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A comparative assessment of space-conditioning technologies
Abstract
With recent technological developments, many space-conditioning technologies have undergone significant breakthroughs. This investigation provides an updated quantitative comparison of 14 air-source heat pump technologies for residential or commercial space conditioning. These technologies are subdivided into three categories based on the working material, which can be solid-state, two-phase, or gaseous. Thermodynamic models are implemented for each technology and three figures of merit – primary-energy-based COP, exergetic efficiency, and power density – are calculated for cooling and heating mode operation. Solid-state technologies (thermoelectrics, thermionics, elastocaloric, magnetocaloric, and electrocaloric), two-phase technologies (vapor absorption, adsorption, ejector heat pump, membrane heat pump, and conventional vapor compression), and gas cycles (Stirling, Brayton, Bernoulli, vortex tube, and thermoacoustics) are analyzed on a common basis, with proper accounting of realistic thermal resistances and estimates of component requirements, rather than just computing idealized performance. Vapor compression outperforms all the not-in-kind technologies in cooling mode; however, in heating mode, vapor absorption with the ammonia-water working pair outperforms vapor compression by ~ 4.3%, 50.2%, and 49.3% when comparing primary energy COP, exergetic efficiency, and power density, respectively. Elastocaloric and thermoelectric devices demonstrate high power density in heating mode, exceeding that of vapor compression by 83.3% and 46.1%, respectively.
... Several electro-mechanical cooling technologies have been deemed unlikely to challenge vapour-compression cycles in the foreseeable future due to combinations of low efficiency and operating temperature. These include Brayton cycle, pulse-tube, vortex-tube, evaporative cooling, Bernoulli heat pump and critical-flow cycle (Brown and Domanski, 2014;Goetzler et al., 2014;El Fil et al., 2021). The inclusion of evaporative cooling on this list refers to its potential in replacing a vapour-compression cycle in an application. ...
... On the other hand, thermoacoustic and membrane heat pumps have been shown to have competitive characteristic in exergetic efficiency and energy savings potentials, respectively (Goetzler et al., 2014;El Fil et al., 2021). Thermoacoustic cooling is third in patent family count in Fig. 12, while membrane heat pumps cooling is the last. ...
... The result of absorption cooling with the largest patent share in this category is in line with previous assessments that argue for its high potential (Bansal et al., 2012;Brown and Domanski, 2014). The performance of absorption cooling is also considered to be relatively competitive among other not-in-kind technologies (El Fil et al., 2021). Furthermore, the technology also has significant market share within the thermally-driven cooling technologies (Keppler, 2018). ...
The rise in global cooling demand will have significant impacts on our efforts to limit climate change and foster sustainable development. Minimising these impacts requires further development of active cooling technologies, starting with an examination of existing technologies and their characteristics. This paper provides an overview of active cooling technologies using a patent landscape based on patent application data over the past 20 years. In developing the patent landscape, we searched the Derwent Innovation patent database, which contains more than 90 million patent documents, using technology-specific keywords and patent classification codes. A careful assessment of the resulting patent dataset shows a range of important trends about the evolution of cooling in the last two decades. Specifically, we discuss annual cooling technology patent application trends, countries of application, and patent assignees. The results show that patenting activity in the field of active cooling has increased significantly since 2010, mainly driven by the rapid patenting trend in China. Patents of the incumbent technology have been dominated by established manufacturers from Japan and the United States. Not-in-kind cooling technologies with a high number of patent applications include thermoelectric, magnetocaloric, evaporative, pulse-tube, absorption, and adsorption cooling. The results from examining this global patent help in understanding and shaping the global development of active cooling technology by providing new information on the major supplier countries, the key manufacturers, and maturity levels of alternative cooling technologies.
... investigated four solid-state technologies: Elastocaloric (ES), magnetocaloric (MG), electrocaloric (EL), and TE, and showed that the only energy-effective technology is MG compared to VC considering the same operating conditions. A comprehensive assessment of 14 space-cooling technologies suitable for residential and commercial applications was done in (Fil et al. 2021). The study investigated the performance of these technologies in terms of primary-energy COP, exergetic efficiency, and power density. ...
... This implies that no collision occurs when electrons move from the cathode to the anode. Consequently, the electric and thermal energy transfer relationship is nonlinear with the voltage supply and temperature gradient (Fil et al. 2021). Hishinuma et al. (2003) experimented with the cooling of a TT device that had a nanometer gap at room temperature to record the relations between current, voltage, gap length, and cooling capacity. ...
Global warming causes an increase in the average ambient temperatures worldwide, resulting in a further increase in the cooling load demand of indoor spaces such as buildings and agricultural greenhouses; both are critically important for humans and other living creatures. While fulfilling the cooling needs of such, there has also been a crucial constraint to reducing the energy consumption and carbon emissions associated with cooling systems. Alternative cooling approaches are being developed in hopes of replacing conventional refrigeration systems. This study first presents findings of a comprehensive comparative literature review and analysis of various active cooling cycles in three main categories: Vapor-compression cycles (vapor-compression with different hydrofluorocarbon, hydrochlorofluorocarbon, and eco-friendly refrigerants), thermally-driven cycles (absorption, adsorption, and ejector), and emerging cycles (elastocaloric, electrocaloric, magnetocaloric, thermoacoustic, thermoelectric, and thermotunneling). Then, it presents investigations on the development of a sustainability performance index to comprehensively compare different cooling approaches. The sustainability performance is derived from several parameters obtained from the environmental, economic, and energy impact of cooling. Vapor-compression cycles joined with two emerging technologies (i.e. electrocaloric and magnetocaloric) achieved high sustainability scores, where vapor-compression-R510A obtained the highest sustainability score of 76.77%, followed by electrocaloric and vapor-compression-RE170, scoring 75% and 73.3%, respectively.
... However, the analysis did not account for real system losses, such as compressor and expander efficiency, regenerator loss, external heat transfer irreversibility, pressure drop, and parasitic power (pump, fan, etc.) and provided only thermodynamic assessments. More recently, El Fil et al. [8] conducted a quantitative comparison of 14 air-source heat pump technologies for residential or commercial space conditioning. Thermodynamic models were implemented for each technology and three figures of merit, i.e., primary-energy-based COP, exergetic efficiency, and power density, have been calculated for heating and cooling mode operation. ...
With increasing concerns about the long-term global warming effect of HFC refrigerants, low-GWP refrigerants and non-vapor compression heat pumps are gaining attention to be the replacements for current vapor compression heat pumps that rely on HFCs. In addition, advanced heat pump solutions, such as heat pump water heaters, cold climate heat pumps, and low-GWP heat pumps are emphasized by regulators to make the heat pump market cleaner, more efficient, and more affordable. However, current research efforts lack comparisons of the new technologies under realistic building loads, climate conditions, and utility rates. In addition, combinations of emerging technologies have also not been considered. This study developed a methodology to systematically evaluate conventional and emerging space conditioning and water heating technologies both from performance and operating costs points of view. This study analyzed eight HVAC configurations for space heating, cooling, and water heating in terms of annual operating cost when coupled with an actual building affected by weather conditions. The eight HVAC configurations covered advanced solutions such as heat pump water heaters, ground source heat pumps, cold climate heat pumps, and membrane heat pumps, and they were compared with traditional vapor compression heat pumps and gas furnaces. The operating cost assessment was conducted based on building energy simulation using the real utility structure. The results revealed the trade-offs between HVAC combinations for the eleven climate zone covered in this study. The two-stage cold climate heat pump can save 10%-20% heating costs than single-stage heat pumps in cold regions. A membrane evaporative cooler can provide cooling cost savings in eight out of the eleven climate zones analyzed. A gas furnace should only be used in cold places where the electricity price per kWh to gas price ratio is higher than 3. HPWH should be recommended to places where the electricity price to gas price ratio is below 3.
