Comfort zone, according to ASHRAE Standard 55-2004, shows
that humidity ratio has relationship (or correlation) with temperature
and relative humidity. Comfort zone at different temperature
and relative humidity must have the highest acceptable humidity
value, that is 12 g/Kg. ANSI/ASHRAE standard 55-2004, Thermal
Environmental Conditions for Human Occupancy, sets an
upper limit to absolute humidity levels—0.012 humidity ratio, or
0.012×7000 = 84 grains moisture/lb dry air [27].
However, there is no lowest acceptable humidity value. Comfort
zone as defined by ASHRAE is the standards used worldwide
because in many countries there are no studies and their own comfort
zone has not been defined although in reality the climate in
each country varies. Comfort zone, therefore, can have different
value. Yamtraipat et al. [15,29] conducted a study of thermal comfort
standards in air-conditioned buildings in Thailand and found
that Thermal comfort standards are that temperature is 26 ◦C, that
relative humidity is 60% and that air velocity is 0.2 m/s.
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.
The aim of this research was to (1). Assess relative humidity
and temperature effects and management on human comfort and
health in Thailand hospital building. Because In hospital wards, the
air quality has to be better than in other buildings because of the
increased risk of infections. (2). The results would be used to design
and develop single phase air-conditioning system which could control
both temperature and relative humidity (precision inverter air
conditioning system) at stable level in a short time with the temperature
changes in the range of±0.5 ◦C and relative humidity changes
in the range of 50–60%. There would be intelligent control system
for air conditioner using inverter to control the growth, spreading
and existence of germs, bacteria, virus, house dust mite and fungi.