Note: Descriptions are shown in the official language in which they were submitted.
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DZTHOD AND APPARATQS FOR RBGIILATING HEATBR
CYCLSS TO IMPROVE FOEL SFFICISNCY
FI$LD OF INVSNTION
The present invention relates to a method and apparatus for improving
heating system efficiency, particularly in heating systems which utilize a
boiler to heat a fluid such as water or steam for transfer of heat via a
heat exchanger to a space to be heated.
BACKGROUND OF INVSNTION
Heating systems utilizing burners and boilers are at their least efficient
when starting up. Prior to achieving operating temperature, the burner burns
less cleanly. Heating systems generally operate at their peak efficiency
when they are fully loaded. But heating systems generally are sized for the
area to be heated in such a fashion that the only time the boiler is
properly matched to the heating load is when the outside temperature is the
value for which the system was designed for. A system is usually sized for
the worst case temperature conditions as expected in a given geographic
area. The net effect of this is that whenever the outside temperature
exceeds this design temperature, the boiler is oversized for the heating
load and is thus less efficient. Evidence of this is the cycling on and off
of the burner which heats the boiler.
Boilers have, as part of their inherent design, a heating media which is
transferred throughout the heating load as a means of transferring the heat
and subsequently heating the area. This heating media has a mass which
retains heat even after the boiler shuts down. Various schemes have been
used to take advantage of this thermal inertia to prolong off times and run
times under certain load conditions.
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US Patent 2,266,245, issued 12/16/1941 to Osterheld for an OFF-PEAK WATER
HEATING SYSTEM. It refers to:
" time and water temperature controlled means to cause energization of
the heater at the start of the off-peak period in case less than a
predetermined fractional part of the water content of a tank is hot at
the start of an off-peak period , to delay energization of the heater for
an adjustably predetermined length of time after start of an off-peak
period in case said predetermined fractional part of the water content is
hot at the start of an off-peak period."
US Patent 4,108,375 issued Aug. 22, 1978 to Keeney for a CONTROL DEVICE AND
PROCESS FOR HEATING AN INSTALLATION and refers to comparing "the heating
medium temperature and the temperature outside the installation" and
lowering the "heating medium to the lowest temperature required."
US Patent 4,381,075 issued April 26, 1983 to Cargill et al. And refers to a
MICRPROCESSOR BASED CONTROLLER FOR HEATING SYSTEM for:
"Modulating heat exchanger temperature as a function of outdoor
temperature and, providing an override period for domestic hot water
production."
US Patent 4,637,349 issued Jan. 20, 1987 to Robinson for a BOILER CYCLING
CONTROLLER which refers to "reducing the tendency to cycle" by reducing
boiler flow temperature "as the outside temperature rises". There is a
sensor:
"to override the control system and switch-on the boilers to ensure that
the temperature at which return water enters the boilers does not drop
below a predetermined value."
US Patent 4,850,310 issued Jan. 20 1987 to Wildgen for a BOILER CONTROL
HAVING REDUCED NUMBER OF BOILER SEQUENCES FOR A GIVEN LOAD and purports:
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"To reduce the number of boiler sequences over time the call signal
applied to the boiler to initiate a sequence in response to a demand
for heating is delayed as a function of outside temperature and time
elapsed since the end of the previous heating cycle."
US Patent 5,470,019 issued Nov. 28, 1995 to Martensson for a DEVICE FOR
CONTROLLING HEATING BOILERS which purports to "measure the time between
exceeding of the second temperature level and underpassing of the first
level" and "to delay the start of the heating means" on the next cycle,
after a boiler thermostat call, for a time interval which is a function of
the measured time. The patent refers also to detecting tap water temperature
and stopping the delay below a predetermined tap water temperature.
OBJECTS OF THE INVENTION
The present invention seeks to reduce the number of cycles without measuring
ambient temperatures or measuring or relying on past off times to calculate
delays.
It is an object of the present invention to measure present load and prevent
burner firing until the present load justifies firing the burner. It is an
object to utilize the thermal mass of the heating media, which retains heat
even after the boiler shuts down. The utilization of this retained heat in
conjunction with more efficient burn cycles by the invention is what causes
the fuel savings of the present invention.
