Note: Descriptions are shown in the official language in which they were submitted.
CA 02777901 2012-06-05
Background of the Invention
Forced air, dual heating systems consisting of a fossil fuel or electric
furnace and a split
air to air heat pump are widely used in colder regions of the continent
especially in
locations where electricity rates are reasonable compared to the cost of
fossil fuel.
= A typical dual heating system for residential use, can consist of a
120.000 BTU mid
efficiency oil or gas furnace and a 36.000 BTU air to air heat pump. When an
electrical
furnace is used the installed capacity is typically an equivalent of 90.000
BTU because of
higher efficiency. Actual heating capacities vary depending on building seize,
heat loss
characteristics and geographical location.
A heat pump is the most efficient heating appliance for heating and cooling an
indoor
,
living space when using forced air. Its capacity requirements for cooling
the living space
= are less when compared to winter heating needs. The installed heat pump
output capacity
in a dual heating configuration is a compromise between summer cooling and
winter
heating needs. Over seizing the heat pump to gain additional heating output
capacity,
results in increased cycling of the heat pump during summer cooling and milder
weather
conditions. This results in degradation of its operating efficiency, as well
as increased
wear and tear on moving parts. A properly seized heat pump typically has
sufficient heat
output capacity to maintain house thermostat daytime set point at outdoor
temperatures
just below freezing point, without supplementary furnace make up heat. The
point when a
heat pump as part of a dual heating system can no longer supply sufficient
heat to
maintain the house thermostat at daytime set point is called "balance point".
Below balance point the indoor temperature slowly decreases. The house
thermostat
detects the temperature drop, disables the heat pump and enables the furnace.
The more
powerful furnace now rapidly raises the house temperature back to daytime set
point,
disables the furnace and again enables the heat pump. As the outdoor
temperature drops
= further below balance point, the heat pump operates for shorter intervals
and the furnace
increasingly longer. When the outdoor temperature reaches a certain low
temperature
point, the heat pump is disabled under control of an electric utility provided
external dry
contact switch or by mean of an outdoor thermostat contact as typically used
for dual heat
With electric furnace. The furnace now takes over the heating process for as
long as the
outdoor temperature remains below the low temperature threshold typically set
between
-10 to -15 C.
CA 02777901 2012-06-05
3
A typical dual heat system consumes most of its annual heating budget when
outdoor
temperatures vary between "balance point" and low temperature heat pump cutoff
point.
The installed furnace heating capacity is derived by calculating the total
worst
case heat loss of the heated space based on regional winter temperature data.
In a dual
heating configuration the furnace spends most of its service life delivering
"make-up"
heat for the heat pump when below "balance point". While the electric furnace
supplies
100% efficient "make-up" heat, the fossil fuel furnace peak output efficiency
is reached
only if heat demand exceeds furnace capacity or during extreme cold days of
winter.
Practically while supplying "make-up" heat, the average operating efficiency
of a fossil
fuel furnace falls far below its rated capacity, making it an inefficient
heating source.
An oil furnace typically has a heat chamber made from cast iron. Each time the
furnace is
enabled it takes several minutes to heat up the heat chamber. During this
time, only
limited heat transfer takes place between the furnace combustion housing and
air flowing
through the furnace. This result in a delayed supply of heat to the indoor
space, resulting
in a slow rise in house temperature at first and accelerating after the
furnace has warmed
up. This sudden intense surge of heat is uncomfortable for its occupants,
especially when
nearby the warm air heat duct registers.
After the furnace has raised the house temperature back to thermostat stage
one, call for
heat the furnace is disabled and the heat pump enabled again. When near
"balance point"
the furnace latent heat buildup of the heat chamber, raises the indoor
temperature further
upwards, quickly satisfying stage one call for heat and disabling the heat
pump only after
a short run time. This unwanted temperature overshoot again contributes to
unwanted
temperature fluctuations causing additional discomfort for its occupants.
After the indoor
space has cooled down, thermostat stage one, call for heat again enables the
heat pump.
