Air to air simply means a heat pump that sits outside of your home and pulls heat from the outside air. This is the most common type of heat pump.
heat is hot, air is cold Heat and air differ in every respect; heat is a form of energy that is transferred by a difference in temperature, and air is a mixture of gases.
Mix air,heat and fuel.
Air is matter but heat is energy.
When you heat air, the air pressure rises and the particles expand.
An air conditioner blows out heat
The convection of the air causes the particles to heat up. In other words, the heated particles hit the air particles, causing the air particles to heat up. So it doesn't "conduct" heat rather that the air heats up from a heat source.
The heating of the air is by radiant heat from the sun.
The body transfer heat to air by a heat transfer method called radiation.
An air conditioner if functioning as air warmer or air chiller can be called as a type of heat pump. If an air conditioner is working as an air de-humidifier then it no more a heat pump.
A heat pump pulls the air back through and recylces it to make heat. A heat strip is just air being pushed across the heat strip to make the air warm.
Air conditioning will expel heat to the outside when cooling. On the heat cycle the reverse is evident