The energy and economic benefits derivable from various waste heat-driven systems integrated with a R744 supermarket refrigeration system were assessed across various locations in India, the Middle East, Europe and the US. The investigated heat-driven systems included a R717 multi-ejector chiller (HEC), a LiBr-H2O absorption chiller (ABC) and an organic Rankine cycle (ORC) operating with isopentane. The waste heat available from the refrigeration unit was utilized to power the HEC and the ABC unit for subcooling the R744 and the ORC unit to generate electricity. A R744 supermarket refrigeration system equipped with a R290 dedicated mechanical subcooling (DMS) unit was used as the baseline. The HEC-based system was found to outperform the ABC-based solution and the ORC-based system at ambient temperatures above 27 degrees C and 30 degrees C, respectively, with efficiency improvements of 4.8 % - 9.3 % relative to the DMS-based system. In terms of energy savings, the HEC-based system was found to be more effective in the hot semi-arid climatic zones in India (4.0-4.3 %) and the hot desert climates experienced in the Middle East (4.5-5.3 %) and the US (2.4-3.9 %), while the ORC-based solution was adjudged the best for use in the tropical climates of India and all the European cities. The economic analysis suggested the HEC-based system to be the best solution, having relatively lower recovery time compared to the ORC unit in all the locations except in Europe, while the ABC-based system was deemed unsuitable due to significantly higher installation costs and relatively lower energy savings.

In this work a novel technology to adapt transcritical R744 supermarket refrigeration systems to warm and hot climates as well as to rising temperatures was proposed and exhaustively investigated. The novel solution consisted of a booster device (increasing the transcritical fluid R744 pressure) followed by an air-cooled gas cooler and located between the conventional air-cooled condenser/gas cooler and high-pressure expansion valve. The results obtained revealed energy savings by from 2.31 % to 2.91 % in Seville (Spain) and from 4.64 % to 5.73 % in New Delhi (India). To further increase the energy benefits from the proposed technology, the use of an expander replacing the high-pressure expansion valve was also considered. As a consequence, energy savings by 7.80 % in Seville and 14.44 % in New Delhi with an additional investment recovery time of about 3 years in both of the selected locations were assessed.

Due to the low critical temperature of R744, supermarket refrigeration systems using this working fluid widely operate in transcritical operating conditions, causing severe penalizations on their energy efficiency. On the one hand, this study explored the economic benefits from integrating a thermal energy ice storage to cool down the R744 leaving the condenser/gas cooler to address the aforementioned performance disadvantages. On the other hand, the literature review brought to light the lack of an algorithm to cost-effectively and dynamically optimize the charging and discharging cycles of thermal energy ice storages in transcritical R744 refrigeration systems, thus limiting their spread in supermarkets. Therefore, an innovative algorithm tailored to different climate conditions was developed in this study with the goal of minimizing yearly electricity expenses by accounting for supermarket refrigeration demand, ambient temperature, and electricity price. The novel optimization method incorporated constraints that reflected realistic requirements for the thermal energy ice storage’s expected capacity, its selected compressor, and desired level of maximum charge/discharge rate. Simulations performed in Seville (Spain), Athens (Greece) and New Delhi (India) revealed a reduction in the annual electricity bill of the supermarket by 6.9 %, 5.7 % and 12.5 % compared to the case without thermal energy ice storage thanks to the new optimization strategy, respectively. The results obtained showcase the efficacy of the innovative algorithm, suggesting a promising approach to improve the energy efficiency and cost-effectiveness in the commercial refrigeration industry.

Data centres generate a significant amount of waste heat that is commonly rejected to the environment, resulting in both energy losses and environmental concerns. This study proposes and evaluates novel configurations of a hybrid compression-absorption-resorption cooling cycle (HCARC) for recovering and utilising waste heat from data centres. The HCARC integrated two sub-cycles: (i) a compression-absorption-resorption sub-cycle (CARC) and (ii) a heat pump cycle. Two configurations were classified based on the heat pump: C1 integrated a vapour compression heat pump, while C2 incorporated an absorption heat transformer, with the CARC. The thermodynamic performance of the proposed configuration was evaluated using the first and second laws of thermodynamics, through thermal coefficient of performance (COPth) and exergy efficiency (7ex). A parametric analysis examined the influence of operating parameters, waste heat temperature, and ambient temperature on COPth and 7ex. An economic assessment quantified the benefits for HCARC in terms of unit production cost for cooling (UPCC, in USD per kWh) and payback period, compared with absorption cycle configurations as base cases. The results showed that configuration C1 achieved a maximum improvement of 77 % in COPth, 30 % in 7ex, and an 18 % reduction in UPCC, compared to the base cases. The HCARC demonstrated a significant economic advantage, with annual savings of about 1.3 million USD, resulted in a payback period of about 8 months for C1, highlighting the techno-economic viability of HCARC for the recovery and utilisation of waste heat from data centres.

