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Modelling Polygeneration with Desiccant Cooling System 448068/FULLTEXT01.pdf · PDF...

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    Modelling Polygeneration with Desiccant Cooling System for Tropical (and Sub-Tropical) Climates

    A dissertation submitted to the Department of Energy Technology, Royal Institute of Technology,

    Sweden for the partial fulfilment of the requirement for the Degree of Master of Science in Engineering

    By

    L.U.Bakmeedeniya

    2010

    Department of Energy Technology Royal Institute of Technology,

    Stockholm, Sweden

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    Modelling Polygeneration with Desiccant Cooling System for Tropical (and Sub Tropical) Climates

    by

    L.U.Bakmeedeniya

    Supervised by

    Prof. Viktoria Martin,

    Prof. Leelananda Rajapaksha

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    Declaration

    The work submitted in this thesis is the result of my own investigation, except where otherwise stated.

    It has not already been accepted for any other degree and is also not being concurrently submitted for any other degree.

    L.U.Bakmeedeniya

    Date

    We/I endorse declaration by the candidate.

    Prof. Viktoria Martin

    Prof. Leelananda Rajapaksha

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    Modelling Polygeneration with Desiccant Cooling System for

    Tropical (and Sub Tropical) Climates

    Abstract

    Space cooling has become a necessity in tropical countries. Maintaining comfortable indoor conditions in industrial environments incur high energy bills due to heavy dependency on electrically operated air conditioning systems. In order to explore ways and means to improve the energy efficiency and alterna-tive energy resources, a feasibility study was conducted using a transient simu-lation software TRNSYS to implement a combined cooling, heating and power system suitable for a tropical country.

    It is proven from the literature search that desiccant dehumidification in conjunction with evaporative coolers can reduce air conditioning operating costs significantly since the energy required to power a desiccant cooling system is small and the source of this required energy can be diverse.(Low exergy heat such as solar, waste heat and natural gas)

    This research is conducted to evaluate the performance and applicability of desiccant cooling systems under tropical climatic conditions. Two operating modes; ventilation and recirculation modes of solid desiccants based open cy-cle air conditioning that use waste heat from a CHP plant are analysed to un-derstand their operating ranges, performances and applicability. The model de-veloped is used to propose a suitable desiccant cooling system for a selected industry environment in Sri Lanka. Preliminary results obtained by a parametric analysis for weather data for Colombo, Sri Lanka shows 0.95 and 1.02 optimum coefficients of performance for the ventilation and recirculation modes respec-tively when heat is available at 85C. Based on the comparisons of the analysis it is seen that the desiccant cooling appears to be a logical supplement for space cooling applications in tropical climates like Sri Lanka. And for the case study taken to investigate can be proposed with a desiccant cooling system with a hot water storage as the energy supply and it can maintain a COP of about 0.48 under tropical weather conditions.

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    ACKNOWLEDGMENTS

    I would like to express my sincere gratitude to Professor Torsten H. Fransson Head, Department of energy technology for expanding the DSEE programme to Sri Lanka and pave the way for us to explore the world of sus-tainable energy engineering, and at the same time awarding me a scholarship to carry out the thesis work at KTH, Sweden. I am really grateful to professor Fransson and everybody at KTH for all what they have done to pacify with me in the most difficult time in my life.

    Then I would like to extend my thanks to my supervisor at KTH Professor Viktoria Martin for her sense of understanding, supervision and the guidance given in completing the task. It is my great pleasure to mention about the con-stant advices and the kindness extended towards me in guiding to the goal by Professor Leelananda Rajapaksha, the local supervisor of the thesis. I am deeply indebted to both of them.

    I would like to pay my deepest gratitude to my late husband Dammika, and the treasure of my life, elder son Kovida, only daughter Imani and my pet younger son Niraj. I am extremely grateful to them for tolerating my absence and all the hardships when I was away from the country. Then the heartfelt thanks are due to my mother, sister Shyama, two brothers and their families for extending their unconditional love and support to my children during my ab-sence. Without them I would have not been able to cope up with my work suc-cessfully.

