U.S. patent application number 09/835955 was filed with the patent office on 2001-10-25 for cooling system for cooling interior of substantially airtight housing.
Invention is credited to Kishita, Koji.
Application Number | 20010033743 09/835955 |
Document ID | / |
Family ID | 18630398 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033743 |
Kind Code |
A1 |
Kishita, Koji |
October 25, 2001 |
Cooling system for cooling interior of substantially airtight
housing
Abstract
A heater protective device of a cooling system includes a couple
of thermostats and one thermal fuse. The thermostats are secured to
opposing sides of one metal plate. When a temperature of each
thermostat rises due to the heat conducted through the metal plate
and substantially reaches 40 degrees Celsius or higher, an internal
connection of the thermostat is turned off, i.e., is opened. When
the temperature of the thermostat decreases substantially below 40
degrees Celsius, the internal contact of the thermostat is turned
on, i.e., is closed. The metal plate is secured to a heat receiving
bracket that is secured to a heater cover and that is heated upon
receiving radiated heat from the electric heater. A thermal fuse
extends through the metal plate in a thickness direction of the
metal plate and is secured thereto.
Inventors: |
Kishita, Koji; (Motosu-gun,
JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, PLC
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
18630398 |
Appl. No.: |
09/835955 |
Filed: |
April 16, 2001 |
Current U.S.
Class: |
392/485 ;
165/48.1; 219/510; 219/517 |
Current CPC
Class: |
G05D 23/1909 20130101;
H05K 7/206 20130101; H05K 7/207 20130101; F24H 9/2071 20130101 |
Class at
Publication: |
392/485 ;
219/510; 165/48.1; 219/517 |
International
Class: |
F25B 029/00; F24H
001/10; H05B 003/78; H05B 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2000 |
JP |
2000-119423 |
Claims
What is claimed is:
1. A cooling system for cooling an interior of a substantially
airtight housing, said cooling system comprising: an internal-air
passage having an internal-air inlet and an internal-air outlet,
both said internal-air inlet and said internal-air outlet
communicating with an interior of said housing; an external-air
passage having an external-air inlet and an external-air outlet,
both said external-air inlet and said external-air outlet
communicating with an exterior of said housing; an internal-air fan
that takes in internal air from said interior of said housing
through said internal-air inlet and expels said internal air into
said interior of said housing through said internal-air outlet; an
external-air fan that takes in external air from said exterior of
said housing through said external-air inlet and expels said
external air to said exterior of said housing through said
external-air outlet; a heat exchanger that exchanges heat between
said internal air introduced into said internal-air passage and
said external air introduced into said external-air passage; and a
heater unit that heats said internal air introduced into said
internal-air passage, said heater unit including: an electric
heater that generates heat upon energization; a power supply
circuit that supplies power to said electric heater; a heater
protective device that is interposed in said power supply circuit,
said heater protective device including a first thermostat and a
second thermostat, said first thermostat being interposed in said
power supply circuit on a first side of said electric heater, said
second thermostat being interposed in said power supply circuit on
a second side of said electric heater that is opposite to said
first side of said electric heater, said first thermostat and said
second thermostat being arranged to open substantially at a first
predetermined temperature or higher to disconnect said power supply
circuit; and a heat receiving plate that receives heat from said
electric heater and conducts said heat of said electric heater to
said heater protective device, said first thermostat and said
second thermostat being secured to said heat receiving plate.
2. A cooling system according to claim 1, wherein said first
thermostat and said second thermostat are secured to opposing sides
of said heat receiving plate.
3. A cooling system according to claim 1, wherein: said heater
protective device further includes a thermal fuse, said thermal
fuse being interposed in said power supply circuit and being
secured to said heat receiving plate; and said thermal fuse opens
to disconnect said power supply circuit when a temperature of said
thermal fuse is substantially equal to or higher than a second
predetermined temperature, said second predetermined temperature
being higher than said first predetermined temperature.
4. A cooling system according to claim 1, further including a
casing, wherein said heater unit further comprises: a heater
bracket that supports said electric heater; a heater cover that is
secured to said casing and supports said heater bracket; and a
dielectric member that is interposed between said heater cover and
said heater bracket to electrically insulate said heater cover from
said heater bracket.
5. A cooling system according to claim 1, further including: a
damper that is disposed in said external air passage to close and
open said external-air passage; and a control device that controls
said cooling system such that when said electric heater is
energized, said control device turns off said external-air fan and
closes said external-air passage by operating said damper.
