This study has been carried out for the LOW-BIN (Efficient Low Temperature 
Geothermal Binary Power) project, which is supported by the European 
Commission FP6 program. Its aim is to study and recommend optimal Rankine 
cycles using Isobutane (R600a) and R134a as working fluids for two 
geothermal binary power machines. The first one (System A) should be able to 
generate electricity from low temperature geothermal resources, with profitable 
operation down to 65C. The second one (System B) should be able to 
cogenerate both heat and power by heat recovery from the cooling water 
circuit, corresponding to geothermal fluids of 120-150ºC and cooling water 
supplying a district heating system at 60/80ºC. The main Rankine Cycle 
parameters and components are modelled, such as the shell and tube 
condenser and the geothermal plate heat exchanger. The objectives of the 
optimization are maximizing overall conversion efficiency and minimizing the 
cost of the plant, which is represented as minimizing the exchangers’ surface. 
Through this study, a set of optimal solutions for Systems A and B are obtained, 
that combine maximum plant’s efficiency (6.7-7.4 %) and minimum cost. Each 
optimal solution corresponds to an optimal Rankine Cycle and every parameter 
of the cycle is defined.

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