When the school districts decided to have them installed. Heating systems in schools, even if just in the form of a wood stove, have been around essentially as long as schools themselves have; air conditioning is a relatively recent development.
electric does it has water that evaporates and it turns in to heat or cold air
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.
The amount of heat in air is measured using the specific heat capacity of air, which is about 1 kJ/kg°C. The total heat in air can be calculated by multiplying the specific heat capacity with the mass of air and the change in temperature.
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.
Removing heat from the air will decrease the air temperature. Heat is what gives particles in the air energy to move and the removal of heat will cause the particles to slow down, resulting in a decrease in temperature.
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.
To be honest, it never really gets that hot for the schools in the UK to close. Even if it did get really hot, I doubt they would send us home as they have air conditioners and wouldn't send us home because of heat.
The heating of the air is by radiant heat from the sun.
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.