Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRIC HEATING SYSTEM WITH PROPORTIONAL
TIMER HAVING A CYCLE OF F:[XED DURATION
Background of the Invention
The conventional hot air heating system, as
used in a residence or commercial establishment, includes
a gas or oil fired furnace which is controlled by a
room thermostat. When the thermostat calls for heat,
the furnace is operated, and then the plenum temperature
reaches a preset value of about 200F, the blower is
operated to deliver the heated air through the duct
system to the area or zone to be heated.
The conventional hot air heating system oper-
ates from a cold condition, meaning that the plenum
and ducts are cold when the furnace is started up, with
the result that the plenum must be initially heated
before the blower is operated to deliver heat to the
zone of the building, and a substantial amount of heat
is lost due to the heating of the duct system.
In addition, there is substantial heat loss
through the chimney in the conventional hot air heating
system, due to stack heat being dissipated to the atmos-
phere and by virtue of natural convection of room heat
through the chimney when the furnace is not operating.
Furthermore, the heating unit, as used in the
conventional hot air heating system, operates at full
capacity whenever the room thermostat calls for heat.
This results in the room temperature going above the
set temperature, and when the heating unit is de-ener-
gized, the room temperature falls beneath the set tempera-
ture before the heating unit is again energized. Theresult is that the room temperature oscillates or hunts
about the temperature setting.
Condition response controllers, as described
in United States Patent 3,509,322, have been utilized
to control the "on" time of the heating unit in accord-
ance with the existing temperature condition. In a
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system such as that, the heating unit is ener~ized at
substantially full capacity when the room temperature
is substantially below the desired temperature level
and as the room temperature approaches the set point,
the energization of -the heating ~mit is reduced.
Period timing devices have also been used in
conjunction with electric resistance heating units for
heating food products, as disclosed in patent 3,666,921.
In devices of that type, pulsations of heat are produced,
and the duration of the heating pulse is controlled by
the timer so that a predetermined amount of heat can be
precisely programmed.
Summary of the Invention
The invention relates to a heating system hav-
ing improved efficiency over conventional heating systems.The heating system includes a closed conduit containing
a liquid, such a~s water, which is continuously circul-
ated through the conduit by a pump. The liquid in the
conduit is heated by an electrical resistance heating
unit through a pulse type of heating, and heat is trans-
ferred from the liquid to a medium to be heated through
a heat exchange unit.
A proportional timer is operably connected to
the resistance heating means and has a cycle of fixed
duration. The cycle includes an "on" interval and an
"off" interval and the duration of the "on" and "off"
intervals can be varied within the fixed cycle.
A temperator sensor senses the temperature of
the liquid in the conduit and i the temperature falls
below a set value, the sensor actuates the timer to
energize the heating unit. A second sensor, which is
responsive to the temperature o the liquid in the con-
duit, is operably connected to the timer in a manner
such that the "on" interval will be proportional to the
deviation of the liquid temperature from the temperature
setting, meaning that if the temperature of the liquid
is only slightly below the temperature setting, the "on"
interval will comprise only a small proportion of the
timing cycle. On the other hand, if the temperature of
the liquia is substantially below the temperature set-
ting, the duration of the "on" interval will be increased.
As a feature of the invention, a frequencybooster is connected in the electrical circuit with the
heating unit and increases the frequently from the nor-
mal value of 60 cycles to about 80 cycles which increases
the penetration and effectiveness of the pulsed heating
operation.
As utilized with a hot air heating system, the
heat exchange unit is located in the plenum of the hot
air duct system and when the room thermostat calls for
heat, the blower is operated to pass air over the heat
exchanger and through the duct system to the area to be
heated. As the heated liquid is continuously circulated
through the heat exchanger, natural convection will cause
heated air to continuously flow through the duct system,
even when the room thermostat is not calling for heat
and the blower is not operating. This results in the
duct system being warm at all times so it is not neces-
sary to heat the entire duct system each time that the
room thermostat calls for heat.
In normal operation, if the liquid temperature
falls beneath the set value, the heating unit is oper-
ated through the proportional timer for a very short
interval to restore the liquid temperature at the setting.
