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.