Note: Descriptions are shown in the official language in which they were submitted.
CA 02944656 2016-10-06
MULTIPLE STAGE MODULATING GAS FIRED HEAT EXCHANGER
TECHNICAL FIELD
[0001] This application is directed, in general, to heating systems such as
furnaces and more
specifically to controlling the operation of the heating systems.
BACKGROUND
[0002] This section provides background information to facilitate a better
understanding of the
various aspects of the disclosure. It should be understood that the statements
in this section of
this document are to be read in this light, and not as admissions of prior
art.
[0003] HVAC systems can be used to regulate the environment within an
enclosure. Typically,
a circulating fan is used to pull air from the enclosure into the HVAC system
through ducts and
push the air back into the enclosure through additional ducts after
conditioning the air (e.g.,
heating or cooling the air). For example, a gas furnace, such as a residential
gas furnace, is used
in a heating system to heat the air. Some gas furnaces are modulating or two-
stage gas furnaces
that can operate at different input rates compared to a single stage furnace
that only operates at
one gas input, i.e., full heating input. The modulating furnaces can operate
more efficiently
compared to conventional single stage furnaces and reduce energy costs.
SUMMARY
[0004] A modulating heating system according to aspects of the disclosure
includes a tube heat
exchanger having a plurality of burners, a combustion air blower (CAB) having
an exhaust vent
connected with the plurality of burners, the CAB operable at a first speed and
a second speed, a
first valve connecting a fuel source to a first subset of the plurality of
burners, and a second valve
1
connecting a fuel source to a second subset of the plurality of burners,
wherein the first and second
valves each have a low fire rate and a high fire rate and the heat exchanger
is operable through multiple
heat stages at a constant fuel-air mixture at each burner.
[0005] In accordance to aspects a heating system has a heat exchanger
comprising burners to burn a
combustible fuel-air mixture, a combustion air blower (CAB) operable at a low
speed and a high speed
to supply air to the burners, a first subset of the burners connected to a
fuel source through a first valve,
a second subset of the burners connected to the fuel source through a second
valve, wherein the first
valve and the second valve each have an off position, a low fire rate, and a
high fire rate, and the burners
operable in a low fire mode at the low speed and the low fire rate and
operable in a high fire mode at the
high speed and the high fire rate and the heat exchanger is operable through
multiple heat stages.
According to an aspect of the present invention, there is provided a heating
system, comprising:
a heat exchanger comprising burners configured to burn a combustible fuel-air
mixture;
a combustion air blower (CAB) operable at a low speed and a high speed to
supply air to the
burners;
a first subset of the burners connected to a fuel source through a first
valve;
a second subset of the burners connected to the fuel source through a second
valve,
wherein the first valve and the second valve each have an off position, a low
fire rate, and a
high fire rate; and
wherein the burners are configured to operate in a low fire mode at the low
speed and the low
fire rate and operated in a high fire mode at the high speed and the high fire
rate and the heat
exchanger is operable through multiple heat stages.
2
Date Recue/Date Received 2021-10-15
According to another aspect of the present invention, there is provided a
heating system,
comprising:
a tube heat exchanger comprising a plurality of burners;
a combustion air blower (CAB) having an exhaust vent connected with the
plurality of
burners, the CAB operable at a first speed and a second speed;
a first valve connecting a fuel source to a first subset of the plurality of
burners;
a second valve connecting a fuel source to a second subset of the plurality of
burners,
wherein the first and second valves each have a low fire rate and a high fire
rate; and
an electronic controller in connection with the CAB, the first valve and the
second valve, the
electronic controller configured to operate the heat exchanger through
multiple heat stages at
constant fuel-air mixture.
According to another aspect of the present invention, there is provided a
method, comprising:
modulating a gas-fired heat exchanger of a heating system through multiple
heat stages while
maintaining a constant gas-air ratio, wherein the heating system comprises:
the heat exchanger having burners;
a combustion air blower (CAB) having an exhaust vent connected with the
burners, the CAB
operable at a first speed and a second speed;
a first valve connecting a fuel source to a first subset of the burners; and
a second valve connecting a fuel source to a second subset of the burners,
wherein the first
and second valves each have a low fire rate and a high fire rate.
