U.S. patent application number 13/140641 was filed with the patent office on 2012-02-16 for underground heat exchanger and air conditioning system including the same.
Invention is credited to Hideaki Asai, Katsuhiro Kawabata, Keisuke Tanimoto.
Application Number | 20120037335 13/140641 |
Document ID | / |
Family ID | 42268540 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120037335 |
Kind Code |
A1 |
Asai; Hideaki ; et
al. |
February 16, 2012 |
UNDERGROUND HEAT EXCHANGER AND AIR CONDITIONING SYSTEM INCLUDING
THE SAME
Abstract
A heat-transfer pipe (12) is formed so as to extend from a top
portion of an outer pipe (11) and to be bent at a bottom portion of
the outer pipe (11) to return to the top portion, and is arranged
such that at least a portion thereof contacts an inner
circumferential surface of the outer pipe (11). The heat-transfer
pipe (12) is configured to allow fluid to be heat-exchanged to flow
thereinside in opposite directions in heating operation and cooling
operation.
Inventors: |
Asai; Hideaki; (Osaka,
JP) ; Kawabata; Katsuhiro; (Osaka, JP) ;
Tanimoto; Keisuke; (Osaka, JP) |
Family ID: |
42268540 |
Appl. No.: |
13/140641 |
Filed: |
December 11, 2009 |
PCT Filed: |
December 11, 2009 |
PCT NO: |
PCT/JP09/06815 |
371 Date: |
June 17, 2011 |
Current U.S.
Class: |
165/45 |
Current CPC
Class: |
Y02E 10/10 20130101;
F24F 2005/0057 20130101; F25B 47/006 20130101; Y02B 10/40 20130101;
F28D 15/02 20130101; F25B 2313/02741 20130101; Y02E 60/14 20130101;
F24F 2005/0053 20130101; F28D 20/0052 20130101; F24F 5/0046
20130101; F24T 10/40 20180501; F25B 13/00 20130101; F25B 30/06
20130101 |
Class at
Publication: |
165/45 |
International
Class: |
F24J 3/08 20060101
F24J003/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2008 |
JP |
2008-323384 |
Claims
1. An underground heat exchanger comprising: an outer pipe
vertically buried under the ground; a heat-transfer pipe, in which
fluid to be heat-exchanged flows, inserted inside the outer pipe;
and a heat medium sealed inside the outer pipe, wherein a change in
phase of the heat medium is used to perform heat exchange with
soil, and the heat-transfer pipe is formed so as to extend from a
top portion of the outer pipe and to be bent at a bottom portion of
the outer pipe to return to the top portion, and is arranged such
that at least a portion thereof positioned inside the outer pipe
contacts an inner circumferential surface of the outer pipe to
allow the fluid to be heat-exchanged to flow thereinside in
opposite directions in heating operation and cooling operation.
2. The underground heat exchanger of claim 1, wherein the
heat-transfer pipe is formed such that at least one of a first body
portion provided from the top portion to the bottom portion of the
outer pipe and a second body portion provided from the bottom
portion to the top portion of the outer pipe is in a helical shape,
and the helical portion is arranged to contact the inner
circumferential surface of the outer pipe.
3. The underground heat exchanger of claim 1, wherein the inner
circumferential surface of the outer pipe includes grooves
extending in a circumferential direction of the outer pipe.
4. The underground heat exchanger of claim 3, wherein an outer
circumferential surface of the heat-transfer pipe includes grooves
extending in a circumferential direction of the heat-transfer
pipe.
5. The underground heat exchanger of claim 3, wherein the outer
pipe is buried under the ground such that a longitudinal direction
thereof is in a vertical direction, and the grooves are formed so
as to extend in a horizontal direction.
6. An air conditioning system, comprising: a refrigerant circuit
including the underground heat exchanger of claim 1; a utilization
side heat exchanger; a compression mechanism; an expansion
mechanism; and a flow path switching unit for switching a flow
direction of refrigerant serving as the fluid to be heat-exchanged,
wherein a switch in the flow direction of the refrigerant inside
the refrigerant circuit by the flow path switching unit can switch
between heating operation and cooling operation.
Description
TECHNICAL FIELD
[0001] The present invention relates to an underground heat
exchanger for exchanging heat between fluid to be heat-exchanged
and soil in the ground.
BACKGROUND ART
[0002] Conventional underground heat exchangers for exchanging heat
between fluid to be heat-exchanged and soil in the ground have been
known. Such underground heat exchangers are configured to perform
heat exchange between the fluid to be heat-exchanged and the soil
through a heat medium undergoing a phase change.
[0003] Specifically, for example, as disclosed in Patent Document
1, a pipe containing a heat medium is buried under the ground, and
a heat exchanger in which fluid to be heat-exchanged flows is
provided such that heat exchange is performed with the heat medium
evaporated by geothermal heat, the heat medium being inside the
pipe. This allows the heat of the heat medium evaporated in the
pipe buried under the ground to be transferred to the heat-exchange
fluid by the heat exchanger, and to be used as a heat source for
heating in a circuit in which the fluid to be heat-exchanged
flows.
