Chapter VII. Cast-iron pipes are either socketed or flanged. In (Part 4)

off to the air by conduction and circulated by convection (especially in the ceiling panels) but has very little effect on the radiation effect, so a ceiling panel will give off as high a percentage as 90 per cent. by radiation while with wall and floor panels the ratio will be about 50 per cent. and 60 per cent. respectively, the remainder being circulated by convection. There is a far greater time lag in the initial heating up of the building in which it is installed, so it is quite unsuited to buildings which will be used intermittently, as in that case a lot of residual heat will leak away, but where a building is to be used all over and needs heating day and night, it is found to be a fairly economical method THE BUILDING—ITS WARMING AND LIGHTING 141 of heating. Obviously it is not a system to be installed as an afterthought in an existing building. Indeed, it needs careful forethought and co-operation between the heating engineer de- signing the heating system, the architect designing the building and the teams of workers carrying out the work, so that the steel- work, brickwork, masonry, pipework, concreting, plastering and finishing can be co-ordinated as the work proceeds. It may be necessary to place an insulating layer behind the grid-iron piping if placed in wall panels in an external wall, or one where heat is not required on both sides or in floor or ceiling panels where rooms below or above require no heat or are in different occupation. As ceiling panels gridiron heating tubes can be clipped or wired to the reinforcing rods of the structure and adjacent to the centring or forms to take the concrete, which will be placed from above, leaving the pipes almost surrounded but on the lower face. The plaster finish is then added on the underside, with muslin scrim worked into the final coat to prevent crazing in the plaster surface. Lime plaster is the most suitable for the purpose. Care should be taken not to overdo the installation of floor panels, as the warmth conducted into the feet of occupants sitting still for long periods can be very tiring. Probably it would be wise to install floor panels only in cases where the occupants will be mainly on the move and not standing or sitting still for long together. A useful combination would be large ceiling panels, at not too great a height from the floor, to provide mainly radiant heat, in combina- tion with smaller wall panels, to provide a little more radiant heat and a good proportion of convected heat to warm the air and circulate it around the rooms. Wall panel systems can generally be designed to work by gravity alone, but floor and ceiling panels usually involve so much nearly horizontal tubing that an accelerating pump on the return just before entering the boiler is nearly always found necessary. A portion of a panel system is illustrated by diagram in Fig. 125. Steam Heating. We come next to steam heating, which was proposed as far back as the sixteenth century, for we find Sir Hugh Platt, before referred to, writes: “‘For the keeping of any flowers abroad, as also seeds sown within doors ...in a temperate heat with small charge, you may perform the same by hanging a cover of tin or other metal over the vessel wherein you boil youre beefe or drive youre buck, which, having a pipe in the top, and being made in the fashion of a funnel, may be conveyed into whatever place you shall think meete.”’ 142 THE BUILDING—ITS WARMING AND LIGHTING It was not, however, until the early part of the nineteenth century that a workable system was installed on very much the same lines as at present adopted. Steam systems are either “low” or “high” pressure according to whether the steam is kept at (or near) atmospheric pressure or is kept above it, 5 lb. per square inch above atmospheric pressure being taken as the dividing line. Low-pressure Steam. In low-pressure steam systems, the steam circulates through strong wrought-iron pipes, laid so that the con- densation water can drain back to the boiler. The principle of warming by steam is the rapid condensation of steam into water on coming in contact with cooling surfaces, the latent heat being given out at the moment of condensation. The quantity of radi- ating surface depends on the system of ventilation, the area of cooling surfaces, the accuracy of fitting of doors, windows, etc., and the desired temperature. L.P. Steam Circuit. Greater care and skill is needed in designing a system of steam heating than with one for hot water, owing to the difficulty of disposing of the condensation water without annoy- ance from vibration or “water hammer”. In steam work the pipes must be given a greater fall than is usual for hot water and care must be taken to avoid obstruction to the return of the con- densation water to the boiler. Fig. 130 gives a rough idea of the application of a low-pressure steam system to a small building on one-pipe lines. If the steam pipes have to dip under a door or similar feature, provision must be made for carrying the con- densation water away and back to the boiler. For the same reason “T” junctions in steam pipes should be constructed as in Fig. 181 rather than as in Fig. 182, so that there shall be no obstruction to the flow of the condensation water back to the boiler. Radiators for L.P. Steam. ‘The radiators can be of similar type to those used in hot-water work, except that the air-cock should be about 4 from the bottom instead of at the top, so that the air, which is heavier than steam, may be expelled when the radiators are put into use at the beginning of the heating season. On opening the cock, the air can be