The subcooling potential of a novel R717-based waste heat-driven multi-ejector chiller (HEC) integrated with an R744 refrigeration system was evaluated for use in supermarkets. The performance was compared with an R744 refrigeration system coupled to R718- and R600a-based HECs, an R744 system equipped with parallel compression (PC), and a standard R744 booster system (CB) in various warm and hot climatic locations. Integration of the R717-based HEC was found to improve the coefficient of performance by 3.7% at 27 °C to 12.1% at 45 °C compared to the R718, and by 1.6% at 27 °C to 7.6% at 45 °C compared to the R600a-based system. The energy-saving potential of the R717 system (6.2% to 9.4%) was also found to be higher than that of the R718 (0.7% to 2.8%) and R600a systems (2.5% to 6.6%). The use of the existing high-pressure controllers of the CB system was found to impose a relatively lower penalty on the system performance compared to the controllers of the PC system. Although the integration of the R718 system incurred a significantly lower additional investment, the recovery time of the R600a-based HEC (2.3–4.8 years) was found to be the shortest.

The rising global temperatures associated with global warming enforce to reduce the emissions from heating and cooling systems. Conventionally, the refrigeration and space heating demand of a supermarket is catered by the refrigeration system and a natural gas fired boiler/electric boiler/district heating network, respectively. The environmental and economic advantage of replacing these systems with a conventional booster CO2 refrigeration system with heat recovery and an integrated heat pump (CB_HP) were analysed in this study. The variation in ambient temperature, electricity price, heat selling price and heating and refrigeration demand of the supermarket on a cold day in Stockholm (Sweden) were considered for the analysis. Furthermore, the optimization of the economic performance of CB_HP for varying gas cooler pressure and outlet temperature was carried out. The results show that the total emissions and operating cost could be reduced by up to 94 % and 91 % as the conventional systems were replaced by CB_HP, respectively.

The target of this study is to experimentally compare the performance of three different expansion devices for small-capacity subcritical R744 vapour-compression refrigeration units. The first considered expansion device was the conventional high-pressure expansion valve, which was selected as the baseline. The second assessed expansion device was a two-phase ejector for expansion work recovery whose refrigerant flow was modulated via the pulse-width modulation (PWM) strategy. Finally, the PWM approach was employed for controlling the refrigerant flow of the ejector motive nozzle while the refrigerant was not permitted to be drawn by the ejector suction nozzle. The results showed that the motive nozzle controlled via PWM effect offers similar effectiveness to a conventional high-pressure expansion valve in the subcritical regime. Furthermore, it was observed that the PWM ejector is able to control the high pressure effectively while increasing the coefficient of performance (COP) by up to 5.3 % without and by up to 7.9 % with overfed evaporator compared to the baseline in the transition regime. The results also showed that the installation of the conventional high-pressure expansion valve is not necessary. Finally, the yearly performance of the aforementioned expansion devices was assessed in five different locations, i.e., Athens (Greece), Phoenix (USA), New Delhi (India), Riyadh (Saudi Arabia) and Bangkok (Thailand). The outcomes revealed that the PWM ejector allows for a higher in yearly average COP (COPyearly avg) from 4.9 % (in Athens) to 11.8 % (in Bangkok) over the baseline.

