April ist, 18S7.] 



SCIENTIFIC NEV/S. 



NOTES ON THE HEATING 

 BUILDINGS. 



OF 



No. I .— Hot- Water Circulation. 



THE efficient and economical heating of buildings is of 

 such great importance that we propose to consider 

 some of the principles which underlie the chief systems in 

 use. This, we trust, will not only assist our readers to appre- 

 ciate the laws on which success depends, and so ensure 



Fig. I. 



more profitable results being obtained ; but will also lead 

 them to see that the subject has really many points of 

 scientific interest. In the present article we deal with heat- 

 ing by a circulation of hot water ; and in the following 

 numbers we hope to refer to heating by steam, by hot air, 

 by fire, and by gas. 



There is no country in which hot water is so extensively 

 used for heating buildings as in England. This is especially 

 the case in relation to glass-houses, and it is doubtless due 



Fig. 3- 

 in great measure to the peculiarities of our climate. The 

 number of persons who use circulating hot water for their 

 dwellings or glass-houses is in fact enormous, and yet we 

 fear there are very few who correctly understand the prin- 

 ciples on which the satisfactory working of such a system 

 depends. Usually people arc content to leave the matter in 

 the hands of a builder or " practical man," who in his turn 

 is oflen ignorantly content to rely solely on rule of thumb. 



^. 



This naturally leads to blunders and alterations, for which 

 the client is generally made to pay, while at the same time 

 there is no certainty that in the end the efficiency of the 

 system is what it should be. There are, of course, some 

 well-known firms of hot-water engineers who fully under- 

 stand their work, and do it well, and we do not refer to 

 them. We speak of the many, not of the few. 



The first essential is to understand why the water circu- 



lates, and for this purpose let us consider Fig. i, which 

 represents a simple form of boiler and pipes generally used. 

 If the boiler and pipes are charged with water, and the fire 

 is lighted, the temperature of the water in the boiler will 

 be raised ; this will render it less dense, and then there 

 will be an effort on its part to rise and leave the boiler. 

 The hottest and lightest portion of the water will be at the 

 top of the boiler, and for this reason the flow-pipe is there 

 inserted. The heated water will follow in the direction of 



the arrows, in the flow-pipe, but as it travels along some of 

 its heat will be lost by conduction and radiation, and as it 

 gets further and further from the boiler it will become less 

 and less hot, and consequently more and more dense, so 

 that the water in the return pipe will be heavier, bulk for 

 bulk, than the water in the flow-pipe. There is, in fact, an 

 unequal pressure in the up and down pipes, and it is this 

 inequality of pressure which causes the continual circula- 

 tion on which the efficiency of the apparatus depends. With 



these facts before us, it will be seen that it is quite a mis- 

 take to suppose that it assists the circulation to give the 

 return pipe a considerable fall, as shown in dotted lines in 

 Fig. I. The water would then have a shorter distance to 

 travel, so that it would not lose so much heat, and conse- 

 quentlj' the difference in temperature of the water in the 

 boiler and in the return pipe would be less, and the circula- 

 tion would be impaired. 



In practice there is seldom any great dilTercncc in the 



^ I 



temperature of the boiler and the return — usually it does 

 not exceed 20° F. — and as the circulation oi the water 

 depends on this difference of temperature, it will be under- 

 stood how extremely small is the power available for doing 

 the work. It is, in fact, of the greatest importance to avoid 

 everything tending to check or interfere with the flow of 



