Air conditioning refers to simultaneous control of temperature, humidity, air flow rate and quality of air. Adding humidity at constant dry bulb temperature is known as humification, while removing moisture is called as dehumidification. 

iN summer, humidity levels are higher, while in winter, they are lower.Hence, Cooling and Dehumidification process is adopted for summer air condtioning, while Heating and Humidificaiton is applied to winter air condtioning.

In summer air conditioning process, cooling coil temperature is lower than dew point tmepature, such that simultaneous cooling and debumidification will occur.

Natural ventilation will cause futher addition of humidity to air during summer as air has more moisture. Hence more work has to be done to remove moisture from air. causing higher energy consumption.      

Humidity in a chamber can be controlled by saturated salt solutions. each saturated salt solution has specific humidity level. in case of controlling humidity with respect to temperature, increase in humidity can be done by using a boiler with solenoid valve to operate at the design temperature. and temperature can be maintained by an air conditioner (in fan mode) with heater for heating and normal air conditioner (compressor run mode) for cooling......

Humidity play a vital role in defining thermal comfort in built environment. We know that same AC will consume more power to give same cooling at higher humidity to that of at RH 50%.

In a passive way, to reduce the effect of high humidity it is advised to use the existing wind to minimize the effect of discomfort.

Water will absorb energy for vaporization. This phenomena is used by our body by seating in hot climate. But vaporization will decrease in hiumid air. AC system will decrease temprature as well as  humidity, by extracting some part of water in its cooling coile, as descibed by Maddali. cooling system should absorb som energy from vaporized water for its phase change to liquid. It means that a part of used energy by cooling system should be considered for extracting water, and decreasing humidity.

Thanks Maddali V S Murali Krishna

I agree with you that "Natural ventilation will cause futher addition of humidity to air during summer as air has more moisture". 

However, people can accept the higher relative humid level when there is more airflow. Hence, I think that if we can created different pressure across the building to have airflow and convection, then we do not need to use energy to remove moisture. Is it possible?

How do you think?

Humid climates require larger air conditioning units to cool the air because it takes more energy to condense moisture out of the air than to simply cool dry air.  The human body regulates temperature through evaporation of sweat.  This is easy when the air is dry.  It has a more difficult task when the humidity is high.  The average human body generates about 205 Btuh when sitting, more when active.  I hope this helps.

hi Tan,

the "well-being" curve Temperature-Humidity for humans has been empirically studied if I well remember, since the first half of last century.

Now is a well established standard.

Please have a look at:

http://en.wikipedia.org/wiki/Thermal_comfort

Ciao!

Alberto

Hi Tan,

Have a look to the following article:

Simulation Analysis of the Four Configurations of Solar Desiccant Cooling System Using Evaporative Cooling in Tropical Weather in Malaysia

You can find it in the uni library website....

Thanks Shaik Saboor,

It is good for me of concept how to controls humidity and maintain air design temperature.

Thanks Manoj Kumar Singh,

As you mentioned, I intent to use passive way to reduce the effect of high humidity by using the wind or create natural airflow to minimize the effect of discomfort.

Hi Ali Mosavari, 

Thanks for your advises.

On the other hand, I intend to consider another way to replace or minimize using air-conditioning system as it is one of much energy consuming.

Thanks Lee Fellows,

It is interesting thing for me to consider about how human body to react the Btuh of human body base on its situation.

If you make a sensitivity analysis of the effects of changing the input variables (metabolic rate, clothing, air temperature, mean radiant temperature, air velocity and partial vapour pressure) in the calculation of the thermal comfort indices PMV and PPD, you will realize that the one related with humidity (partial vapour pressure) is having the weakest effect. This is a pratical exercise that I give to the students of my course about Indoor Environmental Quality. If you are interested I may provide you the figures with results.

Humidity is important in case the human body needs sweating as a major heat loss, which will not happen in case the temperature range is mild (20-25 º C) and the activity level of people is low (e.g. sedentary activity level = 1.2 met). Another issue that you should take into account is that a precise control of humidity is much more difficult than a precise control of temperature. Air conditioning is the most affordable system for that.

In case you want to control something else besides air temperature, the control of mean radiant temperature will have a stronger effect.

Thanks Alberto Moro,

It is useful for me to obtain some notion about the thermal comfort in your link.

Dear Tan,

Hope you find the attached file helpful. 

Thanks Lona Do

I have found that with low level of activity, high skin exposure, and strong air movement, such as I am enjoying right now on this Bangkok afternoon (Tdb=30, Twb=25) humidity is not perceptible.  But when I go outside to walk on hot sidewalks the impact of humidity on sweat evaporation will be uncomfortable. Thus, I am agreeing with Prof da Silva above.

This condition prevails for much of the year in SE Asia. The attached draft chapter shows the situation for Bangkok.

May you opt for desiccant based dehumidification system to control indoor humidity.