This study investigated the energy and economic benefits of a novel sub-cooling technique using a heat-driven multi-ejector chiller (HDEC) in R744 supermarket refrigeration systems. Two configurations were evaluated: a conventional booster system with HDEC (CBEC) and a parallel compression system with HDEC (PCEC). Among various natural refrigerants, R717 was identified as most suitable for the HDEC. Various multi-ejector combinations were examined to assess the potential for waste heat utilization and energy savings in the R744 refrigeration system. The CBEC system provided effective operation only at ambient temperatures above 31 degrees C, whereas the PCEC system was effective above 24 degrees C. Performance of the proposed configurations were compared with a conventional R744 booster system (CB) and a parallel compression system (PC) both devoid of HDEC. The PCEC system showed improvements in the coefficient-of-performance ranging from 4.2 % to 23.9 % at ambient temperatures between 28 degrees C and 40 degrees C compared to the baselines. In various warm-climatic zones, including India, the Middle East, Thailand, and the USA, energy savings of approximately 2.1 %-9.5 % were observed compared to the PC system. Economic analysis indicated a reasonable payback period of 2.1-2.7 years for the additional investment required for deploying the PCEC system in Phoenix.

Small-scale vapour-compression systems for refrigeration, air conditioning, and heat pump (RACHP) applications guarantee several essential human needs. The global energy and environmental policies have compelled these solutions to take a new sustainable growth path, i.e., the adoption of low global warming potential (GWP) refrigerants. The working fluids with GWP below 150 as substitutions in vapour-compression systems across six main applications have been exhaustively reviewed, and focus is given to the aspects of system performance, environmental impacts, operating conditions, and cost. Due to the negligible environmental impacts, natural refrigerants are prioritized to be selected as alternatives to high-GWP synthetics. R744 and R290 are the two most popular natural refrigerants employed across all applications. Compared with using R134a, R744 systems can save energy consumption by up to 37% in commercial refrigeration units while R290 systems can provide higher efficiencies for space heating at low ambient temperatures. R600 and R600a are used in domestic appliances to decrease energy consumption by up to 18.6% and to reduce flammability risks while mixing with R290. R1234yf, as a hydrofluoroolefin (HFO) with negligible-GWP, has been widely used as a substitution in mobile air-conditioning (MAC), although it is under pressure as currently classified as per-fluorinated alkylated substance (PFAS).

This work aims to enhance the performance of a solar air heater (SAH) by introducing broken V-ribs as roughness elements on the absorber plate. The unit with a conventional flat absorber plate is referred to as the “FSAH,” while the unit with a broken V-rib-shaped absorber plate is called the “VSAH.” The experiment was performed for three air velocities: 25 m/s, 20 m/s, and 15 m/s and the corresponding air flow rates were 0.037 kg/s, 0.031 kg/s, and 0.023 kg/s, respectively. The results showed that the maximum temperature was experienced on the absorber plate, followed by the glass plate for both SAHs. Overall, the average absorber and glass plate temperatures of the VSAH were 0.6–1.4 °C and 0.4–1.9 °C lower than those of the FSAH. Compared to the FSAH, the experimental results showed that the VSAH experienced useful power and thermal efficiency that were 16.6–19.8

Building cooling and heating, solar-powered energy production, energy recovery, and other energy-consuming industries have all seen an increase in the use of cold/hot latent thermal energy storage (LH-TES). Through energy recovery, LH-TES that uses phase-change materials (PCMs) as a storage medium helps to close the energy supply and demand gap and raises the possibility of energy savings. However, the stability, thermal, physical, and chemical properties of the PCM play a major role in how effectively it can be used. In recent years, adding gelling and thickening agents (GTAs) has gained popularity apart from the nanoparticles (NPs) and nucleating triggers (NTs), particularly for the creation of stable PCMs. Therefore, the current work’s goal is to provide an overview of how GTAs are used in the process of developing reliable PCMs for TES applications. It has been found that using GTAs not only increased stability but also decreased sedimentation, leakage, and the supercooling degree (SCD). It was noted that the addition of a GTA with a weight percentage of 2–15% resulted in excellent stability with a negligible leakage rate and latent heat reduced by 3.6–35% after only 200 cycles. Furthermore, PCMs for solar-thermal and building heating systems in the medium-temperature range (21–61 °C) were mostly studied for their performance with GTAs, but no study for a cool TES application was reported. Most works have studied inorganic PCM components with GTAs, and a few reports are available for paraffin. However, the GTA blending resulted in reduced thermal performance due to a decrease in thermal conductivity, latent heat, and a rise in viscosity. Further, NTs and NPs with small amounts were seeded into the PCM-GTA for eradicating the SCD with enhanced TC and accelerated energy transfer.

