As the sensible heat gain or cooling load are decreased by using thick thermal insulation in a building, the need for dehumidification increases. Especially in Kushiro, it is rather cool and humid in summer because of its foggy weather. In this study, two types of dehumidification systems were developed and their performances were examined. The first is a heat-recovery type, which uses a cooling coil and a sensible heat exchanger. The second is a moisture-absorbent type, which uses heating and cooling coils and an absorbent. Remarkable improvements in dehumidification were obtained using the first type of dehumidification system. Using the second type of system, although the temperature of the outlet air rose slightly, both the absolute and relative humidity decreased remarkably. These features are desirable for a city such as Kushiro, in which the climate in summer does not necessitate much cooling of inlet air as is the function of an ordinary air conditioner. The moisture-absorbent type makes the most effective use of the cooling power for dehumidification of the three types. The result also showed that dehumidification is indispensable for thick thermal insulation, indicating that thick thermal insulation should be a key factor in passive and low energy architecture.