When further below "balance point", this latent heat buildup from the furnace
is absorbed
by the heat loss component of the building without raising the indoor
temperature
significantly. Intense, excessive heat produced by a furnace when operating
below its
rated capacity also causes temperature stratification in the heated space.
This occurs
when the excessive warm air pumped through the ductwork and through warm air
registers, rises to the ceiling where the temperature can be 4 to 7 C higher
compared to
floor temperature where heat is needed. This leads to temperature buildup near
the ceiling
resulting in increased heat loss. Excessive heat also contributes to a
reduction in relative
humidity in the heated space further increasing the need for humidification.
The natural gas furnace is more efficient to operate and a preferred choice in
dual heating
systems, mainly because of lower natural gas fuel cost.
The oil furnace remains a preferred option in many urban and rural areas where
no
natural gas distribution network exists and propane gas as a commodity
generally is more
expensive compared to fuel oil.
Most thermostats utilized to control dual heating systems with heat pump, are,
brand name, manual or automatic house thermostats with two stages for heat and
one
stage for cooling and separate E heat output. This type of thermostat is
actually designed
for controlling heating systems that consisting of a heat pump with a heating
coil for
backup or aux. heat as utilized in regions that enjoy temperate winter weather
conditions
where a heat pump with heating coil are sufficient to meet winter heating
needs. Utilizing
this type of thermostat in a dual heating system with oil or gas furnace
without additional
circuitry would result in enabling both heat pump and furnace at the same
during stage
CA 02777901 2012-06-05
4
two call for heat. This is not desirable as it causes damage to the heat pump
among other
undesirable side effects. Therefore a separate fossil fuel kit or equivalent
circuitry is
required to enable the heat pump for stage one and oil or gas furnace for
stage two heat.
This kit also accommodates a low temperature heat pump cutoff and furnace
enable
command either from an external utility load control signal or from the E heat
command.
This adaptor circuit is normally installed near the furnace and acts like a
hub between
house thermostat, heat pump and furnace control wiring. This circuit can be as
basic as
one or two inter wired relays or as elaborate as a small printed circuit board
that includes
additional features such as humidistat control and heat pump alarm options.
Another popular configuration on the market with similar functionality
combines a house
thermostat and fossil fuel kit and consists of a non programmable electronic
thermostat
combined with a user console. It is interconnected with a 3 wire communication
and
power supply wire link to a matching remote interface module sometimes called
"heat pump controller". From the remote module the furnace and heat pump
control
wires, the utility low temperature cutoff as well as temperature sensors and
other features
such as humidifier control and heat pump alarm are connected.
Most automatic thermostat models on the market are not adjustable for
hysteresis or
temperature differential adjustments for stage one or two on/off operation.
Factory
hysteresis setting is typically 1 C for each heating stage. When used in dual
heating with
a fossil fuel furnace the hysteresis range is too tight, resulting in frequent
cycling between
heating appliances, thereby adding to operating inefficiencies, effecting
heating cost,
discomfort as well as increased wear and tear on the heating appliances.
When nighttime thermostat setback is used, some automatic thermostats on the
market
have a feature called Smart Response Technology. It uses past response data to
estimate
the time the heat should be raised to arrive at the desired day time set
point. This allows
the heating system additional time to supply make-up heat to compensate for
higher heat
loss at lower temperatures. Another manufacturer uses ERM. This delay function
allows
the heat pump to run about 6 minutes longer for each 1 F in temperature
differential
between set back and daytime set point temperature before stage two, heat is
enabled.
When used in geographical areas with more extreme cold weather conditions and
where
temperatures can vary dramatically on a daily basis, both techniques are
inadequate
because it does not provide adequate time for the heat pump to raise the
indoor space
temperature to any significant level before the furnace is enabled.
Heat pumps are most efficient at outdoor temperatures well above freezing. As
at outdoor
temperature drops the net heating output capacity of the heat pump is reduced.
This is
called COP or the Coefficient of Performance of a heat pump. It can vary
between
manufactures and models as well as the age of the unit and compares to the
efficiency of
a standard electric heating element. Around the freezing point the COP can be
3 or 300%,
or for every 1KW of electrical power supplied to the heat pump the equivalent
of 3kW of
heat is generated. At -10 C the COP typically has dropped below 2 or 200%. At
balance
point in a dual heating configuration the heat pump can still supply very
efficient heat as
compared to any other heat source. However because it cannot supply sufficient
enough
heat it is disabled.