This works aims at evaluating the impact of different ratios of heating design loads to cooling ones on the thermodynamic efficiency of a R290 air-to-water reversible heat pump with the aid of an exergy analysis.The potential improvements of the investigated solution were also assessed.The heat pump was sized for a twopipe fan-coil system designed with supply/return water temperatures of 45/40 °C in winter and 7/12 °C in summer.The outdoor air was cooled from -7 ℃ to -12 ℃ in heating mode and heated from 30 ℃ up to 35 ℃ in cooling mode, respectively.The heating loads were varied in a range from 8 kW to 13 kW, whereas the cooling loads were ranged between 6 kW and 15 kW, respectively.The results obtained showed that heat exchanger sizing plays a significant impact on the distribution of exergy destruction within the system components.As the system was sized based on the cooling load, the air-based heat exchanger was found to be oversized and the water-based heat exchanger was observed to be undersized for covering the heating loads and vice versa.It was also found that for the ratios of heating design loads and cooling ones less than 1.2 the system should be sized based on the cooling design loads.In this case lower system exergy destruction could be obtained.Furthermore, in this case the thermodynamic improvement of the air-based heat exchanger, the water-based heat exchanger and the compressor had approximately the same potential of increasing the efficiency of the system.As the ratios of heating design loads and cooling ones were higher than 1.2, the heating load should have been used for sizing the system components due to higher thermodynamic efficiency of the system compared to the previous case and technical possibilities to be operated.Removing the avoidable irreversibilities within the air-based heat exchanger offered the biggest decrease of the exergy destruction within the system.

Exergy-based methods provide engineers with the best information with respect to options for improving the overall thermodynamic efficiency of an energy conversion system. This paper presents the results of an advanced exergy analysis of an air-to-water reversible heat pump whose performance was analyzed with respect to different working fluids. Environmentally deleterious refrigerants, i.e., R410A and R134a (baselines), and their eco-friendly replacements (R290, R152a, R1234ze(E), and R1234yf) were selected. The evaluations were conducted under the same operating conditions (i.e., with the same cooling and heating demands and outdoor temperatures). Based on conventional exergy analysis, it was determined that different priorities should be given for the thermodynamic improvement of the components according to which heating and cooling modes of the system are in use. Therefore, integrated parameters, i.e., the annual values of exergy destruction, were applied for further analysis. The results obtained showed that the heat pump using R410A provided the largest degree of annual exergy destruction estimated on the basis of conventional exergy analysis (5913 kWh), whereas the heat pump using R290 offered the lowest one (4522 kWh). The annual exergy destruction of the R410A cycle with only unavoidable irreversibilities could be decreased by 50%. In this case, compared to R410A and R134a, R152a and R290 provided lower values of the total annual unavoidable aspects of exergy destruction. Considering technological limitations, when removing all the avoidable irreversibilities within the air exchanger, the largest decrease in the total exergy destruction within the system could be reached. The results obtained from the analysis of the removable irreversibilities showed that the mutual interactions between the compressor, evaporator, and condenser were weak. Finally, it was concluded that, from a thermodynamic point of view, the adoption of R152a and R290 in reversible air-to-water heat pumps as replacements for R410A and R134a is advisable.

In this work the annual and economic performance of a transcritical R744 booster supermarket refrigeration system integrated with an organic Rankine cycle (ORC) was investigated. The results were compared to those of a conventional R744 booster supermarket refrigeration system (i.e. without ORC) in nine different locations worldwide. The benefits from overfeeding the medium temperature (MT) evaporators were also studied. It was found that the ORC can be used at outdoor temperatures above 27 degrees C. Also, it was observed that the proposed systems offer energy savings from 6 % to 16 % in warm and hot locations, such as New Delhi (India), Phoenix (USA), Bangkok (Thailand) and Riyadh (Saudi Arabia). The payback period of the additional investment associated with the ORC was equal to about 3.5 years in Athens (Greece) and less than 1.5 years in New Delhi, Phoenix, Bangkok and Riyadh.

Due to the low critical temperature of CO2, the CO2 supermarket refrigeration systems are often forced to operate in a transcritical regime, which results in poor energy efficiency. In order to overcome this performance penalization, the integration of an ice tank to cool down the CO2 leaving the condenser/gas cooler is considered in this work. A novel optimization method was proposed to minimize the overall energy consumption by optimally scheduling trade-off between the discharge mode and the charge mode. The solution of the optimization problem was achieved based on Particle Swarm Optimization (PSO). The proposed strategy was applied to five sample locations (Copenhagen, Birmingham, San Francisco, Sydney and New Delhi) representing different climates. The results obtained showed an energy saving ranging from 6.4 % to 7.9 % for the hottest day and from 0.4 % to 2.9 % for the entire year compared to the CO2 system without the ice tank.