BRIEF DESCRIPTION OF THE INVENTION
The.invention is a microprocessor controlled device which, when properly
connected to a gas or oil fueled hot water or steam boiler will render the
effect of more fuel efficiency (because of less total burner on time) which
correlates directly to fuel, energy and money savings. An added side benefit
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of the invention is the reduced electrical usage as well as reduced
maintenance costs due to fewer burn cycles and less total "on" time of the
boiler's burner.
Experimentation has shown that by extending the "off" time of the burner
even after called to start will result in a longer "on" time per "on" cycle
but the total number of "on" cycles is reduced. By example if a burner was
cycling "off" for 60 minutes and then "on" for 12 minutes this would result
in a total number of "runs" of 10 and a total "on" time of 120 minutes in a
12 hour period. If we then employed the invention device, the "off" cycle
time might change to 80 minutes with an "on" time of 14 minutes. This when
extended out to a 12 hour period would yield a total number of run cycles of
7.7 with a total "on" time of 107.8 minutes. This is an 11.2%- reduction in
actual fuel and electrical consumption associated with the burner and also a
23k reduction in the number of burner "on" cycles.
For Hot Water Boiler applications the invention intercepts and interrupts
the signal sent by the boiler's built-in thermostat, which activates the
burner. For safety reasons the boiler's bu.ilt-in thermostat is never
overridden by the invention, it is simply interrupted. The boiler thermostat
is still responsible for the maximum temperature setting of the boiler. The
invention determines the optimum instance of allowing the electrical path to
be completed and subsequent starting of the boiler's burner, by taking a
temperature reading (by invention sensors located as close as possible to
the discharge of the boiler and/or domestic hot water heating coil) at the
instant of a "call for heat" by the boiler thermostat, and storing these
readings in the invention. These stored readings are compared to those of
subsequent temperature readings via the same sensor(s). When the desired
amount of difference (user adjustable) between either of the temperature
readings, as compared to its corresponding stored value, is surpassed the
electrical circuit will be completed. The temperature sensors also perform
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the task of monitoring the heating media temperature and or domestic water
temperatures and will override the "temperature differential" determination
(and complete the burner circuit) when a user adjustable absolute minimum
value is reached. For system flexibility the temperature sensor(s) may be
replaced or run in parallel with a pressure dependent switch or thermostat
or any other means by which the sensor signal leads are electrically shorted
when the desired minimum temperature is reached. The number of sensors is
determined by the particular installation and depends on the application.
(i.e. Heating only, Heating and Domestic hot water generation, or Domestic
Hot Water generation only.)
For Steam Boiler applications the invention intercepts and interrupts the
signal sent by the boiler's built-in pressuretroll and/or domestic hot water
thermostat which activates the burner. For safety reasons the boiler's
built-in pressuretroll/thermostat is never overridden by the invention, it
is simply interrupted. The boiler pressuretroll is still responsible for the
maximum pressure setting of the boiler and domestic hot water thermostat the
maximum water temperature. The invention determines the optimum instance of
allowing the electrical path to be completed and subsequent starting of the
boiler's burner, by taking a pressure/temperature reading (by invention
sensors located as close as possible to the discharge of the boiler and/or
domestic hot water heating coil) at the instant of a "call for heat" by
either the boiler pressuretroll or hot water thermostat, and storing these
readings in the invention. These stored readings are compared to those of
subsequent pressure/temperature readings via the same sensor(s). When the
desired amount of difference (user adjustable) between either of the
pressure or temperature readings, as compared to its corresponding stored
value, is surpassed the electrical circuit will be completed. The invention
sensors also perform the task of monitoring the heating media pressure and
or domestic water temperature and will override the "pressure/temperature
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differential" determination (and complete the burner circuit) when a user
adjustable absolute minimum value is reached. For system flexibility the
pressure/temperature sensor(s) may be replaced or run in parallel with a
pressure dependent switch, thermostat, pressuretroll or any other means by
which the sensor signal leads are electrically shorted when the desired
minimum pressure is reached. The number of sensors is determined by the
particular installation and depends on the application. (i.e. Heating only,
Heating and Domestic.
BRIEF DESCRIPTION OF TFIS DRAWINGS
Fig 1 is a system diagram showing the invention installed in a heating
system.
Fig. 2 is a circuit diagram showing the invention installed in a boiler
burner circuit.
Fig. 3 is a circuit diagram of the control circuit of the invention.
Fig. 4 is a set of graphs correlating various system temperatures, without
and with the invention operating.
