The Bigadic Geothermal District Heating System (GDHS) has the longest geo-thermal pipeline in Turkey (considered world's third longest pipeline). The Bi-gadic geothermal field is located 38 km south of the city of Balikesir which is in the west of Turkey (Fig. 7.1). Bigadic geothermal field covers a total used area of about 1 km2. As of the end of 2007, there were three wells ranging between depth of 307 and 429 m, respectively. The well head temperature is 98°C. There were five pumps operational in the Bigadic geothermal field. Three of these are used for the wells and the other two are used to pump fluid to mechanical rooms. The wells 1 and 2 are basically artesian wells. The Pump-3 is designed to pump automatically when the flow rate requirement becomes 100 kg/s, and is generally not used because of the elevation difference between the geothermal source and the mechanical room. This elevation difference is about 200 m and provides enough pressure difference to drive the geothermal fluid. If the mass flow rate demand increases significantly, the Pump-3 will start automatically.
Here, we can explain the system in three main parts as shown in Fig. 7.2. In the first part, the geothermal fluid is pumped into the 'mud and gas separator unit' to separate undesirable particles. After passing through the mud and gas separator unit, the geothermal fluid flows into the first heat exchanger. There is an 18 km long pipeline between the geothermal source and the mechanical room. In-between the geothermal source and the mechanical room, the geothermal fluid temperature decreases between 3 and 4oC, respectively, which essentially causes some high amount of energy losses. In the second part, the geothermal fluid transfers its heat to the tab water for residential buildings and is cooled to about 44oC in the first and second heat exchangers available in the mechanical room. After the heat transfer takes place in the first and second heat exchangers, the geothermal fluid is sent to the first and second center-pipeline. In the third part, clean hot water is pumped to the heat exchangers located under each building. The system is designed to have one or two heat exchangers for each building. One heat exchanger is for heating building and the other is for hot-water requirements. Presently, each building has one or two heat exchanger(s) to supply heat and hot water requirements. Nearly 10% of the total residences in Bigadic may have extra water heaters in case the desired temperature is not obtained. There are three pipelines to transfer the hot water along the different pipelines. The second and third centerpipelines supply the heat requirement of the dwellings, one post office, one dormitory, eight colleges, one state hospital, two police stations, and ten government agency buildings.
Although we have calculated and presented the heating energy demand for winter season of Bigadic GDHS in a recent study (Oktay et al., 2007b), we now focus on its cooling energy demand for summer season. In the following sections, methods and calculations of cooling load are given and explained clearly.
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