Special Issue "Thermodynamics of Heat Pump and Refrigeration Cycles"

A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Thermodynamics".

Deadline for manuscript submissions: closed (15 December 2020) | Viewed by 8304

Special Issue Editor

Prof. Dr. Alojz Poredos
E-Mail Website
Guest Editor
Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia
Interests: HVAC; heat pumps; sustainable development; renewable energies; energy efficiency; district heating, district cooling
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In terms of physics, the operating principle of a heat pump is the same as that of a refrigerator: Moving heat from a low-temperature level to a high-temperature level. If in a refrigerator, the cold at lower temperature is used, and a heat pump provides heat at temperatures high enough for heating. Refrigeration and heat pump systems use various types of thermodynamic processes based on vapor compression, sorption, or caloric technologies.

Today, heating and cooling account for nearly 50% of global energy demand. It is, therefore, essential to make the thermodynamic processes for refrigeration and heat pump systems as energy-efficient as possible. The latest research into heat pump and refrigeration cycles has focused on improving the existing solutions and developing new, alternative, more sustainable technologies.

The purpose of this Special Issue is to highlight the results of research on how to increase the efficiency of thermodynamic processes for heat pump and refrigeration systems. While room remains for further efficiency improvements of classical thermodynamic processes, it is precisely new heat pump and refrigeration technologies that most of the major new discoveries and applications in thermodynamics are expected to yield.

Prof. Dr. Alojz Poredos
Guest Editor

Manuscript Submission Information

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Keywords

  • heat pump
  • refrigeration
  • thermodynamics
  • energy efficiency
  • vapor compression
  • sorption refrigeration
  • caloric technologies

Published Papers (7 papers)

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Editorial

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Editorial
Thermodynamics of Heat Pump and Refrigeration Cycles
Entropy 2021, 23(5), 524; https://doi.org/10.3390/e23050524 - 25 Apr 2021
Viewed by 659
Abstract
Energy consumption for heating and cooling in buildings and industry accounts for almost half of total energy consumption in all sectors [...] Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)

