The volume of air that passes through the heat pump must be cooled (or warmed) at the same rate as it is dehumidified, unless humidity control can be done independent of the pump. If you oversize the pump, the house is cooled faster than it is dehumidified, and the air reaches the desired temp before it reaches the desired humidity, and the compressor turns off while the air is still humid.
It's possible to independently add humidity when heating -- using a mist gun -- but not to remove it during cooling. However, if the heat pump has a "dry mode" it can dehumidify without also cooling by switching back and forth between heat and cool mode. If not, to dry the air further, it must cool it further.
It's possible to independently add humidity when heating -- using a mist gun -- but not to remove it during cooling. However, if the heat pump has a "dry mode" it can dehumidify without also cooling by switching back and forth between heat and cool mode. If not, to dry the air further, it must cool it further.