Axial, Radial, and Digital Scrolls

Courtesy of Emerson

So much of what manufacturers do with modern compressors seeks to make them more efficient with better ability to load match, hopefully without reducing ruggedness. The Copeland Scroll Digital™ or Digital Scroll is one design that has become very popular due to its simplicity and versatility.

But before we go further, let's define some terms.

For years, I've heard about “axial and radial compliance” from Copeland, so let's define those quickly.

Axial 

These are the forces in line with the axis or center of the scroll; they're the “up and down” forces that hold the stationary top plate together with the oscillating bottom plate.

Radial

These are the forces in line with the radius of the scroll plates; they're the “side to side” forces that keep the two plates in contact with one another.

Compliance

Copeland's definition of compliance – “Compliance” is the ability to separate under abnormal conditions. 

In other words, the scroll plates are forced together top to bottom (axial) and side to side (radial), but if something goes wrong, they can separate to help prevent damage.

A Copeland Digital Scroll uses the axial (up and down) compliance to intentionally load (full capacity) and unload the compressor on and off for various periods of time to match compressor capacity to the equipment load.

Courtesy of Emerson

These digital scrolls have a solenoid that allows fully-loaded operation like usual when it's de-energized and allows for fully unloaded operation when energized. By varying the loaded time to unloaded time, the compressor can vary its output over a period of time and provide excellent capacity control. Technicians in the field may hear this loading and unloading and think that something is going wrong because it does SOUND quite unusual to the trained ear.

My brother was working on a large rooftop unit and heard it unloading, so he put his ammeter in the compressor. He observed a consistent increase and decrease of compressor amperage. Sure enough, it was a Copeland digital scroll.

—Bryan

Related Tech Tips

Crankcase Heaters
Belly band crankcase heater When I first started in the trade as an apprentice, we worked on many Trane heat pumps that used crankcase heaters. These crankcase heaters slid into the compressor sump on the big orange Tyler reciprocating compressors, like the one below. It was very common for these heaters to break off where […]
Read more
Top Residential A/C Maintenance Tips
Bert recently made a video about his top residential A/C maintenance service tips. He showed some pretty good practices in there, so we’re going to revisit them in this article. Maintenance procedures are vital to any HVAC business, especially those specializing in residential A/C. When we do maintenances, the customers see our faces, and when […]
Read more
RH, DB, and WB
I recently received a message asking for a discussion of relative humidity (RH), wet-bulb (WB), and dry-bulb (DB). Time and time again, I hear techs say that condensation occurs when “hot meets cold,” which may be true in some cases. However, that is only a shorthand way to describe it and doesn't really address what […]
Read more

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from