Refrigeration Systems

Thermodynamics, Heat Transfer, Fluid Mechanics and Refrigeration and Air Conditioning.

Topics at theoretical classes are presented through an application-driven approach, which tries to trigger discussion within the audience. “What-if” questions are extensively raised to engage students in the discussion. Students are also urged to deepen the study through self-conducted research. Moreover, each student presents two topics, followed by a discussion period. In theoretical-practical classes, problem solving is promoted to verify the knowledge level already acquired. Lab classes are grounded on software and technical catalogs of refrigeration manufacturers, to help in the assignment of designing a refrigeration plant. One or more field visits to industrial and/or commercial units are also provided.

The main aims of this course unit are: to present the thermodynamic mechanisms that govern refrigeration applications; to distinguish the main components of refrigeration systems and how they interact to perform refrigeration; and to select main components and accessories for a refrigeration system, so that students develop engineering skills concerning refrigeration systems.
In the end of the course unit, students are expected to be able to:
• integrate refrigeration fundamentals with refrigeration systems design;
• describe and size the main components (equipment and accessories) of a refrigeration system;
• design a refrigeration system for a specific application;
• identify the principles governing the conservation of perishable goods and associated logistics;
• calculate the heat load in refrigeration systems;
• characterize alternative refrigerants for the HVAC-R sector.

Introduction: Concepts and units used in refrigeration. History of Refrigeration. Major refrigeration systems:
their classification and application examples. Special examples of application: ground freezing and freeze
drying.
Legislation in the refrigeration sector: Legislation, standards and regulations for the refrigeration
sector, at EU and national levels.
Refrigeration Cycles: Theoretical vapor compression refrigeration cycle. Irreversibilities and the real cycle. Performance coefficients (COP, EER, SEER). Absorption refrigeration cycle. Main factors that influence refrigeration capacity and compression power. Changes to the basic refrigeration cycle: Introduction of a heat exchanger. Expansion vessel for gas-flash removal. Expansion vessel for intermediate cooling. Optimum pressure for intermediate cooling. Installations with multiple compressors and multiple evaporators. Multi-stage cycles and cascade cycles.
Refrigerants: General properties of refrigerants. Effects on the performance of a refrigeration cycle. Traditional, transitional and long-term, natural and synthetic refrigerants: CFCs, HCFCs, HFCs, HCs, HFOs, CO2, NH3. Azeotropic and zeotropic mixtures. Temperature glide. Nomenclature adopted. Safety of refrigerants: flammability and toxicity. Impact on the environment: depletion of the ozone layer and greenhouse effect; replacement of CFCs, HCFCs and HFCs. Humidity in refrigeration plants. Filter-dryers: types, localization, sizing and selection of filter-dryers.
Refrigeration compressors: Compressors in refrigeration: Types of compressors and application. Capacity of refrigeration compressors. Volumetric efficiency and adiabatic compression efficiency. Compression ratio. Adiabatic discharge  temperature. Lubrication of compressors. Oil separator: Types, sizing and selection. Compressors of variable capacity; different modes of capacity regulation.
Condensers and evaporators: Types of condensers: air-cooled and water-cooled condensers; evaporative condensers. Determination of the condenser capacity. Types of evaporators. Different methods of feeding refrigerant to the evaporator: direct expansion system, semi-flooded system and flooded system. Parameters that influence the performance of the evaporator. Calculation of the evaporator capacity.
Software for the refrigeration sector: Software for determination of thermodynamic properties of refrigerants, analysis of the performance of a refrigeration cycle, selection of compressors and condensing units.
Control in a refrigeration plant: Expansion valves: automatic valves, float valves, thermostatic valves, and electronic valves; external pressure equalization. Capillary tube; sizing. Thermostats and pressure switches. Other valves and accessories for controlling and regulating a refrigeration circuit. Defrosting methods.
Conservation and transport of perishable products: Cold storage of perishable products. Main methods for cooling, refrigerating and freezing food products. Industrial cold logistics.
Calculation of refrigeration plants: Thermal load of a cold room. Different components involved: physical envelope, product load, internal equipment, service. Calculation of a cold room: total refrigeration capacity to be installed.

NAO

Main Bibliography

· MALÇA J. Instalações Frigoríficas – Textos de apoio da unidade curricular, 2023
· RAPOSO J. Instalações Frigoríficas – Textos de apoio da unidade curricular, 2023
· STOECKER WF. Industrial Refrigeration Handbook. McGraw-Hill, 1998. ISBN: 0-070-61623-X (1)
· CREUS J. Tratado Prático de Refrigeração Automática. Dinalivro, Lisboa, 1978. ISBN: 972-576-129-4 (1)

Complementary Bibliography

· MONTEIRO V. Refrigeração I – Bases e Fundamentos. ETEP, 2015. ISBN: 978-989-8480-12-5 (1)
· MONTEIRO V. Refrigeração II – Aplicações e Certificação. ETEP, 2016. ISBN: 978-989-8480-13-2 (1)
· DOSSAT R, HORAN TJ. Principles of Refrigeration. 5th Ed., Prentice Hall, 2001. ISBN: 0-13-027270-1 (1)
· JUTGLAR L, MIRANDA AL. Técnicas de Refrigeración. Marcombo SA, 2008. ISBN: 978-8426714404.
· COOK N. Refrigeration and Air-Conditioning Technology. Macmillan Education, 1995. ISBN: 0-333-60958-1 (1)
· MEJIAS A. Refrigeration License Examinations. Ed. Thomson-Arco, 2002. ISBN: 0-7689-1019-6 (1)
· HUNDY GF, TROTT AR, WELCH TC. Refrigeration and Air-Conditioning. 4th edition, Elsevier, 2008. ISBN: 978-0-7506-8519-1 (1)
· Instituto Internacional del Frio. Guia del Transporte Frigorifico. Ed. Mundi-Prensa, Madrid, 2002. ISBN: 84-7114-898-6 (1)
· WHITMAN B, JOHNSON B, TOMCZYK J, SILBERSTEIN E. Refrigeration and Air Conditioning Technology – Lab Manual. 6th ed, Delmar Cengage Learning, 2009. ISBN: 978-1-4283-1937-0 (1)
· MAAKE W, ECKERT HJ, CAUCHEPIN JL. Le Pohlmann: Manuel technique du froid. 2e éd., PYC Edition, Paris, 1993. ISBN : 2-85330-127-3 (1)
· McQUISTON F, PARKER J. Heating, Ventilating and Air-Conditioning – Analysis and Design. 4th Ed., John Wiley & Sons, Inc, 1993. ISBN: 0-471-58107-0 (1)
· SANTOS, A J. (2016). Refrigeração I – Fundamentos. Publindústria, Edições Técnicas, Porto. ISBN: 978-989-723-174-2.

(1) Available at ISEC Library