As the outdoor temperature drops frost buildup on the outdoor coil can occur.
In heating
mode, the outdoor heat exchanger or evaporator coil extracts heat from the
outdoor air,
CA 02777901 2012-06-05
cooling it off when flowing through the evaporator coil, resulting in a
temperature drop
between intake and exhausted air. Frost crystals build-up between the outdoor
heat
exchanger coil fins starts to occur when the outdoor temperature drops below
"frost point" or a temperature below 0 C (32 F), at which moisture in the
air condenses
as a layer of frost crystals on any exposed surface.
Leaving this unchecked it causes ice crystals to grow between the heat
exchanger fin
plates, thereby effectively choking off airflow through the outdoor heat
exchanger and
reducing heat transfer between outdoor and indoor heat exchanger, resulting in
potential
compressor damage. The main factors that determine the frost point in the heat
pump
outdoor heat exchanger are relative humidity and the air temperature when
passing
through the evaporator coil. The frost point increases as outdoor air relative
humidity
increases and/or outdoor temperature decreases. A typical heat pump starts to
develop
frost ice crystal buildup at an outdoor temperature of +3 C at 70% relative
humidity.
Depending on the heat pump manufacturer or model the relative spacing between
heat
exchanger fm plates varies. The wider the spacing the longer it takes for ice
crystals to
grow, effecting heat transfer and airflow. As the outdoor temperature drops
and/or the
relative humidity increases, frost buildup accelerates.
To combat this unwanted scenario, a defrost control mechanism is installed in
the heat
pump outdoor unit. In older heat pumps this mechanism can be a set of
mechanical
relays. Heat pumps today are equipped with a printed circuit board using
electronic
sensors and timers for defrost control and can be either Time based or Demand
based.
Time-based defrost control uses a mechanical thermostat clamped onto the
outdoor
evaporator coil. The thermostat contact closes when the evaporator coil
temperature
drops to several degrees above freezing point, enabling the time based defrost
counter.
The contact opens up again after the outdoor coil temperature reaches approx.
+24 C.
Time based defrost control has a field adjustable timer to initiate a defrost
cycle typically
following 30, 60 or 90 minutes accumulated heat pump run time, provided the
outdoor
thermostat is remains in closed position during the entire time. When
accumulated heat
pump runtime reaches the preset time delay the heat pump, defrost control
circuit enables
the reverse valve thereby reverting the heat pump into cooling mode. Now heat
from the
indoor space is transferred to the outdoor coil, melting away any frost
buildup.
The unwanted side effect of the defrost cycle is that warm indoor air is
converted to cold
air resulting in lowering the indoor temperature causing discomfort to its
occupants as
cold air is now flowing through the supply air registers into the living
space. To combat
this cooling effect the heat pump defrost module is equipped with an output
lead to
enable the furnace during each defrost cycle to temper the cold airflow that
can last
between 3 to 8 minutes depending on the outdoor temperature and make / model
heat
pump. In many installations this lead to enable the furnace is not connected
in order to
reduce fossil fuel heating costs. After the outdoor coil temperature at the
outdoor
thermostat has risen to the upper limit of the thermostat the contract opens
resetting the
defrost timer. Outdoor coil thermostat characteristics vary between
manufactures and
models. An unwanted side effect of time based defrost is that defrost cycles
are initiated
with or without actual frost build-up on the outdoor coil. Depending on the
geographical
location usually the majority of all time based defrost cycles initiated are
not required
CA 02777901 2012-06-05
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because the conditions to create ice buildup are not present, making this
method of
defrosting the outdoor coil wasteful, inefficient and unpleasant to the
occupants.
During milder winter weather with the furnace connected to operate during heat
pump
defrost cycles the powerful furnace can cause the indoor temperature to rise
above
thermostat set point, resulting in premature shutdown of the heat pump before
completing
the defrost cycle. After the thermostat calls for stage one heat again, the
heat pump needs
to resume the defrost cycle by raising the evaporator coil temperature again
to open the
coil thermostat. Taking additional time and energy to complete the defrost
cycle.