The heating unit is small and compact and has
particular application for use in residences, mobile
homes, prefabricated homes, and the like. As gas or oil
is not required as the energy source, there is no need
for a chimney or flue. As electrical energy is used as
the heat source, the unit is safe and reliable.
Other objects and advantages will appear in the
course of the following description.
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Description of the Drawings
The drawings illustrate the best mode presently
contemplated of carrying out the invention.
In the drawings:
Fig. 1 is a schematic view of the heating
system of the invention;
~ig. 2 is an enlarged sectional view of the
resistance heating unit;
Fig. 3 is a section taken along line 3-3 of
Fig. 2, showing the heating unit;
Fig. 4 is an enlarged schematic representation
of the connection of the temperature sensor to the timer;
and
Fig. 5 is a wiring diagram of the system.
Description of the Preferred Embodiment
-
Fig. 1 is a schematic representation showing the
heating system of the invention. The system includes a
closed conduit 1 through which a liquid is continuously
circulated by a pump 2. The liquid can be water, or a
mixture of water and ethylene glycol. The mixture of
water and ehtylene glycol is pre~erred because it has a
hi~her boiling point than water and has better heat
transfer properties. A drain valve 3 is located in the
conduit 1 to drain the liquid, if desired.
To heat the liquid, a heating unit indicated
generally by 4,is utilized. The heating unit 4 includes
an outer metal housing or casing 5 having a thick la~er
of heat insulating material 6 on its inner surface. A
pair of high resistance heating elements 7, which can
take the form of rods, wires, ~oil, or the like, are
located within the housing 5 in spaced relation to a
metal jacket 8 which is connected in the conduit 1, so
that the liquid can be circulated through the jacket.
A central wall 9 divides the jacket 8 into a
35 pair of chambers 10 and 11 and a series of openings 12
provide communication between the two chambers. Ba~fles
13 can be mounted within both of the chambers 10 and
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11 to provide a tortuous path for the flow of liquid
through the jacket, As shown in Fig. 1, the liquid
enters the chamber 10 and then passes through the open-
ings 12 into the chamber 11 and is thereafter discharged
from the jacket. The resistance heating elements 7, are
spaced from the ]acket and as the elements are inter-
mittently energized or pulsed, black light heating is
obtained. As an example, the spacing between the resist-
ance heating elements 7 and the jacket 8 can be in the
range of about 1.5 to 3.5 inches when utilizing a heat-
ing element generating between 2500 and 3000 watts.
An expansion tank 14 can be connected to the
conduit 1 through a pipe 15, and in addition, a standard
pressure relief valve 16 can also be connected in the
conduit which will open the line in the event the pres-
sure in the system exceeds a predetermined maximum level.
The invention, as illustrated in the drawings,
is applied to a hot air heating system and heat is trans-
ferred from the liquid within the conduit 1 to the air
through a heat exchange unit, indicated generally by 17.
The specific construction of the heat exchange unit is
not critical and, as shown, the unit can comprise an
A-coil 18 which is connected in the conduit 1. As
shown in Fig. 1, a conduit 19 is connected between the
bottom portions of the legs of the coil 18 and the heated
liquid flows through the tubing in both of the legs and
is discharged from the apex of the coil. The A-coil 18
is contained within a plenum 20 of the hot air duct
system, and air is directed over the A-coil by a blower
or fan 21. The heated air then flows through the duct
system to the various rooms or zones of-the building to
be heated.
A low temperature sensor 22 and a high
temperature sensor 23 are mounted within a well 24 con-
nected to the conduit 1 and the function of the sensors22 and 23 will be described in detail hereinafter. In
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addition, a temperature sensor 25 is located in the
well 26 in conduit 1, and the sensor 25 operates through
a mechanical linkage, indicated generally by 7, to actu-
ate a proportional timer 28 which is operably connected
to the resistance heating element 7~
Fig. 4 illustrates the connection of the sensor
25 to the timer 28. The sensor 25 can take the form of
a capillary heat bulb which is.connected by a tube ~9 to
one end of a bellows 30. The opposite end of the bellows
30 carries a shaft which is operably engaged with a
piStOIl rod 31 attached to the piston 32 which is slidable
within cylinder 33. The closed end of the cylinde.r 33
is provided with an opening 34 which e.stablishes communica-
tion between the cylinder 33 and the interior of a smaller
diameter cylinder 35. Piston 36 is slidable ~ithin
cylinder 35 and piston rod 37 is connected to one end of
a gear segment 38 which is mounted for rotation on a
pivot 39. The gear segment.meshes with a pinion 40
attached to the shaft 41 of the timer 28.
