Numerical evaluation of plate heat exchanger performance in geothermal district heating systems

This paper describes the performance of plate heat exchangers in residential water radiator heating systems receiving their heat from geothermal resources. Radiator theory is reviewed and determination of annual hot water requirements for space heating is discussed. Performance evaluation is made of plate heat exchangers and results obtained by means of two equations commonly used for this purpose, the Sieder-Tare and the Dittus-Boelter equations, compared to results obtained with a simpl@ed equation where heat transfer in the heat exchanger is assumed to depend only on thefluid massflow on both sides. It is found that for prevailing temperature ranges in Icelandic geothermal systems the mass frow approximation gives results very close to those determined by the more complicated conventional equations. K e y words: heat exchangers, district heating, geothermal energy, direct use, utilization economy N 0 TAT I 0 N total heat transfer area of heat exchanger (m') channel cross-sectional area in heat exchanger heat transfer area of each plate in heat exchanger (m2) radiator surface area (m') space between plates in heat exchanger (m) specific heat of water (J/kg "C) specific heat of geothermal water (J/kg "C) specific heat of radiator water (J/kg "C) pipe diameter (m) equivalent diameter of heat exchanger channel (4 function of heat exchanger geometry in Dittus