THE HEAT PUMP
By J. GORDON COOK
IN our present days of coal and fuel shortage, it might be expected that a machine capable of delivering four or five times as much heat from a unit of electricity as an ordinary electric fire would have become a high-priority development 'project. Such a machine—the heat pump—was suggested in principle by Lord Kelvin nearly a century ago ; practical use has been made of it for many years in the domestic refrigerator—and yet the really important application of the principle to domestic and industrial heating has been largely overlooked.
Today we have only one heat pump operating in Britain. For more than two years this machine has worked successfully, pro- ducing central heating for a large block of office buildings at approxi- mately one quarter of the cost in fuel that would have been required by the most efficient form of conventional heating. To the scientist this is simply a result anticipated from the large-scale application of a well-known scientific principle. But to a country whose existence is identified with the efficient use of coal it must be regarded as one of the most significant engineering and scientific experiments of our age. As yet this simple fact has escaped the attention of the public and the Press. ,There is in the heat pump none of the drama of a penicillin or a rocket plane. But there can be no doubt that in the heat pump we have a machine that is to play an outstanding part in the industrial future of our country.
Superficially, there is a suggestion of perpetual motion aboUt the heat pump that taxes the credulity of the layman. More energy is obtained from it in the form of useful heat than is put into it as electricity. The explanation of this phenomenon is simple and quite valid. Electricity used by the heat pump is not converted directly into heat, as in an electric fire ; it is used in transporting existing heat from one place to another, and it is in doing this work that the electricity is consumed. Heat is a form of energy present in everything on earth. In some things the heat is at a higher " pressure " than in others, and we measure this heat pressure as temperature. Our physical sensations of hotness or coldness are a result of differences in the heat pressure in an object as compared with the temperature of our bodies. For heat, like water, tends to flow naturally from a high pressure to a low pressure. When something feels " hot," it means that heat is flowing from it into our fingers, where the heat is at a lower pressure. And when we say a block of ice feels cold, we mean that the heat in the ice is at a lower pressure than that in our bodies, so that the heat flows from our fingers into the ice.
The essential requirement in providing warmth for the human body, therefore, is to raise the heat-pressure, or temperature, of the surroundings so that the flow of heat from the body is minimised or reversed. That is why we raise the air-temperature in a room by turning electricity into heat in an electric fire, or by burning coal in an open grate. In the heat pump we have a machine that is able to reverse the natural flow of heat. Just as a water pump can make water flow from a low level to a high level, so can a heat pump force heat to flow from something at a low temperature to something at high temperature. For many years we have been making use of the heat pump in the domestic refrigerator. Here we remove heat continuously from the cold interior and dispose of it into the air. It is this heat which warms the stream of air coming from the grid of a refrigerator. But we have been slow to develop the heat pump as a refrigerator-in-reverse which can pick up heat from the air or earth outside, bring it into the house, and release it into the air at a useful high temperature. There are no insuperable difficulties to large-scale operation in the principle of the pump itself. On the contrary, it is basically extremely simple, depending on the alternate contraction and expan- sion of a circulating gas. At the point where heat is to be picked up, the gas is allowed to expand. In doing so it cools, and heat flows naturally into it frotn the surroundings. The gas then circu- lates to the point where the heat is to be released, and is compressed. Compression results in a rise in the temperature of the gas above the temperature of its surroundings, and the heat flows from the gas into the air. The net result of the circulating gas is thus to remove heat from one place, which becomes progressively cooler, and release it in another place, which thereby becomes hotter. The pump, in other words, is making heat flow against its natural inclination from a low to a higher temperature.
Disregard of this ingenious method of using available heat until recent times has been due largely to our wanton use of coal as a domestic and industrial fuel before the war. When coal was cheap, and apparently available in inexhaustible quantities, there was little incentive for anyone to spend money on a new machine that would save fuel. Today our outlook on such things has changed, and the heat pump is well on the way to coming into its own. During the war the first large-scale heat pump was built and operated in Britain. It remains the only one in the country, but its successful operation during the last two years has helped to awaken the interest of industrial and municipal undertakings all over the world. This heat pump is at Norwich, where it was erected under the direction and initiative of the City Electrical Engineer, Mr. J. A. Sumner. The pump was built from such constructional materials as were immediately available at the time, and .measured against what a properly built heat pump could be it leaves much to be desired. But for two years now the Norwich heat pump has worked success- fully, providing central heating for a large block of office buildings at something like a quarter of the cost in fuel that conventional heating would have incurred. Source of the heat is the River Wenlock that flows past the building ; as it passes through the pump, water from the river is lowered in temperature by one degree, the heat given up being released inside the building.
In present circumstances any device that can help in making better use of our coal supplies is of vital interest and importance to our country. The Norwich heat pump has shown quite definitely that Lord Kelvin's principle can be worked efficiently on an indus- trial scale, and we have in the pump something that can more than quadruple the heat return from our fuel. All over the world physicists and engineers are experimenting with the heat pump ; in Britain plans are already being made for the production of a small unit for domestic heating. When it arrives, it will be the answer to the housewife's prayer—a source of heat for the home that will maintain an even, controlled temperature in the house throughout the year. No dust, no smoke, no ashes, no chimneys or soot—nothing but a clean, warm air circulating round the house. In summer the pump will be able to reverse its action, pumping heat from inside the house and discarding it outside. The house. will, in effect, be operating as a giant refrigerator working at a higher temperature level. The cost of this domestic heat pump need not be exorbitant—possibly about £2oo. Against this must be offset the fractional fuel consumption and the increased cleanli- ness and convenience to the housewife.
In these days of material progress, when so much lip-service is being paid to science as our guarantee of prosperity, it seems incredible that a device such as the heat pump should have escaped the attention it deserves. Had it not been for a team of enthusiasts determined to carry their theories into practice, we should have been still awaiting evidence of the potentialities of the heat pump in Britain. Now we know that it will work, and the time has come when everything must be done to make the most of the knowledge we have gained. In science it is not enough for us simply to increase the intensity of our research effort. We must ensure in addition that the results of such work are put to immediate practical use for the benefit of the common man. Even penicillin did nobody any good during the ten years it remained a laboratory curiosity.
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