Comparison ALTEK SD-T2L-30 vs Atmosfera CBK-Nano-30HP

— 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.

— Open. Open collectors are called collectors that work without additional pressure in the water circulation system. Usually, such a device is equipped with a tank in the upper part, into which a supply of water is poured; after that, the water by gravity flows to the tap. At first glance, open systems are not very convenient: they need to be placed higher (and the pressure will depend on the height difference between the collector and the water tap), while it is necessary to think over the way to fill the tank (bring a hose with a pump to it), and the purpose of such devices is limited domestic hot water supply and heating pools. On the other hand, such collectors are extremely simple, inexpensive, do not require a connection to the mains and can work even in the absence of electricity (as long as there is water in the tank).

Another design option is devices without a tank powered by a circulation pump. However, they are less common, mainly among models for heating pools (see "Suitable for").

— Closed. Closed collectors require high-pressure operation (about 5–6 bar) and are designed for direct integration into the DHW supply system. In this case, the indirect principle of operation is usually used for heating — the transfer of heat from the water in the collector to the water in the DHW system through a special heat exchanger.

Such devices are noticeably more complicated...and expensive than open ones. At the same time, they are more versatile and efficient; they can be used for domestic hot water and heating. In addition, you can install the heater at any height. It does not affect the pressure in the system, unlike open design.

This category includes solar collectors that can be used throughout the year — including in winter, at sub-zero air temperatures. The only condition for the effective operation of such a device is the presence of sunlight.

The main distinguishing feature of such models is a high degree of thermal insulation, designed not only to reduce heat loss but also to protect the heat carrier circulating inside from freezing. In most of these devices, thermal insulation is provided by vacuum (note that these can be not only vacuum but also improved flat collectors — see "Type" for more details). In addition, the principle of indirect heating is often used in year-round collectors: antifreeze with a freezing point well below zero plays the role of a heat carrier, and the heated water receives heat through the heat exchanger wall. However, modern technologies make it possible to make frost-resistant devices with direct heating.

The convenience of collectors of this type is obvious, but they are not cheap.

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 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.

— Number of collectors. Most modern solar collectors are sold one at a time, but some bundles include two or even three devices at once. Such kits are designed for extensive heating systems, for which one collector is not enough. Purchasing a set of several devices is convenient because they all have the same dimensions, performance and compatibility requirements with other system components. In addition, a set is often cheaper than the same number of collectors purchased separately.

— Water heater. The presence of a water heater in the collector's delivery set.

Usually, it is a storage water heater. The design of such a device is based on a tank of several tens of litres (often 100 or more). The water heated by the collector is stored in this tank until needed; the water heater usually has good thermal insulation, and the temperature of the water in it can be maintained at a constant level for quite a long time.

In general, a storage water heater is one of the most important components of a solar hot water system. However, many collectors allow operation with tankless water heaters when the water that has passed through the device is immediately supplied to the tap. However, this mode is not very convenient — in particular, because the water temperature is unstable, and besides, it is highly dependent on the weather. The tank water heater allows you to keep a guaranteed supply of water at a certain tempera...ture. Such equipment can be sold separately, but buying a water heater at the same time as a collector is usually easier (no need to worry about compatibility), and often cheaper. — Photovoltaic module. The presence of a photovoltaic module in the design of the solar collector.

A photovoltaic module is a solar battery — an element that generates electricity from bright light. In modern solar collectors, such equipment is most often used to ensure electrical battery life: when the external power is turned off, the circulation pump and other components that require electricity are powered by the photovoltaic module, and the system remains operational. Of course, the quality of such power also depends on the intensity of sunlight, but modern technologies make it possible to create quite efficient and, at the same time, compact solar cells. Note that photovoltaic modules in such devices are usually made removable and may not be included in the delivery. The presence of such equipment in the kit should be clarified separately.

Another type of solar heater with photovoltaic modules is the so-called. hybrid models. They combine the actual collector and a large solar battery capable of generating electricity for external consumers. However, such devices are complex and expensive, and home solar power panels are much less common than solar water heating systems.

The volume of the expansion vessel supplied with the solar collector.

The expansion vessel is designed to compensate for the thermal expansion of the liquid in the heating system. With an increase in temperature and the volume of liquid, its excess enters the expansion vessel, which avoids a critical increase in pressure and damage to system components. The volume of the tank must be large enough to handle thermal expansion at the maximum intended operating temperature. One can calculate the minimum capacity using special formulas; they take into account the total volume and characteristics of the heating medium, temperature differences, design features of the heating system, etc.

Note that the expansion vessel is possible to buy separately; however, in some situations, it is more convenient (or even cheaper) to purchase it with a solar collector.