Solar heating systems. Soviet and Russian solar heating - scientific and engineering schools. Air heating system

18.10.2019

Solar heating systems

4.1. Classification and main elements of solar systems

Solar heating systems are systems that use solar radiation as a source of thermal energy. Their characteristic difference from other low-temperature heating systems is the use of a special element - a solar receiver, designed to capture solar radiation and convert it into thermal energy.

According to the method of using solar radiation, solar low-temperature heating systems are divided into passive and active.

Systems are called passive solar heating, in which the building itself or its individual fences (collector building, collector wall, collector roof, etc.) serve as an element that receives solar radiation and converts it into heat (Fig. 4.1.1)).

Rice. 4.1.1 Passive low-temperature solar heating system "collector wall": 1 - sun rays; 2 – translucent screen; 3 - air damper; 4 - heated air; 5 - cooled air from the room; 6 - own long-wave thermal radiation of the wall array; 7 - black ray-receiving surface of the wall; 8 - blinds.

Solar low-temperature heating systems are called active, in which the solar receiver is an independent separate device that is not related to the building. Active solar systems can be subdivided:

by purpose (hot water supply, heating systems, combined systems for heat and cold supply);

by type of coolant used (liquid - water, antifreeze and air);

by duration of work (year-round, seasonal);

according to the technical solution of the schemes (one-, two-, multi-loop).

Air is a widely used coolant that does not freeze over the entire range of operating parameters. When used as a heat carrier, it is possible to combine heating systems with a ventilation system. However, air is a low-heat-capacity coolant, which leads to an increase in metal consumption for the installation of systems air heating compared to water systems.

Water is a heat-intensive and widely available coolant. However, at temperatures below 0°C it is necessary to add antifreeze liquids. In addition, it must be taken into account that water saturated with oxygen causes corrosion of pipelines and apparatus. But the consumption of metal in water solar systems is much lower, which to a large extent contributes to their wider use.

Seasonal hot water solar systems are usually single-circuit and operate in the summer and transitional months, during periods with a positive outside temperature. They may have an additional source of heat or do without it, depending on the purpose of the serviced object and operating conditions.

Solar systems for heating buildings are usually double-circuit or, most often, multi-circuit, and different heat carriers can be used for different circuits (for example, aqueous solutions of antifreeze liquids in a solar circuit, water in intermediate circuits, and air in a consumer circuit).

Combined year-round solar systems for the purposes of heat and cold supply of buildings are multi-circuit and include an additional source of heat in the form of a traditional heat generator running on organic fuel or a heat transformer.

circuit diagram solar heating system is shown in Figure 4.1.2. It includes three circulation circuits:

the first circuit, consisting of solar collectors 1, circulation pump 8 and liquid heat exchanger 3;

the second circuit, consisting of a storage tank 2, a circulation pump 8 and a heat exchanger 3;

the third circuit, consisting of a storage tank 2, a circulation pump 8, a water-air heat exchanger (heater) 5.

Rice. 4.1.2. Schematic diagram of the solar heating system: 1 - solar collector; 2 - storage tank; 3 - heat exchanger; 4 - building; 5 - heater; 6 - understudy of the heating system; 7 - backup system of hot water supply; eight - circulation pump; 9 - fan.

The solar heating system operates as follows. The coolant (antifreeze) of the heat-receiving circuit, being heated in the solar collectors 1, enters the heat exchanger 3, where the heat of the antifreeze is transferred to the water circulating in the annular space of the heat exchanger 3 under the action of the pump 8 of the secondary circuit. The heated water enters the storage tank 2. From the storage tank, water is taken by the hot water supply pump 8, brought, if necessary, to the required temperature in the doubler 7 and enters the hot water supply system of the building. The storage tank is fed from the water supply.

For heating, water from the storage tank 2 is supplied by the pump of the third circuit 8 to the heater 5, through which air is passed through with the help of a fan 9 and, having heated up, enters the building 4. In the absence of solar radiation or a lack of thermal energy generated by solar collectors, the work turn on backup 6.

The choice and layout of the elements of the solar heating system in each case is determined by climatic factors, the purpose of the object, the mode of heat consumption, and economic indicators.

4.2. Concentrating solar receivers

Concentrating solar receivers are spherical or parabolic mirrors (Fig. 4.2.1), made of polished metal, in the focus of which a heat-receiving element (solar boiler) is placed, through which the coolant circulates. Water or non-freezing liquids are used as a heat carrier. When used as a water coolant at night and during cold period the system must be emptied to prevent it from freezing.

To ensure the high efficiency of the process of capturing and converting solar radiation, the concentrating solar receiver must be constantly directed strictly at the Sun. For this purpose, the solar receiver is equipped with a tracking system, including a sun direction sensor, an electronic signal conversion unit, an electric motor with a gearbox for rotating the solar receiver structure in two planes.

Rice. 4.2.1. Concentrating solar receivers: a - parabolic concentrator; b – parabolic trough concentrator; 1 - sun rays; 2 - heat-receiving element (solar collector); 3 - mirror; 4 – tracking system drive mechanism; 5 - pipelines supplying and discharging the coolant.

