1. The Heat Pump-pumps heat from a cold area to a warmer area.
1=condenser 2=expansion valve
3= evaporator 4=compressor

3. A liquid with low boiling point and high specific latent heat capacity evaporates at low pressure inside the cold body. The vapour is pumped through a compressor and condenses under high pressure releasing its latent heat to the outside so cooling the cold body and heating the warm body.
The cooling liquid must have a:
high specific latent heat capacity and
low boiling point.

4. Solar constant The rate at which solar energy falls perpendicularly on unit area when the earth is at its mean distance from the sum.
Conduction: This is the transfer of heat through a solid, without the movement of the solid.
Convection: This is the transfer of heat through a liquid or a gas when molecules of the liquid or gas move and carry the heat..
Radiation This is the transfer of heat by electromagnetic radiation.
U value The rate at which heat energy is transferred through 1m2 area for a 10C temperature difference between the two sides.