Advantages and Benefits of Air Curtains
What is an air curtain?
An air curtain is a fan-powered device that creates an invisible air barrier over the doorway to separate efficiently two different environments, without limiting the access of the people or vehicles.
The energy saving air screen reduces heating and cooling costs by up to 80% while protecting the internal climate and increasing people comfort.
It keeps the atmosphere clean from pest and insects, dust, airborne, pollution, smells, odours and stops draughts and cold or hot air entrance.
The functioning of an air curtain is based on a high velocity jet of air that covers all openings. Heated air curtains creates comfort by the jet of air on people as they cross the air screen and helps to maintain the temperature on the entrance.
Are air curtains effective?
Absolutely!
All studies and tests have proven that air curtains are effective. When an efficient air curtain is well installed it save lots of energy and at the same time the entrance areas remain climate protected, comfortable and free of draughts, insects, odours, etc.
The following advanced Computational Fluid Dynamics CFD diagrams made by UPC (Polytechnic University of Catalunya) show clearly the efficiency of air curtains.
The surface of next diagram is divided in two parts (at X=2): left side considered inside has a heater on the wall and refrigerated right side simulates outside.
Situation without air curtain:
Following the laws of physics, the light heated air on the left of the image, goes up by natural convection and escapes to the cooler side while the heavier unheated cold air penetrate from the outside flowing through the floor. As the air tends to equalize temperatures and pressures and the warm inside are not thermally protected from the outside, the air mixes and we can’t see two separate thermal areas. In this situation we waste lots of energy and the heater is not able to keep comfortable the internal area.
Situation with air curtain:
The air jet of the air curtain placed on top, clearly divide the warm and the cold area in two thermal zones. The air curtain keeps internal environment on the left side of the image at comfortable warm temperature and avoids cold air penetration from the outside. In this second situation, the air curtain saves up to 80% of the energy given by the heater placed on the left wall.
Important Note: Poorly designed air curtains, wrong selected units (less powerful) or inadequate installation will loose part or even all the advantages and became worse than unprotected door.
How air curtains work?
Generally the air entering through the inlet grille, sometimes with filter functions, is compressed by internal fans and forced thought an air outlet, which is directed at the open doorway.
The filter protects the interior components (heat exchanger, fans, electronics, etc.) from dust and particles.
The fans of the air curtain can be direct or belt driven. The most frequently used types are centrifugal, axial and cross-flow.
Some air outlets and/or lamellas can be adjustable to increase the performance of the air curtain according to each situation.
Heated air curtains have a coil (electric, hot/chilled water, steam, indirect or direct gas, direct expansion, etc.) to heat or cool the jet. Heating is used to avoid people feeling a cold jet of air when crossing the doorway and also to heat the volume of air coming in at the entrance.
There are 3 possible directions of blow-out air streams:
Horizontal discharge from top to bottom
Vertical discharge from one side to another side
Horizontal discharge from bottom to top
Most air curtains are installed horizontally, across the top of the opening, and air is expelled from top to bottom of the door. Vertical air curtains can be installed in one or both sides of the door. Horizontal installation integrated on the floor is the most effective in thermodynamic terms and at the same time the most expensive one to install and problematic where public pedestrian traffic crosses the doorway for obvious reasons. So it’s only used in some special industrial applications.
Types of air curtains: non-recirculating or recirculating. A non-recirculating unit discharges the air to the environment. Otherwise recirculating collect and return the air from the discharged air. Recirculating air curtains are more efficient but the majority of installations are non-recirculating due to lower costs.
Non recirculating air curtain
Recirculating air curtain
Air curtains: Technology
It is known that on open doorways with two adjacent areas in different conditions the air is interchanged between them because the laws of physics tend to equalise the temperature and pressure difference between both sides.