The advantage of systems with concentrating solar receivers is the ability to generate heat at a relatively high temperature (up to 100 °C) and even steam. The disadvantages include the high cost of construction; the need for constant cleaning of reflective surfaces from dust; work only during daylight hours, and therefore, the need for large batteries; high energy consumption for the drive of the tracking system for the course of the Sun, commensurate with the generated energy. These shortcomings hinder wide application active low temperature systems solar heating with concentrating solar receivers. Recently, flat solar receivers are most often used for solar low-temperature heating systems.

4.3. Flat solar collectors

Flat plate solar collector - a device with a flat configuration absorbing panel and flat transparent insulation for absorbing the energy of solar radiation and converting it into heat.

Flat plate solar collectors (fig. 4.3.1) consist of a glass or plastic cover (single, double, triple), a heat absorbing panel painted black on the side facing the sun, insulation on the back and a housing (metal, plastic, glass, wood).

Rice. 4.3.1. Flat solar collector: 1 - sun rays; 2 - glazing; 3 - body; 4 - heat-receiving surface; 5 - thermal insulation; 6 - sealant; 7 - own long-wave radiation of the heat-receiving plate.

As a heat-receiving panel, you can use any metal or plastic sheet with channels for the coolant. Heat-receiving panels are made of aluminum or steel of two types: sheet-pipe and stamped panels (pipe in sheet). Plastic panels due to fragility and rapid aging under the action of sunlight, as well as due to low thermal conductivity, are not widely used.

Under the action of solar radiation, heat-receiving panels are heated to temperatures of 70-80 ° C, which exceed the ambient temperature, which leads to an increase in the convective heat transfer of the panel in environment and its own radiation to the sky. To achieve more high temperatures coolant, the surface of the plate is covered with spectrally selective layers that actively absorb the short-wave radiation of the sun and reduce its own thermal radiation in the long-wave part of the spectrum. Such structures based on “black nickel”, “black chrome”, copper oxide on aluminum, copper oxide on copper and others are expensive (their cost is often commensurate with the cost of the heat-receiving panel itself). Another way to improve the performance of flat plate collectors is to create a vacuum between the heat absorbing panel and transparent insulation to reduce heat loss (fourth generation solar collectors).

The experience of operating solar installations based on solar collectors has revealed a number of significant drawbacks of such systems. First of all, this is the high cost of collectors. Increasing the efficiency of their work due to selective coatings, increasing the transparency of glazing, evacuation, as well as the device of the cooling system turn out to be economically unprofitable. A significant disadvantage is the need for frequent cleaning of glass from dust, which practically excludes the use of a collector in industrial areas. During long-term operation of solar collectors, especially in winter conditions, there is a frequent failure of them due to the uneven expansion of the illuminated and dark areas of the glass due to the violation of the integrity of the glazing. There is also a large percentage of collector failure during transportation and installation. A significant disadvantage of the systems with collectors is also the uneven load during the year and day. The experience of operation of collectors in the conditions of Europe and the European part of Russia with a high proportion of diffuse radiation (up to 50%) showed the impossibility of creating a year-round autonomous system of hot water supply and heating. All solar systems with solar collectors in mid-latitudes require the installation of large storage tanks and the inclusion of an additional energy source in the system, which reduces the economic effect of their use. In this regard, it is most expedient to use them in areas with a high average intensity of solar radiation (not lower than 300 W/m2).

Potential opportunities for the use of solar energy in Ukraine

On the territory of Ukraine, the energy of solar radiation for one average annual light day is on average 4 kW ∙ hour per 1 m 2 (in summer days- up to 6 - 6.5 kW ∙ hour) i.e. about 1.5 thousand kW ∙ hour per year for each square meter. This is about the same as in central Europe, where the use of solar energy is the most widespread.

In addition to favorable climatic conditions in Ukraine, there are highly qualified scientific personnel in the field of solar energy use. After the return of Prof. Boyko B.T. from UNESCO, where he headed the UNESCO international program on the use of solar energy (1973-1979), he began an intensive scientific and organizational activity at the Kharkov Polytechnic Institute (now the National Technical University - KhPI) on the development of a new scientific and educational direction of materials science for solar energy. Already in 1983, in accordance with the order of the USSR Ministry of Higher Education N 885 dated July 13, 1983, at the Kharkov Polytechnic Institute, for the first time in the practice of higher education in the USSR, the training of physicists with profiling in the field of materials science for solar energy within the framework of the specialty “Physics of Metals” began. This laid the foundation for the creation in 1988 of the graduating department “Physical Materials Science for Electronics and Solar Energy” (FMEG). The Department of FMEG in collaboration with the Research Institute of Instrument Engineering Technology (Kharkov) within the framework of the space program of Ukraine took part in the creation of silicon solar panels with efficiency thirteen - 14% for Ukrainian spacecraft.

