U.S. patent application number 12/377277 was filed with the patent office on 2011-01-27 for impedance heating for heat exchanger water drainage channels.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Joseph Ballet, Michel Elbaz.
Application Number | 20110016903 12/377277 |
Document ID | / |
Family ID | 39157532 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110016903 |
Kind Code |
A1 |
Ballet; Joseph ; et
al. |
January 27, 2011 |
Impedance Heating for Heat Exchanger Water Drainage Channels
Abstract
Embodiments of the invention provide anti-icing systems (201)
for drainage channels (203; 205) used to remove water run-off
during heat pump evaporator coil defrosting cycles during cold
weather conditions. The invention employs impedance heating to
obviate heat tracing cable, its associated thermal insulation and
any protective mechanical coverings.
Inventors: |
Ballet; Joseph; (Bressolles,
FR) ; Elbaz; Michel; (Feyzin, FR) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C. (UTC)
900 CHAPEL STREET, SUITE 1201
NEW HAVEN
CT
06510-2802
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
39157532 |
Appl. No.: |
12/377277 |
Filed: |
September 5, 2006 |
PCT Filed: |
September 5, 2006 |
PCT NO: |
PCT/US2006/034617 |
371 Date: |
February 12, 2009 |
Current U.S.
Class: |
62/276 |
Current CPC
Class: |
F24F 13/222 20130101;
F25D 21/14 20130101; F24F 2221/34 20130101; F25D 2400/02
20130101 |
Class at
Publication: |
62/276 |
International
Class: |
F25D 21/08 20060101
F25D021/08 |
Claims
1. A drainage channel (203; 205) heating system comprising: a first
terminal (215; 217) electrically coupled to a drainage channel at a
first location; a second terminal (219; 221) electrically coupled
to a drainage channel at a second location, said first and said
second terminals configured to define a resistance; and a
transformer (227) having a primary winding and a secondary winding
(225), said secondary winding (225) coupled between said first
terminal and said second terminal, wherein a predetermined
secondary voltage is present at said secondary winding (225) when a
predetermined primary voltage is impressed across connections of
said primary winding (233), said predetermined secondary voltage
for effecting a current in a drainage channel determined by said
predetermined secondary voltage and said resistance.
2. The system according to claim 1 wherein said predetermined
secondary voltage is in the range of from greater than 0 Volts to
less than or equal to 6 Volts.
3. The system according to claim 2 wherein said drainage channel
(203; 205) is electrically insulated.
4. The system according to claim 3 wherein said drainage channel is
constructed of galvanized steel.
5. The system according to claim 4 wherein said first terminal
(215) and said second terminal (219) are located on the same
drainage channel (203).
6. The system according to claim 4 wherein said first terminal
(215) and said second terminal (221) are located on different
drainage channels (203; 205).
7. The system according to claim 6 wherein said predetermined
secondary voltage is determined by a turns ratio.
8. The system according to claim 7 wherein said predetermined
primary voltage (233) is determined based on said turns ratio and
said predetermined secondary voltage.
9. The system according to claim 8 wherein the drainage channel
heating system is for a heat pump evaporator assembly (101).
10. A drainage channel (303; 305) heating system comprising: a
conductive strip (307; 309) sized in matching correspondence with
an interior of a drainage channel (303; 305); a first terminal
(311; 313) electrically coupled to a conductive strip at a first
location; a second terminal (315; 317) electrically coupled to a
conductive strip at a second location, said first and said second
terminals configured to define a resistance; and a transformer
(321) having a primary winding and a secondary winding (319), said
secondary winding (319) coupled between said first terminal and
said second terminal, wherein a predetermined secondary voltage is
present at said secondary winding (319) when a predetermined
primary voltage is impressed across connections of said primary
winding (233), said predetermined secondary voltage for effecting a
current in a conductive strip determined by said predetermined
secondary voltage and said resistance.
11. The system according to claim 10 wherein said predetermined
secondary voltage is in the range of from greater than 0 Volts to
less than or equal to 6 Volts.
12. The system according to claim 11 wherein said conductive strip
(307; 309) is electrically insulated.
13. The system according to claim 12 wherein said conductive strip
(307; 309) is coupled to an interior of a drainage channel (303;
305).
14. The system according to claim 13 wherein said first strip
terminal (311) and said second strip terminal (315) are located on
the same strip (307).
15. The system according to claim 13 wherein said first strip
terminal (311) and said second strip terminal (317) are located on
different strips (307; 309).
