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 technologyrnwas fully integrated into refrigeration equipment. The traditional compressors could be adapted to the use ofrnVSD provided the frequencies at which the compressors would vibrate too much were skipped. The use ofrnadapted VSD could also create some discussion about how best to utilize the capacity regulation withoutrncausing mechanical stress in the system.rnWith the introduction of compressors specifically designed for the use of VSD ensures many problems – bigrnand small – have been solved. In the past many compressors were using VSD with both the traditionalrncylinder engaging/disengaging in reciprocating compressors or capacity slide in screw compressors. Thisrncould cause vibrations in some speed ranges; perhaps only in certain combinations of speed and capacity. Inrnorder to avoid vibration problems the controller would skip some frequencies meaning that the compressorrnwould not run at these frequencies for a prolonged time, but only pass through them as quickly as the motorrnwould allow. The new compressors - born for VSD- do not have this problem because they are without therntraditional capacity controls and, instead of being adapted to VSD, are designed for it from the beginning.rnVibrations can cause all sorts of damage to the compressor or pipe system and even a major failure orrnreduced lifetime.rnThe possibility of saving money on the power consumption is always interesting for end users. VSD providesrnan opportunity of adjusting the actual compressor capacity to the actual cooling load. One advantage of thernVSD system is the constant adjustment of the capacity and power consumption to the load, but another oftenrnoverlooked advantage is that the service intervals are extended because the mechanical wear on the movingrnparts is less when the compressor is at the slower speed. It is, therefore, beneficial to incorporate thisrnparameter into the compressor control and calculate the extended time until the next service based on thernactual operating speed (among other parameters), instead of the traditional way of only looking at a fixedrnperiod of running hours.rnNow one may say that there is nothing new in this technology since it has been known for some years now.rnThat is also a kind of truth but the systems looked at here the first open type compressor sets especiallyrnoptimised for ammonia. Other companies and contractors have long been working with the technology usingrnsemi-hermetic or hermetic compressors. Using open type compressors has its own challenges because yournare connecting two units with a coupling. However, many of the conclusions and issues are the same for anyrnother refrigerant.