THE PROGRESS OF COAL HEATING SYSTEMS

Press, Volume CVI, Issue 31349, 20 April 1967, Page 23

THE PROGRESS OF COAL HEATING SYSTEMS

How can we explain the fascinationof gazing into the cheery glow of a coal fire? Perhaps it is just laziness, or perhaps it is a convenient way of relaxing, but it is still reflected in the demand for modern coalfired appliances.

For hundreds of years coal has had a very important place in the domestic economy as the main source of heating and firing.

Manufacturers of coal-fired appliances have kept pace with the modem trends in domestic heating and firing by the increased efficiency and pleasing appearance of their products. So successful have they been that today coal still has a considerable share in this field, in spite of the impact of other forms of heating.

From the earliest days, as man learnt to control combustion and as his knowledge of building increased, he began to produce a crude form of open fire from which the heat was radiated into the room and the products of combustion were carried out through a chimney. This was the form of firing for centuries. The old type of open fire was inherently inefficient in that less than 20 per cent of the heat was effective in the room. As early fuel engineers developed their knowledge of combustion processes they saw the need to limit air-flow up the chimney. Although excessive airflow ensured adequate ventilation in the room, too

much heat was lost up the chimney. Not only were costs of operation increased, but fuel had to be applied too frequently for convenience. So air-flow up the chimney was restricted and thermal efficiencies rose. The traditional open fire was still popular, but the demand was increasing for more efficient combustion. Grates were sealed at the front to control the admission of air to the burning coal and the convector type of fireplace was developed. In this the air from the room is drawn into the appliance through grills and heated by contact with the cast-iron surface containing the fire. Efficiencies rose 45 to 50 per cent without any loss of the traditional con-

cept of the open fire. Slow combustion, or closed stoves were developed, being either built into a fireplace or freestanding units, and. thermal efficiency increased even more.

Most of these closed-door stoves have windows of heatresistant glass, through which the cheerful glow of the fire is still visible; thus the fire remains the focal point of the home. More modern developments incorporate a simple form of down-draught combustion, which without detracting from the idea of an open fire, give even higher thermal efficiencies and relatively smokeless combustion.

A back-boiler can be fit ted to most coal-fired domestic heating appliances to provide the normal hotwater requirements and reduce the winter demand for electricity. A recent development is the use of a water-jacketed fireplace from which the hot water is pumped through a small bore system of radiators throughout the house.

In this way the benefits of central heating are obtained at a relatively low capital cost without any loss of the traditional effect of the open fire. Other boiler units are available as the source of heat for a small bore waterheating system, but most of these are used in larger buildings such as schools and for commercial and industrial heating. Units have also been developed, generally on a larger scale, for heating the air in hot-air furnaces. These units operate silently to produce air either at the appliance or through a ducted system for central heating. These units give no visual evidence of coal burning; all that is seen is an attractive steel cabinet.

The coal industry realises that progress in the improvement of appliances is dependent on the development of new ideas and new designs. Coal-selling interests have formed an organisation to promote and improve coalburning appliances best suited to New Zealand condittoes and coals. This has been prcmpted by the realisation that coal firing is only as good as the appliance in which it is burnt. New Zealand is fort'inate in that its coals have some unique properties such as high reactivity, free burning qualities and low ash content and if used to best advantage are clean and convenient; also, they are better suited to automatic operation thin any other coals in the world.