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Status of Not-In-Kind Refrigeration Technologies for Household Space Conditioning, Water Heating and Food Refrigeration

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Status of Not-In-Kind Refrigeration Technologies for Household Space Conditioning, Water Heating and Food Refrigeration International Journal of Sustainable Built Environment (2012) 1,85–101 Gulf Organisation for Research and Development International Journal of Sustainable Built Environment SciVerse ScienceDirect www.sciencedirect.com Review Status of not-in-kind refrigeration technologies for household space conditioning, water heating and food refrigeration Pradeep Bansal ⇑, Edward Vineyard, Omar Abdelaziz Building Equipment Program, Oak Ridge National Laboratory (ORNL), One Bethel Valley Road, P.O. Box 2008, Oak Ridge, TN 37831-6070, USA Received 2 February 2012; accepted 19 July 2012 Abstract 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, ther- moelectric 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 mate- rials and prototypes being manufactured. Ó 2012 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved. Keywords: Efficiency; Thermoacoustics; Thermoelectricity; Stirling; Magnetic refrigerator Contents 1. Introduction . 86 2. Thermoacoustic refrigeration . 87 3. Thermoelectric refrigeration . 88 4. Thermotunneling (thermionic) refrigeration . 90 5. Magnetic refrigeration . 90 ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (P. Bansal). Peer review under responsibility of The Gulf Organisation for Research and Development. Production and hosting by Elsevier 2212-6090/$ - see front matter Ó 2012 The Gulf Organisation for Research and Development. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijsbe.2012.07.003 86 P. Bansal et al. / International Journal of Sustainable Built Environment 1 (2012) 85–101 Nomenclature AMRR active magnetic regenerative refrigeration VS variable speed CCHP combined cooling heating and power Z figure of merit CD-MHHP compressor driven metal hydride heat pumps Greek symbols COP coefficient of performance a seebeck coefficient [VKÀ1] HX heat exchanger D difference HPWH heat pump water heater q electrical resistivity [X-m] i electric current [A] IHPS integrated heat pump system Subscripts K thermal conductivity [WmÀ1 KÀ1] C cold MCE magneto caloric effect H hot NIK not-in-kind adiabatic adiabatic process PTR pulse tube refrigerator L low temperature Q heat transfer rate [W] R room temperature T temperature [K] 6. Stirling cycle refrigeration . 92 7. Pulse tube refrigerator (PTR) . 94 8. Malone refrigeration. 94 9. Absorption refrigeration . 95 10. Adsorption refrigeration . 95 11. Compressor-driven metal hydride heat pump . 96 12. Developments in water heating and space conditioining. 96 12.1. Heat pump water heater (HPWH) using transcritical CO2 ......................................... 96 12.2. Integrated heat pump systems (IHPS) . 96 13. Overall assessment of NIK technologies . 97 14. Conclusions . 99 References. 99 1. Introduction for significant energy savings and environmental benefits compared to existing technologies. In addition, the status The vapor compression refrigeration has remained prac- of emerging technologies that are useful in a household, tically a predominant technology for well over 100 years. including space conditioning, water heating and refrigera- The fundamental principle is to use liquid–vapor and tion, are discussed. vapor–liquid phase transitions to transfer heat from a There have been a few integrated reviews of alternative low temperature state to a higher temperature state. It is technologies in the open literature. Fischer et al. (1994) pre- desirable to have these phase transitions occur at room sented one of the earliest and most comprehensive summa- temperature. The ideal refrigerant for the vapor compres- ries of not-in-kind technologies. This was then updated by sion systems should be non-toxic, noncorrosive, efficient, Fischer and Labinov (2000) with emphasis on economic cost effective and more importantly environmentally impact and potential commercialization. Lately there has benign. There is a general trend of increasing demand for been a flurry of activity (Radermacher et al., 2007; Dieck- heating, cooling and refrigeration services world-wide. This mann et al., 2007) in this area, where Navigant Consulting will eventually lead to the increase in related CO2 emis- Inc. (2009) provided an overview of some of the alternative sions. This trend could be alleviated by the performance technologies targeting energy savings for commercial enhancement of current heat pumping technologies and/ refrigeration applications. This was followed by a report or the development of new energy efficient technologies. from Brown et al. (2010) that assessed the prospects of In this context, the current paper reviews emerging thermoelectric, thermionic, thermotunneling, thermoacou- not-in-kind technologies (NIK) that offer the potential stic and magnetic refrigeration for space cooling and food P. Bansal et al. / International Journal of Sustainable Built Environment 1 (2012) 85–101 87 refrigeration applications. Most recently, Tassou et al. 2. Thermoacoustic refrigeration (2010) provided a broader view of emerging technologies for food refrigeration applications. Thermoacoustic cooling is a technology that uses high- This paper evaluates the status of ten not-in-kind heat amplitude sound waves in a pressurized gas to generate a pump technologies relevant to domestic applications, temperature gradient across a stationary element called namely thermoacoustic refrigeration, thermoelectric refrig- the stack (Newman et al., 2006). A thermoacoustic device eration, thermotunneling, magnetic refrigeration, Stirling is placed inside a sealed pressure vessel consisting of an cycle refrigeration, pulse tube refrigeration, Malone cycle acoustic driver (e.g. a loudspeaker) that generates a high- refrigeration, absorption refrigeration, adsorption refriger- amplitude sound wave, and hence large temperature and ation, and compressor driven metal hydride heat pumps. pressure oscillations into a resonator containing a regener- The paper also discusses the development of heat pump ator or stack. The sound wave may be generated using water heating and integrated heat pump systems and their either thermal or mechanical energy. This cycle is shown respective impact on energy consumption in households. In in Fig. 1(A), and consists of four principal components: addition, the paper presents assessments of potential bene- fits from alternative technologies and a brief summary of 1. A “stack” of porous material, parallel plates, or the R&D opportunities that could develop such technolo- spiral rolls of thin sheets, gies further. Potential barriers to implement these technol- 2. Hot and cold heat exchangers with large area to ogies in the marketplace are discussed along with options volume ratio, for each technology to achieve significant improvements 3. A rigid and sealed tube that may incorporate a in energy efficiency or other environmental benefits for Helmholtz resonator to shorten the device and mini- their application in space conditioning, water heating and mize losses, and refrigeration in households. 4. An acoustic energy source. Fig. 1. (A) Schematic of a thermoacoustic refrigerator. (B) Working principle of a thermoacoustic refrigerator from Largrangian viewpoint. 88 P. Bansal et al. / International Journal of Sustainable Built Environment 1 (2012) 85–101 The sound wave causes the gas to compress and expand Some continuing major difficulties in achieving higher adiabatically, which results in the gas to heat up and cool efficiencies with acoustic refrigerators have been the rela- down respectively. Heat is transferred from the working tively low power density (Brown et al., 2010), low cooling fluid (i.e. gas) to the stack near the phase of greatest com- capacities, large physical size, heat conduction between pression and from the stack to the gas parcel near the phase the heat exchangers and hence poor performance of the heat of greatest expansion. The heat is then respectively dissi- exchangers (Wetzel and Herman, 1997). Design and control pated to and received from an external fluid through a heat of compact heat exchangers in oscillating flow presents a exchanger placed at each end of the stack. The standing- unique challenge for thermoacoustic refrigeration units wave device, such as shown in Fig. 1, generates useful cool- with large capacities. Due to these deficiencies, thermoacou- ing by pumping heat from the cold heat exchanger to the stic refrigeration will continue to be a non-competitive tech- hot heat exchanger. Fig. 1(B) shows an idealized thermoa- nology for domestic applications in the foreseeable future. coustic refrigeration
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