2a
Date Recue/Date Received 2021-10-15
[0006] This summary is provided to introduce a selection of concepts that are
further described below
in the detailed description. This summary is not intended to identify key or
essential features of the
claimed subject matter, nor is it intended to be used as an aid in limiting
the scope of claimed subject
matter.
2b
Date Recue/Date Received 2021-10-15
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BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The disclosure is best understood from the following detailed
description when read with
the accompanying figures. It is emphasized that, in accordance with standard
practice in the
industry, various features are not drawn to scale. In fact, the dimensions of
various features may
be arbitrarily increased or reduced for clarity of discussion.
[0008] Figure 1 is a diagram of a modulating heating system according to one
or more aspects of
the disclosure.
[0009] Figure 2 illustrates an interface with a gas fired heat exchanger
according to one or more
aspects of the disclosure.
[0010] Figure 3 is a graph illustrating a tunable staged modulating gas fired
heat exchanger in
accordance to one or more embodiments.
[0011] Figure 4 illustrates a retrofit or field conversion kit for converting
a gas fired heat
exchanger to a modulating gas fired heat exchanger according to one or more
aspects of the
disclosure.
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DETAILED DESCRIPTION
[0012] It is to be understood that the following disclosure provides many
different embodiments,
or examples, for implementing different features of various embodiments.
Specific examples of
components and arrangements are described below to simplify the disclosure.
These are, of
course, merely examples and are not intended to be limiting. In addition, the
disclosure may
repeat reference numerals and/or letters in the various examples. This
repetition is for the
purposc of simplicity and clarity and does not in itself dictate a
relationship between the various
embodiments and/or configurations discussed.
[0013] Figure 1 is a diagram of an embodiment of a heating unit or system,
generally denoted by
the numeral 10, in accordance to embodiments of the disclosure. The heating
system 10 is for
example a gas fired combustible fuel-air burning furnace. The furnace may be
for a residence or
for a commercial building (i.e., a residential or commercial unit), for
example a rooftop unit
(RTU). In accordance to an embodiment, heating system 10 is a two-stage
furnace having a two-
stage control that has been retrofitted, or upgraded, to be a multiple staged
modulated system.
[00141 Heating system 10 includes a burner assembly 12 having a plurality of
burners 14, a heat
exchanger 16, an air circulation fan 18, a combustion air inducer or
combustion air blower
(CAB) 20, a first gas valve 22, and a second gas valve 24, and a furnace
controller 26. The
furnace controller 26 is operationally connected for example to CAB 20, gas
valves 22 and 24, a
thermostat 28 and a discharge air sensor (DAS) 30. The heating system may be
utilized in single
or multiple zoned systems. Portions of the heating system 10 may be contained
within a cabinet
32. In some embodiments, the furnace controller may be included in the
cabinet. One skilled in
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the art will with benefit of this disclosure will understand that the heating
system may include
additional components and devices that are not presently illustrated or
discussed.
[0015] The burner assembly 12 includes a plurality of burners 14 that are
configured for burning
a combustible fuel-air mixture (e.g., gas-air mixture) and to provide a
combustion product to the
heat exchanger 16. The heat exchanger includes tubes 17, for example a tube
corresponding to
each burner. The heat exchanger 16 is configured to receive the combustion
product from the
burner assembly and use the combustion product to heat air that is blown
across the heat
exchanger by the circulation fan 18. The circulation fan 18 is configured to
circulate air through
the cabinet 32, whereby the circulated air is heated by the heat exchanger and
supplied to the
conditioned space. The CAB 20 is configured to supply combustion air to the
burner assembly
12 (i.e., the plurality of burners 14) by an induced draft and is also used to
exhaust waste
products of combustion from the furnace through a vent 34. In accordance to
aspects of the
disclosure the CAB 20 is operable at two speed settings, low speed and high
speed,
corresponding to two modes of operation of the burners, low fire and high
fire. The CAB 20 is
configured so that the low speed and the high speed correspond respectively to
the low fire gas
rate and the high fire gas rate to provide gas-fuel mixture for the low fire
and high fire modes of
the heat exchanger. In accordance to embodiments, the fuel-air mixture is
constant through the
multiple heating stages.