16. The system according to claim 15 wherein said predetermined
secondary voltage is determined by a turns ratio (319).
17. The system according to claim 16 wherein said predetermined
primary voltage (233) is determined based on said turns ratio and
said predetermined secondary voltage.
18. The system according to claim 17 wherein the drainage channel
heating system is for a heat pump evaporator assembly (101).
19. A drainage channel comprising; a U-shaped structure having a
bottom and two side walls; a conductive material embedded within
said drainage channel structure; and a first terminal at a first
end of the drainage channel and a second terminal at a second end
of the drainage channel wherein said first and said second
terminals conductively couple with said conductive material.
20. The drainage channel according to claim 19 wherein said
conductive material is a metal.
21. The drainage channel according to claim 20 wherein said
conductive metal is flat and sized in correspondence with said
drainage channel bottom.
22. The drainage channel according to claim 20 wherein said
conductive metal is U-shaped and sized in matching correspondence
with said drainage channel bottom and sidewalls.
23. The drainage channel according to Claim 19 wherein said
conductive material is a conductive plastic.
24. The drainage channel according to claim 23 wherein said
conductive plastic is said U-shaped structure.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates generally to the field of heating,
ventilation and air conditioning (HVAC) systems. More specifically,
embodiments of the invention relate to anti-icing systems for
drainage channels that remove water run-off produced during heat
pump evaporator defrosting cycles.
[0002] A heat pump is a machine which moves heat using a compressor
from a low temperature reservoir to a higher temperature reservoir.
The pump operates a refrigeration cycle where the refrigerant
repeatedly changes state from liquid to vapor, and back to liquid.
The refrigerant is condensed to release heat in one part of the
cycle and is boiled (evaporated) to absorb heat in another part of
the cycle. Heat pumps use outside air as a heat source and must be
capable of operating in ambient air temperatures ranging from
14.degree. F. to 50.degree. F. (.+-.10.degree. C.).
[0003] Heat pumps use liquid to air heat exchangers (air coils)
typically made from copper tubes and aluminum fins. Individual heat
exchangers may be arranged in multi-circuits.
[0004] A heat pump heat exchanger located outdoors is an evaporator
where the refrigerant expands at a saturated evaporation
temperature. At air temperatures below 42.8.degree. F. (6.degree.
C.) the evaporating temperature in the heat exchanger is
approximately 28.4.degree. F. (-2.degree. C.). Any humidity in the
surrounding air will condense on the exchanger surfaces and
freeze.
[0005] To operate continuously at these temperatures, the heat
exchanger must be defrosted periodically. Frost will accumulate and
reduce airflow through the exchanger. The reduction in airflow
minimizes thermal exchange and overall heat pump efficiency. Over
time, the heat exchanger may become completely covered in ice.
[0006] A defrost cycle usually initiates gas heating to defrost the
heat exchanger. One method is where the heat pump refrigeration
cycle is reversed using a four-way valve, and hot gas discharged
from the compressor is injected into the heat exchanger. The hot
gas heats the heat exchanger and melts the ice accumulated on the
tubes and fins.
[0007] During a defrosting cycle, many gallons of water may be
released. For example, ice melted from a coil having a frontal area
of approximately 21.5 ft.sup.2 (2 m.sup.2) can result in more than
4 gallons (10 litres) of water. Taking into account the quantity of
water from each heat exchanger per defrost cycle, it is necessary
to channel and remove the water to the outside of the unit. If not,
water present on the interior surfaces of a drainage channel will
gradually freeze and build-up, blocking flow in each channel. The
blocked flow may result in damaged components located within the
evaporator housing.
[0008] Drainage channels having a slope angle of several degrees
are typically provided and guide the melted water outside of the
housing. To prevent the water from freezing in the channels, the
channels are usually heated and insulated.
[0009] A typical heat pump evaporator system 101 is shown in FIG.
1. A pair of heat exchangers 103 and 105 are oriented at an acute
angle with respect to each other and converge away from two
circulation fans 107, 109. The fans 107, 109 are supported by the
coils 103, 105, additional support members 111, 113 and fan motor
support brackets (not shown). Solid covers 115 are positioned on
the ends and around the circulation fans 107, 109 such that the
circulation fans 107, 109 draw air through the exchangers 103, 105.
Two drainage channels 117, 119 are provided to collect and guide
water run-off 121 from the coils during defrosting cycles. To
prevent drainage channel 117, 119 freezing when outside
temperatures are at or below freezing, heat tracing 123 may be
installed running under the length of each channel or wrapped
around each channel.