As part of the design process of a chiller plant, one of the final stages is the energy testing of the system in relation to future operating conditions. Recent studies have suggested establishing robust solutions, but a conservative approach still prevails at this stage. However, the results of some recent studies suggest the application of a new co-design (control–design) approach. The present research involves a comparative analysis between the use of conventional staging and the co-design approach in the design phase of a chiller plant. This paper analyzes the energy consumption estimations of six different chiller plant combinations for a Cuban hotel. For the conservative approach using on/off traditional staging, the results suggest that the best option would be the adoption of a chiller plant featuring a symmetrical configuration. However, the outcomes related to the co-design approach suggest that the best option would be an asymmetrical configuration. The energy savings results were equal to 24.8% and the resulting coefficient of performance (COP) was 59.7% greater than that of the symmetrical configuration. This research lays firm foundations for the correct choice and design of a suitable chiller plant configuration for a selected hotel, allowing for significant energy savings in the tourism sector.

The energy and economic performance of a transcritical R744 booster supermarket refrigeration system with and without parallel compression and integrated with an organic Rankine cycle (ORC) was investigated. The results obtained were compared with those of a transcritical R744 booster supermarket refrigeration system with and without parallel compression and those of a conventional R404A direct expansion (DX) system. Nine different locations, namely Copenhagen (Denmark), Paris (France), Athens (Greece), New Delhi (India), Phoenix and Miami (US), Madrid (Spain), Bangkok (Thailand) and Riyadh (Saudi Arabia), were considered. It was discovered that the ORC is effective only at ambient temperatures higher than 27 °C when operating without parallel compression and 28 °C when operating with parallel compression. By using the heat recovered from the gas cooler to fuel the ORC, the latter was found to be capable of covering between 4% and 24% of the electricity demand of the R744 system in warm and hot climates (without parallel compression). The simple payback period of the additional investment associated with the ORC was found to be between 1.4 and 2.5 years in warm climate locations, while the same was found to be less than about 0.5 years in locations experiencing hot climatic conditions.

Ejector-equipped transcritical R744 condensing units are believed to lead to a low-to-zero commercial refrigeration sector. In order to overcome the persisting barrier to their wider adoption represented by the lack of an affordable ejector control technique, the novel pulse-width modulation (PWM) ejector, being low cost, simple and invulnerable to clogging was recently implemented. However, additional experimental evaluations are needed. Therefore, in this experimental work the performance of two PWM ejector-equipped transcritical R744 condensing units, i.e. with and without overfed evaporator, was carried out. The experimental assessment was implemented at the medium temperature (MT) of about-5 C-degrees, heat sink temperatures from 30 C-degrees to 40 C-degrees and compressor speeds from 40 Hz to 60 Hz.The outcomes obtained revealed that the PWM ejector can effectively control the high pressure in transcritical operating conditions, regardless of the selected heat sink temperature and compressor speed. In addition, at the same cooling capacity, the PWM ejector-equipped R744 system was found to permit energy savings between 7.0% and 11.1% without overfed evaporator and between 11.5% and 16.3% with overfed evaporator compared to the standard R744 unit (i.e. with vapour by-pass valve and without ejector), respectively. Finally, higher values of coefficient of performance (COP) were found to be offered by the PWM ejector compared with its today's available competitors.

This paper presents a procedure to determine the cooling capacity distribution of the chillers composing a chiller plant using a statistical analysis of the building cooling demand. The mathematical-statistical procedure uses tools such as frequency histograms, box-and-whisker plots, stem-and-leaf plots, the generalized least squares method, and finally an iterative factorial procedure to generate from the processed information. Besides the manufacturer's data, all possible chiller plant combinations considering design constraints. The procedure was verified in a hotel facility. Eight thermal demand profiles were simulated. Statistical analysis yielded a range of individual capacities between 100–353 kW. The procedure generated 189 refrigeration plant combinations between 2 to 5 chillers, with a safety factor (SF) between 10%–20%. The highest number of combinations considered plants comprising three and four chillers, reaching 50 and 70 chiller plant options, respectively.