[0016] With additional reference to Figure 2, the burners 14 are separated
into subsets of a
burners and each subset of burners is connected to a fuel source 40, i.e.,
gas, through a respective
gas valve ("GV"). It may be said that the heat exchanger is divided into
subsets utilizing a
common CAB with each subset of the heat exchanger connected to the fuel source
or supply
CA 02944656 2016-10-06
through a respective gas valve. For example, with reference to Figures 1 and 2
the burners 14 of
the heat exchanger are separated into a first subset 36 and a second subset
38. The first subset 36
of burners 14 is connected to the fuel source 40 through the first gas valve
22 and the second
subset 38 of burners is connected to the fuel source 40 through the second gas
valve 24. The
burner assembly may include a manifold 42 connected directly to the burners
for supplying the
fuel 40 to more than one burner at a time. The manifold 42 can include a block
44, i.e., plug, to
separate the burners into subsets. For example in Figure 2 the plug 44
separates the manifold
into a first section 42a and a second section 42b. The fuel supply 40 is
connected through the
first gas valve 22 to the first section 42a and the first subset 36 of burners
and connected through
the second gas valve 24 to the second section 42b and the second subset 38 of
burners.
[0017] In accordance to aspects of the disclosure the first and second gas
valves are each
operable to an off position blocking gas flow, a low fire rate allowing a
first flow rate of gas to
be input to the burners, and a high fire rate allowing a second flow rate of
gas to be input to the
burners, i.e., two-stage valves. In accordance to aspects, the gas input per
burner both on low
fire and high fire remains about the same as current eighty-one percent annual
fuel utilization
efficient (AFUE) products. When a burner is in a low fire mode the respective
gas valve is at the
low fire rate and the CAB 20 (FIG. 1) is on the low speed and when the burner
is in a high fire
mode the respective gas valve is at the high fire rate and the CAB is at the
high fire rate.
[0018] The modulated heating system 10 utilizes burners 14 connected through a
common vent
34 of the CAB 20. The heating system 10 can be modulated through multiple heat
input stages
while supplying a constant fuel-air ratio to the burners through all the
heating stages or steps.
Accordingly, the heating system is not modulated by changing the fuel-air
ratio and the system
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does not utilize complicated variable speed induced blowers and/or variable
pressure gas
regulators, also referred to as modulating gas valves. These typical
modulating heating systems
require complicated software and expensive controls that are required to
maintain air-fuel ratios
in certain ranges. If air-fuel ratios are not properly controlled this can
result in reduction of heat
exchanger thermal efficiency, excessive heat exchanger corrosion, difficulty
in lighting and the
formation of toxic combustion flue products that contain high levels of carbon
monoxide.
Utilizing two gas valves and two subsets of burners the heating system can be
modulated through
six stages. Subsequently adding a third gas valve and an additional subset of
burners can be
modulated through 10 discrete steps or stages of gas heat input. The gas
valves 22, 24 and their
respective subsets of burners are operated in parallel providing increased
reliability. For
example, if one gas valve fails the other gas valve can still be operated.
Further, the modulating
does not utilize variable pressure modulating gas valves.
[0019] The first and second subsets 36, 38 have different numbers of burners
as will be
understood by those skilled in the art with benefit of this disclosure. For
example, in Figure 2
the first subset 36 includes two burners and the second subset 38 includes
five burners. As will
be understood by those skilled in the art with benefit of this disclosure, the
ratio of burners to gas
valve can be adjusted to change the discrete control of the heating system. As
further disclosed
below, the heating system 10 can be modulated for example up to six stages
utilizing two subsets
and two gas valves or ten stages by adding another subset of burners and
another gas valve. In
accordance to an embodiment, a modulated heating system 10 can achieve a turn
down ratio of
five to one (5:1). The turndown ratio is the operation range of system, for
example the ratio of
the maximum output to the minimum output. In accordance to one or more
embodiments the
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turndown ratio of modulated heating system 10 is about 7.5 to one. The heating
system 10 can
be configured with more than two subsets of burners each with a respective gas
valve and
utilizing a common CAB and vent, which will increase the number of available
stages and
increase the turn-down ratio. Burner subsets and numbers of burners assigned
on each subset are
optimized with the number of input stage so each discrete gas input stages
provides close to
equal heating increments as possible, to prevent overheating the discharge
air.