Demand based, defrost control is found in more expensive heat pump models.
Most demand defrost controls monitor temperature differential between outdoor
air and
evaporator coil as a factor to determine if frost build-up exists on the
outdoor coil,
making this method is more energy efficient and preferable.
Furnace air handler airflow and PSC motor noise are a common annoyance factor
in forced air heating systems. Most PSC or split capacitor induction motors,
have up to
three speed settings offering a small range of speed control. In addition PSC
motors
consume lots of electricity during normal use. Some furnaces are equipped with
a control
switch allowing the user to select low fan speed when the house thermostat is
not calling
for heat or cooling in order to maintain airflow throughout the indoor space,
reverting to
high speed when the thermostat calls heat or cooling. Because of limited PSC
fan motor
speed range the low fan speed still produces considerable fan and airflow
noise.
According to most building codes, combustion furnaces require a separate fresh
air intake from the outside of the building to facilitate furnace combustion.
Typically a
4" pipe is connected from the outside of the building onto the return air
plenum near the
furnace. Not installing or intentionally closing off this source of outdoor
air forces the
furnace to draw outside air through cracks and openings in the building for
combustion.
For older, poorly insulated buildings this is generally not an issue. However
with rising
heating costs buildings are made more airtight to reduce heating cost. Not
providing for a
separate outdoor air intake for furnace use can now become a serious health
issue for its
occupants.
During heating season this fresh air intake pipe also causes excessive influx
of outdoor
air when the furnace is not used. This adds to unwanted indoor space heat
loss, placing
more demand on the heating system. Outside the main heating season when the
indoor
space requires little or no heating and air changes per hour (ASH) are low,
the fresh air
intake also brings replacement air into the house aided by the furnace air
handler fan.
CA 02777901 2012-06-05
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Field of the invention
The invention generally relates to control systems for heating ventilation and
air
conditioning (HVAC). More specifically it pertains to implementation of
fundamental
changes in heating equipment configuration, features operation, and methods
for dual
heating systems consisting of a fossil fuel furnace and air to air heat pump
to condition
indoor living space for residential and small commercial buildings, resulting
in
significant improvements in operating efficiency and duty cycle for both
heating
appliances. As added benefit temperature fluctuations normally experienced by
standard
dual heating systems are no longer an issue, resulting in improved home
comfort, lower
heating cost and reduced appliance maintenance.
With the invention significant improvements are achieved following the
introduction of a
programmable tri-heat control module and separate dynamic controlled electric
plenum
heater. The control module is equipped with at least two temperature sensors.
One to
measure outdoor temperature to determine building heat loss and dynamic heat
output for
the electric plenum heater. Another sensor measures the return air temperature
to
determine when the house thermostat is in nighttime setback. The hardware can
be
readily added in existing dual heating systems or as part of a new
installation.
Technology used to design and build this apparatus can be solid state, logic,
microprocessor, mechanical or solid state relays or any combination thereof.
The electric plenum heater can be switched in stages using standard mechanical
or
mercury relay contactors or continuously modulated for added precision in heat
output
control. Tests have shown that both methods result in satisfactory results.
However from
equipment cost and long term reliability point of view the electric plenum
heater with
multiple switched heating elements is preferable.
The tri-heat control module incorporates a number of features and operating
modes for
user specific programming to improve the heating process. Main benefits to the
user are
reduced heating cost and less need for routine furnace maintenance as well as
improved
home comfort by reducing indoor space temperature fluctuations caused by
switching
between heat sources and heat pump defrost cycles. Reduced use of the oil
furnace also
lowers oil burner noise and fumes released when chimney draft is not optimal.
The tri-heat control module is also applicable in dual heating systems with
two or
more stages electric furnace and heat pump. In a typical all electric, dual
heating system
the heat pump indoor coil is located in the bottom compartment, followed by a
blower fan
compartment, and multistage electric furnace in an upper compartment.
