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MECH-PHD-05-301
Investigations on Liquid Desiccant based Energy Efficient Bus Air-conditioning Systems
Roshini Rebecca Easow, Ph.D, 05, 203 pp.
Department of Mechanical Engineering
Indian Institute of Technology Bombay, Powai, Mumbai 400 076.
Supervisor(s): Milind Rane
A 45 seat bus operating in humid environment like in the city of Mumbai uses a 7 TR
air-conditioning system. The fuel consumption increases by 82\% in summer and
60% in winter, when the air-conditioning system is in operation. The extra fuel fired
for driving the air-conditioning system alone adds 28 tonnes of CO2 per year per bus
to the already polluted environment of Mumbai (calculated at 2.82 kg CO2/l of diesel
fired). The aim of the present work is to investigate and recommend an improved air-
conditioning system for a bus that is energy efficient and reduces CO2 emissions.
Liquid desiccant based air-conditioning systems were considered for an improved
system since they are heat operated and can utilize the waste heat available from th
bus engine. The essential components of these systems are the absorbers and theregenerators. A liquid desiccant based dehumidification system incorporating a two
stage regenerator was fabricated. It used improved absorber and regenerator using
rotating contacting devices made of aluminium and/or plastic, which have surface
densities of the order of 465 to 600 m2/m3. Testing showed a moisture removal of
2.5 kg/kWh (thermal COP of 1.55) with recovery of potable water from the dilute
liquid desiccant. Different cycles were studied using the data obtained from these
experiments and Hybrid Air-conditioning System (HAS) was identified as suitable for
bus air-conditioning. A Hybrid Air-conditioning System was designed, fabricated and
tested. Use of liquid desiccants improves the Indoor Air Quality (IAQ) since they havethe ability to remove bacterial and other contaminants. The liquid desiccant used was
aqueous Calcium Chloride. The HAS operates with higher evaporator temperature
and lower condensing temperature as compared to the conventional air-cooled
systems. Experimentation on the HAS using a 1.5 TR compressor demonstrated that
the COP is enhanced by 34%.and moisture removal by 166%. For same cooling
load, the size of compressor reduced to 76% of its size when used in a vapor
compression system. Thus, a HAS equipped with a 4.5 TR compressor will be
capable of handling the 7 TR bus air-conditioning load. The HAS is therefore an
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energy efficient alternative to the conventional bus air-conditioning system with
35.7% reduction in CO2 emissions. Key words: bus air-conditioning, liquid
desiccants, dehumidification, two stage regeneration, hybrid air-conditioning
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