Modeling, design and construction of a micro-scale absorption chiller

In last decades, much effort has been made to drive cooling cycles exploiting renewable energy sources. The use of solar energy is one of the most attractive solutions especially for air conditioning, as availability of solar radiation and cooling loads are approximately in phase. Solar cooling based on water-lithium bromide absorption chillers is the most promising technology for low-medium temperature heat sources (80-100°C). Small (15-40 kW cooling capacity), medium (50-250 kW) and large scale (up to tens of MW) units are currently at commercial stage. In the present work, the development of a novel micro-scale LiBr absorption chiller (around 5 kW) is presented. The objective is to demonstrate the technical feasibility and to investigate the performance under different operating conditions. A computer code has been developed to simulate a LiBr absorption chiller. The model computes mass flow rates, temperatures, pressures and mass concentration of LiBr-water solution in all the chiller components, both in design and off-design conditions. Giving as inputs inlet temperature and mass flow rate of the external circuits (hot water source, cooling water and chilled water), the computer code is able to evaluate the efficiency (COP) and the actual cooling capacity. The simulation code has been used to size the heat exchangers and to design a prototype of a micro-scale chiller. The chiller prototype with a 5 kW nominal cooling capacity has been manufactured and fully instrumented in order to monitor all physical quantities in the internal and external circuits. The prototype is installed on a test rig at the Energy System and Turbomachinery Laboratory of Bergamo University. Measurement devices, data acquisition system and in-house monitoring software are described in the paper. Preliminary results of the experimental investigation are presented.