[0010] Typical heat tracing cable has two conductors inside a cable
insulation which run from end to end and are separated from each
other by a carbon type material which is conductive and produces
the heat. Heat tracing cable is usually rated in Watts (power
dissipation) per unit length.
[0011] After heat tracing cable is applied, it is usually thermally
insulated and mechanically covered for protection. Heat tracing
cable is susceptible to damage and may represent a health risk for
people due to the elevated voltages present (230-400 Vac). Heat
tracing is expensive to install and requires protection against
electric shocks.
[0012] It is desirable to develop a channel drainage heating system
that is simple and effective, and eliminates thermal and mechanical
covers.
SUMMARY OF THE INVENTION
[0013] Although there are various systems that are available to
heat HVAC drainage channels during cold weather conditions, such
systems are not completely satisfactory. The inventors have
discovered that it would be desirable to have systems that heat
drainage channels used to remove water run-off during heat pump
evaporator coil defrosting cycles using impedance heating.
Impedance heating obviates heat tracing cable and its associated
thermal insulation and mechanical covers.
[0014] One aspect of the invention provides a drainage channel
heating system. Systems according to this aspect of the invention
comprise a first terminal electrically coupled to a drainage
channel at a first location and a second terminal electrically
coupled to a drainage channel at a second location, a resistance
defined between the first and second terminals, a transformer
having a primary winding having two connections and a secondary
winding having two connections, a loop defined by the first
drainage channel terminal coupled to one secondary connection and
the second drainage channel terminal coupled to the other secondary
connection, a predetermined secondary voltage at the secondary
connections is present when a predetermined primary voltage is
impressed on the primary connections, and a loop current is present
when the primary voltage is impressed on the primary connections
wherein the loop current is determined by the predetermined voltage
and resistance.
[0015] Another aspect of the invention provides a drainage channel
heating system. Systems according to this aspect of the invention
comprise a conductive strip sized in matching correspondence with
an interior of a drainage channel, a first terminal electrically
coupled to a conductive strip at a first location and a second
terminal electrically coupled to a conductive strip at a second
location, a resistance defined between the first and second
terminals, a transformer having a primary winding having two
connections and a secondary winding having two connections, a loop
defined by the first strip terminal coupled to one secondary
connection and the second strip terminal coupled to the other
secondary connection, a predetermined secondary voltage at the
secondary connections is present when a predetermined primary
voltage is impressed on the primary connections, and a loop current
is present when the primary voltage is impressed on the primary
connections wherein the loop current is determined by the
predetermined voltage and the resistance.
[0016] Yet another aspect of the invention provides a drainage
channel. Drainage channels according to this aspect of the
invention comprise a U-shaped structure having a bottom and two
side walls, a conductive material embedded within the drainage
channel structure, and a first terminal at a first end of the
drainage channel and a second terminal at a second end of the
drainage channel wherein said first and second terminals
conductively couple with said conductive material.
[0017] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is an exemplary perspective view of an evaporator
system.
[0019] FIG. 2 is an exemplary embodiment of the invention.
[0020] FIG. 3 is an alternative embodiment of the invention.
DETAILED DESCRIPTION
[0021] Embodiments of the invention will be described with
reference to the accompanying drawing figures wherein like numbers
represent like elements throughout. Further, it is to be understood
that the phraseology and terminology used herein is for the purpose
of description and should not be regarded as limiting. The use of
"including," "comprising," or "having" and variations thereof
herein is meant to encompass the items listed thereafter and
equivalents thereof as well as additional items. The terms
"mounted," "connected," and "coupled" are used broadly and
encompass both direct and indirect mounting, connecting, and
coupling. Further, "connected" and "coupled" are not restricted to
physical or mechanical connections or couplings.
[0022] Embodiments of the invention provide anti-icing systems for
drainage channels used to remove water run-off during heat pump
evaporator coil defrosting cycles during cold weather conditions.
The invention employs impedance heating to obviate heat tracing
cable, its associated thermal insulation and any protective
mechanical coverings.
[0023] Direct impedance heating involves passing an alternating
current through a material to be heated. The resistance of the
material to the current being passed through it generates heat. Low
frequency current, such as 60 Hz is used to heat the material. High
frequency current, such as 400 Hz may be used to heat just the
surface of the material.
