HEATING
GENERAL CONSIDERATIONS
Heat from Hygienic Standpoint
The subjects of heating, lighting and ventilating will be treated
purely from a hygienic standpoint and in no sense from the standpoint
of engineering. The proper manner of heating a building is not within
the scope of hygiene, but becomes a question of proper engineering
and a subject to be considered from that angle. We are concerned only
as the heating of buildings influences the health of the occupants.
Combustion
In parts of the country where the temperature goes below 60° F. it
becomes necessary to provide artificial heat to warm houses in order
that health may be maintained at the least possible expenditure
of energy. The most common method of producing heat for heating
purposes is by combustion. Its obedience to certain physical laws
is infallible. Heat is liberated from such material as coal and
wood by combustion and is the result of the chemical action of this
combustion; it is then transmitted to the rooms to be heated either
by air, water, or steam unless the combustion takes place in the room
to be heated; then it is distributed throughout the room by radiation
from the open fire or conduction from above.
Molecular Theory
Up until the beginning of the nineteenth century heat was believed
to be a substance that had no weight and the name caloric was given
this hypothetical substance. Davy and Rumford, through a series
of experiments, proved that heat is a violent agitation of the
molecules of matter. From this we have the molecular theory that
as the velocity of the molecules is increased heat is produced
and the temperature raised. The words heat and temperature are
not interchangeable. Heat is the cause and temperature is the
effect. Temperature indicates the presence of heat and the degree
of temperature represents the intensity of the heat, but not the
quantity. Heat in the same amount may be imparted to two bodies of
the same substances, but different mass, and one will be hotter than
the other; therefore, the specific heats of the two substances are
different. To illustrate: Place in the sun a receptacle containing
two gallons of water and one containing one gallon of water, both the
same temperature. Leave them for a given length of time and they will
become warm, but the one gallon will be warmer than the two, because
of the difference in the amount of water to be warmed. The same
amount of heat was applied to each, but this did not produce the same
temperature in both. Again the same quantity of different substances
may be exposed to the same heat, but the temperature will not
necessarily be the same, for some substances heat more rapidly than
others. It requires more heat to raise the temperature of water to
a given degree than it does the same weight of any other substance,
except hydrogen. This is the reason water gives off more heat than
any other substance that cools through the same number of degrees.
Normal heat is produced in the body by the expression of calorific
mental impulses and by the oxidation which is carried on in the
tissue cells. The amount of heat produced in the body is adaptative
to the needs of the body and is under the direct control of Innate
Intelligence.
Air is carried into the lungs in respiration and by the action of
Innate the oxygen is absorbed in the air cells and passes into the
blood. It is carried in the blood by the hemoglobin to the tissue
cells where it comes in contact with the calorific mental impulses
and combustion takes place.
Body Heat
The normal bodily temperature is 98.6° F. Variation above or below
this point indicates abnormality. This heat can not be supplied
artificially from without. It must be generated within the body. It
therefore becomes obvious that the temperature outside of the body
is not regulated for the purpose of supplying the body with heat.
The temperature of the atmosphere must, however, be regulated in
order that there may not be an abnormal loss of the bodily heat. The
bodily heat is being constantly lost to the outside air as follows:
30% by contact with the air, about 43% by radiation and about 27%
by exhalation and other losses. We may sit in a room that is warm
enough, say 75° F., and yet if we are near a cold wall we will feel
chilly. We say we feel the cold coming from the wall, while in
reality we feel chilly and cold because the body is losing its heat
abnormally to the cold wall by radiation through the air.
When the air is comparatively dry the equality of the bodily heat is
maintained by a steady but imperceptible evaporation from the skin.
In moist air this evaporation does not take place so readily since
the air is already laden with moisture, so instead of the moisture
being absorbed by the air it forms on the surface of the body as
perspiration. This is why one perspires more in a moist air than in
an atmosphere having a low humidity. When the air is kept in constant
motion there is an increase both in the evaporation from the surface
of the body and also in the heat conduction by the constant supply
of fresh air to take the place of the moisture-laden and heated air
around the body.
