Solar installations for commercial or industrial applications

Purchase of a solar installation

As with all products, there are big differences between quality and price and in terms of solar installations: in any case it is worth comparing. A good overview of the product range on the market (collector, tank and complete installations) can be found on the Internet.

In the latest publications, the renounced solar installations received good appreciation as a proof that in the meantime they reach a high quality standard; however, one should not ignore the fact that there is always the “black sheep”. Additional, up-to-date information can be obtained from user feedback and / or from research and testing institutes.

In the specific case, the construction planner or engineer comes with offers from several manufacturers.

The higher the number of offers, the harder it is for the user to decide and compare them, because the volume of offers, the prices of each component and the quality are not necessarily recognized and, therefore, cannot be compared. Moreover, there is a risk that some planners or craftsmen will be focused on the products of company X, while another prefers the offers of other products of company Z. Standardized indications valid at European level and, therefore, comparable of the returns offered DIN EN 12975 for solar collector components. Some information according to EN 12975 is also available
prefabricated installations, but these are rarely published by manufacturers. For customer-specific installations, only the DIN EN 12977 rule exists so far. The manufacturers’ associations warn that in the future the predictions regarding the efficiency will be replaced by the norms previously listed, which will create good possibilities for comparison for the user. Regarding the equally important characteristics such as reliability, on-site maneuverability and durability during operation, there are essential data to prove whether a solar installation is reliable or not. It can also be useful if the tenderer is asked for accurate references, as well as information on the spot.

When comparing multiple offers, price does not have to be the only criterion that is considered. As the thermal efficiency of the available and tested installations is almost the same, too much attention should not be paid to the values ​​expressed in ‘kWh’, but rather to the high profitability and the quality of the components and the installation in general. Thus, the good installation also includes short and easy to understand installation and use instructions, but which contain all the important information regarding the installation and commissioning.

Installation

The installation of a solar installation starts with the delivery of all components; then the site preparation (scaffolding, crane, stairs, tools, etc.) is followed, preparation of the installation (access routes through the ceiling and wall, foundation etc.) and finally, the components of the installation are installed. Finally, the process ends by taking over and using the installation by the client and his instruction.

Several craftsmen work on the installation:

  • the roof works are required for the installation of the collector on the roof
  • the installation works mainly include the installation of the pipeline network, including the realization of all the necessary connections, the installation of all the necessary components for the pipeline network, as well as the connection to the already existing system.
  • masonry works are necessary if for the installation of the tubes there have been broken holes in the wall that require subsequent plastering
  • works at the electrical installation generally consist of the connection of the pump, the control and control system, as well as the installation of a lightning bolt.

Mounting the collector

The collectors are predominantly mounted on the roof. Their mounting on the facades is still quite rare; the collectors are mounted on the ground only in the case of installations for swimming pools. Usually, the installation of the collectors on the roof is a chapter of works that belongs to the carpenters, but in the meantime, the installers are also busy, so that all the work is done by a single specialist. In any case, all labor protection rules must be respected.

In principle, collectors can be mounted on flat and flat roofs. Manufacturers supply for all types of mounting suitable sets whose installation is, most of the times, simple and short-lived.

Collectors and tilted roofs

Further installation of the collectors on the roof has two important advantages:

– there is no damage to the roof shell due to the mounting of the supports or pipes. However, if there are any leaks in the collector or damage to the glass (due to hail), damage to the building level is excluded.

– assembly is quick and cost-effective; no more the board connections for the roof covering nor the work of revealing and re-covering it come into question.

However, the following must be taken into account:

  • The roof must bear the additional load of approx. 300 N / m2 (30 kp / m2).
  • The connection of the roof brackets with steel hooks must be so fixed that the collectors do not move away from each other (for example, due to the weight of the snow or wind). It is recommended to avoid fixing the collectors on the tile.
  • Thermal expansion of manifolds and tubes should not be prevented in any way
  • You must make sure that when the snow melts, no water enters the collector.
  • The distance between the roof and the bottom edge of the collector must be at least 6 cm.
  • The pipes must travel as short as possible under the roof, where they can be thermally insulated. There should be no leaks at the intersection with the roof shell.

When mounting above the roof tile, the connecting tubes must always be above the roof and pass through the roof shell using a ventilation tile.

