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Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "B: Energy and Environment".

Deadline for manuscript submissions: closed (22 June 2021) | Viewed by 40017

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Special Issue Editors

Prof. Dr. Fabio Polonara

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Guest Editor

Dipartimento di Ingegneria Industriale e Scienze Matematiche (DIISM), Universita' Politecnica delle Marche, 60131 Ancona, Italy
Interests: refrigeration; refrigerants; thermodynamic properties; heat pumps; demand side management; energy planning; LNG
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Alessia Arteconi

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Guest Editor

1. Dipartimento di Ingegneria, Industriale e Scienze Matematiche, Università Politecnica delle Marche, via brecce bianche 1, 60131 Ancona, Italy
2. Department of Mechanical Engineering, KU Leuven, B-3000 Leuven, Belgium
Interests: demand side management; heat pumps; energy efficiency; renewable energy; energy transition
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Refrigeration, air conditioning, and heat pumps (RACHP) have an important impact on the final energy uses of many sectors of modern society, such as residential, commercial, industrial, transport, and automotive.

Moreover, they have also an important environmental impact due to the working fluids that deplete the stratospheric ozone layer, and which are being phased out according to the Montreal Protocol (1989).

Last, but not least, high-global-working-potential (GWP) working fluids (directly) and energy consumption (indirectly) are responsible for a non-negligible quota of greenhouse gas (GHG) emissions in the atmosphere, therefore impacting climate change. To cope with this aspect, the Kigali Amendment of the Montreal Protocol (2016) has started a phase-down procedure for HFCs, to be completed by the mid-21st century.

All these issues will pose great challenges to the RACHP industry over the next few decades, such as:

the search for new working fluids, able to substitute high-GWP HFCs;
the safety aspects associated to the mostly flammable alternatives to high-GWP HFCs;
the expected growth of air conditioning in developing countries and the subsequent increase in GHG emissions.

The common ground for all these challenges is that the energy efficiency of components and systems has to increase in order to keep energy consumption and GHG emissions associated with RACHP under control.

The topics to be addressed in this Special Issue on “Refrigeration, Air Conditioning and Heat Pumps” include but are not limited to:

Search for alternative, low-GWP working fluids;
Natural refrigerants and their applications;
Advanced thermodynamic analyses of reverse cycles and their applications;
Energy efficiency of vapor compression components and systems;
Demand side management and integration with renewables;
Safety issues and risk assessment for flammable refrigerants;
Control and operations;
Not-in-kind alternatives to vapor compression;
Energy efficiency of RACHP applications (domestic, commercial, industrial, residential, transport, automotive);
Environmental impacts of RACHP;
Market trends and analyses.

Prof. Fabio Polonara
Prof. Alessia Arteconi
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Refrigeration
Air conditioning
Heat pumps
Natural refrigerants
Hydro-fluorocarbons (HFCs)
Hydro-fluoro-olefins (HFOs)
Ozone depletion potential (ODP)
Global warming potential (GWP)
Greenhouse gases (GHG)
Total equivalent warming impact (TEWI)
Life cycle climate performance (LCCP)
Vapor compression
Thermodynamic analysis
Energy efficiency
Not-in-kind technologies
Absorption and adsorption
District cooling
Evaporative cooling
Magnetic refrigeration
Demand side management
Renewable energy
Components and systems
Cold chain and its applications
Safety issues
Risk assessment

Published Papers (11 papers)

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Research

26 pages, 4319 KiB

Open AccessArticle

Using Heat Pumps to Improve the Efficiency of Combined-Cycle Gas Turbines

by Vitaly Sergeev, Irina Anikina and Konstantin Kalmykov

Energies 2021, 14(9), 2685; https://0-doi-org.brum.beds.ac.uk/10.3390/en14092685 - 07 May 2021

Cited by 9 | Viewed by 2887

Abstract

This paper studies the integration of heat pump units (HPUs) to enhance the thermal efficiency of a combined heat and power plant (CHPP). Different solutions of integrate the HPUs in a combined-cycle gas turbine (CCGT) plant, the CCGT-450, are analyzed based on simulations developed on “United Cycle” computer-aided design (CAD) system. The HPUs are used to explore low-potential heat sources (LPHSs) and heat make-up and return network water. The use of HPUs to regulate the gas turbine (GT) intake air temperature during the summer operation and the possibility of using a HPU to heat the GT intake air and replace anti-icing system (AIS), over the winter at high humidity conditions were also analyzed. The best solution was obtained for the winter operation mode replacing the AIS by a HPU. The simulation results indicated that this scheme can reduce the underproduction of electricity generation by the CCGT unit up to 14.87% and enhance the overall efficiency from 40.00% to 44.82%. Using a HPU with a 5.04 MW capacity can save $309,640 per each MW per quarter. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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Graphical abstract