6. A cooling system according to claim 1, wherein said first
thermostat and said second thermostat are secured to said heat
receiving plate in such a manner that said heat conducted to said
heat receiving plate is substantially equally conducted to both
said first thermostat and said second thermostat.
7. A cooling system according to claim 1, wherein said first
predetermined temperature is 40 degrees Celsius.
8. A cooling system according to claim 3, wherein said second
predetermined temperature is 110 degrees Celsius.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2000-119423 filed on Apr.
20, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a cooling system for
cooling an interior of a substantially airtight housing, such as a
housing of a base station of a cellular phone system.
[0004] 2. Description of Related Art
[0005] One type of cooling system for cooling an interior of a
substantially airtight housing exchanges heat between internal air
located within the housing and external air located outside of the
housing to cool the interior of the housing.
[0006] This type of cooling system is used, for example, in a base
station of a cellular phone system. When a temperature of the
external air gets cold (e.g., below freezing temperature),
performance of electronic devices arranged, for example, in a
transmitter-receiver of the base station is degraded. To address
this problem, such a cooling system generally includes an electric
heater that heats the internal air located within the housing of
the base station.
[0007] A power supply circuit that supplies power to the electric
heater includes thermostats to prevent abnormally high heat
generation of the electric heater. Furthermore, a thermal fuse is
additionally provided in the power supply circuit to provide
redundancy in case of failure of the thermostats.
[0008] The U.S. safety standard requires to provide the thermostat
on both sides of the electric heater in the power supply circuit
that supplies power to the electric heater. This requirement poses
a limitation on arrangement of the thermostats. That is, in case of
providing only one thermostat, the best location of the thermostat
(such as one location where temperature is close to that of the
electric heater and where the thermostat can be easily placed) can
be easily selected. However, if two thermostats need to be
provided, it is difficult to place both the thermostats at the best
locations within a limited space. Furthermore, in order to prevent
opening of the thermal fuse before opening of the thermostats,
positional relationship between the two thermostats and the thermal
fuse needs to be concerned.
SUMMARY OF THE INVENTION
[0009] The present invention addresses the described disadvantages.
Thus, it is an objective of the present invention to provide a
cooling system having a heater unit that includes a couple of
thermostats arranged in a manner that achieves a higher degree of
safety.
[0010] To achieve the objective of the present invention, there is
provided a cooling system for cooling an interior of a
substantially airtight housing. The cooling system includes an
internal-air passage, an external-air passage, an internal-air fan,
an external-air fan, a heat exchanger and a heater unit. The
internal-air passage has an internal-air inlet and an internal-air
outlet. Both the internal-air inlet and the internal-air outlet
communicate with an interior of the housing. The external-air
passage has an external-air inlet and an external-air outlet. Both
the external-air inlet and the external-air outlet communicate with
an exterior of the housing. The internal-air fan takes in internal
air from the interior of the housing through the internal-air inlet
and expels the internal air into the interior of the housing
through the internal-air outlet. The external-air fan takes in
external air from the exterior of the housing through the
external-air inlet and expels the external air to the exterior of
the housing through the external-air outlet. The heat exchanger
exchanges heat between the internal air introduced into the
internal-air passage and the external air introduced into the
external-air passage. The heater unit heats the internal air
introduced into the internal-air passage. The heater unit includes
an electric heater, a power supply circuit, a heater protective
device and a heat receiving plate. The electric heater generates
heat upon energization. The power supply circuit supplies power to
the electric heater. The heater protective device is interposed in
the power supply circuit. The heater protective device includes a
first thermostat and a second thermostat. The first thermostat is
interposed in the power supply circuit on a first side of the
electric heater. The second thermostat is interposed in the power
supply circuit on a second side of the electric heater that is
opposite to the first side of the electric heater. The first
thermostat and the second thermostat are arranged to open
substantially at a first predetermined temperature or higher to
disconnect the power supply circuit. The heat receiving plate
receives heat from the electric heater and conducts the heat of the
electric heater to the heater protective device. The first
thermostat and the second thermostat are secured to the heat
receiving plate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention, together with additional objectives, features
and advantages thereof, will be best understood from the following
description, the appended claims and the accompanying drawings in
which:
[0012] FIG. 1 is a schematic side view of a housing including a
cooling system according to a first embodiment of the present
invention, schematically showing an internal structure of the
cooling system;
[0013] FIG. 2 is a partial enlarged cross-sectional view of a
heater unit according to the embodiment;
[0014] FIG. 3 is an electric arrangement of the heater unit
according to the embodiment;
[0015] FIG. 4 is a schematic structural view showing arrangement of
a heater protective device according to the embodiment; and
[0016] FIG. 5 is a schematic side view of a cooling system
according to a second embodiment of the present invention,
schematically showing an internal structure of the cooling
system.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Embodiments of the present invention will now be described
with reference to the accompanying drawings.