Variations in temperature in the liquid flowing
within the conduit 1 will cause expansion and~ntraction
of the liquid within the capillary heat bulb ~to expand
and contract the bellows 30. Expansion and contraction
of the bellows operates through the cylinders 33 and 35
to rotate the gear segment 38 and thus rotate the shaft
41 on the timer to thereby vary the duration of the "on"
and "off" intervals in the fixed cycle of the timer.
The use of the two cylinders 33 and 35 provide.a longer
stroke, and thus a greater arc of.rotation for the gear
segment 38, for a given linear expansion of the bellows 30.
The proportional timer 28 is of conventional
construction, Model HQ9001A5-J78, Eagle Signal Co.
Baraboo, Wisconsin, and has a cycle of fixed duration, as
for example, 15 seconds, and having an "on".inte~val and
an "off" interval. Within the fixed cycle, the duràtion of
the "on" interval and the "off" interval can be varied.
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by rotation of the shaft 41. When the temperature of the
liquid is only slightly below the temperature setting of
sensor 25, only a short linear movement of bellows 30
occurs, and a corresponding small degree of rotation of
gear segment 38 and shaft 41 results, to thereby slightly
increase the "on" interval of the timer and the heating
pulse. When the temperature of the liquid is substantially
below the setting of sensor 25, as for example during
- start-up of the system, a longer linear movement of the
bellows occurs which operates through gear segment 38
and shaft 41 to produce an "on" interval and heating
pulse of greater duration. Thus, the proportional timer
acts to vary the "on" interval and the heating pulse in
direct proportion to the difference between the tempera-
ture of the liquid`and the temperature setting, i.e. thegreater the difference, the longer the duration of the
heàting pulse within the fixed timer cycle.
The sensor 25 and mechanical linkage is desig-
ned so that if the liquid temperature is at least about
140F or below the "on" interval will be at a maximum,
while if the liquid temperature is at about 180F or
above, the "on" interval will be at a minimum.
The wiring diagram is shown in Fig. 5, and the
- single phase, 220 volt power lines 42 and 43 are connected
to the primary side of a transformer 44 and the 110 volt
output side of the transformer is connected to lines 45
and 46. A manual on-off switch 47 is located in the
line 45 and the motor 48 of pump 2 is connected across
the lines 45 and 46. With the manual switch 47 closed,
the pump 2 ~ill operate continuously to circulate li~uid
through the conduit.
A motor 49 of blower 21 is connected across the
110 volt power lines 45 and 46 in series with the low
temperature limit switch 22 and the contacts 50 of a
relay 51. The relay 51 is connected to the 24 volt
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output side of a transformer 52 in series with room
temperature thermostat 53, while the input or primary
side of the transformer is connected to the 110 volt
lines 45 and 46.
The limit switch 22 is normally set to close
when the temperature of the liquid in conduit 1 reaches
approximately 120F. With switch 22 closed, the blower
21 will operate, providing that the room thermostat 53
is calling for heat and the relay contacts 50 are closed.
The high temperature limit switch 23 is con-
nected in series across the lines 45 and 46 with the
proportional timer 28. The switch 23 is normally set to
open at an elevated temperature of about 190F and on
cooling o~ the liquid in conduit 1 from 190F , will
close at a temperture of about 180F.
The timer is operably connected to a solenoid
54 which, when energized, operates to close the contacts
55 in the lines 42 and 43.
