Hydraulics is the physics field that studies fluid mechanics and is divided into Hydrostatic (liquids at rest) and hydrodynamics (liquid in motion).

density of a body d is called the mass m and volume V ratio:

d = m / V

specific gravity pe is the weight (= m g.) and volume ratio:

pe = m. g / V

Fluids (liquids and gases) always exert a pressure pr in all directions.

The pressure is the quotient between a force f (the exerted by the fluid) and the surface area S acted upon by this force:

pr = f / S

The pressure unit in the SI is the Newton divided by m2 (N / m2) and is called pascal.

Pressure exerted by gravity and the forces tending to compress the fluid is called static pressure.

The pressure resulting from movement of a fluid is called dynamic pressure.

Knowing the density or specific gravity of a fluid we can find the static pressure due to gravity at any depth h from either of the following two formulas:

pr = d. g. h

pr = pe. h

The pressure difference is equal to the depths difference h between 2 points or vertical distance between them.

A typical static pressure, is the atmospheric pressure produced in all directions on the bodies placed on earth surface due to the large air column above them. The result of this all directions atmospheric pressure action produces no net force pushing the body to one side, tends to compress it.

In the case of a container, the atmospheric pressure acts inside and outside and therefore their actions cancel each other.

We are interested in knowing the excess pressure above atmospheric pressure that may be inside the container (tanks or pipes) through measuring devices (manometers).

If air can freely enter and leave a container through the edge of the lid, the liquid surface will only be subjected to atmospheric pressure. It is an open or non pressurized reservoir.

If we measured pressure at different heights in the tank with a manometer it will be equal to zero at the surface and maximum at the bottom.

If the container is now sealed and subjected to additional pressure p, transmitted through the pipes that communicate with distribution circuit; the measurement is equal to the previous one but increased in the value of p. Usually the small pressure difference caused by the height difference is negligible compared to the overall circuit pressure p.

Archimedes’s theorem allows us to know a body weight when it is immersed in a liquid.

This theorem can be applied to a same liquid portion.

Suppose that a liquid portion suffer a slight temperature increase relative to other liquid parts.

Bodies expand by its temperature increasing and when increasing its volume density decreases as mass remains unchanged.

If d1 is the new density of the portion considered (d1 < d):

Weight of the liquid portion: p = m. g = V1. d1. g

Thrust acting on the liquid portion: E = V1. d. g

Where V1 is the volume of the liquid portion

These are the called fluids natural convection currents, in which hot parts tend to rise. Natural circulation or thermosyphon systems are based on this phenomenon for supplying hot water by solar collectors.

This content is part of “Solar Energy Introduction” eBook and solar e-learning of Sopelia.

Sorry, this entry is only available in Español.

One of the most important issues in energy conservation areas and solar energy use is undoubtedly homes and workplaces air conditioning application.

This sector accounts about 40% of the total energy consumed. The savings can be achieved by using solar energy for heating is of the order of 60% to 80% depending on house design.

The principles of bioclimatic architecture should be applied in all new urban plans.

When speaking of passive solar architecture, we talk about modeling, selection and use of passive solar technology, which is capable of maintaining a comfortable and pleasant temperature home environment through the sun. This type of architecture is only a small part of the energy efficient buildings design and is considered as part of sustainable design.

There are three types of solar gain:

1) Direct solar gain: refers to the use of windows, skylights and blinds to control the amount of solar radiation reaching the inside of a housing, in combination with mass floors.

2) Indirect solar gain: is achieved through the skin of the building, designed with certain thermal mass. An example of this gain is also the garden roof.

3) Isolated solar gain: is the process in which the main thing is the sun heat passive capture, and then transport it inside or outside the home.

There are considerations to take into account in this type of architecture implementation, to give his best result:

* Building orientation

* Construction features

* Environment use

In existing buildings we can always intervene to improve thermal insulation, sun blinds open in winter or adding a glass gallery on the north side of the house if we are located in the southern hemisphere.

To heat the house with the sun, a clear winter north facade without many neighbors who clog the midday sun is needed.

Main glazings must be on the north facade. For example, if we are located in the southern half of Argentina we need 1.4 to 2 m2 of north glass for every 10 m2 stay we want to heat.

Windows should be closed with curtains or blinds at night to heat captured not escape. It is good to improve thermal insulation as far as possible and have thermal mass (building material in walls, floors) which accumulate the heat of the day to the night. For summer it is necessary to place eaves, awnings, vines, etc. that shade windows in.

