Study of a Solar Assisted Micro-Tri-Generation System

In this work, a micro-tri-generation system integrated with a solar system is studied. A basic micro-cogeneration technology (micro-CHP system) integrating solar collectors, tank, micro-turbine and a thermodynamic cycle based on the organic Rankine cycle (ORC) is applied together with an absorption chiller. The heat rejected at the condenser of the micro-CHP system is used for water heating, and the absorption chiller is used for space cooling. Hot water from the solar circuit tank is the heat source for the cooling system (absorption chiller) and the micro-CHP system. A heat exchanger is used to transfer heat from the hot water circuit to the power cycle (with an organic refrigerant). The micro-CHP system under analysis uses a micro-turbine and an electric generator with a power output of 5 kW. The turbine inlet temperature is 80°C and the working fluid is cyclohexane. The absorption chiller, which is a single-effect water-fired chiller, operates with a lithium bromide and water mixture, and a water inlet temperature between 80°C and 100°C. The performance for different solar collector areas and tank capacities was evaluated through a numerical model. The study was extended throughout the cooling season, from May to October, for climatic conditions of Lisbon (Portugal). The monthly average solar fraction was evaluated for different cases: the micro-CHP system; the cooling system; and the micro-tri-generation system (heat-power-cooling) where the useful condenser energy was used for domestic hot water. The solar fraction of the micro-CHP system was low, compared with the solar fraction of the cooling system, because the efficiency of the micro-CHP system is lower than 7%. However, when the tri-generation system is considered, the monthly average solar fraction is higher due to the utilization of the condenser heat for domestic hot water. The solar system, cooling system and its components were modelled with the TRNSYS simulation program. The micro-CHP system was modelled with EES software.