Since 1994, the FMEG Department, with the support of the University of Stuttgart and the European Community, as well as the Zurich University of Technology and the Swiss National Science Society, has been accepting Active participation in scientific research on the development of film solar cells.

Consumption ecology. Manor: Most of the year we have to spend money on heating our homes. In such a situation, any help will not be superfluous. The energy of the sun is the best suited for these purposes: it is absolutely environmentally friendly and free.

Most of the year we have to spend money on heating our homes. In such a situation, any help will not be superfluous. The energy of the sun is the best suited for these purposes: it is absolutely environmentally friendly and free. Modern technologies allow solar heating of a private house not only in the southern regions, but also in the middle lane.

What modern technology has to offer

On average, 1 m2 of the earth's surface receives 161 watts of solar energy per hour. Of course, at the equator this figure will be many times higher than in the Arctic. In addition, the density of solar radiation depends on the time of year. In the Moscow region, the intensity of solar radiation in December-January differs from May-July by more than five times. However, modern systems are so efficient that they can work almost anywhere on earth.

The problem of using the energy of solar radiation with maximum efficiency is solved in two ways: direct heating in thermal collectors and solar photovoltaic batteries.

Solar panels first convert the energy of sunlight into electricity, then transfer it through a special system to consumers, such as an electric boiler.

Thermal collectors heating up under the action of sunlight heat the coolant of heating systems and hot water supply.

There are several types of thermal collectors, including open and closed systems, flat and spherical designs, hemispherical manifolds concentrators and many other options.

Thermal energy obtained from solar collectors is used for heating hot water or heating system coolant.

Despite the clear progress in the development of solutions for the collection, storage and use of solar energy, there are advantages and disadvantages.

The efficiency of solar heating in our latitudes is rather low, which is explained by the insufficient number of sunny days for the regular operation of the system.

Pros and cons of using solar energy

The most obvious advantage of using solar energy is its availability. In fact, even in the most gloomy and cloudy weather, solar energy can be collected and used.

The second plus is zero emissions. In fact, it is the most environmentally friendly and natural form of energy. Solar panels and collectors do not produce noise. In most cases, they are installed on the roofs of buildings, without occupying the usable area of a suburban area.

The disadvantages associated with the use of solar energy are the inconstancy of illumination. At night, there is nothing to collect, the situation is aggravated by the fact that the peak of the heating season falls on the shortest daylight hours of the year.

A significant disadvantage of heating based on the use of solar collectors is the inability to accumulate thermal energy. Only the expansion tank is included in the diagram

It is necessary to monitor the optical cleanliness of the panels, slight contamination drastically reduces the efficiency.

In addition, it cannot be said that the operation of a solar-powered system is completely free, there are fixed costs for depreciation of equipment, the operation of a circulation pump and control electronics.

Open solar collectors

An open solar collector is a system of tubes that is not protected from external influences, through which a coolant heated directly by the sun circulates. Water, gas, air, antifreeze are used as a heat carrier. The tubes are either mounted on a carrier plate in the form of a serpentine or connected in parallel rows to the outlet.

Open-type solar collectors are not able to cope with the heating of a private house. Due to the lack of insulation, the coolant cools quickly. They are used in the summer mainly for heating water in showers or pools.

Open collectors usually have no insulation. The design is very simple, therefore it has a low cost and is often made independently.

Due to the lack of insulation, they practically do not save the energy received from the sun, they are characterized by low efficiency. They are mainly used in summer period for heating water in swimming pools or summer showers. They are installed in sunny and warm regions, with small differences in ambient air temperature and heated water. Works well only in sunny, calm weather.

The simplest solar collector with a heat sink made from a bay polymer pipes, will provide the supply of heated water in the country for irrigation and domestic needs

Tubular solar collectors

Tubular solar collectors are assembled from separate tubes through which water, gas or steam runs. This is one of the open type solar systems. However, the coolant is already much better protected from external negativity. Especially in vacuum installations, arranged according to the principle of thermoses.

Each tube is connected to the system separately, parallel to each other. If one tube fails, it is easy to replace it with a new one. The entire structure can be assembled directly on the roof of the building, which greatly facilitates installation.

The tubular collector has a modular structure. The main element is a vacuum tube, the number of tubes varies from 18 to 30, which allows you to accurately select the power of the system

A significant plus of tubular solar collectors lies in the cylindrical shape of the main elements, thanks to which solar radiation is captured all day long without the use of expensive systems for tracking the movement of the luminary.

A special multi-layer coating creates a kind of optical trap for the sun's rays. The diagram partially shows the outer wall of the vacuum flask reflecting the rays onto the walls of the inner flask

According to the design of the tubes, pen and coaxial solar collectors are distinguished.

The coaxial tube is a Diyur vessel or a familiar thermos. They are made of two flasks between which the air is pumped out. The inner surface of the inner bulb is coated with a highly selective coating that effectively absorbs solar energy.

Thermal energy from the internal selective layer is transferred to a heat pipe or an internal heat exchanger made of aluminum plates. At this stage, unwanted heat losses occur.

