Cold Link Africa January/February 2018 | Page 11

INTERNATIONAL NEWS
INCORPORATING COLD CHAIN
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REFRIGERANTS AND HEAT PUMPS FOR EFFICIENT USE OF LOW-GRADE THERMAL EFFICIENCY
Thanks to heat pumps, low-grade thermal
energy, such as solar energy, waste heat from industries, and geothermal energy, can be upgraded into high-temperature heat for central heating or industrial manufacturing processes.
The selection of suitable cycles and refrigerants is important for getting good performance of heat pumps. In their paper presented at the 5th IIR Conference on Thermodynamic Properties and Transfer Processes of Refrigerants, R. Z. Wang et al. analysed the performance of typical refrigerants— such as R152a, R1233zd( E), R1234yf, R1234ze, R134a, R245fa, R717, R718, and R744— and various thermodynamic cycles for vapour compression, absorption, solid sorption and chemical HPs. A broad-spectrum diagram of HP applications is provided for different working modes.
system and component design is helping to reduce charge sizes by more than 70 % when compared with pumped circulation. Developments in evaporator technology and the use of variable speed drive technology are ensuring that reduction in charge doesn’ t come at the expense of efficiency. The introduction of packaged systems enables refrigeration plants to be located adjacent or close to evaporators, reducing pipework length and sizing.
• R. Lamb. Low charge packaged ammonia refrigeration systems.
ADVANCEMENT IN INTEGRATED CO 2
SYSTEMS
This was also widely discussed at the IIR Ohrid
Conference. A. Hafner highlighted that integrated CO 2 systems can simultaneously provide refrigeration capacities at various temperature levels as low as-50 ° C, air conditioning( AC), heating, and even sanitary hot water at adequate temperature levels. A further integration of advanced thermal storage devices will enable these systems to become a valuable element within smart( thermal) grids.
to their fast recovery times, low jitter, and low dark count rates.
SNSPDs operate at extremely low temperatures, only a few degrees above absolute zero(-273.15 ° C). Until now, that level of cooling was achieved with liquid-helium systems, which present a few disadvantages: they are large, expensive, complicated, and demand considerable expertise to operate safely.
NIST recently found an alternative and created a very small prototype, adapted to the size of SNSPDs since it measures 0.31m high and 0.61m long. Its power demand is about 250W, whereas the previous best alternative drew 1.5kW of power. The prototype device relies on a hybrid cooling system comprised of a Joule-Thomson cryocooler and a pulse-tube refrigerator that can reach
temperatures as low as 10K. It precools the cryocooler that can reach below 2K, which is an almost adequate temperature for SNSPDs operating at temperatures between 1K and 2K.
The NSA supported the initial planning and asked NIST to write a paper. The project is currently receiving funding under a cooperative research and development agreement.
• Kotsubo V. et al. Compact 2.2K cooling system for superconducting nanowire single photon detectors.
GEOTHERMAL ENERGY TO POWER A COLD STORAGE FACILITY
In Fiji, two remote villages located on the
tiny island of Vanua Levu do not have
• R. Z. Wang et al. Refrigerants and heat pumps for efficient use of low grade thermal efficiency.
REFRIGERANT CHARGE REDUCTION OF AMMONIA REFRIGERATING SYSTEMS
This was a subject of extensive debate during the 7th IIR Ohrid Conference on Ammonia and CO 2 Refrigeration Technologies that took place last year.
In his paper, P. Hrnjak presented recent developments in charge reduction of ammonia systems: both new unitary systems for cooling air or secondary fluid and also conventional ammonia chillers. The paper also presents a case for a small, low-charge, air-cooled ammonia chiller using microchannel air-cooled condensers and hermetic compressors as an extremely strong option for the replacement of current chillers based on positive displacement compressors.
• P. Hrnjak. Efficient very low charged ammonia systems.
R. Lamb stressed that phasing down of HFCs and regulatory requirements associated with large ammonia charges are driving the development of lowcharge ammonia systems. Innovation in
• A. Hafner. Integrated CO 2 system for refrigeration, air conditioning and sanitary hot water.
K. H. Kvalsvik et al. presented an integrated refrigeration and AC system with CO 2 as the only working fluid for use in very hot climates(+ 45 ° C). Based on the simulation results, its feasibility is proven. The use of ejectors is essential for the system performance at these extreme ambient temperatures, and enables, until now, an impossible application for CO 2. The system achieves a similar performance compared to existing solutions applying high-GWP synthetic refrigerants.
• K. H. Kvalsvik et al. Integrated CO 2 refrigeration and AC unit for hot climates.
COOLING SYSTEM FOR SUPERCONDUCTING NANOWIRE SINGLE-PHOTON DETECTORS
Single-photon detectors have many applications, such as optical quantum computing or ultra-secure quantum communications, among others. Superconducting nanowire single-photon detectors( SNSPDs) are very efficient in detecting photons in the near-infrared due priyainfiji. blogspot. co. za NIST
In Fiji, on the tiny island of Vanua Levu, two remote villages are piping hot water from its hot springs( which is coming out of the ground at 70 ° C) to power an absorption chilling facility in Natewa Bay.
Sae Woo Nam( left) and Vincent Kotsubo examine the prototype for their new cryocooler.
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