**3. Thermodynamic analysis of an ORC system utilizing a low-temperature geothermal energy resource:** *A case study with numerical illustration*

A small-scale modular binary fluid ORC geothermal power generation system is proposed for design and installation in Vancouver, BC Canada, near a site characterized by a low-temperature geothermal energy resource. The production well in this resource is capable of supplying hot geo-fluid (mainly liquid water) at a temperature of 90°C (see **state a**, **Figure 1**). The proposed ORC system utilizes R-134a as a working fluid. In this ORC system shown in **Figure 1**, it is required to provide R-134a at a mass flow rate *m*\_ *<sup>R</sup>*of 6.25 kg/s as saturated vapor at 85°C to an inflow radial turbine (**state 3**). The ORC condenser operates at constant pressure with a constant phase-change temperature of 40°C. R-134 then enters an ideal ORC-pump as a saturated liquid (**state 1**, **Figure 1**). The density of the geo-fluid is assumed to be constant at approximately 1000 kg/m<sup>3</sup> . The geo-fluid liquid exits the ORCevaporator (**state b, Figure 1**) to be re-injected into the geothermal resource at 35°C with constant specific heat capacity Cp,Geo = 4.185 kJ/kg.°C.

**Thermal design constraints**: The ORC-evaporator (counter flow-HEx) effectiveness *εEvap*,*ORC*= 90%; the turbine isentropic efficiency η<sup>T</sup> = 100%; negligible pressure drops in the ORC-piping systems.

**Electric generator specification**: ηEG = 92%.

Electricity-driven pump efficiency = 100%.

Required: For this conceptual ORC power generation system, the following thermodynamic performance indicators are determined:

