Controller for a room heating system

A controller for a space heating system employs a room thermostat and a furnace thermostat responsive to the temperature of a room and a furnace, respectively, for firing the furnace. This controller has a power input terminal for receiving primary electrical power. The controller also has a timed switch and a switching means. The timed switch can connect and disconnect the power input terminal to the furnace. Disconnecting this terminal disables the furnace thermostat. The switching means responds to the room thermostat and can connect and disconnect the power input terminal to the furnace.

BACKGROUND OF THE INVENTION 
The present invention relates to heating systems and, in particular, to 
timers for disabling that portion of a furnace which fires it for the 
purpose of providing potable hot water. 
A known furnace employs an aquastat to keep the internal furnace 
temperature above a preset minimum. This aquastat, a thermostatic device, 
assures that the furnace is sufficiently warm to heat potable water 
through an associated heat exchanger. This known furnace also employs a 
room thermostat to fire the furnace and provide space heating. A 
disadvantage with this kind of furnace control is that the furnace cycles 
regularly solely to keep its internal temperature sufficiently high to 
operate the heat exchanger even when there is no demand by an occupant for 
potable hot water. For example, the aquastat subsystem may periodically 
fire the furnace during sleeping hours or other intervals when there is no 
need for domestic hot water. 
A known furnace control reduces the internal furnace temperature when the 
outside temperature is high. This feature can be disabled by a timer when 
hot water is needed. However, this system will always cycle the furnace to 
maintain some elevated internal temperature. Also, these systems for 
modulating boiler temperature are relatively complex, requiring 
significant modification of the existing furnace controls. 
It is known to provide a timed thermostat to reduce the demand for heat 
from a furnace and simultaneously disable a separate hot water heater 
during prescheduled time internals. However, this type of system does not 
teach how to control a dual function furnace employing an internal 
aquastat subsystem. The appropriate technique for disabling the foregoing 
furnace aquastat without eliminating the space heating provided by the 
furnace has not been developed. 
Thus there is a need for simple equipment to reduce fuel consumption in a 
furnace and still obtain from it domestic hot water. 
SUMMARY OF THE INVENTION 
In accordance with the illustrative embodiments demonstrating features and 
advantages of the present invention, there is provided a controller for a 
room heating system. This system employes a controller for a combination 
room heating and water heating system which enables the disabling of the 
water heating without eliminating room heating which combination system 
comprise a furnace, a room thermostat for firing the furnace to provide 
room heating and a furnace thermostat for firing the furnace to provide 
water heating, where said controller utilizes said room thermostat for 
independently firing said furnace to provide room heating to a selected 
temperature and which utilizes said furnace thermostat to operatively 
connect with a timed switch to regulate the heating of water during 
selected time periods. 
By employing the foregoing equipment a relatively simple timing system is 
provided for saving energy and fuel. Effectively the portion of the 
furnace ordinarily requiring cycling of the furnace merely to provide 
potable hot water is disabled by a timing device. However, the room 
thermostat can override the timing device so that the furnace can provide 
space heating as demanded by the room thermostat. 
In a preferred embodiment, a relay having high voltage and low voltage 
contacts is controlled by a relay coil driven by a room thermostat. The 
room thermostat carries a low voltage supplied preferably by a low voltage 
transformer. The low voltage relay contacts are connected to the furnace 
in the same manner as would be the room thermostat to operate the burner 
and if applicable, the circulator associated with the furnace. The high 
voltage relay contacts can connect and disconnect power from the furnace. 
A timer may be employed herein to restore power to the furnace on a 
schedule consistent with the needs of an occupant. 
The type of timer employed herein can preferably divide the day into two or 
more intervals and can be easily reset to change the time schedule 
according to the needs of the occupant. Preferably, the contacts of the 
timer are connected in parallel with a remote switch conveniently 
accessible to an occupant wishing to override the timer and obtain hot 
water.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a controller 10 is shown enclosed by broken lines. A 
switching means 12 is shown herein comprising relay coil 14 which can when 
energized close two pairs of switched terminals shown here as normally 
open contacts 16 and 18. Contacts 18 connect to output terminals T1 and 
T2. 
A timed switch is shown herein as timing device 20, driving a pair of 
contacts 22. Contacts 22 are connected in parallel with contacts 16. Also, 
connected in parallel with contacts 16 is manually operable switch 24, a 
local switch actuated by an occupant when he wishes to eliminate the 
influence of timed switch 20 and obtain hot water continuously. Switch 24, 
normally located at controller 10, can be located anywhere between the 
power input lines and a furnace. For convenience, a manually operable 
switch 26 is connected in parallel with switch 24 but located at a remote 
location conveniently accessible to an occupant wishing to disable timer 
20. 
Room thermostat 28 is shown connected in circuit with the secondary of 
transformer T1 and relay coil 14. The primary of transformer T1 is 
connected between power input terminal P1 and, through fuse F1, to power 
input terminal P2. Similarly connected to terminals P1 and P2 is timer 20. 
Power input terminal P1 is connected to output terminal L1. Input terminal 
P2 is connected through fuse F1, to one terminal of switch 24, its other 
terminal being connected to output terminal L2. 
Referring to FIG. 2, a heating system is shown as furnace 32. Furnace 32 is 
in this embodiment a hot water type of plant, which includes a hot water 
circulator 34 and a burner 36, each controlled through a pair of lines by 
primary control 38. Control 38 includes a furnace thermostat (aquastat) to 
fire burner 36 if the internal temperature of furnace 32 falls below a 
magnitude sufficient to supply potable hot water. Controller 10, 
previously illustrated in FIG. 1, is connected by its terminals T1 and T2 
to a thermostatic input of control 38. Control38 will energize circulator 
34 and burner 36 if a closed circuit occurs across terminals T1 and T2, 
provided power is being supplied to control 38 from terminals L1 and L2 of 
controller 10. Serially connected between terminal L2 of controller 10 and 
controller 38 is a conventional emergency switch 42 for shutting off the 
furnace. Room thermostat 28 is shown connected by a pair of lines to 
optional zones valves 40 which operate conventionally. A pair of lines 
from zone valves 40 connect to controller 10 and apply a short circuit 
thereto when room thermostat 28 operates. 
Referring to FIG. 3, an alternate embodiment is shown employing a furnace 
44 having control 46 driving burner 48 through a pair of control lines. 
Primary power is provided to control 46 from the output terminal L1 and, 
through emergency switch 42, output terminal L2 of controller 10, 
previously illustrated in FIG. 1. Burner control 46 also has a pair of 
thermostatic input lines from terminals T1 and T2 of controller 10. 
Connected in parallel across terminals T1 and T2 is a furnace thermostat, 
shown herein as aquastat 50. In this arrangement aquastat 50 operates as a 
supplemental thermostat and can fire burner 48 in the same manner as room 
thermostat 28. The balance of the components illustrated in this figure 
are the same as shown in FIG. 2 except that no zone valves are employed. 
To facilitate an understanding of the principles associated with the 
foregoing apparatus, the operation of the system of FIGS. 1 and 3 will be 
briefly described. It will be appreciated that the operation of the system 
of FIG. 2 is substantially the same except that a different type of 
furnace is being controlled. It will also be assumed that the state of 
timer 20 (FIG. 1) is such that switch 22 is closed to provide power from 
input terminal P2 through fuse F1 to output line L2. Thus lines L1 and L2 
convey at this time primary power. It will also be assumed that emergency 
switch 42 of FIG. 3 is closed so that power is conveyed from lines L1 and 
L2 to control 46 of furnace 44. As temperature of its room falls, room 
thermostat 28 closes, connecting the secondary of transformer of T1 across 
relay coil 14 (FIG. 1). In response, contacts 18 (FIG. 1) close, providing 
a short circuit across terminals T1 and T2. This short circuit across 
terminals T1 and T2 is conveyed to burner control 46 (FIG. 3) causing it 
to fire burner 48 to provide space geating. It will be appreciated that 
aquastat 50 being connected in parallel with terminals T1 and T2, can also 
fire burner 48 but does so solely to keep the internal temperature of 
furnace 44 sufficiently high to supply potable hot water. When room 
temperature rises room thermostat 28 again opens to restore initial 
conditions and shut off burner 48. 
Eventually timed switch 22 (FIG. 1) opens. It will be assumed that manually 
operable switches 24 and 26 are also open at this time. Consequently, 
there is no longer a direct connection from terminal P2 to terminal L2 as 
contacts 16, 22, 24 and 26 are all open. Therefore, power is removed from 
burner control 46 and, necessarily, burner 48 (FIG. 3). As a result, 
aquastat 50 is unable to fire burner 48 since no power is available. Thus 
energy is saved since furnace 44 does not cycle during an unscheduled 
interval when hot water is not required. It will now be assumed that room 
thermostat 28 closes as its room temperature descends thereby connecting 
the secondary of transformer T1 across relay coil 14 (FIG. 1). 
Consequently, contacts 16 close and restore the power connection from 
terminal P2 to output terminal L2 thereby powering burner control 46. 
Also, at this time contacts 18 (FIG. 1) closed to provide a short circuit 
across terminals T1 and T2. Consequently, the thermostatic input of burner 
control 46 (FIG. 3) connected to terminals T1 and T2 are shorted to cause 
the firing of burner 48. 
Summarizing, it will be appreciated that timed switch 20 can divide the 
operation of furnace 44 (FIG. 3) into two operational modes. In one mode, 
only room thermostat 28 can cause the firing of furnace 44. This mode 
might be appropriate during sleeping hours when potable hot water is not 
required. In the second mode both room thermostat 28 and furnace 
thermostat 50 can fire furnace 44. This mode might be appropriate during 
selected waking hours when potable hot water is required. 
Timed switch 20 can be overridden by manually operable switches 24 and 26 
so that room thermostat 28 and furnace thermostat 50 (FIG. 3) are both 
influential. This feature is useful whenever an occupant may require hot 
water during unscheduled time intervals. 
It is to be appreciated that various modifications may be implemented with 
respect to the above described preferred embodiments. For example, the 
previously illustrated switching devices may be replaced with various 
switching devices such as semiconductor or electromechanical switches. 
Also, various components such as the low voltage transformer may be 
eliminated depending upon the chosen operating potential. It will also be 
appreciated that various types of furnaces can be controlled. Furthermore, 
other timed switches can be employed which may divide a day into two or 
more time zones. In addition numerous components may be substituted for 
those illustrated depending upon the number and type of furnaces, room 
thermostats, aquastats and depending upon the desired speed, power 
handling capacity, etc. 
Obviously, many modifications and variations of the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described.