... In this regard, solar energy is usually utilized, particularly in hot climates, where the cooling necessity coincides with high solar radiation values [27][28][29], but in case of insufficient solar resources (or waste heat), they require a backup heater. Generally, solar sorption systems present COP below 1 [28,30]; in this respect, VCRSs still outperform sorption chillers and are preferred in cooling mode [31]. Besides, sorption cooling plants are generally larger and require higher investment costs than VCRS. ...
Providing spaces with thermal comfort is a critical need, particularly in hot-humid regions, where more than a third of the world's population are settled. In terms of space cooling technologies, the global market is largely dominated by window air conditioners and ductless mini-splits. However, numerous other options are available and require more exploration to clearly identify their advantages against conventional systems. In this regard, there are plenty of studies about active cooling systems, but still little is known about the best choices for their application in high-density buildings in extreme humid climates, where latent loads are dominant. In such a framework, this paper briefly examines and identifies possible solutions for space cooling in non-residential buildings in hot-humid climates. In this sense, an all-air system with heat recovery and a radiant ceiling coupled with air handling were identified as the most recommended options for such environments, based on their working principles. Furthermore, the study includes a detailed assessment of the application of these solutions on a case-study building in Mogadishu, Somalia, from the point of view of the cooling demand to the energy consumption of the selected cooling systems. The findings of this work can be extrapolated to be then applied in other developing cities, and outline the path future research should follow to improve the systems.
... 30,31 For example, elastocaloric systems under development may prove capable of delivering cooling at a COP of five when the temperature lift is 20 C, 32 but in the case of air-conditioning and refrigeration applications, the required lift ranges from 30 C to 40 C 33 and depending on the regenerator and material selected, the system COP may be much lower. 34 Nonetheless, although many of these solid-state technologies are still in development, they could in time become attractive alternatives to VC systems. ...
There is a pressing need to decarbonize our energy sector to limit the effects of climate change. Electrification in the buildings and transportation sectors is being proposed as a critical solution. This paper discusses the impact of rapid electrification by comparing the predicted future electricity demand with different scenarios for electricity generation. The effects on primary energy consumption and CO2 emissions are highlighted. Our analysis shows that the composition of the electricity grid plays a key role in determining a better trajectory toward decarbonization. Another key challenge facing the building energy sector is the eventual phasing out of synthetic refrigerants currently used in vapor-compression heating, ventilation, and air-conditioning (HVAC) systems. This article discusses potential solutions for the building energy sector to address these issues and provides engineering solutions that can guide the safe transition to a decarbonized economy without catastrophic shortages of supply or exacerbation of CO2 emissions. Overall, the paper determines that an ∼5.0 quad reduction in building energy usage can be achieved by switching to carbon-free thermal energy where possible and implementing technologies such as desiccant-coated heat exchangers to judiciously manage dehumidification loads. The entirety of the energy saving methods recommended in this article allows for a reduction in predicted carbon emissions by up to 67%, which, combined with carbon capture and other energy saving techniques, could approach a goal of carbon neutral by 2050.
... vapor absorption, adsorption, ejector heat pump, membrane heat pump), to gas cycles (e.g. Bernoulli, vortex tube, and thermoacoustics) (El Fil et al., 2021). EC stood out for its outstanding power density of about 344.7 kW/m 3 , 83.3% and 46.1% higher than vapor compression in heating and cooling mode, respectively. ...
Refrigerants in vapor-compression systems have a global warming potential thousands of times that of carbon dioxide, yet their spread on the market is unrivalled. Elastocaloric systems, based on solid state cooling, feature among the most promising alternatives. In this paper, an elastocaloric device for air ventilation (ECV) composed by parallel and serial connection of multiple shape memory alloy (SMA) films, is investigated via volume-based finite difference simulation in MATLAB and dynamic building simulation in TRNSYS considering eight cities across the globe. The models assume experimentally demonstrated thermal parameters for the elastocaloric phase transformation around room temperature and a single-storey reference building. The ECV operates according to an optimized, energy-saving logic that includes load partialization and recirculation. Parametric analyses suggest that moderate terminal velocities (∼2 m/s) and a climate-specific design aimed at maximizing the use of the ECV device at nominal cooling capacity are key to reach building cooling needs reductions up to 70% in the considered scenarios. Partialization results in enhanced energy flexibility and conservation, whereas recirculation extends the ECV usability to extreme heat conditions. In absolute terms, the ECV works best under hot climates (e.g. Cairo, Dubai, Brisbane), with monthly cooling load reductions about 2/3-fold compared to cold locations (e.g. Milan, Hobart). The performance is extremely sensitive to the ventilation rate. Thermal zones requiring 1 to 2 air changes per hour are best suited. These findings provide initial insight into design criteria, opportunities and limitations on the use of elastocaloric devices for building ventilation to guide future experimental verification.
The urban heat island and urban overheating are the most documented phenomena of climate change. Higher ambient temperatures increase the cooling energy consumption of buildings, affect human health, raise the concentration of urban pollutants, and affect the quality of life of urban citizens. The phenomenon is experimentally documented in more than 450 large cities around the world. The intensity of urban overheating depends on several parameters like the characteristics of the local climate, the landscape, and the features of the city, such as the materials used and the strength of the local sinks and sources. According to the existing data, the average maximum magnitude of urban overheating is close to 5°C, but it may vary up to 10°C. The highest intensities are observed during anticyclonic climatic conditions, low wind speed, and clear sky conditions. In parallel, precipitation tends to decrease the strength of the urban overheating as it increases the thermal admittance of the rural areas.
To address environmental concerns and the need for more environmentally friendly cooling and heating solutions, the U.S. Department of Energy (DOE) is supporting the development of smarter, more efficient, and affordable heat pumping systems operating with low-or no-GWP refrigerants through the Energy, Emissions, and Equity (E3) Initiative. In the literature, limited studies were found that investigated different combinations of conventional and emerging space conditioning and water heating technologies while accounting for real building loads, different climate zones, utility structures, and state-of-the-art equipment. This paper presents operating cost analyses of eight configurations of space heating, cooling, and water heating technologies for a realistic residential building scenario under typical year-round weather conditions. Different combinations of heat pump water heaters, ground source heat pumps, cold climate heat pumps, dual fuel heat pumps, and conventional furnaces were considered in the study. A building model was developed in EnergyPlus and validated with historical data from the DC Nanogrid House at Purdue. A total of eleven climate zones were considered and both local weather conditions and utility pricing were implemented in the simulations. Climate-based equipment selection guidelines were developed and the paper includes future SEER2/HSPF2 ratings, E3 Initiative targets, and also quantitative discussions on emerging technologies such as membrane heat pumps.
The Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC&R) industry has heavily relied on vapor compression cycles since the early part of the 20th century. However, due to environmental concerns and advances in both material and thermal sciences, non-vapor compression technologies have gained attention as potential alternatives to conventional HVAC&R systems. Non-vapor compression technologies also termed not-in-kind technologies, include solid-state refrigeration technologies, thermally-driven cycles, gaseous cycles, chemical heat pumping, membrane heat pumping technologies, and desiccant systems among others. In 2014, the U.S. Department of Energy's Building Technology Office (BTO) released a report that compared several non-vapor compression technologies and quantified the potential energy savings. Since then, other researchers have reviewed not-in-kind technologies and compared them with vapor compression systems. However, no direct comparison with the current state-of-the-art equipment and forthcoming standards is available in the literature. To this end, this paper addresses three major aspects: (i) assessing the current state-of-the-art to identify key advancements in conventional and novel HVAC&R technologies; (ii) defining suitable figures-of-merit to compare the different technologies from a thermodynamic standpoint as well as technology readiness; (iii) creating a roadmap for the development of novel HVAC&R technologies.
Long duration manned space travel is projected to bring a need for large cooling capacities in microgravity for typical freezing and refrigeration temperatures. Among possible cooling technologies, the vapor compression cycle has the highest coefficient of performance but the confidence for microgravity applications is very low. This research effort experimentally investigated the effects of hyper and microgravity on a vapor compression cycle during parabolic flights. A total of 122 parabolas were flown over four days with a repeating pattern of 5 sequential parabolas. Transient data of the evaporation temperature and cooling capacity for selected parabolas are presented as the test stand experienced alternating hyper and microgravity levels. Most measurements and performance indicators showed mild effects on the cycle operation during the varying g-forces. For example, the refrigerant side cooling capacity fluctuated on average within a band of 15 % through all sets of parabolas. A loss of superheat due to gravity changes was observed for one set of parabolas, in which the operating conditions of the cycle showed only 3 K superheat at the onset of gravity changes. For all other sets of parabolas, superheat and subcooling were maintained. Flight results were compared with inclination testing in a laboratory using the same test stand. Inclination changes from -90° to + 90° impacted both the liquid and suction line mass flow rate while varying the gravity level between 0 and 1.8 g affected the suction line mass flow rate but not the liquid line mass flow rate.
Propositions of vapor compression cycles for microgravity applications have a long history. In contrast, experimental efforts and implemented applications are rare in general and in recent years, even less than in the 1980s and 1990s. The paper shows experimental results from a vapor compression cycle on parabolic flights. The focus lies on the effects of varying gravity forces on the condenser and evaporator. Flow visualizations clearly showed a change to an annular or slug-annular flow regime at the evaporator inlet shortly after the onset of gravity. The discharge pressure was found to consistently increase sharply by 1-3 % across widely varying operating conditions. Oscillations were observed in the evaporator for some parabolas in microgravity. Overall, the cycle response to varying gravity can be categorized in four different groups, which appear to have a dependence on both the mass flow rate and the evaporator superheat.
Heat pumps are extremely common in modern society, facilitating thermal comfort and thermal control in residential, commercial, industrial, and mobile applications. Over the past century, electrically driven mechanical vapor compression heat pumps have been the most common technology. In recent years, concerns have been raised about the high electrical load required to drive mechanical vapor compression heat pumps and the global climate change potential associated with both the generation of electricity and the synthetic refrigerants used in these devices. As a result, investigators have considered alternative heat pump technologies, including some that are driven by thermal energy. One of the types of thermally driven heat pumps is the adsorption heat pump. This chapter serves as a prelude to the detailed discussion of adsorption heat pumps throughout the rest of this work by introducing the operating principles of mechanically driven and thermally driven heat pumps and the figures of merit that can be used to evaluate their performance.
Enabled by the discovery of giant electrocaloric effect (ECE) in inorganic ceramics and organic polymers, Electrocaloric (EC) cooling technology has attracted considerable attention from both academia and industrial. However, there remains many challenges in the refrigeration efficiency and/or capacity of the currently reported electrocaloric refrigeration devices. In this work, we propose a concept design of EC refrigeration device, in which the working bodies are rotating in a plane perpendicular to the direction of fluid flow. The rotary EC device adopting heat transfer fluid as an intermediate medium allows for improved heat exchange between EC materials and outside environment, and efficiently delivers cooling effects to where it’s needed. Simulations have been performed to investigate the system cooling performance under different operating strategies. Meanwhile, comparative researches on different heat transfer fluid are conducted and the corresponding cooling effects are studied. When using deionized water as heat transfer medium, the system can achieve a cooling power density of 9.89 W·cm⁻³ and COP of 10.48 over 10 K temperature span. In general, this work provides a highly-efficient rotary EC refrigeration device concept that employs fluid-solid conjugated heat transfer, and guides the optimization of operating strategy and selection of heat transfer fluid.
Materials that show large and reversible electrically driven thermal changes near phase transitions have been proposed for cooling applications, but energy efficiency has barely been explored. Here we reveal that most of the work done to drive representative electrocaloric cycles does not pump heat and may therefore be recovered. Initially, we recover 75-80% of the work done each time BaTiO3-based multilayer capacitors drive electrocaloric effects in each other via an inductor (diodes prevent electrical resonance while heat flows after each charge transfer). For a prototype refrigerator with 24 such capacitors, recovering 65% of the work done to drive electrocaloric effects increases the coefficient of performance by a factor of 2.9. The coefficient of performance is subsequently increased by reducing the pumped heat and recovering more work. Our strategy mitigates the advantage held by magnetocaloric prototypes that exploit automatic energy recovery, and should be mandatory in future electrocaloric cooling devices.
A numerical analysis was conducted to study a room temperature magnetocaloric refrigerator with a 16-layer parallel plates active magnetic regenerator (AMR). Sixteen layers of LaFeMnSiH having different Curie temperatures were employed as magnetocaloric material (MCM) in the regenerator. Measured properties data was used. A transient one dimensional (1D) model was employed, in which a unique numerical method was developed to significantly accelerate the simulation speed of the multi-layer AMR system. As a result, the computation speed of a multi-layer AMR case was very close to the single-layer configuration. The performance of the 16-layer AMR system in different frequencies and utilizations has been investigated using this model. To optimize the layer length distribution of the 16-layer MCMs in the regenerator, a set of 137 simulations with different MCM distributions based on the Design of Experiments (DoE) method was conducted and the results were analyzed. The results show that the 16-layer AMR system can operate up to 84% of Carnot cycle COP at a temperature span of 41 K, which cannot be obtained using an AMR with fewer layers. The DoE results indicate that for a 16-layer AMR system, the uniform distribution is very close to the optimized design.
