Development of desiccant air conditioning system of energization-regeneration type using conductive polymer (PEDOT/PSS)

In recent years, environmental measures to cope with global warming problems are required in all fields. Desiccant air conditioning is one of the technologies for saving energy in the architectural field. This study focused on desiccant air conditioning to improve dehumidifying and energy saving performance by devising a new method of regenerating a dehumidifying element. We called the method "energization-regeneration," which regenerates a dehumidifying element using a conductive desiccant material by joule heating. Achieving energization-regeneration requires the use of a material having both hygroscopicity and conductivity. We adopted PEDOT/PSS, poly (3, 4-ethylenedioxythiophene: PEDOT) doped with poly (4-styrenesulfonate: PSS), fulfilling such requirements. The chapter 2 describes the hygroscopicity of PEDOT/PSS evaluated through steam adsorption isotherms whose curves show the steam amount of adsorption measured at some relative pressure points under isothermal condition. The maximum adsorption amount and the structure of desiccant materials such as pore shapes can be assessed from the adsorption isotherms curves. Our measurement results showed that the maximum adsorption amount of PEDOT/PSS was higher than that of conventional desiccant materials (zeolite and high performance inorganic material). Moreover, PEDOT/PSS presented sufficient changes of adsorption amount to relative pressure in any relative pressure area than the other materials, suggesting that desiccant air conditioning using PEDOT/PSS is capable of rapidly performing dehumidification and regeneration. Here the adsorption isotherm evaluates the adsorbability under a steady-state; however, desiccant materials are under an unsteady-state in actual desiccant air conditioning operations. We thus conducted experiments assuming an unsteady-state. The chapter 3 describes the performance of energization-regeneration type desiccant air conditioning evaluated by experiments. A total of 19 experimental cases were categorized into 4 groups (CASE A to D). CASE A is where the energization quantity is changed, CASE B where the structure of dehumidifying elements is changed, CASE C where the operation of desiccant air conditioning is changed, and CASE D where the regeneration temperature (regeneration by a conventional method) is changed. In CASE A, the dehumidification amount increased with the increase of energization quantity. In CASE B, the dehumidification amount increased with the expansion of the surface area of the desiccant material. In CASE C, the dehumidifying performance of hybrid regeneration method (combined use of the energization and conventional types) was higher than that of other cases, but the energy utilization performance was lower than that of the energization only type. The chapter 4 describes our simulations based on previous studies. We added an enegization-regeneration term to a heat balance formula to incorporate the effect of energization-regeneration and compared the simulations and experiments. Obtained results of outlet air humidity were almost idential between the experiments and simulations. We then investigated the effect of cell density which represents contact surface area. The dehumidification amount increased when the cell density was increased while the other conditions including input energy were constant. Finally, we compared energization-regeneration with the conventional method of regeneration in the simulation by changing the input energy while the other conditions were constant. The dehumidification amount of energization-regeneration was greater than that of the conventional method of regeneration though the input energy was the same. The present study shows the possibility that the performance of desiccant air conditioning could surely be improved if a dehumidifying element having high cell density can be manufactured with the use of PEDOT/PSS.