Basically air transfer on doorways happens due to these 3 factors:
- Temperature difference: is the natural convection effect that creates an air transfer between two areas with temperature difference. Warm air will escape through the top of the doorway and being replaced by cold air coming in at the bottom. As bigger temperature difference bigger air infiltrations and energy losses
- Pressure difference: it is recommended to equilibrate the pressure difference as much as possible because it affects the air curtain performance. But in some installations like clean zones a little pressure difference helps to prevent the particles entering from outside
- Wind, stack effect and draughts: by modifying the air jet strength and the outlet discharge angle, the air curtain can work against forced air movements like wind or draughts. But if the velocity of the incoming air is excessive the air curtain will become less efficient
Schematic representation of the main parameters involved in the performance of an air curtain produced by the UPC (Polytechnic University of Catalonia).
The efficiency of an air curtain depends on the optimization of performance factors.
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h = effective width of the jet α = discharge angle U0 = discharge velocity θ = negative impact angle H = opening height P1 = outside pressure P2 = inside pressure |
The most important ones are:
Turbulence of the jet: low turbulence jet will be much more efficient and save energy
Air speed: air velocity should be enough across the doorway
Air volume: a wider jet makes the air curtain stronger against air transfer on doorways
Angle discharge: according to a situation if jets are well oriented it will increase the energy saving
Fan type: axial, tangential wheel, centrifugal, etc. Higher pressure fans create a higher pressure jet that reaches farther. For instance, if we compare an air curtain with tangential fan against an air curtain with centrifugal fan (with same air volume), the jet made of centrifugal fans will be stronger and larger.
UPC University air curtain studies have proven that air turbulences are one of the most important parameters that will affect the distance of the air jet.
UPC University schema shows the air turbulences behaviour:
Optimized shape of the outlet plenum, the position and fans type, the shape of lamellas, etc. substantially affects the air jet performance.
Air curtains angle discharge
Tests and University studies have proven that the angle discharge helps substantially helps the air curtain to be more efficient.
When factors like wind, temperature or pressure difference causes air transfer from outside to inside, we can aim the jet towards outside some degree. Then the jet direction against the air entrance will help to keep the air outside. The trajectory of the jet will be parabolic but at the end will reach the floor approximate by the doorway. If we can’t adjust the angle discharge, the jet will be pushed in by the external air forces.
The forces parallelogram theory explains how the forces behave on a doorway. The following diagrams show the difference between air curtains with fixed lamellas against adjustable ones.
Air curtain with fixed lamellas less efficient (1)
Air curtain with oriented lamellas more efficient (2)
(1) The first one, fixed vanes, where the entrance air velocity pushes the jet of the air curtain, the resultant of the parallelogram of forces is diverted inwards. This allows outside air to enter inside.
(2) The second one, adjustable lamellas, when the air jet is oriented against the entrance, the resultant of the parallelogram forces is directed perpendicularly to the floor. This means that outside air does not enter and inside air does not escape. Besides internal temperature level is maintained.
We classify the air curtains advantages in 4 groups:
Commercial profitability
- Sales increase due to the “open door effect”. It is known that when doors are open, people affluence increases substantially
- Doors open is an invitation for customers
- Doorway acts as a shop window and allow people to see the inside of the shop
- Free access for disabled people (wheelchair) or people using baby strollers, trolleys, umbrellas, etc.
- Help to control uncomfortable sensations of draughts
- Increases available usable space on entrances
- Increases customers and staff comfort
Hygienic and healthy atmosphere
- Helps maintain adequate enviroment
- Reduces employee absenteeism
- Pest and insect control
- Barrier against airborne dust, pollution, fumes and bad odours
Energy saving
- Reduces the energy losses from the conditioned space
- Reduce central plant capacity (heating/cooling)
- Reduces the building running cost
- Reduces the CO2 emissions
Increased safety
- Increase visibility and avoid collisions because there isn’t a physical obstruction
- In cold rooms reduces misting, dry out the doorway and prevents ice forming on floors
- Easy evacuation through the exit doorway in case of fire or emergency
- Act as a barrier against fire smoke (special application)
To achieve those advantages it is absolutely necessary to select the right air curtain.
Inefficient air curtain (losing money)
Efficient air curtain (saving money + advantages)
If we select a wrong unit the air jet won’t reach the floor and the separation of two adjacent areas will disappear. Then all heated/cooled air will cross the doorway and we will loose energy and all other advantages.
