Study On Variable Effect Libr-water Absorption Refrigeration Cycle And System For Solar Utilization

Solar absorption refrigeration is environmentally friendly and energy saving. It is an important research field of solar refrigeration. The system is mainly composed by solar collector and chiller and the Li Br-water absorption chiller is always adopted as the cooling output unit. The solar collector can only supply hot water on sunny days and its working temperature varies with time. It is intermittent and unstable. One the other hand, the absorption chiller requires stable heat source and offers steady COP. The absorption chiller has the mismatching property compared with the solar collector. The intermittent solar energy brings the need for auxiliary heat source and its instability brings the waste of energy grade. This paper carried out its research aiming at the mismatching:(1) Considering the solar intermittency, the solar absorption refrigeration system needs an auxiliary heat source and fossil fuel is usually used. System with single effect Li Br-water absorption chiller causes great waste of energy grade due to the high energy grade of fossil fuel burning. This kind of waste can be improved by utilizing single/double effect absorption chiller. This chiller works in solar driven single effect mode and gas driven double effect mode. This paper researched a so lar/gas driven single/double effect Li Br-water absorption refrigeration system through its whole year operation. The system ran reliably. It could reach a solar cooling COP of 0.62 and save 50.3% of gas consumption compared with the non-solar system.(2) Considering the instability of low temperature solar heat source, low temperature solar driven variable effect(0.n effect) absorption refrigeration cycle was proposed. The cycle was obtained by changing the cooling process of half effect cycle. Based on the model calculation, the cycle COP varied from 0.3 to 0.7. The cycle could work under the heat source of 83.5oC-110 oC and 104oC-127 oC when the cooling water temperatures were 32 oC and 40 oC respectively. Compared with single effect cycle, the working ranges of heat source were enlarged twice and six times respectively.(3) Considering the instability of medium temperature solar heat source, medium temperature solar driven variable effect(1.n effect) absorption refrigeration cycle was proposed. To get the 1.n effect cycle, theoretical analysis and construction analysis of the absorption refrigeration cycle were carried out. The cycle construction methods were classified as thermal/mass coupling between and inside solution loops. Traditional absorption cycles had bad adaptation with the variation of heat source temperature because the cycles were constrained by the coupling between loops. Several construction principles were obtained. For the utilization of medium temperature solar collector, 1.5 effect cycle was analyzed based on the construction principles. Several new 1.5 effect cycles were constructed through coupling between loops. Coupling inside loops were added into these 1.5 effect cycles by extending the concentration change, another 4 cycles were obtained. One of the 3 cycles was the 1.n effect cycle we needed.(4) Theoretical analysis of the Li Br-water 1.n effect absorption refrigeration cycle was carried out. This cycle separated the vapor from high pressure generator into two parts to the condenser and high pressure absorber. Vapor in high pressure absorber diluted the solution and reduced its equilibrium temperature. The diluted solution can be boiled by the high pressure condensation heat now even its temperature was lower than the double effect cycle. The cycle could adapt to different heat source temperature by changing the flow rate of the high pressure absorber. Based on t he model calculation, the cycle obtained COP from 0.75 to 1.08 under generation temperature from 85 oC to150 oC.(5) The 1.n effect Li Br-water absorption chiller was designed and evaluated experimentally based on the proposed cycle. Design condition of 125 oC generation temperature, 40 oC condensation temperature, 35 oC absorption temperature and 5 oC evaporation temperature was confirmed through calculation. A 50 k W chiller was designed, manufactured and tested. The chiller COP rose from 0.69 t o 1.08 unde r generation temperature from 95 oC to 120 oC. Compared with the theoretical COP, the experimental COP had an average error of 7.3%.(6) The ANN model of 1.n effect Li Br-water absorption chiller was obtained from the experimental data. Heat source inlet temperature, cooling water inlet temperature, chilled water inlet temperature and the required cooling output were set as input. Cooling water outlet temperature and chilled water outlet temperature were set as output. The TRNSYS type of the 1.n e ffect Li Br-water absorption chiller and CPC were coded and the solar driven absorption system was built based on the two types. Simulation and optimization of the system were carried out. The proposed solar absorption cooling system reached an instantaneous COP of 1.1 and an average COP of 0.8 according to the calculation.