• Energy Research

Decoupled desiccant dehumidification and evaporative cooling technologies can efficiently dehumidify and cool air using predominantly low-grade heat and water. However, as the target temperature and humidity decrease, the temperature required for desiccant regeneration increases, which in turn decreases sorption capacity. In this study, we introduce the concept of Combined Sorption Dehumidification and Evaporative Cooling (CoSDEC) wherein air is simultaneously dehumidified via sorption and cooled via evaporative cooling in a pair of adjacent desiccant-coated and water-wet channels. A 900-mm proof-of-concept system employing mesoporous silica gel desiccant regenerated at 40 °C is demonstrated to dehumidify and cool 1.0 m/s of hot and humid air from 30 °C and 20 g/kg da to a minimum of 15.6 °C and 4.8 g/kg da. This yields a cooling effectiveness of εwb = 3.76 and εdp = 2.85, and a dehumidification effectiveness of MREadb = 5.2 and MREiso = 1.75. Further enhancements were achieved by decreasing flow velocity (15.4 °C and 4.6 g/kg da at 0.8 m/s), increasing regeneration temperature (15.3 °C and 2.8 g/kg da at 50 °C), or increasing system length (13.9 °C and 4.2 g/kg da at 1200 mm). The remarkable capability of CoSDEC to efficiently dehumidify and cool air to substantially low humidity and temperatures using a low-temperature heat source and water represents a significant achievement in heat-driven air conditioning technology. The potential for further reduction in temperature and humidity levels through the optimization of operational and design parameters underscores the promise of a combined sorption dehumidification and evaporative cooling system.

Six samples from the TMPS family of mesoporous silica nano-materials from Taiyo Kagaku Co., Ltd. were studied for their potential as a medium for the adsorption thermal energy storage. Selected specimens are distinguished by their pore size from 1.9 to 4.1 nm and aluminium doping. As the adsorbate for the adsorption pair was selected water with the most advantageous properties of high latent heat and safe chemical properties. The tested materials doped with aluminium show high affinity towards the selected adsorbate and high uptakes. The theoretical storage energy density of the materials spans from 700 to 1700 kJ kg−1 based on the adsorption heat. The storage capacity depends mostly on the pore volume and partially on the pore size. The theoretical estimation shows the temperature gain of the adsorption potential as high as $$\varDelta T= 23\,^{\circ }\text {C}$$ for the material TMPS-1.5A with the smallest pore diameter and aluminium doping and as low as $$\varDelta T= 6\,^{\circ }\text {C}$$ for the TMPS-4R with the biggest pore diameter and without aluminium doping.

Abstract Adsorption cycles have been gaining significant interest in waste-heat recovery and renewable energy utilization. Adsorption isotherm data and the equilibrium cycle analysis are crucial steps in evaluating a typical adsorbent + adsorbate pair. In this paper, the performance of Maxsorb III + R245fa and spherical activated carbon, SAC-2 + R245fa were studied for adsorption cooling and adsorption heat transformer (AHT) cycles. Adsorption isotherms of these pairs were measured using the constant-volume-variable-pressure apparatus for temperatures ranging from 30 °C to 60 °C, and fitted with the Dubinin–Astakhov (D–A) and the Toth isotherm model. An improved equilibrium model was developed, accounting the effects of thermal masses. The specific cooling energy (SCE) and the coefficient of performance (COP) of the adsorption cooling cycle were evaluated for various thermal mass to adsorbent mass ratios. It is observed that SAC-2 + R245fa pair offers better SCEs (20 kJ kg−1and 160 kJ kg−1 at 60 °C and 90 °C, respectively) when compared to that of Maxsorb III + R245fa. The impact of thermal mass is found to be significant for all regeneration temperatures for Maxsorb III + R245fa while the deterioration of COP in SAC-2 + R245fa is notable for high regeneration temperatures (> 75 °C). When employed in the AHT cycle, Maxsorb III offers a slightly higher useful heat while SAC-2 provides a better Q u h / Q Q R albeit by a small margin. The Q u h / Q Q R values for both studied pairs are more than 0.6 for all regeneration temperatures for the heat extraction at 120 °C.

A new model of adsorption isotherms Type IV and V is proposed as a basis for theoretical calculations and modelling of adsorption systems such as adsorption heat storage and heat pumps. As the current models have decent yet limited applicability, in this work, we present a new combined model with universal use for micro-mesoporous silica/water adsorption systems. Experimental measurement of adsorption isotherm of water onto seven different samples of micro and mesoporous silica and aluminium-silica were used to fit new adsorption models based on a combination of classical theories and a distribution function related to the pore-size distribution of the selected materials. The fitting was conducted through a repeated non-linear regression using Trust Region Reflective algorithm with weighting factors to compensate for the scalability of the adsorption amount at low relative pressure with optimization of the absolute average deviation fitting parameter. The results display a significant improvement for most of the samples and fitting indicators compared to more common models from the literature with average absolute deviation as low as AAD = 0.0025 g g−1 for material with maximum uptake of q = 0.38 g g−1. The newly suggested model, which is based on a combination of BET theory and adjusted normal distribution function, proved to bring a higher degree of precision and universality for mesoporous silica materials with different levels of hydrophilicity.