The present work is about CFD modelling of condensing flow inside a supersonic ejector. The geometry used for the simulations reproduces a small-scale prototype ejector chiller built at Georgia Institute of Technology (Atlanta). The working fluid is R134a, whose expansion inside the primary nozzle and mixing chamber can lead to non-equilibrium condensation phenomena. These alter the pressure and Mach profiles along the ejector, thus generating severe thermodynamic losses. The numerical analysis of non-equilibrium condensation requires modelling of the microscopic behaviour of the fluid with a high level of fidelity. In this study, the condensation of R134a is simulated by means of two in-house developed numerical models. The first considers equilibrium conditions between the phases whereas the latter reproduces the non-equilibrium behaviour of the phase transition. Comparisons are made to understand the limitations and advantages of both approaches.
Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). The MCE originates from coupling a magnetic field with magnetic moments carried by itinerant or localized electrons. In the case of ferromagnetic materials MCE is a warming as the magnetic moments of the atom are aligned by the application of a magnetic field, and the corresponding cooling upon removal of the magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). A FOMT shows a discontinuity in the first derivative of the Gibbs free energy, whereas a SOMT is continuous in the first derivative but exhibits discontinuity in the second derivative. The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle) where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. In this paper, attention is directed towards the near room-temperature range. We compare the energetic performance of a commercial R134a refrigeration plant to that of a magnetic refrigerator working with an AMR cycle. Attention is devoted to the evaluation of the environmental impact in terms of a greenhouse effect. A vapor compression plant (VCP) produces both a direct and an indirect contribution to global warming, whereas an AMR cycle has only an indirect effect. The comparison is performed in term of TEWI index (Total Equivalent Warming Impact) that takes into account both direct and indirect contributions to global warming. This paper compares the refrigeration plant and the AMR cycle working with different magnetic refrigerants: pure gadolinium, second order phase magnetic transition Pr0.45Sr0.35MnO3 and first order phase magnetic transition alloys Gd5(SixGe1-x)4, LaFe11.384Mn0.356Si1.26H1.52, LaFe11.05Co0.94Si1.10 and MnFeP0.45As0.55. The comparison, carried out by means of a mathematical model, clearly shows that GdSi2Ge2 and LaFe11.384Mn0.356Si1.26H1.52 has a TEWI index always lower than that of a vapor compression plant. Furthermore, the TEWI of the AMR cycle working with FOMT materials is always better than that of SOMT materials. Gd5Si2Ge2 is the best FOMT material.
In recent years, several emerging technologies in the domain of solid-state physics have been investigated as serious alternatives for future refrigeration, heat pumping, air conditioning, or even power generation applications. These technologies relate to what is called caloric energy conversion, i.e., barocalorics, electrocalorics, magnetocalorics, and elastocalorics. Of these technologies, the greatest progress has been observed in the domain of magnetic refrigeration. However, in the recent few years, significant research efforts have also been made in the field of electrocaloric and elastocaloric refrigeration. Many of these technologies suggest the possibility for improvements in energy efficiency, compactness, noise level, as well as a reduction in environmental impacts, so it seems very probable that they will start to fill particular market niches as a replacement for vapor-compression technology in the future.
The EU Regulation No 517/2014 is going to phase-out most of the refrigerants commonly used in refrigeration and air conditioning systems (R134a, R404A and R410A) because of their extended use and their high GWP values. There are very different options to replace them; however, no refrigerant has yet imposed. In this paper we review and analyze the different mixtures proposed by the AHRI as alternative refrigerants to those employed currently. These mixtures are composed by HFC refrigerants: R32, R125, R152a and R134a; and HFO refrigerants: R1234yf and R1234ze(E). It is concluded, from the theoretical analysis, that most of the new HFO/HFC mixtures perform under the HFC analyzed (although some experimental studies show the contrary) and, in most cases, do not meet the GWP restrictions approved by the European normative. Furthermore, some of the mixtures proposed would have problems due to their flammability.
This article identifies and describes five alternative cooling technologies (magnetic, thermionic, thermoacoustic, thermoelectric, and thermotunnel) and qualitatively assesses the prospects of each technology relative to vapor compression for space cooling and food refrigeration applications. Assessment of the alternatives was based on the theoretical maximum percent of Carnot efficiency, the current state of development, the best percent of Carnot efficiency currently achieved, developmental barriers, and the extent of development activity. The prospect for each alternative was assigned an overall qualitative rating based on the subjective, composite view of the five characteristics.
A study of four Gd samples of different purities using ac
susceptibility, magnetization, heat capacity, and direct measurements of
the magnetocaloric effect in quasistatic and pulse magnetic fields
revealed that all techniques yield the same value of the zero-field
Curie temperature of 294(1) K. The Curie temperature determined from
inflection points of the experimental magnetic susceptibility and heat
capacity is in excellent agreement with those obtained from the
magnetocaloric effect and Arrot plots. Above 2 T the temperature of this
transition increases almost linearly with the magnetic field at a rate
of ~6 K/T in fields up to 7.5 T. The spin reorientation transition,
which occurs at 227(2) K in the absence of a magnetic field, has been
confirmed by susceptibility, magnetization, and heat-capacity
measurements. Magnetic fields higher than 2-2.5 T apparently quench the
spin reorientation transition and Gd retains its simple ferromagnetic
structure from the TC(H) down to ~4 K. The nature of anomaly
at T≅132 K, which is apparent from ac susceptibility measurements
along the c axis, is discussed. The presence of large amounts of
interstitial impurities lowers the second-order
paramagnetic<-->ferromagnetic transition temperature, and can
cause some erroneous results in the magnetocaloric effect determined in
pulsed magnetic fields. The magnetocaloric effect was studied utilizing
the same samples by three experimental techniques: direct measurements
of the adiabatic temperature rise, magnetization, and heat capacity. All
three techniques, with one exception, yield the same results within the
limits of experimental error.
This paper presents a review of the next generation not-in-kind technologies to replace conventional vapor compression refrigeration technology for household applications. Such technologies are sought to provide energy savings or other environmental benefits for space conditioning, water heating and refrigeration for domestic use. These alternative technologies include: thermoacoustic refrigeration, thermoelectric refrigeration, thermotunneling, magnetic refrigeration, Stirling cycle refrigeration, pulse tube refrigeration, Malone cycle refrigeration, absorption refrigeration, adsorption refrigeration, and compressor driven metal hydride heat pumps. Furthermore, heat pump water heating and integrated heat pump systems are also discussed due to their significant energy saving potential for water heating and space conditioning in households. The paper provides a snapshot of the future R&D needs for each of the technologies along with the associated barriers. Both thermoelectric and magnetic technologies look relatively attractive due to recent developments in the materials and prototypes being manufactured.
A combination of factors—notably environmental concerns about global warming and ozone depletion due to refrigerants and the increasing demand for electronics and optoelectronic cooling—led to renewed activity in alternative cooling technologies. Currently, thermoelectric cooling is considered a popular cooling technology. This paper provides a critical review of thermoelectric technology and assesses its potential applications in air conditioning and refrigeration. The first part of this paper is devoted to the basic concept of thermoelectrics, with an overview of current thermoelectric materials and devices. The second part is a general overview of the applications of thermoelectric technology, with an emphasis on those related to air conditioning and refrigeration.
