Conventional Dehumidification Systems Research Articles

Numerical investigation and comparison on energy performance and exergy destruction of cascading deep dehumidification systems with dehumidification amount exceeding 95%

Liquid desiccant and desiccant wheel systems are feasible approaches for the dehumidification process in modern buildings. Some specialized buildings and industrial fields have the demand for deep dehumidification process to produce supply air with low dew point temperature below 0 °C. In this study, the numerical investigation has been conducted to evaluate the energy and exergy performance of multiple cascading deep dehumidification systems assisted with liquid desiccant and desiccant wheel under a great dehumidification gradient. To process the air from 21 g/kg to 1 g/kg, the results indicate that the cascading liquid desiccant and desiccant wheel deep dehumidification system (LD-DW system) driven by two stages of heat pump exhibits the lowest demand of power consumption compared with the conventional dehumidification systems. It also shows less exergy loss and significantly higher exergy efficiency than other systems. The effects of influencing parameters on the dehumidification performance are also evaluated. The LD-DW system can effectively match the air state with the proper treatment dehumidification process, thus achieving a superior coefficient of system performance (COPsys) of 3.70, and it is an energy and exergy efficient method for advancing the deep dehumidification process.

Energy saving potential of a vacuum-based membrane dehumidifier in a dedicated outdoor air system

As a novel energy-conservative ventilation system for buildings, a dedicated outdoor air system (DOAS) assisted by a vacuum-based membrane dehumidifier is proposed, and its energy performance is investigated via detailed energy simulations. The vacuum-based membrane dehumidifier dries the air by an isothermal process, which is difficult to realize in conventional dehumidification systems. The proposed system consists of an enthalpy exchanger, a vacuum-based membrane dehumidifier, and a cooling coil. Its dehumidification performance and operation energy are compared with those of the following conventional DOASs: a DOAS that employs a cooling coil (Reference A) and a DOAS that employs an active desiccant wheel (Reference B). To evaluate the energy performance of the proposed system, the energy consumptions of all the DOASs were estimated by simulation programs (i.e., TRNSYS and EES) with mathematical models. The simulation results indicate that the average coefficient of performance of the DOAS we devised (i.e., 1.34) is lower than that of Reference A (i.e., 2.70) and higher than that of Reference B (i.e., 0.80). However, owing to the isothermal dehumidification process, the latent cooling ratio in the case of the proposed system (i.e., 1.0) is significantly higher than those in the cases of Reference A (i.e., 0.43) and Reference B (i.e., 0.11). Consequently, the annual energy consumption of the proposed system is 17.4% and 56.2% lower than those of Reference A and Reference B, respectively.

Detailed experimental analysis of the energy performance of a desiccant wheel activated at low temperature

Desiccant dehumidification systems, such as those using desiccant wheels (DW), are an interesting alternative to conventional dehumidification systems based on vapor-compression cycles. The aim of this work was to obtain experimentally the performance of a DW activated at low temperature along the heat and mass transfer surface under different working conditions. The air temperature and humidity were measured at 32 different points, in order to analyse the performance of the DW at different circular sectors of the rotor.The results showed that the surface temperatures of the desiccant material on the process side decreased when the rotation speed decreased. Conversely, the surface temperatures of the desiccant material on the regeneration side increased when the rotation speed decreased.The minimum outlet process air temperatures and the maximum process air dehumidification were obtained in the circular sector closest to the regeneration side. In this circular sector the highest efficiency values were obtained. The number of circular sectors where the highest efficiency values were obtained increased when the rotation speed or air flow rates increased. Using these data, the wheel control strategy could be designed to increase the dehumidification capacity.

Validation of multitask artificial neural networks to model desiccant wheels activated at low temperature

Desiccant wheels (DW) could be a serious alternative to conventional dehumidification systems based on direct expansion units, which depend on electrical energy. The main objective of this work was to evaluate the use of multitask artificial neural networks (ANNs) as a modelling technique for DWs activated at low temperature with low computational load and good accuracy. Two different ANN models were developed to predict two output variables: outlet process air temperature and humidity ratio. The results show that a sigmoid unit neural network obtained 0.390 and 2.987 for MSE and SEP, respectively. These results outline the effective transfer mechanism of multitask ANNs to extract common features of multiple tasks, being useful for modelling a DW activated at low temperature. On the other hand, moisture removal capacity of the DW and its performance were analysed under several inlet air conditions, showing an increase under process air conditions close to saturation air.

Geometrical parameters analysis of improved circulating inclined fluidized beds for general HVAC duct systems

This study experimentally investigated the influence of geometrical parameters on improved circulating inclined fluidized beds (ICIFB) for HVAC duct systems. The geometrical parameters include the inclined angle, base height of the regeneration bed, and particle channel height of the adsorbent bed. An optimal ICIFB system was developed based on the experimental results. Compared to the circulating erect fluidized bed system (CEFB) and the circulating inclined fluidized bed system (CIFB), the optimal ICIFB system could increase adsorption/desorption performance by 32.4% and 23.5%, respectively, under the same operating conditions. The optimal ICIFB system had the highest energy factor with up to 0.67 kg/kW h, which was 77.9% and 40.1% higher than the CEFB system and the CIFB system, respectively. The total adsorption was also measured for the optimal ICIFB system working nine hours per day (air volume = 850 cm3/h) under different monthly outside air conditions in Taiwan. The results showed that year-round total adsorption of 729.5 kg, which was 14.1% more than the CIFB system. The ICIFB system can combine with HVAC duct systems set up above the ceiling. Compared to conventional dehumidification systems, it saves space, has better dehumidification performance, and has a lower pressure drop, thus, it is suitable for residential air-conditioning systems.

The Use of Moving Yarn Belts for Continuous Dehumidification

A novel low-energy alternative to conventional dehumidification systems has been devised. A moving loop of cellulosic yarns adsorbs water vapor from an air space, transports it outside where it is desorbed by solar or other heating, and returns to the interior to repeat the process, so that moisture is removed and disposed of continuously. The method is based on the potential of cellulosic yarns for rapid interaction with water vapor, the strong inverse dependence of water uptake on temperature and the tensile strength and flexibility of yarns. A laboratory-scale unit, found capable of reducing humidity to a satisfactory level in a reasonable time, has supplied data for potential scaling-up using practical equipment dimensions, air flow rate, yarn velocity, etc. Experience with the demonstration unit indicates that the yarn is far from saturated under the dynamic conditions of operation, and that the transient water is taken up on the most accessible yarn surfaces and does not diHuse to any great extent into the interior.