DBTAILSD DSSCRIPTION OF TH8 DRANIN(iS
As shown in Fig.1, a heating system, generally designated 2, is designed to
heat a space 4. The system includes a boiler 6. Boiler 6 is fired by burner
8 for heating the boiler. The term boiler is conventionally used, whether or
not the boiler actually boils water as in steam heat, or merely heats water
as in forced hot water heating.
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Flame 10 from burner 8 heats the internal walls 14, or heat exchange tubes
not shown , of boiler 6, which contains fluid heat transfer medium 16 such
as water or steam, which delivers heat through an outflow line 17
communicating fluid heat transfer medium 16 to heat exchanger, such as
radiator 18. Heat exchanger or radiator 18 is usually located remote from
the boiler in space 4. Radiator 18 transfers heat to space 4.
Domestic hot tap water is created by passing cold water from the domestic
water supply 19A through coil 19B which absorbs heat from fluid heat
transfer medium 16 and outflows through domestic hot water outflow pipe
19C, when demanded, as by hot water tap 19D.
In a forced hot water heating system the cooled water from radiator 18
returns via return pipe 22 and is pumped by circulator pump 24 back to
boiler 6.
In a steam system the steam pressure within the boiler drives the steam
through the outflow pipe 20 to radiator 18, where it re-cools to water and
drains back via return pipe 22 to boiler 6.
Some steam systems have no return pipe. The cooled water returns by draining
back down outflow pipe 20.
Energy value sensor 26 is a thermostat in a forced hot water system or is a
pressuretrol in a steam system. Energy value sensor 26 is within boiler 6
and senses a low energy, either temperature or steam pressure, at which
boiler 6 requires more heat.
Conventionally the sensor 26 would switch on electrical power from power
supply 27 which would supply and fire burner 8 to ignite the oil or gas and
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air mixture that burns and heats boiler 6 at said low energy until the
sensor 26 senses a maximum energy, and terminates firing at or above the
maximum energy,
In the present invention, however, a control circuit 28 is interposed
between sensor 26 and burner 8 along wires 30 and 34. Control circuit 28
accomplishes the following steps:
sensing a firing signal on wire 30 from the boiler energy value sensor
26; and
preventing the boiler energy value sensor 26 from firing burner 8 by
interrupting the power. Control circuit 28 opens the circuit from sensor
26, switching the power to burner 8 off.
Meanwhile, on outflow pipe 20, and located at the outflow of the boiler, is
means 38 for sensing an energy value of the outflow at the boiler. This
outflow energy sensor means 38 should be a sensor capable of sending a
signal usable by an electronic circuit. In a hot water system, the energy
value is temperature. There are various usable temperature transducers such
as a thermocouple, but the applicant presently prefers a thermistor mounted
at the boiler outflow. By using a negative energy value coefficient
thermistor, said thermistor has an inherent non-linearity, with greater
voltage drops at lower temperatures, which non-linearity serves as means for
a control program to respond linearly to thermistor voltage while having
non-linear and increased sensitivity to smaller temperature decreases at
lower temperatures.
If a linear energy sensor is used, the control program can logically induce
non-linearity, making the system quicker to fire in response to lower energy
drops at lower temperatures.
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In a steam system, the outflow energy sensor means 38 is a pressure sensor.
Outflow energy sensor 38 senses an energy value of the outflow line 20 at
boiler 6. Outflow energy sensor 39 senses an energy value of the domestic
hot water outflow line 19C at'boiler 6. Control circuit 28 continuously, or
at frequent intervals, monitors the outflow energy values at sensors 38 and
39 . Control circuit 28 records the outflow energy values at a first time of
the firing signal. When either sensor 38 or 39 communicates a sufficient
voltage drop, below the value at the first time of the firing signal, to
control circuit 28, circuit 28 allows the burner to fire. In installations
where the boiler does not supply domestic hot water, domestic hot water
cLt__tw sensor 39 will not be provided or sensed or monitcred by the contrc:
Fig. 4 illustrates an outflow energy value over time without using the
present invention 40, and illustrates an outflow eneray value over time
usin? =he present invention 42. Without the invention, boiler temperature
causes thermostat 26 (Fia. :) to turn off burner 8 at ?80 F and turr. ::n
bur-er 3 at 170 F. In fig. 4 at time TO the boiler has -ust shut off and
..._?re 44 decavs slowly because the water remains still inside t:e boiler. it
._ ::~om =emperature 45 has fallen to a lower limit 68 F and space thermost-a:
50 1) calls for circulator pump 24 by supplying power tc it via wire
c-... :.zol water from heat exchanger 18 is forced by pump 24 into boiler ~.
