A Comprehensive Energy Model for an Optimal Design of a Hybrid Refrigerated Van

The path towards decarbonization requires a progressive adaptation of all refrigeration systems, but only stationary ones have been intensely studied to improve their environmental performance. However, refrigerated transport is vital in the cold chain and must be considered in the green transition. In this paper, we propose a model for a hybrid refrigerated van that includes photovoltaic panels and electric batteries to decrease total greenhouse gas emissions from the engine. Thermal, electrical, and battery sub-models are considered and integrated into the comprehensive hybrid solar-powered refrigerated van model. Different technologies are compared, including lithium and lead-acid batteries and three different types of photovoltaic panels. The model was validated regarding van fuel consumption, showing a 4% deviation. Single and multiple delivery scenarios are considered to assess the energy, economic, and environmental benefits. Monthly CO2,e emissions could be reduced by 20% compared to a standard refrigerated van. Despite the environmental benefits provided by this sustainable solution, the payback period is still too long (above 20 years) because of the necessary investment to adapt the vehicle and considering fuel and electricity prices currently

Experimental study of R1234yf as a drop-in replacement for R134a in a domestic refrigerator

This paper presents an experimental study for three identical domestic refrigerators using R1234yf as a drop-in replacement for R134a. An alternative methodology was proposed to estimate the optimal mass charge for R1234yf; with the use of such methodology, new evidences were sought on the thermal behavior of the refrigerator compartments as well as at the heat exchangers. Additionally, energy performance for both refrigerants was measured, and, finally, a TEWI analysis was conducted. For the type of refrigerator evaluated, results showed that R1234yf presented an average (for the 3 refrigerators) of 0.4 °C for the fresh food compartment, and 1.2 °C for the freezer, among different charges with respect to R134a. The optimal charge for R1234yf was 92.2 g, which is about 7.8% lower than the one for R134a, which represents a small increase of 4% in energy consumption in comparison to R134a. Finally, the TEWI analysis for the R1234yf was 1.07% higher than the R134a.We thank Universidad de Guanajuato for the support in the realization of this research. We also want to thank the Company Honeywell (through Marco García) for the donation of the refrigerant R1234yf, and to acknowledge the support of Mabe TyP in the performing of the tests. The authors wish to thank to Montoro Sanjosé Carlos Rubín for their support in the editing of the English-language version of this paper

Correlated-informed neural networks: a new machine learning framework to predict pressure drop in micro-channels

Accurate pressure drop estimation in forced boiling phenomena is important during the thermal analysis and the geometric design of cryogenic heat exchangers. However, current methods to predict the pressure drop have one of two problems: lack of accuracy or generalization to different situations. In this work, we present the correlated-informed neural networks (CoINN), a new paradigm in applying the artificial neural network (ANN) technique combined with a successful pressure drop correlation as a mapping tool to predict the pressure drop of zeotropic mixtures in micro-channels. The proposed approach is inspired by Transfer Learning, highly used in deep learning problems with reduced datasets. Our method improves the ANN performance by transferring the knowledge of the Sun & Mishima correlation for the pressure drop to the ANN. The correlation having physical and phenomenological implications for the pressure drop in micro-channels considerably improves the performance and generalization capabilities of the ANN. The final architecture consists of three inputs: the mixture vapor quality, the micro-channel inner diameter, and the available pressure drop correlation. The results show the benefits gained using the correlated-informed approach predicting experimental data used for training and a posterior test with a mean relative error (mre) of 6%, lower than the Sun & Mishima correlation of 13%. Additionally, this approach can be extended to other mixtures and experimental settings, a missing feature in other approaches for mapping correlations using ANNs for heat transfer applications

Scheduling optimization of a cabinet refrigerator incorporating a phase change material to reduce its indirect environmental impact

Phase Change Materials (PCMs) incorporated in refrigerators can be used to shift their energy consumption from peak periods, when the electric network energy demand is the highest, to off-peak periods. While PCMs can flatten the energy demand curve, they can achieve economic savings if Time-of-Use (TOU) electricity tariffs are applied. However, the hourly carbon emission factor is not commonly linked to the hourly tariff, and the final CO2 emitted due to the operations of the refrigerator would not be fully optimized. In this work, a method based on the Simulated Annealing optimization technique was proposed to identify the optimal working schedule of a cabinet refrigerator incorporating a PCM to reduce its indirect carbon emissions. Data from countries with different representative carbon intensity profiles were used. The normalized standard deviation and normalized range are the best statistical indexes to predict carbon emission reduction in the proposed solution. These parameters proved that countries with a higher hourly carbon intensity variation (Uruguay, France, Denmark, and Germany) benefit from the application of the algorithm. Cost and carbon emission reduction cannot be maximized simultaneously, and a trade-off is required

Achieving a running cost saving with a cabinet refrigerator incorporating a phase change material by the scheduling optimisation of its cyclic operations

Phase Change Materials (PCMs) can absorb and release a high amount of energy, and therefore, can be used for shifting electricity demand in some household appliances. Indeed, the use of PCMs in a cabinet refrigerator leads to increase its OFF time and flexibility and moves the energy consumption to other periods for a reduction of the peak energy demand. The higher flexibility of the refrigerator with PCM can be exploited to reduce its running cost considering that many countries adopted Time-of-Use (TOU) tariffs, in which the electricity cost is based on the time of energy use over a day and a week. Hence, this work proposes an algorithm based on Simulated Annealing (SA) method to identify the optimal working scheduling of a refrigerator with PCM to reduce its running costs. Experimental results have been used as inputs for the algorithm, and nine 2-TOU and three 3-TOU electricity tariffs from different European countries have been selected to test the methodology. The possibility to achieve running cost savings for various case studies has been proven. Furthermore, higher is the difference between the peak and off-peak electricity cost; more significant is the economic benefits reached by the proposed method

