Global reliance on traditional cooling systems is a pressing concern, especially given their substantial energy demands and refrigerant-related greenhouse gas emissions. The need for sustainable ...cooling solutions is especially urgent in hot and humid regions. This study presents an innovative solution by introducing a compact, solar-driven cooling system that integrates a Desiccant Wheel (DW) and a Thermoelectric Cooler (TEC). This novel combination leverages solar energy to enhance cooling efficiency while reducing environmental impact. The system's performance was tested through experimental methods and non-dimensional analysis, which served to validate the TRNSYS simulation. The simulation included custom components representing the DW and TEC's physical characteristics. Results demonstrated that the system effectively reduces air temperature and humidity to maintain thermal comfort, achieving Coefficients of Performance (COP) of 0.94 and 1.13in Toronto and Vancouver, respectively. A key feature of the system is the heat recovery design, which uses waste heat from the TEC to regenerate the desiccant material, enhancing COP by 68%. Further analysis through TRNSYS simulation explored the system's adaptability to various climate conditions by testing a range of temperatures (26–43°C) and relative humidity levels (30–100%). This analysis identified three operational regions, optimizing the system's application based on environmental conditions. A life cycle assessment determined a Global Warming Potential (GWP) of 0.0172 kg CO2 per kW of cooling capacity and an Energy Payback Time (EPBT) of 3.34 years. The economic analysis indicated a total system cost of $2719, predominantly due to the DW and TEC components. In conclusion, this research offers a sustainable and efficient cooling system that provides thermal comfort in hot and humid climates, marking a significant advancement in climate control technology.
•Evaluation of innovative hybrid cooling for improved indoor climate control.•The validated system boosts COP from 0.56 to 0.94, ensuring thermal comfort.•Heat recovery strategy boosts system efficiency by 68% in diverse climates.•Life cycle assessment shows 0.0172 kg CO2 per kW of cooling capacity.•The system demonstrates a 3.34-year energy payback, highlighting cost savings.
Recently, solid desiccant air conditioning system has been proposed as an alternative to the conventional vapor compression refrigeration air conditioning systems for efficient control over humidity ...of conditioned air especially in hot and humid areas. The solid desiccant cooling can be more favorable over the traditional vapor compression refrigeration air conditioners, because it assures more accessible, economical and cleaner air conditioning. It is still more important when it is powered by free energy sources like solar energy and waste heat with temperatures of between 60°C and 80°C. In addition, it can significantly reduce the operating cost as well as save energy. In the present paper, principle of solid desiccant cooling system is recalled and its technological applications and advancements are discussed. Through a rigorous literature review, different configurations of desiccant cooling cycles, conventional and hybrid desiccant cooling cycles, different types of mathematical models of rotary desiccant dehumidifier, performance evaluation of desiccant cooling system, technological improvement and the advantage it can offer in terms of energy and cost savings are highlighted. This paper also gives a detailed account of the general features and performance of the solid desiccant cooling system when it is powered by solar energy or industrial waste heat for regenerating the desiccant. This review is useful for making opportunities to further research of solid desiccant cooling system and its feasibility which is becoming common in the coming days.
•Solid desiccant cooling is reviewed as a potential alternative to traditional cooling.•Energy saving and active use of renewable energy and waste heat is also illustrated.•Various mathematical models of rotary desiccant dehumidifier are described.
Display omitted
•Return air and all fresh air are compared for heat pump desiccant wheel system.•Fresh air is more energy saving than primary return air for low humidity control.•Optimized fresh air ...is summation of regeneration and positive pressure flowrate.•Low temperature-humidity and high temperature-humidity fresh air is energy saving.•Primary return air for hot summer warm winter region when indoor humidity over 30%
Hybrid desiccant wheel systems are widely adopted for low humidity control in industrial field. The clarification of process and regeneration air management is required to achieve energy saving. The all-fresh air dehumidification and primary return air dehumidification are compared for a high-polymer desiccant wheel and heat pump system. The system simulation model was established and validated by field test results of a low humidity industrial workshop. Firstly, the fresh air flowrate and air stream pattern are analyzed and optimized, for achieving low annual energy consumption. Secondly, the system power of the optimized fresh air mode and primary return air mode were compared for different outdoor air temperature, outdoor air humidity and indoor humidity requirement. At last, energy saving rate of all fresh air dehumidification mode was analyzed for five typical climate zones in China. It was found that the optimized fresh air flowrate numerically equals to the summation of regeneration air flowrate and the positive pressure required air flowrate. With the optimized fresh air flowrate, 20.4% of the annual energy can be saved compared with primary return air system. Outdoor air conditions were divided into three zones on psychrometric chart, and the boundaries are related to indoor temperature and humidity ratio. Fresh air is energy efficient for high temperature high humidity and low temperature low humidity conditions. By using fresh air dehumidification mode, the energy saving rate can reach 69.6% for severe cold region. Primary return air dehumidification mode is suitable for HSCW and HSWW region for indoor relative humidity of 40%, and 41.8% of the energy can be saved.
