Air curtain
The air curtain (also air curtains , air curtains , Torluftschleieranlage , air curtain , air door , air curtain , air wall , air Schott system ) refers to a plant that open to frequently or continuously doors and gates by means of powerful blowers differently conditioned air mass by a barrier of air flowing from one another and so their Exchange prevented. This barrier consists of a directed flow of air that circulates in the manner of an air cylinder between the exhaust opening and the intake opening of the device.
Typical areas of application are to shield warm room air from cold outside air, for example at the entrances of a department store , at the gates of industrial plants and factory halls or at the entrance areas of airports and train stations. In these applications, the systems mostly work with heated air. In addition to the cold air, warm air masses, odors, insects, dirt, dust and smoke are also kept away by air curtains, depending on the area of application.
The systems are differentiated according to their design and the direction of movement of the air roller. The main types of construction are systems with adjustable blades and systems with nozzles based on the Venturi principle . In general, a vertical direction of the air roll is preferred. Where the structural conditions do not allow this, systems with horizontal discharge directions are used. Air curtain systems with a horizontal discharge direction are also preferred for design reasons. By using air curtains in open passages, heating costs can be saved up to 80%. Only a locked door or a properly functioning porch can be even more effective. A combination is often used in which the air curtain system switches on as soon as the door is opened.
history
The Swiss department store Jelmoli in Zurich had an air curtain entrance as early as 1958. Additional air curtain systems were installed on the doors of department stores in the 1960s. These early versions still worked with an ascending warm air curtain. In 1974 the first air curtain system developed in Germany was presented. It worked with a discharge direction from top to bottom and has now become the standard. In this type of system, the air curtain is aligned with rigid or adjustable slats. The introduction of an air curtain system based on the venturi nozzle principle in 1994 brought a significant improvement in shielding performance.
Working principle
Using an air curtain system that works against the ingress of cold air into a building, the following functional principle can be defined, which, in a modified form, applies to all areas of an air curtain system:
Air masses of different temperatures have the properties to balance each other out. Cold air flows into a warm room, while warm air escapes from the room. This process is only ended when the temperatures are equalized. The task of the air curtain device is to counter the incidence of cold air (K) with a counterflow (H). The volume flow, speed, temperature and impulse must correspond to the incoming cold air. The air curtain jet (R) results from the required horizontal and vertical components. In conjunction with the air duct, the system achieves optimum air shielding with the lowest possible energy consumption. The three important parameters of the blow-out angle, volume flow and speed are precisely controlled in such a way that the force H is the counter-pulse. Cold air from the outside that is induced in the air jet should also be brought to at least room temperature by heating. In addition, the discharge height is a decisive criterion when selecting the air curtain system. With balanced pressure conditions in the building and low wind load at the entrance, the following rule of thumb applies: the lower the system is installed, the lower the amount of air required for shielding. Depending on the system, an air curtain system should be placed above the door if possible. The selection of power, design and air flow enables practicable solutions for all entrance situations.
Use
Air curtain systems have great potential benefits. You save energy, increase the quality of stay in rooms, protect the environment from unpleasant odors and harmful substances and ensure production quality, for example in clean room technology.
Possible energy saving
In most cases, air curtain systems are used where warm rooms need to be protected against the ingress of cold air. In warm areas and at midsummer temperatures, air curtain systems shield the cooled room air from warm outside air.
Quality of stay and environment
Another benefit of air curtain systems is that there are almost no drafts inside the building. In shopping centers and in industrial halls with air curtains, the sick leave rate for employees is significantly lower. There is also a significantly higher quality of stay for visitors. In industrial companies with strong odor emissions, such as B. fish processing companies or waste treatment plants, air curtain systems make a contribution to environmental quality.
Types
Lamella principle
Conventional air curtain systems based on the slat principle blow the air against adjustable slats. The exiting air flow depends to a large extent on the position of the lamellas and on the arrangement of the fans within the device. As a rule, an unevenly strong, turbulence-rich air curtain is created. The setting of the air outlet angle against the air mass to be shielded is only possible to a limited extent or not at all. In order to achieve the required shielding performance, a large amount of air must be sucked in, heated and blown out. This in turn brings with it an increased energy requirement of such a lamella air curtain.
Nozzle principle
In the case of air curtain systems with a pressure chamber nozzle system, the air that is sucked in is first fed into a pressure chamber and then through the air outlet nozzle. Since air always seeks the path of least resistance, the air flow is evened out over the entire width before it is pressed through the nozzle by the air flowing in. The nozzle, which works according to the Venturi nozzle principle, bundles the air flow and accelerates it. This creates a high pressure. Since the nozzle is rotatably mounted on a disc, the blow-out angle can be set exactly. This creates a controlled air curtain that achieves an almost even blow-out speed over the entire width of the nozzle. The air flow is always consistently strong, regardless of the position of the nozzle. If the air flow is directed outwards, an additional force component builds up which counteracts the pressure of the outside air. The higher blow-out speed and the targeted air control make it possible to operate an air curtain device with a nozzle system with a significantly smaller amount of air than a lamella system.