Citation List
Patent Document
[0004] Patent Document 1: International Publication No.
WO2004/111559
SUMMARY OF THE INVENTION
Technical Problem
[0005] In addition to the geothermal heat used as the heat source
for heating as described above, there is a case where a
configuration for cooling operation which dissipates heat to soil
in the ground is required as an air conditioning system using the
underground heat exchanger.
[0006] In the above configuration for heat exchange between the
fluid to be heat-exchanged and the soil in the ground through the
heat medium undergoing the phase change, the heat medium is
evaporated and condensed repeatedly in the heat exchanger which
functions as an evaporator and a condenser during heating operation
and cooling operation, respectively. That it, during heating
operation, the heat medium of the heat exchanger repeats a cycle of
condensation by contacting a heat-transfer pipe in which the fluid
to be heat-exchanged flows and evaporation by the geothermal heat.
During cooling operation, on the other hand, the heat medium of the
heat exchanger repeats a cycle of condensation by the geothermal
heat and evaporation by contacting the heat-transfer pipe in which
the fluid to be heat-exchanged flows.
[0007] Accordingly, when the heat exchanger buried under the ground
is used for heating operation and cooling operation, a
heat-transfer pipe for heating operation and a heat-transfer pipe
for cooling operation are configured to be each provided inside an
outer pipe buried under the ground so as to switch the
heat-transfer pipes according to the operation states, each of the
heat-transfer pipes having the fluid to be heat-exchanged flowing
therein. Also, the heat-transfer pipe for heating operation and the
heat-transfer pipe for cooling operation are configured to be
respectively arranged on an upper side and a lower side inside the
outer pipe. During heating operation, such configurations allow the
heat medium to be condensed on a surface of the heat-transfer pipe,
then to be evaporated by the geothermal heat while moving downward,
and to return upward again. During cooling operation, on the other
hand, the heat medium is evaporated on the surface of the
heat-transfer pipe, is then condensed while moving upward, and
returns downward again. Thus, the heat medium efficiently
circulates inside the outer pipe.
[0008] However, in the heat exchanger configured to include the
heat-transfer pipes for the respective heating and cooling
operations as described above, heat exchange is not efficiently
performed due to limitation of a range in which heat exchange
capability is ensured. Consequently, when heating capability and
cooling capability are to be ensured, each of the heat-transfer
pipes needs to have a certain length, causing an increase in an
entire length of the heat exchanger. Moreover, the number of the
heat-transfer pipes needed is twice as much as that of a heat
exchanger only for heating or cooling, causing an increase in
costs.
[0009] The present invention has been made in view of the foregoing
problems, and it is an object of the invention to provide an
underground heat exchanger including an outer pipe that contains a
heat-transfer pipe, in which fluid to be heat-exchanged flows,
inserted thereinside and a heat medium sealed thereinside to
efficiently exchange heat between the fluid to be heat-exchanged
and soil in the ground in both heating operation and cooling
operation with a low cost configuration.
Solution to the Problem
[0010] To achieve the foregoing object, in an underground heat
exchanger (10) of the present invention, a heat-transfer pipe (12)
is formed in such a position as to be in an entire length direction
of an outer pipe (11) and is arranged such that at least one
portion thereof contacts an inner circumferential surface of the
outer pipe (11). In addition, fluid to be heat-exchanged is
provided to flow inside one heat-transfer pipe (12) in opposite
directions in heating operation and cooling operation.
[0011] Specifically, a first aspect of the invention is intended to
provide the underground heat exchanger (10) including: the outer
pipe (11) vertically buried under the ground; the heat-transfer
pipe (12), in which fluid to be heat-exchanged flows, inserted
inside the outer pipe (11); and a heat medium (13) sealed inside
the outer pipe (11). The underground heat exchanger (10) performs
heat exchange with soil by using a change in phase of the heat
medium (13).
[0012] The heat-transfer pipe (12) is formed so as to extend from a
top portion of the outer pipe (11) and to be bent at a bottom
portion of the outer pipe (11) to return to the top portion, and is
arranged such that at least a portion thereof positioned inside the
outer pipe (11) contacts an inner circumferential surface of the
outer pipe (11), thereby allowing the fluid to be heat-exchanged to
flow therein in opposite directions in heating operation and
cooling operation.
[0013] According to such a configuration, during heating operation
and cooling operation, the fluid to be heat-exchanged flows in the
heat-transfer pipe (12) inside the outer pipe (11) vertically
buried under the ground. The underground heat exchanger (10)
functions as an evaporator during heating operation and as a
condenser during cooling operation. In the outer pipe (11), the
heat-transfer pipe (12) extends from the top portion of the outer
pipe (11) and is bent at the bottom portion of outer pipe (11) to
return to the top portion, and at least a portion thereof contacts
the inner circumferential surface of the outer pipe (11), so that
the heat medium (13) can efficiently circulate inside the outer
pipe (11) during both heating operation and cooling operation. That
is, such a configuration of the heat-transfer pipe (12) allows the
heat medium (13) condensed on a surface of the heat-transfer pipe
(12) during heating operation to repeat a cycle of reaching the
inner circumferential surface of the outer pipe (11) along an outer
surface of the heat-transfer pipe (12) and evaporating on the inner
circumferential surface of the outer pipe (11) by geothermal heat.