The normal heat given off from the body raises the temperature of
the air surrounding the body and tends to create upward currents.
This is Nature’s method in freeing the body from the envelope of
vitiated air which surrounds it as a result of the natural processes
carried on through it. Therefore, if the temperature of the room
is too nearly the same as that of the body it will be necessary to
make more provision for the ventilation since the temperature of the
body would not be enough greater than that of the surrounding air to
create sufficient movement to carry the vitiated air away from the
body. That is why a cool room does not require the same amount of
ventilation that a hot room does.
Innate Intelligence is capable of adapting the heat of the body to a
great range in atmospheric temperature, but in order to do this there
must be a sufficient length of time to enable Innate to bring about
the necessary adaptative changes in the body. If the atmospheric
changes take place too rapidly this adaptation cannot be effected and
the metabolic equilibrium of the body will be disturbed. This makes
it necessary to exercise care in properly heating our dwellings.
Proper Temperature of Building
It is certain that temperature of the dwelling should be properly
regulated and that it should not vary with the temperature outdoors,
especially in the winter time. The heat equilibrium of the body may
be easily disturbed by sudden changes in the temperature of the
dwelling. Because there is an increased expenditure of the internal
energy to bring about adaptation, the internal forces are dissipated
and this lowers the resistance of the body and makes the individual
susceptible to incoördination.
A high temperature with a relatively low percentage of humidity will
cause an abnormal evaporation from the skin and mucous membrane. This
gives not only a sense of chilliness but causes an abnormal dryness
of the skin and produces an irritation in the throat and nose. On
the contrary, the bodily heat will be withdrawn too rapidly in a
temperature that is too low.
There are many factors to consider in determining the proper
temperature of a room or a dwelling. The time of year, the processes
carried on within the dwelling, the use of the rooms—that is, whether
they are used for sleeping-rooms, living-rooms, or workrooms—all
tend to influence the degree of temperature most advantageous to the
inmates of the room.
In determining the proper temperature of a room the relative humidity
that is to be maintained must be considered. A hot dry air is more
desirable than a cool damp air. In winter the variation in the
temperature of the average dwelling should be between 58° F. and 70°
F. with a relative humidity of 40% to 60%. The temperature should be
lower in the bedroom than in the living-room.
The great objection to the average heating system is that the air is
kept too dry; therefore, it is necessary to keep the temperature of
the rooms too high in order for the individuals to keep warm.
Requirements for Heating System
In order for a system of heating to meet the demands of hygiene
there must be a minimum cost of production and absence of impurities
produced in the process of heat; the heat must be equitably
distributed over the house; the temperature must be kept even, thus
insuring continuous heating; and there must be a proper degree of
humidity. There must also be freedom from explosions and danger from
fire.
There are three methods of heating; radiation, conduction and
convection. There are two systems by which these methods are used:
they are local and central. In local systems the heat is produced in
the room by combustion or burning of fuel in grates and stoves.
In central heating the heat is produced at a central place outside of
the rooms and conveyed to them by hot air, hot water or steam.
Even though these three methods of heating are usually given, it
is difficult to draw hard and fast lines of demarcation between the
different methods, for, as a matter of fact, they overlap to quite an
extent. The element of radiation is involved in both conduction and
convection.
LOCAL HEATING
Radiation
The vibrating molecules of a heated substance will set into motion
the ether of space and in this way the heat may be transmitted as
wave motion. We have an illustration of this in the transmission of
heat to the earth from the sun. Ether waves are generated by the
violent vibration of the molecules of the sun and the vibrations
are transmitted to the earth and they in turn generate molecular
vibrations of the bodies of the earth. This is spoken of as radiant
heat and is illustrated by the heat from the open fireplace.
Open fireplaces give off heat by direct radiation. This is the oldest
method of heating and has been in use for many generations. It is not
a satisfactory method, however. The radiation of heat takes place
through air very readily, but air is not a good conductor of heat.
