hermetic vs. scroll compressor 1

[offset]

What is the difference between a hermetic and scroll compressor?

 

Basically all refrigeration systems that use compressors are sealed systems. The compressor is one component in the system. There are several types of compressors and a "scroll" compressor is one type. It is desireable for any compressor to be hermetically sealed within the system so that no pressures are lost, no refrigerant is lost, and no external contaminants can enter the system. "Hermetic" in not a type of a compressor, rather it is the type of construction of any compressor which seals it as a component itself and withing the system.

 

[ludikris]

Winthrop has explained it very well. I worked for Copeland Corporation and among other things, we made hermetically sealed scroll compressors. After assembly of all the internal parts, the top cap was welded onto the unit thus preventing the refrigerant from leaving the system via the compressor.

http://www.copeland-corp.com/

 

[APME]

Scroll is just a trademark of Copeland reciprocating Compressors. They are ofcourse hermetically sealed as explained by winthrop. Copeland Scroll compressors have unprecedented liquid-handling capacity. No accumulator or crankcase heater is required in most system applications. In addition, it is designated to start under any system load. This feature eliminates the need for start kits. Combined, these characteristics simplify system design and increase system reliability.

 

[MintJulep]

No, "scroll" is not a trademark of Copeland or any other manufacturer. As Winthrop stated, a scroll is one type of positive displacement compressor. A Google search on "scroll compressor" will turn up a bunch of sites that explain how they work. This one has a nice animation:

http://www.mat.dtu.dk/info/experiencing/scroll/model.html

All major compressor manufacturers currently produce scroll compressors.

The term hermitic, when applied to compressors means that the compressor and the motor that drives it are permenanetly sealed in an enclosure (usually welded). In contrast "semi-hermetic" is used for a motor/compressor sealed in an openable enclosure (typically bolted-gasketed joints).

 

[superheat]

Liquid handling ability is vastly overrated on scrolls. Liquid will enter the oil in the crankcase in most compressor before entering the "cylinder". Some low temp, aircooled system do not have that luxury. Bearings can be damaged on scroll compressor just like recips due to oil dilution. I have heard the number 1 cause of valve failure is oil foaming on start-up. Oil foam gets into the "cylinder" and acts just like liquid after being compressed. Scrolls would be better for that, but they do not have valves anyway.
The latest I have heard is: larger scrolls are being retrofitted with crankcase heater to prevent liquid damage. I would never buy a heatpump without an accumulator.