20 pages, 3441 KiB

Open AccessArticle

Real Air-Conditioning Performance of Ejector Refrigerator Based Air-Conditioner Powered by Low Temperature Heat Source

by Tongchana Thongtip and Natthawut Ruangtrakoon

Energies 2021, 14(3), 711; https://0-doi-org.brum.beds.ac.uk/10.3390/en14030711 - 30 Jan 2021

Cited by 2 | Viewed by 2169

Abstract

In this present work, the air-conditioning test performance of an ejector refrigerator-based air-conditioner (ERAC) was proposed. The ERAC was operated as the water chiller to produce the cooling load up to 4.5 kW. The chilled water temperature was later supplied to the fan-coil unit for producing the thermal comfort condition. The cooling water used to cool the condenser was achieved from the cooling tower which was operated under the hot and humid ambient. This is to demonstrate the feasibility of using the ERAC in real working conditions. The cooling load supplied to the air-conditioned space was applied by the air heater. The ERAC could efficiently be operated to produce the thermal comfort condition which was driven by the hot water temperature (T_hot) of 90–98 °C. The system performance could vary with the heat source temperatures, cooling load, primary nozzle, and air-conditioned space temperature. The optimal performance was determined when varying the T_hot, and, hence, the optimal T_hot was indicated. The optimal T_hot varied significantly with variations in the working condition. The test results demonstrated high potential to further using the ejector refrigeration system in the actual air conditioning application. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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30 pages, 8987 KiB

Open AccessFeature PaperArticle

Energy Flexibility as Additional Energy Source in Multi-Energy Systems with District Cooling

by Alice Mugnini, Gianluca Coccia, Fabio Polonara and Alessia Arteconi

Energies 2021, 14(2), 519; https://0-doi-org.brum.beds.ac.uk/10.3390/en14020519 - 19 Jan 2021

Cited by 7 | Viewed by 2583

Abstract

The integration of multi-energy systems to meet the energy demand of buildings represents one of the most promising solutions for improving the energy performance of the sector. The energy flexibility provided by the building is paramount to allowing optimal management of the different available resources. The objective of this work is to highlight the effectiveness of exploiting building energy flexibility provided by thermostatically controlled loads (TCLs) in order to manage multi-energy systems (MES) through model predictive control (MPC), such that energy flexibility can be regarded as an additional energy source in MESs. Considering the growing demand for space cooling, a case study in which the MPC is used to satisfy the cooling demand of a reference building is tested. The multi-energy sources include electricity from the power grid and photovoltaic modules (both of which are used to feed a variable-load heat pump), and a district cooling network. To evaluate the varying contributions of energy flexibility in resource management, different objective functions—namely, the minimization of the withdrawal of energy from the grid, of the total energy cost and of the total primary energy consumption—are tested in the MPC. The results highlight that using energy flexibility as an additional energy source makes it possible to achieve improvements in the energy performance of an MES building based on the objective function implemented, i.e., a reduction of 53% for the use of electricity taken from the grid, a 43% cost reduction, and a 17% primary energy reduction. This paper also reflects on the impact that the individual optimization of a building with a multi-energy system could have on other users sharing the same energy sources. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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21 pages, 2543 KiB

Open AccessArticle

Water Extraction from Air: A Proposal for a New Indicator to Compare Air Water Generators Efficiency

by Lucia Cattani, Anna Magrini and Paolo Cattani

Energies 2021, 14(1), 224; https://0-doi-org.brum.beds.ac.uk/10.3390/en14010224 - 04 Jan 2021

