A study of solar regenerated solid desiccant for air conditioning in a tropical humid climate | |
| Author | Sutavadee Techajunta |
| Call Number | AIT Diss. no. ET-99-2 |
| Subject(s) | Air conditioning Drying agents Silica gel |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Air-conditioning for comfort has penetrated widely in tropical climates. Most airconditioning systems use conventional refrigerants and are based on a vapor-compression cycle. However, most such refrigerants are harmful to the atmosphere and the systems consume high levels of electricity. As a result, solar-power vapor absorption cycle airconditioning received brief interest over a decade ago, but the system is complicated and difficult to maintain. Solid-desiccant based adsorbent systems for dehumidification and cooling have received attention because the systems are less complicated and because such systems can utilize solar energy or other renewable energy. Most of the studies involving such systems so far have been based on an indirect application of solar energy. This dissertation reports on a study into the use of silica gel, a solid desiccant, in systems incorporating a desiccant panel for dehumidification and cooling of air for airconditioning. The desiccant panel is regenerated directly by solar radiation. 'The first part of the work comprises a study on desiccant regeneration in the laboratory using a solar simulator to examine the effects of insolation and air flow rate on the performance of the system. The results indicate that the regeneration rate is influenced more by insolation than air flow rate, especially for insolation above 400 W/m2 • A mathematical model was compiled to calculate the temperature and humidity of the air exiting from the desiccant panel. Results of the calculations from the model agree well with experimental results. The mathematical model was also applied to study other effects that were not carried out in the laboratory such as the temperature and the moisture content of the inlet air, moisture content in silica gel, etc. The results from the mathematical model also clarify the relative influence of air flow rate and solar insolation. An air-dehumidification study in the laboratory is included to examine various factors influencing the performance of the system. The results from the experiment indicate that the adsorption rate increases with a higher air flow rate. However, the adsorption rate could. be reduced if solar radiation is applied. The mathematical model developed was applied to calculate the temperature and the moisture content. of the air from the desiccant panel. All calculation results agree well with the experimental results. A system of solar-regenerated desiccant dehumidification was devised. During the day time, the desiccant system is disconnected from the space to be conditioned and the regeneration of the desiccant is achieved through solar heating. During the night, ventilation air is passed through a set of regenerated desiccant panels. The warm air exiting from the panels is cooled by cool water in a water-air heat exchanger. After the water is used to cool the wa1m air, it is itself cooled in the cooling tower. Known mathematical models of heat exchangers and cooling towers were used with the model for the desiccant panels. The combined desiccant dehumidification model was then used to calculate the condition of the ventilation air through the system. Temperature, relative humidity and other weather data for Bangkok, Thailand in 1985 was used in a simulation study. lll In this desiccant assisted air-conditioning (DAAC) system study, the desiccant panels and its cooling system formed a desiccant dehumidification system to dehumidify the ventilation air which is supplied to a bedroom. The dehumidified air is mixed with the return air from the room and then cooled by a conventional air-conditioner and supplied into the bedroom at night. The simulation results indicate that the DAAC system is able to remove substantial moisture from the ventilation air. A total reduction of 36% of the load at the cooling coil results. Another system of desiccant air-conditioning was devised. This larger system was used to dehumidify the supply air for the same bedroom. The dehumidified air was evaporatively cooled and supplied to the bedroom. Simulation calculations using the aforementioned weather data indicates that the system can replace a conventional airconditioning system. In terms of thermal comfort, or thermal neutrality, the system could achieve the same level of acceptance of comfort as that from a conventional system. In both cases of the simulation study, the results indicate that solar-regenerated desiccant systems can be used to achieve acceptable levels of thermal comfort, but also use lower amounts of electricity. |
| Year | 1999 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Energy Technology (ET) |
| Chairperson(s) | Surapong C.; |
| Examination Committee(s) | Exell, R.H.B. ;Bhattacharya, S.C. ;Jindal, V. K. ;Charters, W. W. S.; |
| Scholarship Donor(s) | Royal Thai Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1999 |