Heating element
The design of the heating element installed in the thermal curtain.
— Tubular heater. Accordingly, a heating element in its classical form is a metal tube, inside of which there is a spiral made of an alloy with high resistance, which heats up when an electric current passes. The spiral is isolated from the body of the heating element with the help of a filler that conducts heat well but does not transmit electric current. And to increase heat transfer, the tubes can be made curved, supplemented with radiators in the form of characteristic ribs or plates, etc. At a relatively low cost, such heaters are quite efficient, reliable and resistant to adverse factors (moisture, pollution, temperature changes, etc.). In addition, a rather low operating temperature prevents the combustion of contaminants on the heating element and the appearance of unpleasant odours (although this phenomenon is still not completely excluded). Due to all this, most electric air curtains (see "Type") are equipped with this type of heater.
- Stitch heater. It is a set of thin and long protrusions mounted on a special base. The protrusions are made of wire or metal tape. The main advantage of a stitch heater is the high heating rate — such an element reaches the operating temperature in a matter of seconds after switching on. On the other hand, this temperature is much higher than that of tubular heating elements, which leads to the effect of drying the air as well as the appearanc...e of unpleasant odours when dirt gets on the heater. In addition, these contaminants lead to corrosion and burnout of the metal parts of the heater, and for powerful air curtains (more than 5 kW), the stitch heaters are poorly suited. Therefore, this option is found mainly in inexpensive models of low thermal power.
- Ceramic. Another type of electric heater; considered the most advanced to date. Ceramic elements are fundamentally different from tubular heaters and stitch heaters in that they consume full power only during the heating process, and while maintaining the temperature, this power is noticeably reduced, which provides significant energy savings. In addition, they are reliable and durable (surpass tubular heaters in terms of service life by 2-3 times). The key disadvantage of ceramics is the high cost.
— Heat exchanger. A type of heater found exclusively in water-type air curtains (see above). Heat exchangers have a complex shape with protrusions, fins, plates and other elements that increase the area of contact with air and, accordingly, increase the efficiency of heat transfer.
Max. heat output
The highest heating power provided by a air curtain.
The simplest general rule for the selection of heaters is that for 2.5 – 3 m3 of heated space in a room with good thermal insulation, it is necessary to have at least 100 W of thermal power. In other words, for rooms with a standard ceiling of 2.5 m, one can proceed from the formula of 100 W per 1 m2 of area.
At the same time, it must be taken into account that the air curtain's purpose is not so much to heat the premises but to prevent the entry of outside air into them through open openings. Therefore, the main performance specs for such units are airflow rate and range (see below), and it makes sense to pay close attention to the heat output only if it is planned to use the air curtain also as the main heater. At the same time, it must be borne in mind that part of the power (sometimes very significant) can be lost especially when it comes to a frequently opening door without a vestibule. If other sources of heating are used in the room, the power of the air curtain can be quite low.
Anyway, to calculate the optimal values of heat output, it is best to use special formulas (or entrust the calculations to a specialist) — so that, on the one hand, the device successfully handles its tasks, and on the other hand, does not consume excess electricity, because energy consumption is directly related to the intensity of heating. (See "Fan power" for details on
...electricity consumption.)
Also note that for water-type models (see above), the actual heat output depends on several external factors: the type of coolant, its temperature, the temperature difference at the inlet and outlet, etc. Therefore, the heat output given in the official specifications is quite approximate and does not always correspond to practical indicators. Airflow
The amount of air that the air curtain can drive through itself in a certain time (usually indicated on an hourly basis).
Performance is one of the main parameters that determine the efficiency of the air curtain. The optimal value of this parameter depends primarily on the size of the door to be blocked. However, when calculating, it is also necessary to take into account several additional issues: the width and general configuration of the door, the presence of a vestibule, etc. Specific recommendations for calculating the required performance can be obtained from special sources or heating engineers.
Max. airflow speed
The highest airflow speed that a air curtain is capable of delivering.
