The use of the two-phase closed thermosyphons (TPCTs) is increasing for many heat transfer applications. This paper reviews the most recent published experimental and theoretical studies on the TPCT. After a description of the TPCT operating principle and the performance characteristics, the heat transfer analysis in condenser and evaporator sections that depends on the complex two-phase process are described. The influence of the affecting parameters on the performance of TPCTs such as the geometry (diameter, shape and length), the inclination angle, the filling ratio (FR), the working fluid, the operating temperature and pressure analyzed by various researchers is discussed. The various operating limits occurring in a thermosyphon includes viscous, sonic, dryout, boiling and flooding are also analyzed. Considering the application of TPCTs, the paper presents a review of experimental tests and applications. This paper can be used as the starting point for the researcher interested in the TPCTs and their renewable energy applications.

Two-phase closed thermosyphons: A review of studies and solar applications

Application of seasonal thermal energy storage with heat pumps for heating and cooling buildings has received much consideration in recent decades, as it can help to cover gaps between energy avail ...

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Seasonal thermal energy storage with heat pumps and low temperatures in building projects—A comparative review

Carbon dioxide is a safe, economic and environmentally sustainable refrigerant which can be used in heat pump and refrigeration systems. Research into the performance and benefits of a transcritical heat pump cycle using carbon dioxide began in the early 1990s. Theoretical and experimental research, as well as commercial system development, has improved transcritical system performance to a level similar to that of conventional heat pump systems. This paper presents an overview of transcritical carbon dioxide heat pump systems. The paper begins with a summary of carbon dioxide's use as a refrigerant and the distinctions of the transcritical cycle, followed by a numerical analysis of transcritical cycle performance. The study will then present a review of research on transcritical carbon dioxide heat pump systems, which covers system components, configurations and modifications and how these factors affect overall system performance.

Transcritical carbon dioxide heat pump systems: A review

The effects of water-side operating conditions (mass flow rates and inlet temperatures) of both evaporator and gas cooler on the experimental as well as simulated performances (cooling and heating capacities, system coefficient of performance (COP) and water outlet temperatures) of the transcritical CO2 heat pump for simultaneous water cooling and heating the are studied and revised. Study shows that both the water mass flow rate and inlet temperature have significant effect on the system performances. Test results show that the effect of evaporator water mass flow rate on the system performances and water outlet temperatures is more pronounced (COP increases by 0.6 for 1 kg/min) compared to that of gas cooler water mass flow rate (COP increases by 0.4 for 1 kg/min) and the effect of gas cooler water inlet temperature is more significant (COP decreases by 0.48 for given range) compared to that of evaporator water inlet temperature (COP increases by 0.43 for given range). Comparisons of experimental values with simulated results show the maximum deviation of 5% for cooling capacity, 10% for heating capacity and 16% for system COP.

http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.baztech-article-BGPK-3780-4453/c/Sarkar.pdf

Operating characteristics of transcritical CO2 heat pump for simultaneous water cooling and heating

The CO2 with superior thermo-physical properties has numerous applications in nuclear reactor, power plant, refrigeration and air conditioning systems as well as in many engineering and industrial applications. The complex phenomenon of thermal and hydrodynamic behaviour associated with supercritical CO2 is a continuing research topic for many researchers. The conventional correlations of turbulent forced convection heat transfer failed to predict the heat transfer and flow behaviour especially in the vicinity of the critical condition. The present paper presents a comprehensive review of heat transfer characteristics and correlations with supercritical CO2 employed under heating and cooling condition in horizontal channel or tube. An exhaustive review of implementation of supercritical CO2 used with horizontal and vertical orientation of tubes under turbulent flow condition and other operating parameters (inlet sCO2 pressure, mass flux, temperature, and heat flux) is also reported. In the present work, possible reasons for heat transfer deterioration under heating of supercritical CO2 are discussed. The characteristics of pressure drop, convective heat transfer behaviour, effect of buoyancy, the wall temperature distribution and finally the comparison among different correlations are reviewed extensively for supercritical CO2. The study of these correlations with their range of applicability provides a good insight for efficient thermal design and optimization of heat exchanger especially in thermal power plants.

A comprehensive review on heat transfer and pressure drop characteristics and correlations with supercritical CO2 under heating and cooling applications

This article presents a Heat Pump for Simultaneous heating and cooling (HPS) designed for hotels, luxury dwellings and smaller office buildings. The main advantage of the HPS is to carry out simultaneously space heating and space cooling in a dual mode. The ambient air is used as a balancing source to run a heating or a cooling mode. The HPS also participates to domestic hot water preparation all year round. The second advantage is that, during winter, some energy recovered by subcooling of the refrigerant is stored at first in a cold water tank that is not used for cooling. This energy is used subsequently as a cold source at the water evaporator in order to improve the average coefficient of performance and to run a defrosting sequence at the air evaporator. Two refrigerants are studied: HFC R407C and carbon dioxide. HFCs provide good performance, but new restrictive regulations on F-gases lead us to study low-GWP refrigerants as well. Highly efficient models of compressors and heat exchangers have been defined. Annual simulations show that CO2 is a refrigerant which adapts rather well to the operation of the HPS thanks to the higher amount of energy available by subcooling and the large temperature glide at heat rejection used for DHW production.

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Design and simulation of a heat pump for simultaneous heating and cooling using HFC or CO2 as a working fluid

https://hal.archives-ouvertes.fr/hal-00719292/document

Experimental study of an air-source heat pump for simultaneous heating and cooling – Part 2: Dynamic behaviour and two-phase thermosiphon defrosting technique

https://hal.archives-ouvertes.fr/hal-00719288/document

Experimental study of an air-source heat pump for simultaneous heating and cooling - Part 1: Basic concepts and performance verification

The heat pump for simultaneous heating and cooling (HPS) carries out space heating, space cooling and hot water production for small office and residential buildings. It works under heating, cooling and simultaneous modes to produce hot and chilled water according to the thermal demand of the building. A subcooler connected to a water tank is placed after the condenser to recover some energy by subcooling of the refrigerant during a heating mode. The water loop at a higher temperature than ambient air is used subsequently as a source for a water evaporator. Average winter performance is improved compared to a standard reversible heat pump (HP). The air evaporator is defrosted by a two-phase thermosiphon without stopping the heat production. The operation of the HPS is modelled using TRNSYS software. The model is validated using results of an experimental study carried out on a HPS prototype working with R407C. Annual simulations of the HPS coupled to a hotel are run in order to evaluate annual performance and energy consumption of the system. The results are compared to the ones of a standard reversible HP. Depending on the scenario, savings in electric energy consumption and annual performance improvement can reach respectively 55% and 19%.

/pdf/modelling-and-simulation-of-a-heat-pump-for-simultaneous-4skqxef5ze.pdf

Yves Lénat

Papers

Design and simulation of a heat pump for simultaneous heating and cooling using HFC or CO2 as a working fluid

Experimental study of an air-source heat pump for simultaneous heating and cooling – Part 2: Dynamic behaviour and two-phase thermosiphon defrosting technique

Experimental study of an air-source heat pump for simultaneous heating and cooling - Part 1: Basic concepts and performance verification

Modelling and simulation of a heat pump for simultaneous heating and cooling