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.
Fan power
The highest electrical power consumed by the air curtain when operating in ventilation mode, without air heating.
The performance, speed and range of the airflow depend on this parameter (see below). However, this dependence is not unambiguous — units similar in fan power can differ markedly in other specs. But what this parameter directly affects is energy consumption. For water models (see "Type"), as well as curtains that do
not have a heating function at all (see "Features"), it is the power in fan mode that describes the total electricity consumption. And if an electric heater is provided in the design, then the total energy consumption can be derived by adding the power in fan mode and the maximum heat output (see above).
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.
Air temperature increase (ΔT)
This indicator describes the difference between the air inlet temperature and the outlet temperature — in other words, by how many degrees the air temperature rises as it passes through the unit. The higher ΔT, the hotter the outgoing air will be and the more attentively it is necessary to observe safety measures.
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.
