16 October 2024
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BITZER says its high efficiency ammonia compressor packs offer an attractive zero-GWP solution for industrial and large commercial applications
Ammonia as a refrigerant is efficient, cost-effective and has outstanding green credentials, says Phil Godbehere of BITZER UK. Here, he highlights recent developments in design and manufacturing that address its well-known downsides, and open the way for more widespread adoption.
Ammonia is arguably one of the greenest refrigerants available. Due to its thermodynamic properties it is highly energy efficient, requiring the lowest energy input of any refrigerant to produce a given refrigerating effect.
In economic terms, not only are ammonia systems efficient and cost less to run, but the refrigerant itself is relatively inexpensive, even in the high-purity grade required for use in refrigeration. Given the large charges required by some industrial systems, this can translate into substantial savings over synthetic refrigerants.
In environmental terms, ammonia has impeccable credentials. Its zero Ozone Depletion Potential and Global Warming Potential, combined with its inherent efficiency, means ammonia has the lowest Total Equivalent Warming Impact (TEWI) of any refrigerant (where TEWI is the sum of the direct and indirect effects of an ammonia system on global warming over its lifetime).
Although ammonia is made through industrial processes for use in refrigeration, as the substance occurs in nature it is considered a natural refrigerant. Ammonia is part of Earth’s nitrogen cycle and is produced in soil as a result of decomposition of organic matter. This contrasts with synthetic fluorinated refrigerants, which are entirely man-made and do not occur naturally in Earth’s ecosystems.
For all these reasons, ammonia has been used in industrial refrigeration for more than a century. While there have been many changes in refrigerants used in smaller commercial refrigeration and air conditioning over this time, due mainly to growing understanding of their impact on the environment, ammonia has remained the industry’s mainstay for industrial applications.
Mitigating risk
Against these major upsides, ammonia has two well-known and important downsides — being flammable in certain concentrations under certain conditions, and toxic. In terms of flammability, it is considered relatively low-risk due to its chemical affinity to moisture in the air. This gives it an advantage over hydrocarbon refrigerants, such as propane, which have a much higher flammability rating.
Ammonia’s chief Achilles heel is its toxicity. The risk is mitigated to a degree by two factors: ammonia’s distinctive, pungent smell is detectable at concentrations well below those considered to be harmful. This so-called “self-alarming” property is not shared by other potentially hazardous refrigerants.
Secondly, ammonia is lighter than air. In the event of a leak, it tends to rise and dissipate in the atmosphere. This contrasts with other common refrigerants which are generally heavier than air, and therefore tend to collect in depressions and pose an asphyxiation risk.
Recent advances in technology, system design and manufacturing have addressed these potential risks and open the way to safer and more widespread application of ammonia cooling in the future.
For example, due to the nature of industrial refrigeration applications, ammonia systems have traditionally often been built as one-offs and assembled on site. This approach inevitably incurs additional risk due to the less-than-ideal conditions often encountered.
The recent move towards production of complete ammonia systems in pristine factory-controlled conditions eliminates the rough-and-tumble of working on site. Modern modular ammonia compressor packs are now built to the highest standards of quality assurance, ensuring system integrity and minimising the risk of leaks.
Ground-breaking projects
The availability of such high-quality factory-built, modular plug-and-play ammonia systems transforms the safety of ammonia refrigeration and, in turn, its perceived user-friendliness for contractors and end users.
My own company has played a pioneering role in this regard, with the development of the BITZER ammonia compressor pack (ACP). The technology has been well received by end users and contractors in the UK, with some ground-breaking projects already successfully operating around the country.
Several systems have been installed to date here, in a variety of applications. These include a food manufacturing facility for a large high street bakery chain, a commercial ice-making plant, and a large pizza production site.
Key benefits include the pack’s excellent part-load efficiency and resilience, with a back-up compressor in the unlikely event of a failure. Rapid installation and commissioning are made possible due to the plug-and-play design. Contractors can quickly connect up ACP units on site with a few simple pipework and electrical connections.
Crucially, ACP is built in factory-controlled conditions to ensure the highest standards of manufacturing for safety and leak tightness in the field.
The packs are based on BITZER high-performance screw compressors optimised for use with ammonia, which result in a smaller footprint than equivalent-capacity reciprocating compressors. In addition to the inherent efficiency of screw compressors, the speed of the lead compressor is controlled by an integrated variable speed drive (VSD), which significantly increases part-load efficiency and enables soft-start. Efficiency can be further enhanced with the addition of an optional economiser module.
Screw compressors also have much longer maintenance intervals than reciprocating compressors, reducing the cost of ownership over the life-time of the plant.
Use of either two or three compressors per pack gives standby capacity and resilience for critical process application where continuity of cooling is vital. It also enables engineers to service one compressor while the other remains operational, reducing process down-time and improving life-cycle cost.
Compressor performance is enhanced by the new OAHC three-stage horizontal oil separator, pictured, which significantly reduces oil carry over, typically within the range 2-5ppm.
For engineers, the design allows ready access to valves, sensors and connections during installation and servicing, with packs equipped as standard with Bluetooth connectivity and Modbus integration.
Attractive solution
Complementing ACP, advances in the design of ultra-low charge ammonia chillers also open up exciting possibilities. For example, the AMChill packaged chiller, developed by natural refrigeration specialist KGM Refrigeration Ltd with support from BITZER UK, runs on an ultra-low charge of ammonia, made possible by a new design that overcomes the need for a flooded evaporator.
Based on reliable open-drive BITZER W-series compressors optimised for use with ammonia, the chiller is designed for roof-top mounting without the need for expensive risk mitigation measures, such as high capacity exhaust ventilation, required in plant room applications.
The chiller's light weight and compact dimensions (1m wide by 1.6m long and 1.9m high) enable it to be easily transported onto rooftops without the use of a crane via a standard lift, saving installation time and cost.
Overall, we believe high efficiency ammonia compressor packs and low-charge chillers offer an attractive zero-GWP solution for industrial and large commercial applications, with the added benefits of factory-controlled production for maximum safety, and modular plug-and-play design for ease of installation and servicing.
With a modern approach and in appropriate applications, this long-established refrigerant provides a solution to one of the most pressing environmental challenges of our time.
