Comparison Paradigma Star 19/49 vs Atmosfera SPK F4M

— Vacuum. All solar collectors that use vacuum-based thermal insulation are called vacuum — including flat models (see the relevant paragraph). However, in our catalogue, only tubular devices that are not related to thermosiphons (see the relevant paragraph) and are capable of operating all year round are included in this category.

In all tubular models, the role of absorbing elements is played by specially designed vacuum tubes that transfer solar energy to the water inside and, at the same time, almost do not release heat to the outside. It ensures high efficiency and minimum heat loss. Another important advantage of such devices over flat-plate collectors is their increased efficiency in terms of receiving energy: the tubes work well at almost any angle of sun rays and even in cloudy weather. At the same time, tubular vacuum collectors are also noticeably easier to install. The structure is installed in parts: first the frame, then the heat exchanger housing, then the tubes themselves. And most models allow you to change only individual tubes in case of breakdowns.

If we compare vacuum collectors with thermosiphon ones, vacuum ones are more efficient and can be used for heating (including in the cold season, at temperatures below zero), but it is more complicated and more expensive.

— Flat. A relatively inexpensive type of solar collector and the simplest type of such de...vice, massively presented on the market. On the front of such a device, there is a transparent coating (made of special glass or transparent plastic), under it there is an absorbing layer (absorber) with a heat-conducting system, and a thermal insulating layer is provided on the backside.

Theoretically, such systems are capable of heating the water inside to a temperature of about 200 °C. At a low cost, they have good efficiency in the warm season. On the other hand, flat-plate collectors have a low degree of thermal insulation, which significantly reduces their efficiency in the autumn-winter period. There are improved varieties of such devices — in particular, devices that use a deep vacuum instead of a heat-insulating layer (do not confuse them with vacuum collectors — see the relevant paragraph). They can work at low temperatures; however, they are more expensive, and the actual efficiency is still highly dependent on the angle of the sun rays.

Also, note that flat-plate collectors can be quite difficult to install: the collector has to be lifted and installed as a whole, which in some conditions causes inconvenience. Yes, and in the event of a breakdown, you have to change such a device entirely.

— Thermosiphon. Thermosiphon is a specific type of vacuum collector (see the relevant paragraph). They are designed for use in the warm season, from spring to autumn. In winter, when the temperature is below zero, the water in such collectors freezes and they become useless.

On the one hand, thermosiphons are less versatile than other vacuum models: they are limited in time of the year and cannot be used for heating (in cold weather, when heating is most relevant, the collector becomes useless). On the other hand, such devices have certain advantages: they are simpler, cheaper, more compact and easier to install. Among the best options for using thermosiphon systems are summer cottages, hotels and other places where people stay mainly in summer.

— Hybrid. A specific type of equipment that combines the capabilities of a solar collector and a photovoltaic cell. The solar cell, usually, is located on the outside, and under it is the collector itself. An interesting feature of such models is that at high air temperatures and intense sunlight, they are more efficient in generating electricity than traditional solar panels. The fact is that photovoltaic cells do not tolerate heating up to temperatures of 50 °C and above — their efficiency drops sharply. And in a hybrid cell, the solar collector also plays the role of a cooling system, removing excess heat from the solar cell and reducing its temperature. On the other hand, the thermal efficiency of such models is lower than that of specialized collectors of a similar size — a significant part of the solar energy is absorbed and dissipated by a solar cell. Another disadvantage of such devices is their high cost. In addition, solar energy requires not only batteries but also complex control systems, storage batteries, etc.; and although the energy itself is free, the equipment for its production is also expensive. Thus, this option is much less common than other types of solar collectors.

The material from which the absorber is made. It is a layer that absorbs solar energy. It is the main part of the collector; the general specs of the device largely depend on its design.

In most modern models, regardless of type, the absorber is made of copper with a special coating. This metal has a high thermal conductivity and effectively transfers heat to the heating medium. And the coating is used to improve the absorption of sunlight, reduce its reflection and, accordingly, achieve good efficiency indicators.

Another option found in solar collectors is aluminium. It is somewhat cheaper than copper and weighs less, but it is inferior to copper in terms of thermal conductivity and performance.

The total area of the absorbing surface of the collector. For kits with multiple collectors (see "Number of collectors"), the area for one device is indicated.

Note that the meaning of this parameter depends on the type of collector (see the relevant paragraph). In flat devices, we are talking about the working area — the size of the surface that is exposed to sunlight. In tubular models (vacuum, thermosiphon), where tubes play the role of an absorber, the total surface area of the tubes is taken into account — including that which is “in the shade” during operation and is not heated by the sun. Special reflectors can be used to overcome this problem.

All of the above means that only collectors of the same type and similar design can be compared with each other in terms of absorber area. If we talk about such a comparison, then a large area, on the one hand, provides greater efficiency and heating speed, and, on the other hand, it accordingly affects the dimensions of the device and the amount of space required for its installation. Thus, the total area of a flat collector approximately corresponds to the area of the working surface; it is slightly larger, but this difference is small. But in tubular models, there is a paradox when the total area is less than the absorber area.

Collector aperture area; in sets of several devices (see "Number of collectors") is indicated for one collector.

