Editorial

3 pages, 175 KiB

Open AccessEditorial

Heat Transfer, Refrigeration and Heat Pumps

by Moonis R. Ally and Brian Fricke

Energies 2021, 14(23), 7988; https://doi.org/10.3390/en14237988 - 30 Nov 2021

Cited by 1 | Viewed by 1547

The Special Issue entitled “Heat Transfer, Refrigeration and heat Pumps” accepted papers covering a wide range of topics related to heat pumps, thermal energy storage, and low-Global Warming Potential (GWP) alternative refrigerants [...] Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

Research

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15 pages, 3010 KiB

Open AccessArticle

Numerical Study of Hydrocarbon Charge Reduction Methods in HVAC Heat Exchangers

by Ehsan Allymehr, Geir Skaugen, Torsten Will, Ángel Álvarez Pardiñas, Trygve Magne Eikevik, Armin Hafner and Lena Schnabel

Energies 2021, 14(15), 4480; https://doi.org/10.3390/en14154480 - 24 Jul 2021

Cited by 4 | Viewed by 2080

Abstract

Required refrigerant charge in heat pump systems with propane is analyzed. Two systems are compared: the first a direct heat pump, with fin-and-tube heat exchangers, and the second an indirect system, with plate heat exchangers with an additional brine-to-air heat exchanger. Each system [...] Read more.

Required refrigerant charge in heat pump systems with propane is analyzed. Two systems are compared: the first a direct heat pump, with fin-and-tube heat exchangers, and the second an indirect system, with plate heat exchangers with an additional brine-to-air heat exchanger. Each system was considered to be able to work reversibly, with 5

k W

design cooling capacity in summer and 8

k W

design heating capacity in winter. Two separately developed simulation codes were used to calculate the required refrigerant charge and the efficiency of each of the systems. The charge was reduced by the use of microfinned tubes up to 22% in direct system reduced using microfinned tubes compared to the smooth tube. For the indirect system using specially designed plate heat exchangers with the minimum internal volume, their charge was reduced by up to 66% compared to normal plate heat exchangers. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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17 pages, 2942 KiB

Open AccessArticle

A Flow Rate Dependent 1D Model for Thermally Stratified Hot-Water Energy Storage

by Joseph Rendall, Fernando Karg Bulnes, Kyle Gluesenkamp, Ahmad Abu-Heiba, William Worek and Kashif Nawaz

Energies 2021, 14(9), 2611; https://doi.org/10.3390/en14092611 - 02 May 2021

Cited by 7 | Viewed by 2509

Abstract

Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained [...] Read more.

Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems. The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used in building energy simulations because of the short computation time but often do not include flow-rate dependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, and two convection eddy-diffusivity models were compared with experimental data sets for discharging a 50-gal residential tank and recharging the tank with hot water from an external hot-water source. A minimum and maximum relationship for the eddy diffusivity factor were found at Re <2100 and >10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold water at the bottom. The root mean square error decreased from >4 °C to near 2 °C when considering flow-based mixing models during heating, while the exponential decay of the eddy diffusion results in a root mean square error reduction of 1 °C for cone-shaped diffusers that begin to relaminarize flow at the inlet. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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15 pages, 3928 KiB

Open AccessArticle

Pressure Exchanger for Energy Recovery in a Trans-Critical CO₂ Refrigeration System

by Ahmed Elatar, Brian Fricke, Vishaldeep Sharma and Kashif Nawaz

Energies 2021, 14(6), 1754; https://doi.org/10.3390/en14061754 - 22 Mar 2021

Cited by 4 | Viewed by 2518

Abstract

Trans-critical CO₂ vapor compression (VC) refrigeration cycles require a high compression ratio, which is associated with high expansion losses. To recover these expansion losses, a pressure exchange process between the low- and high-pressure sides of the VC cycle is proposed and examined [...] Read more.