First Embodiment
[0018] With reference to FIG. 1, a cooling system 1 according to a
first-embodiment of the present invention can be used, for example,
in a base station of a mobile radio communication system (e.g., a
cellular phone system, automobile telephone system or the
like).
[0019] Such a base station normally includes electronic devices 2
that are sensitive to foreign matter, such as dust, dirt, moisture,
rain, snow or the like. Thus, the base station generally has a
substantially airtight housing 3 that receives and protects the
electronic devices 2 from the foreign matter.
[0020] As shown in FIG. 1, the cooling system 1 is mounted within
the housing 3 in such a manner that the cooling system 1 airtightly
closes one side of the housing 3. The cooling system 1 includes a
casing 4, a heat exchanger 5, an external-air fan 6, an
internal-air fan 7, a heater unit 8 (best seen in FIG. 2) and a
controller 9 (best seen in FIG. 3).
[0021] The casing 4 has an external-air inlet 10 and an
external-air outlet 11 on its exterior side. The casing 4 also has
an internal-air inlet 12 and an internal-air outlet 13 on its
interior side.
[0022] The heat exchanger 5 includes a plurality of first and
second air passages (both not shown) that are arranged alternately
and adjacently in a manner that allows heat exchange between the
first air passages and the second air passages.
[0023] The casing 4 also accommodates an external-air passage 14
and an internal-air passage 15 that are airtightly separated from
each other. The external-air passage 14 communicates the
external-air inlet 10 to the external-air outlet 11 through the
external-air fan 6 and also through the first air passages of the
heat exchanger 5. The internal-air passage 15 communicates the
internal-air inlet 12 to the internal-air outlet 13 through the
internal-air fan 7 and also through the second air passages of the
heat exchanger 5.
[0024] The external-air fan 6 faces the external-air inlet 10 and
is positioned on the bottom side of the heat exchanger 5. Upon
energization, the external-air fan 6 rotates to take in the
external air through the external-air inlet 10 and then to expel it
through the external-air passage 14.
[0025] The internal-air fan 7 faces the internal-air inlet 12 and
is positioned on the top side of the heat exchanger 5. Upon
energization, the internal-air fan 7 rotates to take in the
internal air through the internal-air inlet 12 and then to expel it
through the internal-air passage 15.
[0026] As shown in FIG. 1, the heater unit 8 is arranged at the
internal-air outlet 13 of the casing 4 to heat the internal air
within the housing 3 when a temperature of the internal air within
the housing 3 is substantially equal to or below a predetermined
temperature (e.g., 10 degrees Celsius).
[0027] As shown in FIGS. 2 and 3, the heater unit 8 includes a
heater cover 16, an electric heater 17 and a heater protective
device (to be described later).
[0028] The heater cover 16 is secured to a side wall of the casing
4 such that the heater cover 16 extends at an oblique angle
relative to the side wall of the casing 4 to cover the internal-air
outlet 13. At a bottom side of the cover 16, there is provided an
outlet grille 16b that has a plurality of outlet openings 16a
through which the internal air is discharged from the casing 4.
[0029] With reference to FIG. 4, the electric heater 17 includes a
pipe 17a. A heating wire (e.g., nichrome wire) extends through an
interior of the pipe 17a between ends of the pipe 17a and is
surrounded by dielectric powder (not shown), such as magnesium
oxide powder, that fills the interior of the pipe 17a. The electric
heater 17 is supported by a heater bracket 19 such that the ends of
the pipe 17a are held by the heater bracket 19 via grommets 18,
respectively. End terminals of the electric heater 17 are connected
to an alternating-current (AC) power source through a power supply
circuit that includes the heater protective device (to be described
later) and the relays 20 (FIG. 3).
[0030] With reference to FIG. 3, the relays 20 include first and
second relays 20a and 20b. The first relay 20a is inserted in the
power supply circuit on a first side of the electric heater 17, and
the second relay 20b is inserted in the power supply circuit on a
second side of the electric heater 17 that is opposite to the first
side of the electric heater 17. The first and second relays 20a and
20b are normally simultaneously turned on and off, i.e., closed and
opened by the controller 9. If one of the first and second relays
20a and 20b is short circuited and thus is always closed, the
electric heater 17 can be still appropriately controlled through
the other relay 20a or 20b as long as the other relay 20a or 20b is
operative.
