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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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