Trans-critical CO₂ vapor compression (VC) refrigeration cycles require a high compression ratio, which is associated with high expansion losses. To recover these expansion losses, a pressure exchange process between the low- and high-pressure sides of the VC cycle is proposed and examined in this study. The proposed pressure exchange system is an open type constant volume process where the high- and low-pressure flows mix inside the system. This prototype is inspired by the pressure exchangers used in reverse-osmosis (RO) desalination systems. In this system, a 2D model was generated and modeled using the computational fluid dynamics (CFD) technique. The numerical model ignored any losses due to leakage or hydraulic friction and the process is considered adiabatic. For the modeling, it was assumed that the inlet conditions for the two pressure exchanger flows are similar to the flow conditions at the evaporator and gas cooler outlets in a VC cycle. Two parameters are examined to test the validity of the system and understand their effect on the performance, including the inlet flow rate represented by the inlet velocity and the process time represented by the speed of rotation. A total of nine cases were simulated and analyzed in this study. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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24 pages, 7710 KiB

Open AccessArticle

Heat Pump Bridge Analysis Using the Modified Energy Transfer Diagram

by Florian Schlosser, Heinrich Wiebe, Timothy G. Walmsley, Martin J. Atkins, Michael R. W. Walmsley and Jens Hesselbach

Energies 2021, 14(1), 137; https://doi.org/10.3390/en14010137 - 29 Dec 2020

Cited by 10 | Viewed by 2263

Abstract

Heat pumps are the key technology to decarbonise thermal processes by upgrading industrial surplus heat using renewable electricity. Existing insight-based integration methods refer to the idealised Grand Composite Curve requiring the full exploitation of heat recovery potential but leave the question of how [...] Read more.

Heat pumps are the key technology to decarbonise thermal processes by upgrading industrial surplus heat using renewable electricity. Existing insight-based integration methods refer to the idealised Grand Composite Curve requiring the full exploitation of heat recovery potential but leave the question of how to deal with technical or economic limitations unanswered. In this work, a novel Heat Pump Bridge Analysis (HPBA) is introduced for practically targeting technical and economic heat pump potential by applying Coefficient of Performance curves into the Modified Energy Transfer Diagram (METD). Removing cross-Pinch violations and operating heat exchangers at minimum approach temperatures by combined application of Bridge Analysis increases the heat recovery rate and reduce the temperature lift to be pumped at the same time. The insight-based METD allows the individual matching of heat surpluses and deficits of individual streams with the capabilities and performance of different market-available heat pump concepts. For an illustrative example, the presented modifications based on HPBA increase the economically viable share of the technical heat pump potential from 61% to 79%. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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19 pages, 3939 KiB

Open AccessArticle

Cooling and Mechanical Performance Analysis of a Trapezoidal Thermoelectric Cooler with Variable Cross-Section

by Tianbo Lu, Yuqiang Li, Jianxin Zhang, Pingfan Ning and Pingjuan Niu

Energies 2020, 13(22), 6070; https://doi.org/10.3390/en13226070 - 19 Nov 2020

Cited by 10 | Viewed by 2435

Abstract

In this study, a full-scale three-dimensional trapezoidal thermoelectric cooler model is constructed to study its cooling performance and mechanical reliability using finite element simulation. Temperature dependent material properties are considered in this work. The boundary conditions similar to those in a real experimental [...] Read more.

In this study, a full-scale three-dimensional trapezoidal thermoelectric cooler model is constructed to study its cooling performance and mechanical reliability using finite element simulation. Temperature dependent material properties are considered in this work. The boundary conditions similar to those in a real experimental environment are applied. The effects of the input electrical current and geometry of the thermoelectric leg on the cooling performance and reliability of a trapezoidal thermoelectric cooler are analyzed, and a comparison is made with a rectangular thermoelectric cooler. The results indicate that increasing the leg height and the variable cross-sectional design of the leg can improve the cooling performance of the trapezoidal thermoelectric cooler. Compared to the original rectangular thermoelectric cooler, the minimum chip temperature was reduced by 0.87% under the trapezoidal thermoelectric cooler with optimized geometry. Furthermore, increasing the leg height enhances the mechanical reliability of the trapezoidal thermoelectric cooler, while the trapezoidal design of the leg reduces its mechanical reliability. The maximum von Mises stress of the leg for the trapezoidal thermoelectric cooler with optimal cooling performance increased by 40.1%. The results of this work provide useful guidance for the structural design of trapezoidal thermoelectric coolers. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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18 pages, 3147 KiB