Some people only care about the air curtain price and select a less performance or inadequate air curtain, following sometimes other seller recommendations. Being confident you should always compare the characteristics of the air curtain, especially the kind of fans used and the air volume.
At the end if we calculate the amount of money of the air curtain and the energy savings we will achieve that selecting the wrong unit can be more expensive and moreover the end client won’t be satisfied.
In conclusion, on open doorways it is highly recommended to use an air curtain because of the many benefits.
Door climate protection
First and foremost air curtains are designed to prevent a climate area (heated or cooled) from the influx of outside air through an open doorway.
The air curtains reduce energy costs by keeping heated or cooled air in the internal building atmosphere.
Efficient air curtains will save up to 80% energy looses across a doorway compared with a door without air curtain.
During the winter an air curtain creates a barrier that keeps out the cold air while in the summer the air stream keeps out the hot air from outside.
Bearing in mind the energy saved, the average payback time for an air curtain is between 2 and 5 years depending on usage and climate conditions.
Although doors are open the air curtain separates internal and external conditions
Pest and flying insect control
Insect air curtains are commonly used, when necessary, to stop insects from entering a buildings like food processing plants, bakeries, restaurants, hospitals, etc. Bugs in flight approaching will be stopped by a barrier of air too powerful to penetrate.
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| Air curtain stops flying insects entrance from the outside | |
You need to select the correct air curtain for insect repellent applications. A very powerful air jet along the all doorway is needed (stronger than standard applications).
Cold storage
Due to big temperature differences, it is highly recommended to install air curtains to reduce the energy losses when the door is open. The higher the temperature differences between inside/outside, then higher are the energy losses when a door is unprotected.
So the payback period of the air curtain is very short and then the energy/money saving is very high.
Not only we will save money avoiding air transfer through the door but also will keep the frozen goods in perfect condition and help to reduce defrost costs of the cold room.
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| Air curtains are the safest way to save lots of energy in cold rooms |
For cold rooms and freezers air curtains are the safest way to protect the energy losses without any physical barrier that can create accidents or collisions on the doorway. For example, when plastic strip curtains are used the view across the doorway is limited and people or vehicles accidents occur, with compensation consequences. Besides it prevents bothersome and potentially dangerous fogging, humidity and ice formation in the door entrance area.
Dust, pollution and airborne control. Clean rooms.
Always installed in the clean side of the doorway, air curtains act as a barrier against dust, particles and humidity.
Other applications
Drive-thru windows, separate smoking from non-smoking areas, industrial ovens, refrigerated display cabinets, Dam Twin system, etc.
Common places where air curtains are installed:
To select an air curtain the following factors should be kept in mind:
- The height of the installation measured from the discharge diffuser to the floor
- The width of the door
- The location of the building to determine the level of protection needed against weather conditions (temperature, humidity and wind)
- If the building has several doors in the same area, different or opposite façade
- If the building has several storeys connected by escalators/stairs
- Pressure differences between the inside and outside of the building
- Door characteristics: If always open, it opens automatically, it opens manually, revolving door, etc.
- Characteristics of the ventilation and air conditioning installation
- Voltage and electrical power availability
- Type of business, style and decoration of the premises
- Free hanging or recessed, horizontal or vertical installation, heated or unheated, etc.
Some installations with strong wind conditions may compromise the air curtain due to: Severe wind, extreme temperature difference indoor/outdoor, more than one door, different levels, big halls, high pressure difference, etc.
In those situations a higher performance model is recommended.
As explained, the air curtain selection depends on the installation situation. Here we show 4 different situations from the most favourable to the air curtain to the most unfavourable.
Air curtain control is essential to prevent unnecessary energy usage by modifying the performance of the air curtain according to the situation of each moment.
Using the appropriate control together with auxiliary devices the user can adjust the air flow to optimise the barrier and avoid air penetration across the doorway.
Basic control
Hand Auto control
Clever control
Basic controllers allow modifying the ventilation speed and heating stages manually.
