Product category:
Heating Systems, Controls and Management
News Release from: AmbiRad - Airbloc | Subject: Air Curtains: technical guide
Edited by the Buildingtalk Editorial
Team on 16 December 2005
Air Curtains: technical guide from
Airbloc
Air curtains from Airbloc are the energy-saving solution to an effective separation of internal and external environments when doors must be kept open.
INTRODUCTION Air curtains from Airbloc are the energy-saving solution to an effective separation of internal and external environments when doors must be kept open
This article was originally published on Buildingtalk on 5 Oct 2005 at 8.00am (UK)
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There are many potential applications for air curtains.
For example:.
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* In retail shops, they allow doorways to remain open, encouraging footfall while maintaining interior comfort conditions.
* In warehouses, they help maintain the correct atmospheric conditions that keep stock viable, even when loading bay doors are opened many times a day.
* In food preparation/serving areas, they ensure a dust- and insect-free environment that is hygienic and more inviting to customers.
Air curtains offer numerous cost, comfort and safety advantages, such as:.
* Minimisation of heat loss from interior to exterior air, and of cold air/humidity gain from exterior to interior air.
* Low fuel consumption, even on heated units.
* Protection against ingress of dust, fumes and flying insects.
* High visibility, no obstructions - reduces risk of accident.
This guide is designed to help specifiers and design engineers fully understand air curtain technology and how it can benefit different types of premises using the Airbloc range of products.
WHY DO WE NEED AIR CURTAINS?.
When doors are opened in heated buildings, colder air from outside (which is denser than the heated air inside (negative air pressure)) flows in through the bottom half of the doorway.
At the same time, warm internal air (positive air pressure) escapes through the upper half of the opening.
In some circumstances, the prevailing wind can bombard the entire area of the doorway, resulting in significant loss of energy.
In cold storage or air conditioned areas, the cooler air from inside the building spills out at low level and is replaced by warm, moist air.
In both cases, the internal air is compromised - comfort temperatures drop making staff feel cold or, in summer, conditioned air loses its power to cool.
When doors are opened many times during the day, fuel costs for heating or air conditioning will soon begin to rise.
Staff and customers may be uncomfortable and goods may be damaged or perish.
When external air flows into the building, it may bring with it dust and other unwanted airborne particles, and flying insects, both of which will compromise hygiene and sanitation.
The European Food Safety Inspection Services (EFSIS) advises that where food is handled or stored, doors should be adequately proofed.
An Airbloc energy saving air curtain will prevent and protect a building's interior environment from all these factors while reducing the costs associated with open doorways.
HOW AIR CURTAINS WORK.
Air curtains are positioned over or down the side of a doorway (please refer to diagrams overleaf), on the interior wall of heated buildings or exterior wall to a cold store.
They operate using fans and nozzles to create a stream of air that is directed down or across the door opening, forming a barrier of air that separates the internal and external atmospheres by deflecting natural convection airflow.
This air shield reduces the incidence of cold/humid air, dust, fumes or flying insects entering, and warm or cooled air escaping.
Air is drawn into the air curtain unit and discharged at critical velocity, volume flow and temperature, and at an angle to ensure optimum performance.
The kinetic energy that is transferred to the air by this process provides the necessary resistance to unwanted external air and particles.
In order to achieve efficient low energy usage, the air jet width, velocity and pattern of the airflow are crucial.
Optimum effectiveness can only be achieved when there is uniform linear flow across the full door width and fan speed control for additional wind resistance.
BENEFITS OF AIR CURTAINS.
An air curtain provides an invisible barrier across the doorway that maintains separation between internal and external environments, preventing extremes of environmental change.
Studies have shown that premises without an air curtain show appreciable fluctuations in temperature of between 4C and 10C within the building.
With an air curtain, a difference of only 1C is the norm.
Unlike a plastic strip or roller-shutter door, an air curtain does not limit visibility or movement of people and goods through the doorway.
This means it is much safer than other kinds of physical barrier, reducing the risk of accidents to people, vehicles, equipment or the building structure.
If used in place of a mechanical door, it will reduce door maintenance costs.
