Experimental analysis of a high temperature heat pump prototype with low global warming potential refrigerant R-1336mzz(Z) for heating production above 155 °C

There is an urgent need to reduce fossil fuel dependency on heating processes in many sectors, highlighting industries. Vapour compression heat pumps are the most promising technologies for decarbonisation in high temperature processes. However, a climate-friendly working fluid is required for a sustainable transition. This paper presents one of the first experimental assessments of a high temperature heat pump operating refrigerant with R-1336mzz(Z). This refrigerant is an alternative to R-245fa because it is the only high temperature fluid with low global warming and zero ozone depletion potential. Fifty-one steady-state experiments were performed in a scroll compressor prototype with a liquid-to-suction heat exchanger at production temperatures between 100 and 160 °C and waste heat temperatures between 80 and 118 °C. The main considerations for the experimental campaign have been discussed, such as the control of the operational temperatures, compressor operation and liquid-to-suction heat exchanger influence. The volumetric heating capacity varied between 9.2 and 12.3 kW, and the heating coefficient of performance resulted between 1.9 and 4.4. Considering the working fluid's negligible global warming potential and high system energy performance, all considered carbon emission factors make this solution more climate-friendly than a natural gas boiler

Influence of operational modes of the internal heat exchanger in an experimental installation using R-450A and R-513A as replacement alternatives for R-134a

This paper presents a first and second law of thermodynamics study using experimental data from a medium capacity refrigeration system using R-450A, R-513A and R-134a as working fluids and an internal heat exchanger (IHX) operating in three different modes: disabled (Off), activated at 38% thermal effectiveness (Middle), and activated at 78% thermal effectiveness, which is the maximum value by design (ON). When the IHX is in the Middle mode, R-513A showed to be the best option and its coefficient of performance (COP) overcomes that of R-450A and R-134a. On the other hand, for temperatures above of −7.5 °C, both R-450A and R-134a reached the highest COP when the ON and Off modes were set, respectively.Regarding the second law study, for the Off and Middle mode, the largest exergy destruction happens in the compressor for the three refrigerants. The influence of the IHX can be observed directly in the increase of the global exergetic efficiency which passes from being 8.7% in Middle mode to 18.3% for the ON mode. Additionally, a reduction of exergy destruction ratio is seen from the Middle mode, 10.6%–22.2% in the ON mode

Renewable and waste heat applications for heating, cooling, and power generation based on advanced configurations

Using renewable heat energy sources, recovering the waste heat, and enhancing the processes and energy efficiency can reduce the electricity dependency of several industrial applications. Renewable and waste heat have a low-grade enthalpic level and should be combined with other technologies to bring it to a practical level. This could be achieved by increasing the variety of heat sources and their combinations (multi-function systems), resulting in a high overall energy performance and reducing greenhouse gas emissions. Recent research on this topic has been conducted considering solar-assisted geothermal heat pumps (single and combined), low-grade waste heat, organic Rankine-vapour compression cycles (ORC-VCC), and absorption refrigeration. In the current research, comprehensively review of the state-of-the-art advanced arrangements using renewable heat sources and waste heat utilisation for simultaneous heating, cooling, and power generation was performed. To the best of the author’s knowledge, the use of waste heat from VCC systems represents one of the most promising technologies in the future. Solar and geothermal heat pumps are considered for different applications and at different temperatures, presenting a high coefficient of performance. However, their utilisation is beneficial only when both renewable heat sources are considered. Although both the ORC and ejector refrigeration systems demonstrated low thermal performance, the overall system performance remained similar to that of the original system. Absorption refrigeration is promising as an up-and-coming alternative to a VCC system, but it is often hampered by excessive cooling unit sizes and a low COP.Funding for open access charge: CRUE-Universitat Jaume

Micro-generation and micro combined heat and power generation using “free” low temperature heat sources through Organic Rankine Cycles

Ponencia presentada en International Conference on Renewable Energies and Power Quality (ICREPQ’13) celebrada en Bilbao del 20 al 22 de marzo de 2013.The Organic Rankine Cycle (ORC) technology is an efficient way for small-scale generation. It offers great benefits from low temperature heat sources, recovering waste heat and revaluing renewable thermal energy. This paper presents the use of ORC for power and combined heat and power generation from low temperature heat sources. Specifically, two recent applications successfully implemented in Spain are reported, based on Rank® technology: a micro generation for waste heat recovery in a ceramic industry using HT-20 kWe and a micro combined heat and power generation using solar heat with HT-C 5 kWe. Experimental data have been evaluated to check economical and technical ORC feasibility. From waste heat recovery, now up to 23 kWe are generated, 336 MWt of primary energy are saved and 44 tonnes of CO2 emissions are avoided, with a suitable payback lower than 5 years. From renewable thermal energy, now 37 MWt of primary energy are saved, 5 tonnes of CO2 emissions are avoided with a payback lower than 8 years