The pen tube is glass cylinder with a feather absorber inserted inside.

For good thermal insulation, air is pumped out of the tube. Heat transfer from the absorber occurs without loss, so the efficiency of feather tubes is higher.

According to the method of heat transfer, there are two systems: direct-flow and with a heat pipe (heat pipe).

A thermotube is a sealed container with a volatile liquid.

Inside the thermotube is a volatile liquid that absorbs heat from inner wall flask or from a pen absorber. Under the action of temperature, the liquid boils and rises in the form of vapor. After the heat is given off to the heating or hot water coolant, the steam condenses into a liquid and flows down.

Water at low pressure is often used as a volatile liquid.

A direct-flow system uses a U-shaped tube through which water or a heating system coolant circulates.

One half of the U-shaped tube is designed for cold coolant, the second takes the heated one. When heated, the coolant expands and enters the storage tank, providing natural circulation. As with thermotube systems, the minimum angle of inclination must be at least 20⁰.

Direct-flow systems are more efficient because they immediately heat the coolant.

If solar collector systems are planned for use all year round, then special antifreezes are pumped into them.

Pros and cons of tubular collectors

The use of tubular solar collectors has a number of advantages and disadvantages. The design of a tubular solar collector consists of the same elements, which are relatively easy to replace.

Advantages:

low heat loss;
ability to work at temperatures up to -30⁰С;
effective performance throughout the daylight hours;
good performance in areas with a temperate and cold climate;
low windage, justified by the ability of tubular systems to pass air masses through them;
the possibility of producing a high temperature of the coolant.

Structurally, the tubular structure has a limited aperture surface. It has the following disadvantages:

not capable of self-cleaning from snow, ice, frost;
high price.

Despite the initially high cost, tubular collectors pay for themselves faster. They have a long service life.

Flat closed solar collectors

The flat collector consists of an aluminum frame, a special absorbing layer - an absorber, a transparent coating, a pipeline and a heater.

As an absorber, blackened sheet copper is used, which is characterized by ideal thermal conductivity for creating solar systems. When solar energy is absorbed by the absorber, the solar energy received by it is transferred to a heat carrier circulating through a system of tubes adjacent to the absorber.

From the outside, the closed panel is protected by a transparent coating. It is made of anti-shock tempered glass with a bandwidth of 0.4-1.8 microns. This range accounts for the maximum solar radiation. Anti-shock glass is a good protection against hail. On the back side, the entire panel is securely insulated.

Flat plate solar collectors are characterized by maximum performance and simple design. Their efficiency is increased due to the use of an absorber. They are able to capture diffuse and direct solar radiation.

The list of advantages of closed flat panels includes:

simplicity of design;
good performance in warm climate regions;
the ability to install at any angle if there are devices for changing the angle of inclination;
the ability to self-clean from snow and frost;
low price.

Flat plate solar collectors are especially advantageous if their use is planned at the design stage. The service life of quality products is 50 years.

The disadvantages include:

high heat losses;
big weight;
high windage when the panels are located at an angle to the horizon;
limitations in performance at temperature drops of more than 40 ° C.

The scope of application of closed collectors is much wider than open-type solar installations. In summer, they are able to fully satisfy the need for hot water. On cool days that are not included by public utilities during the heating period, they can work instead of gas and electric heaters.

Comparison of characteristics of solar collectors

The most important indicator of a solar collector is efficiency. The useful performance of solar collectors of different designs depends on the temperature difference. At the same time, flat-plate collectors are much cheaper than tubular ones.

The efficiency values depend on the manufacturing quality of the solar collector. The purpose of the graph is to show the efficiency of using different systems depending on the temperature difference.

When choosing a solar collector, you should pay attention to a number of parameters showing the efficiency and power of the device.

There are several important characteristics for solar collectors:

adsorption coefficient - shows the ratio of absorbed energy to total;
emission factor - shows the ratio of the transferred energy to the absorbed;
total and aperture area;
efficiency.

The aperture area is the working area of the solar collector. A flat collector has a maximum aperture area. The aperture area is equal to the area of the absorber.

Ways to connect to the heating system

Since solar-powered devices cannot provide a stable and round-the-clock supply of energy, a system that is resistant to these shortcomings is needed.

For central Russia, solar devices cannot guarantee a stable supply of energy, therefore they are used as an additional system. Integration into an existing heating and hot water system is different for a solar collector and a solar battery.

Heat collector connection diagram

Depending on the purpose of using the heat collector, different connection systems are used. There may be several options:

Summer option for hot water supply
Winter option for heating and hot water supply

The summer version is the simplest and can even do without a circulation pump, using the natural circulation of water.

Water is heated in the solar collector and due to thermal expansion enters the storage tank or boiler. In this case, natural circulation occurs: cold water is sucked into the place of hot water from the tank.