Of course, more aesthetically beautiful and more cost-effective in terms of heat (because the thermal losses due to the wind are smaller) is the mounting on the roof surface. In snowy areas this solution – assuming that the roof has a sufficient degree of inclination – has the advantage that the snow slides more easily.

In this case, the static loading of the roof does not change with anything, because the tile roof is usually harder than the collector. In new buildings the costs for that part of the shed where the collector is mounted are avoided.

Collectors and flat roofs

All manufacturers offer different mounting sets.

When mounting on flat roofs, it is recommended to fix the supporting structure with sufficiently heavy concrete slabs. They are mounted after removing the gravel layer, on the sand, on a felt support or on a polystyrene foam plate. The collector should be mounted at a sufficiently large distance above the ground so that the snow does not form piles that would shade the collector. Collectors with larger areas are usually located behind one another. In order to avoid shading in the rear rows, a minimum distance between rows must be respected, depending on the height of the collectors, the degree of inclination and the height h of the sun.

Other aspects of collector mounting

  • Orientation

The roofs with an inclination degree between 0 and 60̊ are common for heating the water in the basins.

swimming, 25-80̊ for domestic water heating installations and support of the house heating system, the same is true for deviations from the south orientation up to 45̊. For this purpose, the capture surfaces should not be covered by the shadow. While the oblique roofs the degree of inclination and orientation are already established, on the flat roofs a more south-facing orientation and a better inclination degree can be chosen. Optimal placement is also possible in the case of heatpipe vacuum collectors, where the absorbent element can rotate in a certain direction.

  • lightning

As long as the roof is provided with lightning bolt, the metal frames of the collectors and those of the roof are also protected by the lightning bolt system as are all other larger metal components on the roof. For this, however, the safety rules in force must be taken into account. The installation must be performed by a specialist in the field.

  • connection

A field of collectors usually consists of several collectors (dimensions of about 2 x 1 m). Up to 6 such units can be mounted in parallel; if the surface is larger then mixed and parallel bonding is recommended. To ensure that the thermal agent flows balanced across all collectors it is necessary to keep the upper and lower distribution according to the “Tichelmann” scheme (the principle of equal distances between all collectors connected in parallel).

  • tubes

The distribution and collection pipes must be mounted in such a way that changes due to temperature variations (5 mm / m in the length of the tube) do not cause any damage. At larger installations, compensators should be fitted, if applicable.

All tubes must be fitted with a 30 mm thick insulation on the outside, weatherproof and UV radiation.

  • air venting

Depending on the filling, at the highest point inside the manifold, a ventilator must be fitted. Manual vents are mounted if air voids appear in the collector circuit connected in parallel. If the vents are in a difficult to reach location, then it is advisable to install tubes to facilitate access.

  • mounting

After installation, the collectors do not have to remain stagnant for a long time, because the materials are overloaded due to the high temperatures. Therefore it is recommended to start the circuit immediately after installation or cover the collector until it is put into operation.

Installing the tank

The tanks must be transported with caution, as damage to the link holders and / or the casing may occur by striking them; In the case of the enamelled tanks, the internal e-mail can be destroyed (it is unpacked at the installation site). Right from the moment you choose the tank you have to think about whether the tank fits on doors and other access roads because of its size.

The installation site should be chosen in such a way that the length of the hot water pipes is as small as possible. Here the tank must be mounted in such a way that the hot and cold water pipes, as well as those in the solar circuit, can be mounted to the tank fittings. At the same time, the tank thermometer must be easy to read and there is enough room for insulation.

As long as the tank is not in the cellar (as in the case of gravitational installations), both the carrying capacity of the construction element on which the tank is mounted and the weight (of a full tank) must be taken into account and, if it is in this case, mount the wooden edges on a surface large enough to take over from the load.

If the reservoir is equipped with ribbed tube heat exchangers, then these exchangers must now be fitted. To ensure optimum protection against corrosion, heat exchangers with ribbed tubes must be electrically insulated and mounted in the closure cap, and the tubes of the solar circuit must be connected by means of special insulating screws. Particular attention must be paid to the mounting location of the exchanger. The heat exchanger connections must be marked so that the hot thermal agent coming from the collector flows through the exchanger from top to bottom.

