| Title | Direct and Indirect Low Temperature Geothermal District Heating Systems |
|---|---|
| Authors | Chuanshan Dai and Jun Liang |
| Year | 2000 |
| Conference | World Geothermal Congress |
| Keywords | low temperature geothermal |
| Abstract | The selection of direct or indirect use of low temperature geothermal district heating systems is based on the quality of geothermal water. An indirect geothermal heating district system is strongly recommended if the concentration of some corrosion inducing chemicals such as chlorite in geothermal water is high. In the paper, a theoretical method capable of quantitatively evaluating the thermodynamic differences between direct and indirect geothermal district heating systems is proposed. The contents include: the main factors effecting the difference between the two kinds of heating systems; the determination of a best operation mode for an indirect geothermal district heating system and the method of finding optimum design parameters. Since plate and frame heat exchangers (PHEs) are commonly used in indirect geothermal district heating systems; the advantages of using the PHEs with variable plate spacing are also discussed. For comparing the thermal performance between direct and indirect geothermal district heating systems, a concept of relative thermal efficiency is proposed. Once the PHEs are designed in an indirect geothermal district heating system; the optimum flowrate ratio of geothermal water to circulating water can be found through an equation derived in the paper, which has been proved in practice. |