Thailand is a hot and humid country [30]. According to Fig. 4
[31], the profile of air temperature, relative humidity and humidity
ratio (outdoor) in each hour for all year long in 2008 showed
that air temperature, relative humidity and humidity ratio were
quite out of comfort zone range by ASHRAE Standard 55-2004. In
Thailand, there were quite few studies and research on humidity
effect on human comfort and health. References were mainly
based on foreign studies which depended on ASHRAE Standards
only. In fact, each country has different climate, so humidity effect
on human also differs. At present, studies on thermal comfort in
building are not sufficient since it needs additional studies on
humidity effect on human comfort and health in office, residence
and hospital buildings. Therefore, the design and the installation
of air conditioning system which complies with the climate in
Thailand building, especially hospital buildings, should emphasize
relative humidity because it has a great effect on human comfort
and health.
Medical studies from foreign countries have shown that it is
important to control humidity in hospital buildings and the law
is enacted. In Thailand, however, there has no such action and
the research on the influence of relative humidity on thermal
comfort and good health of human beings is scarce. At present,
air-conditioning system used in most houses and offices is split
type air conditioner which cannot control temperature and relative
humidity at stable level. Inverter air-conditioner can only control
temperature at stable level; it cannot control relative humidity at
stable level. Therefore, a device to increase or reduce humidity is
needed and cost a lot of money. Moreover, it cannot control relative
humidity at stable level in the desired range