Experimental assessment of R134a and its lower GWP alternative R513A

Lower GWP refrigerants are essential to mitigate the impact of refrigeration systems on climate change. HFO/HFC mixtures are currently considered to replace HFCs in refrigeration and air conditioning systems. The aim of this paper is to present the main operating and performance differences between R513A (GWP of 573) and R134a (GWP of 1300), the most used refrigerants for medium evaporation temperature refrigeration systems and mobile air conditioners. To perform the experimental comparison, 36 tests are carried out with each refrigerant at evaporating temperatures between −15 and 12.5°C and condensing temperatures between 25 and 35°C. The conclusion of the experimental comparison is that R513A can substitute R134a with only a thermostatic expansion valve adjustment, achieving better performance and higher cooling capacity. The discharge temperature of R513A is always lower than that of R134a.The authors thankfully acknowledge the Ministry of Education, Culture and Sports, Spain for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012 (Grant number FPU12/02841)” and “Ayudas complementarias para beneficiarios de ayudas (FPU): Estancias Breves. Convocatoria 2015 (Grant number EST15/00154)”. This research is also done within the Effsys Expand P08 project that is funded by the Swedish Refrigeration Cooperation Foundation, KYS and Swedish Energy Agency with the support of Bosch Thermoteknik AB, Danfoss Värmepumpar AB, Nibe AB, Nowab, Svensk Energi & Kylanalys AB and Svenska Kyltekniska Föreningen

Refrigerant R32 as lower GWP working fluid in residential air conditioning systems in Europe and the USA

Because air conditioning and heat pump systems contribute greatly to greenhouse gas emissions, equipment with both lower global warming potential (GWP) working fluids and a higher level of performance should be used. R32 (difluoromethane) has been proposed to substitute R410A, particularly in residential air conditioning (RAC) systems. This study collected the most relevant and recent researches into R32 as a refrigerant so as to assess its viability in RAC systems in both Europe and the USA, as compared to R410A and other lower GWP RAC alternatives. The R32 value of GWP is 677, which is below the F-gas regulation limit in RAC equipment (750). According to ASHRAE standard 34, R32 is less flammable than hydrocarbons, and the amount of charge permitted for R32 is above the necessary level in RAC equipment. It can be concluded that R32 has significantly good heat transfer characteristics and a level of performance that make it acceptable at low condensing temperatures, thereby avoiding overly high compressor discharge temperatures. Its performance is very similar to that of R410A across the entire operating range, and it is therefore believed that R32 will be utilized in RAC systems in the remaining countries that prioritize lower GWP fluids but are less strict in their security regulations. To replace R410A under extreme conditions, some system modifications can be conducted, or R32 mixtures with hydrofluoroolefins (HFOs) can be used. Such mixtures achieve a lower performance than R32, but are acceptable replacements when considering their lower GWP compared to that of R32, and similar level of flammability. Finally, other (R32-based) alternative mixtures have also been developed and their behaviours studied under a wide range of operating conditions.The authors thankfully acknowledge the Spanish Ministry of Education, Culture, and Sport for supporting this work through “Becas y Contratos de Formación de Profesorado Universitario del Programa Nacional de Formación de Recursos Humanos de Investigación del ejercicio 2012 (Grant number FPU12/02841)” and “Ayudas complementarias para beneficiarios de ayudas (FPU): Estancias Breves. Convocatoria 2015 (Grant number EST15/00154)”. The authors are also grateful to the Swedish Energy Agency for supporting this study under the “EFFSYS EXPAND P08” research program

Performance evaluation of modified compound organic Rankine-vapour compression cycle with two cooling levels, heating, and power generation

This work analyses a novel combined organic Rankine-compound ejector vapour compression cycle for power, cooling and heating production using a low-grade ground heat source as the primary heat source. Ultra-low global warming potential working fluids (R1234ze(E), R1243zf, and R1234yf) and parameters quantifying energy and exergy efficiency are considered. The system can be adapted to three operating modes, depending on the ground source temperature, ranging from 55 to 90 ◦C: power-cooling, power-heat pump heating, and powerground source heating. The results indicate that this system notably increases the overall performance of all investigated refrigerants. Compared to conventional organic Rankine and vapour compression cycles (ORC and VCC), the R1234ze(E) power-cooling mode shows the highest coefficient of performance (COP) increase, 18 %. Besides, including a recapture heat exchanger for condenser waste heat recovery can increase power generation by 58 %. At ground source temperatures up to 65 ℃, power generation and thermal efficiency increased in the power-heating mode due to the absence of the compressor power consumption. The exergy efficiency follows the ground source temperatures for all modes. In power-ground source heating mode, the exergy efficiency notably increased due to the absence of the heat pump exergy destruction.Funding for open access charge: CRUE-Universitat Jaume

