This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol3", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The radiator branches are taken from tees in the flows and returns as shown, and each radiator is usually given a stop or regulating valve. Whenever possible the connection should be effected as with the radiator Fig. 48, as by means of an angle valve and a union elbow a very neat effect is produced without any pipes being visible. This is almost always possible when the main pipes run beneath the floor on which the radiators stand ; and it is of the greatest importance in residence works and in other good interiors, such as those of hotels and similar buildings, that the best possible effect be produced. There are numbers of people, especially of the gentler sex, who are prejudiced against hot-water heating wholly on account of the "ugly pipes." There can be no doubt that much work that has been done, and done recently, has, by its appearance, greatly retarded the progress of this mode of heating. The radiator has been of enormous help, but there are fitters who can make it unsightly by its connections.
It is the best plan, in connecting radiators, to have a union to each connection, - that is, a union valve and union elbow. This may not facilitate fixing very much, but it greatly facilitates removal and refixing. There are few jobs in which, when the hot-water engineer has finished his work and tested, he is not asked to take down all his radiators to admit of the decorators working on the piece of wall and skirting behind each of them, and when this is done the radiators have to be put back again. This should always be remembered, particularly when giving an estimate for work to be done a long distance from the shop. Figs. 44 and 45 illustrate a union angle valve and a union elbow. Both can be obtained from customary sources either in plain gun-metal or nickle-plated.
Each radiator has to be provided with an air vent, and as a rule an air cock is used, such as is shown near the top of each of the radiators in Fig. 46. The best air vent is an open pipe, as it does not require attention, but in most cases pipes are out of the question, and cocks, fortunately, do not need opening often after the first heating up. The writer has several radiators, the air cocks of which are only opened once yearly.
All pipes in heating works are carried with a rise from the boiler of at least 1 inch in 10 feet. The need of the rise, to enable air to get away, is specially marked in these works, as there are no draw-off cocks to disturb the air (by the rush of water they occasion) as there is with hot-water supply installations. It is quickly noticed, when experimenting with a glass model apparatus, how persistently the bubbles of air hang in the horizontal pipes. The circulatory movement of the water does not disturb them even though the water movement is in the same direction as the air should go. This is so noticeable that there is a strong feeling that the customary minimum rise of 1 inch in 10 feet should be abandoned and 1 inch in 5 feet substituted. It is important that the air get away freely, for although it may not stop a circulation it will certainly check it by being an obstacle which about half closes the pipe.
Sizes Of Pipes For The Two-Pipe System Of Low-Pressure Hot- Water Hcatimr Works
Size of Pipe.
Will supply this Area of radiating or heat-losing Surface.
4 inches .
. 1300 sq. feet
. 750 "
2 1/2 "
• 270 "
I 1/2 "
• 150 "
I 1/4 "
The above figures are for horizontal basement pipes ; when the work is largely vertical (as that shown in Fig. 43 would be considered to be) a size less pipe may be used, i.e. 270 feet of surface could be put on to 1 1/2-inch pipes. There is such a difference in the speed of circulation in horizontal and vertical pipes that the latter will keep the radiators served nearly twice as well as the former. The sole purpose of the pipes is, of course, to keep the heat-losing surfaces supplied sufficiently fast that they may always be as near the temperature of the water in the boiler as possible. It must be borne in mind, when calculating the area of heat-losing surface, that the circulating pipes are heat losers, and their surface must be included if they are not well covered to prevent loss of heat.
In planning the sizes of the pipes it is possible in this system of apparatus to graduate them to the work they have to do. For instance, if the whole heat-losing surface amounted to 250 feet (on horizontal mains), the pipes leaving the boiler would have to be 2 inches, but they need not extend to the distant work in this size. They need only be 2 inches while the surface to be supplied is between 150 feet and 250 feet, and when sufficient work is passed to leave the remaining heat-losing surface less than 150 feet the mains can be reduced to 1 1/2 inch, and so on. Fig. 46 will give an idea of this.
The One-pipe System In Fig. 47 is illustrated a simple apparatus from which the chief points of the One-pipe System may be described. Each radiator, it will be seen, is connected to a single main pipe, and from this detail the term " One-pipe system " is obtained ; but it is not that the radiator is connected by a single branch pipe (as it is with the one-pipe system of steam heating), for without flow and return branches the water will not circulate through the radiator.
The peculiar detail of the apparatus - peculiar as compared with the two-pipe system, is that when the radiator has dissipated what heat it can from its water, and so made it of less heating efficacy, this water is returned to the main pipe which carries the hottest water, and which corresponds with the flow main in the other system. It will be found, however, that this does not prejudice the heating of the remaining radiators, for, in the first place, the water which passes through one or even two radiators is still sufficiently hot to be useful; and secondly, it is found that the cooler water arranges itself as a lower stratum, beneath the hotter water, in the pipe.