The trend towards low-charge ammonia refrigeration is enhancing efficiency and improving safety.
Ammonia (NH3) refrigeration was invented by the Frenchman Ferdinand Carré in 1858, using water as an absorbent with the refrigerant. Refrigeration with compressed NH3 was introduced by David Boyle in 1872. Four years later, Carl Linde invented the first reliable and efficient compressed ammonia refrigerator.
Soon after, it started to be commercialised as an industrial gas and was used for refrigeration all over the world. Ammonia refrigeration still has a strong position, especially in industrial applications. It is the one of the oldest refrigerants used.
NH3 continued to be used as an industrial refrigerant even after the introduction of synthetic refrigerants (CFCs). After a link between the use of CFCs and the destruction of the ozone layer was found, they were replaced by HFCs. The HFCs have an extremely high global warming potential (GWP), so those are currently being phased down, as confirmed by UN Environment
“The Kigali Amendment adds to the Montreal Protocol the phase-down of the production and consumption of HFCs." - UN Environment
The refrigerant itself consists of one atom of nitrogen and three hydrogen atoms; hence the chemical formula NH3. Its refrigeration code is R717. It is part of many natural processes, so it occurs in abundance worldwide. Of the more than 2 billion metric tons of it in the world, 5% is man-made, and less than 2% of that is used for refrigeration, according to IIAR.
“Approximately 18 million metric tons of ammonia are produced annually in North America alone, and of this amount, less than two percent is used for refrigeration." - IIAR
The abundance of NH3 decreases its purchase price. The running costs are low as well. It requires less energy than most competitors, because the refrigerant has a great ability to absorb a large amount of heat when it evaporates. This makes R717 an economical choice as a refrigerant. John S. Scherer from low-charge system provider NXTCOLD talked about these advantages in his presentation during ATMOsphere America 2017.
Currently, the trend in ammonia refrigeration is towards low-charge systems, which allows a charge reduction of 75% to 95%. Despite the reduction in charge, the operation runs well over the full range of possible operating conditions.
Technological advancements allow this reduction in charge. An example of this is a packaged chiller that pumps water, CO2 or glycol. More low-charge inventions are being developed all the time, according to a technical paper from 2016 by John D. Collins, P.E. Industrial Sales Manager at Zero Zone Inc. for IIAR (page 9).
Low-charge systems that need less NH3 have been found to further increase the energy efficiency. A lower charge also improves safety. These advantages are key for a good refrigeration system. The American company Liberty Cold Storage shared its story on going low-charge in Accelerate America’s April 2018 issue.
“We saw the benefits with the cost of energy. We’re trying to raise the bar by being more efficient with energy and having less ammonia." – Tim Cox, Liberty Cold Storage
In North America, low-charge systems are being increasingly installed.
This development is good news for the environment as well. The harm done to the environment by indirect emissions decreases because less energy is needed, and its zero GWP eliminates any global warming effect from direct emissions, according to an EPA white paper from 2010. This makes it a very sustainable choice.
Low-charge is a leap forward for ammonia refrigeration in large-scale industrial applications. Generally, it is accepted as a very effective and energy-efficient refrigerant for large-scale refrigeration. IIAR also described the economic advantages. The trend towards low-charge enhances these advantages.
The different types of low-charge systems are:
In the next part of this series, we will cover the different definitions of low-charge.
Check the links below to find out more:
GL 2018: NH3-cooled heat pumps ‘outperform’ HFCs
Snowman sees growing interest in ammonia refrigeration systems in Australia
Pearson: Low-charge trend marks ammonia 'reinvention'