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

Leave a Reply

Your email address will not be published. Required fields are marked *

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

Related Tech Tips

What Does "Air Free CO" (Carbon Monoxide) Mean?
  Almost everyone knows that CO (carbon monoxide) is really nasty stuff and nothing to play around with. Humans will often begin exhibiting symptoms of CO poisoning at 200 ppm (parts per million) of CO in a space. Studies have also shown that the effects of CO exposure can accumulate over time, resulting in health […]
Read more
What's the scoop on PM10 and PM2.5 Particles?
MATLAB Handle Graphics It was December 5th, 1952, only seven years after the end of WWII in London, England, when the “great smog” settled across the city. The “great smog” was the result of a meteorological anomaly combined with unchecked industrial pollution. Still, even once it settled on the city, bringing business to a screeching […]
Read more
Crankcase Heaters and Single-Pole Contactors
We keep two-pole, 40-amp 24v coil contactors on all of our vans. They are versatile and reliable, and you can replace most residential A/C contactors with them. There are a few things to watch for, though, especially when you have a crankcase heater. Many brands power the crankcase heater constantly and shut it on and […]
Read more
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