parameters such as thermal conductivity of soil or application area, thermal properties of fluid, peripheral area of GHEs and flow rate of fluid inside GHEs. When we have spiral GHEs it means that we have more peripheral area of heat exchanger and so we have more heat transfer. Or for pond/lake types GHEs, since we have fluid around heat exchangers this means that we will have more heat transfer and more temperature difference between inlet and outlet fluid. This issue is one the most important advantages of pond/lake GHEs.
caption: Fig.1 Spiral GHE
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