Two-stage cooling means the air conditioner or heat pump has a compressor with two levels of operation: high for hot summer days, and low for milder days. Since the low setting is adequate to meet household-cooling demands 80% of the time, a two-stage unit runs for longer periods and produces more even temperatures.
Two-stage systems have two operating capacities, typically 50% and 100%. The thermostat will first attempt to maintain comfort by operating only the lower (50%) stage, since it is more efficient. When the system cannot maintain comfort with the lower stage, it will begin to operate the second stage.
- A two-stage system operating at 25% demand will run the first stage 50% of the time. Runtime would be 50% for this case.
- A two-stage system operating at 50% demand runs first stage 100% of the time. Runtime would be 100% for this case.
- A two-stage system operating at 75% demand run first stage 50% of the time and second stage 50% of the time. Runtime would be 100% for this case.
- A two-stage system operating at 100% demand runs second stage 100% of the time. Runtime would be 100% for this case.
Longer cooling cycles also translate to quieter, more efficient operation and enhanced humidity control. Compared to a single-stage unit, a two-stage air conditioner or heat pump can remove twice as much moisture from the air. This is important because when moisture levels are high, there's a higher potential for mold and other pollutant problems.