Configurations
may vary between manufacturers and applications. The electric furnace is used
to supply
measured heat for aiding the heat pump to maintain house thermostat daytime
set point as
well as furnace only heat when outdoor temperatures are below heat pump low
temperature cutoff point. Although typical achievable heating cost savings for
this
configuration do generally not measure up with potential heating cost savings
achieved
using a fossil fuel furnace, the use of the tri-heat control system results in
improvements
in heat pump efficiency by allowing it like in the previous application to
operate
whenever stage one or two heat is called, down to low temperature cutoff
point.
A standard programmable automatic house thermostat with two stage heat, and
one stage cool, is required as user interface for most dual heat applications.
For dual heat
systems with fossil fuel furnace a "fossil fuel kit" or similar device is
required. The house
thermostat enables the heat pump with stage one call for heat. Stage two, call
for heat
CA 02777901 2012-06-05
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enables both heat pump and electric plenum heater. When the temperature drops
below
the low temperature cutoff point the furnace is enabled either at stage one or
two call for
heat (user selectable at the tri-heat control module). When in E-heat, the
furnace enables
and both heat pump and plenum heater are disabled. The invention also includes
the use
of an application specific manual or automatic thermostat with 2 wire
communication
link for the remote tri-heat control and interface unit.
While the heat pump operates intermittently in a standard dual heating system,
a much
improved duty cycle, and output efficiency are achieved with tri-heat control
by always
allowing the heat pump to contribute to the heating process when the house
thermostat
calls for stage one or two heat down to the low temperature cutoff point.
Whenever the
house thermostat calls for stage two heat, measured heat is supplied by an
electric plenum
heater installed upstream from the heat pump indoor coil. To achieve a good
balance
between building heat loss and heat supply to maintain thermostat daytime set
point and
prevent temperature stratification, the electric plenum heat output is
regulated by the tri-
heat control unit to be slightly higher compared to the net heat loss of
indoor space which
includes the heat gain produced by the heat pump. Calibration of the electric
plenum heat
output is achieved by offsetting the outdoor temperature sensor output with
the actual
building heat demand. This process can be achieved manually or automatically.
Below
"balance point" the heat pump generates continuous, efficient heat only
interrupted by
defrost cycles or when the house thermostat is turned down.
For dual heating systems with fossil fuel furnace, heat recovery following
nighttime
thermostat setback often requires the fossil fuel furnace to raise the indoor
temperature
back to thermostat daytime set point. Often even at outdoor temperatures well
above the
freezing point. The tri-heat control unit is equipped with a feature called
"first-heat"
enable. Following a house thermostat setback it detects a temperature drop in
the return
air duct. Following an outdoor temperature dependent delay that decreases as
the outdoor
temperature drops, "first heat" mode is enabled to confirm the house
thermostat is in
nighttime setback. When raising the house temperature back to daytime set
point "first
heat" allows the heat pump an additional programmable or outdoor dependent
controlled,
dynamic15 to 120 minutes delay to raise the house temperature to daytime set
point. If
daytime set point is not reached after the delay expires, a measured amount of
dynamic
electric plenum heat is enabled to assist the heat pump in raising the indoor
temperature
to daytime set point. This method makes first-heat heat recovery more cost
efficient and
timely in reaching daytime set point following a pre determined delay. Several
tri-heat
control programming modes can be used for heat recovery following house
thermostat
nighttime setback.
For manual night time setback and fast daytime heat recovery without furnace
use the
tri-heat control can be programmed to enable the heat pump only for a set time
delay,
followed by adding electric plenum heat in "boost mode" to enable all
available electric
element heat for maximum heat output, independent of actual outdoor
temperature. When
daytime set point is reached, tri heat control detects the higher return duct
air temperature
and disables first heat mode. This reverts, plenum heat to outdoor temperature
dependent
dynamic mode. In house thermostat daytime, heat-maintain mode stage one heat
enables
the heat pump. Following a stage two call for heat the electric plenum heater
is enabled in
outdoor temperature dependent dynamic heat mode supplying measured heat to
raise the
CA 02777901 2012-06-05
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house thermostat back to stage one call for heat, thereby disabling the
electric plenum
heater. In this fashion the daytime thermostat set point is regulated within a
very narrow
temperature margin.
