Vacuum solar collector: installation, connection, operation

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Today, the most rational way to use solar energy is vacuum collectors of the DHW system. Our review will answer the main questions about the features of the operation of solar plants, their installation and use for the domestic needs of a private house.

Vacuum solar collector: installation, connection, operation

How the vacuum collector works

In contrast to a flat panel collector, where a massive radiator is heated, in which a heat exchanger with water is enclosed, vacuum solar plants operate differently. In them, the coolant circulates through thin tubes enclosed in transparent flasks, rising from the bottom to the top under the action of convection, which is accompanied by heating. Optionally, the vacuum manifold can have the following design features:

  • Mirror bottom of the bulb, focusing the light flux on the tube.
  • The presence of radiators on the inner tubes, which contributes to more efficient heat absorption.
  • Coating the inner tubes for a similar purpose.
  • Use of heat pipes filled with a substance with a low boiling point instead of pipes with a coolant.
  • Vacuum-filled flasks and laminated glass shell to reduce heat return.

Solar collector vacuum tube deviceThe device of the solar collector vacuum tube: 1 – inlet of the cooled coolant; 2 – heat exchanger (collector); 3 – heat sink body; 4 – thermal insulation; 5 – heat pipe condenser; 6 – heated coolant outlet; 7 – hermetic plug; 8 – working fluid; 9 – heat pipe; 10 – aluminum plate (absorber); 11 – vacuum tube;

The introduction of such solutions increases the cost of the collector, but the higher the price, the more solar energy the installation is able to collect and send for water heating. This is especially important in the Russian climate, where short daylight hours and low illumination levels make it possible to use only highly efficient installations. Collector performance is determined by its passport data in accordance with the needs of the DHW system.

Assembling and installing the collector on the roof

One of the main differences of the vacuum manifold is that it does not require lifting to the roof and installation as an assembly. Installation can be carried out in separate units, which greatly facilitates independent work.

The base frame is initially assembled. It is quite voluminous, but lightweight, so the assembly is easier to carry out on the ground. The main supporting element of the frame is the side rails, which have a square or U-shaped profile. In the upper part, the roof rails are attached to the manifold – a collecting manifold to which heating flasks are connected. At the bottom, the profiles are connected by a spacer rail, on which a strip with grooves is fixed – a holder for vacuum tubes. Additionally, the roof rails are connected in the middle part by one or two spacers, which can have shock-absorbing pads on top.

Vacuum solar collector: installation, connection, operation

At the corners, headscarves with radial grooves are attached to the sides of the frame. Legs are bolted to them: long from the side of the manifold and short in the lower part. Due to the possibility of inclined attachment to the gussets, the installation angle can be adjusted, however, only the axial screws with bushings need to be tightened immediately, the clamps are tightened upon completion of the installation. The hind legs in many collectors are connected to each other by steel braces. In the lower part, inclined legs are screwed to the legs for attachment to the roof.

After pre-assembly, the frame is lifted onto the roof and placed on a slope facing south. First, the manifold is attached at the bottom, then the installation position is adjusted by shifting or adjusting the length of the rear legs. The legs are fastened into the crate through the roof covering, under the feet are installed special seals from the delivery set. Place the collector on the roof in such a way that the legs rest on the ridges of the embossed surface. If necessary, intermediate slats are mounted on the roof or tubular snow holders are used as such.

Vacuum solar collector: installation, connection, operation

It is believed that the optimum tilt angle is equal to the latitude at which the collector is located, however, depending on the season and design features, there may be adjustments indicated by the manufacturer in the installation instructions. On some collectors, the hind legs are fixed in longitudinal slots for the possibility of changing the slope at different times of the year. Also note that on steep slopes, the front and hind legs can be swapped to maintain the required mounting angle.

Heat accumulator installation

The heat absorbed by the collector tubes is transferred to the hot water supply system, however, operation in a flow-through mode is impossible due to insufficient instantaneous power. The heated water is accumulated in the heat accumulator, from where it is then supplied to the points of water intake. There are two options for placing the battery.

