Consider The Following Case Study:
In a survey of 100 office buildings, 23% of office
workers experienced frequent symptoms of
SBS such as respiratory ailments, allergies and
asthma.
The impact was usually hidden in sick days,
medical costs and lower productivity, but the
economic impact is enormous, with an estimated
decrease in productivity around 2% nationwide,
resulting in an annual cost of approximately
USD60 billion.
Source: Emerging Energy-Efficient Technology in
Promoting Workplace Productivity and Health, a
report by Lawrence Berkeley National Laboratory
Figure 1: Outside air load - Mumbai
Outdoor Air Requirements For Ventilation
Of Air Conditioned Spaces
The LEED standard states to “Increase breathing
zone outdoor air ventilation rates to all occupied
spaces by at least 30% above the minimum rates
required by ASHRAE Standard 62.1-2007 as
determined by EQ Prerequisite 1.” This increased
amount of ventilation has definitely solved IAQ
related problems, but the inability to maintain the
right humidity using our HVAC systems has led
to other problems. Mould and mildew, which are
caused by lack of humidity control are a serious
dilemma in themselves. The question is: have we
traded one problem for another?
IAQ & Relative Humidity (RH) Control
The benefits of increased ventilation have been
clearly established and absorbed by the HVAC
industry at large. The health of occupants is
of great concern and more and more systems
are being designed with the right amount of
outside air.
The outside air however, while solving this
problem, poses a great challenge for the HVAC
system. The saviour of IAQ brings along with it a
quandary of high latent load, cornering the HVAC
equipment and resulting in high levels of RH
inside. Let us examine the load profile of outside
air in a tropical country like ours.
Figure 1 shows the outside air for the city of
Mumbai, which is similar to Kuala Lumpur. The
curve defines the load of outside air in terms of
the sensible and latent load in tonnes for the
entire year. Clearly one can see that latent load
of the city is quite high and is around 78% of the
cumulative fresh air load.
Similarly, if one studies the profile of the
cumulative loads (i.e. cooling and dehumidification
only) for major cities in Asia, one can see that the
latent load component of fresh air is quite high
(ranges between 60% and 85%).
With outside air bringing in high amounts of
latent energy, RH management becomes difficult.
The HVAC fraternity received a wakeup call for
IAQ and RH control when the bacteria spread by a
hotel air conditioning system killed 34 people and
afflicted more than 200 people at an American
Regional Convention in Philadelphia around 20
years ago.
Lack of RH control leads to growth of mould
and mildew which leads to various health
related issues. Mould releases tiny spores to
reproduce. These spores then waft through the
indoor air and start developing in damp areas.
They can cause several problems like rashes,
asthma, runny noses and respiratory problems
including serious diseases like hypersensitivity
pneumonitis.
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