Conference Agenda

Cold storage facilities for horticultural produce typically use vapor compression refrigeration (VCR) systems. The large electricity consumption ofVCR systems is a hurdle in the wider use of cold stores in developing countries since access to reliable and affordable electricity supply from the power-grid is limited in those countries' rural areas. In addition, most of the electricity supplied by the power grid still comes from fossil fuels. Solar thermal vapor absorption/adsorption refrigeration (VAR) systems offer an attractive alternative. They require minimal electricity and the required heat input can be obtained from the Sun. However, any solar driven cooling system for a cold store needs energy storage to ensure 24x7 operation. Especially for a vapor absorption refrigeration, that requirement leads to a system with complex configuration, with both hot and cold storage tanks apart from solar collectors and absorption chillers. Since it is driven by an intermittent source of energy, complexity of the supervisory control system also increases: constant setpoints are not possible. That makes both the system sizing problem (how big should the components be?) and the control design problem (how should the setpoints be changed over time?) both challenging and intertwined.
In this paper we present a method for co-solution of the system design and supervisory controller design problems of a solar thermal absorption refrigeration with energy storage (STARES) system. The method takes solar irradiance and cooling load - over a planning period - as input data. It solves an optimization problem that yields the optimal component sizes and optimal set points over that planning horizon. We develop a simple dynamic model of the STARES system that acts as dynamic constraints, making the optimization problem solvable for a year's hourly data in just a few seconds. User-chosen weights in the optimization problem have a strong impact on the solution. This feature allows incorporating human expertise to guide the solution. We also compute the hourly cooling load for a year for a small cold store at a specific location in India. Numerical results show that the proposed method can obtain a system design with minimal component sizes and a supervisory controller that can meet cooling load with that system.

In the perishable food industry, cold storage is generally achieved using vapor compression refrigeration. However, the dependence of vapor compression on electricity, due to the compressor, limits its applicability in the developing world where a reliable electric grid may not be available. Currently, $936 billion in value from food is wasted annually, and a significant portion of this is due to limitations in the cold chain (40-50% in sub-Saharan Africa).

A thermally driven adsorption refrigeration system driven by waste biomass from farmers is a possible solution to this issue. Adsorption chillers operate by replacing the electrical compressor with thermal compression to limit the reliance on electricity. These systems employ adsorber and desorber beds in place of the compressor along with the evaporator, condenser, and expansion valve. However, these systems can be large and expensive; therefore, accurate modeling for proper design and sizing is essential.

This work analyzes a thermally driven adsorption chiller, specifically comparing options for liquid-coupled and air-coupled heat rejection in the condenser. Individual heat and mass transfer models for each component of the adsorption chiller are developed and coupled into a transient cycle model for performance characterization. The adsorption and desorption beds are modeled in a transient lumped capacity while a hybrid moving boundary-partially discretized methodology is employed for the evaporator and condenser. Adsorption systems with liquid-coupled condensers often maintain higher COPs and specific cooling densities; however, the higher water consumption can create problems in areas with limited water availability. Thus, the benefits and drawbacks, including performance comparisons, of each option are quantified using this model and discussed.

A nominal 10-kW system is used as a basis for the modeling, and each system contains identical components aside from the condenser. Various ambient conditions and cycle times are tested to determine the optimal performance of both systems, including COP and average and peak cooling duty. The appropriate applications for each system are discussed.

We report the design of a new system capable of using low concentration saline solutions to regenerate high concentration saline solutions through a spontaneous process. The system consists of multiple entrochemical amplifiers in a novel ring structure, which spontaneously generates a thermal gradient, driving the solvent from the solution. We construct a numerical simulation to examine this design and demonstrate the ability of this configuration to generate significant thermal gradients. Under some use cases, these thermal gradients grow sublinearly with the increase in amplifier number, while in other use cases, these thermal gradients grow superlinearly with amplifier number. When configured as a ring, the array is capable of quickly generating a thermal gradient, which can drive solvent from a solution. We demonstrate self-concentration of a saline solution, where the saline solution is used as the driving solution for the concentration. Our simulated rings concentrate the solutions from an initial simulated concentration of 1.81 M to between 3.01 and 16.53 Molar (increase of between 66.3 and 812.9%), a concentration factor of up to 9.1, using between 2 and 8 amplifiers in the ring. We experimentally explore this ring regenerator as a tool for concentrating hard to dry salt solutions. We report the concentration of a proprietary saline solution from an initial concentration of 1.3M, 1.5M and 2.2 M to between 1.51 M and 7.42 M (increase of between 69.2 and 388.2%), depending on the time in the ring regenerator. We additionally demonstrate self-concentration of CaCl₂ over 240 minutes which concentrates a 7.4 M CaCl₂ solution to a 9.6M CaCl₂ solution (increase of 29.7%), reducing the additional CaCl₂ solutions to concentrations of up to 4.13M. Such a system could realistically result in the expansion of thermal sources useful in regenerating saline solutions to include low grade heat sources, such as low grade waste heat and environmental heat.

The present research compares the results of the experimental evaluation of a low-capacity single-effect absorption cooling prototype, operating with NH₃-H₂O and NH₃-H₂O-LiBr, to understand the potential advantages of using the ternary mixture over the binary one. To carry out an objective comparison of the system's performance with both substances, the mass fractions of NH₃ to H₂O were set at 0.38 for the binary mixtures and 0.4 for the ternary mixture, while the mass fraction of LiBr to H₂O was maintained at 15%, a concentration recommended by studies available in the literature. In both cases, the absorption cooling prototype was evaluated under similar operating conditions. The range of the heat source temperature varied between 85 and 105°C, while the temperature of the cooling medium used in the condenser and absorber varied between 20 and 34°C. Under these operating conditions, a parametric analysis was conducted, evaluating desorption and evaporation pressures, evaporation temperature, cooling power, and coefficient of performance. The results indicate that the binary mixture offers better energy performance for the specified operating conditions. However, the ternary mixture could provide interesting operational advantages

The work presents further research in Hybrid Compression (HC) Refrigeration. Introduced by the author more than a decade ago, HC couples synergic two technology sections, of absorption (ATS) and of mechanical vapor compression (MVCTS). ATS and MVCTS base on author’s coabsorbent technology (CBS) and on an integral mechanical vapor compression technology (IMVC), respectively. Besides HC, the work presents as well results of a recent technology, the Mother & Father HC, (M&FHC), introduced by the author about three years ago. M&FHC aims at producing useful (electrical) work, when supplied by just ambient temperature heat. The work analyses several thermodynamic ideal and real interactions of ATS and MVCTS. It is done with the help of a lemma, proved in the manuscript, which lays down the basis of this and other similar works. Results cover applications in refrigeration, ultra-low temperature refrigeration (ULTR) and work yield. ATS and MVCTS operate with ammonia-water and ammonia working fluids, respectively. The following input data hold true for external sink, -18 C deg. to +54 C deg., and desorber, -76.5 C deg to -42 C deg. temperatures. The output data hold for the COPc,HC cooling coefficient of performance, [kJ refrigeration / kJ work input], in operation of HC working mode, and Wnet useful work, [kJ work / kg refr.], in operation of M&FHC working mode. The modeled results indicate much higher COPc,HC values as compared to those of initial HC refrigeration, i.e. of about 7.6 > COPc,HC > 5.05, while Wnet is in the range of 110 > Wnet > 195.