CHAPTER V Tue BurtpiInc—Its WARMING AND LIGHTING (Part 1)

CHAPTER V Tue BurtpiInc—Its WARMING AND LIGHTING Historical Note. As an introduction to this part of the subject, a brief historical note may be of interest. The origin of fire is about as uncertain as the date of discovery of coal as a fuel. Innumerable other kinds of fuel have been used in ancient and modern times. For centuries, wood, peat, and turf were the staple fuels of Great Britain, but the consequent denuding of the land of timber led to a proclamation by Queen Elizabeth to the effect that no oak, ash, or beech tree that was 1 foot through at the stub and growing within 14 miles of the sea or of a navigable river, should be used as fuel for smelting iron. It is believed that coal was known before Roman times, coal cinders having been found under Roman foundations in England. The word coal, also, is British—that is to say, of earlier than Anglo-Saxon date. In 1289 Henry III granted a charter to the inhabitants of Newcastle, permitting them to dig for coal, and at the end of that century it was imported into London. The smoke produced by burning it in improperly constructed grates caused such a prejudice against its use that in 1306 an Act was passed making it a capital offence to burn coal in the city of London, and there are records of execution for the offence. Probably the first composite fuel used was that introduced by Sir Hugh Platt, an eminent sixteenth-century lawyer, who says, “to speake trulie of it, coal and cowdunge maketh a sweete and pleasing fier”: a statement which seems open to question. In any case, and however “‘sweete and pleasing the fier”, we have too much regard for the farmer and his craft to-day, to wish to warm our homes at the expense of the soil’s fertility. Ancient Methods of Warming Buildings. The methods of warming buildings are almost as numerous as the varieties of fuel. A favourite primitive method was a sort of stove or oven inside the room, stoked from the outside, this structure serving as couch by day and bed by night, the whole family often sleeping on the top of it. Examples could be seen in modern times among the poor of Russia, and the method has been used as far afield as Egypt and China. According to Homer, the Greeks used fires in hearths for both warmth and light; they also used charcoal braziers. The Romans 88 THE BUILDING—ITS WARMING AND LIGHTING used hypocausts, consisting of a sort of hollow floor with a space about 2 feet high, in which a fire was made, with pipes or flues up the walls to spread the heat, the openings into the rooms being in the form of lions’ heads, and this method was used in Roman villas in England. The forms of chimney, hearth, and fireplace have gone through great changes before reaching their present character. In ancient British houses, the hearth was put in the middle of the hall so that as many as possible could get round it, and this practice was followed till as late as the fifteenth century, though at the time of the Norman Conquest the hearth was often placed against the wall, with a sort of pyramidal flue terminating in a hole in the outer face of it. Generally speaking, from the Conquest to the time of Henry VII, fireplaces were put on outside walls, but the Elizabethan architects put them on inside walls opposite the windows. Huge fireplaces were used, with large flues often put one behind the other, instead of side by side as nowadays. Fires were at one time a great luxury in the house, the right to use the fire being sometimes bequeathed. Thus the will of one Richard Byrchett (1516) reads: “I will yt the sayd Nell my wyfe shal have ye chamber she lyes in and lyberte at ye fyer in the house; all yese things shal she have so long as she ys wido.” In order to consider the problems arising out of modern heating practice, it is necessary to recall some of the physics of the school- room. Definition of Heat. Heat is a form of energy in the nature of waves through the ether or of vibration of the molecules of which a substance is composed. It may be formed in a variety of ways, but, for our present purpose, we may assume that it results from the combustion of some type of fuel, from the condensation of steam, from the friction or “resistance” which an electric current meets in a poor electric conductor or filament, from the processes taking place in the human body, from the vast stores of heat in the sun and in the interior of the earth. Heat is necessary to our comfort and health and the range of variation in temperature to which the human body can accommo- date itself is really remarkably small. Measurement of Heat and Temperature. Heat has both quan- tity and intensity. Quantity can be measured in Calories or British Thermal Units with a “calorimeter”: intensity of heat is measured in degrees with a “thermometer” or “‘pyrometer”’. THE BUILDING—ITS WARMING AND LIGHTING 89 The British Thermal Unit (or B.Th.U.) is that quantity of heat absorbed by 1 lb. of water when raised in temperature by 1° F. (strictly from 39° F. to 40° F.). The Continental unit for technical use is the large Calorie, which may be described as the quantity of heat required to raise 1 kilo. of water 1°C. The Gramme Calorie (or small calorie), consisting of the quan- tity of heat required to raise 1 gram of water 1° C., is seldom used by heating engineers and may be ignored. 