Humidification-dehumidification desalination (HDD) systems offer a feasible approach for the production of fresh water in inaccessible areas as they can be operational using renewable energy and require little maintenance. Various studies are being carried out to boost the system performance. In this paper, an open air open water HDD system is proposed that exploits the enhanced evaporation and condensation processes by implementing with the Maisotsenko cycle (M-cycle). The system utilizes solar energy as the energy input to heat the saline water. A thermodynamic model is formulated under steady-state conditions, considering the first and second law of thermodynamics. The energetic and exergetic performance of the system is studied. The model is first validated with the experimental data and a good agreement is found where the maximum discrepancy is about 6.0 %. Effects of different operating conditions on key performance parameters such as the Gain Output Ratio (GOR), specific energy consumption (SEC), exergy destruction, and exergy efficiency are analyzed. An improvement is observed in the GOR when the inlet air temperature is raised at constant humidity ratio. The system exhibits better performance in dry air environment when compared with humid air environment. The analysis shows a maximum mass flow rate of desalinated water of 22.3 kg/h, recovery ratio (RR) of 0.223, GOR of 3, SEC of 0.23 kWh/kg and an exergy efficiency of 43.21 %.

Desiccant dehumidification systems can be utilized for decoupling moisture removal duty from the conventional mechanical vapor compression systems. Dehumidification using desiccant dehumidifiers is expected to exhibit a better energy efficiency. However, the high energy needed in the regeneration process limits its applicability. To realize the full potential of this technology, it is necessary to develop materials that can be regenerated using heat sources under 70 °C. In this study, activated carbons (ACs) derived from waste biomass were developed as desiccant materials. The ability of activated carbon (AC) to remove the moisture was controlled by carefully preparing the material to achieve the right operation window for optimum moisture sorption processes. The porous and surface characteristics of the newly-prepared AC were analyzed and compared with those of silica gel. The adsorption isotherm measurements were conducted, and the data were fitted with Henry–Sips and Do–Do isotherm models. The current ACs exhibit an excellent water adsorption capacity (up to 0.41 g/g). The efficacy of the ACs for dehumidification applications was assessed using the weather data from several regions of Indonesia, from North Sumatera to Papua. The results revealed that under the studied conditions, the new desiccant material showed a better dehumidification capacity than silica gel. Moreover, the reported AC can be regenerated using temperatures as low as 40 °C, which is readily available from waste heat, including the heat rejection from the condenser of an air-conditioning unit.

Adsorption thermal energy storage plays a vital role in supporting the availability of renewable energy. Activated carbons produced from local waste biomass have been attracting considerable attention in adsorption technology due to their unique properties and sustainability. However, their limitation in water vapor uptake hinders the practical application of this material. In this work, acorn nutshells were utilized as a base material to produce activated carbon. Air oxidation was performed as a versatile and low-cost technique to enhance the material’s properties and water adsorption capacity. By applying air oxidation as a post-treatment during material production, the amount of active functional groups and the water adsorption on activated carbon has been successfully enhanced. From the theoretical calculation, it is found that activated carbon–water working pairs shown promising performance to be used for adsorption thermal energy storage applications. The adsorption of water vapor on the post-treated-activated carbon releases the isosteric heat between 2400 kJ/kg to 2500 kJ/kg. Moreover, this study’s working pair can be driven by a temperature of less than 50 °C. From the results, it is confirmed that by controlling the adsorbent’s surface properties, activated carbon–water working pairs can be a promising way to provide alternative material and reduce the energy demand for driving the system.

Renewable energy-based microgrid systems are widely being studied as electrification methods for rural communities in developing countries. Waste heat generated by the components of the microgrid systems, such as the biogas driven generators (BDG), presents the potential of utilizing the low-grade heat in a way that can contribute to the sustainability of such energy systems. From the points of view of affordability, local manufacturability, and applicability for agriculture, thermally driven pumps (TDP) may be attractive for coupling with such microgrid systems. Therefore, the current study has focused on the development of a new type of thermally driven pumping system as a potential waste heat utilization component for microgrid applications in rural areas. A liquid piston-type TDP concept without moving parts, except few valves, was developed and parametric experimental investigations were carried out. The performance and characteristics of the system were studied, which revealed that the proposed system has a superior performance compared to the literature. It was also found that the system performance strongly depends on the heat addition rate and delivery capacity of the system, which are suitable characteristics for the intended application. Hence, the experimental data were used to estimate whether the proposed system can pump enough water that needs to be supplied for the biogas production to supply a 10 kW BDG unit of a microgrid. It was found that 87 - 93% of the total pumped water (13 - 27 m3) would be available for agricultural and other purposes while only 6 - 13% would need to be fed to the biogas digester. Generally, the results seem to be promising, and yet there are potentials for the optimization and improvement of the proposed system, hence they have been pointed out.