In a psychrometric chart there are target thermal comfort co

In a psychrometric chart, there are target thermal comfort conditions with regards to temperature and humidity. Describe two methods of humidification used in buildings and two methods of dehumidification used in buildings and provide a benefit and drawback or each method listed.

Solution

Based on type of energy source to be used in humidification process, there are two major types /methods of humidification - 1) ISOTHERMAL SYSTEM HUMIDIFIERS 2) ADIABATIC SYSTEM HUMIDIFIER

1. STEAM HUMIDIFIER METHOD OF OPERATION

In contrast to evaporation humidifiers, a steam humidifier generates steam before the mixing process.
The steam in this process can then be fed into indoor air directly via a ventilation unit, or added to the air in an air conditioning system during conditioning. The steam is either taken from a central steam generation unit or produced decentrally for air conditioning at the point of humidification. Electricity, natural gas, hot water and boiler steam are isothermal heat sources used to boil water into steam for humidification.Electrical steam humidifiers are often a good option when steam needs to be produced immediately at the point of consumption.

BENEFIT-- If there is an on-site boiler or hot water source, direct steam injection or a heat-exchanger-type isothermal system may be most appropriate.

DRAWBACK--Maintaining a steam humidifier involves regular removal of lime scale that may build up within the system. Also compared to other humidifiers, steam humidifiers consume more power.

2. EVAPORATIVE HUMIDIFIERS-An evaporative humidifier is one of the most common humidifiers used in the home.Like all humidifiers an evaporative humidifier is designed to produce moisture and relieve any dry air that may be lingering in your home. The only difference is that is doesn\'t require much technology and can increase humidity levels in large areas of your home.

A significant feature of an evaporative humidifier is that it uses a fan and wick filter to operate properly.

Depending on the humidity level, it can be difficult evaporating water from the wick filter.

For example, if the relative humidity is high, it will be hard for water to be evaporated from the filter once the fan is powered on.This makes an evaporative humidifier a self- monitoring appliance because if the humidity levels are high it is likely that the humidifier will not work. This can be checked by closely monitoring humidifier to ensure that it is working properly.

These are based on Adiabatic systems which use heat from the surrounding air to change water into vapor for humidification (evaporation). Foggers, ultrasonic and pezio disk humidifiers are typical adiabatic humidifiers.

BENEFIT--The price for this humidifier is relatively lower than other ones and it is capable of raising humidity in spacious areas at fast rate.

drawback--not suitable for high level of humidity

DEHUMIDIFIERS

1.Thermal condensation dehumidification-

These methods rely on drawing air across a cold surface. Since the saturation vapor pressure of water decreases with decreasing temperature, the water in the air condenses on the surface, separating the water from the air.Mechanical/refrigeration dehumidifiers, the most common type, usually work by drawing moist air over a refrigerated coil with a fan.

BENEFIT--more economical than dessicant dehumidifiers at high temperatures and high humidity level.

DRWABACK--expensive when operated at low temp. and low humidity level.

2.Absorption/desiccant dehumidification--This process uses a special humidity-absorbing material called a desiccant, which is exposed to the air to be conditioned. The humidity-saturated material is then moved to a different location, where it is \"recharged\" to drive off the humidity, typically by heating it. The desiccant can be mounted on a belt or other means of transporting it during a cycle of operation.

BENEFITS--especially suited for high humidity levels at low temperatures.Desiccant dehumidifiers can also operate at lower temperatures than compressor dehumidifiers as the unit lacks coils which are unable to extract moisture from the air at lower temperatures.

DRAWBACK---the capacity of compressor less dessicant dehumidifier is relatively much lesser than that with compressor.it also gives off a smell of pungent odour.