In the running of hot-water piping on ordinary work the supply lines to fixtures are run as directly as possible to them, the different branches ending at the fixtures. This method is shown in Fig. 285. There is great objection to this course many times, and for the following reason. Although the water in the piping is supposed to be hot, it cools very fast under certain conditions, and especially in branches at a distance from the boiler. In many of these branches, particularly those which supply fixtures not in constant use, the hot-water pipe for a considerable distance from the fixture is generally filled with water that is either cold or nearly so. This means that before hot water can be drawn at the fixture, a considerable length of pipe filled with cold water must be drawn off before the water comes hot. Under all circumstances, this is an annoyance to the person using the fixture, and in many cases, where the supply of water is limited, this unnecessary waste of water cannot be afforded. When the public supply is metered, and must be paid for by the foot, such waste means unnecessarily high water bills.
Fig. 286. - Circulation Applied to a Single Fixture.
A remedy for these troubles can generally be applied to nearly all the fixtures of the house, and while the remedy means the outlay of a certain additional amount of money, under most conditions such outlay is an economy in the end. The remedy is the circulation pipe.
Fig. 286 shows the circulation pipe applied to a single fixture, and in Fig. 287 is shown a hot-water boiler providing hot water for the kitchen sink and the bath room, the system being supplied with a circulation pipe. This pipe is nothing more than a return, connected to the flow pipe, and with the latter, forming a complete circuit from the water front back to the water front. The water in the circulation pipe being cooler than that in the flow pipe, falls back into the cold-water range pipe, to enter the water front and be again heated. Thus, the upward tendency of the hot water in the flow pipe from the boiler, and the downward tendency of the cold water in the circulation pipe, produces a continuous circulation of hot water through any line of pipe to which the circulation pipe is connected.
When the hot-water supply line is provided in this manner with a circulation pipe, as in Fig. 286, only a very small amount of cold water in the branch to the fixture must be drawn off before the water will run hot. Branches may be taken off the flow pipe at any point, and run up to fixtures above or carried down to fixtures below. As the work is constructed in Fig. 287, the kitchen sink does not have full advantage of the circulation pipe, as its branch must drop down for a considerable distance to supply it.
The circulation pipe in this illustration might have been run in another way to provide more fully for the kitchen sink. Instead of running the circulation back to the boiler, parallel with the flow pipe, it might have been dropped down to the sink, after passing the lavatory, and a branch to the sink taken out of the circulation pipe, the latter then being carried back and entered into the cold-water range pipe, as shown in Fig. 288.
Fig. 287. - Use of Circulation Pipe.
Fig. 288. - Use of Circulating Pipe.
In Fig. 289 is shown the same system of hot-water supply as that shown in Fig. 285, with the addition of circulation. As seen from the illustration, the hot-water supply to fixtures is carried directly to the top floor, where it turns and runs horizontally to the farthest fixture. From this point, the circulation pipe A is carried down and connected to the return of the range connection. If necessary, branches may be taken to fixtures from this circulation pipe, although it is not to be expected that water may be at once drawn as hot as branches taken off the flow pipe will deliver. Above the boiler a branch connection is taken out of the main flow pipe to serve fixtures in other parts of the house on the two floors above the boiler. After passing the last fixture on the third floor, the circulation pipe B is connected and carried down, being entered into the return or circulation pipe from the first line.
Fig. 289. - Hot-water Supply with Circulation.
Fig. 290. - The Three-tube Boiler.
For fixtures below the boiler a branch is taken out of one of the flow lines and carried down to the desired points. Circulation cannot be provided for these fixtures because of their position as related to that of the boiler. Therefore, in obtaining hot water at the laundry tubs, it will generally be necessary to draw off the cold water standing in the greater part of the length of pipe running to this fixture. In connection with the work thus far illustrated, the return or circulation pipe has in each case been carried back-into the return of the range connection. This is ordinarily the method followed. In the use of the three-tube boiler another and neater method may be employed. This method is shown in Fig. 290. In the three-tube boiler a second boiler tube may be used, which should run down to a point near the bottom of the boiler, as in the case of the boiler tube used on the boiler supply. To this second tube, the circulating pipe may be connected as shown, which results in returning the cooled water as well as by means of the connection into the return of the range connection. This illustration will also serve to show the manner in which circulation may be provided for fixtures on the same floor as the boiler. This is accomplished, generally, by running the flow pipe from the boiler horizontally, on the ceiling, above the points where the fixtures to be supplied are located, and dropping from this main flow pipe with branches to the. several fixtures. From a point just beyond the branch to the farthest fixture a circulation pipe is carried back to the boiler and connected to the return of the range connection. This is the best that can be done toward securing circulation for fixtures thus located. Necessarily, the cold water must be drawn out of the branch from the main to the fixture before the water will come hot, but even so, the use of circulation under these circumstances will be found to be of benefit. Another method of providing circulation for fixtures on the same floor as the range boiler will be seen in Fig. 288. In this method, instead of running the circulation pipe back to the boiler, just below and parallel to the flow pipe, it is dropped down from the ceiling to a point considerably below, and then carried horizontally back to the range return.
Fig. 291. - Circulation Applied to Fixtures of Small House.
In this method, branches to fixtures may be dropped down from the flow pipe on the ceiling, or taken out of the circulation pipe. While the use of circulation in connection with large hot-water supply systems is a matter of considerable additional expense, in applying it to many small systems, such as commonly found in small residences, cottage houses, etc., where the plumbing is usually centralized, it often means the use of only a very small amount of additional piping. This fact may be seen by reference to Fig. 291, in which circulation is applied to the fixtures of the entire house, by the running of a comparatively small length of pipe. In the foregoing illustrations, circulation has been shown in connection with direct pressure systems only. In Fig. 292 is shown a tank-pressure circulating system of hot-water supply for a residence. There is no material difference in the work, except the use of an expansion pipe on the tank-pressure system. Fig. 292 shows the range boiler heated by means of both kitchen range and gas range, a very common combination.
In Fig. 293 is illustrated a tank system of hot-water supply, without the use of circulating pipes. A comparison of the two illustrations should prove conclusively to the student the practical advantages of circulation and the great saving in water bills following its use.
Fig. 292. - Hot-water Supply for Residence, with Circulation.
Fig. 293. - The Tank System of Hot Water Supply without Circulation.
Fig. 294. - Pressure Hot and Cold Water Supply for Residence, with Circulation.
In Fig. 294 is illustrated a complete pressure hot- and cold-water supply system for a residence, with circulation, there being three separate lines of the latter. By many workmen the subject of circulation is not well understood, but a clear understanding of the subject is necessary, if satisfactory supply work is to be constructed. The subject of circulation must be considered at every point on the hot-water supply system, and as conditions are of such great variety, it will be readily understood that to be successful, the workman should be familiar enough with the subject to apply its principles under any and all conditions.
As previously stated, not only is this knowledge necessary, but practical experience in the installation of such work is of very great value. From the preceding consideration of the subject, it should now be clear that the use of the circulating system of hot-water supply is of very great advantage, and this is especially true of large work. It will be found that on large work, and on smaller systems as well, the saving in water bills will not be long in covering the additional first cost of installing circulation, and it goes without saying that such a system is far more convenient than the ordinary system of hot-water supply. •