High temperature heat pump integration into district heating network

This study illustrates the potential of high temperature heat pumps (HTHPs) integration into district heating network (DHN) through a twofold approach, using DHN as a heat sink and source. It is used as a heat sink of HTHP that uses waste heat from the supermarket’s refrigeration system as a heat source whereas it is used as a heat source to HTHP that provides heat to industrial applications. When the DHN acts as the heat sink, the integrated system provides a coefficient of performance (COP) of the waste heat recovery (WHR) system between 3.2 and 5.4, reducing the operating costs between 50% and 100% with an average price ratio of 2.25 compared with the standard CO2 refrigeration system. If the DHN is the heat source, the integrated system provides a COP from 2.8 to 5.7 for a heat sink of 110 °C. The alternative low-GWP refrigerants assessment illustrates that HC-290, HFO-1234ze(E) and HFO-1234yf were considered the ideal candidates to replace the HFC-134a, whereas HCFO-1233zd(E) and HCFO-1224yd(Z) were the most promising low-GWP refrigerants to replace HFC-245fa. Finally, the environmental results showed that the utilisation of the DHN as the heat sink in the integrated system solution produces about 60% lower equivalent CO2 emissions than the DHN generation mix. Moreover, using DHN as the heat source, the equivalent CO2 emissions can be reduced up to 98% in Sweden compared to conventional natural gas boilers. Hence, the combination of HTHPs and the DHN represents a step forward in the mitigation of climate change through the utilisation of sustainable energy conversion technologies

Multi-objective optimization of a novel reversible High-Temperature Heat Pump-Organic Rankine Cycle (HTHP-ORC) for industrial low-grade waste heat recovery

Nowadays, a high amount of industrial thermal energy is still lost due to the lack of competitive solutions for energy revalorization. Facing this challenge, this paper presents a novel technology, based on a reversible High-Temperature Heat Pump (HTHP) and Organic Rankine Cycle (ORC). The proposed system recovers low-grade waste heat to generate electricity or useful heat in accordance with consumer demand. Compressor and expander semi-empirical models have been considered for the reversible system computational simulation, being HFC-245fa the working fluid selected. The built-in volume ratio and Internal Heat Exchanger (IHX) effectiveness have been optimized to reach the maximum energy efficiency in each operating condition. Although HFC-245fa exhibits energy performance attributes, its high Global Warming Potential (GWP) is an issue for climate change mitigation. Hence, multi-objective optimisation of the environmentally friendly working fluids Butane, Pentane, HFO-1336mzz(Z), R-514A, HCFO-1233zd(E) and HCFO-1224yd(Z) has been carried out. The results show that the system proposed, working with HFC-245fa, achieves a Coefficient of Performance (COP) of 2.44 for condensing temperature of 140 °C, operating in HTHP mode, whereas the ORC mode provides a net electrical efficiency of 8.7% at condensing temperature of 40 °C. Besides, HCFO-1233zd(E) and HCFO-1224yd(Z) are both appropriate alternatives for the HFC-245fa replacement. These working fluids provide a COP improvement of 9.7% and 5.8% and electrical net efficiency improvement of 2.1% and 0.8%, respectively, compared to HFC-245fa. This paper provides a reference study for further designs and developments of reversible HTHP-ORC systems used for industrial low-grade waste heat recovery

Influence of subcooling in R-449A supermarket refrigeration system and screening of refrigerant mixtures for its energetic and environmental improvement

Current demands of the cooling sector are focused on using refrigerants with a low Global Warming Potential (GWP) and increasing energy efficiency in vapour compression installations. The main objectives of this paperwork arise from these needs, in which the use of subcooling in an R-449A commercial refrigeration system is evaluated. In addition, eco-friendly alternative refrigerants are proposed and studied. Firstly, the effect of an integrated type of subcooling is semi-empirically analysed with Engineering Equation Solver (EES). Then, the refrigeration system’s operation is simulated using low-GWP alternative refrigerants, R-454C and R-290, which have been scarcely studied in commercial refrigeration systems due to their safety classification. Moreover, new refrigerant mixtures are searched from the binary and ternary combination of pure refrigerants using the software REFPROP. The best refrigerant with safety classification A1, A2L, and A2/A3, for both medium temperature (MT) and low temperature (LT) systems is obtained from this search. After their determination, the supermarket’s operation is simulated with these refrigerants. Finally, an environmental assessment is performed. The highest energy efficiency is obtained with R-152a for the MT system and the R-290/R-1270 mixture for the LT system. However, the highest reduction of GHG emissions is achieved by R-290, with a reduction of 73.78 % with respect to the baseline system.Funding for open access charge: CRUE-Universitat Jaume IThis scientific publication is part of the R + D + i project PID2020-117865RB-I00, funded by MCIN/AEI/10.13039/501100011033, and UJI-A2022-03, funded by Universitat Jaume I. Adrián Mota-Babiloni acknowledges contract IJC2019-038997-I, funded by MCIN/AEI/10.13039/501100011033. Cosmin Mihai Udroiu acknowledges grant PRE2021-097369 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. Pau Giménez-Prades acknowledges grant CIACIF/2021/182, funded by the Generalitat Valenciana (GV) and the European Social Fund (ESF)