In Japan, the “Law for Maintenance of Sanitation in Buildings” is applied to offices whose total floor areas exceed 3,000 m2. It states that the relative humidity in an office space should be kept between 40 and 70%RH. The ASHRAE Standard 55-92 prescribes a lower boundary humidity of 4.5 g/kg. This standard was revised as the ASHRAE Standard 55-2004, which does not specify a minimum humidity level. The ASHRAE Standard 62-2001 recommends the relative humidity of 30-60%RH. The lower boundaries of these criteria are intended to limit the low humidity conditions in winter. However, improvement of recent HVAC technology has allowed engineers to use desiccant dehumidifier and cold air distribution systems in many office buildings, creating a thermal environment with low humidity during summer. Air tightness, the reduction of the ventilation rate for saving energy and use of chemical materials cause problems of high indoor air concentration of formaldehyde or VOCs in many office buildings. Indoor chemical pollutants irritate occupants’ mucous membranes and they possibly perceive this irritation as dryness sensation caused by low humidity. Also, due to the usage of HVAC system, computers and contact lenses, the problem of dry eye syndrome has been getting more serious in office spaces.
The objective of this study is to investigate the effects of low humidity on human comfort and productivity.