Recommendations for Using Air curtains

The main purpose of air curtains is to cut off cold air penetrating into a building through open embrasures.

Cold air density is higher than that of warm air, hence it is heavier. There appears the so-called "gravitational" pressure difference between outside and inside the building. The air pressure on building's embrasure level is lower, than it is outside. Outer air flows inside an open embrasure pressing out room's inner air. At the same time warm air may flow out of the upper part of the same embrasure or through some other elements (aeratic windows, ventilation shafts, other embrasures, loose windows, window leaves, etc.).

The same situation appears with an open embrasure of a refrigerator (freezer): cold air flows from them on the bottom part, and warm air flows through embrasure's upper part.

There are two types of air stream protection, namely, mixing and sliding protections. Air curtains of mixing protection type do not any counteraction to incoming cold air. They simply dilute cold air current with warm streams, thus raising air current's temperature up to a required one. The air curtains with mixing protection type are usually mounted in tambours.

Air curtains of sliding protection type form counteraction to outer cold air flowing into an embrasure. At the same time, air currents should be directed outside at angle of embrasure's plane. Touching cold air masses, air curtain's air currents form a "pushing-off" effect and then they turn back and flow inside through an embrasure. Thus, there is a constant airflow going through an open embrasure, which is equal to air consumption sum through an embrasure, and partially - to air currents injected by the air curtain, as well as some airburst through from outside. Heating the air in air curtains, it is possible to reach the temperature of air mixture flowing inside through an embrasure, which corresponds to norm.

The airflow directed vertically down from a air curtain, mounted horizontally over an embrasure, is curved under the influence of pressure difference and it flows inside. The curving degree, hence, the quantity of cold air entering under the airflow, depends under other equal conditions on overflow velocity of air curtain's nozzle and nozzle's width. The more is the speed higher and the nozzle wider, the more reliable is the protection. The protection of an upper-mounted air curtain is more effective when the airflow directed outside by angle to embrasure's plane.

Depending on working conditions, the air curtains produced by the TEPLOMASH Research-and-Production Association can fulfill both mixing and sliding functions.

In general case, the air curtains of Series 100, 200, 300, 600 are chosen considering:
- embrasure's width and height;
- parameters of a air curtain (air, thermal power, jet velocity's productivity, etc.).

Concrete recommendations will be given by TEPLOMASH specialists in the process of ordering.

In some cases, it is necessary to carry out a more detailed project's developmental work for mounting air curtains of Series 400, 500, 700.

Requirements to organization of air curtains are laid down in Paragraph 7.7 of the construction regulations SNiP 41-01-2003 "Heating, Ventilation and Air-Conditioning".

Settlement parameters of outdoor air are accepted according to construction regulations SNiP 23-01-99* "Construction Climatology".

In general cases, rational organization of embrasure's air flow protection (i.e. optimal choice of a air curtain according to its air consumption, heat power and its mounting at a required angle to embrasure's plane) depends on the following parameters:
- embrasure's height (for upper-mounted air curtains over an embrasure);
- embrasure's width (for one-sided and two-sided vertical side air curtains);
- settlement winter temperature of outdoor air and settlement wind speed);
- settlement indoor air temperature;
- requirements to air temperature (mixture) flowing into an embrasure under the influence of a air curtain (accepted in accordance with SNiP 41-01-2003 Paragraph 7.7.3);
- presence and location of windows, aeratic apertures, lanterns in a room;
- indoor air pressure with respect to the atmospheric one (influx-and-extract ventilation equilibrium degree).

In order to choose a air curtain preliminary, such a parameter as "Effective jet length" is introduced in the Tables of technical parameters.
It should be remembered that its values could help estimate permissible height of air curtain's mounting or estimate embrasure's width (half-width) for side-mounted air curtains only for "mild" outdoor conditions, when outdoor air temperature is not below 0^oC and the wind is not more than 1m/sec. Please, follow recommendations presented in Table.

Table 1. Wind 1m/sec.

Table 2. Wind 4m/sec.

Notes to Tables 1 and 2.

1. All the recommendations are suitable only for buildings without having any aeration apertures and with balanced combined extract and input ventilation. Special calculation is necessary in case of having the above-mentioned peculiarities.
2. The information is cited:
     - For indoor temperature +15⁰C.
     - For air curtains with water heater with water inlet/outlet temperature 90/75⁰C.
     - For air curtains with electric heater (except models series 400E) with minimal power mode for necessary length of air curtain (for example for air curtains Series 300E with 6kW power it is KEV-6P323E, or 9 kW - KEV-9P301E, or 12 kW - KEV-12P304E)
     - For air curtains series 400E with minimal power mode for necessary length of air curtain (with power 18kW - KEV-18P403E, 24kW - KEV-24P404E, 36kW - KEV-36P402E.)
3. Each cell contains recomended number of curtain series with added abbreviation "opt." and "sat.".
"opt." means "optimal", provided that average temperature of air entering the aperture lies in the range from 12^oC to 18^oC.
"sat." means "satisfactory" - temperature of air in the range from 5^oC to 12^oC. Angle of the current towards the opening level is shownin parentheses.
4. It should be taken into consideration that deviations from real outer conditions outside the limits of chosen estimated gradation will lead to worsening the aperture's protection (during fall of temperature and wind strengthening) or to reduction in economy of air curtain's work (during rise in temperature). Temperature or water consumption should be used in the first case by means of increasing air current angle up to 30⁰ during the re-installation of the air curtain. In the second case, it is possible to undertake such measures as to reduce air consumption through an air curtain or water temperature or consumption (a mixing unit) or electric power. Air consumption and electric power are changed manually from a control panel. The air temperature adjusted at an aperture is carried out automatically with the help of control panel's thermostat at air consumption and electric heaters' power (or temperature of supplied water) adjusted manually.
5. Reliable justification of choosing this or that type of an air curtain can be given only with the help of design estimation taking into consideration a multifactor character of the problem of selection.