    Next I would like to pass my sincere thanks to Maria Gomez for helping me in every possible way and allowing me to share her apartment during the early days in Stockholm. Then special thanks are for Jeevan Jayasooriya and Chamindie, for their concern and the encouragement during the short stay in Sweden. Also my thanks go to Nalin and Ruvini and all the friends at KTH and in Sweden for their encouragement and various supports given to me.

    Lastly, I should thank many individual friends and colleagues who have not been mentioned here personally in making this educational process a suc-cess. I could not have made it without their support.

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    NOMENCLATURE

    List of Abbreviations A ASHRAE Cpda Cpg Cpwl Cpwv CHP CCHP CEB COP Fi had hda hdm hg hHT hMT hm hvap hwl hwv Hm J KTH L mg Mm MGT MSW

    Surface area associated hHT and hMT American Society of Heating Refrigerating and Air-conditioning Engineers Specific heat of dry air Specific heat of gas Specific heat of liquid water Specific heat of water vapour Combined heat and power Combine cooling, heating and power Ceylon Electricity Board Coefficient of Performance ith characteristic potential Enthalpy of adsorbed water Specific enthalpy of dry air Enthalpy of the dry matrix Enthalpy of gas Heat transfer coefficient Water vapour transfer coefficient of moist air stream Enthalpy of the matrix Specific heat of vapourization Specific enthalpy of liquid water Specific enthalpy of water vapour Enthalpy of matrix Lumped matrix fluid film transfer coefficient per unit mass of fluid Kungliga Tekniska Hogskoolan (Royal Institute of Technolo-gy) Passage length in fluid flow direction Mass flow rate of gas Mass of desiccant matrix Micro Gas Turbine Municipal Solid Waste

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    Ps-wv Pwv R SLSEA t T Tdew TDC Tg Tm w wm wmax WHO x

    Partial pressure of water vapour at saturation Partial pressure of water vapour in the air Separation factor that defines the isotherm shape Sri Lanka Sustainable Energy Authority Time from beginning of period Thermodynamic temperature Dew point temperature Thermally Driven Cooling Temperature of gas Temperature of matrix Humidity ratio Moisture content of matrix Loading of desiccant at 100% relative humidity World Health Organisation Distance from matrix inlet flow direction

    Units C J/kg

    Degree Celcius Joules per kilogram

    kg kilogram kg/kgda kilogram per kilogram of dry air kJ/kg kilojoules per kilogram kg/s kilogram per second kPa K kJ/kg.K

    kilopascal Degree Kelvin kilojoules per kilogram per degree Kelvin

    m2 Square meters W/m2K Watt per square meter per Kelvin s Seconds Greek symbols Relative humidity ith specific capacity ratio Matrix mass divided by fluid mass contained in matrix

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    TABLE OF CONTENTS

    1 INTRODUCTION ................................................................. 11 1.1 Objectives ............................................................ 14

    1.1.1 The research problem ........................................................................... 15 1.1.2 Aim and scope ........................................................................................ 15

    1.2 Methodology ....................................................... 16 1.2.1 TRNSYS (Transient Simulation Systems) ........................................ 17

    2 STATE-OF-THE-ART COMBINED COOLING, HEATING AND POWER 18 2.1 Concept of cogeneration and trigeneration .. 18 2.2 Thermally driven cooling systems ................. 19 2.3 State of the art: Desiccant cooling systems . 19

    2.3.1 History and status .................................................................................. 19 2.3.2 Principle of operation ............................................................................ 21 2.3.3 Working media ........................................................................................ 21 2.3.4 Overview of the research history of the desiccant cooling ........... 22 2.3.5 Systems: Status of technology ............................................................ 24

    2.4 Promising CCHP systems for Tropical climates: Literature review .................................................................................................26

    3 MODELLING AND ANALYSIS............................................ 29 3.1 Polygeneration facility at KTH-HPT Lab ........ 29 3.2 Modelling of a desiccant cooling system ...... 30

    3.2.1 Ventilation mode ..................................................................................... 30 3.2.2 Recirculation mode ................................................................................ 32 3.2.3 Model components and selection of input data ............................... 34

    3.3 Case study: Selected garment factory in Sri Lanka 37 3.4 Results ................................................................. 38

    3.4.1 Polygeneration facility at KTH ............................................................. 38 3.4.2 Case study: Garment factory ................................

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