In an efficient Stirling-cycle cryocooler, the cold piston or displacer recovers power from the gas. This power is dissipated into heat in the orifice of an orifice pulse tube refrigerator, decreasing system efficiency. Recovery of some of this power in a pulse tube refrigerator, without sacrificing the simplicity and reliability inherent in a system with no cold moving parts, is described in this paper. In one method of such power recovery, the hot ends of both the regenerator and the pulse tube are connected to the front of the piston driving the refrigerator. Experimental data is presented demonstrating this method using a thermoacoustic driver instead of a piston driver. Control of time-averaged mass flux through the refrigerator is crucial to this power recovery, lest the refrigerator{close_quote}s cooling power be overwhelmed by a room-temperature mass flux. Two methods are demonstrated for control of mass flux: a barrier method, and a hydrodynamic method based on turbulent irreversible flow. At {minus}55{degree}C, the refrigerator provided cooling with 9{percent} of the Carnot coefficient of performance. With straightforward improvements, similar refrigerators should achieve efficiencies greater than those of prior pulse tube refrigerators and prior standing-wave thermoacoustic refrigerators, while maintaining the advantages of no moving parts. {copyright} {ital 1999 Acoustical Society of America.}
The design of loudspeaker-driven 50 W cooling power thermoacoustic refrigerators operating with helium at 3% drive-ratio and 10 bar pressure for a temperature difference of 75 K using the linear thermoacoustic theory is discussed. The dimensional normalization technique to minimize the number of parameters involved in the design process is discussed. The variation in the performance of the spiral stack-heat exchangers’ at 75% porosity as a function of the normalized stack length and center position is discussed. The resonator optimization is discussed, and the optimized one-third-wavelength (tapered, small diameter tube and divergent section with hemispherical end), and one-fourth-wavelength (tapered and divergent section with hemispherical end) resonator designs show 41.3% and 30.8% improvements in the power density compared to the published 10 W designs, respectively. The back volume gas spring system for improving the performance of the loudspeaker is discussed. The one-third-wavelength and one-fourth-wavelength resonator designs are validated using the DeltaEC software, which predicts the cold heat exchanger temperature of − 3.4 °C at 0.882 COP, and − 4.3 °C at 0.841 COP, respectively.
This paper comprehensively reviews household refrigerator technologies including current cycle options and future not-in-kind options. Most of the refrigerators are based on a vapor compression cycle (VCC), so that its options are reviewed and compared. The refrigerator cycles based on the VCC are categorized in three groups: dual evaporator cycles, expansion loss recovery cycles, and multi-stage cycles. For dual evaporator cycles, several methods of applying two evaporators are presented. For the expansion loss recovery cycle, ejector and expander cycles are explained. For multi-stage cycles, two-stage cycle and dual-loop cycle are mainly discussed. Moreover, refrigerants as a working fluid are reviewed. Lastly, not-in-kind technologies that are not based on the VCC, such as an absorption, thermoelectric, magnetic, thermoacoustic, and thermoelastic are presented for the application of domestic refrigerators. Even though they have not been widely used for household refrigerators due to insufficient reliability and lower performance, their potential is discussed.
The magnetocaloric effect and its most straightforward application, magnetic refrigeration, are topics of current interest due to the potential improvement of energy efficiency of cooling and temperature control systems, in combination with other environmental benefits associated to a technology that does not rely on the compression/expansion of harmful gases. This review presents the fundamentals of the effect, the techniques for its measurement with consideration of possible artifacts found in the characterization of the samples, a comprehensive and comparative analysis of different magnetocaloric materials, as well as possible routes to improve their performance. An overview of the different magnetocaloric prototypes found in literature as well as alternative applications of the magnetocaloric effect for fundamental studies of phase transitions are also included.
Solid-state refrigeration offers potential advantages over traditional cooling systems, but few devices offer high specific cooling power with a high coefficient of performance (COP) and the ability to be applied directly to surfaces. We developed a cooling device with a high intrinsic thermodynamic efficiency using a flexible electrocaloric (EC) polymer film and an electrostatic actuation mechanism. Reversible electrostatic forces reduce parasitic power consumption and allow efficient heat transfer through good thermal contacts with the heat source or heat sink. The EC device produced a specific cooling power of 2.8 watts per gram and a COP of 13. The new cooling device is more efficient and compact than existing surface-conformable solid-state cooling technologies, opening a path to using the technology for a variety of practical applications.
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.
Screening analyses based on thermodynamic and heat transfer principles are conducted for adsorption heat pumps to enable the comparison of working pairs on the basis of common figures of merit. After a broad survey of working pairs in the literature, 110 are analyzed for cooling mode operation, while 81 are analyzed for heating mode operation. The analyses are conducted at operating conditions based on American Heating and Refrigeration Institute (AHRI) standards. Working pairs with ammonia as the refrigerant and activated carbon as the adsorbent are found to perform well in the heating mode and yield compact systems for both modes. Certain activated carbon + ethanol working pairs are found to perform well in the cooling mode, and some metal-organic framework + ethanol pairs perform well thermodynamically in heating mode. Based on these assessments, working pairs are recommended for both modes.
Regenerative heat exchange method internally recovers useful cooling and heating energy inside a closed-loop cooling system. However, depending on the specific cooling mechanisms for various cooling technologies, the configurations and characteristics of regeneration methods diverge significantly. Therefore, it is necessary to review the fundamental principles and clarify the common features and major differences of the regeneration methods for various typical cooling technologies. This study classified regeneration methods into three categories: recuperative type for steady state operated systems, regenerative type for systems under cyclic operation, and heat recovery type for systems with solid-state functional materials. The first group of regeneration methods are recuperative heat exchangers, transferring heat continuously between two streams of fluid with different inlet temperatures to pre-cool one stream and enhance the cooling power, such as the suction-line heat exchanger for vapor compression systems. The second group of regeneration methods are regenerative heat exchangers, which fundamentally are energy storage devices to cyclically transfer heat from gaseous refrigerant flowing through them. The third group of regeneration methods are internal heat recovery processes, wherein fluid is applied as a regenerator to store/release thermal energy cyclically to pre-cool and pre-heat the solid-state functional materials. For each of the three regeneration methods, their physical principles, a summary of their state-of-the-art development status, and assessments of their advantages, limitations and unique features are presented.
This paper provides a critical review of ejector technology for chiller applications, combining an understanding of ejector fluid flow fundamentals with cycle applications. An ejector is a passive momentum-transfer device that requires no external mechanical input or moving parts. The progression of studies on ejectors from the early 1940s to the present from analytical and numerical modeling to visualization studies of the ejector itself is discussed. Included is an assessment of the most recent computational models. Suggestions for future research include improved computational modeling of shock phenomena and the effects of two-phase flow in ejectors. Application of ejectors in chillers is also reviewed, with an emphasis on the basic ejector-based chiller cycle and the development of passive systems that require zero mechanical input for operation. Important connections are made between ejector component- and system-level studies that would together lead to improved overall system performance.