Heat may be radiated from the body very rapidly through the air to
cold objects. As for instance, sitting near a cold wall one will feel
chilly due to the radiation of the heat from the body to the cold
wall, although the air in the room may be sufficiently warm to be
otherwise comfortable.
Heat may be readily radiated from an open fire, but it must be
remembered that the intensity of the radiated heat is inversely
proportional to the distance of the heated object from the place
where the heat is produced. To illustrate: If one object is one foot
from the source of heat, the open fireplace, and another object is
three feet from the fireplace, the object that is farther away will
receive only one-ninth as much heat as the one nearer. This is one
of the disadvantages of the open fireplace as a means of heating
a room. A fireplace is very cheery and gives a room a comfortable
appearance and is very popular in the modern home. It is adequate
to take the chill away when the weather is not very cold, but it is
certainly a very undesirable means of heating a house in cold weather.
[Illustration: _Local Heating_]
Another objection to the open fireplace is that it requires a great
deal of fuel. About 75% of the heat is lost through the chimney.
There is, however, an advantage in the open fireplace since it
affords an excellent means for ventilation; there is always a draft
up the chimney.
Conduction
Heat is carried through such metals as iron by molecular action and
such heat transference is known as conduction. The fact that heat is
transferred through metals by conduction is of vital significance
in the question of heat losses and dissipation, as through walls of
buildings for example.
If heat be applied to any part of an iron bar or piece of metal it
will be transferred to all parts of that iron by the molecular action
until it is all heated. This can be illustrated nicely by placing the
end of the poker in the furnace fire and in a short time the heat
will be felt in the other end of the poker.
[Illustration: _Undesirable Local Heating_]
The =stove= is a good example of the conduction of heating. The heat
is conducted through the iron of the stove to the air in the room,
and then by convection through the air to all parts of the room. The
molecules that are in contact with the fire first have their motion
accelerated by the heat and this motion is passed from molecule to
molecule until all the molecules in the entire iron are accelerated
in their motion and thus the temperature of the metal is increased.
Some metals are better conductors of heat than others, owing to the
difference in the character of the connection between the molecules.
Silver forms the best conductor of heat among the metals and is used
as a standard of conductivity.
In conduction heat is produced inside a fire pot, as in a stove, and
conducted through the iron then radiated from its outer surface. This
is also called indirect radiation and is a more satisfactory method
than the direct radiation since the material of the stove will retain
the heat for a longer period of time and allow for its more equitable
distribution. In this way it is possible to heat the room more evenly
than with an open fire.
One of the objections to this method is that it is local and has
all the disadvantages of a local heating system. The combustion
takes place in the room and as a result there are certain amounts of
impurities that are admitted into the breathing zone. There is the
added disadvantage of having dirt and dust from the fuel and from the
ashes and refuse from the process of combustion. These disadvantages
are not encountered in a central system.
In extremely cold weather the stoves are likely to become overheated
in an effort to keep the rooms warm, and overheated stoves not only
increase the hazard from fires, but tend to scorch the air. Red hot
iron consumes oxygen and gives off carbon dioxide which produces an
unfit atmosphere for breathing. It is difficult to maintain an even
heat in a room that is heated by a stove for the stove requires a
great amount of attention.
CENTRAL HEATING
Convection
The most desirable system of heating is the central. In this system
the heat is conveyed from the central heating plant to the rooms
either by air, hot water, or steam. The heat may be produced in the
house that is to be heated, usually in the basement, or it may be
produced at a distance, as in the case of steam plants, and carried
through pipes to the house. There are three principal systems of
central heating: Hot air, hot water, and steam.
Heat is carried through air by convection. The air exposed to heat
becomes specifically lighter and hence rises and the cooler air takes
its place. In this way the air of a room is heated by its constant
movement brought about by this phenomenon. The air becomes heated in
the air jacket of the hot air furnace and creates an upward draft.
As soon as the cool air rushes downward to take its place a downward
draft is formed through the cold air ducts. In this way the air in
the room is kept in circulation and at the same time properly warmed.
=Hot air=, or as it is sometimes called, furnace heating, is a very
satisfactory system for an ordinary dwelling or small building.
