Low-carbon Desiccant Cooling System with Combination of Low-temperature Regenerative Periodic Total Heat Exchanger
Date Issued
2012
Date
2012
Author(s)
Yang, Cheng-Min
Abstract
Nowadays, indoor air quality has become a critical issue in the air-conditioning industry. To maintain a healthy indoor environment, it is inevitable to ventilate with outdoor air. Nevertheless, this ventilation causes dramatic energy loss. One solution to this problem is to install a total heat exchanger. In contrast to the conventional rotary-type total heat exchanger, this research employs the periodic flow to fixed desiccant wheels. Moreover, to maintain solid adsorptive effect, traditional desiccant dehumidifier uses high temperature and low humidity gas to regenerate the desiccant wheel. The request for environmental humidity control of the general residential space is , however, not so rigorous. As a result, the total heat exchanger in this research adopts the lower regeneration condition to fulfill the requirement for comfortable environment, which could save substantial energy since the additional regeneration heat source would not be needed. Finally, this research aims at investigating the practical performance and the energy conservation of the low-carbon desiccant cooling system.
The first part of this research investigates the performance of low-temperature regenerative periodic total heat exchanger based on the experimental method. The experiments are divided into two parts, one are material tests and the other are periodic operation tests. According to the result of the fundamental material tests, activated alumina packed bed has great capacities for both the adsorption and desorption as the temperature of the regeneration air is 25℃, which shows that activated alumina packed bed is more applicable to the total heat exchanger under the low-temperature regeneration condition. In addition, the result of the periodic operation of the total heat exchanger displays that the sensible heat effectiveness and latent heat effectiveness of the total heat exchanger increase as the time of operating period is abridged. At a operating period of 2 minutes, the total heat exchanger has the highest sensible, latent, and total heat effectiveness, which are 84.2%, 63.8%, and 70.9% respectively.
The second part of the research investigates the performance of the radiant ceiling cooling piping with different inlet water temperatures. The theoretical model is established to determine the cooling capacity of the system based on the experimental data. The results indicate that the cooling capacity of the cooling piping increases as the decreasing of the inlet water temperature. In addition, as the system operates with the 22℃ tap water, the cooling output is about 65.0W/m2, and the natural convection and radiation heat flux are 30.6 W/m2 and 34.4 W/m2 respectively.
In the last part of this research, the components and the operating mode of the low-carbon desiccant cooling system are depicted in detail. Furthermore, the actual performance of the system are investigated in an office room located at Taipei Water Department, and the result indicates that the usage of the radiant ceiling cooling piping for precooling the indoor environment enables the traditional air conditioner to reduce two-third of the original operating time. Besides, the test of the whole system is conducted in the same office, and it is observed that using this system to handle the incoming air could save up to 67.4% of the energy consumption compared to the case that the untreated fresh air is directly introduced. Finally, a design of an ameliorative low-carbon desiccant cooling system without using a traditional air conditioner, which is composed of a heat pump, radiant ceiling cooling piping, and a desiccant dehumidifier, is proposed.
Subjects
Periodic total heat exchanger
Low-temperature regenerative
Packed bed
Radiant ceiling cooling piping
Low-carbon desiccant cooling system
Type
thesis
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