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50 – 60 % of the electricity consumption, and that 56 % of all food cold chain CO 2 e emissions emanated from supermarkets.
They examined 81 technologies that can save direct and indirect emissions in a typical baseline UK supermarket, and calculated the application timescales and cost per tonne of CO 2 abated using a model of the supermarket.
Considerable carbon savings( over 300 tonnes CO 2
e per annum) could be achieved in the baseline supermarket with a single technology. This was related to both direct and indirect savings. The levels of CO 2
e savings are greater for new cabinets and refrigeration systems than for retrofitting. Cabinet technologies tended to save indirect emissions, whereas the largest savings in refrigeration systems were in direct emissions.
For retrofitting to current cabinets, the greatest savings could be achieved by fitting doors( between 103.3 and 140.7 tonnes CO 2
e / year). Strip curtains were also an option to reduce emissions, but were unlikely to be acceptable to the supermarket. Air deflectors were estimated to be a good option if doors were not acceptable to the supermarket. For new cabinets, the best option was to select the best cabinets currently available. The greatest savings in emissions for the current refrigeration system were related to alternative refrigerants.
Using lower GWP HFC could save up to 142.8 CO 2 e / year and the use of HFO could save up to 208.4 CO 2 e / year. A large proportion of these savings were from reductions in direct emissions. For new refrigeration systems, the use of tri-generation and water loop systems looked the most attractive options to save emissions. Although not providing such large savings, the use of R744 with or without ejectors and the use of secondary systems also had high emissions savings.
PCM2016 highlights
The two following summaries refer to three papers presented during the 11th Phase-Change Materials and Slurries for Refrigeration and Air Conditioning( PCM2016) conference, which took place last year in Karlsruhe, Germany.
Promising technique for ice slurry generation To store cold energy in the field of refrigeration, ice slurry is a technology with great potential. The cold energy is stored in latent form in a suspension consisting of ice particles and a carrier fluid, using either water or an aqueous solution.
For ice slurry generation, the supercooled water method is a promising technique. Contrary to ordinary ice slurry generators, this method does not need auxiliary power to drive scrapers. Furthermore, the heat exchange area can be designed on a large scale, resulting in a high evaporation
temperature and a high coefficient of performance of the refrigeration unit. However, the stability of the process depends on successful avoidance of ice blockage. At first, the flowing fluid is refrigerated in a heat exchanger below freezing temperature, but still remains in a metastable, liquid state. In a second step, nucleation is initialised to create the ice particles. This is usually done outside the heat exchanger to avoid ice blockage. In the present study *, the influence of wall surface roughness of a heat exchanger on the super-cooling degree of flowing water was investigated.
Numerous super-cooling experiments using heat exchanger walls with four different surface roughness values were performed. A significant influence of the surface roughness on the maximum super-cooling degree is demonstrated. The smoother the surface, the higher is the maximum super-cooling degree. Ice blockage in the subsequent flow path behind the super-cooling heat exchanger was successfully avoided.
* Ernst, G., Kauffeld, M.‘ Influence of the wall surface roughness on the super-cooling degree of water flowing inside a heat exchanger’.
Benefits of PCMs in a cold room B. Copertora et al.* presented the results of an experimental study on the performance of a cold room with a novel air heat exchanger containing phase change material( PCM), which was experimentally investigated. Specifically, an air heat exchanger consisting of aluminium containers with finned surface filled with PCM( 5 ° C melting temperature), was located in a channel near the evaporator of a cold room. The aims were to reduce cooling energy consumption and to improve the maintenance of thermal conditions of stored products.
For this purpose, an experimental campaign was carried out and a monitoring system was developed. The cold room thermal behaviour, with and without PCM, was studied under steady state operating conditions. As expected, a reduced number of on / off compressor cycles( six cycles instead of 13 cycles) in the PCM added cold room was observed.
Test results showed that by storing PCM in the air heat exchanger, up to 16 % of energy savings can be achieved.
* Copertora, B., Fioretti, R., Principi, P.‘ Experimental analysis on a novel air heat exchanger containing PCM( Phase Change Material) in a cold room’.
Miniaturised air-torefrigerant heat exchangers
The University of Maryland, US, used direct metal printing— a 3-D printing technology— to manufacture a unique energy. gov pixabay miniaturised air-to-refrigerant heat exchanger as a single, continuous piece. This project aims at developing the next generation of air-to-refrigerant heat exchangers that would improve the heat transfer, reduce pressure drop, increase robustness, and improve competitiveness.
The heat exchanger will feature at least 20 % less volume, material volume, approach temperature compared to current multiport flat tube designs, and it could be commercially produced within five years. The heat exchanger, which acts as both an evaporator and a condenser, can be applied to commercial and residential airconditioning or heat pump systems.
Prototype 1kW and 10kW designs will be tested and then improved as necessary for final tests and demonstration in a 10.5kW heat pump.
Unique miniaturised air-to-refrigerant heat exchanger.
Safer, greener, cheaper route to ultra-cold freezers
Scientists at Brunel University, London, claim to have engineered an innovative new method to build freezers capable of reaching temperatures as low as-180 ° C by using advanced cryogenically cooled heat pipe technology.
“ The cold in our design comes from liquid nitrogen. But unlike conventional cold storage using the liquefied gas, we don’ t need to physically transfer the nitrogen. The cryogenic heat pipe is literally just moving the cold,” explained Dr Hussam Jouhara of Brunel’ s Institute of
Energy Futures.“ In safety terms this has major implications as in the US alone, eight deaths a year are attributed to nitrogen asphyxiation. Our innovations mean the gas tanks can be situated safely outside in the open air.”
The system’ s‘ green’ and moneysaving credentials come from a highly efficient energy recovery process, which means a potential of up to 50 % reduction in liquid nitrogen use compared to conventional equipment. Initial real world users are likely to be for medical storage, and the team will be working with the NHS Blood and Transplant Service to develop prototype freezers to rapidly cool and store plasma made from donated blood.
“ We also see strong demand from facilities that store cord blood, eggs or sperm or other biological materials at very low temperatures,” said Jouhara.
Modulating ejectors to improve the effectiveness of transcritical CO 2 systems in warmer climates
Carel and Carrier Commercial Refrigeration Europe have joined forces to put an end to the concept of the‘ CO 2 equator’— the until now accepted geographical limit for the cost-effective deployment of CO 2 systems in stores— by developing a new range of modulating ejectors.
These modulating ejectors are claimed to increase the energy efficiency of transcritical CO 2 systems in warmer climates, sustainably extending the possibility to use CO 2 from smaller convenience stores to large hypermarkets.
The modulating ejector, moreover, would reduce installation costs and complexity, as it can continuously and instantly adapt to specific operating conditions. These ejectors are known to exploit the Venturi effect, using a primary fluid flow— typically the high pressure gas cooler outlet— which is then accelerated to draw in, mix, and carry a
Scientists have invented an innovative new method to build freezers capable of reaching temperatures as low as-180 ° C by using advanced cryogenically cooled heat pipe technology.
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