99550 - TECNICA DEL FREDDO M

Learning outcomes

At the end of the course, the student has the knowledge about the design of refrigeration systems based on vapor compression and absorption cycles, evaluating their energy performance and environmental impact. In particular, the student is able to: - study the possible configurations of a compression refrigeration system (single-stage, two-stage) ; - evaluate the performance of a compression refrigeration system according to its main components and the refrigerant fluid used ; - evaluate the functioning of an absorption refrigerator and calculate its performance ; - design variable refrigerant volume (VRV) refrigeration systems.

Course contents

The Course on brief: Youtube link. Video showing in brief Course contents, teaching and assessment methods.

Introduction to the course and recall of thermodynamics principles. Refrigeration: application examples, global trends. Reverse Carnot cycle, refrigeration unit and heat pump. Efficiency indixes. Thermodynamic diagrams.

Vapor-compression refrigeration cycles. P-h diagram. Ideal and real thermodynamic cycle of a vapor compression refrigeration unit. Single-stage and two-stage cycles. Cascade cycles. Cycles with steam injection.

Refrigerant fluids for refrigeration cycles. Classification, functional and environmental requirements of refrigerant fluids. Synthetic refrigerants and natural refrigerants. Actions of refrigerant fluids towards the environment. Current regulation.

The main components of the vapor compression refrigeration cycle. Volumetric compressors (reciprocating and rotary), dynamic compressors. Air and water condensers. Flooded and dry evaporators. Laminating devices. System auxiliaries (control devices, valves, safety systems, lubrication systems). The heat pump technology. The defrost problem.

Different typologies of refrigeration cycles. Absorption refrigeration cycles. Refrigerating machines with water-ammonia absorption. Energy balances and mass balances. Lithium bromide-water absorption refrigeration machines. Outline of solar cooling technologies. Trans-critical refrigeration cycles with CO2 as refrigerant: system configuration and applications.

Direct expansion systems VRF-VRV. General outline of direct expansion air conditioning systems. Maximum refrigerant content of air conditioning units. Comparison with hydronic systems: energy efficiency at full load and partial load.

Use of REFPROP software. Thermo-physical refrigerant properties analysis with the REFPROP database. Refrigeration cycle efficiency analysis.

Towards the end of the course there will be a visit to the Applied Thermal Engineering Laboratory of the Department of Industrial Engineering (site of the Engineering Faculty of Lazzaretto, via Terracini 34, Bologna), where there is a climatic chamber for tests on air-source heat pumps and water-water heat pumps, coupled to a field of geothermal probes. The climatic chamber will be used to carry out some simple tests on a heat pump.

Readings/Bibliography

Lecture notes by the teacher

Handouts and slides used by the teacher in class can be downloaded from the website https://virtuale.unibo.it/ using your academic institutional credentials.

Recommended texts for eventual personal study:

• ASHRAE 2022 Handbook – Refrigeration

• C. Pizzetti, Condizionamento dell'aria e refrigerazione, CEA, 1980/2

• W. Stoecker, Manuale della refrigerazione industriale, Edizioni Tecniche Nuove, 2001

• G.F. Hundy, A.R. Trott, T.C. Welch, Refrigeration, Air Conditioning and Heat Pumps, Butterworth-Heinemann, 2016

Teaching methods

The course is based on lectures held in person at the historical site of the Faculty of Engineering (Viale del Risorgimento 2) through which theoretical and applicative contents of the course will be illustrated. Lessons will be illustrated through slides and with the aid of simulation software.

One or more lessons will be provided at the Applied Thermal Engineering Laboratory of the Department of Industrial Engineering (via Terracini 34, Bologna), where there is a climatic chamber for tests on air-to-water and water-to-water heat pumps, coupled to a field of geothermal probes. At the laboratory there is also a computer room that will be used for the use of the software REFPROP (database of thermodynamic properties of refrigerant fluids)

There will also be interventions by experts from the world of industry and, if the logistics are feasible, a visit to a production plant of a manufacturer of refrigeration units will be planned.

In consideration of the types of activities and teaching methods adopted, the attendance of this training activity requires all students to carry out modules 1 and 2 in e-learning mode and to participate in module 3 of specific training on safety and health in study places. Information on dates and methods of attendance of module 3 can be consulted in the specific section of the degree program website.

Assessment methods

The acquired knowledge will be verified through an oral test, which includes a series of theoretical and applicative questions on the topics covered during the course. The final grade that can be obtained can vary between a minimum of 18 (very limited preparation) and a maximum of 30 cum laude (substantially exhaustive preparation).

Students can consult the list of exam sessions on the teacher's website and must register for the chosen test through the website https://almaesami.unibo.it/

Teaching tools

PC-assisted presentations, display of theoretical and applicative contents on the blackboard (virtual or traditional), use of simulation software (REFPROP, Matlab-Simulink, Trnsys), experimental apparatus of the Applied Thermal Engineering Laboratory. Educational material available on https://virtuale.unibo.it/

Links to further information

https://www.youtube.com/watch?v=yUZwaoacBSc

Office hours

See the website of Matteo Dongellini