In winter, at negative temperatures, direct water heating is not possible. A special antifreeze circulates through a closed circuit, ensuring the transfer of heat from the collector to the heat exchanger in the tank

Like any system based on natural circulation, it does not work very efficiently, requiring compliance necessary slopes. In addition, the storage tank must be taller than the solar collector.

In order for the water to remain hot as long as possible, the tank must be carefully insulated.

If you want to really achieve the most efficient operation of the solar collector, the wiring diagram will become more complicated.

A non-freezing coolant circulates through the solar collector system. Forced circulation is provided by a pump controlled by a controller.

The controller controls the operation of the circulation pump based on the readings of at least two temperature sensors. The first sensor measures the temperature in the storage tank, the second - on the hot coolant supply pipe of the solar collector. As soon as the temperature in the tank exceeds the temperature of the coolant, the controller in the collector turns off the circulation pump, stopping the circulation of the coolant through the system.

In turn, when the temperature in the storage tank drops below the set value, the heating boiler is switched on.

Solar battery connection diagram

It would be tempting to apply a similar scheme for connecting a solar battery to the power grid, as is implemented in the case of a solar collector, accumulating the energy received during the day. Unfortunately, for the power supply system of a private house, it is very expensive to create a battery pack of sufficient capacity. Therefore, the connection diagram is as follows.

When power is reduced electric current from a solar battery, the ATS unit (automatic transfer switch) ensures the connection of consumers to a common electrical network

From the solar panels, the charge goes to the charge controller, which performs several functions: it provides constant recharging of the batteries and stabilizes the voltage. Next, the electric current is supplied to the inverter, where the conversion takes place direct current 12V or 24V to 220V single-phase AC.

Alas, our power grids are not adapted to receive energy, they can only work in one direction from the source to the consumer. For this reason, you will not be able to sell the produced electricity or at least make the meter spin in the opposite direction.

The use of solar panels is beneficial in that they provide more universal view energy, but at the same time cannot be compared in efficiency with solar collectors. However, the latter do not have the ability to store energy, unlike solar photovoltaic batteries.

How to calculate the required collector power

When calculating the required capacity of a solar collector, it is very often mistaken to make calculations based on the incoming solar energy in the coldest months of the year.

The fact is that in the remaining months of the year the entire system will constantly overheat. The temperature of the coolant in summer at the outlet of the solar collector can reach 200°C when heated by steam or gas, 120°C of antifreeze, 150°C of water. If the coolant boils, it will partially evaporate. As a result, it will have to be replaced.

provision of hot water supply no more than 70%;
provision of the heating system no more than 30%.

The rest of the necessary heat should be generated by standard heating equipment. Nevertheless, with such indicators, an average of about 40% is saved per year on heating and hot water supply.

Power generated by one tube vacuum system depends on geographic location. The indicator of solar energy falling per year on 1 m2 of land is called insolation. Knowing the length and diameter of the tube, you can calculate the aperture - the effective absorption area. It remains to apply the absorption and emission coefficients to calculate the power of one tube per year.

Calculation example:

The standard tube length is 1800 mm, the effective length is 1600 mm. Diameter 58 mm. Aperture is the shaded area created by the tube. Thus, the area of the shadow rectangle will be:

S = 1.6 * 0.058 = 0.0928m2

The efficiency of the middle tube is 80%, solar insolation for Moscow is about 1170 kWh/m2 per year. Thus, one tube will work out per year:

W \u003d 0.0928 * 1170 * 0.8 \u003d 86.86 kW * h

It should be noted that this is a very approximate calculation. The amount of energy generated depends on the installation orientation, angle, average annual temperature, etc. published

Classification and main elements of solar systems

According to the method of using solar radiation, solar low-temperature heating systems are divided into passive and active.

Solar heating systems are called passive, in which the building itself or its individual fences (collector building, collector wall, collector roof, etc.) serve as an element that receives solar radiation and converts it into heat (Fig. 3.4)) .

Rice. 3.4. Passive low-temperature solar heating system "collector wall": 1 - sun rays; 2 – translucent screen; 3 - air damper; 4 - heated air; 5 - cooled air from the room; 6 - own long-wave thermal radiation of the wall array; 7 - black ray-receiving surface of the wall; 8 - blinds.

Solar low-temperature heating systems are called active, in which the solar receiver is an independent separate device that is not related to the building. Active solar systems can be subdivided:

- by purpose (hot water supply, heating systems, combined systems for heat and cold supply);

- by type of coolant used (liquid - water, antifreeze and air);

- by duration of work (year-round, seasonal);

- according to the technical solution of the schemes (one-, two-, multi-loop).

Air is a widely used coolant that does not freeze over the entire range of operating parameters. When used as a heat carrier, it is possible to combine heating systems with a ventilation system. However, air is a low-heat-capacity heat carrier, which leads to an increase in metal consumption for the installation of air heating systems compared to water systems.

A schematic diagram of a solar heating system is shown in Figure 3.5. It includes three circulation circuits:

- the first circuit, consisting of solar collectors 1, circulation pump 8 and liquid heat exchanger 3;

- the second circuit, consisting of a storage tank 2, a circulation pump 8 and a heat exchanger 3;

- the third circuit, consisting of a storage tank 2, a circulation pump 8, a water-air heat exchanger (heater) 5.

