Large open spaces such as warehouses, loading bays, workshops, garages, churches, sports halls, community centres, factory canteens, libraries, restaurants, public areas, aircraft hangars and airports all benefit from this clean, efficient heat source.
Figure 1 shows clearly how quartz infrared compares with other forms of heating. With an average lamp/emitter life of 7000 hours and the choice of reduced glare tubes it is a clean, instant answer to zone heating applications.
Efficiency is achieved especially in areas of intermittent use. The instant heat produced can be felt immediately by people and is not lost through open doors or wasted heating ceiling voids. The heat can be aimed and reflected exactly to where it is needed.
Economy can be achieved by only heating the areas requiring warmth, even within the largest of buildings. There is a wide choice of models to suit every application and these can be controlled zone by zone.
Safety is an additional benefit of an infrared heating system. As it uses a tungsten light source, it produces no harmful gasses or emissions. All reputable products are manufactured to conform to CE regulations on electrical safety.
What is infrared heat?
Put simply, infrared radiation is thermal energy transported by electromagnetic waves travelling at the speed of light. Selecting the right type of infrared heat source is dependent upon the emitter's radiation wavelength matched to the absorption characteristics of the object or product that requires heating.
Infrared wavelengths are measured in microns and will exhibit typical corresponding temperature outputs within a particular wavelength range: long wave = 3-10 micron range producing 700°C; medium wave = 1·4-3 microns (950-1600°C); and short wave = 0·78-1·4 microns (2200°C).
Temperatures exceeding 1000°C are reached in seconds, and heating efficiency is typically 60% compared to just 25% for convection heating. The fast response of infrared means that only 50% of conventional operating power is required.
Linear infrared lamp designs comprise a tungsten filament and a halogen gas sealed in a quartz envelope that can be clear, translucent or feature a ruby/neutral density sleeve for glare reduction. They are produced in a wide variety of configurations and range in power from 200-6000 W.
Tungsten filament lamps only produce 5% of their energy as visible light; they are much better infrared radiators. As a lamp operates at around 2200°C, evaporation of the tungsten filament takes place. The vapour migrates to the cooler end of the tube, where it condenses as a black film that absorbs heat and thus reduces radiant efficiency and the working life of the lamp.
If the design incorporates a halogen gas, the bulb walls are not blackened, resulting in a long-life, efficient radiant heat source. This is because of the halogen cycle. When the halogen gas comes into contact with the tungsten vapour, tungsten halide is formed. This halide compound will remain in a gaseous form and will not condense provided that the coolest part of the lamp remains above 250°C. The tungsten is prevented from condensing so finds the coolest surface close to the filament and its supports, where it then deposits itself. The halogen gas is released and combines with more vapourised tungsten forming the halide again, thus the cycle continues.
As a general guide, clear quartz halogen lamps offer the best infrared transmission. Translucent quartz involves some infrared radiation absorption but appeals as a lower cost option. Clear, jacketed lamps protect the inner bulb from substances that may affect performance and are ideally used in areas where contamination is a possibility. Sodium deposits, for instance, can cause devitrification of the quartz bulb and eventual failure.
Heating requirement
A simple calculation can be made regarding the amount of total heat required for any given area using the guidelines in table 1 overleaf. Choose the nearest figure to application of work undertaken and type of premises, then multiply this by the total area in m2. This will give an idea of the total wattage required to heat the area.
Fittings are available in 1-18 kW modules, with standard infrared ruby quartz lamp options in 1, 1·5 and 2 kW versions. All fittings can be wall-mounted or ceiling suspended for optimum flexibility.
Mounting heights of the fittings differ according to the lamp type and kilowatt loading, but vary in general between 2·5 and 10 metres. Portable systems are also available in various formats ie tripod, floor cradle etc, along with newly developed, weatherproof, exterior models for wall and pole-mounting.
Many factors must be thought about when considering equipment:
Heater guards Guards are essential for low level mounting and hazardous installations (sport halls etc) but are unnecessary when fittings are mounted out of reach. Any guard will absorb some of the radiation, so unguarded fittings will produce maximum heat efficiency.
PIR controls As short wave infrared reaches maximum temperature virtually instantaneously, PIR switching in low occupancy areas can help run a system at the lowest possible cost. When used in conjunction with contactors, they can cope with virtually any kW load or fitting configuration.
Power supplies Fittings requiring loads of 4·5 kW and over are usually wired to accept single or three-phase connection. Due to the power requirement in some large installations, it becomes essential that the load is balanced over three phases.
Heater controls Equally important to the energy efficient application of infrared heat source lamps is: the employment of reflectors to dissipate radiation and focus on heating targets; the control of inrush currents; and the provision of control circuits for operation on reduced power.
Reflectors Reflector coatings vary in cost and efficiency but generally the choice lies between gold, zirconium dioxide, titanium dioxide and aluminium oxide. Gold offers the highest infrared reflection properties but is more expensive and can evaporate at high temperatures. The cheaper option is zirconium dioxide. It comes a close second in reflectivity and, because of the coating process employed, it will not wear throughout the life of the lamp.
Inrush current The initial current passing through the filament, the inrush current, can be as high as 12 times the normal operating current depending upon the cold or hot resistance of the lamp filament. Fortunately this inrush lasts only for around 20 milliseconds, but if inrush power consumption is an economic consideration, applying a low voltage before the normal operating voltage can reduce the inrush.
Control Where necessary, lamps of this type can be dimmed as per normal incandescent lamps, but caution must be exercised. Although a 5 % under-voltage will extend life by 80 % and the wattage by 8 %, if the bulb wall temperature falls below 250°C the halogen cycle will break down. Strictly speaking, the best applications will always be where the lamp is designed for a specific operating voltage.
Where there is a need to operate at reduced power, there are a number of methods by which this can be controlled with lamps operating on ac or dc power at 50 or 60 Hz:
Fixed resistive Lamps are used in series. Such circuits can only provide a limited number of control steps.
Variable resistive If the output can be varied continuously over a specified power band, a variable resistor can be used.
Diodes These may be used with resistive circuits or on their own. Such devices are only suitable on ac supplies but do have the major advantage of reducing energy losses within the control circuit. Diodes can be used for fixed power steps and continuous control.
Burst fire circuits Provide a useful heating control technique where visible pulsing is not objectionable. The design of such control circuits can be achieved by using either mechanical or electronic devices.
Variable transformers Variable transformers provide a more effective way of adjusting the supply voltage than a series resistive load.
Tapped transformers Lamps can be controlled with predetermined fixed valves. The limited number of tappings available makes this type of control suitable only when a small number of steps are required.
Specifying
In order to be certain that an infrared lamp supply matches the operational parameters required, here is brief checklist of product details that a potential supplier would need to know:
- nominal voltage;
- operating voltage;
- wattage (according to heater length);
- rated wattage;
- colour temperature;
- rated life;
- heated length;
- overall length;
- emitter base (connection or electrical contact element);
- expected temperatures;
- applications;
- competitive supplier's equivalent.
Source
Electrical and Mechanical Contractor
Postscript
Jeff Webber is sales director with HeatLight Technology.
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