The aperture area is, in fact, the working area of the device: the size of the space directly illuminated by the sun. In flat models (see "Type") this size corresponds to the size of the glass surface on the front side of the collector; in this case, the aperture area is usually either equal to the area of the absorber (see the relevant paragraph) or slightly less (because the edges of the collector can cover the edges of the absorbing surface. But in tubular collectors (vacuum, thermosiphon), the aperture area can be measured in different ways, depending on the presence of a reflector. If it is present, the working area is equal to the absorber area, since the tubes are irradiated from all sides. If a reflector is not provided, then the aperture area is taken as the sum of the projection areas of all tubes; projection length at this corresponds to the length of the tube, the width to the inner diameter of the glass bulb or the outer diameter of the inner tube, depending on the design.

The aperture area is one of the most important parameters for modern solar collectors; many performance specs depend on it. At the same time, by recalculating these specs per 1 m2 of the aperture area, one can compare different models (including those belonging to different types) with each other.

The total area of the collector. If there are several collectors in the kit, this indicator is given for one device.

The total area determines, first of all, the dimensions of the collector and the amount of space required for its installation. In this case, if we are talking about horizontal placement (see "Mounting"), then the total area of the collector will correspond to the area of the space that it will occupy after installation. But with inclined installation, the base of the entire structure occupies a slightly smaller area — this is due to the specifics of the installation.

It is worth talking about the total area and aperture area. The practical specs of a solar collector are determined primarily by its aperture area, for more details on it, see the relevant paragraph. At the same time, in flat models (see “Type”), the aperture area will inevitably be less than the total. But in tubular models, it can be the other way around — in some cases, the aperture surface area of all tubes may exceed the total area of the device itself. There is nothing strange in this, such a phenomenon is associated with the geometric features of the design.

The total number of tubes provided in the design of the solar collector (vacuum or thermosyphon, see "Type").

This parameter largely depends on the area of the device: for a large collector, more tubes are required. However, there is no hard dependence here. Devices of similar size may differ in the number of tubes. In general, this parameter is quite specific, it is used in some formulas for calculating the required collector power.

The maximum pressure of the heating medium for which the collector is designed. This parameter is indicated only for closed models (see "Loop system") — by definition, open models operate at atmospheric pressure.

The maximum pressure allowed for the collector must not be lower than the operating pressure in the heating system (DHW, heating, etc.) to which it is planned to be connected. And ideally, you should choose a device with a pressure margin of at least 15 – 20% — this will give an additional guarantee in case of various failures and malfunctions.

Collector efficiency.

Initially, the term "efficiency" refers to a characteristic that describes the overall efficiency of the device — in other words, this coefficient indicates how much of the energy supplied to the device (in this case, solar) goes to useful work (in this case, heating the medium). However, in the case of solar collectors, the actual efficiency depends not only on the properties of the device itself but also on environmental conditions and some features of operation. Therefore, the specs usually indicate the maximum value of this parameter — the so-called optical efficiency, or "efficiency at zero heat loss." It is denoted by the symbol η₀ and depends solely on the properties of the device itself — namely, the absorption coefficient α, the glass transparency coefficient t and the efficiency of heat transfer from the absorber to the coolant Fr. In turn, the real efficiency (η) is calculated for each specific situation using a special formula that takes into account the temperature difference inside and outside the collector, the density of solar radiation entering the device, as well as special heat loss coefficients k1 and k2. Anyway, this indicator will be lower than the maximum — at least because the temperatures inside and outside the device will inevitably be different (and the higher this difference, the higher the heat loss).

Nevertheless, it is most convenient to evaluate the specs of a solar collector and compare it with oth...er models precisely by the maximum efficiency: under the same practical conditions (and with the same values of the coefficients k1 and k2), a device with a higher efficiency will be more efficient than a device with a lower one. .

In general, higher efficiency values allow to achieve the corresponding efficiency, while the collector area can be relatively small (which, accordingly, also has a positive effect on dimensions and price). This parameter is especially important if the device is planned to be used in the cold season, in an area with a relatively small amount of sunlight, or if there is not much space for the collector and it is impossible to use a large-area device. On the other hand, to increase efficiency, specific design solutions are required — and they just complicate and increase the cost of the design. Therefore, when choosing according to this indicator, it is worth considering the features of the use of the collector. For example, if the device is bought for a summer residence in the southern region, where it is planned to visit only in summer, relatively little water is required and there are no problems with sunny weather — you can not pay much attention to efficiency.

The absorption coefficient of the absorber used in the collector design.

This parameter directly affects the overall efficiency of the absorbing coating and the efficiency of the device as a whole. The absorption coefficient describes how much of the solar energy reaching the absorber is absorbed by it and transferred to the heat carrier. Ideally, this parameter should reach 100%. However, it is extremely difficult and unreasonably expensive to achieve this. Therefore, the absorption coefficient is usually somewhat lower — about 95%; this is more than enough for the efficient operation of the collector. The rest of the energy is reflected as radiation; for more details, see “Absorber emissivity coef ε". Also note here that in the design of tubular collectors, tubes with a special inner coating are often used, which returns the reflected rays to the absorber and increases the actual absorption coefficient.