An air curtain is beneficial where a doorway needs to be inviting to customers.
It can be heated or ambient, creating an aesthetically pleasing aspect and a welcoming feel as customers enter.
At the same time, the barrier of air will prevent 11 - 15 mph wind, draughts, dust, flies and other unwanted particles from passing across.
AIR CURTAIN APPLICATIONS.
Air curtains provide protection to internal environments in the following ways:.
* As a thermal barrier.
* To resist against the wind.
* Fly and insect control.
* Environmental separation.
Thermal Barrier.
The air curtain prevents the natural flow of air caused by different temperatures.
Indoor and outdoor temperature differentials create an imbalance in air density and pressure that causes outside air to penetrate into the building.
The results are energy loss and consequent increase in energy consumption as the heating or air conditioning system works hard to bring the internal air back to comfort conditions.
An air curtain will provide a shield against heat loss and cold air gain in winter and against heat gain in summer.
Wind Resistance.
A prevailing wind can cause discomfort to personnel and potentially threaten the condition of goods if it infiltrates a building regularly.
An air curtain across an open doorway will resist the infiltration of external air by blocking and deflecting the air flow.
However, the air shield must be set at sufficiently high velocity to ensure it is strong enough to deflect the force of 11 -15 mph wind.
When the air curtain is installed, providing the appropriate velocity and volume of air and angled correctly, prevailing winds can be deflected.
Flying Insect Control.
A high velocity sheet of air across a door opening will prohibit unhygienic flies and other flying insects from entering the building.
This is an important factor in restaurants, bars and food service premises, where strict Environmental Health Regulations apply.
Environmental Separation.
Air curtains are highly effective at maintaining separation between internal and external environments, but they are equally effective in separating two internal areas, particularly where the presence of a physical doorway would be inhibiting or inappropriate.
This may include, for example, where a manufacturing or production area is adjacent to offices, or where an area must maintain a 'clean room' environment.
An air curtain can keep all contaminants at bay, but without restricting movement between areas.
The units are also effective in protecting cold storage areas which need to maintain a constant sub-zero temperature, but which need to offer easy access at all times.
PRODUCT SELECTION.
Air curtains are available in four heated forms, powered either by gas, electricity, steam, or low or medium pressure hot water.
Ambient models are unheated and are used primarily to maintain stable internal temperatures or to prevent warm air ingress to chill or cold stores.
Ambient models are typically installed in spaces where an effective heating or cooling system is already in place and there is a requirement to prevent external air from entering the building.
In most applications, the air curtain can be positioned discreetly and unobtrusively above or, in the case of large industrial buildings, down the side of the doorway.
Recessed and surface-mounted models are available for commercial and retail premises.
A recessed air curtain, such as the Airbloc ACR, can be mounted in bulkheads and above false ceilings to serve a doorway without obtruding on the eye line or aesthetics of the entrance.
A smaller ceiling tile heater, such as the Airbloc ACT, will provide additional heat distributed throughout the building, yet fit neatly into modular T-bar ceiling tile systems.
The selection of surface-mounted or recessed will depend on the requirements of the building and its use.
The AC surface mounted unit has the option of emergency lighting which complies with Health and Safety regulations for emergency lighting, is available in white RAL9010 or Metallic Silver and can be backlit to display company logo or venue name.
The ACR recessed air curtain is mainly used in bulkheads or suspended T bar ceilings.
It is a popular unit with architects due to its non-vision grille in white RAL9010 making it barely perceptible once inside the building, and popular with contractors due to the ease of fitting.
Regardless of the product type selected effective air velocity from ceiling to floor is essential.
The table below outlines typical airflow distances the above mentioned products are capable of achieving.
TECHNICAL INFORMATION.
Airbloc has calculated exactly how much money flows out with heated air when the door opens.
The calculation is based on BSRIA/ASHRAE heat loss formulae (publications available through their web sites) using a fuel cost equivalent of 1.5p/kWh, and shows how much energy can be lost through open doorways of all sizes in just one hour. Request a free brochure from AmbiRad - Airbloc ...
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