Isentropic efficiency and volumetric efficiency of a refrigeration compressor are very important for system operations. It is known that both efficiency values will be attenuated with running time.
Some services engineers asked me about how to size the CAP tube properly, and/or the "current" cooling capacity and COP of a unit with some running years, say 3/5/8 years. It is needed to know the compressor performance attenuation and heat exchangers performance change.
Are there any lab test data or onsite data of a fridge or air conditioner compressor available or published?
Dear Jeff,
You are right about the reduction in the performance of both heat exchangers and compressor. However, it is hard to assign a certain COP or efficiency values for the cooling equipments considering the various operational conditions during the lifetime of the system, the type of refrigerant agent, the ambient conditions, etc.. You may find the volumetric and isentropic efficiency values of several refrigeration systems in the literature, but non of them will give you the right numbers because of the reasons at the previous sentence. The numbers of the efficiencies are valid if you run your system as explained in the papers. On the other hand, you can evaluate your system performance after the temperature and pressure measurements via using the empirical formula in the book named "Refrigeration and Air Conditioning by W.F. Stoecker". I hope it helps you.
Thanks, Alper!
For a new compressor, no problem to estimate the efficiencies using the performance data from its manufacturer. My question is how the efficiencies are attenuated with the running years at a certain operating condition. We know that real operating conditions quite vary but it is possible to do testing under a certain rated condition at a lab.
Are there any test data published?
For full load and at design conditions the efficiency of screw and centrifugal is quite similar. For pressure lift, screw compressors are able to adapt to fluctuating condensing and evaporating pressures. So, screw compressors can reduce their condensing pressure when ambient temperature is reduce.For screw compressor, costs for maintenance are low. With its higher rotational speeds, a centrifugal compressor requires special attention, especially on the bearings. Enhanced monitoring is also required for clearance and vibration. The most serious problem of a centrifugal compressor is reduced operating efficiency at part load conditions. Below 25 % rated output, this machine suffers from surges that cause compressor damage if left unchecked. This may translate into higher life cycle .
Thanks, Saad!
It looks that you focus on the compressor performance variation with the loading ratio. The two papers that you uploaded are helpful for the part-loading performance analysis. Thank you!
However, I want to explore the efficiency attenuation with running time/year. Do we sing exactly the same song?