A TREATISE ON HEATING AND VENTILATING BUILDINGS. CHAPTER I. INTRODUCTION. NATURE AND PROPERTIES OF HEAT. 1. Demand for Artificial Heat. The necessity for artificial heat depends to a great extent upon the climate, but to a certain extent on the customs or habits of the people. In all the colder regions of the earth artificial heat is necessary for the preservation of life, yet there will be found a great difference in the temperature required by people of different nations or races living under the same circumstances. On the continent of Europe, 15 degrees centigrade, corresponding to about 59 degrees F., is considered a comfortable temperature; in America it is the general practice and custom to maintain a temperature of 70 degrees in dwellings, offices, stores, and most workshops, and a heating apparatus is considered inadequate which will not maintain this temperature under all conditions of weather. 2. Magnitude of the Industry of Manufacturing and Installing Heating Apparatus.-The industry connected with the manufacture and installation of the various systems for warming is a great one and gives employment to many thousand workmen. The manufacture of heating apparatus is not only of great magnitude, but it is varied in its nature; all kinds of apparatus for heating-as, for instance, the open fireplace built at the base of a brick chimney, the cast-iron stove with its unsightly piping, the furnace and appliances for warming air, apparatus for heating by steam and also by hot water-can be readily bought on the market in almost every form, from that of the simplest to that of the most complicated design. The exact amount of capital invested in this industry could not be ascertained by the author, but in twenty cities, selected in alphabetical order from a list of one hundred and sixty-five cities of the United States containing over twenty thousand inhabitants, the total amount invested in the business of erecting and installing heating apparatus as given in the Census Report by the U. S. Government for 1890 was $12,910,250, and the yearly receipts for 1890 from this business in the same cities was $5.592,148. The aggregate population of these cities was 1,573,508 people. This would indicate an investment of $8.20 and a yearly expenditure of $3.52 for each inhabitant. Reckoning on the same basis for the cities of the United States which contain over 25,000 inhabitants each, we should have an invested capital of over $106,000,000 and a yearly expenditure of over $46,000,000. These numbers are probably less than the amount actually invested, but they serve to give an idea of the magnitude of the industry connected with the supply of apparatus for artificial warming. 3. Nature of Heat.-Before consideration of the methods of utilizing heat in warming buildings a short discussion of the nature and scientific properties of heat seems necessary. Heat is recognized by a bodily sensation, that of feeling, by means of which we are able to determine roughly by comparison that one body is warmer or colder than another. From a scientific standpoint heat is a peculiar form of energy, similar in many respects to electricity or light, and is capable, under favorable conditions, of being reduced into either of the above or into mechanical work. We shall have little to do with the theoretical discussion of its nature, but, as it is well to have a distinct understanding of its various forms and equivalents, we will consider briefly some of its important properties. Heat was at one time considered a material substance which night enter into or depart from a body by some kind of conduction, and the terms which are in use to-day were largely founded on that early idea of its material existence. The theory that heat is a form of energy and is capable of transformation into work or electricity is thoroughly established by fact and experiment. It probably produces a molecular motion among the particles of bodies into which it enters, the rate of such motion being proportional to the intensity of the heat. Heat has two qualities which correspond in a general way to intensity on the one hand and quantity on the other. The intensity of heat is termed temperature-this can be measured by a thermometer; but, except in scientific discussion, no name has been applied to designate the unit-quantity of heat,* and there is no method of measuring it directly, although it is of as much importance as temperature. Qualy It is a fact which will appear from later statements that the Specifie amount of heat contained in two bodies of different kinds, but of the same weight and temperature, may be essentially different. A familiar analogy might perhaps be seen in the case of the dimensions and weight of men. The weight would depend on the general dimensions, height, breadth, etc., and it would probably be the case that two men having equal heights would have quite different weights. In a similar manner the amount of heat depends upon the temperature and also upon the property of the body to absorb heat without showing any effects which may be measured on a thermometer. This latter property in itself depends upon the nature of the body and also upon that peculiar quality of heat to which reference has been made. Under every condition heat must be quite different in nature from temperature. Note that heat is equivalent, not to mechanical force, but to mechanical work. Work. defined scientifically, is the application of force in overcoming some resistance; it is the result of a force acting through a certain distance; the distance moved through having as much effect on the result as the force acting. The work done is proportional to the product of the force exerted, multiplied by the space passed through. In English measures the unit of this product is a foot-pound, which signifies one pound raised to a height equal to one foot; it is itself a complex quantity resembling heat in this respect. Heat an be transformed into work. *The term entropy is now applied in scientific discussions to this property. 