Advanced controllers may include options such as:
- Automatic functioning: Modifying ventilation and/or heating depending on the situation
- Connection to external sensors and/or devices
- Include internal sensors (temperature, movement, etc.)
- Interface connection to BMS systems, external ON/OFF, thermostatic control...
- Internal security programs (protect components and avoid damages)
- Door contact, valves, anti-freezing sensors, etc.
Door contact (magnetical, mechanical)
Solenoid valve
Anti-freezing sensor
External sensors and devices help to control and modify the performance of the air curtain to protect the unit and be more efficient in each situation.
For instance, if we install a door contact connected to the air curtain, when the door remains closed the air curtain is OFF or working at low ventilation speed and/or lower heating stage, saving energy. When the door is opened, the air curtain will increase the ventilation speed and/or heating stage to protect the doorway.
Another example is connecting the air curtain to a room thermostat. Then the unit will increase/decrease or stop the heating when reached the desired temperature.
Airtecnics has a wide range of controllers from standard manual ones to advanced automatic functioning and interface to connect the air curtains to BMS systems.
Besides we offer a large range of accessories: All kind of supports, room thermostats, door contacts, solenoid valves, anti-freezing sensors, etc.
Heat pump technology
Heat pump is a device that uses a small amount of energy to move heat from one location to another. This system is extremely efficient because it simply transfers heat, rather than burn fuel to create it.
It consists on a closed circuit through which a special fluid (refrigerant) flows. This fluid turns into a liquid or gaseous state according to temperature and pressure conditions.
The circuit is composed by: compressor, condenser, expansion valve and evaporator.
Advantages and benefits
The new Airtecnics heat pump air curtains are absolutely efficient reducing the heating cost and CO2 emissions up to 70%.
- Very high energy efficiency ratings to save big amounts of money on your energy bill
- Short payback period thanks to very high level of energy saving
- Heating and cooling included in the same system (reverse cycle)
- Environmentally friendly as uses such low amounts of energy
Available Airtecnics heat pump air curtains:
- Heating / Cooling: Windbox M-G, Dam, recessed Windbox, Smart, recessed Dam and the models Windbox BB and Windbox L-XL, on request.
- Only heating: Rund, Zen, Rotowind and Invisair
Heat pump vs Electrical air curtain - Energy saving example
How much money can I save using a heat pump air curtain?
Result: The payback period is 1,2 years. We recover the price increase of heat ump air curtain in nearly 14 months and then we start saving money. From the beginning we save energy and reduce CO2 emissions to the enviroment.
EC technology
EC technology (Electronically Commutated) combines AC and DC voltages, bringing the best of both technologies: the motor runs on a DC voltage, but with a normal AC supply.
The EC motor incorporates voltage transformation within the motor. The non-rotating part of the motor (stator) is extended to make room for an electronic PCB board which includes power transformation AC to DC, as well as the controls.
EC motor have no slippage losses, reducing losses and increasing efficiency versus AC motors.
EC motor principles
- Permanent-magnet brushless DC motor within the rotor
- The stator is driven by electronic switches (which replace the carbon brushes), controlled by a microcontroller
- Electronic system (hall effect sensor or software) is used to recognize the rotor position
- AC operated 230Vx1 or 400Vx3, valid for 50/60Hz
Advantages and benefits
The new Airtecnics EC air curtains are extremely efficient reducing the running cost of the ventilation up to 67% using EC instead of AC fans.
- Energy savings: Minimum power consumption & better efficiency than AC equivalent
- Low motor temperature: for longer lifetime than AC equivalent
- Simplicity: Electronic & power transformation are completely integrated within the motor
- High performance: Speed can be driven up to 3600rpm
EC air curtain vs AC air curtain - Energy saving example
How much money can I save using an EC air curtain?
Result: The payback periode is 1,2 years. We recover the price increase of EC air curtain in just over a year. We save energy and reduce CO2 emissions to the environment.
SOURCE: https://www.airtecnics.com/technology/advantages-and-benefits-of-air-curtains