1 B.Th.U. is equal to about 0-252 of a Calorie, while, reciprocally, 1 Calorie equals approximately 4 B.Th.U. A “Therm” is a collective unit and equals 100,000 B.Th.U. There are several thermometer scales still in use, but the only two the heating engineers needs are the “Fahrenheit” and “Centigrade” scales. Thermometer Scales. The Fahrenheit scale divides the interval between the freezing- and boiling-points of water at sea level into 180°, fixing “‘zero”’ at 32° of these units below the freezing-point of water, so that boiling-point becomes 212° F. The “Centigrade” scale (used for scientific work in this country and for every kind of work on the Continent) divides the same interval in 100 units, and fixes the freezing-point of water as an arbitrary “zero”, so that boiling-point becomes 100° C. “Absolute zero” was unknown at the time these scales were introduced, or undoubtedly the Centigrade scale would have started there. As it is, absolute zero is — 273°C. or — 459° F. Conversion Formulae. To convert a Centigrade reading to Fahrenheit, the formula is F = $C + 82, where F’ = the required number of Fahrenheit degrees, and C = the given Centigrade reading. In the other direction, and using the same symbols C = 4(F — 82). The ordinary thermometer consists of a vacuum tube partially filled with mercury or coloured spirit, while the pyrometer (used for more intense degrees of heat) employs the expansion and con- traction of a metal member, the movement being transmitted to a needle or indicator working on a dial. Latent Heat. ‘Latent heat’, for our purposes, is the heat absorbed by water in the process of conversion into steam, or by ice in the process of conversion into water. When heat is applied 90 THE BUILDING—ITS WARMING AND LIGHTING to intensely cold ice, the ice goes on absorbing heat and rising in temperature at a uniform rate until 32° F. is reached, when 142 B.Th.U. of heat would be absorbed by the ice in thawing, for each pound of water formed. In the same way, when heat is applied to water, the temperature of the water rises steadily until 212° F. is reached. At this point the temperature remains at a standstill until 966 B.Th.U. have been absorbed in the process of converting each pound of the water into steam. The real value of this quality is seen in low-pressure steam heating, where the steam, in condensing back into water, gives off its latent heat again. , Specific Heat. “‘Specific heat” is the capacity of a substance for absorbing heat, the specific heat of water being taken as the standard. Thus, iron has only one-ninth of the specific heat of water, which means that whereas 1 lb. of water raised 1° F. absorbs 1 B.Th.U. of heat in the process, 1 lb. of iron raised 1° F. absorbs only 0-111 B.Th.U. of heat. This makes water a very good medium for heating purposes, for it has a good capacity for absorbing heat and, after passing around the circuit of pipes to the various radiating surfaces, has a large amount of heat to give up. Transfer of Heat. Three methods of transferring heat are made use of in heating schemes, namely, radiation, conduction and convection. “Radiation” is the transfer of heat by heat waves through the ether. In ‘‘ Conduction” the transfer is caused by the vibration of the molecules of which the substance is com- posed being transferred to the molecules of a neighbouring body by physical contact, while “Convection” is the transfer of heat by the circulation of a fluid or gas. Convection is really one application of the law of gravity. The open fireplace furnishes a good example of radiant heat. From each particle of fuel, and from the fire-brick sides and back, the heat is radiated in straight lines. The rays diverge and affect objects at a greater distance to a less degree; the air is not warmed but the heat is radiated to individuals and objects, being re-radiated from the latter to a certain extent. Consider the phenomenon illustrated in Fig. 80. The black dot represents a particle of incandescent fuel and the diverging lines show the diverging rays of heat. At A is a small sereen which receives all the heat from that particular particle of fuel. If A be removed, and a sereen be placed at B, it will have to be of a larger size to receive the same total amount ; THE BUILDING—ITS WARMING AND LIGHTING TOP INDEX BOTTOM INDEX MAIN CISTERN WITH COTTON FINGER-STALL TO SLIP ON FOR 'WET’ READING _ KATA THERMOMETER 91 92 THE BUILDING—ITS WARMING AND LIGHTING of heat as would be received by A, therefore receiving less heat per unit of area. Similarly, if there be no screen at either A or B, a screen placed between the same rays at C would have still less heat per unit of area. Putting it another way, the heat decreases as the distance increases, and in a ratio of the square of the dis- tance. Thus, compare a surface 1 square inch in area at a distance of 1 foot, with a similar surface at a distance of 10 feet. The latter will only receive one-hundredth of the heat that would be received by the surface 1 foot away. Again, suppose a screen to be placed at C, there being none at A and B; if the small screen A be placed in the position shown, it will shut off all the radiant heat from C. A practical example of such a case is the use of a fire screen. It is not strictly correct to say that with open fireplaces the room is entirely warmed by radiant heat. The walls, furniture, etc., become warmed by the radiated heat and warm the air in contact with them; this circulates around the room. “Conduction” may be seen used indirectly in most heating schemes. The heat of the burning fuel is transferred (mainly by conduction) to the iron of the boiler, by conduction through the iron to the water inside. The water now illustrates heat transfer by “convection”’, for the warmed particles expand, become lighter and float upwards to the top of the boiler, being pushed up by the heavy cold water in the return pipe, and the circulation in the hot-water pipes thus begins. In the radiators the heat is