Elastocaloric cooling is a new alternative solid-state cooling technology undergoing early stage research and development. This study presents a comprehensive review of key issues related to achieving a successful elastocaloric cooling system. Fundamentals in elastocaloric materials are reviewed. The basic and advanced thermodynamic cycles are presented based on analogy from other solid-state cooling technologies. System integration issues are discussed to characterize the next generation elastocaloric cooling prototype. Knowledge acquired from the elastocaloric heat engines is provided as the basis for the design of cooling system configuration. Commercially available drivers enabling proper compression and tension are also presented. A few performance assessment indices are proposed and discussed as guidelines for design and evaluation of future elastocaloric cooling system. A brief summary of the up-to-date elastocaloric cooling prototypes is presented as well.
The realization that fossil fuel resources are becoming more and more scarce and considered the largest greenhouse gas emitters and its relationship with climate change, is becoming more pronounced leading to look for adequate strategies concerning energy saving and environmental protection. To achieve this target, much current interest was addressed to Stirling engine since it meets the demands of the efficient use of energy and environmental security. Hence, the development and the investigation about the Stirling engine have come to the attention of many scientific institutes and commercial companies. The engine operates on a closed thermodynamic cycle, which is a regenerative externally heated engine operating with a cycle that has the same thermal efficiency with Carnot cycle if it is ideal and lossless. Several prototypes have already been studied and produced specially gamma and beta configuration. Although the alpha Stirling engine using the Ross Yoke linkage has the advantage of minimizing lateral forces acting on the pistons leading to a more efficient and compact design compared to beta or gamma Stirling configuration, this kind of engine it is not well studied. The objective of this paper was to study the Ross Yoke Stirling engine, which has been developed and validated, by different kind of Stirling engine in order to perform a numerical modelisation of this engine. This model has been used to investigate the effect of the geometrical and physical parameters on Ross Yoke Stirling engine performance in order to determine die significant thermodynamic parameters having an impact on the performance of the engine. As a result, this analysis indicated that the performance of a Ross Yoke Stirling cycle engine with air as working gas depends critically on the heat input and the regenerator effectiveness.
Concerns over environmental impacts of hazardous refrigerants have spurred much research into alternative technologies as well as more environmentally friendly refrigerants. A thermoacoustic refrigeration system uses no refrigerant but is currently not a feasible solution due to the still immature technology with much still unknown about the theories that explain the thermoacoustc cooling effects and the desired performance. This paper reviews past studies to achieve the desired outputs; lowest temperature, the highest temperature difference generated across the stack, the lowest acoustical work required for cooling, or/and the highest coefficient of performance (COP) of the standing wave thermoacoustic refrigerator and various attempts at optimization in terms of the many parameters that represent the outcomes. The review looked at methods employed to analyze the performance with discussions on the relevant parameters that must and have been be considered by past researchers. To date, most studies have been focused on the stack, the heart of the system. Optimization work has been performed parametrically, experimentally or/and numerically, where discrete variations of the parameters investigated are completed whilst others are held constant. Lately, genetic algorithm, a statistical approach, has been utilized in simultaneous optimization of the parameters of the desired outputs where conflicting objectives are possible. To date, thermoacoustic refrigerator remains an attractive alternative technology towards a global agenda of a more sustainable future.
With advances in solid-state cooling materials in the past decade, non-vapor compression technologies, or not-in-kind (NIK) cooling technologies have garnered great attention. Therefore, a universal performance index is urgently needed to compare these NIK technologies with each other and vapor compression cooling as well. In this study, a systematic method is developed to visualize the contributions to the coefficient of performance (COP) from materials (working fluids) level to the system level as a function of temperature lifts. Since the materials level COP depends solely on the materials properties under the specified cycle, it can be used for comparing refrigerants for all NIK technologies. We chose the water-cooled water chiller operating under identical conditions as the basis for the system performance comparison of all NIK cooling technologies. Upon normalizing the system COP to the Carnot COP, its variation with the system temperature lift reveals the intrinsic potential applications for each NIK cooling technology. © 2015 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
The elastocaloric effect (eCE) has recently attracted attention due to the large available latent heat and large adiabatic temperature changes (an order of magnitude higher compared to the magnetocaloric effect (MCE) in the magnetic field accessible with permanent magnets) associated with the martensitic phase transformation. According to a report by the US Department of Energy, elastocaloric cooling shows the largest potential among all alternatives to vapor-compression technologies due to the potentially
high efficiency of such systems. However, there is still a lack of knowledge and information about the actual cooling potential of elastocaloric cooling devices, although some ideas about such systems have already been presented. Here we show that the elastocaloric alloys Ni-Ti and Cu-Zn-Al in a regenerative refrigeration device, analogue to the active magnetic regenerator (AMR) applied in magnetic refrigerator, operating at a 30 K temperature span can produce outstanding results with up to 20-times larger cooling powers per mass compared to gadolinium (Gd), a benchmark magnetocaloric material, with comparable coefficient-of-performance (COP) values (≈5). These results can open up a new way of making cooling devices with much more compact systems and with the possibility of avoiding expensive rare-earth materials.
To avoid global warming potential gases emission from vapor compression air-conditioners and water chillers, alternative cooling technologies have recently garnered more and more attentions. Thermoelastic cooling is among one of the alternative candidates, and have demonstrated promising performance improvement potential on the material level. However, a thermoelastic cooling system integrated with heat transfer fluid loops have not been studied yet. This paper intends to bridge such a gap by introducing the single-stage cycle design options at the beginning. An analytical coefficient of performance (COP) equation was then derived for one of the options using reverse Brayton cycle design. The equation provides physical insights on how the system performance behaves under different conditions. The performance of the same thermoelastic cooling cycle using NiTi alloy was then evaluated based on a dynamic model developed in this study. It was found that the system COP was 1.7 for a baseline case considering both driving motor and parasitic pump power consumptions, while COP ranged from 5.2 to 7.7 when estimated with future improvements.
We report on the elastocaloric effect in a Cu-Zn-Al shape memory alloy. We show that both the isothermal entropy and adiabatic temperature changes are large and reproducible upon field cycling over a very broad temperature span of ∼130 K. The combination of large entropy and such a broad temperature span results in an outstanding refrigerant capacity of ∼2300 J/kg.
This paper provides an update on alternative cooling technologies in the context of a report by Fischer et al. [2], which contains an extensive assessment of “not-in-kind” technologies including their state-of-the-art, development issues, and potentials to replace vapor compression equipment. After nearly 20 years, it is now of interest to update the status of alternative technologies considering regulatory actions aimed at refrigerants with high global warming potential. Several technologies are considered with sorption cooling, desiccant cooling, magnetic cooling, thermoacoustic cooling, thermoelectric cooling, and transcritical CO2 being discussed in some detail. For each technology we present its physical principle, a brief summary of the findings of Fischer et al., the technological advancements since their study leading to the current state-of-the-art, and our assessment as to the potential of each technology to enter the market as a supplement to or replacement of vapor compression equipment in the next 20 year period.
