[sustran] Improving bus design cools passengers, saves fuel

[etts at indigo.ie]

The concept sounds good and is worth testing (although I expect it has been
researched already). I agree with Alan that air-con is expensive to buy,
expensive to run, and expensive to maintain. For many
warm-but-not-excessively-hot countries, "semi-aircon" is a reasonable
compromise - especially if we must trade-off among comfort, frequency and
fares for passengers who are vey price-sensitive (i.e. a small increase in
tariffs has a direct impact on the family diet).

About the earlier e-mail on ventilation design, one little problem is that
the bus needs to be moving to gain the cooling benefits. In most cities
where we need this simple technology, we also face serious congestion with
long periods of slow (or no) movement of buses. Windows cease to function
as ventilation and instead become 'windows of opportunity' for hawkers and
vendors plying their wares and cold drinks to the perspiring passengers.  

This worthy technology must be supported by good bus priority in some
locations, and in other locations by the elimination of roadside 'friction'
caused by encroachment, vendors, stopping traffic, etc. Once you have a
reasonable technical design, stop seeking perfection on the aerodynamics
and focus on the traffic flow. 

Effectiveness is the product of the ventilation characteristics and the
speed - if either approaches zero, the outcome is zero. Optimal result will
come from good performance in both, whereas perfection in one without the
other is of little value to the long-suffering passenger. 

Bus priority is the fundamental enabler for profitable, reliable, efficient
bus operations. Without good operating conditions, bus services degenerate
on every parameter. By contrast, when we provide the conditions for the
buses to operate as the designers made them, we tick all the other boxes.
Unfortunately, this is not easily achieved. However, the more we understand
how much damage it causes to all else that we try to do, the more we
appreciate that we must face this challenge. 

With best wishes, 


Brendan.
____________________________________________________________________________
__________
Brendan Finn          e-mail : etts at indigo.ie          tel : +353.87.2530286

----- Original Message ----- 
From: Alan Howes 
To: sustran-discuss at list.jca.apc.org 
Sent: Wednesday, July 22, 2009 10:17 PM
Subject: [sustran] Re: Improving bus design cools passengers, saves fuel


Interesting indeed. A/C in buses is not only expensive to install and
run, but in my experience is also a maintenance nightmare - A/C faults
being about as prevalent as all the other faults put together.

The principles seem sound. But I would be interested in views on another
long-standing idea of mine, which could be applied to hot-climate buses
with or without A/C.

This is an exterior false roof - an extra roof 5-10 cms above the
existing one, with an air space between the two roofs and gaps all
around. So the false roof keeps the sun off the real roof, reducing heat
transference. 

Would it work? (I am not a mechanical engineer!) And if it would, why
has it not been tried - or has it?

Cheers, Alan

-- 
Alan Howes, Perthshire, Scotland
----- Original Message ----- 
From: Eric Britton 
To: sustran-discuss at list.jca.apc.org 
Cc: srk at mech.iitd.ac.in 
Sent: Tuesday, July 21, 2009 8:13 AM
Subject: [sustran] Improving bus design cools passengers, saves fuel

I thought this was interesting. Any comments, further background?

Eric Britton

Contact: Sunil Kale
srk at mech.iitd.ac.in
Inderscience Publishers 

Slotted buses keep passengers cool
Improving bus design cools passengers, saves fuel
A simple redesign of public buses used in hot and dry climates could make
passengers more comfortable without the need to use extra fuel running air
conditioning, according to a study published in the International Journal
of Heavy Vehicle Systems.

Sunil Kale of the Department of Mechanical Engineering, at the Indian
Institute of Technology Delhi, India, and colleagues point out that the
majority of passenger trips are taken in open window buses.

Worldwide, buses are the principal means of commuting within and between
cities, the researchers explain. For cost reasons, particularly in the
developing world, only a small fraction (less than 5%) of inter-city
vehicles are air-conditioned. They add that air-conditioning is not a
commercially or environmentally viable alternative to simply opening the
side windows and even the doors.

Opened windows are supposed to improve airflow and keep passengers cool
while the bus moves. However, the cooling effect of open side windows is
inadequate for comfort in the hottest parts of the world on a crowded bus.

Kale's team has now carried out an aerodynamic study of fluid flow in a
1:25 model. Their findings suggest that a few simple modifications to
conventional design could significantly boost cooling airflow with none of
the cost or energy requirements of an air- conditioning system.

The turbulent flow into a standard bus does not allow air into all areas.
Passengers sitting near or standing in the aisle do not receive any
ventilation, while those in the front seats receive airflow from the rear.
The team has found that a wide vent at the front and rear of a bus will
draw air into the bus at a much better rate than side windows. A similar
boost can be obtained with adjustable roof vents.

These modifications would allow cooling air to increase the comfort zone of
the bus from a mere 11% of the interior volume to more than 50%. This means
that all passengers will experience some cooling airflow. In addition to
improved comfort there is an overall reduction in drag. Some of this drag
reduction could be sacrificed to provide grills and filters to prevent the
influx of insects and dust. Optionally a passive evaporative cooling system
could be incorporated into the vents to cool the incoming air and further
boost the comfort inside the bus.

"In a long-term policy perspective of sustainable transport, buses form an
important mode of transport that needs to be strengthened," the researchers
say, "Besides improving fuel economy, passenger comfort is a major issue
with such buses especially in tropical climates."

###

"Aerodynamics of a bus with open windows" in International Journal of Heavy
Vehicle Systems, 2009, 16, 459-488 
 
With all good wishes,

Eric Britton 

Managing Editor



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