Hybrid Desiccant Air Conditioning System Research Articles

Effects of different air inlet temperatures and regeneration air inlet velocities on the performance of Hybrid Desiccant Air Conditioning System

A hybrid desiccant air conditioning unit is treated as an effective alternative to the conventional air conditioning system due to independent control of humidity, temperature, and eco-friendliness. The decrease in environmental impact and energy saving is more when the desiccant recovered by utilizing “free” thermal energy. This current work has experimented with a performance study of a hybrid desiccant air conditioning unit for typical humid and hot Indian (Aligarh) climatic conditions. Here, the effects of different air inlet temperatures at the process section, i.e. (28, 29.5, 31, 32.5, 34, 35.5 and 37°C) and regeneration section, i.e. (50-58.8°C) and different regeneration air inlet velocities (2.5 and 4.5 m/s) on the performance of hybrid desiccant air conditioning system are analyzed. Thus, optimization of performance parameters i.e. refrigerating effect, heat rejection rate, VCOP, ECOP, compressor work, dehumidification effectiveness, moisture removal capacity, DCOP, regeneration effectiveness and regeneration rate is identified for attaining maximum efficiency of hybrid desiccant air conditioning system under above operating states.

Performance evaluation of hybrid desiccant air conditioning system regenerated by waste heat from air cooled condenser: Experimental Investigation

Heating ventilation and air conditioning units reject a large quantity of heat to the surroundings as waste. Thus proper reclamation of this unused heat could also enhance the COP of such arrangements and their lesser adverse effect on the environment. Therefore hybrid desiccant air conditioning unit using unused heat from condenser for regeneration can be more effective than the conventional air conditioning unit under hot and humid climatic conditions. In this paper, various performance parameters of hybrid desiccant air conditioning unit using unused heat from condenser is determined at different process air inlet temperatures (28, 29.5, 31, 32.5, 34, 35.5 and 37°C) and different process air inlet velocities, i.e. (1.5, 2.5, 3.5 and 4.5 m/s) and at fix (2.5 m/s) air velocity at regeneration inlet. Refrigerating effect, heat rejection rate, VCOP, ECOP, dehumidification effectiveness, moisture removal capacity and DCOP decreases with increment in different air temperatures at process inlet. While compressor work, regeneration effectiveness and regeneration rate increases with increment in different air temperatures at process inlet. On the other hand, refrigerating effect, heat rejection rate, VCOP, ECOP, dehumidification effectiveness, regeneration effectiveness, and regeneration rate decrease with increased air velocities at process inlet. Whereas compressor work, moisture removal capacity and DCOP increases with an increase in air velocities at the process inlet. Thus, optimization of these performance parameters is determined to achieve the maximum efficiency of the hybrid desiccant air conditioning system under the above operating states.

Performance assessment of hybrid desiccant air conditioning systems: A dynamic approach towards achieving optimum 3E solution across the lifespan

This study aims to assess a hybrid desiccant air conditioning system to provide cooling, heating, and water demand for hot and humid regions using multi-response optimization from the energy, economic, and environmental (3E) perspective. A solar heating system was used to provide the thermal energy required to regenerate the desiccant material. A thermal energy storage unit packed with phase change materials was considered to enhance the solar contribution during periods of low solar radiation. Furthermore, exhaust air of the regeneration process was used to harvest the moisture content of the air to produce fresh water. Using response surface methodology (RSM), a series of novel correlations were achieved for predicting resource consumption, provided thermal comfort, economic, and environmental indicators over the system's lifespan. The results of the dynamic evaluation reveal that the proposed optimum system achieves a higher solar fraction while using a smaller solar collector area. Moisture harvesting is also capable of producing 70% higher water than the system's consumption. The findings show a significant improvement in all 3E indicators compared to reference systems. Moreover, overall results indicate that dynamic and 3E approaches should be employed to achieve the foremost design for desiccant air conditioning systems.

Performance evaluation of a solar energy assisted hybrid desiccant air conditioner integrated with HDH desalination system

In this study, the performances of a solar energy assisted hybrid desiccant air conditioning system integrated with humidification–dehumidification (HDH) desalination system are numerically investigated. The aim of this study is to benefit from the temperature rise of the regeneration air outside of the desiccant conditioning system as well as the water vapor content in this regeneration air by feeding it to the humidification-dehumidification water desalination unit to produce distillate water. The distillate water productivity, human thermal comfort issues, and energy saving represent the main objective of the present numerical study. The simulated results developed for subsystems are validated with the published experimental results. The effects of regeneration air temperature and flow rate on supply cooled air temperature, distillate water productivity, the cooling coefficient of performance and overall daily coefficient of performance of the proposed system are investigated. The results show that (i) the distillate water productivity increases from 3.175 to 5.011L/h and overall daily coefficient of performance decreases from 4.392 to 3.636 with increasing the regeneration air temperature from 75 to 95 as (ii) the increase in the regeneration air flow rate from 70 to 130 m3/h, increases the distillate water productivity from 2.988 to 4.78L/h and decrease the overall daily coefficient of performance from 4.66 to 3.386. The study demonstrates that the proposed system represents the best options in hot and humid regions.