Rice. 3.5. Schematic diagram of the solar heating system: 1 - solar collector; 2 - storage tank; 3 - heat exchanger; 4 - building; 5 - heater; 6 - understudy of the heating system; 7 - backup system of hot water supply; 8 - circulation pump; 9 - fan.

The choice and layout of the elements of the solar heating system in each case is determined by climatic factors, the purpose of the object, the mode of heat consumption, and economic indicators.

Concentrating solar receivers

Concentrating solar receivers are spherical or parabolic mirrors (Fig. 3.6), made of polished metal, in the focus of which a heat-receiving element (solar boiler) is placed, through which the coolant circulates. Water or non-freezing liquids are used as a heat carrier. When using water as a heat carrier at night and during the cold period, the system must be emptied to prevent it from freezing.

The advantage of systems with concentrating solar receivers is the ability to generate heat at a relatively high temperature (up to 100 °C) and even steam. The disadvantages include the high cost of construction; the need for constant cleaning of reflective surfaces from dust; work only during daylight hours, and therefore, the need for large batteries; high energy consumption for the drive of the tracking system for the course of the Sun, commensurate with the generated energy. These shortcomings hinder the widespread use of active low-temperature solar heating systems with concentrating solar receivers. Recently, flat solar receivers are most often used for solar low-temperature heating systems.

Flat solar collectors

Flat plate solar collector - a device with a flat configuration absorbing panel and flat transparent insulation for absorbing the energy of solar radiation and converting it into heat.

Flat plate solar collectors (Fig. 3.7) consist of a glass or plastic cover (single, double, triple), a heat absorbing panel painted black on the side facing the sun, insulation on the back and a housing (metal, plastic, glass, wooden).

Rice. 3.6 Concentrating solar receivers: a - parabolic concentrator; b – parabolic trough concentrator; 1 - sun rays; 2 - heat-receiving element (solar collector); 3 - mirror; 4 – tracking system drive mechanism; 5 - pipelines supplying and discharging the coolant.

Rice. 3.7. Flat solar collector: 1 - sun rays; 2 - glazing; 3 - body; 4 - heat-receiving surface; 5 - thermal insulation; 6 - sealant; 7 - own long-wave radiation of the heat-receiving plate.

Under the action of solar radiation, heat-receiving panels are heated to temperatures of 70-80 °C, which exceed the ambient temperature, which leads to an increase in the convective heat transfer of the panel to the environment and its own radiation to the sky. To achieve higher coolant temperatures, the surface of the plate is covered with spectrally selective layers that actively absorb short-wave radiation from the sun and reduce its own thermal radiation in the long-wave part of the spectrum. Such structures based on “black nickel”, “black chrome”, copper oxide on aluminum, copper oxide on copper and others are expensive (their cost is often commensurate with the cost of the heat-receiving panel itself). Another way to improve the performance of flat plate collectors is to create a vacuum between the heat absorbing panel and transparent insulation to reduce heat loss (fourth generation solar collectors).

Solar heating is a way of heating a residential building, which is becoming more and more popular every day in many, mostly developed, countries of the world. The greatest success in the field of solar thermal energy today can boast in the countries of Western and Central Europe. On the territory of the European Union over the past decade, there has been an annual growth in the renewable energy industry by 10-12%. This level of development is a very significant indicator.

solar collector

One of the most obvious applications of solar energy is its use for heating water and air (as heat carriers). In climatic regions where cold weather prevails, for comfortable living people are required to calculate and organize heating systems for each residential building. They should have hot water supply for various needs, besides, houses need to be heated. Certainly, the best option here there will be an application of a scheme where automated heat supply systems operate.

Industrial enterprises require large volumes of daily hot water in the production process. An example is Australia, where almost 20 percent of all consumed energy is expended on heating a heat transfer fluid to a temperature not exceeding 100 o C. For this reason, in some of the developed countries of the West, and to a greater extent in Israel, North America, Japan and, of course, in Australia, the production of solar heating systems is expanding very quickly.

In the near future, the development of energy will undoubtedly be directed in favor of the use of solar radiation. The density of solar radiation on earth's surface averages 250 watts per square meter. And this despite the fact that two watts per square meter is enough to meet the economic needs of a person in the least industrial areas.

The advantageous difference between solar energy and other energy industries that use fossil fuel combustion processes is the environmental friendliness of the energy received. Work solar equipment does not result in separation harmful emissions in atmosphere.

Selection of equipment application scheme, passive and active systems

There are two schemes for using solar radiation as a heating system for a home. These are active and passive systems. Passive solar heating systems - those in which the element that directly absorbs solar radiation and generates heat from it is the structure of the house itself or its individual parts. These elements can be a fence, a roof, separate parts of a building built on the basis of a certain scheme. Passive systems do not use mechanical moving parts.