Usually, the speed is measured directly at the outlet because airflow weakens with distance. The practical significance of this parameter is that high speed has a positive effect on performance (see above) and range (see below) because a highspeed air curtain drives a lot of air through itself, and the airflow travels a long distance. At the same time, note that models with the same airflow speed may differ markedly in other performance specs due to differences in design and technology. Therefore, we can say that this parameter is of secondary importance and only complements the range and performance data.
Max. range
The greatest effective range provided by an air curtain, in other words,
the greatest distance that the airflow travels from the device before dissipating and losing effectiveness.
It is worth choosing a device according to this parameter in such a way that it is guaranteed to block the corresponding opening. Of course, one should not forget about other specs, first of all, performance (see above); however, if the range is insufficient, then even the most efficient air curtain will be ineffective.
More features
Additional functions provided in the design of the air curtain.
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Air heating. The ability to use the unit for heating the air. Despite their name, not all over-door heaters have this function — many of them are not heaters, but rather "air" curtains. It is because the main task of any curtain is to cover open openings, and not to heat the room. Nevertheless, air heating not only allows the air curtain to be used as a heater (additional, or even the main one) but also increases the efficiency of its main purpose in cold weather.
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Thermostat. The presence in the design of the thermal curtain of a thermostat — a device for adjusting the outlet air temperature. This function is found only in models with heating mode (see above); it allows you to adjust the temperature in such a way as to ensure efficient and comfortable operation of the curtain and, at the same time, avoid unnecessary consumption of electrical or thermal energy (depending on the type of curtain, see above).
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Overheat protection. The presence of a safety system that protects the thermal curtain from overheating during operation. Overheating can occur for various reasons: clogged or blocked air ducts, electrical circuit failures, etc. However, it is a sign of an emergency and can lead to unpleasant consequences — up to accidents with injuries to people. Special protection avoi
...ds these consequences: it turns off the device when the temperature rises critically.
— Remote control. Presence of the remote control in a set of delivery of an air curtain. The ability to control the unit from a distance is very convenient, and it can be especially useful for thermal curtains installed in hard-to-reach places — for example, at high altitudes, where it is simply impossible to reach without a ladder or other devices.Noise level
The highest level of noise generated by the air curtain during normal operation.
The
lower this figure, the more comfortable the use of the unit, the better it is suitable for cases where noise is undesirable. When choosing according to specific values recorded in the characteristics, it should be taken into account that the decibel used to measure the noise level is not a linear quantity: for example, an increase in sound power by 2 times corresponds to an increase of 3 dB, 10 times — by 10 dB, 100 times — by 20 dB. Therefore, to assess the noise level, it is easiest to refer to comparative tables, where the correspondence of specific values in decibels to various real sound sources is recorded. In most modern air curtains, the noise ranges from 25 to 70 dB, here is the simplest table for this range:
20 – 25 dB — a weak audible sound, comparable to a whisper at a distance of 1 – 2 m;
25 – 30 dB — intelligible whisper at a short distance, ticking of a wall clock;
35 dB — muffled conversation;
40 – 45 dB — normal human speech;
50 – 55 dB — talking in raised tones, noise in the office;
60 dB — loud conversation at a distance of 4 – 5 m.
70 dB — loud conversation nearby.
Dimensions (WxHxD)
General dimensions of the over-door heaters. The amount of space occupied by the unit during installation depends on the dimensions, but also the dimensions of the space it covers — namely the width of the airflow (or height, if the flow is directed not down, but to the side). Most air curtains have characteristic elongated proportions, and the mentioned width/height corresponds to the largest dimension of the device.
Note that the width and height of the air curtain, in this case, are indicated for the standard installation method (see above): for example, devices installed on top will have a large width at a low height, and side ones vice versa. For models with universal mounting, the dimensions can be indicated in different ways, but it is usually not difficult to evaluate the characteristics of the flow in them if we take into account the elongated proportions described above — the largest dimension is usually the same as the width/height of the flow.
Features of choosing an air curtain in terms of dimensions (and, accordingly, the width of the covered space) also depend on the type of its installation. When mounted above the doorway, the width of the unit must be no less than the width of the doorway (and ideally, a little more, with some margin). If the curtain is installed on the side, it is enough that its height is 3/4 of the height of the opening — due to the peculiarities of the movement of heated air, this will completely cover the required space.
