Desiccant Wheel Air Conditioning System Research Articles

Desiccant wheel air-conditioning system driven by gas engine cogeneration of heat and power: simulation and analysis by Dymola

Based on the combination of gas engine cogeneration of heat and power (GECHP) technology and temperature and humidity independent control air-conditioning technology, an air-conditioning system combined with desiccant wheel driven by GECHP was proposed to decrease cooling energy consumption and utilize the waste heat of gas engine. In this study, Dymola software was adopted to model the hybrid system and conduct hourly simulation throughout the cooling and heating season for two types of large public buildings: the supermarket building and the office building. Results show that the hybrid system applied to target buildings can meet the requirements of each index of air-conditioning energy supply. Comparing two types of application scenarios, the system primary energy conversion ratio of the supermarket building reaches 112%, 19% higher than that of the office building. And the system CO2 emission reduction rate per unit of capacity of the supermarket building is 0.18 kg/kWh, lower than the 0.22 kg/kWh of the office building. Therefore, the hybrid system has superior energy-saving and environmental performance and is especially suitable for high-temperature and high-humidity areas in summer as well as building application scenarios with high indoor moisture gain and fresh air demand.

Experimental study on desiccant evaporative combined chilled air/chilled water air conditioning systems

• A desiccant evaporative combined chilled air/chilled water systems was proposed. • The dynamic characteristics was presented by experimental investigation. • The temperature of the chiller air and the chiller water is below 20℃ and 18℃. • Regeneration temperature and air–water ratio have great impacts on performance. • 70 °C regeneration temperature was recommended in high humidity regions. Evaporative cooling technology is limited by the environmental wet-bulb temperature and is not suitable for humid climates. Desiccant wheels adsorb water vapour, thereby converting high-humidity air into low-humidity air, and they can be regenerated by solar energy or waste heat. In this study, a desiccant evaporative combined chilled air/chilled water air-conditioning system is proposed. The proposed system integrates a desiccant wheel air conditioning system and a direct-evaporative cooler, which can be used for temperature and humidity independent control systems in humid climates. An experimental setup was built and used to test the system performance and important system parameter effects under moderate temperature and humidity (32 °C, 60% RH), moderate temperature and high humidity (32 °C, 80% RH), and high temperature and humidity (36 °C, 80% RH). The results indicated that for the system at a regeneration temperature of 70 °C, the chilled air temperature was lower than 20 °C, the chilled air humidity ratio was lower than 13 g/kg, and the chilled water temperature was lower than 18 °C, which meets the temperature and humidity independent control requirements.

Performance evaluation of a hybrid solar powered rotary desiccant wheel air conditioning system for low latitude isolated islands

Low latitude isolated islands have the climate characteristic of high temperature and high humidity, but in short of conventional energy. This study proposes a novel hybrid solar powered rotary desiccant wheel air conditioning (SRDAC) system to improve the indoor temperature of buildings on low latitude isolated islands. The SRDAC system combines photovoltaic power generation, solar thermal collector, vapor compressed cooling system and a two stage rotary desiccant wheel system. In this study, mathematical models of the subsystems of the SRDAC system are established firstly. MATLAB was used to analyze the performance of the SRDAC system, which includes the dehumidification capacity, cooling capacity, condensation heat quantity and thermodynamic performance coefficient. Then, the photovoltaic area and solar thermal collector area of the SRDAC system were matched and optimized based on meteorological parameters of low latitude isolated islands. Finally, the SRDAC system’s economic performance was analyzed. The results show that, for every 10 ℃ increase in regeneration temperature, the dehumidification capacity and cooling capacity increase by 0.9 g/kg-2.7 g/kg and 0.4 kW-1.9 kW, respectively. For every 1 g/kg increase of outdoor air moisture content, the total installed area increased by 2.2%-2.3%. The SRDAC system shows a good operating performance, can better adapt to the climate characteristics of low latitude isolated islands, and effectively reduces the temperature and moisture content of the air. This study serves as a reference for the application of SRDAC system in extremely hot and humid climates.

The performance of a desiccant wheel air conditioning system with high-temperature chilled water from natural cold source

A novel desiccant wheel air conditioning system that uses high-temperature chilled water from natural cold source (DWACS + HCW) is proposed. The proposed system integrates the renewable regeneration heat source and natural cold source, which are beneficial for energy saving. A model of the proposed system was developed, and the main components and the overall model were experimentally validated. The performance and the effects of the important parameters of the system under high humidity (32 °C, 80% RH), moderate humidity (32 °C, 60% RH) and low humidity (32 °C, 40% RH) conditions was studied numerically. The results showed that the system could achieve the supply air to the required temperature and humidity ratio in high, moderate and low humidity conditions, and compared to conventional solar desiccant wheel air conditioning systems (SDWACS), the energy performance is more efficient mainly due to high cooling and dehumidification capacity of surface air-cooler with high temperature chilled water.