To increase the frequency from the normal 60
cycles to a range of about 75 to 80 cycles, a frequency
changer 56 is connected across the lines 42 and 43 and
the output side of the frequency changer is connected to
the resistance heating elements 7.
While the wiring diagram shows a pair of resis-
tant heating elements 7 there may be any number, depend-
ing upon the nature and capacity of the heating system.
To begin operation of the system, the on-off
switch a7 is closed, which will operate the pump 2 to
circulate water through the system. As the high tempera-
ture limit switch 23 is closed at this time, the propor-
tional timer 28 will be energized to actuate the solenoid
54 and close the contacts 55 and energi~e the heating
elements 7. As the temperature of the water at start-up
will be well below 140F, sensor 25 will adjust the "on"
interval of the timer, so that it is o~ maximum duration.
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At start-up, the temperature of the liquid
will be below the setting of the lowe temperature switch
22 so that switch 22 is open and the blower 21 will not
operate even if the room thermostat 53 is calling for
heat. When the temperature reaches approximately 120F,
the switch 22 will close, and if the room thermostat 53
is then calling for heat, the blower 21 will operate to
pass air over the heat exchanger 17 and deliver the
heated air through the duct system to the room or zone
to be heated.
As the temperature of the water circulating
within the conduit is increased above 140F, the sensor
25 will operate to progressively reduce the duration of
the "on" interval.
When the temperature reaches the "cut-off
setting of the switch 23, which is about 190F, the
switch will open to shut off the power to the heating
elements 7, but the pump 2 will continue to operate and
circulate water through the conduit. If the room thermo-
stat 53 is not calling for heat at this time, natural
convection of air over the heat exchanger 17 will deliver
heated air by convection through the duct system to the
room to be heated and thus maintain the plenum and the
duct system at a warm temperature.
In this "free wheeling" condition, when the
temperature of the liquid in the conduit drops to approx-
imately 180F, the switch 23, will close to energize the
heating elements 7, but the blower 21 will not operate
unless the room thermostat 53 is calling for heat. With
the liquid temperature at 180F, the sensor 25 will
operate to set the "on" interval of the timer 28 at a
very minimum value. ~hen the temperature is restored
to the 190F level, the switch 23 will open to shut o~f
the supply of power to the heating elements 7.
If the room thermostat 53 calls for heat, the
blower 21 will operate to direct air over the heat
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exchanger 17 and heat will be rapidly dissipated from the
liquid. ~hen the temperature alls to 180~F, the switch
23 will close to energize the heating elements 7 and
if the heat loss is great, the sensor 25 will increase
the duration of the "on" int~rval. As the temperature
of the liquid again rises, the duration of "on" interval
will be correspondingly decreased.
In normal operation, the temperature of the
liquid will never fall to a vlaue below about 1~0F, and
at this liquid temperature the "on" interval would be
at its maximum duration, where the "off" interval would
be only momentary.
The heating system of the invention is an
efficient system, in that the pulse of power supplied
to heat the liquid will be proportional to the deviation
between the liquid temperature and the set temperature,
meaning that if the liquid temperature is only slightly
below the temperature setting, only a small amount of
power will be supplied to the liquid in order to restore
its temperature to the setting.
As used with a hot air heating system, the
heated liquid is continuously circulated through the
heat exchanger, and natural convection will cause heated
air to continuously flow through the duct system, even
when the room thermostat is not calling for heat and the
blower is not operating. This results in the duct system
being warm at all times, so it is not necessary to heat
the entire duct system from a cold condition each time
the room thermostat calls for heat.
Furthermore, as the system utilizes electrical
energy, there is no need for a chimney or a flue and this
reduces the normal heat losses which occur with a chimney
due to stack heat being dissipated to the atmosphere and
the natural convection of room heat through the chimney
during periods when the furnace is not operating.
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While the drawings and description have shown
the heating system as associated with a hot air system
for space heating, it is contemplated that the invention
can be used with a hot water system in which the heated
liquid is circulated directly t the space or zone to
be heated. Moreover, the invention can be used in other
heating application, which require precise temperature
control, efficiently delivered, such as heating a die or
mold, heatiny a liquid bath, and the like.
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