It consists of a large stove much as that used in local heating.
Surrounding this stove is a jacket with an air space between it
and the stove. Pipes lead from the air space through the top of
this jacket and convey the air that is heated by the stove to the
different rooms. The cold air is taken from the rooms and conveyed
through the cold air pipes back to the furnace and is admitted to the
air jacket from beneath. In this way the warm air, being lighter than
the cold air, passes upward through the hot air pipes and is replaced
by the cold air through the cold air pipes. In this way there is a
constant circulation of air through the pipes.
This kind of a furnace requires much attention, but not as much as
a local heating stove. Great care must be taken that the air is not
overheated in the air jacket. If it is, the air in the room will be
dry and stuffy and may even have a scorched odor. The furnace should
be equipped with a water receptacle inside the air jacket. This
receptacle should be kept full and in this way a proper relative
humidity will be maintained. If this is not done, the air in the room
will be too dry and it will require a higher temperature to keep the
room comfortable. Another objection to this system is that dust and
dirt are likely to enter the rooms from the furnace.
The =hot water= is a very desirable system of heating. Heat
convection through water is practically the same as that through air.
The particles of water at the point where the heat is applied become
lighter as they become heated and because of this change naturally
rise to the top and the particles that are cooler and therefore
heavier sink to the bottom, thus forming currents. For this reason
water heats much more rapidly when the heat is applied to the bottom
than it does when heat is applied at the top of the receptacle. These
principles are utilized in hot water systems. The hot water rises in
the radiators and gives off its heat to the cooler atmosphere and the
cool water returns to the boiler to be reheated. In this way there is
a constant circulation of the water through the system.
The hot air system is entirely satisfactory for small buildings, but
is not so desirable for large buildings. For large dwellings and
public buildings the hot water system is much more satisfactory.
In the hot water system a water jacket is provided instead of an
air jacket. The water is carried from the boiler over the fire
box through pipes to the different rooms where it passes through
radiators and is returned to the boiler by continuous pipes. At the
top of the pipes an expansion tank is placed to take care of the
expansion of the water when heated. The heated water circulates
freely through the system of pipes. Each radiator is provided with
a valve to regulate the amount of water admitted and in this way the
degree of heat may be regulated in the different rooms. Each radiator
is provided with an air valve to allow the air to escape when the
water is admitted, or to allow the steam to escape in case the system
becomes overheated and the water is converted into steam.
[Illustration: _Central Heating Showing boiler, pipes, and
radiators._]
This system is easily cared for and easily operated. It requires
a relatively small amount of coal and maintains a very even heat,
and when properly operated there will be no sudden changes in the
temperature of the rooms. There is less danger of overheating the
air and lowering the humidity with this system than with the hot air
furnace.
The radiators may be placed in the rooms that are to be heated or
they may be placed in the basement and the air admitted and passed
over the radiator and warmed and then forced into the rooms. This
is known as the indirect method and is used in connection with the
system of ventilation. It is used more with steam than with hot water.
Heating by =steam= is by far the most satisfactory method, especially
for larger dwellings and buildings. This system is somewhat like
that of hot water, except the water is converted into steam. The
temperature of the pipes and radiators is therefore higher than with
hot water, but the pipes and radiators do not need to be as large.
Very often this system is used in connection with the ventilation.
The radiators are placed in the basement or in another convenient
place and cool fresh air from the outside is passed over them and
warmed. It is then forced into the rooms. Very often this air is
washed, as described in the chapter on ventilation, and thus freed
from suspended matter. At the same time the relative humidity can
be controlled and this is very essential, not only as a means of
providing air that is most desirable for breathing, but also in point
of fuel economy, since air of high humidity is more easily heated and
is more desirable in conserving the heat of the body as has already
been explained. Steam heating is especially suitable for high and
irregularly shaped buildings. The fact that the radiators and pipes
are empty when not in use reduces the risk of damage to the house
furnishings from bursted or leaky pipes.
It is well to have the radiators placed near windows so that in
ventilating the air will pass over them and be warmed before entering
the room.