Experimental investigation of precooling desiccant-wheel air-conditioning system in a high-temperature and high-humidity environment

Desiccant-wheel air-conditioning systems driven by low-grade thermal energy have many advantages compared with traditional air-conditioning systems, including energy savings, comfort and environmental protection. Because of the insufficient dehumidification capacity of traditional air-conditioning systems, a precooling desiccant-wheel air-conditioning system that operates under high-temperature and high-humidity conditions was developed. To study the performance of the precooling desiccant-wheel air-conditioning system, experimental devices were built. The effects of the air parameters, regeneration temperature and water supply temperature on the performance of the precooling desiccant-wheel air-conditioning system were experimentally studied. The performance indices included the moisture removal capacity, dehumidification efficiency, refrigeration capacity, enthalpy efficiency and thermodynamic efficiency. The process air temperature, process air humidity ratio, regeneration temperature and water supply temperature had significant effects on the system's performance. When a renewable low-grade heat source was used, the energy consumption of the precooling desiccant-wheel air-conditioning system was reduced. This study provides guidance on the energy conservation design for precooling desiccant-wheel air-conditioning systems intended for use in high-temperature and high-humidity environments.

Advanced Technology in Desiccant Wheel Air Conditioning System: A Review

Desiccant wheel air conditioning have been considered as one of the effective process to control humidity of ambient air. Desiccant wheel air conditioning system do not use any ozone- depleting refrigerant and also intake lesser energy compared to vapour compression system. All the types and kind of desiccants have been discussed here. Such as solid desiccant system, liquid system have been reviewed briefly. Finally, a summary of economic prospect, future scope, environmental friendly technology and future scope of desiccant wheel air conditioning system have been discussed briefly.

Simulation and energy saving analysis of high temperature heat pump coupling to desiccant wheel air conditioning system

The objective of this work is to investigate the energy saving potential of HTHP&DW (high temperature heat pump coupling to desiccant wheel) system by means of comparative analysis based on reference technologies. A complete numerical model of HTHP&DW system is established and the iterative algorithm is successfully applied and tested. The energy consumption, COP (coefficient of performance) and energy saving rate of HTHP&DW system are simulated under the different outdoor climates and indoor design conditions. The results show that energy saving rate of proposed system is 45.6% compared to CVC (conventional vapor compression) system and 30.5% compared to advanced HDC (hybrid desiccant cooling) system under the AHRI (Air-conditioning, Heating and Refrigeration Institute) design conditions. The impact of outside air humidity ratio is significant on the performance of HTHP&DW system. When the humidity is lower than 11 g/kg, the energy saving rate is up to 65% compared to CVC system. The lower indoor design temperature and higher indoor design humidity ratio are in favor of the energy saving of HTHP&DW system. Especially the energy consumption will decrease 20% when the indoor design humidity ratio increases 1.0 g/kg.

Experimental analysis and regression prediction of desiccant wheel behavior in high temperature heat pump and desiccant wheel air-conditioning system

• The desiccant wheel is regenerated by heat pump without additional heat. • Regeneration temperature and outdoor air humidity ratio influence wheel performance. • Numerical models for wheel are established based on regression theory. • Predicted values and experiment data are compared and agreement is good. The objectives of this study are to evaluate the performance of desiccant wheel (DW) in the running system and obtain the useful data for practical application. The combined influences of multiple variables on the performance of desiccant wheel are investigated based on evaluating the indexes of moisture removal capacity, dehumidification effectiveness, dehumidification coefficient of performance and sensible energy ratio. The results show that higher effect on the dehumidification is due to the regeneration temperature and outdoor air humidity ratio rather than the outdoor air temperature and the ratio between regeneration and process air flow rates. A simple method based on multiple linear regression theory for predicting the performance of the wheel has been proposed. The predicted values and the experimental data are compared and good agreements are obtained. Regression models are established which can easily predict the behavior of DW and also helpful for developing a DW performance map for the further optimization of automatic control of the system.

Optimization analysis of high temperature heat pump coupling to desiccant wheel air conditioning system

The high temperature heat pump and desiccant wheel (HTHP&DW) system can make full use of heat released from the condenser of heat pump for DW regeneration without additional heat. In this study, DW operation in the HTHP&DW system was investigated experimentally, and the optimization analysis of HTHP&DW system was carried out. The performance of DW had influence on the dehumidification (evaluated by dehumidification and regeneration effectiveness) and cooling load (evaluated by thermal and adiabatic effectiveness). The results show that the enthalpy increase occurred in all the experiments. Compared to the isosteric heat, heat accumulation in the desiccant and matrix material and heat leakage from regeneration side to process side have greater influence on the adiabatic effectiveness. Higher regeneration temperature leads to lower adiabatic effectiveness that increases more cooling load of the system. When the regeneration temperature is 63°C, the maximal dehumidification effectiveness is 35.4% and the satisfied adiabatic effectiveness is 88%, which contributes to the optimal balance between dehumidification and cooling.

Calculation on Energy Saving Potential of a New Dry-Type Air-Conditioning System

Temperature and humidity independent control can be made by a new dry-type air-conditioning system, the combination of silica gel rotor and heat pump. Heat pump cycle can simultaneously cool the process air and heat the regeneration air, so it can cancel each other out in the cold and heat energy consumption within the system. This novel form of system not only solves the regeneration energy issues fundamentally but also avoids energy waste by reheating in conventional cooling dehumidification air-conditioning system. Based on the establishment of the component model, MATLAB program has been compiled to simulate the combined system running at nominal operating conditions and calculate the performance parameters and energy efficiency. Comparison of the energy efficiency was made of this dry-type air-conditioning system with ones of other regeneration desiccant wheel air conditioning system and conventional cooling dehumidification air-conditioning system, the results of which show that the new dry-type system provided regeneration energy, overcomes the restriction from climate, region and using conditions of other regeneration. Moreover, compared with conventional re-heat air-conditioning system, its energy saving is up to 35.1% and the energy efficiency is increased by 38.1%.