Picture this: it’s a mildly warm day in mid-July in Seattle and you hear your AC system click on. The system quickly satisfies the temperature change to within a degree or two of your setpoint, say, 72 degrees F and the AC system abruptly shuts down. Then about fifteen minutes later, the process is repeated and does so until the evening when the outside temperature drops. This is known as short cycling and over the long term it uses more energy than necessary through pressure cycling and transient heat loss and can severely impact the lifespan of your compressor.
Most compressors out there are of the fixed-speed type: all or nothing, 0 or 100. This is kind of like having a vehicle that only drives at 70 mph. While it would be great if you lived on a freeway on-ramp, it would not be practical for 90% of your driving scenarios: picking up the kids from school, going on a quick grocery run to PCC, etc. In this analogy, the average cooling or heating demand is an errand within a mile of your home. Instead of repeatedly driving one mile at 70 mph it would be much more efficient to get there at a reasonable speed and then remain in the vicinity. That is exactly what having an inverter driven compressor is like.
Relatively recently in the HVAC industry, inverter-driven compressors have become much more commonplace. These innovative designs initiate at around 15% operating capacity and only go to as high as what is needed to satisfy the demand for heating or cooling. Then the compressor ramps down to a level where it can maintain the temperature and efficiently hovers there. Over a long period such as a whole cooling season, the ability of the inverter drive to more efficiently modulate cooling capacity can really add up in terms of energy costs saved. It also keeps a more consistent temperature in the space. The following chart compares an inverter driven compressor with a traditional fixed-speed compressor, in terms of energy costs saved.