TEMPERATURE REGULATION
The method used for regulating the temperature of a house will depend
on its size, the conditions under which it is to be used and the method
of heating. In small houses the temperature may be satisfactorily
governed entirely by hand, that is, the furnace drafts may be changed
by hand to suit the varying conditions of temperature. A more
satisfactory method is that of thermostatic regulation, in which a
thermostatic governor and a motor automatically control the furnace
dampers so as to keep a constant temperature at one point, generally
the living room. Where hot-water or steam heating plants are used,
another device is frequently employed to keep the temperature of the
heat supply at a constant degree. This is known as the automatic damper
regulator. The damper regulator is one of the boiler accessories which
so governs the drafts of the furnace as to keep a constant water
temperature in the hot-water heater or a constant steam pressure in the
steam boiler.
In some cases both the damper regulator and the thermostat are used as
a more complete means of temperature control.
=Hand Regulation.=--As a means of changing the dampers of the
furnace from the floor above, to suit the prevailing conditions, the
arrangement shown in Fig. 49 does away with the necessity of a journey
to the basement, to remedy each change of temperature.
A plate is fastened to the wall at any convenient place, to which the
end of a chain is attached as shown in the figure. This connects with a
second chain, the ends of which are fastened, one to the direct draft
or ash-pit damper _F_, and the other to the check draft _E_, in the
chimney. As the furnace appears in the drawing, the direct draft is
closed and the check draft is open. By changing the ring from _G_ to
_H_, the movement of the chain opens _F_, and closes _E_, admitting
air to the furnace. When the temperature of the room is raised
sufficiently, the drafts are restored to their original position by
replacing the ring at _G_. Sometimes one or more intermediate points
are made on the plate between _G_ and _H_, which permits both drafts
to be kept partly open and fewer changes are required to keep the
temperature approximately normal.
[Illustration: FIG. 50.--Cross-section of damper regulator for steam
boiler.]
[Illustration: FIG. 51.--Steam boiler for house heating, with the
damper regulator, in place, attached to the dampers.]
=Damper Regulator for Steam Boiler.=--The damper regulator used on
a steam boiler is a simple device that automatically controls the
draft dampers by reason of the changing pressures of the steam. The
object of the damper regulator is to prevent the generation of steam
in the boiler beyond a certain pressure at which the valve is set.
This point is usually 3 or 4 pounds below the pressure at which the
safety valve would act. If in proper working order the damper regulator
will so control the dampers that the boiler will always contain a
supply of steam, but the pressure will not reach a point requiring
the action of the safety valve. Fig. 51 illustrates its connections
with the furnace dampers. In Fig. 18 the regulator appears at _D_. In
external appearance and in operation of the dampers, it is the same
as the regulator for a hot-water boiler but its internal construction
is simpler. Fig. 50 shows its construction. It is attached to the
steam space of the boiler at _E_. The steam pressure acts directly on
the flexible metallic diaphragm _B_. As the pressure of the steam
approaches the desired amount the diaphragm is raised and with it the
lever _V_. A chain _D_, attached to the end of the lever, opens the
check draft, and another at _C_ closes the draft damper. When the steam
pressure falls, the diaphragm lowers the lever and the dampers are
restored to their original position. The same movements are repeated
with each rise and fall of the steam pressure.
[Illustration: FIG. 52.--Damper regulator for hot-water boiler.]