[0020] The first and second gas valves 22, 24 are described above as single
two-stage valves.
however, it should be recognized that each of the gas valves 22, 24 may
include a first and
second single stage valve without departing from the scope of this disclosure.
For example, the
first gas valve 22 may include a low fire valve and a high fire valve. In
response to a low fire
rate signal the low fire valve would open and in response to a high fire rate
signal both the low
fire and the high fire valves would open.
[0021] The ignition system includes one or more ignition switches or
controllers denoted
generally with the numeral 43, one or more ignitors denoted generally with the
numeral 45 and
one or more flame sensors generally denoted with the numeral 47. Figure 2
depicts a system
having a first ignition controller 45a, a first ignitor 45a and first flame
sensor 45a located with
the first subset of burners and a second ignition controller 43b, a second
ignitor 45b and a second
flame sensor 47b located with the second subset of burners. The system can
transition up and
down the gas inputs with essentially zero lag between the stages as long as
one stage remains lit.
Transition from one set of burner subsets to another occurs using flame carry
over from the lit
burners to the un-lit burners, this happens very quickly as the flame speed is
in excess of 20 cm/s
with almost no delay.
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[0022] In accordance to some embodiments a lighting or ignition sequence
includes a single
ignition controller, e.g., ignition controller 43a, used with a single flame
sensor, e.g. sensor 47a,
and a single flame ignitor, e.g., flame ignitor 45b, either spark or hot
surface. The unit controller
26 has a pre-programed ignition sequence that includes fully energizing all
the burner subsets so
that ignition is created at one extreme end, i.e., at flame ignitor 45b, of
the gas manifold and the
flame is confirmed to be present by the use of a flame sensor, i.e., sensor
47a, at the other
extreme end of the gas manifold. The flame sensor will be located at the stage
one-gas input or
the input step with the lowest burner count. When there is a heat demand for
the first time in a
heating cycle the controller will energize all the burner sub-sets and the gas
valves in order to
prove that there is a continuous flame path from the flame ignitor to the
flame sensor.
Immediately after the flame is sensed the other gas valve(s) associated with
gas delivery to the
other burner-subset(s) will be de-energized. At this point the system will
respond to demand
signals as shown in Figure 3, staging up as tl, t2 timers and the thermostat
signals WI and W2
deem necessary. If the thermostat transitions from W2 back to W1 the unit will
start back at the
lowest heat input to prevent overheating the occupied space and to prevent the
thermostat
demand from cycling off directly after W2. The purpose of the control circuit
is to increase the
amount of time the burners are on so that the system can effectively respond
instantly to a
thermostat demand for additional heat.
[0023] In accordance to another embodiment, dedicated ignition controllers 43a
and 43b are
associated with each burner subset. The dedicated ignition controllers 43a and
43b communicate
with respective single dedicated flame ignitors 45a and 45b and single
dedicated flame sensors
47a and 47b. The each ignition system then independently controls the gas
valve that feeds fuel
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to each of the burner subsets. Each ignition controller would be responsible
to produce a spark,
flame and prove the flame from one end of the burner subset to the opposite
end of burner
subset.
[0024] Operation of a heating system 10 through multiple operational, or
heating, stages is now
described with reference to Tables 1 and 2 below. The heating system 10
described with
reference to Table 1 includes seven burners 14 connected through a single CAB
20 to a common
vent 34. The first subset 36 of burners includes two burners 14 connected to a
first gas valve 22
(GV1) and the second subset 38 includes five burners connected through a
second gas valve 24
(GV2). One skilled in the art with benefit of this disclosure will recognize
that although six
stages are available, the system may be implemented (e.g., via controller 26)
to utilize less than
six stages, for example four stages.