You can acces more Spanish language content like this in Manual Técnico – Comercial de Energía Solar Térmica by Sopelia.

What qualities should we consider when selecting a solar thermal collector?

Are two:

1- Its constructive qualities. Determines the durability and architectural integration possibility.

2- His energetic qualities. Determines economic performance.

In some respects both qualities are interrelated.

A good solar collector is one who possesses both qualities well balanced for the intended application.

There is no use a solar collector with an extraordinary energy intake if their constructive qualities fail or degrade quickly, since the profitability of these facilities is measured in the medium term.

There is no use a solar collector with extraordinary constructive qualities if their energetic qualities fail, because, simply, it is not fulfilling its main task.

By observing the solar collector performance curve, we see that it depends on a variable which is the temperature T, which in turn depends on the solar radiation I, on solar collector fluid inlet temperature Te and on ambient temperature Ta.

That is, the performance of a collector depends:

– On one side of the weather conditions, given by I and Ta,

– On the other side of the working conditions, that is, of what it is used, given by Te.

Therefore, when selecting a collector must be considered:

1) The application will have (only ACS, only heating, hot water and heating, pool heating, etc.).

2) Climatic and radiation conditions of facility location.

3) Models performance curves.

4) Equipment price.

5) The economic profitability (based purely on the relationship between price and yield) and investment recovery period.

6) Its construction quality.

You need to balance construction quality with energetic quality.

There is an open debate among professionals about which of the two most used collectors technologies is the most appropriate: flat or vacuum tube collector?

Those who opt for vacuum tube collectors consider them more advanced and argue that in the future this technology will eventually displace definitely flat plate collectors because of their better performance.

The increased cost gap of vacuum tube collectors respect to flat collectors has been reduced and we can find collectors of both technologies at the same price.

Supporters of the vacuum tube collectors consider opting for them is compensated, because by offering higher performance per m2 we will need to purchase less collectors.

This is not necessarily true, especially in small facilities:

In a small facility that only provides ACS with good weather and radiation conditions, flat plate collectors performance and profitability will be greater.

As you increase the size of the installation, the vacuum tube collector highest performance will offset the lower absorbing surface.

We will also consider building integration of vacuum tubes direct flow collectors (U-Pipe) that can be placed vertically covering a façade or balcony.

In short, a properly trained professional must assess based on the following factors choosing one or the other technology:

• Specific requirements of the installation

• Location climatology in every season

• Previous experience

• Budget availability.

You can find content like this in the Technical – Commercial Solar Thermal Energy Manual by Sopelia

When Federico Redin answered the phone call at his office in Bahia Blanca (Argentina) he was happy because it was to request their installation services in a new solar energy project.

But when he came to the house where the project would be located, he realized that the facility had some complexity.

It was a continuous use indoor pool with bathroom, dressing room and kitchen.

The pool was closed with rustic solid brick walls, aluminum DVH low quality openings in the enclosure and transparent polycarbonate roof. A challenge.

After the visit, which solution adopt to optimally configure the installation was going around in his head.

Appealing to the characteristic creativity of Argentine people, Federico took an unconventional solution: swimming pool conditioning by floor heating (in the transit zones of the enclosure and in the pool itself).

In this way it would achieve heat the pool regardless of the type of water containing the glass and more efficiently, since conventional pool heating has the negative inertia of moving water.

By heating the pool water with a conventional boiler the water is set into motion with the same pool pump, causing cooling it by this movement; which decreases the overall installation performance.

Therefore, a more powerful source of energy and more thermal reaction is needed.

We know that using solar energy do not have a large thermal reaction, ie the heating time is slower.

By heating the pool with underfloor heating water turns hot through the concrete, once in regime, it has more thermal inertia and allows solar energy to maintain that regime.

The radiant “glass” pool and the transit floor area of the enclosure receive input from a conventional gas boiler, which is responsible for putting installation in system, and 7 heat pipe collectors supplying directly fluid to the circuit (without heat exchanger) that transfers heat in sunshine.

Temperature is regulated with a mixing thermostatic valve to not degrade the soil at high temperatures.

The system has a thermostat for transit zones and a thermostat for swimming pool water.

Then room or water temperature are discriminated with electric heads located at the underfloor heating collector, separating pool and transit zones of the enclosure.

The pool has a natural salt chlorination system (salt water 5%) thus avoiding the use of chlorine.

Having 2 separate circuits (the pool and underfloor heating), we protect the boiler to heat salt water, which quickly will cause severe and irreversible damage to it.

Federico Redin is Sopelia facilities expert advisor.