I recently received the following question: Mike – have you posted a blog about the difference between recip and scroll compressors? We run into some resistance in some areas because we don’t use all scrolls. We try to answer this by stating that we design the compressor to fit the application, and that scrolls are not always the best fit. But you know contractors and if they think scrolls are better, we lose.
Well, I have not posted anything on this subject and I know the factory answer is just what is stated above — that the compressor selection is based on best performance fit for the product. Most manufacturers can use either reciprocating or scroll compressors. It usually is not a matter of “space” since either will usually fit in the cabinet. I’m sure most manufacturers would love to have to stock only one type of compressor but, with the government changing efficiency requirements and manufacturers trying to keep up with those requirements, sometimes a recip gives the best efficiency and some times a scroll does.
Now, as I have stated in the past, I am not an engineer so, as a “student of HVAC”, I started to research the subject. Believe it or not, PURDUE UNIVERSITY Department of Engineering actually did a study on the very subject. Below is a link to a paper they published and I have copied and pasted the conclusions they found from that paper.
Over all, the scroll has some advantages but not in all cases which takes us back to why engineers use both types in equipment design. Keep in mind that engineers are designing to meet efficiency requirements. One of the disadvantages of scrolls is the higher power consumption by the scroll at overcharged condition. In fact, they found COP is reduced with significant under- and over-charging — and we all know that charge in today’s equipment is becoming more and more critical. So if a tech is not taking their time, and is not accurate on their charge, the scroll could be less efficient than the recip.
CONCLUSIONS: A series of steady state performance experiments were carried out using a scroll and a reciprocating compressor at two condenser operating conditions. The results show that the scroll compressor generally produces cooling capacities and COPs that are equal to or greater than the reciprocating compressor. The performance of the scroll compressor improves relative to the reciprocating compressor at the higher condenser temperature. The use of a liquid injection system allows the scroll compressor to produce lower discharge temperatures than the reciprocating compressor.
A number of tests were also carried out to investigate the performance of both compressor types at varying charge levels. The scroll and reciprocating compressors show similar characteristics for cooling capacity and COP with respect to system charge level. The deterioration of the cooling capacity in the scroll is slower during overcharging than in the reciprocating but this is offset by the higher power consumption by the scroll at overcharged condition and so the COP variation is similar. Generally, COP is slightly reduced with under-charging and significantly reduced with over-charging.
The scroll and reciprocating compressors also show similar characteristics for superheat and subcooling with respect to charge level. For both compressor types, superheat decreases with increased charge level and subcooling increases significantly at charge levels above the nominal. The scroll compressor produces slightly greater superheat and considerably greater subcooling than the reciprocating compressor. The increase in subcooling for the scroll design is a result of the liquid injection system reducing the amount of de-superheating required in the condenser.
The results suggest that scroll compressors may deliver performance advantages over reciprocating compressors at some operating conditions, particularly at higher condenser temperatures and this is because of the lower discharge temperature observed in the scroll. Both compressor types exhibit the same general characteristics with respect to system charge. In particular, COP is reduced with significant under- and over-charging. Superheat and subcooling are shown to be functions of system charge level for both compressors and thus may be used as a general indicator of charge level, irrespective of the compressor type. (Taken from Purdue University. Purdue e-Pubs
Grace, I.; Datta, D.; and Tassou, S. A., ” Comparison Of Hermetic Scroll And Reciprocating Compressors Operating Under Varying Refrigerant Charge And Load ” (2002). International Compressor Engineering Conference. Paper 1518. http://docs.lib.purdue.edu/icec/1518 )