[0031] A temperature of the heater bracket 19 generally gets very
high (about 700 degrees Celsius) due to the heat generated from the
electric heater 17. Thus, the heater bracket 19 is preferrably
fabricated from a non-corrosive heat resistant material, such as
stainless steel SUS 430, SUS 316 or the like. As shown in FIG. 2,
the heater bracket 19 is supported by the heater cover 16 via an
insulator (dielectric member) 21 made, for example, of alumina.
More particularly, the heater bracket 19 is secured to the
insulator 21 with a bolt 22 that extends through the heater cover
16 and the insulator 21 and also with a nut 23 that is threadably
tightened on the bolt 22.
[0032] With reference to FIG. 3, the heater protective device
includes a couple of thermostats 24 and one thermal fuse 25.
[0033] One of the thermostats 24 is interposed in the power supply
circuit on the first side of the electric heater 17 and is referred
as the first thermostat 24a. The other of the thermostats 24 is
interposed in the power supply circuit on the second side of the
electric heater 17 and is referred as the second thermostat 24b.
With reference to FIG. 4, these two thermostats 24 are secured to
opposing sides of one metal plate 26. When a temperature of each
thermostat 24 rises due to the heat conducted through the metal
plate 26 and substantially reaches 40 degrees Celsius or higher, an
internal connection of the thermostat 24 is turned off, i.e., is
opened. When the temperature of the thermostat 24 decreases
substantially below 40 degrees Celsius, the internal contact of the
thermostat 24 is turned on, i.e., is closed.
[0034] As shown in FIGS. 2 and 4, the metal plate 26 is secured to
a heat receiving bracket 27 that is secured to the heater cover 16
and that is heated upon receiving radiated heat from the electric
heater 17.
[0035] As shown in FIG. 4, the thermal fuse 25 extends through the
metal plate 26 in a thickness direction of the metal plate 26 and
is secured thereto. When a temperature of the thermal fuse 25 rises
due to the heat conducted through the metal plate 26 and
substantially reaches 110 degrees Celsius or higher, the thermal
fuse 25 substantially melts or opens to disconnect the power supply
circuit.
[0036] With reference to FIG. 3, the controller 9 monitors a
temperature of the internal air within the housing 3 with a
temperature sensor 28, such as a thermistor. The controller 9
controls the external-air fan 6, the internal-air fan 7 and the
electric heater 17 based on the measured temperature of the
internal air within the housing 3.
[0037] Operation of the cooling system 1 will be briefly
described.
[0038] When the controller 9 is activated, the controller 9 reads
the temperature value from the temperature sensor 28 and controls a
rotational speed of the internal-air fan 7 based on the measured
temperature value of the temperature sensor 28. At this stage, if
the measured temperature value of the temperature sensor 28 is
substantially equal to or greater than, for example, 25 degrees
Celsius (normal temperature), the controller 9 turns on the
external-air fan 6. On the other hand, if the measured temperature
value of the temperature sensor 28 is below this temperature, the
controller 9 turns off the external-air fan 6. Furthermore, if the
measured temperature value of the temperature sensor 28 is
substantially equal to or below a predetermined temperature value
(e.g., 10 degrees Celsius) for energizing the electric heater 17,
the controller 9 turns on the relays 20 to energize the electric
heater 17.
[0039] The electric heater 17 is normally turned on and off through
the relays 20. When the relays 20 fail for some reason and thereby
cannot be turned off upon the temperature exceeding the
predetermined temperature value, the thermostats 24 can be turned
off by the heat transmitted through the metal plate 26, so that the
electric heater 17 can be deenergized.
[0040] Furthermore, when both the thermostats 24 fail (i.e., the
thermostats 24 do not turn off upon substantially exceeding 40
degrees Celsius), the thermal fuse 25 substantially melts or opens
at a predetermined temperature (e.g., 110 degrees Celsius) to
disconnect the power supply circuit, so that the electric heater 17
is deenergized.
[0041] The controller 9 also monitors an electric current value
with an electric current sensor 29 interposed in the power supply
circuit. If any abnormal electric current value is measured with
the electric current sensor 29 (for instance, if the measured
current value is zero although the relays 20 are turned on, or if
an excessive electric current value is measured continuously over a
predetermined period of time), the relays 20 are turned off to
deenergize the electric heater 17. In addition to or as an
alternative to this, a signal indicating the incidence of this
abnormality can be sent, for example, to a control center that
monitors the base stations.