Research

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Article
Performance and Exergy Analyses of a Solar Assisted Heat Pump with Seasonal Heat Storage and Grey Water Heat Recovery Unit
Entropy 2021, 23(1), 47; https://doi.org/10.3390/e23010047 - 30 Dec 2020
Cited by 3 | Viewed by 925
Abstract
The main research objective of this paper was to compare exergy performance of three different heat pump (HP)-based systems and one natural gas (NG)-based system for the production of heating and cooling energy in a single-house dwelling. The study considered systems based on: [...] Read more.
The main research objective of this paper was to compare exergy performance of three different heat pump (HP)-based systems and one natural gas (NG)-based system for the production of heating and cooling energy in a single-house dwelling. The study considered systems based on: 1. A NG and auxiliary cooling unit; 2. Solely HP, 3. HP with additional seasonal heat storage (SHS) and a solar thermal collector (STC); 4. HP with SHS, a STC and a grey water (GW) recovery unit. The assessment of exergy efficiencies for each case was based on the transient systems simulation program TRNSYS, which was used for the simulation of energy use for space heating and cooling of the building, sanitary hot water production, and the thermal response of the seasonal heat storage and solar thermal system. The results show that an enormous waste of exergy is observed by the system based on an NG boiler (with annual overall exergy efficiency of 0.11) in comparison to the most efficient systems, based on HP water–water with a seasonal heat storage and solar thermal collector with the efficiency of 0.47. The same system with an added GW unit exhibits lower water temperatures, resulting in the exergy efficiency of 0.43. The other three systems, based on air–, water–, and ground–water HPs, show significantly lower annual source water temperatures (10.9, 11.0, 11.0, respectively) compared to systems with SHS and SHS + GW, with temperatures of 28.8 and 19.3 K, respectively. Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)
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Article
Exergy Analysis of Advanced Adsorption Cooling Cycles
Entropy 2020, 22(10), 1082; https://doi.org/10.3390/e22101082 - 26 Sep 2020
Cited by 5 | Viewed by 908
Abstract
This study conducted an exergy analysis of advanced adsorption cooling cycles. The possible exergy losses were divided into internal losses and external losses, and the exergy losses of each process in three advanced cycles: a mass recovery cycle, heat recovery cycle and combined [...] Read more.
This study conducted an exergy analysis of advanced adsorption cooling cycles. The possible exergy losses were divided into internal losses and external losses, and the exergy losses of each process in three advanced cycles: a mass recovery cycle, heat recovery cycle and combined heat and mass recovery cycle were calculated. A transient two-dimensional numerical model was used to solve the heat and mass transfer kinetics. The exergy destruction of each component and process in a finned tube type, silica gel/water working paired-adsorption chiller was estimated. The results showed that external loss was significantly reduced at the expense of internal loss. The mass recovery cycle reduced the total loss to 60.95 kJ/kg, which is −2.76% lower than the basic cycle. In the heat recovery cycle, exergy efficiency was significantly enhanced to 23.20%. The optimum value was 0.1248 at a heat recovery time of 60 s. The combined heat and mass recovery cycle resulted in an 11.30% enhancement in exergy efficiency, compared to the heat recovery cycle. The enhancement was much clearer when compared to the basic cycle, with 37.12%. The observed dependency on heat recovery time and heating temperature was similar to that observed for individual mass recovery and heat recovery cycles. Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)
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Article
Effect of Machine Entropy Production on the Optimal Performance of a Refrigerator
Entropy 2020, 22(9), 913; https://doi.org/10.3390/e22090913 - 20 Aug 2020
Cited by 9 | Viewed by 1034
Abstract
The need for cooling is more and more important in current applications, as environmental constraints become more and more restrictive. Therefore, the optimization of reverse cycle machines is currently required. This optimization could be split in two parts, namely, (1) the design optimization, [...] Read more.
The need for cooling is more and more important in current applications, as environmental constraints become more and more restrictive. Therefore, the optimization of reverse cycle machines is currently required. This optimization could be split in two parts, namely, (1) the design optimization, leading to an optimal dimensioning to fulfill the specific demand (static or nominal steady state optimization); and (2) the dynamic optimization, where the demand fluctuates, and the system must be continuously adapted. Thus, the variability of the system load (with or without storage) implies its careful control-command. The topic of this paper is concerned with part (1) and proposes a novel and more complete modeling of an irreversible Carnot refrigerator that involves the coupling between sink (source) and machine through a heat transfer constraint. Moreover, it induces the choice of a reference heat transfer entropy, which is the heat transfer entropy at the source of a Carnot irreversible refrigerator. The thermodynamic optimization of the refrigerator provides new results regarding the optimal allocation of heat transfer conductances and minimum energy consumption with associated coefficient of performance (COP) when various forms of entropy production owing to internal irreversibility are considered. The reported results and their consequences represent a new fundamental step forward regarding the performance upper bound of Carnot irreversible refrigerator. Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)
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Article
Superstructure-Based Optimization of Vapor Compression-Absorption Cascade Refrigeration Systems
Entropy 2020, 22(4), 428; https://doi.org/10.3390/e22040428 - 10 Apr 2020
Cited by 5 | Viewed by 1434
Abstract
A system that combines a vapor compression refrigeration system (VCRS) with a vapor absorption refrigeration system (VARS) merges the advantages of both processes, resulting in a more cost-effective system. In such a cascade system, the electrical power for VCRS and the heat energy [...] Read more.
A system that combines a vapor compression refrigeration system (VCRS) with a vapor absorption refrigeration system (VARS) merges the advantages of both processes, resulting in a more cost-effective system. In such a cascade system, the electrical power for VCRS and the heat energy for VARS can be significantly reduced, resulting in a coefficient of performance (COP) value higher than the value of each system operating in standalone mode. A previously developed optimization model of a series flow double-effect H2O-LiBr VARS is extended to a superstructure-based optimization model to embed several possible configurations. This model is coupled to an R134a VCRS model. The problem consists in finding the optimal configuration of the cascade system and the sizes and operating conditions of all system components that minimize the total heat transfer area of the system, while satisfying given design specifications (evaporator temperature and refrigeration capacity of −17.0 °C and 50.0 kW, respectively), and using steam at 130 °C, by applying mathematical programming methods. The obtained configuration is different from those reported for combinations of double-effect H2O-LiBr VAR and VCR systems. The obtained optimal configuration is compared to the available data. The obtained total heat transfer area is around 7.3% smaller than that of the reference case. Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)
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Article
Exergetic and Economic Evaluation of a Transcritical Heat-Driven Compression Refrigeration System with CO2 as the Working Fluid under Hot Climatic Conditions
Entropy 2019, 21(12), 1164; https://doi.org/10.3390/e21121164 - 28 Nov 2019
Cited by 5 | Viewed by 1135
Abstract
The purpose of this research is to evaluate a transcritical heat-driven compression refrigeration machine with CO2 as the working fluid from thermodynamic and economic viewpoints. Particular attention was paid to air-conditioning applications under hot climatic conditions. The system was simulated by Aspen [...] Read more.
The purpose of this research is to evaluate a transcritical heat-driven compression refrigeration machine with CO2 as the working fluid from thermodynamic and economic viewpoints. Particular attention was paid to air-conditioning applications under hot climatic conditions. The system was simulated by Aspen HYSYS® (AspenTech, Bedford, MA, USA) and optimized by automation based on a genetic algorithm for achieving the highest exergetic efficiency. In the case of producing only refrigeration, the scenario with the ambient temperature of 35 °C and the evaporation temperature of 5 °C showed the best performance with 4.7% exergetic efficiency, while the exergetic efficiency can be improved to 22% by operating the system at the ambient temperature of 45 °C and the evaporation temperature of 5 °C if the available heating capacity within the gas cooler is utilized (cogeneration operation conditions). Besides, an economic analysis based on the total revenue requirement method was given in detail. Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)
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Article
Exergy Analysis of Fluidized Desiccant Cooling System
Entropy 2019, 21(8), 757; https://doi.org/10.3390/e21080757 - 02 Aug 2019
Cited by 4 | Viewed by 1596
Abstract
One of the main challenges in the design and implementation of fluidized desiccant cooling (FDC) systems is increasing their low COP (coefficient of performance). Exergy analysis is one of the tools especially suitable for improvement and optimization of FDC systems. The improvement of [...] Read more.
One of the main challenges in the design and implementation of fluidized desiccant cooling (FDC) systems is increasing their low COP (coefficient of performance). Exergy analysis is one of the tools especially suitable for improvement and optimization of FDC systems. The improvement of performance is impossible as long as the main sources of exergy destruction are not identified and evaluated. In this paper, the exergy analysis was applied in order to identify these components and processes of the FDC system that are mainly responsible for exergy destruction. Moreover, the exergy efficiency of a simple fluidized desiccant cooler was determined. The results showed that fluidized beds and regenerative heat exchanger were the main exergy destruction sources with a 32% and 18% share of total exergy destruction, respectively. On the other hand, the direct evaporative cooler and air cooler placed after the desorbing fluidized bed were characterized by the lowest exergy efficiencies. This work contributes to better understanding of FDC operation principles and improvement of the performance of FDC technology. Full article
(This article belongs to the Special Issue Thermodynamics of Heat Pump and Refrigeration Cycles)
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