Solar vacuum collector with tankSolar vacuum collector with storage tank

The first one is in the upper part of the collector, while the tank is combined with the manifold and the heat from the collector pipes is absorbed directly by the water. This placement of the battery is beneficial only from the point of view that it does not have to be installed in the house, wasting useful space. However, despite the presence of thermal insulation, heat losses are quite high, which allows the use of external batteries only in regions with a temperate climate. Since water is used in the solar circuit, a heating element is installed inside the tank, which prevents the coolant from freezing during idle time, or a reverse heating system is implemented by means of limited circulation of the solar circuit.

Solar water heating circuitSolar system for heating water from the sun: 1 – cold water supply; 2 – heat exchanger; 3 – indirect heating boiler (heat accumulator); 4 – temperature sensor; 5 – coolant circuit; 6 – pumping station; 7 – controller; 8 – expansion tank; 9 – hot water; 10 – three-way valve; 11 – solar collector

A heat accumulator located inside the house is able to retain the heat of heated water all night, regardless of the outside temperature; moreover, the volume of stored water is practically unlimited. As a rule, for this purpose, indirect heating boilers are used; propylene glycol solution is used as a heat carrier in the external circuit for heating systems.

Laying of pipelines

One of the most difficult tasks when installing a collector is to connect it to the internal plumbing. The pipeline must not only be resistant to temperature extremes, but also have high-quality insulation. The best option for these purposes is considered to be PEX pipes with a system of push-in fittings, which are used in hot water supply systems..

Vacuum solar collector: installation, connection, operation

Ideally, the length of pipes should be minimal, especially in the outer part of the line. Therefore, it is customary to mount the collectors in the lowest part of the slope, leading the connecting pipes under the cover in the Mauerlat area. Such placement is not always acceptable due to the shading of the installation site, which forces the collector to be lifted upward, making the passage of pipes through the roof using special sealing entries. The outer part of the pipelines must be wrapped in an insulating shell made of foamed polyisocyanurate or rubber capable of withstanding temperatures above 150 ° C. The thermal insulation must have a UV-resistant outer sheath. The internal parts of the line must also have thermal insulation..

Strapping and additional devices

The most interesting technical challenge when installing a solar collector is to interconnect it with other plumbing systems and ensure correct operation, while solving a number of childhood diseases of the solar plant. The connection is most simple when the battery is located externally: cold water is supplied to its lower branch pipe, hot water is drawn from the upper branch pipe, the liquid is moved under the working pressure of the water supply system.

The connection of the internal accumulator to the manifold of the collector is carried out with two parallel pipes, while a circulation pump with a wet rotor and a special hydraulic circuit for solar systems is installed in the cold gap. The pump passport must provide for the ability to work in systems with propylene glycol.

Vacuum solar collector: installation, connection, operation

One of the main problems that arise during the operation of a solar collector is stagnation, when the temperature in both circuits reaches a practical maximum and the coolant begins to boil in the manifold or the collector tubes themselves. This phenomenon is mainly observed several hours before noon due to the fact that by the most active heating period, the water in the battery did not have time to completely cool down. The most primitive solution to the problem is to turn on active circulation a few hours before daylight hours to completely cool the battery, which does not completely solve the problem and is also not quite convenient for residents.

An alternative option is to turn on the additional circuit when overheating. This solution is realized by installing at the point of connection to the manifold a pair of three-way valves with servo drives, connected by a tube 3-4 meters long. When the maximum temperature in the primary circuit is reached, the controller opens the taps, due to which the line is lengthened and additional cooling of the coolant entering the manifold occurs.

Vacuum solar collector: installation, connection, operation

Another, more rational option is to connect the heat accumulator to the heating system. When stagnation occurs, the main heating unit stops and part of the water from the return flow is sent to the third heat exchanger of the indirect heating boiler, cooling its contents. Structurally, such a solution is more complicated and, moreover, more expensive to implement, but at the same time it is much more profitable in terms of energy efficiency. All the methods described do not work well in the warm season, therefore, the collector can only be protected from overheating by artificial shading..

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