[0025]
TABLE 1
First Subset 36 Second Subset 38
Heat % of CAB GV1 GV I GV2 GV2 GV2 GV2 GV2
Stage Input Burner Burner Burner Burner Burner Burner Burner
1 2 1 2 3 4 5
1 20 Low Low Low
2 29 High High High
3 54 Low Low Low Low Low Low
4 71 High High High High High High
75 Low Low Low Low Low Low Low Low
6 100 High High High High High High High High
[0026] As shown in Table 1 the heating system may be operated through six
stages, for example
by the controller 26, in responses to heat calls. In stage 1 the first subset
of burners are in the
low fire mode and the second subset of burners are off. In the second stage
the first subset of
CA 02944656 2016-10-06
burners are in the high fire mode and the second subset of burners are off. In
the third stage the
first subset of burners are off and the second subset of burners are in the
low fire mode. In the
fourth stage the first subset of burners are off and the second subset of
burners are in the high fire
mode. In the fifth stage the first subset of burners are in the low fire mode
and the second subset
of burners are in thc low fire mode. In the sixth stage the first subset of
burners are in the high
fire mode and the second subset of burners are in the high fire mode.
[0027]
TABLE 2
Heat GV 1 GV2 Burners Burners Input Input Total
Firing
Stage Input/Burner Input/Burner GV1 GV2 GV1 GV2 Input Rate
(1,000 (1,000 (1,000 (1,000 (1,000 (%
of
BTU/hr) BTU/hr)
BTU/hr) BTU/hr) BTU/hr) Input)
1 15 0 2 5 30 0 30 20
2 20 0 2 5 40 0 40 29
3 0 15 2 5 0 75 75 54
4 0 20 2 5 0 100 100 71
15 16 2 5 30 75 105 75
6 20 20 2 5 40 100 140 100
[0028] Table 2 illustrates calculation of the firing rate of the heating
system for each stage. The
second column of Table 1 and the last column of Table 2 show that the heating
system achieves a
turndown ratio of about 5:1 or about 20 percent of input. The gas orifice size
on the lesser heat
input may be tuned to compensate for any change to CAB flow characteristics
when operating at
a lower flue temperature and this may result in a different turndown ratio.
Table 1 indicates an
eighty-one percent (81%) AFUE at the lowest input condition of stage 1, with
two burners
operating at a twenty-one percent (21%) input rate (BTU/hr.).
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[0029] Table 3 below illustrates the firing rate for stages of a heating
system having five burners
14, i.e., a five tube heat exchanger, connected through a common vent and
separated into two
subsets of burners. In this example the first subset 36 includes two burners
14 connected through
a first gas valve 22 (GV1) and a second subset 38 of three burners 14
connected through a
second gas valve 24 (GV2). This five burner arrangement achieves a turndown
ratio to about
3:1.
[0030]
TABLE 3
Heat GV1 GV2
Burners Burners Input Input Total Firing
Stage Input/Burner Input/Burner GV1 GV2 GV1 GV2 Input Rate
(1,000 (1,000 (1,000 (1,000
(1,000 (% of
BTU/hr) BTU/hr)
BTU/hr) BTU/hr) BTU/hr) Input) _
1 15 0 2 3 30 0 30 33
2 20 0 2 3 40 0 40 40
3 0 15 2 3 0 45 45 45
4 0 20 2 3 0 60 60 60
15 16 2 3 30 45 75 75
6 20 20 2 3 40 60 170 100
[0031] Table 4 below illustrates the firing rate for stages of a heating
system 10 having eleven
burners 14, i.e., eleven tube heat exchanger, connected through a common vent
and separated
into two subsets of burners. In this example the first subset includes three
burners connected
through a first gas valve (GV1) and a second subset of eight burners connected
through a second
gas valve (GV2). Similar to the seven burner system of Tables 1 and 2, the
eleven burner
arrangement in Table 3 achieves a turndown ratio of about 5:1.