The water temperature in boiler 6 begins to drop as shown 44 between T1 and
TZ :.. Fig.4. At T2 the boiler thermostat detects 170 F and fires the burner
whic: zerminates quickly at T3 when the boiler again reaches 180 F. By 76
enouga hot water has been forced out of the boiler 6(Fig.l) by circulator
pump 24 and through radiator 18 to heat space 4 to thermostat 50's upper
72 F in fig 4. Thermostat 50 stops the circulator pumn 24 which
reduces boiler load and cycling between T6 (Fig.4) and T7. But notice hcw
SUBSTITUTE SHEET (RULE 26)
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many boiler cycles 60 occur between T2 and T6. Each of these cycles has a
start-up period
of inefficient burning and greater air pollution.
Contrast now the performance graphs WlTH INVENTION in Fig.4. At T1 room
temperature
45 causes room thermostat 50 (Fig. 1) to call for water circulation, pump 24
pumping hot
water 16 from boiler 6 outflow pipe 20 past thermistor 38 which reads outflow
temperature
42 (Fig.4) as a voltage. The hot outflow causes outflow temperature 42 to rise
towards
boiler temperature between T1 and T2. Eventually cool water from radiator 18
(fig.1) re-
enters boiler 6 and boiler temperature 62 (fig. 4) drops to 170 F at T2.
As shown in Fig. 2 control circuit 28 interrupts the power supply from boiler
thermostat 26 to
burner 8, and serves as means for preventing the boiler energy value sensor
(boiler
thermostat 26) from firing the boiler, including a break 47 in a power supply
wire 48
between:
energy value sensor 26 within boiler 6 (Fig. 1), and
the burner 8 (Fig. 1 & 2); and
means 74 (Fig. 3) for switchably bridging said break.
But voltage on hot wire 30 (Figs. 2 & 3) is sensed in Fig. 3 by switch means
for actuation by
a voltage on the hot wire, which switch means is an electronic circuit capable
of a wide
range of voltage inputs, preferably optoisolator circuit 70. The wide range of
voltage inputs
is between 24 VAC and 240 VAC, which copes with any heating system power
supply
known to the inventor throughout the world.
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Circuit 28 (Figs. 2 & 3) monitors outflow temperature 42 (Fig. 4) and records
the outflow
temperature at T2 when the optoisolator detects the boiler call. Circuit 28
(Figs. 1, 2 & 3)
continues to monitor outflow temperature. When circuit 28 detects a change of
a
predetermined outflow energy value, ie. A temperature drop 42 (fig 4.) between
T2 and T3
reflected by a voltage drop across thermistor 38 (Figs. 1, 2 & 3), said change
being an
energy drop from the outflow energy value at the first time of the firing
signal, circuit 28
responds to the change by de-energizing relay 74 (Fig. 3) to its normally
closed condition,
and thereby supplying power to fire the burner. (Since relay 74 is normally
closed, a failure
in the invention will result in normal operation of heating system 2 of Fig.
1.)
Because the required change in outfiow temperature caused the boiler
temperature to fall to
160 F, the burner must remain on longer to reach its upper limit of 180 F.
This results in
fewer burner cycles 80 (fig.4) between T2 and T6. By eliminating the waste of
many start-
ups, the invention achieves the same room temperature 45 with less burner time
80,
greater efficiency, and less air pollution.
When the system has been shut off long enough to allow the boiier or hot water
coil to
reach ambient temperature, the outflow energy value will not drop from the
initial value at
the burner firing signal. The burner would never fire. Thus, to enable an
initial start-up, the
invention provides for a lowest limit to the energy outflow sensors, at which
lowest limits a
boiler thermostat call will result in immediate burner firing.
It can be seen that, by reacting to the outflow energy drop, the invention
reacts to the
present thermal load on the heating system. The invention adapts itself to
load changes
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immediately. Therefore, it can be said that the invention serves as self
adaptive means for
reacting to immediate load changes to avoid reaching a boiler energy value low
limit.
