Next Generation of Efficient NH_3 Refrigeration Systems

摘要

With the introduction of variable speed drives (VSD) it has only been a matter of time before this technology was fully integrated into refrigeration equipment. The traditional compressors could be adapted to the use of VSD provided the frequencies at which the compressors would vibrate too much were skipped. The use of adapted VSD could also create some discussion about how best to utilize the capacity regulation without causing mechanical stress in the system. With the introduction of compressors specifically designed for the use of VSD ensures many problems - big and small - have been solved. In the past many compressors were using VSD with both the traditional cylinder engaging/disengaging in reciprocating compressors or capacity slide in screw compressors. This could cause vibrations in some speed ranges; perhaps only in certain combinations of speed and capacity. In order to avoid vibration problems the controller would skip some frequencies meaning that the compressor would not run at these frequencies for a prolonged time, but only pass through them as quickly as the motor would allow. The new compressors - born for VSD-do not have this problem because they are without the traditional capacity controls and, instead of being adapted to VSD, are designed for it from the beginning. Vibrations can cause all sorts of damage to the compressor or pipe system and even a major failure or reduced lifetime. The possibility of saving money on the power consumption is always interesting for end users. VSD provides an opportunity of adjusting the actual compressor capacity to the actual cooling load. One advantage of the VSD system is the constant adjustment of the capacity and power consumption to the load, but another often overlooked advantage is that the service intervals are extended because the mechanical wear on the moving parts is less when the compressor is at the slower speed. It is, therefore, beneficial to incorporate this parameter into the compressor control and calculate the extended time until the next service based on the actual operating speed (among other parameters), instead of the traditional way of only looking at a fixed period of running hours. Now one may say that there is nothing new in this technology since it has been known for some years now. That is also a kind of truth but the systems looked at here the first open type compressor sets especially optimised for ammonia. Other companies and contractors have long been working with the technology using semi-hermetic or hermetic compressors. Using open type compressors has its own challenges because you are connecting two units with a coupling. However, many of the conclusions and issues are the same for any other refrigerant.