A passive desiccant wheel is a rotating dehumidifier that can be regenerated using the room's return (exhaust) air and does not require hot air for regeneration as in the active desiccant wheel. In ...this study, a one-dimensional mathematical model has been developed to analyze the parameters of the passive wheel and to compare this with the existing active desiccant wheel. To transform the active desiccant wheel into the passive desiccant wheel, silica gel B has been utilized as the desiccant material since it operates better in a saturated air environment. Additionally, a cooling coil has been placed in front of the wheel to provide saturated and cold air. Therefore, regeneration has been accomplished without the usage of external heat due to the relative humidity difference between the return air and the saturated air. From the mathematical results of this study, it has been found that the optimal ratio of process area to regeneration area and rotational speed of the passive desiccant wheel are 0.44 (i.e., regeneration area is equal to the 69% of total wheel cross section) and 7-15 rph, respectively. Similarly, the optimum regeneration and process velocity of the passive desiccant wheel was found to be 2 m/s. Further, the exit temperature of the process air of the passive wheel is less than the active wheel in all cases because the return air of the room has been used for reactivation, which is the fundamental advantage of a passive wheel over an active wheel and is suitable to supply in the room.
Display omitted
•Desiccant air conditioning system integrated with PV/T units was simulated.•Optimum area ratio of PV module to PV/T unit is 0.2 and number of the units is 441.•Seasonal thermal and ...electrical solar fractions are 1 and 1.16, respectively.•Seasonal thermal, electrical and total COP are 0.46, 4.09 and 0.42, respectively.•Proposed air-conditioning system is a self-energizing sustainable system.
This paper proposed and simulated a solid desiccant air-conditioning system integrated with a direct evaporative cooler, a dew-point indirect evaporative cooler and heat recovery units during a complete cooling season for a building located in Adana, Turkey. The thermal and electrical energy required for the proposed system are provided by water-cooled PV/T units. The generated thermal energy is used to regenerate the desiccant wheel, while the electrical energy generated is used to power air fans, water pumps and other equipment of the air-conditioning system. The area ratio of PV module to PV/T unit, the number of PV/T units required and the optimum connection strategy of PV/T units are investigated in detail. Five different area ratios are tested to determine optimum total PV/T unit number considering the seasonal thermal and electrical solar fractions during cooling season. The optimum area ratio, total PV/T unit number, seasonal thermal and electrical solar fractions are found to be 0.2, 441, 1 and 1.16, respectively. Seasonal thermal, electrical and total coefficient of performances are calculated as 0.46, 4.09 and 0.42, respectively. The net seasonal primary energy consumption is negative at −102.82 kWh, which demonstrates that the proposed air-conditioning system is a self-energizing sustainable system, and can be considered as an alternative air-conditioning solution for office buildings in the Mediterranean region.
In this study, a desiccant-based hybrid cooling system supported by a vapor compression system and a heat recovery unit (rotary heat wheel) was analyzed from energetic and exergetic perspectives ...during the daily working hours of an office building in Istanbul to meet the desired comfort conditions. We focus on the impact of different refrigerants; namely R32, R1234yf, R290, R134a, R600a, R245fa, and R717, on hybrid rotary desiccant-vapor compression systems. While the highest electricity consumption was obtained in the system using R1234yf, the lowest electricity consumption was achieved with R717. However, with the effectiveness of the desiccant wheel, the best results were obtained for R1234yf with those pertinent to R717 at the other extreme. Considering the total electricity consumption of the system, the highest energetic and exergetic performance parameters were achieved with the use of R717 as the refrigerant. Compared to R1234yf, the daily average energetic performance parameters obtained with R717 increased by 22.3 % for COPr, 21.8 % for COPel, and 4.7 % for COPth. Similarly, compared to R1234yf, the daily average exergetic performance parameters in R717 presented increases of 13.6 % for COPx,el, 7.5 % for COPx,th, and 8.1 % for ηx.
•The effects of different refrigerants on the hybrid cooling system were compared.•Power consumption of compressor can be significantly reduced with the use of R717.•The highest performance parameters in the system belong to the use of R717.•The performance results obtained with R1234yf and R32 in the system are very close.•In the system, R600a exhibits better performance compared to R134a and R32.