[0024] The resistance of the material to be heated cannot be too
low or a high current may be necessary to reach a desired power
level. Similarly, the resistance may not be too high or a high
voltage will be necessary as witnessed using Ohm's law,
V=IR, (1)
[0025] where V is Voltage, I is current in Amps and R is resistance
in Ohms. By using a low voltage, for example .ltoreq.6 Vac, the
drainage channels may be direct impedance heated.
[0026] An isolation transformer having a high power (VA) rating is
used to provide a low secondary voltage to the drainage channels.
The transformer decouples and isolates the transformer primary
winding from the transformer secondary winding.
[0027] A transformer allows alternating current to be supplied to a
device from a source without a common electrical connection between
the two circuits. The transformer has primary and secondary
windings which are not electrically coupled to one another. The
windings are coupled by magnetic effects in the iron core. Since
the neutral connection of the ac source is directly connected to
earth (ground), grounded objects near the load coupled to the
secondary windings may be at a hazardous potential difference with
respect to the load. By using a transformer, the common coupling
between the two neutrals is eliminated and any shock hazard will be
contained (isolated) in the load. To avoid shock hazards, each
drainage channel may be grounded to the unit frame.
[0028] The transformer power dissipation is usually expressed in VA
(Volts-Amps). The transformer used for the preferred embodiment is
rated at 475 VA and is coupled to a 400 Vac mains supply. The
transformer construction may comprise a plurality of stacked
laminations or one continuous lamination (toroid).
[0029] The number of windings is determined by,
V 1 = V 2 n , ( 2 ) ##EQU00001##
[0030] where V.sub.1 is the primary side voltage, V.sub.2 is the
secondary side voltage and n is the turns ratio
N 2 N 1 . ##EQU00002##
The turns ratio in the exemplary embodiment is defined to output a
predetermined voltage in the range of from greater than 0 Vac to
less than or equal to 6 Vac. 6 Vac is preferred in view of the
safety standards for protecting against electric shock when in high
humidity environments or if immersed in water. The secondary
winding N.sub.2 may only comprise several turns.
[0031] Shown in FIG. 2 is a first embodiment 201 of the invention.
The embodiment 201 employs two drainage channels, a first channel
203 and a second channel 205, one for each evaporator exchanger
assembly (not shown) or assemblies, each having a substantially
U-shaped cross section. Other drainage channel cross sections such
as V-shaped may be used. An evaporator exchanger assembly may
comprise a plurality of individual exchangers.
[0032] Forward exchanger end caps 207, 209 are shown in phantom for
exchanger position reference. Exchanger assembly base plates 211,
213 are positioned such that water run-off during defrosting cycles
may cascade down through the tubes and fins to the base plates 211,
213 and spill into each evaporator assembly's respective drainage
channel 203, 205. Each drainage channel 203, 205 is positioned at
the edge, or under a lip of the base plate 211, 213, and mounted at
an angular slope with regard to level to allow collected water to
seek a lower level.
[0033] The invention may be practiced with evaporator exchanger
systems having one drainage channel, as well as evaporator
exchanger systems having a plurality of individual drainage
channels. The invention may be adapted for any number of drainage
channels and configurations.
[0034] The drainage channels 203, 205 employed in this embodiment
are constructed of galvanized steel for strength, and corrosion and
rust resistance. The drainage channels 203, 205 are electrically
insulated from each other and all exposed framework by using
insulating hardware between each channel-to-frame mounting point
except where grounded. The insulating hardware may comprise
washers, fasteners, or pads made of nylon, plastic, rubber,
phenolic or other electrically insulating material. The electrical
resistance of steel is 17.4.times.10.sup.-6 .OMEGA.cm and the
electrical resistance of zinc is 5.9.times.10.sup.-6 .OMEGA.cm.
[0035] In an alternative embodiment, the drainage channels 203, 205
may be made of a predetermined carbon/plastic composite having a
known electrical resistivity per unit length. In another
alternative embodiment, a metal sheet is embedded in the bottom of
a drainage channel made of a non-conducting material 203, 205 at
the time of molding or extrusion. The metal sheet may be planar, or
generally of a U-shaped configuration sized to match the
configuration of the drainage channel. For coupling with electrical
conductors, the internal metal sheet may be accessed using rivets,
sheet metal screws, or other penetrating hardware.