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[0032]
TABLE 4
Heat GV1 GV2
Burners Burners Input Input Total Firing
Stage Input/Burner Input/Burner GV1 GV2 GV1 GV2 Input Rate
(1,000 (1,000 (1,000 (1,000
(1,000 (% of
BTU/hr) BTU/hr)
BTU/hr) BTU/hr) BTU/hr) Input)
1 15 0 3 8 45 0 45 20
2 20 0 3 8 60 0 60 27
3 0 15 3 8 0 120 120 55
4 _______ 0 20 3 8 0 160 160 73 _
15 15 3 8 45 120 , 165 75
6 20 20 3 8 60 160 220 100
[0033] Most commercial thermostats are only available with two-stage gas
heating stages. The
majority of the gas heating products are sized around peak periods of the year
where maximum
heat input is required. The means that under a large portion of the heating
season the products
are cycled more frequently and high discharge air temperatures can create
issues with the
comfort of the conditioned space. The heating system 10 has a control system
that is capable of
allowing users the benefits of a four stage step modulated heating system. The
control is
comprised of timers, see, e.g., electronics 50 (FIG. 4), that will allow the
unit to stage up to the
next available heat increment based on the amount of time that the thermostat
delivers a heating
demand. The system allows users to operate a series of adjustable timers that
allow installers to
tune the delay before the system stages up to the next available heat input
level. This will allow
the system to match the heat-load of the occupied space and provide better
comfort than typical
2-stage systems that tend to overheat the discharge air and create large
temperature swings in the
conditioned space. Timers also function in reverse order and will allow the
unit to stage down
from a higher input to a lower input as required. Any time the thermostat
delivers a call for high-
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heat the system will start at stage 3 and will cycle to stage 4 after timer t3
has expired. Figure 3
is a graph illustrating the benefits of a tunable staged modulating heating
system 10 (i.e., gas
fired heat exchanger), wherein "WI " is a first heating call (low heat demand)
and "W2" is a
second heating call (high heat demand). Figure 3 illustrates four heating
stages utilizing a
heating system 10 as described for example with reference to Tables 2-4.
[0034] Table 5 below illustrates the firing rate for stages of a heating
system 10 having eleven
burners 14, i.e., eleven tube heat exchanger, connected through a common vent
and separated
into two subsets of burners. In this example the first subset 36 includes two
burners connected
through a first gas valve 22 (GV1) and a second subset of nine burners
connected through a
second gas valve (GV2). This arrangement indicates a low stage firing rate of
about fourteen
percent (14%) and a turndown ratio of about 7.5:1.
TABLE 5
Heat GV1 GV2 Burners Burners Input Input Total Firing
Stage Input/Burner Input/Burner GV1 GV2 GV1 GV2 Input Rate
(1,000 (1,000 (1,000 (1,000 (1,000 (%
of
BTU/hr) BTU/hr)
BTU/hr) BTU/hr) BTU/hr) Input)
1 15 0 2 9 30 0 30 14
2 20 0 2 9 40 0 40 18
3 0 15 2 9 0 135 135 61
4 0 20 2 9 0 180 180 82
15 15 2 9 30 135 165 75
6 20 20 2 9 40 180 220 100
[0035] The furnace controller 26 is configured to control the operation of the
heating system 10
including the combustion air blower 20 and the circulation fan 18,
respectively. Additionally,
furnace controller controls operation of the gas valves (i.e., valves 22, 23).
As discussed above,
the controller can operate the CAB 20 and the respective gas valves to their
respective low speed
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and low fire rate and high speed and high fire rate to achieve the desired
burner mode (low fire
or high fire) for each operational stage of the heating system 10 without
using look-up tables or
modulating the gas flow rate.
100361 The furnace controller 26 may include a memory section having a series
of operating
instructions stored therein that direct the operation of the furnace
controller 126 (e.g., the
processor) when initiated thereby. The series of operating instructions may
represent algorithms
that are used to prevent or reduce temperature overshooting in the conditioned
space. The
furnace controller 26 also includes or communicates with a delay timer. The
delay timer can be
a conventional clock that can be reset and can be used to keep track of a
designated amount of
time that is used to allow settling of discharge air temperatures. As
illustrated in Figure 1, the
controller 26 is coupled to the DAS 30, the thermostat 28 and components of
the heating system.
The controller 26 may also be connected to other elements and systems, such as
a zone
controller. In some embodiments, the connections are through a wired-
connection. A
conventional cable and contacts may be used to couple the controller to the
various components
of the heating system. In some embodiments, a wireless connection may also be
employed to
provide at least some of the connections.
