A study on desiccant system regenerated by waste heat from home-use solid oxide fuel cell cogeneration system

Since the spread of covid-19 in 2019, it is necessary to realize an indoor environment that takes measures against viral infections such as covid-19 and influenza virus. One method for realizing such an indoor environment is to control indoor humidity. In a high-humidity environment, mold grows, indoor air quality deteriorates, and physical fatigue increases. On the other hand, in a low-humidity environment, viruses easily suspend and the immune system gets weaker. Therefore, controlling indoor humidity is necessary for human health.
Furthermore, in order to achieve carbon neutrality by 2050, there is a need for significant energy savings in facilities. As energy-saving facilities, cogeneration systems such as those utilizing fuel cells are one of the effective methods. Exhaust heat from fuel cells is commonly used to supply hot water, but a lot of waste heat goes unused in summer and warm regions, because the demand for hot water supply is low. Therefore, by utilizing this unused waste heat to control indoor humidity, it is possible to save energy and improve the total energy efficiency of the fuel cells.
In this way, by researching a desiccant system that utilizes waste heat from home-use solid oxide fuel cell cogeneration system (hereafter Ene-Farm or EF), we aim to contribute to energy conservation and to realize an indoor environment that has a good influence on human health. The results were as follows:
1) Waste heat from the EF (about 450W) is transferred to desiccant system by water, and the amount of available waste heat at this system changes with the water flow rate. As a result of experiment how to maximize the amount of waste heat utilization, we were able to transfer 380W of heat, which is approximately 80% of the waste heat from the EF, to the desiccant system by setting the flow rate to 0.2L/min.
2) In order to maximize the dehumidification amount of the desiccant unit under the condition of 1), an experiment was conducted using the return air volume (RA) and outdoor air volume (OA) as parameters. A maximum dehumidification rate of 350g/h under summer conditions (outdoor:30℃75%, indoor:27℃50%) was obtained when RA was 160m3/h and OA was 160m3/h.
3) As a result of simulating the room size that can be controlled to an appropriate relative humidity environment (40% to 60%) with a dehumidification amount 350g/h, it is possible to control the room size of about 30 m2 in Tokyo and about 20m2 in Okinawa (the highest humidity environment in Japan).
4) As a result of a demonstration experiment in Okinawa, the indoor absolute humidity environment was 10g/kg' lower than the outdoor absolute humidity environment. Furthermore, we clarified the relationship between outdoor absolute humidity and indoor absolute humidity when this system was introduced.