One measures temperature in degrees (°C or °K) according to a scale which is defined arbitrarily once for ever. For instance, for the Celsius scale, it has been decided that 0 °C is the temperature of melting ice and that 100 °C is the temperature of boiling water. For the Kelvin scale,it has been decided that 1 degree °C is equal to 1 degree °K and that 0 °K is the same temperature as -273 °C which is the theoretical temperature of the "back" of the universe (the absolute zero, i.e. nothing in the world can be colder).
2) Thermal energy and thermal power
Thermal energy is measured in Joules (J). It is a total quantity of energy you can receive, or you need to capture, or you have at disposition and you can use. If you compare it with water, it is like the quantity of water you have in a container.
The increase in temperature of a material is in relation with a given quantity of added heat or thermal energy. To get this quantity of thermal energy, you need a flow of energy (an intensity), during a given duration of time; this flow of energy is called thermal power, and is measured in Watt (W) - see Physics Units.
(drawing by David Wright)
We have the following relation between thermal energy and thermal power: a thermal power (in W) will last for a given time (number of hours) and provide a quantity of energy (in J): 1 J = 1Wh or 1 W = 1 J/h, i.e. one Watt is the thermal power of an energy flow which will bring the total quantity of energy of one Joule if it lasts for one hour. If you compare the flow of energy to the flow of water, the thermal power (in W) is similar to the flow in litre/min. The quantity of thermal energy we receive from the sun is measured in Watt/m2; if you expose a bigger surface (in m2) to the sun, you capture a bigger quantity of energy (in J) during a given time.
3) The specific heat C of a material The specific heat C of a material (in J/kg °C or in kcal/kg °C) is the quantity of heat needed to increase the temperature of 1 kg of this material by 1 degree. It is also the quantity of heat this material will restitute when its temperature drops by 1 degree. For water, the calorific heat is 1000 cal/kg °C, it means you need 1000 cal to increase the temperature of 1 kg of water by 1°C. For concrete it is only 156 cal/kg °C and for steel only 120. This data is very interesting because it means that 1 kg of water can store 6.4 times more heat than 1 kg of concrete.
4) The calorific capacity of a material The calorific capacity is the same as the specific heat but related to volume instead of to weight. It means that it takes into account the specific weight of the given material (i.e. the weight of this material per volume unit). You can therefore calculate the calorific capacity of each material by multiplying the specific heat by the specific weight of this same material. We said that 1 kg of water can store 6.4 times more heat than 1 kg of concrete, but concrete is 2.3 times heavier (it means denser) than water. It means then that the calorific capacity of water is only 2.7 times higher than the one of concrete.
Water contains 3 .5 times more heat than the same volume of sand (drawing by David Wright)
5) The latent heat The latent heat is the quantity of energy (in J/kg or in cal/kg) which is needed to change the state of a material from solid to liquid or from liquid to gas without changing its temperature. It is for instance 80 kcal/kg (334kJ/kg) for water. It means you need 80 kcal to transform 1 kg of ice into 1 kg of water at 0 °C, without changing its temperature!
This data is very interesting because it shows the quantity of energy the change of state can consume or return. For instance, the evaporation of water is used for cooling and each kg of water which evaporates absorbs 80 kcal which are taken in the surrounding air, of which the temperature drops according to the specific heat (cal/kg °C) or the calorific capacity of air (in cal/m3. You can see how theses data can be used practically.
(drawing by David Wright)
The 6 characteristics of heat transfer by conduction