heard emerging. Soon after steam begins to appear, the cock should be turned off. There may still be a little air left, but it will do no harm. L.P. Steam Boiler. The boiler can be similar to that for low- pressure hot water, except that the top is usually domed to collect the steam and direct it into the steam pipes, while the feed tank is usually placed near the boiler instead of above the highest radiator. THE BUILDING—ITS WARMING AND LIGHTING 143 Condensation Water and Steam Traps. If the system is an extensive one, involving long runs of nearly horizontal pipes as well as vertical ones, it is wise to put condensation water outlets at the junctions, with steam traps incorporated as in Fig. 122, so that the steam is kept in its proper course, while the “condense” can run back to the boiler by the most convenient route. The expansion and contraction of the pipes is much greater than in the case of hot-water systems, and the changes of tempera- ture are more rapid. Ample provision must be made for this, the difficulty being overcome by using expansion joints on the straight lengths, and plenty of bends where junctions and connections occur. It is better not to fix steam radiators at a level lower than the boiler, but, if this is done, a steam trap must be placed on the outlet from the bottom of the radiator, so that the condensation water may be run away to waste without loss of steam, as it cannot be passed back to the boiler by gravity. Steam Circuits. The methods of arranging the pipes and con- nections to radiators in steam work are very similar to those described for low-pressure hot water, i.e. the one-pipe, two-pipe, or drop systems. In the one-pipe system a single connection is used at the bottom of each radiator instead of two, the branch conveying the steam to the radiator and the condensation water from it. In the two-pipe system the steam is conveyed by the flow pipe to the top of the radiator and the water carried back by the return, whereas with the one-pipe system the single pipe con- veys both steam and condensation water, In the two-pipe system, each radiator has therefore both a flow and a return connection, with a valve on each, In the case of the drop system, there is usually only one connection to each radiator, as the system works better if radiators are not connected to the flow pipe; but if any radiators are served by the main flow pipe they should have two connections. No matter which system is used each radiator should have an air valve near the bottom, Dry and Wet Returns. In the two-pipe system, the return is sometimes connected to the boiler above the level of the water in it and sometimes below, the former being termed a dry and the latter a wet return. The condensed water may be pumped back, but in the low pressure it generally returns by gravitation, giving what is termed a gravity return. gid | Exhaust Steam Heating. Exhaust steam heating is a form of low-pressure warming in which exhaust steam, or steam which has been partly used in the cylinders of engines, is employed. 144 THE BUILDING—ITS WARMING AND LIGHTING Such exhaust steam has about 90 per cent. of its original energy on leaving the engine and can well be utilised for such a purpose. As it leaves the engine, however, it contains oily, greasy matter taken up from the lubrication of the cylinders, and this matter must be removed by special apparatus before admitting it to the heating system, or it will lower the efficiency of the radiators. The drop system is the usual method of arranging the piping, the water of condensation being collected into a tank and pumped back to the boiler, it being usually heated before reaching the boiler, either by an “‘economiser”’, as used in conjunction with the supply of water to large steam boilers, or by some other method. The system can be arranged so that both exhaust and live steam are available for heating, but this complicates the arrangement and greatly increases its cost. Special combined air and vacuum valves are fitted to the radiators. The cost of running an exhaust system is low, by reason of using steam which would otherwise be wasted, but the system is a rather expensive one to install, owing to the fittings and apparatus required. High-pressure Steam. High-pressure steam heating utilises superheated or “dry” steam at a pressure greater than 5 Ib. per square inch above atmospheric pressure, 10 Ib. per square inch being a good working pressure. Steam Boilers and Calorifiers. The arrangement of the units in this system is similar to that just described, but a different type of boiler is used, such as the Cornish, Lancashire, water-tube, or multi-tubular boilers. The system is, as a rule, only adopted where steam at high pressure is used in the same building for other purposes than heating, or when several detached buildings have to be heated from a common, centrally situated, boiler-house. In such a case, well-lagged steam pipes will convey the dry steam over a wide area without difficulty, but the direct heat would be too great to admit safely into ordinary radiators, so it is usual either to embed the pipes in semi-insulating plaster panels (the ‘“*Panel”’ system), or to use a calorifier in each building to heat up the water for a low-pressure hot-water circulation, which can then be arranged with radiators in the ordinary way. Fig. 123 illustrates one form of steam calorifier. Reducing Valves. Sometimes the steam for a low-pressure steam system is taken from a boiler which is principally used for generat- ing steam at high pressure for the driving of machinery. In such a case a special reducing valve is used on the system, in order to reduce the pressure from high to