Open AccessArticle

Energy and Exergy Analysis of Low-Global Warming Potential Refrigerants as Replacement for R410A in Two-Speed Heat Pumps for Cold Climates

by Bo Shen and Moonis R. Ally

Energies 2020, 13(21), 5666; https://doi.org/10.3390/en13215666 - 29 Oct 2020

Cited by 14 | Viewed by 2437

Abstract

Heat pumps (HPs) are being developed with a new emphasis on cold climates. To lower the environmental impact of greenhouse gas (GHG) emissions, alternate low global warming potential (GWP) refrigerants must also replace the exclusive use of the refrigerant R410A, preferably without re-engineering [...] Read more.

Heat pumps (HPs) are being developed with a new emphasis on cold climates. To lower the environmental impact of greenhouse gas (GHG) emissions, alternate low global warming potential (GWP) refrigerants must also replace the exclusive use of the refrigerant R410A, preferably without re-engineering the mechanical hardware. In this paper, we analyze the performance of four low-GWP alternative refrigerants (R32, R452B, R454B, and R466A) relative to the conventional R410A and draw conclusions on the relative performances for providing heating in cold climates based on the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) 210/240 standard for two-speed heat pumps. The simulations are carried using the Department of Energy, Oak Ridge National Laboratory (DOE/ORNL) Heat Pump Design Model (HPDM), a well-known heating, ventilation, and air conditioning (HVAC) modeling and design tool in the public domain and the HVAC research and development community. The results of the simulation are further scrutinized using exergy analysis to identify sources of systemic inefficiency, the root cause of lost work. This rigorous approach provides an exhaustive analysis of alternate low-GWP refrigerants to replace R410A using available compressors and system components, without compromising performance. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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13 pages, 2719 KiB

Open AccessArticle

Virtual Pressure Sensor for Electronic Expansion Valve Control in a Vapor Compression Refrigeration System

by Jian Sun, Jin Dong, Bo Shen and Wenhua Li

Energies 2020, 13(18), 4917; https://doi.org/10.3390/en13184917 - 19 Sep 2020

Cited by 2 | Viewed by 2189

Abstract

Virtual sensor technology, which uses simulation models/algorithms to calculate a value to represent an unmeasured variable or replace a directly measured reading, has attracted many studies in the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry. However, most virtual sensor technologies are developed [...] Read more.

Virtual sensor technology, which uses simulation models/algorithms to calculate a value to represent an unmeasured variable or replace a directly measured reading, has attracted many studies in the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry. However, most virtual sensor technologies are developed for fault detection and diagnostics (FDD) purposes, which generally compare the virtual sensor values with actual measured values to detect if any fault occurred and identify the causes that led to the fault. It is rare to see studies focus on control performance of virtual sensors after substituting an actual sensor. This is particularly important for the system with no redundant sensor since a virtual sensor is the most effective way to operate the system in the desirable region when any sensor failure occurs. To address this gap, this paper develops a new virtual pressure sensor technology to substitute the actual pressure measurement for electronic expansion valve (EXV) control in a vapor compression refrigeration system by integrating compressor and valve characteristics. The control performance of this proposed virtual pressure sensor technology under various operating conditions is validated with experimental data. Closed loop EXV control simulations with the proposed virtual pressure sensor are conducted, and the results are analyzed. Full article

(This article belongs to the Special Issue Heat Transfer, Refrigeration and Heat Pumps)

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