This paper presents a study on the technical feasibility of efficient/cost-effective use of relatively low temperature geothermal waters for co- and tri-generation of electricity and heat for heating and/or cooling by absorption refrigeration for building integration. As a result of global warming a need for cooling, particularly air-conditioning of buildings is in extreme growth. In Central and Southeastern Europe, as well as in many other regions in the world rich in low temperature geothermal waters <100Â°C (<212Â°F), there is a growing interest of governmental, public and private investors in funding the construction of energy plants which could utilize these waters in an efficient and cost effective way. In addition, current irreversibility of fossil energies/environmental exhaustion increases the importance of R&D search for new technologies of low-exergy sources utilization for higher-exergetic energy production. It is well known that Kalina thermodynamic cycle can convert relatively low temperature energy, at relatively low temperature difference towards environment, to mechanical power and further to electricity using as a working fluid mixture comprised of at least two different components (water and ammonia). The ratio between these components is varied in different parts of the system to increase thermodynamic reversibility and therefore increase overall thermodynamic efficiency. The Kalina cycle thermodynamic efficiency can be much closer to the Carnot cycle efficiency than the Rankine cycle (with the reference to the same temperatures of heat source and heat sink). However, its value at the heat source temperatures below and about 100ÃÂºC is too low for the most of the commercial plant/equipment suppliers and they normally do not consider it financially viable option. The minimum temperature limit due to financial restrictions is usually set at 110-120Â°C (230-248Â°F). That was the reason to explore technical possibilities to expand the low-temperature Kalina cycle's geo-water utilization for co- and tri-generation based on the co-utilization - hybridization of geothermal with solar or other renewable energy sources (RES). Parametric analysis and the determination of relevant thermodynamic limits of corresponding systems have been conducted, encompassing relevant parameters including the cooling source and local site climate conditions, beside the HVAC and other energy loads demands.
Citation: ASHRAE Conference Papers, Las Vegas, NV