Air curtains for air quality
With up to 80% of our time being spent indoors, good comfort and a constant supply of clean, conditioned air is essential to ensure a safe and healthy environment in which to live, work and play. Air curtains can greatly contribute to a high level of indoor air quality in our working lives, and, through doing so, increase the energy efficient performance of a building.
The main uses of air curtains are threefold. First, they increase the energy efficient operation of a building by preventing or reducing the unwanted exchange of hot and cold air at an entrance. Secondly, they improve comfort conditions in the entrance area by preventing or warming any incoming cold draughts, thus creating a pleasant and welcoming environment that is comfortable for staff and visitors alike. Finally, air curtain technology can be used to separate atmospheric zones within a building. For example, between smoke free and smoking zones; to keep out air that has been polluted by traffic fumes, smells, dust, pollen etc; to repel insects and also between areas of high and low humidity.
Air curtains can be applied to almost any entrance, from smaller retail outlets to larger openings in commercial and industrial buildings. They can be employed as purely functional units, to create an energy efficient air barrier across an opening, or to increase comfort by warming the entrance area for occupants and visitors. They can also contribute to the aesthetic environment, such as a corporate reception area, to keep within the parameters of the architect’s vision. Some of today’s most attractive designs are symmetrical and have stainless steel finishes that hide high quality components and aerodynamically efficient internal geometry, resulting in air curtains that are unobtrusive as well as effective.
Property occupiers have the option to employ door curtains for smaller entrances. They are widely used in kiosks, service windows, in between double doors or as a zone heater for a single person in a large environment. There are important differences between this kind of compact air curtain and full performance air curtains, which are primarily designed to provide an air barrier from top to bottom of the door.
Door heaters heat incoming air and produce a low airflow with high output. The heater may be less expensive than an air curtain and provide a similar heat output figure, but will only cover part of the opening, allowing cool air to enter and warm air to escape. Depending on the application, door heaters may be a sufficient source of heat, but air curtains are a preferred option in both smaller and larger installations and can be used on doors up to 6m in height.
In contrast to door heaters, air curtains minimise leakage of heated or conditioned internal air by means of high airflow at high outlet speeds, creating an invisible door. Air curtains reduce the cost of maintaining temperature by preventing energy loss, especially in summer. It is often stated that air conditioning costs the bill payer more in summer than heating in winter. This is a growing trend with climate change and increased expectation of summer comfort. In summer, an air curtain is running in ambient mode (fan only) so energy savings far outweigh energy consumption.
Further energy savings can be achieved by ducting warm air from heat pumps, air conditioners or extract fans (from computer rooms for example), through the air curtain to boost the outlet air temperature.
To provide the most effective barrier, the entire width of the door must be covered and the airflow should be sufficient for the door height. Before installation, it is important to study the structure of the building and the proposed ventilation, taking into consideration draughts, likely wind loads and artificial pressure. Balanced ventilation is essential. Aside from preventing cold draughts and reducing heat losses, additional heat can also be provided to a building, maintaining desired temperatures in areas adjacent to the access doors.
A number of factors affect the performance of air curtains such as fan speed, air volume, mounting height, output and acceptable noise level. Building design also has a major influence on performance. Manufacturers strive to provide ‘out-of-the-box’ solutions for optimum performance in most doorways. However, this may often require compromise to allow for all the building characteristics in standardised solutions. In some situations, it may be necessary to tailor the unit’s performance or design to meet a client’s criteria;
Even so, there are inevitably limitations to what an air curtain can achieve. They cannot block excessive draughts – an incoming wind speed of 3m/sec is considered the acceptable maximum – nor can they compensate for significant over or under pressure inherent in a building design. In such situations efficiency is reduced but air curtains can still provide a comfort benefit. If incoming draughts cannot be blocked, they can at least be warmed and filtered, creating an acceptable environment for staff and visitors, while also supplementing the building’s heating system, which may otherwise struggle to cope.
In high exposure locations, vertical mounting of air curtains can be a solution to provide greater output power, constant velocity from the top to the bottom of the door and also offer a very pleasing architectural look.
Air curtains are also popularly used in cold-store applications where the air curtain effect is reversed to seal a chilled area. The aim of these air curtains is to keep the cold air inside and keep ambient air out. Typical applications are entrances of cold stores in dairies, flower storerooms and food storage areas. The application of air curtains in cold stores can be extremely effective. It is possible to create total separation between ambient external and sub-zero internal climates, within around 600mm of horizontal space. Air curtains also prevent ingress of dust, air-borne contaminants and vehicle fumes that may contaminate food or other delicate, perishable products.
An issue for all air curtains is whether or not to include filtration. Most manufacturers offer some filtration options. However, clients should be advised that filters will need regular cleaning, which could be as often as every two weeks in certain environments. As the air curtain draws through large air volumes, particularly close to the door where the air pollution level may be considered higher, it is not possible to give general cleaning and maintenance advice. Air curtains, partly because they are usually located at high level in areas of constant use, are often considered as maintenance-free equipment, in which case additional filters should be avoided.
‘Invisible’ recessed air curtains are another popular choice for ceiling mounting. However, with regard to air quality, clients should consider where the air curtains draw in their inlet air from. Models which pull from the roof space risk drawing in dust, dirt, fumes and potentially damaging flotsam left in the roof void. This can obstruct the airflow or be blown in to the room space. The best recessed solutions are those specifically designed for enclosed installation that draw and blow the air from the room space rather than the ceiling space.
Over the past few years, Frico has experienced a growth in demand for air curtains, in an increasingly varied range of specifications, as awareness grows among building services specialists of their overall energy efficiency benefits. Taking into account the added advantages they bring to maintaining clean and conditioned indoor air, this trend it set to continue.