The heating by means of pipes through which are conveyed hot water
and steam is a science by itself and yet one claiming some degree of
familiarity by all engineers, steam users, and architects.
[Illustration: Fig. 123.]
[Illustration: Fig. 124.]
In practice it requires a knowledge of steam, air and temperatures,
of pressure and supply; a familiarity with heat and heating surfaces
and with all contrivances, appliances and devices that enter into the
warming and ventilation of buildings. So long as factories, public and
private buildings are erected, so long will warming and ventilation
keep progress with steam engineering and remain a part of the general
mechanical science required of the supervisory and practical engineer.
In what is called _the system of open circulation_, a supply main
conveys the steam to the radiating surfaces, whence _a return main
conducts the condensed water either into an open tank for feeding the
boiler, or into a drain to run to waste_, the boiler being fed from
some other source; the system of what is called _closed circulation_
is carried out either with separate supply and return mains, both of
which extend to the furthest distance to which the heat has to be
distributed, or else with a single main, which answers at once for
both the supply and the return, either with or without a longitudinal
partition inside it for separating the outward current of steam supply
from the return current of condensed water.
In either case suitable traps have to be provided on the return
main, _for preserving the steam pressure within the supply main and
radiators_. These two systems, in any of their modifications, may
also be combined, as is most generally done in any extensive warming
apparatus.
The system of closed circulation requires the boiler to be placed so
low as will allow all the return pipes to drain freely back to it above
its water-level. This condition has been modified mechanically by the
automatic “trap,” a device frequently employed for lifting from a lower
level, part or all of the condensed water, and delivering it into the
boiler; it is, in fact, a displacement pump.
The same result has been attained by draining into a closed tank,
placed low enough to accommodate all the return pipes, and made
strong enough to stand the full boiler pressure with safety, and then
employing a steam pump, either reciprocating or centrifugal, to raise
the water from this tank to the proper level for enabling it to flow
back into the boiler, the whole of the circulation being closed from
communication with the atmosphere.
[Illustration: Fig. 125.]
[Illustration: Fig. 126.]
[Illustration: Fig. 127.]
There are two systems of steam heating, known as the _direct_ and the
_indirect_ system.
Direct radiating surfaces embrace all heaters placed within a room or
building to warm the air, and are not directly connected with a system
of ventilation.
Indirect radiation embraces all heating surfaces placed outside the
rooms to be heated, and can only be used in connection with some system
of ventilation.
For warming by direct radiation, the radiators usually consist of
coils, composed of 3/4-inch and 1-inch steam pipes, which are arranged
in parallel lines and are coupled to branch tees or heads. In a
few exceptional cases, radiators of peculiar shapes are specially
constructed. In all cases the coils must have either vertical or
horizontal elbows of moderate length, for allowing each pipe to expand
separately and freely. Sometimes short lengths of pipe are coupled by
return-bends, doubling backwards and forwards in several replications
one above another, and forming what are called “return-bend coils,” and
when several of these sections are connected by branch, tees into a
compact mass of tubing, the whole is known as a “box-coil.”
Steam and Hot Water heating have long been acknowledged as altogether
most practical and economical in every way—and their universal adoption
in all the better class of buildings throughout the country is positive
proof of their superiority.
[Illustration: Fig. 128.]
[Illustration: Fig. 129.]
[Illustration: Fig. 130.]
The heat from steam is almost exactly identical with that from hot
water, and few can distinguish between the two systems when properly
erected.
They are both healthful, economical and satisfactory methods of
warming. They give no gas, dust nor smoke; are automatically regulated,
and therefore allow of an even and constant temperature throughout the
house, whatever be the condition of the weather outside.
The circulation of the steam through the warming pipes is effected
in an almost unlimited variety of ways, and the cause producing the
circulation throughout the pipes of the warming apparatus is solely
the difference of pressure which results from the more or less rapid
condensation of the steam in contact with the radiating surfaces.
A partial vacuum is formed by this difference of pressure _within
the radiating portions of the apparatus_, and the column of steam or
of water equivalent to this diminution of pressure, constitutes the
effective head producing the flow of steam from the boiler, at the
same time the return current of condensed water is determined by the
downward inclination of the pipes for the return course.