A air gate or air curtain is a device used to prevent air or contaminants from moving from one open space to another open space. The most common use is a downward-facing blower fan mounted above the entrance to the building, or opening between two conditioned rooms at different temperatures.
Video Air door
Definition
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines the air gates as follows: "In its simplest application, the air curtain is a continuous wide flow of air circulated across the door of conditioned space, reducing the penetration of insects and unconditioned air becomes conditioned space by forcing airflow across the entrances The air flow layer moves at speed and angle such that any air that tries to penetrate the curtain is relaxed. The air curtain action in preventing infiltration through the entrance generally ranges from 60 to 80% ".
The Air Movement and Control Association defines the air curtain as: "A direct controlled air stream, travels across the entire height and width of the opening, which reduces infiltration or air transfer from one side of the opening to another and/or inhibits flying insects, dust or debris from passing ".
Maps Air door
Usage
Air doors are often used where doors are requested to remain open for operational purposes, such as at loading docks and vehicle entrances. They can be used to help repel flying insects by creating strong turbulence, or help prevent outside air, thereby reducing infiltration through opening. Cold drafts can be avoided by mixing warm air heated by air gates. Heated air doors are usually used when additional heat is required for space, and to reduce the cold wind factor in the opening, in cold climates.
Further applications include customer entrances, aircraft hangars, cargo doors, drive through windows, restaurant doors, or delivery door. Non-heated air blinds are often used along with cold storage and refrigerated spaces.
The air door can be equipped with or without heating to heat the air. The fan should be strong enough to produce an air jet that can reach the floor. There are several studies in the scientific literature that present analytical methods to predict sealing efficiencies obtained by air curtains.
Effectiveness
The flow of air through the door depends on the force of the wind, the temperature difference (convection), and the pressure difference. The air door works best when the pressure difference between the inside and outside of the building is as close as possible to neutral. Negative pressure, extreme temperature differences, near lifts, or extreme humidity can reduce the effectiveness of air gates.
The most effective air gates to accommodate air conditioning inside the building with open doors will have high face speed at opening, generated by top-down flow, and air recovery by air recirculation and channel back to fan sources. This configuration is feasible for new construction, but it is difficult to apply in existing buildings. The most effective air gate with low exterior wind speed; at higher wind speeds, the air mixing rate increases and the outer air portion of the total face flow increases. Under the ideal conditions of zero wind, the maximum airway effectiveness, but in windy location of the air door can not make a perfect seal, but often used to reduce the amount of infiltration of the opening.
For industrial conditions, high face speed is acceptable. For commercial applications such as store entrances, user comfort dictates low-speed faces, which reduces the effectiveness of exterior air separation from interior air.
Comparison with overheating
The UK-based HEVAC Air Curtain group describes overdoor heating as a heated electric or water heating unit with low airflow rate. They are intended to be installed in doors that have low pedestrian traffic where the doors are mainly covered, and are useful in providing warmth. However, they should not be seen as an alternative to the air curtain, which also serves to separate the indoor and outdoor air space.
The main differences are:
- The aerial door is designed to completely cover the threshold, while the outside heater may be too narrow.
- Fans at air gates are strong enough to provide airflow for projection across open doors. Excessive heating may have less powerful fans.
- The exhaust nozzle on the air gates is optimized to provide uniform airflow across the width of the threshold, which may not occur with outdoor heaters.
Energy savings
Air curtains consume electrical energy during their operation, but can be used for clean energy savings by reducing heat transfer (through mass transfer when air is mixed across the threshold) between two spaces. However, closed and well-closed physical doors are much more effective at reducing energy loss. Both of these technologies are often used simultaneously; when the solid door is opened the air curtain lights up, minimizing the exchange of air between inside and outside.
An air curtain can pay for itself in a few years by reducing the load on the heating system or building air conditioning. Normally, there is a mechanism, such as a door switch, to turn on and off the unit when the door is open and closed, so the air curtain only operates when the door is open.
Design
Authoritative engineering design procedures for calculating air supply flow and thermal air curtain capacity for HVACR applications are described in BSRIA 2/97 Application Guide Procedures for "Buildings with Tight Air Specifications" should be followed, ie practical buildings with multiple leaks air. In the BSRIA Application Guide , Section 4.2 describes the design procedure and Section 5.2 provides examples that work for buildings with various airtight specifications. This allows engineers to calculate the air supply flow rate and thermal capacity of the air curtains required for a particular application.
References
External links
- Video Illustration Air Curtains
Source of the article : Wikipedia
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