For scheduled nighttime set back and daytime heat recovery using the house
thermostat
in automatic programmable mode the tri-heat control module can be programmed
for
dynamic heat pump /dynamic plenum heat mode.
Following a call for heat from the house thermostat the heat pump starts
heating the
indoor space. Following an outdoor temperature dependent delay that decreases
as the
outdoor temperature drops further, the dynamic output controlled electric
plenum heater
is enabled. As the outdoor temperature drops more available heating elements
are
switched on. In this fashion the heat recovery process is completed within a
narrow
margin of error in arriving at daytime temperature set point within a fixed
time delay
independent of the outside temperature or heat loss of the indoor space. Like
in the
previous heating mode sequence the electric plenum heater reverts back to
dynamic mode
once it has reached thermostat day time set point. A number of different
heating modes
can be programmed for different heating system configurations and preferences.
At outdoor temperatures above 0 C stage two, electric plenum heat is can be
disabled to
allow the heat pump to complete the heat recovery process without plenum heat.
Most electronic automatic thermostats on the market only have a narrow
temperature differential or hysteresis between stage one or two call for heat
enable/disable. When used in dual heating systems it results in frequent
cycling of the
furnace when operating below the low temperature cutoff point and the heat
pump when
operating above balance point. This contributes to inefficiency and increased
heating
costs especially during fossil fuel furnace use. The tri-heat control module
is equipped
with a feature allowing the user to program individually or for both furnace
and heat
pump increase the on/off hysteresis following a call for heat from the house
thermostat.
This reduces the number of heating cycle intervals. When enabled the heating
appliance
turns on only when the indoor temperature has dropped to house thermostat
stage two call
for heat. The heating appliance is disabled again after thermostat stage one,
call for heat
is satisfied. This feature automatically reverts back to normal 2 stage heat
operation
whenever the outdoor temperature drops below +3 C and the heat pump low
temperature
cutoff point.
Heat pump defrost cycles can be a major cause of unwanted temperature
fluctuations in the indoor space. When the fuel furnace is connected to turn
on during
defrost cycles it produces a blast of hot air from the intake vents often
interrupting the
defrost cycle as the house thermostat call for stage one heat is now
satisfied. When not
connected to enable the fuel furnace, it can produce a blast of cold air from
the vents,
cooling down the indoor space, shutting down the defrost cycle prematurely to
enable the
furnace. During heat pump defrost cycles the tri-heat control unit enables the
electric
plenum heat in dynamic mode. By adding dynamic heat to temper the cold air
generated
by the heat pump during defrost the air temperature at the intake vents
throughout the
house is neutral, not hot not cold. In this fashion the indoor temperature
remains stable
allowing the heat pump defrost cycle to complete avoiding extended defrost
cycles.
CA 02777901 2012-06-05
Because the heat pump duty cycle and total operating time increases
dramatically with
the tri-heat control module An optional demand defrost module can be installed
for a heat
pump with time based defrost. This module is installed at the outdoor heat
pump unit. It
controls the defrost cycle by controlling the outdoor coil thermostat contact
output to the
existing heat pump defrost board by adding an additional switch in series with
the
outdoor coil thermostat. This switch is controlled by the demand defrost
module.
Making the installation of this demand defrost module easy, without
modifications
needed to the existing time based defrost board. With this module in place the
heat pump
defrost control circuit can initiate a defrost cycle only when actual when
sufficient frost
build up exists on the outdoor coil to warrant a defrost cycle.
Dirty air handler filters or failure of the blower fan can result in
incomplete heat
exchange at the indoor coil, raising the head pressure. This can lead to
permanent
compressor damage when left unattended. To prevent this from occurring, the
tri-heat
control module can be programmed to interlock with an external air flow switch
located
in the plenum heater to detect minimal airflow in the supply air duct. When
insufficient
airflow is detected it disables both plenum heater and heat, until sufficient
airflow is
restored. During this time the fossil fuel furnace is enabled for heating the
indoor space.
