Experimental Study of Performance Improvement of 3-Bed and 2-Evaporator Adsorption Chiller by Control Optimization

Abstract

The main challenge facing adsorption cooling technology is low Coefficient of Performance (COP), which becomes a key factor of the commercialization of this technology. This paper presents the results of modifications, aiming to increase COP, applied to the control software of a prototype three-bed two-evaporator adsorption chiller. Changes were mainly related to the sequence of the switching valves and had no influence on the hardware of the chiller. The sequence changes enabled the introduction of heat recovery and mass regeneration. Moreover, the precooling process was improved. The applied modifications not only resulted in significant improvement of the chiller's COP, but also improved the cooperation adsorption unit heating source, which is of great importance in case of district heating supply. The improvement was also observed concerning such operational aspects as noise and vibrations. In the authors' opinion, the presented modifications can be introduced to most exploited adsorption chillers and could potentially lead to similar improvements in performance.Energies 2019, 12, 3943 2 of 17 Methods of Improving COP of Adsorption ChillerThe issue of COP improvement of adsorption chillers is the subject of much research, which focuses on two main fields of study: Improvements via hardware modification and via software modification. Hardware modifications mainly consist of the proper selection of working pairs, the optimization of the adsorption beds [8], and the general system design. Software modifications reported in the literature optimize the switching time and cycle allocation. Some of the optimization methods, like the application of heat or mass recovery, usually require both hardware and software modifications. Working PairsThe appropriate selection of the working pair was reported in [9,10] as a crucial factor influencing the COP of adsorption chillers. Therefore, much reported research is related to adsorption working pairs and their properties [10]. The most popular pairs are microporous silica gel and water, zeolite and water (including alumino-silicate zeolites) [11,12], and Y-type zeolite with methanol or ethanol combinations [9,13]. Moreover, some novel adsorption working pairs are investigated, that is (silico) aluminophosphate-water, consolidated adsorbents such as LiBr-silica-ethanol or water, CaCl 2 -silica and water, and activated carbon with ethanol, methanol or water [9].Each adsorption working pair has unique properties that make it possible to obtain good performance in the conditions considered. For example, water-based pairs cannot be applied to achieve temperatures lower than 0 • C (due to water's freezing point). Some of the adsorbates, like methanol, are harmful, and its application would probably require additional safety procedures. An overview of working pairs was presented by [14]. Other important factors which must be considered are the expense and availability of the selected adsorption working pair.

Modeling of a Combined Cycle Gas Turbine Integrated with an Adsorption Chiller

“…In the course of this process, adsorbate vapour from the evaporator is transported to the adsorption bed while absorbing heat in the process, which leads to lowering the temperature of the liquid that is to be cooled down. The bed saturated in this way is heated again by an external source, which causes the refrigeration cycle to begin once again [16,[18][19][20]. Reduced electricity demands, simple design (no moving parts, pumps or compressors), quiet and vibrationless operation and low maintenance requirements are the main features of adsorption chillers.…”

“…Therefore, the trigeneration [10,11] system would be an ideal solution for heat generating plants that face a serious hindrance to their operation during the summer months. The systemic generation of cooling would also reduce power consumption for air conditioning, which would have a favourable effect on the entire power system and would relieve the demand for power during the summer months [14][15][16][17]. Advantages of the generation of district cooling include increased power safety as a result of increased generation of electricity during the summers' peak electricity demand and by improved effectiveness of the utilisation of the heat generation systems (generation sources as well as heat networks) will result in more effective use of primary energy resources as well as elimination of CFCs used in compressors, which are harmful to the environment.…”

Performance Results of a Solar Adsorption Cooling and Heating Unit

“…The equations for the power consumption of the HT, medium temperature (MT), and LT pumps of Figure 1 can be found in Reference [22]. Moreover, the fan coil pump is identical to the LT pump; thus, the same power consumption profile is realized.…”

“…The nominal driving heat temperature was set at approximately 90 • C. Under varying experimental conditions, the optimal working point of the chiller was determined to be achieved at an evaporator temperature of 6.6 • C, which corresponded to a COP of 0.55. Chorowski et al [22] investigated the performance effects of the control strategy on a three-bed, two-evaporator adsorption chiller. The authors demonstrated that changes to the control system can improve the performance of the chiller, especially in terms of COP.…”

Performance Results of a Solar Adsorption Cooling and Heating Unit

“…Under varying experimental conditions, the optimal working point of the chiller was determined to be achieved at an evaporator temperature of 6.6 °C, which corresponded to a COP of 0.55. Chorowski et al [19] investigated the performance effects of the control strategy on a three-bed, two-evaporator adsorption chiller. Authors demonstrated that changes to the control system can improve the performance of the chiller, especially in terms of COP.…”