Desiccant Air-Conditioning System for Storage of Fruits and Vegetables : Pakistan Preview

In the present study the desiccant air-conditioning system has been investigated for the on-farm storage of fruits and vegetables in Pakistan. In this regard, ideal storage zone for the studied agricultural products is established in order to ascertain the system applicability. The dehumidification performance of the silica-gel based desiccant wheel has been analysed with low regeneration temperature (50°C) by using the model of Beccali et. al. Three environmental conditions (A: highly humid, B: moderately humid & C: less humid) are considered for the analysis of desiccant air-conditioning system. The latent and sensible loads of air-conditioning are achieved by the silica-gel desiccant wheel dehumidification and Maisotsenko cycle evaporative cooling respectively. The results of the study envisaged that desiccant wheel performs higher dehumidification in climatic condition ‘A’ due to higher ambient air relative humidity as compared to the other climatic conditions. However, higher heat energy is required for its regeneration in the climatic condition ‘A’. This study concluded that the desiccant air-conditioning system can be efficiently used for on-farm storage of fruits and vegetables in Pakistan. Also, the renewable energy sources of the country like solar energy and bio-gas can be potentially harvested for the regeneration of desiccant wheel. The study further proposes the use of hybrid desiccant air-conditioning system where standalone DAC system cannot achieve the sensible load.

Performance Analysis of Heat Pipe Heat Exchanger for Solar Hybrid Desiccant Air-Conditioning System

This paper reports the development of a novel solar hybrid desiccant cooling system with heat pipe heat exchanger (HPHE). The aim is to achieve higher efficiency to reduce the use of electricity by utilizing the desiccant dehumidification system to remove latent load, while the vapour-compression and heat pipe heat exchanger meet the sensible load. Novelty comes as the heat pipe heat exchanger in the system operates efficiently without external power. Experimental set-up has been built by combining the rotary desiccant wheel, heat pipe heat exchanger with a compressive cooling system. Tests are carried out at typical operative ranges for air-conditioning applications, specifically for high hot and humid locations in Bangi, Malaysia. Acetone is used as refrigerant in the HPHE. Performance of HPHE are tested and proven to have direct impact on Coefficient of performance (COP). The results shows good performance of heat pipe heat exchanger efficiency with average efficiency and capacity of 0.65 and 2kw respectively. It is found that the hybrid system can achieve a higher energy performance in hot humid regions.

Theoretical Analysis and Case Study on Solar Driven Two-stage Rotary Desiccant Cooling System Combined with Geothermal Heat Pump

Abstract In this paper, a solar hybrid desiccant air conditioning system, which combines the technologies of two-stage desiccant cooling system and geothermal heat pump together, has been configured and theoretically analyzed. The hybrid system mainly includes a two-stage desiccant cooling system with design cooling capacity of 80 kW, a geothermal heat pump for fresh air handling with 75 kW in nominal cooling capacity, a geothermal heat pump for capillary radiation terminal with cooling capacity of 244 kW, an evacuated tubular solar collector array of 530 m 2 , a hot water storage tank and a cooling tower. Performance model of the system has been created in TRNSYS simulation studio. The aim of this paper is to evaluate the performance of the solar hybrid air conditioning system, thereby providing useful data for practical application in the demonstration project. Simulation results show that, under typical weather condition, the solar driven desiccant cooling unit can achieve an average cooling capacity of 70 kW, which contributes 31.4% of the cooling capacity provided by the hybrid system. Corresponding average thermal COP is about0.83 under Shanghai weather conditions.

Theoretical and Experimental Analysis of Desiccant Wheel Performance for Solar Hybrid Desiccant Air-Conditioning System

Dehumidification is considered as a key feature of HVAC systems for thermal comfort. Malaysia is located in the South East Asia region which has a sufficiently high temperature and humidity of approximately 80% RH. This requires a process which can reduce moisture in the air. Desiccant wheel is used to provide dehumidification. Desiccant wheel with model no. 770 WSG produced by NOVELAIRE having operating system 1:1 and maximum flow rate of 1500 cfm has been theoretically and experimentally analyzed for its performance. The results show good matching between theoretical and experimental results in term of sensible and latent effectiveness of dehumidification process as well as regeneration process. This desiccant wheel is capable of condensing water at 0.05kgH2O/s and providing 3.3639 kW load reduction. With this significant load reduction, the component integrated in solar hybrid desiccant air-conditioning system can perform comfort cooling to area with high latent load such as hall, hyper market and commercial building.