=Damper Regulators for Hot-water Furnaces.=--The damper regulator for
a hot-water boiler automatically controls the dampers of the furnace
so as to keep the water of the boiler approximately at a constant
temperature. The regulator is shown in Fig. 52. The ends of the lever
are connected to the direct-draft and check-draft dampers, as in the
case of the damper regulator for the steam plant. A cross-section of
the working parts shows the details of construction. The lever _d_
is operated by a diaphragm _g_, which tightly covers a brass bowl,
containing a mixture of alcohol and water, of such proportions as will
produce a vapor pressure at the desired temperature, say 200°. The
hot water from the boiler passes through the valve, entering at _a_
and leaving at _b_. When the water reaches the desired temperature,
the contained liquid vaporizes and a pressure is produced that is
sufficient to lift the diaphragm and the lever. The chain attached to
the right-hand end closes the direct-draft damper; at the same time the
other end of the lever opens the check draft, and the supply of air to
the furnace fire is entirely cut off. As soon as the water has cooled
sufficiently, the vapor pressure in the bowl is reduced, allowing
the weight _W_ to depress the diaphragm and the lever is restored to
its first position. The weight _W_ is for adjusting the valve to the
desired temperature. The plug _f_ tightly closes the orifice through
which the liquid is introduced into the bowl.
The object of the damper regulator on a hot-water boiler is to govern
the fire of the furnace so as to keep the water in the boiler at the
desired temperature. In case there is a demand for heat at any part of
the house, a supply of hot water will always be on hand. It has nothing
to do with the regulation of the temperature of the house. The control
of the house temperature is the office of the _thermostat_.
=The thermostat= is a mechanical device for automatically regulating
temperature. It may be arranged to operate the valve of a single
radiator or register and so control the temperature of a room, or as
commonly used in the average dwelling, the controller may be placed
to govern the temperature of the living room and in so doing keep the
furnace in condition to satisfactorily heat the remainder of the house.
Thermostats are made in a variety of forms by different manufacturers
but they may be divided into two general classes: the electric, and
the pneumatic types. The electric thermostat depends on an electric
current as a means of controlling the action of the motor which in turn
operates the furnace dampers so as to maintain a constant heat supply.
The pneumatic thermostat regulates the supply of heat by means of
pneumatic valves. It will be considered later in discussing mechanical
ventilation. This type of temperature regulation is particularly
adapted to large buildings.
Fig. 53 illustrates one style of electric thermostat that is very
generally used for temperature regulation in the average dwelling. It
consists of three distinct parts--the controller, the electric battery
and the motor. In the drawing the motor is shown connected with a
steam valve, such as may be used for furnishing steam for a series of
radiators. It may with equal facility be attached to the dampers of a
furnace or other heating apparatus.
The controller occupies a place on the wall of the room to be heated
and makes electric connections between the battery and the motor.
Whenever the temperature varies from the required degree, a change of
electric contact in the controller starts the motor, and the radiator
valve or the furnace drafts are opened or closed as occasion requires.
The controller appears in Fig. 54 as commonly seen in use. The
upper part carries a thermometer and the pointer _A_ indicates the
temperature to be maintained in the room. The middle division indicates
70°F. Each division to the right of the middle point raises the
temperature 5°. Each division to the left lowers the temperature a like
amount.
In addition to the ordinary type this controller is furnished with
a time attachment by means of which the controller may permit the
temperature of the room to fall to any desired degree at night and
raise it again in the morning at the time for which it is set.
This is accomplished by a little alarm clock shown at the bottom of the
controller in Fig. 54. The indicator _B_ is arranged to correspond with
the indicator _A_; the middle point representing 70°F. To set the time
attachment, the alarm is wound and set as in any alarm clock, 1/2 hour
earlier than the desired time for rising. The indicator _B_ is set for
the day temperature and _A_ is set for the temperature desired during
the night. At the appointed time the alarm moves the indicator _A_ to
the desired point for the day and the controller raises the temperature
accordingly.