Cited by 12 | Viewed by 4190

Abstract

Water extraction from air, based on reverse cycle systems, is becoming a technology more and more diffused and various models of air to water generators (AWG) are now available, all claiming the best efficiency. To date, there is not a standard indicator stating energy efficiency for AWGs, neither in the literature nor in technical practice. The only evaluation parameter, that can be found is a sort of specific energy consumption (SEC) without any clear indications about the involved calculation terms, definition of hypotheses, or environmental conditions. The current work is a first proposal of an indicator to standardise the AWG efficiency evaluation. The indicator is called WET (Water Energy Transformation); it states water production as a useful effect of an AWG machine and calculates its energy performance with an approach similar to COP (Coefficient of Performance) and EER (Energy Efficiency Ratio) evaluation. The indicator is meant to be a normalised tool that permits comparing different AWG machines, but it is also the first part of a wider study, currently under development that is oriented to obtain a global index formulation that combines WET itself, EER and COP, and it is intended for a comprehensive evaluation of all the useful effects of a reverse cycle in integrated machines, in compliance with the current efficiency evaluation approach. The current paper presents the WET equation, with a discussion about involved terms, a set of normalised calculation conditions and some application examples, including a comparison with SEC. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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23 pages, 13800 KiB

Open AccessArticle

Experimental Investigation of Desiccant Dehumidification Cooling System for Climatic Conditions of Multan (Pakistan)

by Muhammad Aleem, Ghulam Hussain, Muhammad Sultan, Takahiko Miyazaki, Muhammad H. Mahmood, Muhammad I. Sabir, Abdul Nasir, Faizan Shabir and Zahid M. Khan

Energies 2020, 13(21), 5530; https://0-doi-org.brum.beds.ac.uk/10.3390/en13215530 - 22 Oct 2020

Cited by 19 | Viewed by 3429

Abstract

In this study, experimental apparatus of desiccant dehumidification was developed at lab-scale, using silica gel as a desiccant material. Experimental data were obtained at various ambient air conditions, while focusing the climatic conditions of Multan (Pakistan). A steady-state analysis approach for the desiccant dehumidification process was used, and thereby the slope of desiccant dehumidification line on psychrometric chart (ϕ*) was determined. It has been found that ϕ* = 0.22 in case of silica gel which is lower than the hydrophilic polymeric sorbent, i.e., ϕ* = 0.31. The study proposed two kinds of systems, i.e., (i) standalone desiccant air-conditioning (DAC) and (ii) Maisotsenko-cycle-assisted desiccant air-conditioning (M-DAC) systems. In addition, two kinds of desiccant material (i.e., silica gel and hydrophilic polymeric sorbent) were investigated from the thermodynamic point of view for both system types, using the experimental data and associated results. The study aimed to determine the optimum air-conditioning (AC) system type, as well as adsorbent material for building AC application. In this regard, perspectives of dehumidification capacity, cooling capacity, and thermal coefficient of performance (COP) are taken into consideration. According to the results, hydrophilic polymeric sorbent gave a higher performance, as compared to silica gel. In case of both systems, the performance was improved with the addition of Maisotsenko cycle evaporative cooling unit. The maximum thermal COP was achieved by using a polymer-based M-DAC system, i.e., 0.47 at 70 °C regeneration temperature. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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16 pages, 4436 KiB

Open AccessArticle

Temperature Distribution in Insulated Temperature-Controlled Container by Numerical Simulation

by Bin Li, Jiaming Guo, Jingjing Xia, Xinyu Wei, Hao Shen, Yongfeng Cao, Huazhong Lu and Enli Lü

Energies 2020, 13(18), 4765; https://0-doi-org.brum.beds.ac.uk/10.3390/en13184765 - 12 Sep 2020

Cited by 7 | Viewed by 3756

Abstract

Cold-storage containers are widely used in cold-chain logistics transportation due to their energy saving, environmental protection, and low operating cost. The uniformity of temperature distribution is significant in agricultural-product storage and transportation. This paper explored temperature distribution in the container by numerical simulation, which included ventilation velocity and the fan location. Numerical model/numerical simulation showed good agreement with experimental data in terms of temporal and spatial air temperature distribution. Results showed that the cooling rate improved as velocity increased, and temperature at 45 min was the lowest, when velocity was 16 m/s. Temperature-distribution uniformity in the compartment became worse with the increase in ventilation velocity, but its lowest temperature decreased with a velocity increase. With regard to fan energy consumption, the cooling rate of the cooling module, and temperature-field distribution in the product area, velocity of 12 m/s was best. Temperature standard deviation and nonuniformity coefficient in the container were 0.87 and 2.1, respectively, when fans were located in the top four corners of the container. Compared with before, the average temperature in the box was decreased by 0.12 °C, and the inhomogeneity coefficient decreased by more than twofold. The results of this paper provide a better understanding of temperature distribution in cold-storage containers, which helps to optimize their structure and parameters. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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19 pages, 4833 KiB