Active systems operate on the basis of the opposite home heating scheme, they actively use mechanical devices (pumps, motors, when using them, they also calculate the required power).

The simplest in design and less costly in financial terms when installing a circuit are passive systems. Such heating circuits do not require the installation of additional devices for the absorption and subsequent distribution of solar radiation in the home heating system. The operation of such systems is based on the principle of direct heating of the living space directly through the light-transmitting walls located on the south side. An additional heating function is carried out by the outer surfaces of the house fencing elements, which are equipped with a layer of transparent screens.

To start the process of converting solar radiation into thermal energy, a system of structures is used based on the use of solar receivers with a transparent surface, where the "greenhouse effect" plays the main function, the glass's ability to retain thermal radiation is used, which increases the temperature inside the room.

It should be noted that the use of only one of the types of systems may not be entirely justified. Often, a careful calculation shows that a significant reduction in heat loss and a reduction in the energy needs of a building can be achieved through the use of integrated systems. General work both active and passive systems by combining positive qualities will give the maximum effect.

A commonly used efficiency calculation shows that passive use of solar radiation will provide approximately 14 to 16 percent of your home's heating needs. Such a system will be an important part of the heat generation process.

However, despite certain positive traits passive systems, the main possibilities for fully meeting the needs of the building in heat, it is still necessary to use active heating equipment. Systems whose function is directly absorption, accumulation and distribution of solar radiation.

Planning and calculation

Calculate the possibility of installing active heating systems using solar energy (crystalline solar cells, solar collectors), preferably at the design stage of the building. But still, this moment is not mandatory, the installation of such a system is also possible on an existing task, regardless of the year of its construction (the basis for success is the correct calculation of the entire scheme).

Installation of equipment is carried out on the south side of the house. This location creates conditions for maximum absorption of incoming solar radiation in winter. Photocells that convert the energy of the sun and are installed on a fixed structure are most effective when they are mounted relative to the earth's surface at an angle equal to the geographical location of the heated building. The angle of the roof, the degree of turn of the house to the south - these are significant points that must be taken into account when calculating the entire heating scheme.

Solar photocells and solar collectors must be installed as close as possible to the place of energy consumption. Remember that the closer you build a bathroom and a kitchen, the less heat loss will be (in this case, you can get by with one solar collector that will heat both rooms). The main criterion for evaluating the selection of the equipment you need is its efficiency.

Active solar heating systems are divided into the following groups according to the following criteria:

The use of a backup circuit;
Seasonality of work (throughout the whole year or in a certain season);
Functional purpose - heating, supply hot water and combined systems;
The heat carrier used is liquid or air;
Applied technical solution for the number of circuits (1, 2 or more).

General economic data will serve as the main factor in choosing one of the types of equipment. A competent thermal calculation of the entire system will help you decide correctly. The calculation must be carried out taking into account the indicators of each specific room where the organization of solar heating and (or) hot water supply is planned. It is necessary to take into account the location of the building, climatic natural conditions, the size of the cost of the displaced energy resource. The correct calculation and the successful choice of the heat supply organization scheme is the key to the economic feasibility of using solar energy equipment.

Solar heating system

The most common heating scheme used is the installation of solar collectors, which provide for the accumulation of absorbed energy in a special container - a battery.

To date, the most widespread are double-circuit heating schemes for residential premises, in which a forced circulation system of the coolant in the collector is installed. The principle of its work is the following. Hot water is supplied from the top storage tank, the process occurs automatically according to the laws of physics. Cold running water is supplied by pressure to the lower part of the tank, this water displaces the heated water collected in the upper part of the tank, which then enters the hot water supply system of the house to meet its household needs and heating needs.

For a single-family house, a storage tank with a capacity of 400 to 800 liters is usually installed. To heat up the heat carrier of such volumes, depending on natural conditions it is required to correctly calculate the surface area of the solar collector. It is also necessary to justify the use of equipment economically.

The standard set of equipment for mounting a solar heating system is as follows:

Directly the solar collector itself;
Mounting system (supports, beams, holders);
storage tank;
Tank compensating for excess expansion of the thermal carrier;
Pump control device;
Pump (set of valves);
Temperature sensors;
Heat exchange devices (used in schemes with large volumes);
Heat-insulated pipes;
Safety and control fittings;
Fitting.

System based on heat-absorbing panels. Such panels, as a rule, are used at the stage of new construction. For their installation, it is necessary to build a special structure called a hot roof. This means that the panels must be built directly into the roof structure, while using the roof elements as integral elements of the equipment enclosure. Such an installation will reduce your costs for creating a heating system, however, it will require high-quality work on waterproofing the joints of devices and the roof. This way of installing equipment will require you to carefully design and plan all stages of work. It is necessary to solve many problems related to piping, placement of a storage tank, installation of a pump, adjustment of slopes. Quite a lot of installation problems will have to be solved if the building is not turned to the south in the most successful way.

In general, the project solar systems heating will be different from others in varying degrees. Only the basic principles of the system will remain unchanged. Therefore, it is impossible to give an exact list of the necessary parts for the complete installation of the entire system, since during the installation process it may be necessary to use additional elements and materials.

