06-10-2012, 03:59 PM
TREATING FRESH AIR OPTIONS AND USES
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Evaporative Coolers
The Evaporative Coolers have been used to cool from almost time immemorial.
They are the most simple and at times most cost effective, system of pretreating fresh air
for comfort applications.
The evaporative cooler constitutes of a pad (corrugated/khus/wood wool) kept wet by
water sprayed on it continuously.
Outside (fresh air) is cooled when drawn over the wet pads.
And, cool air is supplied into the area to be "conditioned" with help of a fan.
Large Evaporative Cooling Systems
Conventional Water spray type evaporative cooling/ventilation
systems have given way to systems incorporating cellulose pads due
to benefits offered. Cellulose pad based systems are efficient, less
messy and takes up less space.
The evaporative pads or cooling pads as they are also known as, are
made of treated, corrugated cellulose paper.
Application needs and cooling efficiency dictate pitch size and angle
of the flute of the corrugated paper.
Evaporative cooling pads, under brand name, Ecocool is now being
manufactured in India by Arctic India Engineering and can be
customised to application requirement. Figure l
Cooling is achieved by saturating the Ecocool Evaporative Pads with water, sprayed on
to it through prefixed channels.
Fresh air, which is warm or hot, is blown (with the help of a fan) through the wet Ecocool
pad. The water evaporates when it comes in contact with the warm/hot air, thus cooling as
well as humidifying the air entering the area.
Desiccant Based Cooling (DBC) Systems
Desiccant ventilation has come of age and has moved from 'research' to
commercialisation. Desiccant based evaporative cooling system provide environment
friendly technology for comfort airconditioning with added advantage of simple
robustness and low power consumption.
Desiccant Based Cooling eliminate CFCs and
essentially comprise of the following :
Desiccant dehumidifying rotor
Sensible heat recovery wheel
Evaporative pads
Regeneration heating system
Blowers
Outdoor air to be treated is passed through a dehumidification rotor, where the moisture is
educed. The air leaves the dehumidification rotor at lower moisture content but at an
elevated temperature.
(The process takes place along the enthalpy line or a psychometric chart).
This, hot, dry air is passed through the rotating sensible wheel, where it give up sensible
heat, and cools down.
This air which now has a very low moisture content, (much lower than desired in the area
to be conditioned), passed through the direct evaporative pads, where the air cools and
picks up moisture. (This process takes place along the wet bulb line on a psychometric
chart). This cool air is now delivered into the area to be conditioned.
The equipments for this millennium
Having understood the basic operating principle of various equipments available for
treating fresh air, it is evident that the solution to the problem faced by the designer,
today, can be provide a by basically the last three products discussed in the earlier pages
i.e. the Treated Fresh Air units incorporating Energy Recovery Devices, rotating
desiccant based dehumidifiers and desiccant based cooling systems.
Let us look a little more closely at needs of Indoor Air Quality which dictate the choice of
a system for Treating Fresh Air.
In recent years, the attention of environmental researchers
has been focused on indoor air pollution, as a result of reports
of symptoms or specific diseases that occur mainly in
airconditioned and mechanically ventilated buildings. Studies
have proved that level of contaminants in the indoor air can
be often several times higher than outdoor air. This combined
with the fact that people tend to spend 90% of their time
indoors, proves the point that a person's major source of
exposure to airborne contaminants can be indoors
Airconditioning is a major factor affecting Indoor Air Quality (IAQ). Majority of
airconditioning systems are designed with very little or almost no provision for fresh air,
as fresh air means, more kilowatts of conditioning and thus, higher energy cost.
Inadequate ventilation, coupled with recirculation of state air,
result in Poor Indoor Air Quality (IAQ), due to a build up of
pollutants like cigarette smoke, carbon-dioxide, mold, bacteria,
viruses and potentially dangerous chemicals emitted from
copying machines, furniture, carpets and paint.
Conclusion
There have been changes in the air! The rules have changed for the way the buildings
have to be designed and built. The demands for stringent indoor air quality, additional
fresh air ventilation, concerns about humidity and microbial contamination and the need
to find non toxic replacements for CFCs have posed a challenge to the technical creativity
and design finesse of the engineers, to find solutions to these needs. The new generation
of Treated Fresh Air Units have remarkably successfully addressed the market needs of
the coming millennium and has integrated the task of providing indoor air quality with
efficient use of energy.