Open AccessArticle

Experimental Investigation on a Vapor Injection Heat Pump System with a Single-Stage Compressor

by Hongzhi Liu, Katsunori Nagano, Takao Katsura and Yue Han

Energies 2020, 13(12), 3133; https://0-doi-org.brum.beds.ac.uk/10.3390/en13123133 - 17 Jun 2020

Cited by 6 | Viewed by 5141

Abstract

In this study, a heat pump of 10 kW with vapor injection using refrigerant of R410A was developed. A vapor injection pipe connecting a gas–liquid separator at the outlet of the main expansion valve and the suction of a single-stage rotary compressor was designed. The heating performance of this vapor injection heat pump was investigated and analyzed at different compressor frequencies and primary temperatures. The experimental results show that for the heat pump without vapor injection, the heating capacity increased linearly with the compressor frequency, while the heating coefficient of performance (COP) decreased linearly with the compressor frequency for each tested primary temperature. The developed vapor injection technique is able to increase the heat pump system’s heating capacity and heating COP when the injection ratio R falls into the range 0.16–0.17. The refrigerant mass flow rate can be increased in the vapor injection heat pump cycle due to the decreased specific volume of the suction refrigerant. The power consumption of vapor injection heat pump cycle almost remains the same with that of the conventional heat pump cycle because of the increased refrigerant mass flow rate and the decreased compression ratio. Finally, it was found that the developed vapor injection cycle is preferable to decreasing the compressor’s discharge temperature. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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18 pages, 6378 KiB

Open AccessArticle

Study on Desiccant and Evaporative Cooling Systems for Livestock Thermal Comfort: Theory and Experiments

by Muhammad Kashif, Hassan Niaz, Muhammad Sultan, Takahiko Miyazaki, Yongqiang Feng, Muhammad Usman, Muhammad W. Shahzad, Yasir Niaz, Muhammad M. Waqas and Imran Ali

Energies 2020, 13(11), 2675; https://0-doi-org.brum.beds.ac.uk/10.3390/en13112675 - 26 May 2020

Cited by 22 | Viewed by 4498

Abstract

The present study considers evaporative cooling and desiccant unit-based air-conditioning (AC) options for livestock AC application. In this regard, proposed systems are investigated by means of experiments and thermodynamic investigations. Air-conditioning requirements for animals are theoretically investigated and temperature-humidity index (THI) is estimated. A lab-scale heat mass exchanger based on the Maisotsenko-cycle evaporative cooling conception (MEC) is set up and its performance is evaluated at different ambient air conditions. In addition, a desiccant-based air-conditioning (DAC) unit is thermodynamically evaluated using a steady-state model available in the literature. The study focuses on the ambient conditions of Multan which is the 5th largest city of Pakistan and is assumed to be a typical hot city of southern Punjab. The study proposed three kinds of AC combination i.e., (i) stand-alone MEC, (ii) stand-alone desiccant AC, and (iii) M-cycle based desiccant AC systems. Wet bulb effectiveness of the stand-alone MEC unit resulted in being from 64% to 78% whereas the coefficient of performance for stand-alone desiccant AC and M-cycle based desiccant AC system was found to be 0.51 and 0.62, respectively. Results showed that the stand-alone MEC and M-cycle based desiccant AC systems can achieve the animals’ thermal comfort for the months of March to June and March to September, respectively, whereas, stand-alone desiccant AC is not found to be feasible in any month. In addition, the ambient situations of winter months (October to February) are already within the range of animal thermal comfort. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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23 pages, 15201 KiB

Open AccessArticle

A Compact Thermally Driven Cooling System Based on Metal Hydrides

by Christoph Weckerle, Marius Dörr, Marc Linder and Inga Bürger

Energies 2020, 13(10), 2482; https://0-doi-org.brum.beds.ac.uk/10.3390/en13102482 - 14 May 2020

Cited by 10 | Viewed by 2646

Abstract

Independent of the actual power train, efficiency and a high driving range in any weather conditions are two key requirements for future vehicles. Especially during summertime, thermally driven air conditioning systems can contribute to this goal as they can turn the exhaust heat of internal combustion engines, fuel cells or of any additional fuel-based heating system into a cooling effect. Amongst these, metal hydride cooling systems (MHCSs) promise very high specific power densities due to the short reaction times as well as high reaction enthalpies. Additionally, the working fluid hydrogen has a very low global warming potential. In this study, the experimental results of a compact and modular MHCS with a specific cooling power of up to 585 W