Liquid heating systems

In systems operating on the basis of a liquid heat carrier, ordinary water is used as a storage medium. Energy absorption takes place in solar collectors flat design. Energy is stored in a storage tank and used as needed.

To transfer energy from the storage device to the building, a water-to-water or water-to-air heat exchanger is used. The hot water supply system is equipped with an additional tank, which is called the preheating tank. Water is heated in it due to solar radiation and then enters a conventional water heater.

Air heating system

Such a system uses air as a heat carrier. The coolant is heated in a flat solar collector, and then the heated air enters the heated room or into a special storage device, where the absorbed energy is stored in a special nozzle, which is heated by the incoming hot air. Thanks to this feature, the system continues to supply the house with heat even at night when solar radiation is not available.

Systems with forced and natural circulation

The basis of the operation of systems with natural circulation is the independent movement of the coolant. Under the influence of rising temperature, it loses density and therefore tends to upper part devices. The resulting difference in pressure makes the equipment function.

The main share of maintenance costs own house accounted for by heating costs. Why not use the free energy of natural sources, such as the sun, to heat the building? After all, modern technology makes it possible!

To accumulate the energy of sunlight, special solar panels installed on the roof of the house are used. After receiving, this energy is transformed into electrical energy, which then diverges through the mains and is used, as in our case, in heating devices.

Compared to other energy sources - standard, autonomous and alternative - the advantages of solar panels are obvious:

practically free to use;
independence from energy supply companies;
the amount of energy received is easily regulated by changing the number of solar panels in the system;
long service life (about 25 years) of solar cells;
lack of systematic maintenance.

Of course, this technology has its drawbacks:

dependence on weather conditions;
the presence of additional equipment, including bulky batteries;
rather high cost, which increases the payback period;
Synchronization of the battery voltage with the voltage of the local substation requires the installation of special equipment.

Application of solar panels

Batteries that convert solar energy are mounted directly on the surface of the roof of the house by connecting them to each other to form a system of the required power. If the configuration of the roof or other structural features do not allow them to be fixed directly, then frame blocks are installed on the roof or even on the walls. As an option, it is possible to install the system on separate racks in the vicinity of the house.

Solar panels are a generator of electrical energy, which is released in the process of photovoltaic reactions. Low efficiency of circuit elements with total area 15-18 sq. m nevertheless allows you to heat rooms whose area exceeds 100 square meters. m! It is worth noting that modern technology Such equipment makes it possible to use the energy of the sun even during periods of moderate cloudiness.

In addition to the installation of solar panels, the implementation of the heating system requires the installation of additional elements:

a device for the selection of electric current from batteries;
primary converter;
controllers for solar cells;
batteries with their own controller, which will automatically switch the system to the substation network in case of a critical lack of charge;
a device for converting direct electric current into alternating current.

Most best option heating system when using alternative source energy - electrical system. This will allow you to heat large rooms by installing conductive floors. What's more, the electrical system allows the flexibility to change temperature regime in residential premises, and also eliminates the need to install bulky radiators and pipes under the windows.

AT ideal the heating electrical system using solar energy must be additionally equipped with a thermostat and automatic temperature controllers in all rooms.

Application of solar collectors

Heating systems based on solar collectors allow you to heat not only residential buildings and cottages, but also entire hotel complexes and industrial facilities.

Such collectors, the principle of which is based on the "greenhouse effect", accumulates solar energy for further use with virtually no loss. This allows for a number of possibilities:

provide residential premises with full heating;
set an autonomous mode of hot water supply;
implement water heating in swimming pools and saunas.

The work of a solar collector is to convert the energy of solar radiation entering a closed space into thermal energy, which is accumulated and stored for a long time. The design of the collectors does not allow the stored energy to escape through the transparent installation. The central hydraulic heating system uses the thermosyphon effect, due to which the heated liquid displaces the colder one, forcing the latter to move to the place of heating.

There are two implementations of the described technology:

flat collector;
vacuum manifold.

The most common is a flat solar collector. Due to its simple design, it is successfully used for space heating in residential buildings and domestic water heating systems. The device consists of an energy absorber plate mounted in a glazed panel.

The second type, the direct heat transfer vacuum manifold, is a water tank with tubes set at an angle to it, through which the heated water rises to make room for the cold liquid. Such natural convection causes the continuous circulation of the working fluid in the closed collector circuit and the distribution of heat throughout the heating system.

Another vacuum manifold configuration is a closed copper tubes with a special liquid of low boiling point. When heated, this liquid evaporates, absorbing heat from the metal tubes. The vapors raised upward condense with the transfer of thermal energy to the coolant - water in the heating system or the main element of the circuit.

When implementing home heating through the use of solar energy, it is necessary to take into account the possible restructuring of the roof or walls of the building to obtain the maximum effect. The project must take into account all factors: from the location and darkening of the structure to the geographical weather indicators of the area.