Modeling and experimental validation of the desiccant wheel in a hybrid desiccant air conditioning system

Modeling can be strong asset to the operation of air conditioning plants taking into account e.g. the strong dependency of local climate conditions for the operation of HVAC systems. This paper presents a validated physical model and a simplified model based on the results of the physical model for a desiccant wheel, which is the central part of a hybrid air conditioning system. The two models offer different advantages: While the physical model is complex and can be adapted flexibly to different wheel dimensions, desiccant materials or climatic conditions; the simplified model requires no knowledge of underlying equations and modeling language utilized and can be used for a first assessment of the potential of a desiccant cooling system in a certain location or for the use within online control systems. The coexistence of both models ensures that information tailored to the users' needs are made available. The validity of the physical model, and therewith the simplified model, is ensured through comparison with measurement obtained from a hybrid air conditioning system situated in northern Europe. The demonstration plant combines the advantages of a dedicated outdoor air system (DOAS) with the advantages of the common hybrid desiccant system to allow for energy efficient air conditioning in one installation. The availability of primary measurement data is extremely valuable to the process of model validation because knowledge about uncertainties and bias in measurement data unlikely to be known for secondary data can be used to understand and validate model results. A comparison of simulation results from the physical model to measurement data from the demonstration plant shows good compliance for a typical day of wheel operation after adjusting relevant model parameters.

Case study and theoretical analysis of a solar driven two-stage rotary desiccant cooling system assisted by vapor compression air-conditioning

In this paper, a solar hybrid desiccant air conditioning system, which combines the technologies of two-stage desiccant cooling (TSDC) and air-source vapor compression air-conditioning (VAC) together, has been configured, experimentally investigated and theoretically analyzed. The system mainly includes a TSDC unit with design cooling capacity for 10 kW, an air-source VAC unit with 20 kW in nominal cooling capacity, a flat plate solar collector array for 90 m2, a hot water storage tank and a cooling tower. Performance model of the system has been created in TRNSYS simulation studio. The objective of this paper is to report the test result of the solar hybrid air conditioning system and evaluate the energy saving potential, thereby providing useful data for practical application. Experimental results show that, under typical weather condition, the solar driven desiccant cooling unit can achieve an average cooling capacity of 10.9 kW, which contributes 35.7% of the cooling capacity provided by the hybrid system. Corresponding average thermal COP is over 1.0, electric COP is up to 11.48. Under Beijing (temperate), Shanghai (humid) and Hong Kong (extreme humid) weather conditions, the solar TSDC unit can remove about 57%, 69% and 55% of the seasonal moisture load, thereby reducing electric power consumption by about 31%, 34% and 22%, respectively. These suggest that the solar hybrid system is feasible for a wide range of operating conditions.

Performances of the Hybrid Active Desiccant Wheel System with Type III Desiccant

A new type of hybrid desiccant air conditioning system combining an active desiccant wheel with a conventional front-positioned cooling coil is presented, in which Type Ⅲ desiccant is used in the active desiccant wheel. Then a preliminary experiment is carried out in order to investigate the feasibility of the hybrid desiccant system serving as a dedicated outdoor air system (DOAS). The result shows: under the two typical outdoor air conditions in the area of South China, the desiccant system which only needs to adopt a regeneration temperature of 45°C without lowering the cooling coil temperature can satisfy the requirements of the dehumidification; when operating in the climate with a high humidity of 90% and a high-temperature of no more than 36.5°C, the desiccant system only driven at a regeneration temperature of 60°C can also provide enough dehumidifying capacity; but compared with the active desiccant wheel using Type Ⅰor Type Ⅱ desiccant, this system can not reach a lower dew point. Therefore, this system can operate effectively at a moderate regeneration temperature, suitable for the high quality and comfortable air conditioning.

4-30 太陽エネルギーを用いたハイブリッド・デシカント空調システム((8)エネルギーシステム1,Session 4 新エネルギー)

4-30 太陽エネルギーを用いたハイブリッド・デシカント空調システム((8)エネルギーシステム1,Session 4 新エネルギー)

Analysis on a hybrid desiccant air-conditioning system

Hybrid desiccant-assisted preconditioner and split cooling coil system, which combines the merits of moisture removal by desiccant and cooling coil for sensible heat removal, is a potential alternative to conventional vapor compression cooling systems. In this paper, experiments on a hybrid desiccant air-conditioning system, which is actually an integration of a rotary solid desiccant dehumidification and a vapor compression air-conditioning unit, had been carried out. It is found that, compared with the conventional VC (vapor compression) system, the hybrid desiccant cooling system economizes 37.5% electricity powers when the process air temperature and relative humidity are maintained at 30 °C, and 55% respectively. The reason why the hybrid desiccant cooling system features better performance relative to the VC system lies in the improvement brought about in the performance of the evaporator in VC unit due to desiccant dehumidification. A thermodynamic model of the hybrid desiccant system with R-22 as the refrigerant has been developed and the impact of operating parameters on the sensible heat ratio of the evaporator and the electric power saving rate has been analyzed. It is found that a majority of evaporators can operate in the dry condition even if the regeneration temperature is lower (i.e. 80 °C).