{kg}_{MH}^{- 1}

referred to one cold generating MH are presented, while reactor and MH weight in total is less than 30 kg and require a volume < 20 dm³. The system is driven by an auxiliary fuel heating system and its performance is evaluated for different operating conditions, e.g., temperature levels and half-cycle times. Additionally, a novel operation optimization of time-shifted valve switching to increase the cooling power is implemented and investigated in detail. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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19 pages, 5528 KiB

Open AccessArticle

Investigation and Analysis of R463A as an Alternative Refrigerant to R404A with Lower Global Warming Potential

by Piyanut Saengsikhiao, Juntakan Taweekun, Kittinan Maliwan, Somchai Sae-ung and Thanansak Theppaya

Energies 2020, 13(6), 1514; https://0-doi-org.brum.beds.ac.uk/10.3390/en13061514 - 23 Mar 2020

Cited by 29 | Viewed by 4430

Abstract

This research presents the development of R463A refrigerant, a nonflammable refrigerant that was retrofitted to replace R404A. R463A is primarily composed of hydrofluorocarbons/hydrocarbons/carbon dioxide (HFCs/HCs/CO₂), and has global-warming potential (GWP) of 1494. It is a nonazeotropic mixture of R32 (36%), R125 (30%), R134a (14%), R1234yf (14%), and R744 (6%). R463A is composed of polyol ester oil (POE), and it is classified as a Class A1 incombustible and nontoxic refrigerant. R463A has a higher cooling capacity (Qe) than that of R404A, as it is composed of hydrofluorocarbons (HFCs) R32 and carbon dioxide (CO₂) R744, and has lower GWP than that of R404A due to the use of hydrofluoroolefins (HFOs) from R1234yf. The results of this research showed that R463A can be retrofitted to replace R404A due to its composition of POE, Class A1 incombustibility, and lower toxicity. The properties of R463A and R404A, as analyzed using national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software, are in accordance with the CAN/ANSI/AHRI540 standards of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI). The normal boiling point of R463A was found to be higher than that of R404A by 23%, with a higher cooling capacity and a 63% lower GWP value than that of R404A. The critical pressure and temperature of R463A were found to be higher than those of R404A; it can be used in a high-ambient-temperature environment, has higher refrigerant and heat-rejection effects, and has lower GWP than that of R404A by 52% due to the HFOs from the R1234yf component. The cooling coefficient of performance (COPc) of R463A was found to be higher than that of R404A by 10% under low-temperature applications. R463A is another refrigerant option that is composed of 7% carbon dioxide (CO₂), and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs, HFOs, HCs, and natural refrigerants, which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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17 pages, 6373 KiB

Open AccessArticle

Numerical Study on Effects of Air Return Height on Performance of an Underfloor Air Distribution System for Heating and Cooling

by Yaming Fan, Xiangdong Li, Minfeng Zheng, Rengui Weng and Jiyuan Tu

Energies 2020, 13(5), 1070; https://0-doi-org.brum.beds.ac.uk/10.3390/en13051070 - 01 Mar 2020

Cited by 6 | Viewed by 2083

Abstract

The exhaust/return-split configuration is regarded as an important upgrade of traditional under-floor-air-distribution (UFAD) systems due to its higher energy efficiency. Moreover, existing studies are mostly focused on the effect of the return vent height on the performance of an UFAD system under cooling conditions. Knowledge of the performance under heating conditions is sorely lacking. This paper presents a numerical evaluation of the performance characteristics of an UFAD system with six different heights of the return vents in heating operation by comprehensively considering thermal comfort, air quality, and energy consumption. The results show that, in the heating mode, the general thermal comfort (predicted mean vote-predicted percentage dissatisfied (PMV-PPD) values) and indoor air quality indices (mean age of air and volatile organic compounds (VOCs) concentration) were greatly improved and energy consumption was slightly reduced with a lower return vent height. Although these were opposite to the findings of our previous study regarding the performance in cooling mode, an optimal return vent height in terms of the comprehensive all-year performance can be recommended. This method provides insight into the design and optimization of the return vent height of UFAD for space heating and cooling. Full article

(This article belongs to the Special Issue Refrigeration, Air Conditioning and Heat Pumps: Energy and Environmental Issues II)

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