Preliminary design of a hot water distribution system for greenhouse heating, Olkaria, Kenya

Abstract

Geothermal energy may be utilized directly or indirectly. Its main use in Kenya is the generation of electricity. Direct utilization of geothermal energy in Kenya is minimal. However, potential direct users are located a few kilometres from the already developed geothermal fields and there is usage potential for a hot water supply for greenhouse heating. Chemistry for re-injection brine has shown that a substantial amount of heat energy may be extracted from the brine without risk of silica scaling. Greenhouse farming requires temperature and humidity control for enhanced plant growth, especially during the night when temperatures are as low as 8°C. Heating domestic water with electricity is expensive in Kenya, therefore utilization of geothermal energy to heat it would be a much cheaper and greener option. Based on the saturation index of silica, the available heat energy of brine from Olkaria North East field is about 16.58 MWt using a mass flow rate of 238 ton/hr. at a supply temperature of 150°C and a return temperature of 90°C. In this study, an evaluation was made on direct use of geothermal energy for one greenhouse complex, one hotel and three residential estates. The study was aimed at coming up with a preliminary design for a hot water distribution system, mainly for greenhouse heating. The design model was generated using the Engineering Equation Solver (EES) software and the design was done as per ASME B31.3-2002 standards. The design considered has a closed loop circuit with heat exchangers at all ends. The total cost of the distribution network is €8,848,000 and the unit cost of heat production is €13.24 per MWh