The accepted design and air-heater's orientation at air curtains' vertical mounting with their outlet ducts directed down requires special measures to be undertaken in order to fill up the system with water. The recommended diagram for connecting a vertical two-sided air curtain 1 to a heating system using a mixing unit 8 is presented in Figure. The direct (Т1) and reverse (Т2) mains have air-escape pipe-bends with the cocks 4 and 5 in their upper points and emptying fittings with cocks 6 in their lower points. Ball stopcocks 2 and 3 are located in the mixing unit 8. In order to starting up and adjusting an air curtain, the system's direct and reverse mains are equipped with manometers 10 and thermometers 9. Cocks 11 installed in air heaters' inlet/outlet ducts are used for connecting heat exchangers preliminarily filled up with water to the system.

The experience of operating water air-heaters shows that no influences of pressure differences can fully remove the air from air-heater's pipes at their vertical mounting with the ducts directed downward.
If an air-curtain is located in a room, which air temperature cannot be lower 0⁰C, the remaining air will only reduce its heat rate. Should the air temperature near the air curtain be lower than 0⁰С, there will be an inevitable and quick (within 1-5 min.) freezing of water in the pipes in which water circulation is disturbed by stuck air locks. Integrity of those pipes will be disturbed. In order to avoid such failures we strongly recommend connecting vertical air curtains to heating systems as follows:
1) The room temperature should be higher 0⁰С.
2) Flexible ducts are connected to both ducts of a heat exchanger, and then the cocks 11.
3) Put the air curtain horizontally. Connect a water source (it can be cold water) to one of the ducts; the second duct is connected with atmosphere and fill up a heat exchanger with water. In this position, all the air is removed from a water track under the influence of pressure differences. First, close the cock connecting with atmosphere after visible air removal, then close the second cock.
4) Install the air curtain(s) near an aperture with closed cocks 11 (i.e. filled up with water).
5) Open slightly the cock 3 in a direct main, let the air out from all the supplying pipes closing in series the connecting places with the help of temporal easy-off pipe-plugs. Close the cock 3.
6) Connect flexible ducts with closed cocks 11 in series to the places of their connection taking temporal pipe-plugs off.
7) Open the cock 3 in a direct main. Open the air-escape cock 5 in a reverse main. First, open inlet and then outlet cocks 11 in flexible ducts of air curtains. Close the air-escape cock 5 after the air has been out from the pipes of the reverse main. Check with your hand the temperature of heat exchanger's U-bends through a hatch (do it accurately in order to avoid burns). All of them should be equally hot. If some of the U-bends remain cold, it means that there is some air stuck inside. Repeat the filling up starting with the Step 1.
8). The described procedure of filling up with water vertical air curtains should be repeated every season during the start of a heating system, as well as in cases of system's emergency disconnection and water discharge. The procedure can be simplified by means of closing the cocks at an air curtain and letting the system stay filled up with water.

If the cocks gave present, vertical installation of air curtains with ducts directed downward allows discharging the water fully duringm system's emergency disconnection.

Multi-purpose curtains are fitted with air heater, which has additional collector with inlet valve 12 on the opposite side to inlet and outlet nozzles. Therefore multi-purpose air heater is fitted wotch two outlet valves 12 and 13. this allows any vertical orientation of the air-heater. Other elements and picture symbols coincide with the previos example.

The order of connection:
1) The room temperature should by heigher then 0^oC.
2) Connect to flexible nozzles and the taps 11 to both nozzles of the air-heater.
3) Assemble the curtain near opening. Connect inlet and outlet nozzles behind the tap 11 to the network.
4) Fill the system with water by opening the taps 11, 3 and 7 in T2 line (or 5). Close the taps 11 and 7 in T2 (or 5).
5) Screw out the screw plug of valves 12, located in upper parts. Put on the rubber tubes and place the opposite ends of the tubes into water container. After visible air outlet from the air heater tubes close the taps 11, replace the screw plug and open taps 11 again.
6) Open the taps 4 and 5 for final are discharge from tubes. Close the taps 4 and 5.
7) Open the tap 2.
When taps 6 are not located int the lowest place (left on the picture), water discharge is fulfilled throught valves.
 

After filling the system by heat-carrying agent it is necessary to remove air from the system and warm air curtains by means of taps 4 and 5.

Required water consumption is set by balance tap in direct line in front of mixing block (not shown on the scheme). During emergency shutdown of the heat supply for the period, dangerous to defreeze the air-heaters, it is necessary to close taps 6 and 7, and also 12 and 13.