Fig. 55 shows the mechanism that is exposed to view when the cover
of the controller is removed. The bent strip _C_ is the part that is
influenced by the change of temperature. It is made of two thin strips
of metal, one of brass and the other of steel. The two strips are
soldered firmly together. Any change in temperature will affect the
strip and cause it to bend and touch the contact point--_K_ or _J_. The
bending of the strip is due to the unequal expansion of the brass and
steel due to the change of temperature. Brass expands 2.4 times as much
as steel with the same change of temperature. The amount of bending
is sufficient to make an appreciable movement in a small fraction of
a degree change. The brass part of _C_ is on the left and since it
expands the greater amount, a rising temperature causes _C_ to come
into contact with the point _J_. When this happens the motor is started
and makes one-half cycle. In so doing it shuts off the air supply
of the furnace, opens the check draft and at the same time the motor
changes the electric contact from _J_ to _K_. When the temperature
begins to fall, the brass contracts in the same ratio to the steel as
it expands during the rising temperature and as a consequence the bar
bends to the left. When the strip touches the point _K_ the motor again
makes one-half circle, admitting air once more to the furnace, closes
the check draft and shifts the electric contact back to _K_. When
properly started the thermostat will regulate the temperature within a
degree of temperature.
=The Thermostat Motor.=--The thermostat motor automatically opens
and closes the furnace dampers or the valve that admits steam to the
radiators as heat is demanded by the controller.
The motor, as shown in Fig. 53, consists of a system of gears and a
brake _S_, which regulates the speed, a cam _M_, and armature _I_, for
starting and stopping the motor, and the electromagnet _H-H_ which
operates the bar _I_. Two lever arms _L_, one in front and the other
at the back of the motor furnish means for attachment to the valve or
furnace dampers. An emergency switch at _D_ is shown in detail in Fig.
56. The battery _B_ furnishes the current which energizes the magnets
and an iron weight supplies the motive power for the motor.
The description of the operation of the motor applies to the steam
valve shown in Fig. 53. The same motor might be used for opening and
closing of the dampers of the furnace in any kind of heat supply. The
method of communicating the motion of the motor arms to the dampers of
the furnace will be described later. The connections with the furnace
drafts are shown in Figs. 3, 6, 8, 34, etc.
Suppose that the valve for admitting steam to the radiators, as
that in Fig. 53, is closed and that the temperature of the house is
falling. The strip _C_ of the thermostat controller is moving toward
_J_. When contact is made, the current from the battery _B_ energizes
the magnets _H-H_ and the bar _I_ is lifted. As the bar _I_ is raised
the catch _J_ is released and permits the motor to start. The bar _I_
is held suspended by the cam _M_ until the arm _L_ has made one-half
revolution, when the lug _K_ drops into the depression in the cam made
to receive it and the catch _J_ engages with the brake and stops the
motor.
[Illustration: FIG. 53.--Thermostat complete with the regulator,
battery and motor, attached to a steam supply valve.]
During this movement the arm _L_ has lifted the valve arm _N_ and the
valve admits steam to the radiators, at the same time the contact _M_
has been shifted from the right-hand contact to the left, and the
electric circuit is ready to be made in the controller at the point
_K_. When the temperature has fallen a sufficient amount the controller
bar _C_ will make contact at _K_ and the motor will again make a half
cycle, changing the valve back to its original position. This process
will be kept up so long as the motor is wound and there is sufficient
fuel in the furnace to raise the temperature.
Fig. 55 shows the method of connecting the electric wires from the
battery to the controller. A three-wire cable connects the battery, and
makes contacts as indicated at _H_, _K_ and _J_. The wires are shown
attached to the motor as in Fig. 55. A wire is taken from either pole
of the battery and attached to one of the ends of the magnet coil.
Passing through the magnet the wire is attached to the frame of the
motor. This makes the cam _M_ a part of the electric circuit. The other
two wires are attached to the brass strips on each side of the arm _L_.
The strips are insulated from the frame. The electric circuit through
the magnet is made alternately by contact with the strips at right and
left of the arm _L_.
[Illustration: FIG. 54.--Thermostatic regulator with clock attachment
for control of day and night temperature.]
In case the motor, through neglect, runs down, a safety switch at _D_
(Fig. 53) disconnects the battery and keeps it from being discharged.