In recent years, the use of solid desiccant wheels has become attractive not only for air-conditioning applications, but also for food drying processes and storage due to their capacity to use waste ...heat in order to meet dry and hot air demand. It is very important that solid desiccant wheels be modelled for different purposes in such a way that the equipment can be well analysed in various systems. Modelling the solid desiccant wheel is a difficult and complex process because of the coexisting heat and mass transfer. In this study, six Artificial Neural Network (ANN) models with various activation functions and Multiple Linear Regression (MLR) models with six different structures have been formed to observe the process air outlet conditions of the solid desiccant wheel, and compared with each other to identify the suitability of the use of these models. In comparison, R2, RMSE and MAE values were taken into consideration as performance criteria. At the end of the study, ANN models were observed to provide better convergence than MLR models. The best convergence for the process air outlet conditions was provided by the ANN-V model. Of all the MLR models, the best convergence was provided by MLR-VI model.
In this paper, the principles underlying the operation of desiccant cooling systems are recalled and their actual technological applications are discussed. Through a literature review, the ...feasibility of the desiccant cooling in different climates is proven and the advantages it can offer in terms energy and cost savings are underscored. Some commented examples are presented to illustrate how the desiccant cooling can be a perfective supplement to other cooling systems such as traditional vapour compression air conditioning system, the evaporative cooling, and the chilled-ceiling radiant cooling. It is notably shown that the desiccant materials, when associated with evaporative cooling or chilled-ceiling radiant cooling, can render them applicable under a diversity of climatic conditions.
•Multi-stage MOF-based dehumidification can achieve 90% efficiency.•This efficiency is 2–5 times that reported in the literature to date.•Procedure articulated to identify optimal system ...configuration for any conditions.•A composite wheel performs nearly as well as separate multi-stage wheels.
Dehumidification systems including desiccant wheels are widely used in commercial and a few residential air conditioning systems to remove latent loads. These wheels require high-temperature heat to regenerate and are often quite inefficient, with a typical single-pass efficiency of around 20%. In this work we propose a novel desiccant wheel system that takes advantage of the unique behavior of metal-organic frameworks (MOF) sorbents. We show that for any given entering air condition, there exists an optimal MOF that if included in the dehumidification systems will result in maximum efficiency. Based on this idea, we develop a multi-stage dehumidification system in which each stage uses the optimal MOF. To do so, we first mathematically model and validate a MOF-based desiccant wheel system and use it to systematically identify the optimal MOF isotherm shape as a function of inlet air conditions. Then we extend the model to different multi-stage MOF-based desiccant wheel systems and optimize them to achieve energy performance far exceeding a single-desiccant wheel. We use our validated discretized dynamic model to compare the energy needed for operation of these systems with other possible configurations. Finally, we show that an optimized staged MOF system can approach the theoretical maximum energy performance for desiccant dehumidification, using nearly 100% of regeneration energy for desorption of water and wasting very little. The results also show that a multi-stage MOF-based dehumidification system can have a regeneration efficiency 2 to 5 times greater than a single-stage system. Adding adsorption heat removal stages between the desiccant wheel stages can increase the regeneration efficiency by 5–20%, and the dehumidification effectiveness of the system 20–40%.
•An isothermal process improves the dehumidification performance around 48%.•A mathematic model could be used to predict the performance of the new wheel.•The overlap of desiccant layers restricts ...heat exchange performance of the wheel.•Desiccant cooling system with the new wheel has an energy efficiency ratio of 9.3.
Desiccant wheels are commonly used to dehumidify air in air-conditioning system to reduce the energy consumption. The objective of this study was to design, test and analyse the performance of a novel tube-shell, internally water-cooled desiccant wheel. Cooling water was used in the supply section of the new wheel to shift the dehumidification process from nearly adiabatic to nearly isothermal. We conducted a series of experiments to investigate the wheel’s performance and used the experimental results to validate a mathematical model. The model was then applied to investigate the influence of modifications to the base design, including changing the number of desiccant layers inside the heat-exchange tubes, and the size and number of tubes. We also analysed the influence of water temperature and flow rate on both dehumidification and temperature rise across the wheel. Our results show that isothermal dehumidification performance can be achieved, but only with no more than two desiccant layers inside the heat-exchange tubes. More layers reduced heat transfer between the air in the innermost layers and the cooling water. Lower cooling water inlet temperatures led to lower air outlet humidity and temperature. A cooling water temperature of approximately 24 °C was required to achieve isothermal dehumidification for process air with inlet temperature of 30 °C and absolute humidity of 16.3 g/kg and regeneration air with the inlet temperature of 50 °C and absolute humidity of 16.3 g/kg. This corresponds to a 48% improvement in dehumidification performance (the maximum absolute humidity change between inlet and outlet process air) compared with a conventional adiabatic desiccant wheel while using super-adsorbent polymer as the desiccant material.