The nozzle system can be improved by accelerating the air flow over the convex nozzle cheeks in such a way that a concentrated, low-induction air curtain is created.
interpretation
The design of an air curtain system depends primarily on the building situation. In the case of individual shops or single-storey buildings with a single entrance door, a relatively small system with simple controls is a good solution. In multi-storey buildings, when there is wind pressure, thermals in the building and leaks in the roof area or uncontrolled ventilation conditions, the proportion of outside air entering is increased. In addition, the larger the room volume, the greater the unwanted exchange of air masses at different temperatures. The size of the door opening is also crucial. The practical maximum size has proven to be around 30 m² (mostly industrial door openings). Even larger door openings require energy expenditure that includes almost the entire volume of air in a building and must therefore be assessed critically.
Mounting forms
There are basically two types of installation: one variant with an inwardly rotating air roller (IDW) and a second with an outwardly rotating air roller (ADW). Air roll denotes the air flow circulating between the exhaust opening and the suction opening.
Internally rotating air roller
With IDW installation, the air is sucked in from the interior of the room while the exhaust opening is above the door. The direction of rotation of the air cylinder acts in the room. This form is particularly suitable for small and medium-sized buildings in which there are no permanent workplaces in the door area or where there is overpressure in the building and only pressure equalization takes place.
If the air is sucked in from the front end of the interior when the IDW is installed, an air cylinder develops with a relatively large penetration depth into the room. The system design has a very low energy requirement, as only room air is sucked into the heat exchanger. With suction from underneath via a suction chamber, the penetration depth into the room is significantly reduced. The effect is focused more on the door area. This allows doors with medium wind loads and slightly exposed locations to be shielded well.
External rotating air cylinder
If there is negative pressure in the building, ADW installation is generally recommended. The suction is in the direction of the door and the air cylinder rotates outwards. It is directed directly against the incoming outside air.
When installing in a vestibule, it makes sense to position it on the inner door. The air is sucked in at the front from the direction of the outer door, the outlet is in the immediate vicinity of the inner door. Due to the admixture of outside air and the associated reduction in pressure differences, a device in this installation form has a significantly higher shielding performance. The area of application is when there is negative pressure in the building and opposite entrances - as it is e.g. B. be found at hardware stores. The arrangement is suitable for all common wind loads and also for unfavorable business locations.
A further increased shielding performance results with outwardly directed underside suction and also outwardly rotating air cylinder.This design creates almost no circulation in the interior and offers a very high shielding performance by adding outside air and reducing pressure differences. Due to the design, slightly larger dimensions and a higher energy requirement are necessary, since the intake temperature is usually lower. This arrangement is also particularly suitable for negative pressure in the building. It meets all the usual wind loads and also unfavorable business situations.
control
The control of an air curtain system makes a significant contribution to economy and comfort. While a manually switched multi-level control is often sufficient for smaller shops, the increasing complexity of the building also requires more extensive control options. For example, the control can only switch the system on when a gate is opened. However, a very complex control system can also be connected to various sensors, including anemometer, and can be completely integrated into the building management system.
Applications
Air curtain can be connected to swing doors , sliding doors , automatic doors, on revolving doors as well as rolling and sectional doors use.
In addition to applications that keep cold air out, the protection of cooled rooms from warm outside air is an important area of application. Cooling shelves, cold rooms, cold stores and deep-freeze stores can also be protected against warm air with air curtain systems.
The shielding of the ambient air has proven itself in waste recycling plants and in manufacturing plants with strong odors. In supermarkets, for example, the general area can be protected from unpleasant odors from the fresh fish department.
Further areas of application for air curtain systems are in clean room technology and in shielding the environment from industrially contaminated air.
Certification / standardization
There is currently no generally recognized standard for air curtains that evaluates the technology in terms of energy and economy. The international Air Movement & Control Association AMCA has a set of rules, but these are very general. It is measured using laboratory methods and the energetic evaluation is only roughly based on the electrical power. Leading European manufacturers work together in an ISO committee to create and certify a corresponding standard.
Individual evidence
- ↑ H. Mürmann: Kälte und Klimatechnik , No. 9/1979, pp. 414–417.
- ↑ Hans Rudolf Schmid: The Jelmoli book. About the life of a company. , Verlag Grands Magasins Jelmoli SA, Zurich 1958, on the 125th anniversary of the Jelmoli department store.
literature
- Recknagel, Sprenger, Schramek: Pocket book for heating and air conditioning , R. Oldenbourg Verlag Munich, Vienna 2001
- Modern building technology, edition 6/2005
- Modern building technology, issue 4/2007
- RWE compact, December 2006