100371 The DAS 30 is a temperature sensor that is designated and positioned to
determine the
discharge air temperature of the heating system. The DAS 30 may be a
conventional
temperature sensor configured to determine the ambient temperature of the area
where positioned
and provide this temperature data to the controller 26 to use in directing the
operation of the
heating system. In Figure 1, the DAS is located in the cabinet. In other
embodiments, the DAS
can be positioned in other locations to measure the discharge air temperature
of the heating
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system. For example, the DAS can be positioned in a duct between the cabinet
and the
conditioned space. In some embodiments, multiple temperature sensors can be
used and an
average discharge air temperature determined therefrom. The discharge air
sensor 30 can be, for
example, a 10 k Negative Temperature Coefficient (NTC) sensor.
[0038] The thermostat(s) 20 can be a conventional thermostats employed in II
VAC systems that
generate heating calls based on temperature settings. The thermostat is a user
interface that
allows a user to input a desired temperature for a designated area or zone of
the conditioned
space. Thermostat(s) 20 may be a two-stage thermostat. In retrofit
applications the modulating
system is compatible with two-stage thermostats.
10039] Aspects of this disclosure may be utilized for retrofit applications.
For example,
currently it is known for heating, ventilation and air conditioning (HVAC)
systems to be
retrofitted with modulating gas valve controls. The thermal efficiency of the
heat exchanger is
reduced with these retrofitted modulating gas valve controls and should also
require modulating
the CAB to be in AFUE compliance. The tunable modulating system disclosed
herein provides a
mechanism to retrofit current HVAC systems to achieve a higher turndown ratio
while
maintaining AFUE compliance, and providing more discreet heating control. As
described
above the retrofit heating system 10 can be modulated through multiple stages
while maintaining
a constant fuel-air mixture through the stages.
[0040] In accordance to embodiments a field conversion kit may be provided for
retrofitting a
unit, such as a two-stage furnace having a two-stage control, to be a multiple
staged modulated
system. Figure 4 illustrates elements that may be included in a tunable
modulating system
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retrofit kit 46 in accordance to one or more aspects. The retrofit kit 46 may
include, for example,
and without limitation one or more gas valves, generally denoted by the
numeral 48, to be
installed as one or more gas valves 22, 24 in Figure 1, a manifold 42 having a
block 44, and
electronic elements, generally denoted by the numeral 50, for installation in
the unit controller 26
(FIG. 1). The electronics may include various elements such as timers, relays
as well as ignition
controllers and the like. A retrofit kit 46 may include only one two-stage
valve 48 as the heat
exchanger to be upgraded, i.e., retrofitted, may already include one two-stage
gas valve.
[0041] Accordingly, methods are disclosed for retrofitting a heating system to
have a modulating
gas-fired heat exchanger that is operable through multiple heat stages at a
constant fuel-air
mixture, wherein the heating system includes the heat exchanger having
burners, a combustion
air blower (CAB) having an exhaust vent connected with the burners, and a
first valve
connecting a fuel source to the burners, the first valve operable at a low
fire rate and a high fire
rate, and a controller connected to the CAB and the first valve to operate the
burners between a
low fire mode and a high fire mode. In accordance to an embodiment the
retrofitting includes
connecting a first subset of the burners to the fuel source through the first
valve and connecting a
second subset of the burners to the fuel source through a second valve,
wherein the second valve
is operable at the low fire rate and the high fire rate. In accordance to
embodiments, the
controller of the heating system can be connected to the second valve such
that the first gas valve
and the second gas valve can be operated independent and in parallel to
provide for multiple,
e.g., more than two, heat stages that are operated at a constant fuel-air
ratio. The retrofitting may
include reprogramming the controller and or adding electronics 50, such as and
without
limitation, relays and timers.
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[0042] The foregoing outlines features of several embodiments so that those
skilled in the art
may better understand the aspects of the disclosure. Those skilled in the art
should appreciate
that they may readily use the disclosure as a basis for designing or modifying
other processes and
structures for carrying out the same purposes and/or achieving the same
advantages of the
embodiments introduced herein. Those skilled in the art should also realize
that such equivalent
constructions do not depart from the spirit and scope of the disclosure, and
that they may make
various changes, substitutions and alterations herein without departing from
the spirit and scope
of the disclosure. The scope of the invention should be determined only by the
language of the
claims that follow. The term "comprising" within the claims is intended to
mean "including at
least" such that the recited listing of elements in a claim are an open group.
The terms "a," "an"
and other singular terms are intended to include the plural forms thereof
unless specifically
excluded.
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