MAN-MADE WEATHER

Evening Star, Issue 23025, 2 August 1938, Page 3

MAN-MADE WEATHER

MARVELS OF HEATING Tremendous advances in / the heating, cooling, and air-conditioning of buildings are completely transforming the modern city (says the Melbourne ‘ Argus’). N'ew developments of refrigeration .have already revolutionised food preservation both on a large scale, for the purposes of commerce, and in the home. * The maintenance of the proper temperature and atmospheric conditions in dwellings has been one of the greatest problems with which man has been faced from the earliest times. There lias always been a time when we have been either too hot or too cold, and against those extVemes we have waged an unending battle. The open fire of prehistoric times was superseded, when man learned to build dwellings, by the fireplace and chimney. The stove and warm-air furnace followed, and, as buildings became larger, steam and hot water systems were developed. All these methods of heating are still in use. but the scientist and the engineer have evolved new methods and improvements which would have been beyond the wildest dreams of our ancestors. Progress in refrigeration came suddenly. Until comparatively recent times ancient and crude methods of cooling by air and water were commonly in use. In some countries foodstuffs were preserved by burying with natural ice. The development of heatextracting apparatus has. in a short period, revolutionised civilisation. A combination of heating and cooling equipment, together with methods of cleansing and drying or moistening the air, has given us air-conditioning. So great has been the development in this direction that it is certain that in the near future “ man-made climate ” will be a standard feature of most homes. MANY USES. The three main purposes of refrigeration to-day are cold storage and food preservation, ice-making, conditioning and cooling. By means of refrigeration the season for sale of fruits and vegetables is increased from a few weeks to many months. Eggs may be kept for long periods, and without refrigeration the modern meat packer could not exist. In Australia alone the capital invested in the perishable food industry, which depends entirely on refrigeration, runs into millions of pounds. Mechanical refrigerators for the home rely principally on two methods of heat extraction—the compressor svstem and the absorption system. ; The compressor type is operated by a small electric motor. The liquid refrigerant in ;the cooling coils vaporises, and, in doing so, extracts'heat from its surroundings. The refrigerant, having absorbed the heat, passes through a copper tube to the_ compressor or pressure pump. the action of which, in conjunction with the cooling or condenser coil, converts it back to a liquid. The heat of the compressed and liquefied refrigerant is dispelled through a radiator. It is then readmitted to the cooling i, coil, where it evaporates and extracts more heat, and so repeats the cvcle. . COLD FROM HEAT. Another, appliance, which does not require the use of motors or pumps, is now widely in use. Heat is applied to a boiler containing a solution of ammonia i in water, the ammonia being expelled from solution in gaseous form and then condensed to liquid by external cooling air or water. The liquid ammonia enters an evaporator in the cabinet and there evaporates to reduce the temperature.

The now gaseous ammonia passes into the absorber, where it meets the water coming from the Jjoiler, and the ammonia is absorbed again by the water, which is returned to the boiler. The necessary difference in pressure of ammonia in the boiler-condenser part of the system and the evaporator-absorber part is provided by the use of hydrogen, which automatically circulates because of the difference in weight of two gas columns. The ammonia solution is pumped back into the boiler through a pipe constantly heated. The advantage of this type of appliance is that it may be operated bv electrical, gas, or oil heating. In modern cities one of the principal applications of refrigeration is for airconditioning and cooling, in conjunction. with a heating device for’use in winter. _ In theatres, shops, and offices the main purpose is usually to make the premises “ feel cool ” in summer. This is usually done by reducing the relative humidity and at the same time cooling the air. All the air passes through a cold water spray chamber before it enters the room or hall to be ventilated. For single offices and homes air-con-ditioning units, complete with refrigeration and heating appliance in one enclosure, are being used. WATER VAPOUR METHOD. Many people in Melbourne will have noticed in the last few months a strange, tower-like erection on the roof

of one of the largest shop buildings. The appearance of this addition to the skyline is certainly neither romantic nor beautiful, but behind its design and development lies a tale of engineering achievement. Actually it is a barometric condenser serving a steam-jet water vapour refrigerating unit, and the installation is to keep the busy bargainhunter cool in the hot summer months. Most of us associate refrigeration with the use of ammonia, carbon dioxide, or some of the more modern refrigerants, but engineers have long recognised that the logical refrigerant tor moderate temperatures is water vapour. Water is universally available, and has n i appreciable cost, and has the added advantage of safety.) As a refrigerating medium water, in evaporating, will effect more cooling than nnv other refrigerant. Expressed technically. its latent heat of evaporation is nearly twice that of ammonia and many times that of carbon dioxide and freon. EARLY EXPERIMENTS. Why, then, has water vapour refrigeration been a commercial possibility only in the last few years?' The answer lies in the fact that the practical problems involved were considered by early experimenters to rule the system out. The problem to be faced is the maintenance of aii extremely high vacuum in the evaporating chamber, and at the same time the (removal of an enormous volume of vapour. These difficulties arise from the fact that water is a decidedly non-volatile refrigerant. The story of how these difficulties, once considered insuperable, have been successfully overcome, is one of the most, interesting pages in the history of engineering. The earnest experimenter worthy of note is Dr William Cullen, a Scot who, in 1755, 10 years before the invention of Watt's steam engine, experimented with vacuum refrigeration, using several refrigerants, one of which was water. Cullen’s work was never carried beyond the laboratory stage. The theory was helped by the experiments anil tables ' published by the Frenchman, Henri Regnault, about 85 years ago. More than 30 years Qgo that famous engineer. Sir Charles Parsons, suggested the use of steam ejectors to produce cooling of water by evaporation in high vacuum. DIFFICULTIES OVERCOME. Early experiments failed principally because they' lacked the means of evacuating large volumes of' vapour under very high vacuum. It was left to the Ingersoll Rand Company to put the whole system on a practical bomtnercial footing. The company’s experience in the design of centrifugal compressors, steam boosters, condensers, and centrifugal pumps gave it a store of knowledge to draw from. Extensive experiments conducted over a period of many months demonstrated that a practical and commercial type of evaporator could be built to cool water down to 35deg Fahr., only 3deg above freezing point. Two types were evolved, the centrifugal, in whicli the necessary vacuum was produced by a high-speed multistage centrifugal booster, and the

steam-jet type, where the vacuum was produced by jets of steam. Water vapour refrigeration for airconditioning is now an established fact, and its extension from the United States to other countries is well under way. The fact that one unit has been installed in Melbourne is evidence that its possibilities have been recognised already by Australian engineers.