4. Measure of Heat-Heat-unit.-As explained heat cannot be measured by the thermometer; it can, however, be measured by the amount that some standard is raised in temperature. The standard adopted is water, and heat is universally measured by its power to raise the temperature of a given weight of water. In English-speaking countries the heat-unit is that required to raise one pound of water from a temperature of 62 to 63 degrees, and this quantity is termed a British thermal unit; this will be referred to in this work, by its initial letters B. T. U., or simply as a heat-unit. The amount of heat required to change the temperature of one pound of water one degree is not the same at all temperatures; the variation, however, is slight and for practical purposes can be entirely disregarded. The unit of heat used by the French and Germans, and for scientific purposes generally, is called the calorie; it is equal to one kilogramme (2.20 pounds) of water raised one degree centigrade (1.8 degrees Fahrenheit) and is equal to 3.9672 B. T. U. The calorie is referred to water at a temperature of 15-16° Centigrade (60 degrees Fahrenheit). 5. Relation to Mechanical Work and to Electrical Units. The relation of heat to mechanical work was accurately measured by Joule in 1838 by noting the heating effects produced in revolving a paddle-wheel immersed in water. The wheel being revolved by a weight falling a given distance, the mechanical work was known; this compared with the rise in temperature of the water enabled him to determine that the value of one heat-unit estimated from 39° to 40° F. was equivalent to 772 foot-pounds. Later investigation has slightly increased this result, so that when reduced to a temperature of 62 degrees F., and for this latitude, it is 6 foot-pounds greater, so that at present the work equivalent of one heat-unit is generally regarded as 778 foot-pounds. This signifies that the work of raising 1 lb. 778 feet is equivalent to the energy required to change the temperature of 1 lb. of water, at 62° F. in temperature, I degree. The equivalent value of heat and mechanical work is now thoroughly established, and under favorable conditions the one can always be transformed into the other. As illustrations of the transformation of heat into work we have only to consider the numerous forms of steam-engines, gas-engines, and the like. A transformation from mechanical work into heat is shown in the rise of temperature accompanying friction in the use of machines of all classes. The heat produced in the performance of any mechanical work is exactly equivalent to the work accomplished, 778 foot-pounds of mechanical work being performed in order to produce a heating effect equivalent to raising 1 lb. of water 1° Fahr. The term horse-power has been used as the measure of the amount of work. It has been fixed as 33,000 foot-pounds per minute. This is equivalent to 42.42 B. T. U. per minute, or to 746 watts in electrical measures. For the work done in one second the above numbers should be divided by 60; for that done in one hour they should be multiplied by 60. In all English-speaking countries the capacity of engines and machinery in general is expressed in horse-power, so that it is necessary to become familiar with this term and its equivalents in heat and electrical units. The electrical units are all based on French measures, the centimetre (0.3937 inch) being the standard of length, the gramme (15.432 grains) the standard of mass, and the second the unit of time; the system being generally denominated the C. G. S. system. In this system the unit of force, the dyne, is 1 gramme moved so as to acquire) a velocity of one centimetre per second. As the force of gravity in latitude of Paris is 32.2 feet = 981 cm., the dyne is equal to the weight moved, expressed in grammes divided by 981, for latitude of Paris. The unit of work and of energy is called an erg and is equal to the force of one dyne acting through one centimetre, or to a gramme-centimetre divided by 981. One million ergs is equal to 0.0738 foot-pound. One watt is equal to 10 million ergs per second, or 738 foot-pounds per second. One calorie is 42,000 million ergs, one minor calorie 42 million ergs. One B. T. U. is 10,550 million ergs. Expressed in work we have the following equivalents: One horse-power = 746 watts = 550 foot-pounds per second = 0.707 B. T. U. per second. = 0.1767 calories per second = 176.7 minor calories per second = 7460 millions of ergs per second. (See full table of equivalents in back of book.) |