Why Green - Inspired to be Green

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DIVIDE AND CONQUER FREE COOLING AND ITS IMPLICATION IN A
DOAS
R. Mark Nunnely & several other authors have
DESIGN APPLIED ON GLOBAL WEATHER
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explained in various papers the advantages of PROFILE
the “Divide
& Conquer (DAQ)” approach which
To apply the free cooling concept for the most •
energy efficient
separate the fresh air unit from the parallel terminal
DOAS design (enthalpy wheel, cooling coil & passive desiccant
unit. To explain further in a DAQ approach the
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dehumidification wheel). The idea is to get holistic picture with a
fresh air unit takes care of the entire fresh air load global
prospect. To further demonstrate the importance of hourly
and deliver the ventilation /supply air at design
data the study is further categorized into a 24 x 7 scenario and a
temperature neutral with a dew point sufficiently normal working hours 9am
to 5pm scenario.
lower than
the design dew point to take care of
the Internal latent load. Thus the parallel unit, be As it is evident from the above data (Table3)
the free cooling hours
it FCU/Chilled Beams / AHUs has to only cater for basis from one city to another, the DOAS (Dedicated Outdoor Air
the building
envelop & internal sensible loadas System)
should be intelligently designed to decide its control logic
both can be handled and managed independently.
on the basis of free cooling available. This can be done by controlling
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This design provides a very simple and economical
various parameters like supply air fan speed and bypass, different
approach to the building air conditioning design. component speed and cooling coil
temperature. An intelligent
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DOAS will offer a logical solution to
ably utilize advantage of free
cooling.
DEDICATED OUTDOOR AIR SYS-
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Free cooling from an HVAC perspective and is inclined to find that
TEM (DOAS) APPROACH
the most important
criteria that governs
free cooling
is the
ambient
As explained above, in the DAQ approach the
air condition. The HVAC equipment system design will
govern the
importance shifts to configuration and type of
way
free cooling is applied in the most effective manner.
fresh air unit,often referred to as Dedicated
Outdoor Air System (DOAS). Depending on
different
geographical
reasons
& several
other considerations
various DOAS have been
configured,
designed & developed. The authors
have been continuously studding & developing
different configurations for a DOAS by using one
or more of the following:
• Enthalpy wheel
• Cooling
Coil
• Active dehumidification wheel
• Passive
dehumidification wheel
• Sensible Wheel
Figure 3
• Evaporative Cooling Pads
An intelligent
combination of a total enthalpy wheel,
cooling coil & passive desiccantdehumidification
wheel (refer
figure 3) offers the best solution in
terms of substantial energy saving, offsetting
internal latent load and “effective RH (relative
humidity) management” by supplying air at a
dew point lower than room design to take care of
internal latent load in addition to
removing fresh
air latent & fresh air sensible load.
GLOBAL WEATHER PROFILE
Geographical weather profiling is an understanding
and study of various measurable parameters
which govern the natural climatic conditioning of
the various geographical region. Profiling plays a
major role in assisting & applying HVAC concepts
& designs with a weather profile backdrop.
The
weather
profile of any
city is the key driving
parameter in assessing free cooling value, the
climate offers to any HVAC design.
Inspired to be GREEN I January - February 2010 I 45
Mumbai