Experimental and Computational Study of Indirect Expansion Solar Assisted Heat Pump System with Latent Heat Storage for Domestic Hot Water Production
Total Page：16
File Type：pdf, Size：1020Kb
Experimental and computational study of indirect expansion solar assisted heat pump system with latent heat storage for domestic hot water production A thesis submitted for the degree of Doctor of Philosophy (PhD) by Walid Mohamed Khalil Abdalla Youssef College of Engineering, Design, and Physical Sciences Brunel University London Abstract Solar assisted heat pump (SAHP) systems have been widely applied in domestic hot water (DHW) production due to their sustainability and stability in operations. However, their performance efficiency requires further improvement using advanced technologies such as energy storage with phase change materials (PCM) and optimal system controls. Undoubtedly, employing PCMs for latent heat storage (LHS) application has a great potential to improve a solar thermal application performance. Despite this fact, the use of PCM in this area is quite limited due to the poor thermal conductivity of available PCMs. Therefore, heat transfer enhancement is one of the essential strategies that can overcome this obstacle. Accordingly, a test rig of a new indirect expansion solar assisted heat pump (IDX-SAHP) system has been designed, built and instrumented. The system can handle heating capacity up to 9 kW. The IDX-SAHP system consists of three operational loops: solar thermal, solar-air assisted heat pump and load profile. A 2 kW PCM heat exchanger (HX) was purposely designed and installed in the system solar thermal loop to store solar energy, when applicable, and release heat when required by the heat pump. The PCM HX is employed with a novel heat transfer enhancement method. The maximum coefficient of performance (COP) of the IDX-SHAP system reached 4.99 during the sunny day with the PCM (HX) integration. However, the maximum energy saving was achieved during the cloudy day with the PCM HX integration. Moreover, the proposed heat transfer enhancement method has been modelled through CFD package and validated with the experimental results. This allows a clear understanding of the reasons for the longer discharging process compared with the charging process. Furthermore, the inlet flow rate and temperature variation of the PCM HX was simulated during charging and discharging processes. The optimum inlet flow rate for this application was found at 0.1 kg/s while the optimum inlet temperature was found at 40°C. Meanwhile, the whole system was modelled by the coupling of TRNSYS, EES and CFD to investigate the potential and advantages of using the system in locations with rich solar intensity such as Cairo and Madrid. The simulation shows that the solar thermal operation loop was called more frequently in these locations. This had a significant impact on the system energy consumption, especially during winter. The maximum COP and solar performance factor (SPF) of the modelled system were 5.3 and 0.83 respectively. I Acknowledgements I would like to express my appreciation and gratitude to my supervisors, Dr Yunting Ge and Professor Savvas Tassou, for allowing me to work on this project, and for extending and guiding my potential; both intellectually and tactfully. I was blessed to have their support and encouragement during my PhD research. I also would like to extend my appreciation to Centre for Sustainable Energy Use in Food Chains (CSEF) – Brunel University, Tridium Europe, Spirotech b.v and Kingspan UK for their contribution with the necessary material and equipment for my research. I am also to thank Brunel University Technician team; Costa Xantho, Eamon Wyse, John Fosbery and Guy Fitch for their support and help in my experimental study. I would like to thank CSEF members; Dr Konstantinos Tsamos, Dimitri Parpa, Hassan Moure, Thiago Santos and Maureen Senatore for being always side by side. Special thanks to my dear friend Dr Evangelia Topriska who was always there for me whenever needed. A very special thanks to my father Mohamed Khalil for his moral, emotional and financial support. Also, I could not achieve what I have reached now without the support of my mother’s Zanouba and my sisters’ Nashwa and Nehal. Finally, I would like to thank my wife Dr Kalliopi Koutsou from the deepest of my heart for her unlimited support all the way. I would like to award this success I have achieved to my future baby who will light our life in October 2017. II Contents Chapter 1. Introduction ........................................................................................ 1 1.1. Research motivation .......................................................................................... 2 1.2. Objective of the research ................................................................................... 5 1.3. Thesis structure ................................................................................................. 5 1.4. Publication ........................................................................................................ 8 Chapter 2. Background Information ................................................................ 10 2.1. Introduction ..................................................................................................... 11 2.2. Domestic water heating ................................................................................... 11 2.3. Heat pumps ..................................................................................................... 12 2.4. Solar assisted heat pumps ............................................................................... 14 2.5. SAHP Control strategies ................................................................................. 20 2.6. Phase change materials ................................................................................... 21 2.7. The use of PCM in solar and heat pump systems ........................................... 26 2.8. Summary of Chapter 2 .................................................................................... 28 Chapter 3. Experimental Components and Processes ..................................... 29 3.1. Introduction ..................................................................................................... 30 3.2. Experiment setup and test rig components...................................................... 30 3.3. Instrumentation ............................................................................................... 46 3.4. Phase change material heat exchanger ............................................................ 49 3.5. Control strategy ............................................................................................... 53 3.6. Building management system ......................................................................... 56 3.7. Logic block connection graphics design ......................................................... 63 3.8. Summary of Chapter 3 .................................................................................... 64 Chapter 4. Experimental Findings and Analysis ............................................. 65 4.1. Introduction ..................................................................................................... 66 4.2. Start-up measurements and procedure ............................................................ 66 III 4.3. Thermodynamic analysis ................................................................................ 69 4.4. Experiment finding and discussion ................................................................. 70 4.5. Uncertainty analysis ........................................................................................ 78 4.6. Summary of Chapter 4 .................................................................................... 79 Chapter 5. Numerical Model Development ...................................................... 80 5.1. Introduction ..................................................................................................... 81 5.2. Introduction to numerical simulation .............................................................. 81 5.3. Model development strategy ........................................................................... 82 5.4. Numerical model validation ............................................................................ 97 5.5. Summary of Chapter 5 .................................................................................. 102 Chapter 6. Analysis of Numerical Model ........................................................ 103 6.1. Introduction ................................................................................................... 104 6.2. PCM model applications ............................................................................... 104 6.3. Coupled model case studies .......................................................................... 115 6.4. Summary of Chapter 6 .................................................................................. 122 Chapter 7. Conclusion and Further Recommendation ................................. 123 7.1. Concluding remarks ...................................................................................... 126 7.2. Recommendation and further work ............................................................... 129 References .............................................................................................................. 130 Appendices ............................................................................................................. 141 Appendix A ..............................................................................................................