Before connecting the tubes – if they are not already pre-installed – the diving covers for thermometers, thermostats, thermometers, as well as magnesium anodes, hemp and insulating paste must be fitted. To control the temperature of the tank must be fitted two thermometers: one up to indicate the temperature requested by the consumer and one at the same height with the solar heat exchanger to control the functions and to determine the load of the tank. The other unused openings of the tank stop with corks.

When the tubes are mounted from the side of the tank directly upwards, thermal losses occur due to the thermosiphon effect. A remedy could be to install a siphon pipe from the fittings or a convection brake.

Finally, the insulation must be fitted. The manufacturer usually offers prefabricated insulating materials that fit perfectly. This often means that the supports remain uninsulated. In such cases, a remedy should be found on the spot.

The solar circuit

  • Connecting the tubes in the solar circuit

When connecting tubes from the solar circuit, classical materials and techniques from the heating and sanitary fields can be used. There are, however, the following peculiarities that result from the very high temperatures in this area and the fact that it is necessary to introduce antifreeze substances:

* In principle, copper tubes must be fitted, as those made of galvanized steel, in combination with glycol, are prone to forming misery; Synthetic tubes are usually not sufficiently resistant to temperature.

* The most commonly used connection technique for copper tubes is welding; there are several types of hard or soft welding. Soft welding is allowed for temperatures up to 110 ° C; therefore, hard welding is recommended (for example fluid-free L-Ag2P for Cu-Cu or L-CuP6 fluid-only for Cu-bronze connections). Of course, soft welded joints are allowed in places where the temperature does not exceed 110 ° C (for example S-Sn97Cu 3 together with liquid type 3.1.1C).

* In principle, connections can also be made with threaded or pressed fittings. Joints with clamping rings are often used, as this (temporary) effort is avoided compared to welding. The fastening rings with fastening rings are indispensable in the case of connections with tubes for quick installation, as their insulation can be damaged by welding (fire hazard).

* Flexible hoses or connections may also be useful. The top steel tubes are well known. Rubber hoses are not sufficiently resistant to heat and glycol, as are most insulation of the same type.

* The threaded joints must be sealed by hemp winding, as the Teflon tape is not good enough due to the flowing properties of the antifreeze substance. Also cone-shaped screws are not suitable, while the joints by cutting and those by pressing are very good

  • Connections between the collector and the tank:

The connections between the collector and the tank should be as short as possible and fitted as far as possible inside the house. The access paths through the floor or through the walls, respectively, must be so large that tubes with sufficient thermal insulation (a minimum thickness of 30 mm) can be mounted through them.

  • Recirculation pumps and fittings

It is recommended that recirculation pumps and fittings in the solar circuit be mounted close to the tank on a wall. The pump, the check valve, the safety valve and the pressure gauge expansion vessel are mounted near the cooler pipe, near the exhaust system. Meanwhile, most manufacturers deliver compact groups of components for wall mounting or units that can be delivered with the tank assembly, in which case installation work is done much faster.

A very important factor for the safety of the installation is the lack of locking elements between the manifold and the safety valve (there should not even be a reflux stop element).

  • Expansion vessel with membrane

Since the expansion vessel is not usually insulated, it must be installed in such a way that it loses as little heat as possible. Moreover, the membrane is not resistant to high temperatures. Therefore, the membrane expansion vessel must be mounted by hanging down in a “dead” area of ​​the exhaust system.

  • Expansion vessels with a volume greater than 12 I must have their own support system.

There must be a way to access the pressure regulator and valve (especially at the bottom).

  • Control / control system

For the installation of the control and control system, the manufacturers usually supply detailed installation instructions, which must be given special attention due to the differences in concept and connection.

The consumer circuit

The connection of hot and cold water pipes to the public water network has no particularity with respect to the classic hot water tanks.

Extra heating

When connecting, it must be checked whether the adjustment systems of both systems are balanced. Most modern control systems have a function for adjusting the subsequent heating. Because of the differences between the locations where the assembly takes place and taking into account the brushes

Commissioning 

Prior to the commissioning of the solar installation, all installation work from the manifold circuit to the isolation of the tank and tubes must be completed; the connection to the cold and hot water must be made, as well as the electrical work, and the tank must be full. The collectors must cover for washing and filling the solar circuit to avoid the formation of vapors.