This switch is shown in detail in Fig. 56. When the weight has reached
its limit, the piece _C_ on the chain comes into contact with _D_ and
lifting it out of contact, breaks the circuit. When the motor is again
wound, _C_ engages with _E_ and restores the contact. The switch is so
arranged that when open, the valve will always be closed.
[Illustration: FIG. 54_A_.--Showing the clock attachments to the
thermostatic regulator.]
[Illustration: FIG. 55.--Mechanism of the thermostatic regulator.]
=Combined Thermostat and Damper Regulator.=--It is evident that, in
heating a house by steam, the _damper regulator_ governs only the
steam pressure of the boiler. In the use of a thermostat alone, the
regulation is that of the temperature of the rooms only, and has
nothing to do with the steam pressure. As an example: Suppose that in
cold weather the house is cold and that the gage of the steam boiler
shows no pressure. The desire is to get up steam as soon as possible.
In so doing a hot fire is made with a large amount of fuel. As soon
as the steam begins to form, the pressure rises rapidly. When the
radiators have become hot and the steam is no longer taken away as
fast as it is formed, the pressure of the steam in the boiler keeps on
rising. The thermostat will not close the furnace dampers until the
temperature of the rooms is normal. This may require so great a length
of time as to produce a great excess of steam that cannot be used at
the time and the pressure will be relieved by the safety valve. This
may not be dangerous but it is disagreeable. To prevent the safety
valve from blowing except in case of emergency, a combined thermostat
and draft regulator is used. In such a combination, the draft
regulator closes the draft as soon as the pressure reaches the desired
point, after which the thermostat does the regulating according to suit
the temperature of the house.
In Fig. 2 is shown such a combination attached to a boiler. The cord
from the regulator, instead of extending directly to the direct-draft
damper, passes over the pulley _P_ and connects to the thermostat cord.
The regulator may now close the damper to suit the steam pressure,
but after the temperature in the rooms is normal, the amount of heat
necessary to maintain the desired degree is regulated entirely by
the thermostat which opens and closes the dampers regardless of the
position of the damper regulator.
If occasion should require but a very slight amount of steam to keep
the house at the desired temperature, the thermostat will govern
the drafts aright. If the steam pressure is in danger of becoming
excessive, the damper regulator will govern the drafts.
[Illustration: FIG. 56.--Automatic switch which opens the battery
circuit when the thermostat motor weight, reaches its limit.]
=Thermostat-motor Connections.=--The arrangement of cords and pulleys
used for attaching the thermostat motor to the furnace dampers will
depend very much on local conditions. The motor can be placed in
any convenient position so that the connecting cords will act most
directly. The motor opens and closes the direct draft and check draft
in accordance with the demand for heat. The connections for all kinds
of furnaces are made in much the same manner. The pulleys supplied
with the motor are placed to work as freely, and the cords to pull as
directly as possible.
In Fig. 57 the motor is connected with a hot-air furnace. The cord
_D_ is attached to the front arm of the motor and connects with the
direct-draft damper _F_. The cord _C_ connects the rear arm of the
motor with the check-draft damper at _E_. In the position of the
dampers shown, the direct-draft damper is closed and the air is
entering the chimney through the check draft _E_. While this damper is
open there is very little induced draft to supply the fire with air
that might leak through the crevices around the ash-pit door, but the
gases from the furnace are completely carried away to the chimney by
the air entering at _E_.
[Illustration: FIG. 57.--Thermostat motor connected with the dampers of
a hot-air furnace.]
In Figs. 3, 6, 8, 34, etc., the same motor is connected with the
furnaces of various other systems of heating. The object is the same
in all; when less heat is required, the air supply is cut off and the
furnace fire subsides; when more heat is demanded the air is again
admitted to produce greater combustion. The check draft is an important
feature as it checks the flow of air through the furnace regardless
of the position of the direct-draft damper. Even should the direct
draft be left open, the check draft when open would destroy in a great
measure the supply of air entering the furnace.