Assessment of the utilization of equivalent warming impact metrics in refrigeration, air conditioning and heat pump systems

The refrigeration, air conditioning and heat pump (RACHP) industry is a significant contributor to the climate change through its associated direct and indirect greenhouse gas (GHG) emissions. Several policies and regulations are being approved to control the working fluids used in existing and future installations, but the equivalent environmental benefit is not clear. In works that analyze the operation of environmentally friendly refrigerants in different configurations, various metrics based on different assumptions have been used to calculate the CO2 equivalent reduction. This work reviews and analyses the environmental metrics used in RACHP systems and the assumptions proposed for their calculation, depending on the application, to promote their inclusion in future works. The peculiarities of each work are discussed together with an interpretation of their main considerations and simplifications. From the literature review and analysis, it is seen that despite the existence of guidelines for the environmental metrics calculation, considerations with notable differences for the same applications are still assumed, even in the case of the Life Cycle Climate Performance (LCCP) metric. Recommendations for the Total Equivalent Warming Impact (TEWI) metric application are provided

Looking for energy losses of a rotary permanent magnet magnetic refrigerator to optimize its performances

In this paper, an extensive study on the energy losses of a magnetic refrigerator prototype developed at University of Salerno, named ‘8MAG’, is carried out with the aim to improve the performance of such a system. The design details of ‘8MAG’ evidences both mechanical and thermal losses, which are mainly attributed to the eddy currents generation into the support of the regenerators (magnetocaloric wheel) and the parasitic heat load of the rotary valve. The latter component is fundamental since it imparts the direction of the heat transfer fluid distribution through the regenerators and it serves as a drive shaft for the magnetic assembly. The energy losses concerning eddy currents and parasitic heat load are evaluated by two uncoupled models, which are validated by experimental data obtained with different operating conditions. Then, the achievable coefficient of performance (COP) improvements of ‘8MAG’ are estimated, showing that reducing eddy currents generation (by changing the material of the magnetocaloric wheel) and the parasitic heat load (enhancing the insulation of the rotary valve) can lead to increase the COP from 2.5 to 2.8 (+12.0%) and 3.0 (+20%), respectively, and to 3.3 (+32%), combining both improvements, with an hot source temperature of 22 ◦C and 2 K of temperature span

HFC404A vaporisation inside a Brazed Plate Heat Exchanger (BPHE): Comparison with the possible long-term low GWP substitutes HC290 (Propane) and HC1270 (Propylene)

This paper presents the heat transfer coefficients and the pressure drops measured during HFC404A vaporisation inside a commercial BPHE and the comparison of this data with previous measurements carried out during HC290 (Propane) and HC1270 (Propylene) vaporisation inside the same BPHE and similar operating condition in order to assess the capability of HydroCarbon refrigerants as long-term low GWP substitutes for HFC404A in commercial and industrial refrigeration. Propane and Propylene exhibit boiling heat transfer coefficient very similar and frictional pressure drops higher than to those of HFC404A, therefore, taking into account also their good thermodynamic properties, they seems to be very promising as long-term low GWP substitutes for HFC404A. The HFC404A boiling heat transfer coefficients were also compared with a new model for refrigerant boiling inside BPHE (Longo et al., 2015): the mean absolute percentage deviation between calculated and experimental data is 6.0%. The heat transfer measurements were also complemented with an IR thermography analysis for a better understanding of refrigerant vaporisation heat transfer regime inside a BPHE

Novel molecules as working fluids for refrigeration, heat pump and organic Rankine cycle systems

Hydrofluorocarbons (HFCs), one of the most used working fluids in HVAC&R and ORC applications, are being phased down rapidly because of their high global warming potential (GWP). Consequently, this sector is looking for suitable eco-friendly low-GWP alternatives to the most representative 3rd generation HFC refrigerants (R-134a, R-404A, R-410A, and R-245fa). This article reviews the publicly available investigations regarding thermodynamic and transport properties and system performance of several low-GWP molecules. First, working fluids added to the ANSI/ASHRAE Standard 34 since 2015 (R-1130(E), R-1336mzz(Z), R-1336mzz(E), R-1233zd(E), R-1224yd(Z), R-13I1, and R-1132a) are considered. Then, other molecules identified in recent studies but not been added yet to that standard (R-1123, R-1243zf, R-1225ye(Z), R-1132(E), R-1252ye, R-1261ze, and R-1141) are investigated. The thermodynamic properties of R-1233zd(E) and R-1224yd(Z) are well described, and their suitability in high-temperature heat pump (HTHP) and Organic Rankine cycle (ORC) systems is experimentally confirmed. R-1336mzz(Z) and R-1336mzz(E), and R-1132a are considered promising working fluids in HTHP and ORC systems, and ULT applications, respectively. R-13I1 is used as a flame suppressant in recently developed blends, such as R-466A. Properties of R-1123, R-1243zf, and R-1225ye(Z) have been well studied, and they are not considered single compound working fluids due to their safety concerns. Therefore, further studies regarding their properties and system performance are needed to confirm their suitability. R-1130(E), R-1132(E), R-1252ye, R-1261ze, and R-1141 are recently identified as potential molecules, so scarce property data is available, and no conclusions can be extracted about them.Funding for open access charge: CRUE-Universitat Jaume