low. Atmospheric Steam Heating. A system known as atmospheric THE BUILDING—ITS WARMING AND LIGHTING 145 steam heating is largely used on the Continent, but is not exten- sively used in this country. The boiler pressure is usually from 5 to 8 oz. per square inch. The pipes are arranged similarly to those in the low-pressure steam system, but a pipe is carried up from the upper end of each return pipe and left open to the at- mosphere at the top. The lower ends of the return pipes are col- lected together and taken into an enclosed tank and thence into the boiler. The system is said entirely to overcome the difficulty of water-hammer. Vacuum Steam Heating. Vacuum steam heating is a system which provides for increasing the efficiency of the radiators by extracting the air from them and thus accelerating the circulation. The return pipes are always in a state of partial vacuum, being in direct communication with an exhaust pump, which extracts the air and returns the water of condensation. In a vacuum, water will boil at a lower temperature than otherwise. Automatic valves are provided on both inlets and outlets of the radiators and at cer- tain points on the pipes. Ina system of this kind the temperature is much more under control than is the case with other steam systems. In a variation of this system termed the ‘ Nuvacuum- ette”’, no valves are provided on the outlets of the radiators, which has the effect of causing a partial vacuum in both radiators and return pipes. The chief advantages claimed for the vacuum systems of heating are the following: the difficulties with regard to dips are easily overcome, there is economy of fuel compared with other steam systems and with hot water, there is no danger from frost or leaks, and the cost of the installation is not high, though greater radiating surface is required. Advantages of Steam Heating. There are certain advantages incidental to steam heating as compared with hot water, the prin- cipal of which is that the radiators are quickly raised to their full temperature and soon cool down again if desired. On the other hand, a steam installation is more costly than one for hot water, both as regards first cost and annual maintenance, and the heat is apt to be dry and fierce, tending to scorch the air. There is also a system involving the use of both steam and hot water. It is a rather complicated system, but the mixture of the steam and hot water greatly increases the velocity of the circulation in the system, and the heat can be better transmitted for long distances. ; f Hot-air Heating. Hot-air heating is usually carried out in conjunction with air-conditioning, as described in Chapter IIT under the heading of ‘‘plenum ventilation”’. 146 THE BUILDING—ITS WARMING AND LIGHTING Air Heaters. Unit air-heaters were described in the early pages of this chapter, the Musgrave and Manchester grates being examples. “Central” air-heating stoves are not usually successful unless mechanical blowers or fans are employed to drive the heated air along the ducts to the apartments to be warmed, Even so, they need careful design to avoid roasting or drying of the air and it is seldom that sufficient access is provided for cleaning away the dust which is apt to settle on the heating surfaces and so taint the incoming air. A type of air heater in which excellent use is made of the insulating effect of the incoming air is shown in Fig. 124. In this, the stove may be in the basement with a grating in the floor of the hall or apartment immediately above. The stove is provided with a double air jacket, the grating being divided in such a way that the cold air, at floor level in the apart- ment above, passes through the outer openings into the outer jacket, to start warming as it falls (because it is cold and therefore heavy). At the bottom it turns into the inner air jacket, close to the combustion chamber, where it absorbs heat rapidly, expands, and rises with increased velocity, passing through the centre openings of the grating to diffuse in the hall or room above. Such an air-heater will work very economically without any lagging at all, except that provided by the double air jacket, but an insulating jacket is no doubt an advantage in keeping the boiler-house cool and preventing the waste of heat where it is not needed. Air heaters of this type, placed under the hall, will provide warm air for the whole of a small house, if suitable inlets and outlets are provided in the apartments opening into the hall, or into the main staircase leading from it, but, of course, such an arrangement could be considered as auxiliary only, open grates or similar units being used as well. A one-storey building like a church or concert hall can be warmed very effectively by such a a unit, or by several such units if the building is a large one, while ventilation can be introduced at the same time by inserting a fresh air duct, controlled by a valve or damper, leading to a grat- ing in an outer wall. If the warm air outlet from a stove of this type is connected to a vertical trunk with branch ducts, leading to the various rooms of a fairly small compact building of three or four floors, there is no doubt convection currents would provide sufficient motive force to impel the warm air to its destination, but for an equal number of rooms more widely spread in a building of one or two floors only, a fan on the fresh air intake would ensure the air being driven into the rooms concerned and make it possible to get THE BUILDING—ITS WARMING AND LIGHTING 147 complete control, by means of dampers or “‘hit and miss” gratings at the delivery points. It would, in fact, have become a miniature plenum ventilation plant without