Currently, one of the most interesting alternatives to conventional compressor refrigeration is magnetic refrigeration. However, despite its great potential, some important obstacles, relating mostly to the relatively low power density and the related high costs, must be overcome. Another alternative, which also shows great potential, is electrocaloric refrigeration. Until recently, electrocaloric materials were not so common; however, a number of different electrocaloric materials exist today. Like magnetocalorics, these can be used in the form of a regenerator in order to increase the temperature span. Based on a previously developed numerical model, we have made a comparison between electrocaloric and magnetocaloric regenerators. The results suggest that electrocaloric energy conversion represents a serious alternative, not only to compressor-based technologies, but also to magnetocalorics.
Electrocaloric refrigeration represents a new, alternative technology for refrigeration, cooling, heating or even power generation. As a technology it can be characterized as being analogous to magnetocaloric energy conversion. Therefore, any knowledge acquired from magnetocaloric energy conversion can be usefully applied to future electrocaloric applications. This article presents a review of electrocaloric refrigeration and heat pumping, supported by a basic description of the thermodynamics of the different processes. There are also a few examples provided to demonstrate the operation of the electrocaloric refrigeration cycle. A comprehensive review of existing electrocaloric materials and their properties is given. Since it is one of the most important issues with regard to electrocaloric regenerators, different heat-transfer mechanisms and solutions are presented and discussed. These are required to obtain both the high energy efficiency as well as the large power density in a device, i.e., to be able to produce a compact device. This article also presents some guidelines for the future research and development of electrocaloric refrigeration and heat pumping.
We explore the possibilities for refrigerants having low global warming potential (GWP). A set of about 1200 candidate fluids is identified from more than 56 000 small molecules examined by applying screening criteria to estimates for GWP, flammability, stability, toxicity, and critical temperature. Methodologies for this screening have been presented in earlier works and are summarized here. The fluids with critical temperatures between 300 K and 400 K (i.e., those that could be used in current types of equipment with minor modifications) number 62. The fluids include halogenated olefins; compounds containing oxygen, nitrogen, or sulfur; as well as carbon dioxide. We discuss the tradeoffs presented by these 62 candidates, considering their thermodynamic properties and their stability and toxicity characteristics. No fluid is ideal in all regards—all have one or more negative attributes: poor thermodynamic properties, toxicity, chemical instability, low to moderate flammability, or very high operating pressures.
Thermoacoustic engines and refrigerators use gas inertia and
compressibility to eliminate many of the mechanical contrivances
required by traditional engines and refrigerators while providing
potentially attractive options that might reduce environmental impacts.
The operation of both standing-wave and traveling-wave devices will be
described and illustrated with thermoacoustic devices that have been
used outside the laboratory.
With the mandate of Montreal Protocol banning ozone depleting substances, and Kyoto Protocol later on curtailing the use of substances which contribute to global warming, conventional refrigerants are to be replaced by environment-friendly working fluids. Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are being substituted by hydrofluorocarbons (HFCs), hydrofluorooelifins (HFOs), and a variety of mixtures. In view of the global warming potential of these newly synthesized refrigerants, the recent trend is to go back to the originally used natural fluids such as ammonia, carbon dioxide, hydrocarbons, water vapour, etc. In this article, various issues related to this changeover of refrigerants being used in vapour compression refrigeration systems are discussed.
Anovel system for air conditioning is proposed which combines membrane air-drying and an indirect/direct evaporative cooling (M/ID) system. This combination extends the operating range of the evaporative cooler for small differences of dry and wet bulb temperatures. The study investigates the feasibility of operating the proposed system for the cooling of ambient air to an outlet temperature of 19°C and a relative humidity of 90%. The analysis is performed for the summer weather data of Kuwait, which varies from extremely hot and dry conditions (50°C and less than 20% relative humidity) to warm and humid conditions (35°C and more than 60% relative humidity). System analysis shows limitations imposed on air cooling by the direct evaporative cooler (DEC), the indirect evaporative cooler (IEC), and the indirect/direct evaporative cooler (ID). For ambient temperatures above 35°C, operation of the ID system requires relative humidity values below 30%. Operation of the DEC or the IEC systems is limited to temperatures below 30°C and relative humidity below 50%. The ID system operates at temperatures above 45°C and relative humidity below 50%. The M/ID operation covers a relative humidity range between 30–100% and a temperature range between 25–45°C. Energy consumption for various cooling combinations, including mechanical vapour compression (MVC), is evaluated by the energy efficiency rating (EER). The M/ID system shows savings of up to 86.2% of the energy consumed by the stand-alone MVC system. Also, the combined systems of MVC/IEC and the MVC/ID show savings of 49.8 and 58.9% over the conventional MVC.
In ejector refrigeration systems, the performance of the ejector is a crucial factor in determining the coefficient of performance, refrigeration power, component size and cost of the whole system. Most of the previously published mathematical models to predict the performance of ejectors consider ideal gas fluids. This paper presents a new approach which takes into account both ideal and real gases. The use of real gas equations of state enables considering either dry or wet vapor working fluids. For wet vapor ejectors, the choking phenomenon is analyzed considering a relaxation model for the calculation of the speed of sound in two-phase mixtures. The effectiveness of the model is verified by comparing the predicted results with experimental data available in the literature, using three different working fluids namely R141b, steam, and carbon dioxide. The results were found to be in good agreement with the experimental data and better than the estimations obtained applying previously published models.
In this paper, the performance comparison of a waste heat driven Organic Rankine Cycle (ORC) powered Vapour Compression Refrigeration (VCR) system and a waste heat driven NH3–H2O Absorption Refrigeration (AR) system were carried out through modelling and simulation using IPSEpro PSE simulation tool. The simulation result shows that at the given design constraints, the ORC driven VCR system gives a better COP and second law efficiency than the AR system. Also at the breakeven pressure ratio (pressure ratio at which the COP of both system is the same) the ORC driven VCR system also gives a better second law efficiency than the AR system. However, at pressure ratios higher than the breakeven point, performance behaviour seems to contradict the well known notion that systems with low irreversibility should be more efficient that those with high irreversibility. This is a paradox and might be as a result of high number of thermal systems in the AR system. However, the trend in the COP and Φ obtained for each of the systems conforms to expectation (i.e. increase in COP leads to decrease in Φ).
Nonisothermal transport in InGaAsP-based heterostructure integrated thermionic coolers is investigated experimentally. Cooling on the order of a degree over 1 mum thick barriers has been observed. This method can be used to enhance thermoelectric properties of semiconductors beyond what can be achieved with the conventional Peltier effect.
Numerical investigations on the performance of a traveling-wave thermoacoustic refrigerator are described. This refrigerator consists of a looped tube attached to an acoustic driver. A regenerator with many narrow flow channels is installed in the looped tube. When acoustic power is supplied by the acoustic driver to the looped tube, heat pumping occurs inside the regenerator. The coefficient of performance (COP), i.e., the ratio of cooling power to input power, of the refrigerator was calculated by varying the position, length, and flow-channel radius of the regenerator. When the three factors were simultaneously optimized, the COP was found to exceed 60% of the Carnot COP.