The electric plenum heater used is generally custom OEM supply CSA/ UL
approved and build to individual requirements especially for mostly non
standard seize
and heating capacity add-on installations. Special control wiring between
electric plenum
heater is required to accommodate binary electric element switching and
supervisory
functions are tri heat control application specific. The typical application
with multi stage
heating elements deploys a two stage electric plenum heater allowing for three
independent heating stages. Stage one heating element is typically 4kW, stage
two 8kW.
The tri-heat control module increases the electric plenum heater output as the
outdoor
temperature drops. Stage one heat, 4kW stage two, 8kW, stage three, (4 +8kW)
resulting
symmetrical staged heat with less control hardware resulting in lower plenum
heater unit
cost.
Most forced air dual heating systems are equipped with a PSC blower fan motor.
Noise and vibrations generated by fan motor and air flow through duct work are
unwelcome side effects of a forced air heating system, especially for older
buildings
where ductwork construction no longer meet today's standards. The PSC motor is
also
inefficient and costly to operate because of its high electricity consumption
when
compared to the ECM or electronically commutated, motor which typically
consumes up
to 65% less electricity to operate. The ECM blower fan motor is increasingly
more used
for HVAC applications such as high efficiency gas furnaces. The tri-heat
control module
is equipped with optional ECM fan motor speed control output, to accommodate
variable
blower fan speed control for idle speed, heating and cooling needs. Idle and
maximum
fan speeds are adjustable according to the heating /cooling requirements.
Without heating or cooling requirement and the house thermostat in fan on mode
the tri-
heat control is adjusted to idle speed which can be set between 100 RPM to
maximum
speed to provide air circulation throughout the indoor space without producing
noticeable
fan motor or airflow noise. When stage one heat pump in heat or cooling mode
is enabled
by the house thermostat the fan speed increases slowly to allow head pressure
to build up
before increasing to heat pump defined maximum speed. When in heat mode with
one or
CA 02777901 2012-06-05
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more electric heating elements enabled the fan speed increases proportionally.
When the
more powerful furnace is enabled the fan speed increases typically to maximum
speed.
Dual heating system is equipped with a low or medium capacity fossil fuel
combustion furnace require a separate fresh air intake to supply outside air
to the heated
indoor space as essential part of the furnace combustion process. An unwelcome
side
effect is cold air infiltration into the heated space. As the outdoor
temperature drops an
increasingly larger air pressure differential develops between cold outdoor,
and warm
indoor air. Cold outside air is forced into the house making the fresh air
intake pipe also a
major source of unwanted heat loss especially during the colder days of
winter.
The tri-heat control module accommodates an optional fresh air damper equipped
with
end-switch for installation into an outside air intake pipe. The fresh air
damper now
prevents cold outside air from entering the heated space when the furnace is
not enabled.
Following a thermostat E heat command or low temperature cutoff command the
damper
=
opens and the end switch closes enabling the furnace. For buildings without
separate
fresh air intake heat exchange mechanism the tri-heat control unit can be
programmed to
open the fresh air damper when the outdoor temperature exceeds +3 C to allow
fresh air
into the building with aid of the forced air blower fan.
Description Of Prior Art.
To be completed
Summary Of The Invention
To be completed
Brief Description Of The Drawings.
Fig.1 Shows a basic single wire diagram of a dual heating system with fossil
fuel
furnace tri-heat control and electric plenum heater.
Fig.2 Shows a basic single wire diagram of a dual heating system with electric
furnace and tri-heat control.
Fig.3 Shows first heat recovery sequence curve with fixed plenum heater
enable delay and above balance point heat maintain.
Fig.4 Shows first heat recovery sequence curve with dynamic plenum heater
enable
Delay and below balance point heat maintain
Fig.5 Shows the advantage using hysteresis doubling for furnace operation.
Fig.6 Tri-heat control functional block diagram (not included)
CA 02777901 2012-06-05
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Fig.7 Not defined
Fig.8 Not defined
Fig.9 Not defined
Fig.10 Not defined
Description Of The Preferred Embodiment
To be completed
The Embodiment Of The Invention In Which an Exclusive Property Or Privilege Is
Claimed are Defined As Follows:
To be completed