Washing and starting

The commissioning of the solar system with collectors begins with a good washing of the circuit (about 10 minutes) to remove the dirt and other residues. The filling valve connects to the cold water network by means of a hose; another hose is connected to the drainage network for the drain valve. The closing valve is kept closed during this time.

After washing, the pressure test follows. If the drain valve is closed and the fill valve open, the pressure must increase to near the limit of the safety valve. The pump starts with the filling valve closed and the circuit is vented with the air pumps and air vents of the pump itself. After closing the vent valves, the pressure increases again. When there is no air in the system, the pressure should not drop for an hour (or more). On the other hand, it must be checked whether there are cracks or not. All welded connections

or threaded must be checked manually. Increasing the pressure may ultimately mean checking the quality of the safety valve.

After that, the system empties completely by opening the drain valve and the vents and – to determine the volume of the installation – the quantity of water coming out is measured. Thus, the required amount of antifreeze substance can also be determined. Since there is always little water left in the circuit (eg in the heat exchanger and manifold), certain additional safety measures are required.

Filling

To fill the system, a pump is needed that can create a pressure between 1.5 – 2 bar. The craftsman can also use a small centrifugal pump for this purpose, but if necessary a cheaper or manual pump is sufficient. If there is no ventilation valve at the highest point of the installation, in the upper half of the manifold, then it must be filled with a higher power pump.

The process of introducing the thermal fluid is similar to that of washing and is carried out through the filling valve. It has proven to be more practical if the heat agent can flow back into the mixing vessel through the open drain valve; In this way most of the existing air quantity is released from the system. Finally, by closing the drain valve, the pressure in the system increases until it reaches the desired level.

When the air is completely removed from the system (by recirculating and / or activating the vents), the pump can start operating. The solar circuit will be carefully ventilated with the help of the ventilation valves, this being best accomplished by a flap and a multifunctional stop and start pump. If the pressure of the installation decreases due to the air coming out, the filling pump has the role of bringing it back to the pressure level necessary for the operation of the system.

When the air is out and the operating pressure is at the desired level, the last part of the pressure check follows (all welded places and all screws are checked again). Since in water and glycol mixtures there are leaks faster than in pure water there is a possibility of visible leaks only later.

Finally, the vent valves are closed and the check valve is put back in working order. Of course the insulation of the tubes and the tank must be carefully installed. The packaging of the collectors is also being removed.

Control system and pump efficiency

For the control system a starting temperature difference of 6 – 8̊C is established and, if possible, a temperature difference at a stop of approx. 3°C. Now the pump can operate based on the adjustment system. As long as the sun is shining, the collector is warm enough and there are no mistakes when installing the electrical system, the pump must be running. After a few minutes, the tube from the collector should be heated and both thermometers should indicate a temperature difference between supply and outlet.

Through long-term monitoring of the operating system it is verified that the installation works optimally based on the settings of the adjustment system; this is best done on a day when the radiation is changeable, and the tank is only partially filled.

If the installation works properly, then the setting settings must be checked; shale

the control emulator can now operate automatically. When the radiation reaches the maximum levels, ie around noon, the efficiency of the recirculation pump (if the pump is a multi-stage pump) must be chosen such that the temperature difference between supply and outlet is 10-15C. The average temperature in the collector circuit should be 5-10̊C higher than the temperature in the tank, measured at the height of the solar heat exchanger. These values ​​are valid for high-flow installations. At the low-flow installations, the manufacturer’s instructions must be observed.

Adjusting the temperature limitation in the tank or the thermostat usually does not present any problems. The practical efficiency of the thermostat’s functions must be verified.

As long as there is an instrument for hourly measurement of pump operation, then more accurate values ​​of plant operation can be determined. The pump in the solar circuit should operate about how many hours of sunshine there are in a year, ie approx. 1,400 hours per year. If the operating intervals are significantly larger, then the tank can be filled through the manifold; In this case, the frequency of the start and stop phases of the adjustment system must increase. If the operating intervals of the pump are shorter, then the operating frequency and its decrease, if any, should be checked; It may also be useful to properly mount the temperature sensors.

Taking over the plant

When submitting the installation, users must be provided with an exact description of it with the assembly diagram, technical sheet and written instructions for use. It would be better if these documents were attached to the installation in a visible place, along with the installer’s address and telephone number. The operation of the system, as well as the importance of the switches and adjustments, must be explained very clearly.

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