Electrical Outdoor Heating Overview
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Outdoor heating systems have been becoming more and more popular in commercial settings over recent years, and are in increasing demand following the introduction of the ban on smoking in enclosed public places, which has resulted in a pressing need for comfortable outdoor spaces where smokers can indulge their habit in peace.
As businesses consider their energy bills and also their carbon emissions, the choice of heating system is likely to be an important one over the long-term, affecting the success of the outdoor area, their energy bills, and also the cost of maintenance. It is highly possible that many businesses that have bought in haste, will be repenting at leisure, and will be revisiting their options over the coming months, creating more business opportunities for electrical contractors.
For convenience in a commercial setting electric radiant heating is likely to be the method of choice, as there will be no gas cylinders to order, store or change. In addition, selecting a wall mounted electric heater will ensure that no valuable floor space is wasted and that public safety is optimised because the heaters can be mounted well out of reach. There are, however, significant differences between the kinds of electric radiant heaters available and major differences in their efficacy in an outdoor setting. The principle of radiant heating is well known, and there are important differences between long wave emitters and medium or short wave emitter quartz lamps. For example, the radiant efficiency of a short wave infrared heater is up to 96 per cent, and that of a medium wave heater around 40 per cent. Electric infrared energy travels outwards in straight lines from the heat source, diffusing over distance, and is directed into specific patterns by optically designed reflectors. For successful comfort heating, there must be reasonably even levels of heat throughout the area to be heated. Proper mounting heights of the individual heaters, accurate heater spacing, reflector beam patterns, and heat wattage must all be specified to generate the appropriate heating levels.
The heat of the moment
The ban on smoking in enclosed public spaces has meant that businesses are looking at outdoor heating to help create a comfortable environment in which to smoke. Short wave high intensity quartz radiants work like sunshine and have a warming effect the instant the heaters are switched on. Short wave heaters warm people and objects within the beam rather than the air, resulting in a pleasantly fresh rather than stuffy environment, whereas long and medium wave heat has comparatively poor heating characteristics, especially when used outdoors, as it relies on heating the air and does not penetrate the skin to warm up the person. In addition for long and medium wave heat the heat is susceptible to air movement and so is not directional. In reality, a medium wave filament, which only heats up to around 900oC, is more suitable for curing and drying processes than for outside heating applications, although cheap heaters with medium wave filaments can be purchased as exterior heaters. Long wave heaters are most suited to heating inside areas where a low level of heat is required and it is acceptable for the heaters to be in use for some time to pre-heat the area before it is occupied. Ceramic plaque heaters fall between medium and long wave, heating up to around 500oC but, again, are of little use for al fresco heating as they warm the air rather than penetrating through it and warming the individuals in the vicinity.
Short wave lamps
Short wave halogen heat lamps consist of a tungsten filament heated by the passage of an electric current to a temperature of some 2,200oC. At this temperature most of the emission is in the short wave infrared band.
The moment that they are switched on, a warming effect can be felt, so the heaters only need to be switched on when the area is occupied and when the ambient temperature dictates that heating is needed. 92 per cent of the energy used is converted to heat within seconds of the heater being switched on - the remainder is converted into light as a by product of the process, giving a cosy and welcoming glow that adds to the ambience of the area. For heating applications a ruby sleeve or gold dichroic coating encloses the halogen heat lamp, to filter out the intense white light and provide an aesthetically pleasing warm glow.
What to look for
When selecting short wave band electric quartz heaters, it is important to consider the place in which they will be mounted. As a rule, ordinary lamps should only be mounted horizontally and will quickly burn out in a vertical position. If you need to mount heaters vertically, check with the manufacturer that it offers lamps suitable for this purpose, specify which you need at the time of ordering, and always look at the lamp inside the heater.
A quartz linear heater should always have a highly reflective, long lasting reflector which directs a focused energy beam on an area as required. A special benefit of the adjustable beam direction is that high intensity radiant heating can be provided at low level even though the heater is mounted at a high, safe level. Look for heaters with a dedicated reflector, not ones relying on the surface of their extrusion to reflect heat back. The method of extrusion production leaves draw marks on the surface and it is usually not of mirror quality so cannot act as a true reflector. It is merely a cost saving measure for the manufacturer, and one which will impact both on the heater's performance and on its life span. It is essential that the parabola shape of the reflector is accurate and the lamp is placed in the correct focus within the reflector in order to obtain maximum heat output. The lamp should be mounted in such a way to dissipate heat away from the ceramic on the lamp towards the heater body, which in turn will act as a heat sink. Specify heaters with side reflectors as they keep the heat away from the critical part of the lamp and significantly improve the output of the heater.
Some heaters for outdoor use are marketed with a high ingress proof (IP) rating, for example, IP65. Before paying extra for it, consider whether it is really necessary for the specific application. Many heaters in a patio area will be installed under an awning or umbrella, which in itself provides protection. Even if they are not under cover, IP24 is usually a sufficient rating for permanent outdoor installation. If a heater has an IP65 rating, check whether it can be re-lamped. In a heater with a wire guard, the wiring is normally such that the heater will either need to be stripped down for re- lamping or returned to the factory, which is both expensive and inconvenient as the heater will be out of service for some time. Equally, don't be too keen to secure a bargain. Beware cheap copies of quartz patio heaters - the old adage 'you get what you pay for' applies to patio heaters as it does to most things in life. Cheap heaters usually use ordinary glass which does not allow heat to pass through efficiently and can shatter under the heat duress. The component parts give poor heat output and an inadequate lamp life of around 12 hours rather than 1,100 - 7,000 hours, depending on the heater model, of a good quality product.
Some patio heaters are available with a glass front guard which has been specially designed for the purpose, as opposed to those where a heating element has been placed in a floodlight fitting, and the result is both better heat output and extended lamp life. Because these types of heaters have been designed and engineered for the purpose, they require minimal maintenance, typically a quick wipe of the front glass to ensure optimum heat transfer.
The running costs of good quality electric quartz radiant heaters are around nine pence per kilowatt hour and there are ways to ensure that costs are kept to a minimum without compromising on comfort. As we have seen, the efficient nature of short wave heaters mean they can be left switched off when the area is not in use - some manufacturers offer other cost saving measures such as PIR detectors, coin slot operation, and controllers which can provide on/off or proportional power inputs. Creating a convivial outdoor area that can be used year round inevitably requires an efficient heating solution in the UK and in much of northern Europe. A little research into the available options now will ensure that the heating system used will be both cost effective and thermally efficient for a long time to come, and that the customer is a happy one.
Pete Rana is managing director of electric quartz heating specialist Tansun, which was set up in 1982 and is now the UK's leading manufacturer and exporter of electric quartz radiant heaters. Pete is highly active in his local business community and he has received a string of regional and national awards for his success, including the government's Trade Partners UK small business export award. In 2003 he was awarded an MBE for his services to business and export.