What is integrated heat capacity in air source heat pumps?

The integrated heat capacity refers to a time-averaged capacity that includes defrost.

In other words, the point at which capacity and integrated heat capacity do not match, you expect the defrost cycle to come on intermittently.  The further apart the two numbers are, the greater the frequency of defrost cycles.

The table below shows an example of what integrated capacity will look like as the outdoor temperature drops. The defrost switch is enabled when the outdoor temperature drops below 41°F, which is shown by the values in red text.  Integrated capacity is important as it will help to size a unit more accurately under actual performance conditions. This table will also include energy recovery performance if selected.