32 Commercial Compressors


Dr. Rajan Rajendran, vice president of engineering services and sustainability at Emerson Climate Technologies gives a global view of how governmental regulations, total cost of ownership and green initiatives are driving changes in commercial refrigeration and equipment


The cold winds of change


THE LANDSCAPE of the commercial refrigeration industry is changing and will continue to change based on many key factors.


Cost is the most obvious, and can come in many forms – first cost, energy cost and maintenance cost. Purchasers of commercial refrigeration systems must take a balanced approach to these cost drivers to get the overall best value, and the final decision can be very different, depending on facility type or location. Refrigerants that deplete the upper atmosphere ozone, such as R22, and refrigerants that have a relatively high GWP, such as R404A, are the focus of governmental agencies and legislation.


Organisations are reacting to these new requirements in a variety of ways. For example, R290 is being considered for small refrigeration systems with less than 150 grams of charge, large warehouses use ammonia successfully, and in colder climates such as Scandinavia,


transcritical CO2 systems have been applied successfully.


Many companies now have a sustainability director or manager and document their efforts through publicly- circulated sustainability reports and join voluntary groups. This type of high visibility leads to an increased interest in measuring results, which in turn leads to new programs designed to achieve desired outcomes.


In order to curtail usage of higher GWP gases, other regions in the world have already implemented tighter leakage requirements and countries such as Australia levee taxes on the use of certain classes of refrigerant gases with high GWP. Regulations also impact system efficiency levels, and to address these concerns, the commercial refrigeration industry has many options at hand.


Compressor technology


Today’s new compressors offer the highest energy efficiencies available, which result


in lower utility bills while reducing CO2 emissions.


This is accomplished by improving the motor, compression mechanism and bearing design.


Many of today’s compressors come equipped with onboard computer diagnostics, which prevent unnecessary


ACR News November 2013


HFC refrigerant such as R404A or R134a is used for the medium-


temperature cases and then CO2 is used for the low-temperature cases.


A heat exchanger is placed in the circuit between the liquid line from the HFC condenser


and the discharge of the CO2 compressors. This keeps the condensing temperature low


enough to keep the CO2 in a subcritical state.


The latest natural solution for North America is to use transcritical CO2.


service calls, reduce callbacks and extend compressor life.


These low-cost electronics are now enabling more information to be mined from systems in order to make intelligible troubleshooting and optimisation decisions.


System design


Parallel rack systems have been the standard for years in the US, but recently the industry has moved toward distributed and secondary-loop system installs. Secondary-loop systems use a secondary


fluid such as CO2 or glycol, that is pumped to the cases and back to the machine room or rooftop. This allows for significantly less refrigerant charge, reducing the leak-rate potential of the system. Distributed systems locate the compressors closer to the cases. Instead of having two to three racks in a machine room, five to six smaller refrigeration units may be located throughout the building. Like secondary systems, the distributed architecture also enables less refrigerant charge with the added benefit of efficiency gains in comparison to standard parallel- rack systems.


Refrigerants


The role of refrigeration is very prominent in terms of energy consumption and emissions that could potentially escape to the atmosphere, two very important sustainability measures. A very recent trend in North America is to use natural refrigerants to further the improvements of GWP reductions. Natural refrigerants,


such as CO2, have almost zero global warming impact and have been used for years in Europe.


The most pervasive usage of CO2 as a refrigerant is in a cascade system, where an


This is an ‘all-natural’ solution


where CO2 is the refrigerant for both the low and medium temperature cases and the GWP impact of the refrigerant on the environment is virtually eliminated.


These systems operate most efficiently in colder climates, but functionally, they operate under very high pressures, so safe maintenance challenges are present. However, it is important to draw attention to the energy consumption of these newer systems, both annually and at peak load. While the subcritical


CO2 system can be energy efficient, the standalone transcritical CO2 system may not be as efficient as an HFC system in all climate zones.


This could lead to the transcritical CO2 system being coupled with other energy


saving measures like heat recovery, which could lead to a more complicated system to service and maintain.


Moving forward


With all of these different options for system architectures and refrigerants, as well as advances with electronics, what should industry professionals be doing to prepare?


First, acknowledge that the systems of tomorrow will be different than those of today. The industry can expect changes in refrigerants to continue and new and creative ways will make those systems more efficient and maintenance friendly. Second, be proactive and look for training opportunities, especially those focusing on electronics used in the newer systems, in order to adapt to these changes. Manufacturers often take responsibility to educate their customer base on how these new products work.


Take advantage of these tools that are offered and keep up or stay ahead of the game.


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