

Basic theory of water
heating

Solar energy
The sun is a star located at some 150 million km from
earth. It is made of 85% hydrogen and 15% helium. Its temperature
fluctuates between 15 and 20 million degrees Celsius. This flow of
energy comes from the transformation of hydrogen into helium. Every
hour our sun consumes 10 billions tons of hydrogen. This energy is
diffused into space as light and heat.


Earth, our small planet gets some of this energy
produced by the sun. We receive the equivalent of some 1000
watts/square meter. A one square meter surface placed at a angle of
90 degree to the sun will get two kinds of energy: Direct solar
radiations and diffused radiations. The former comes from the sun
where as the latter is the reflexion from various objects. The
addition of both radiations is called global radiation. This global
radiation may reach some 1400 watts per square meter in some
instances. 
Solar captors
There are two types of solar captors: The one that
transforms solar radiation into electricity and the one that
transforms it into heat. The former is very expensive and not very
efficient. The solar captors presented in the DVD transform solar
radiations into heat. This heat will then be used to heat up your
swimming pool.
Like
others, you have noticed that any black object exposed to the sun
radiations becomes warm. The explanation is quite simple: Any dark
object transforms solar radiations into heat which is then
dissipated into the atmosphere. A black surface is therefore a
simple solar captor.
A perfectly black surface exposed to the sun rays
will transform this solar radiation into calorific energy, in other
words heating energy. As already mentioned, the energy is about 1000
watts/m² during a nice sunny day.

The idea is to recuperate this enormous amount of
energy coming from the sun and use it to heat up the water of a
swimming pool using a series of solar panels which you will build
yourself following the instructions on the DVD.




Thermodynamic
All matter is made of atoms and molecules in constant
movement. The movement of these particles generates an internal
energy called thermal energy. Temperature measurement informs us on
the intensity of these movements. The higher the temperature, the
higher the level of agitation.
Heat is
defined as being a transfer of thermal energy. When
something is heated, a
transfer of energy occurs between the heating body and the heated
one. Both thermal energy and heat are expressed in joules and the
symbol is Q.
All bodies do not absorb heat in the same manner.
Depending on their nature and weight, they heat up and cool down at
different speeds. For that reason, the notion of thermal mass has
been introduced. Thermal mass of any substance is the amount of heat
needed to bring an increase of 1 Kelvin to a kilogram of this
substance. This thermal mass is represented by the letter C. For
instance, the thermal heat of water is 4186.8. This means that
4186.8 joules of energy must be supplied to 1 kg of water to
increase the temperature of 1 Celsius or 1 Kelvin.

Thermal mass of few substances

Notice that water as such has a very high thermal
mass. This is the reason why it is so difficult to heat up the water
of a swimming pool which shows how important it is to have an
efficient heating system.
When a hot material is put in contact with a cold
one, there is a spontaneous transfer of heat from the hot to the
cold material until both material reach the same temperature. We
then say that the system is in thermal equilibrium. This is the
basic principle surrounding the solar heating system presented in
this document. The correlation between heat and temperature is
currently expressed by the following mathematical equation: 

Let us calculate the heat needed to bring 1 liter of
water to the boiling point (100°C), assuming that the atmospheric
pressure is constant:

Q
= mcDt
Q= Amount of heat in Joules
m= 1 kg (because 1 liter of
water = 1kg)
c= 4186j/kg•C
Δt= Difference in
temperature = 100°C  20°C = 80°C
Q= 1kg X 4186j/kg.C X 80°C
Q= 334944 joules or 335 Kj


We could have solved this problem differently if the
notion of Calorie had been used.
A calorie is defined as the amount of energy needed
to bring a 1 degreeCelsius increase in temperature of 1cm³ (1 ml)
of water. Therefore:
1 calorie =
4.1868 joules 
We could have solved this problem in a different way:
Since it takes 1 calorie to increase by 1 degree 1 cm^{3}
of water, 1000 calories are needed to increase by 1 degree 1 kg
(1000 cm³) of water. Therefore 80000 calories (80 x 1000) to
increase by 80°C 1 kg of water. Since 1 calorie = 4.1868 joules, the
result is 80000 calories X 4.1868= 334944 joules or 335 kj.

Miscellaneous
technical information

Here is another example: A coffee machine contains 1
liter of water. Knowing that the electrical resistance is 1500
watts, how long will it take to bring the water from 15° C to 80° C
?

1500 watts= 1500 j/s = 358
calories/second (1500/4.186)

Difference in temperature (Δt)
= 80°  15° = 65° C

1 Liter of water = 1000ml =
1000 cm^{3}

To increase 1000 ml by 1° C
requires 1000 calories.

To increase 1000 ml by 65° C
requires 65000 calories.

65000 calorie/358 calories per
second = 181 seconds = 3 minutes

To
summarize, we must remember that:
· On
the earth surface, the power of solar radiations is a little over
1000 watts per square meter;
· A
black object converts the solar radiation into heat;
· Water
is difficult to heat up;
· Finally,
to heat up the water of a swimming pool, a large quantity of heat is
needed.

Make you own solar water heater four your pool!
WWW.SOLARPANELSFORPOOL.COM
