Variable
refrigerant volume technology using compressors with magnetic bearings achieves high efficiencies that produce a quick return on investment.
by Alfredo Sotolongo*
The most economical energy to produce is the one that is saved!
In the previous issue I concentrated on the new trends in the design of efficient air conditioning systems, applying variable volume to the three fluids that make up a central cold water system: air, water and refrigerant. As we all know, air conditioning systems operate most of the time at partial loads and therefore by modulating fluids using variable frequency drives, the decrease in electricity consumption is reflected exponentially.
In that article I explained the behavior of the air by varying the thermal load and the savings that are achieved in the consumption of the engines of the air handling units. When the smart diffusers modulate the volume of air supplied to the conditioned area, the variable frequency drive modulates the revolutions of the supply fan.
The second fluid, water, varies when the discharge temperature of the air supplied by the unit is satisfied and to keep that temperature constant, the two-way valve controls the flow to the cooling coil. Any change in water flow is reflected in the primary pumping system. When the flow rate decreases, the variable frequency drive adjusts the revolutions per minute of the pump motor, also exponentially reducing the consumption of the motor. This was explained in the article that appeared in the publication that coincided with the ASHRAE fair last January.
In this new article I will concentrate on the variable volume of refrigerant, using compressors with magnetic bearings that do not require oil for lubrication. With which considerably high efficiencies are achieved, especially at partial thermal loads which is where the systems operate most of the time.
These centrifugal compressors, Turbocor brand manufactured by Danfoss, which modulate the volume of refrigerant by means of frequency inverters, operate without friction because they use magnetic bearings that make the shaft float and not support, avoiding the need for oil for lubrication.
In many of our projects we have had the opportunity to analyze different manufacturers of chillers that operate with this type of compressor. We have found that, in both water and air condensation, the Arctic Cool brand achieves the most satisfactory NPLV (kW/tonne) efficiencies, as a result of the design of both the condenser and the evaporator and the control system manufactured by Danfoss for its Turbocor compressors.
Arctic Cool is one of the pioneers in the application of Turbocor compressor technology and for the many years of experience that its engineering department has in the application of this technology, they have created many innovations. These high efficiencies exceed the requirements of ASHRAE 90.1 and depending on the cost of electricity, represents recovery of investment in short periods of time very attractive to the investor.
In addition, they have achieved the lowest sound levels, most compact sizes and lowest operating weight. As far as the environment is concerned, they use CFC-free refrigerants, HFC-134ª that do not emit gases with Ozone reducing harmful emissions. They can also operate with the new R1234ZE refrigerant with the lowest carbon footprint.
By varying the volume of air, water and coolant adapting it to the thermal load present at all times, controlled and intertwined by the control system, it results in the ideal combination: energy savings with the lowest possible environmental pollution at the moment.
If you need more information on any of the topics covered in this column, please contact me at the mail: [email protected]
* President of Protec, Inc., is certified as a professional engineer in Puerto Rico and the state of Florida; has more than 40 years of experience in the application and sale of systems and equipment for energy conservation. He is a member of ASME (American Society of Mechanical Engineers), AEE (Association of Energy Engineers), ASHRAE and was president of the Miami chapter of that association.