[0036] At least two terminals 215, 217, 219, 221 are electrically
coupled to each drainage channel 203, 205. A first terminal 215,
217 is positioned at a first channel end and a second terminal 219,
221 is positioned at a second channel end. The terminals for each
drainage channel are located on a channel such that the maximum,
localized channel heating is at the bottom of the channel where the
greatest likelihood of freezing will be experienced. In the same
manner, the width of a channel may be sized to increase bottom
heating. The terminals may be screw-type terminals, spade-type
terminals, ring-lug type terminals or others, for fastening onto a
welded, threaded stud, or tapped hole.
[0037] If more than one drainage channel is used for an evaporator
exchanger system, the channels are coupled together as an
electrical series circuit where the second terminal of one channel
is coupled to the first terminal of another channel. The two
drainage channels 203, 205 are coupled together using a single
conductor cable 223 coupled to the second terminal 219 of the first
channel 203 and to the first terminal 217 of the second channel
205. The common coupling 223 may be grounded. The first terminal
215 of the first channel 203 and the second terminal of the second
channel 205 are coupled to secondary windings 225 of a transformer
227 using two single conductor cables 229, 231. The circuit
arrangement of the two drainage channels 203, 205 and secondary
winding 225 constitutes a low voltage secondary loop in which a
high current flux (Amps) circulates. The primary winding 233 is
coupled to a 400 Vac source (not shown).
[0038] In the preferred embodiment, a voltage of 1.8 Vac and a
current of 280 A is delivered at the secondary transformer taps.
The power dissipated in the drainage channels is,
P=IV. (3)
[0039] Substituting,
P=(280A)1.8V, (4)
P=504VA. (5)
[0040] The total load is 504 VA. Both channels 203, 205 used in the
preferred embodiment are of equal size, with each drainage channel
203, 205 dissipating approximately 252 VA.
[0041] The current through the channels provides the necessary
heating to allow the heat pump to be operated continuously during
cold weather despite frequent defrosts that may last upwards of one
half hour. After more than 15 hours of continuous operation, no
phenomenon of localized ice build-up in the drainage channels was
observed at a low ambient temperature of 14.degree. F. (-10.degree.
C.) and a high relative humidity of >90%. The galvanized steel
drainage channels were without insulation.
[0042] The mains voltage 233 supplied to the transformer 227 may be
interrupted using a thermostat contact (not shown) or temperature
controller (not shown) when the outside temperature is above a
predetermined set point. The mains voltage may also be applied
continuously.
[0043] Shown in FIG. 3 is a second embodiment 301 of the invention
applied to the same heat exchanger assembly configuration. Instead
of directly heating the drainage channels 303, 305, heat is applied
by direct impedance heating of two insulated metal strips 307, 309
disposed at the bottom of each drainage channel 303, 305. The first
307 and second 305 strips may be galvanized steel, stainless steel,
a conductive composite, or other conductive metal dimensioned to
and in conformance with each channel bottom. The bottom surfaces of
the strips 307, 309 are electrically insulated from each channel
303, 305. Insulating material having a high electrical resistance
but low thermal resistance is used, such as conformable
high-strength foams (3M VHB tape) or others.
[0044] At least two terminals 311, 313, 315, 317 are conductively
coupled to each heating strip 303, 305. A first terminal 311, 313
is positioned at a first strip end and a second terminal 315, 317
is positioned at a second strip end.
[0045] If more than one drainage channel is used for an evaporator
exchanger system, the strips are coupled together as an electrical
series circuit where the second terminal of one channel is coupled
to the first terminal of another channel. The two strips 303, 305
are coupled together using a single conductor cable 223 coupled to
the second terminal 315 of the first strip 303 and to the first
terminal 313 of the second strip 305. The first terminal 311 of the
first strip 303 and the second terminal 317 of the second strip 305
are coupled to secondary windings 319 of a transformer 321 using
two single conductor cables 229, 231. The circuit arrangement of
the two strips 307, 309 and secondary winding 319 constitutes a low
voltage secondary loop in which a high current flux (Amps)
circulates. The primary winding 233 is coupled to a 400 Vac source
(not shown).
[0046] A voltage of 4.0 Vac is delivered by the secondary winding
with a 108 A secondary current. Total power dissipated through the
heating strips 303, 305 is 432 VA.
[0047] The advantages of the invention are increased system safety
for service personnel due to the use of very low voltage, increased
system reliability since the only component susceptible to failure
is the transformer, no heaters to become unfastened from the
channels or degraded due to UV exposure and no significant
maintenance of the system is required on site.
[0048] One or more embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
* * * * *