Thermally activated systems based on sorption cycles, as well as mechanical systems based on vapor compression/expansion are assessed in this study for waste heat recovery applications. In particular, ammonia-water sorption cycles for cooling and mechanical work recovery, a heat transformer using lithium bromide-water as the working fluid pair to yield high temperature heat, and organic Rankine cycles using refrigerant R245fa for work recovery as well as versions directly coupled to a vapor compression cycle to yield cooling are analyzed with overall heat transfer conductances for heat exchangers that use similar approach temperature differences for each cycle. Two representative cases are considered, one for smaller-scale and lower temperature applications using waste heat at 60 °C, and the other for larger-scale and higher temperature waste heat at 120 °C. Comparative assessments of these cycles on the basis of efficiencies and system footprints guide the selection of waste heat recovery and upgrade systems for different applications and waste heat availabilities. Furthermore, these considerations are used to investigate four case studies for waste heat recovery for data centers, vehicles, and process plants, illustrating the utility and limitations of such solutions. The increased implementation of such waste heat recovery systems in a variety of applications will lead to decreased primary source inputs and sustainable energy utilization.
When a traveling acoustic wave propagates through a regenerator, the gas in the regenerator undergoes the Stirling thermodynamic cycle, and thus, the energy conversion between heat flux and acoustic power takes place. A cooler that utilizes this energy conversion is called as a traveling-wave thermoacoustic cooler. Swift et al. [The Journal of the Acoustical Society of America, 105, 711 (1998)] have proposed a new traveling wave thermoacoustic cooler that is equipped with a looped tube. This paper describes a numerical method to estimate the performance of this thermoacoustic cooler and shows a comparison between the estimated and experimentally obtained performances.
The thermodynamic analysis of a V-type Stirling-cycle Refrigerator (VSR) is performed for air, hydrogen and helium as the working fluid and the performance of the VSR is investigated. The V-type Stirling-cycle refrigerator consists of expansion and compression spaces, cooler, heater and regenerator, and it is assumed that the control volumes are subjected to a periodic mass flow. The basic equations of the VSR are derived for per unit crank angle, so time does not appear in the equations. A computer program is prepared in FORTRAN, and the basic equations are solved iteratively. The mass, temperature and density of working fluid in each control volume are calculated for different charge pressures, engine speeds, and for fixed heater and cooler surface temperatures. The work, instantaneous pressure and the COP of the VSR are calculated. The results are obtained for different working fluids, and given by diagrams.
A thermodynamic cycle model is used to select an optimum adsorbent-refrigerant pair in respect of a chosen figure of merit that could be the cooling production (MJm−3), the heating production (MJm−3) or the coefficient of performance (COP). This model is based mainly on the adsorption equilibrium equations of the adsorbent–refrigerant pair and heat flows. The simulation results of 26 various activated carbon–ammonia pairs for three cycles (single bed, two-bed and infinite number of beds) are presented at typical conditions for ice making, air conditioning and heat pumping applications. The driving temperature varies from 80°C to 200°C. The carbon absorbents investigated are mainly coconut shell and coal based types in multiple forms: monolithic, granular, compacted granular, fibre, compacted fibre, cloth, compacted cloth and powder. Considering a two-bed cycle, the best thermal performances based on power density are obtained with the monolithic carbon KOH-AC, with a driving temperature of 100°C; the cooling production is about 66MJm−3 (COP=0.45) and 151MJm−3 (COP=0.61) for ice making and air conditioning respectively; the heating production is about 236MJm−3 (COP=1.50).
This project was initiated by the Department of Energy in response to a request from the HVAC industry for consolidated information about alternative heating and cooling cycles and for objective comparisons of those cycles in space conditioning applications. Twenty-seven different heat pumping technologies are compared on energy use and operating costs using consistent operating conditions and assumptions about component efficiencies for all of them. This report provides a concise summary of the underlying principals of each technology, its advantages and disadvantages, obstacles to commercial development, and economic feasibility. Both positive and negative results in this study are valuable; the fact that many of the cycles investigated are not attractive for space conditioning avoids any additional investment of time or resources in evaluating them for this application. In other cases, negative results in terms of the cost of materials or in cycle efficiencies identify where significant progress needs to be made in order for a cycle to become commercially attractive. Specific conclusions are listed for many of the technologies being promoted as alternatives to electrically-driven vapor compression heat pumps using fluorocarbon refrigerants. Although reverse Rankine cycle heat pumps using hydrocarbons have similar energy use to conventional electric-driven heat pumps, there are no significant energy savings due to the minor differences in estimated steady-state performance; higher costs would be required to accommodate the use of a flammable refrigerant. Magnetic and compressor-driven metal hydride heat pumps may be able to achieve efficiencies comparable to reverse Rankine cycle heat pumps, but they are likely to have much higher life cycle costs because of high costs for materials and peripheral equipment. Both thermoacoustic and thermionic heat pumps could have lower life cycle costs than conventional electric heat pumps because of reduced equipment and maintenance costs although energy use would be higher. There are strong opportunities for gas-fired heat pumps to reduce both energy use and operating costs outside of the high cooling climates in the southeast, south central states, and the southwest. Diesel and IC (Otto) engine-driven heat pumps are commercially available and should be able to increase their market share relative to gas furnaces on a life cycle cost basis; the cost premiums associated with these products, however, make it difficult to achieve three or five year paybacks which adversely affects their use in the U.S. Stirling engine-driven and duplex Stirling heat pumps have been investigated in the past as potential gas-fired appliances that would have longer lives and lower maintenance costs than diesel and IC engine-driven heat pumps at slightly lower efficiencies. These potential advantages have not been demonstrated and there has been a low level of interest in Stirling engine-driven heat pumps since the late 1980's. GAX absorption heat pumps have high heating efficiencies relative to conventional gas furnaces and are viable alternatives to furnace/air conditioner combinations in all parts of the country outside of the southeast, south central states, and desert southwest. Adsorption heat pumps may be competitive with the GAX absorption system at a higher degree of mechanical complexity; insufficient information is available to be more precise in that assessment.
Two-thirds of input energy for electricity generation in the USA is lost as heat during conversion processes. Additionally, 12.5% of primary fuel and 20.3% of electricity are employed for space heating, water heating, and refrigeration where low-grade heat could suffice. The potential for harnessing waste heat from power generation and thermal processes to perform such tasks is assessed. By matching power plant outlet streams with applications at corresponding temperature ranges, sufficient waste heat is identified to satisfy all USA space and water heating needs. Sufficient high temperature exhaust from power plants is identified to satisfy 27% of residential air conditioning with thermally activated refrigeration, or all industrial refrigeration and process heating from 100 to 150 °C. Engine coolant and exhaust is sufficient to satisfy all air conditioning and 68% of electrical demands in vehicles. Overall, this study demonstrates the potential to reduce USA primary energy demand by 12% and CO2 emissions by 13% through waste heat recovery. A detailed analysis of thermal energy demand in pulp and paper manufacturing is conducted to demonstrate the methodology for improving the fidelity of this approach. These results can inform infrastructure and development to capture heat that would be lost today, substantially reducing USA energy intensity.