[0042] The present embodiment provides the following
advantages.
[0043] As described above, the heater protective device arranged in
the heater unit 8 includes the first thermostat 24a interposed in
the power supply circuit on the first side of the electric heater
17 and the second thermostat 24b interposed in the power supply
circuit on the second side of the electric heater 17. Furthermore,
the thermostats 24a and 24b are secured to the opposing sides of
the metal plate 26. With this arrangement, the two thermostats 24a
and 24b are operated under substantially the same temperature
condition. Thus, it is possible to simultaneously disconnect the
power supply circuit on both the first and second sides of the
electric heater 17 when the temperature of the metal plate 26
substantially reaches the predetermined temperature value
(temperature value selected for turning off the thermostats 24) or
higher. Thus, even if the failure of the relays 20 or the
abnormality (e.g., short circuit) of the power supply circuit
occurs, the electric heater 17 can be reliably prevented from
reaching the abnormally high temperature, providing the safer
heater unit 8.
[0044] Since the two thermostats 24 are symmetrically arranged on
the metal plate 26, the space required for accommodating the
thermostats 24 is reduced. Furthermore, since the two thermostats
24 receive the heat from the metal plate 26 under substantially the
same condition, the best locations of the two thermostats 24
relative to the electric heater 17 can be easily selected.
[0045] As described above, the electric heater 17 used in the
heater unit 8 has the heating wire (e.g., nichrome wire) extending
through the interior of the pipe 17a and being surrounded by the
dielectric powder (e.g., magnesium oxide powder) that fills the
interior of the pipe 17a. Therefore, the heating wire does not
directly contact the pipe 17a, providing a high degree of
dielectricity.
[0046] Furthermore, since the heater bracket 19 that supports the
electric heater 17 is insulated from the heater cover 16 via the
insulator 21, a double insulating structure is achieved according
to the present embodiment. For instance, during a maintenance
operation, a maintenance worker may touch the heater cover 16 as
well as the casing 4 of the cooling system 1 with bare hands.
However, the heater bracket 19 that supports the electric heater 17
is insulated from the heater cover 16 via the insulator 21. As a
result, even if the insulation of the electric heater 17 fails
(short circuiting), excessive electric current will not flow from
the heater bracket 19 to the heater cover 16 and to the casing 4 of
the cooling system 1. This arrangement assures a higher degree of
safety.
Second Embodiment
[0047] A second embodiment of the present invention will be
described with reference to FIG. 5.
[0048] As shown in FIG. 5, the cooling system 1 of the second
embodiment further includes a damper 30 that opens and closes the
external-air passage 14 of the casing 4.
[0049] When the electric heater 17 is energized, the controller 9
operates the damper 30 to close the external-air passage 14.
[0050] In the first embodiment, the external-air fan 6 is turned
off when the electric heater 17 is energized. However, in such a
case, natural conversion occurs in the external-air passage 14, so
that undesirable heat transfer (heat loss) from the internal air to
the external air occurs within the heat exchanger 5.
[0051] Thus, in the second embodiment, when the electric heater 17
is energized, the external-air fan 6 is turned off, and also the
external-air passage 14 is closed by the damper 30. In this way,
the natural conversion on the external air side can be restricted,
so that the heat transfer (heat loss) from the internal air to the
external air within the heat exchanger 5 can be minimized. This
arrangement advantageously allows a reduction in power consumption
of the electric heater 17.
[0052] The damper 30 can be placed at any desired location as long
as the damper 30 is able to open and close the external-air passage
14. In addition to or as an alternative to the damper 30, a shutter
that opens and closes the external-air inlet 10 or the external air
outlet 11 can be provided.
[0053] The cooling system 1 according to the first or second
embodiment can be modified as follows. That is, in the
above-described cooling system 1, the heat exchanger 5 is the air
to air heat exchanger that directly exchanges the heat between the
internal air and the external air. In place of this air to air heat
exchanger, a boiling cooling system that transfers the heat from
the internal air to the external air by boiling heat transfer can
be used as the heat exchanger 5.
[0054] Additional advantages and modifications will readily occur
to those skilled in the art. The invention in its broader terms is
therefore, not limited to the specific details, representative
apparatus, and illustrative examples shown and described.
* * * * *