trans- ferred to the iron tubes or sections by conduction, thence to the air in contact, also by conduction, after which the air begins to circulate around the room, transferring the heat by convection. It will be seen, then, that the fittings we call ‘‘radiators” have very little real radiating value and they would really be better described as “convectors”. The relative amount of heat given off by radiation and convection into a room warmed by hot- water “radiators”? depends on the circumstances, but it is easy to put the case to practical test by holding the hand 12 inches away from an average radiator, first at the side and then over the top. Radiant heat, then, does not warm the air; this can only be done by bringing the air in contact with heated surfaces. Materials which absorb heat readily just as readily part with it again. Iron fulfils the condition well and is cheap and is therefore used almost exclusively for pipes and radiators used in heating. Modern Methods of Warming. Modern methods of warming THE BUILDING—ITS WARMING AND LIGHTING 93 include both “ Unit”’, “Central” and “ District” heating systems, which, again, may be divided broadly into the following groups: Unit Heating Schemes—using open grates, closed stoves, oil stoves, gas radiators, electric radiators. Central Heating Schemes—including low-pressure hot-water pipes and radiators, high-pressure hot water, low-pressure steam pipes or radiators, high-pressure ditto and hot air heating—the latter fre- quently combined with air conditioning and ventilation as the “plenum system” already referred to. District Heating Schemes. This term refers to arrangements whereby the heat is produced in an independent building and passed by pipes or ducts to the owners of as many houses, flats or buildings in the district as can be persuaded to take and pay for it in a manner rather similar to the Gas Boards with their gas or the Electricity Undertakings with their current. This rough classification is by no means exhaustive, but it must be borne in mind that the central heating of large buildings is specialists’ work, and the aim of this chapter is merely to indicate the general principles involved and perhaps to help the student and the man in general practice to select his system wisely, to choose the right firm to carry out the work for his client and, finally, check over the work on completion and see that his client has received a fair deal. Those who intend to specialise will find numbers of treatises available, some devoted to the whole subject, others restricted to some single section of the work in all its technical details. ‘Unit’? and ‘‘Central’’ Schemes. Discussing ‘“‘ Unit” and ‘Central’? heating schemes generally, it may be said that the unit scheme is simpler, easier to manage by the novice, or by the care- taker without technical knowledge, is cheaper to install and is more suitable for use in buildings which will need to be warmed intermittently and one room at a time. Central heating schemes usually need greater capital outlay in the first place, are more complicated, need rather more skill in management (in some cases an attendant with technical knowledge is essential to satisfactory running) and they are more suitable for buildings which will need to be warmed all day and every day in every part. Of course, a large building heated by low-pressure hot-water radiators can have certain radiators, or even certain sections of the building, cut right out by control valves, but the general truth remains that, for real economy of running, a central heating 94 THE BUILDING—ITS WARMING AND LIGHTING scheme needs to be used for the whole of the building continu- ously. For this reason, comparative tables of fuel cost, such as are often put forward by the manufacturers of different classes of heating apparatus, need to be judged with a good deal of cireum- spection. Relative Costs. As an example, the following is quoted. Rela- tive cost of fuel needed to produce 1 therm (100,000 B.Th.U.) in Coke-fired boilers for low-pressure radiator system = 8d. Closed stoves burning coke or anthracite == is. Open grates burning bituminous coal at £8 per ton = 2s. Gas fires burning gas at 1s. 11d. per therm = Is. lid. Oil heaters burning paraffin at 2s. ld. per gallon = 3s. 14d. Electric radiators consuming current at 14d. a unit = 3s. 9d. Even when similar comparative costs are given by such impartial research workers as Dr. Margaret Fishenden of the Fuel Research Board, allowance still has to be made for possible variations in the cost and quality of fuel, in the stoking and, more important still, in the conditions of use. No price is given for the coke and anthracite employed in the above example, and it may therefore be assumed that prices comparable with coal at £8 per ton were being paid. Oil-fired boilers would probably cost a figure about midway between coke-fired boilers and closed stoves. It requires 29} B.T.U. (Board of Trade Units) of electricity to produce 1 therm (100,000 B.Th.U.) of heat. Measurement of Gas. Coal gas is usually measured by meters recording thousands of eubie feet, but the charge (by statute) is by the “therm” or 100,000 B.Th.U. according to the declared calorific value of the gas. This varies with the Gas Board con- cerned and with the date and the general policy of production. At the present date a calorific value in common use is about 500 B.Th.U. per cubic foot which, at 1s. 11d. per therm, would give a charge (according to the old rating of thousands of cubic feet) of: 1000 x 500 x 1-9 | - — — sh ys 100,000 Tel == 9s. 7d. per 1000 cubie feet. To convert the meter reading in “thousands” into “therms” multiply the reading