On the other hand, the heat medium (13) evaporated on the surface
of the heat-transfer pipe (12) during cooling operation repeats a
cycle of condensing on the inner circumferential surface of the
outer pipe (11) by geothermal heat and moving to the surface of the
heat-transfer pipe (12). Accordingly, the heat medium (13) can
efficiently circulate inside the outer pipe (11) across an entire
longitudinal direction of the outer pipe (11).
[0014] Therefore, the above configuration allows the heat medium
(13) to efficiently circulate inside the outer pipe (11) with one
heat-transfer pipe (12) in heating operation and cooling operation,
thereby efficiently exchanging heat of the fluid to be
heat-exchanged with soil in the ground in both heating operation
and cooling operation at low costs.
[0015] Moreover, the above configuration can simplify an internal
structure of the underground heat exchanger, so that the
underground heat exchanger can be divided in a longitudinal
direction into units, or an inside of the underground heat
exchanger can be divided into a plurality of spaces. This leads to
enhancement of uniform capability, manufacturing cost reduction,
and simplification of on-site construction work of the underground
heat exchanger.
[0016] In the above configuration, the heat-transfer pipe (12) is
arranged such that at least one of a first body portion (12d)
provided from a top portion to a bottom portion of the outer pipe
(11) and a second body portion (12e) provided from the bottom
portion to the top portion is formed in a helical shape, and the
helical portion contacts an inner circumferential surface of the
outer pipe (11) (second aspect of the invention).
[0017] Thus, at least one of the first body portion (12d) provided
from the top portion to the bottom portion of the outer pipe (11)
and the second body portion (12e) provided from the bottom portion
to the top portion is formed in a helical shape, thereby having a
larger surface area of the heat-transfer pipe (12) inside the outer
pipe (11). Hence, heat exchange is efficiently performed between
the fluid to be heat-exchanged in the heat-transfer pipe (12) and
geothermal heat through the heat medium (13).
[0018] Moreover, the inner circumferential surface of the outer
pipe (11) is preferably formed to include grooves (11a) extending
in a circumferential direction of the outer pipe (11) (third aspect
of the invention). This allows the heat medium (13) condensed on
the surface of the heat-transfer pipe (12) and moved to the inner
circumferential surface during heating operation or the heat medium
(13) condensed on the inner circumferential surface of the outer
pipe (11) during cooling operation to be held in the grooves (11a)
formed on the inner circumferential surface of the outer pipe (11),
and to be moved in a circumferential direction, thereby reducing or
preventing an occurrence of flowing down of the heat medium (13) to
a lower portion of the outer pipe (11). Thus, the heat medium (13)
efficiently circulates inside the outer pipe (11), so that heat
exchange is more efficiently performed between the fluid to be
heat-exchanged in the heat-transfer pipe (12) and soil through the
heat medium (13).
[0019] In addition, the outer circumferential surface of the
heat-transfer pipe (12) is preferably formed to include grooves
(12f) extending in a circumferential direction of the heat-transfer
pipe (12) (fourth aspect of the invention). This allows the
condensed heat medium (13) to be held in the grooves (12f) formed
on the outer circumferential surface of the heat-transfer pipe (12)
and to be moved in the circumferential direction of the
heat-transfer pipe (12), thereby reducing or preventing an
occurrence of flowing down of the condensed heat medium (13) at the
outer circumferential surface of the heat-transfer pipe (12) with
more certainty. Therefore, a combination with the third aspect of
the invention reduces or prevents an occurrence of flowing down of
the heat medium (13) to a lower portion of the outer pipe (11) with
more certainty, and leads to circulation of the heat medium (13) in
the outer pipe (11) more efficiently.
[0020] Moreover, the outer pipe (11) is preferably buried under the
ground such that a longitudinal direction thereof is in a vertical
direction, and the grooves (11a, 12f) are preferably formed so as
to extend in a horizontal direction (fifth aspect of the
invention).
[0021] Hence, the heat medium (13) condensed on the inner
circumferential surface of the outer pipe (11) or the outer
circumferential surface of the heat-transfer pipe (12) is held in
the grooves (11a, 12f) extending in a horizontal direction, thereby
reducing or preventing an occurrence of vertically flowing down of
the heat medium (13) with more certainty.
[0022] A sixth aspect of the invention is intended to provide an
air conditioning system (1) including the underground heat
exchanger (10) of any one of the first through fifth aspects of the
invention so as to perform a refrigeration cycle.
[0023] Specifically, the air conditioning system (1) of the sixth
aspect of the invention includes a refrigerant circuit (2)
including: the underground heat exchanger (10) described in any one
of the first through fifth aspects of the invention; a utilization
side heat exchanger (5); a compression mechanism (3); an expansion
mechanism (6); and a flow path switching unit (4) for switching a
flow direction of refrigerant serving as fluid to be
heat-exchanged. The air conditioning system (1) is configured such
that a switch in the flow direction of the refrigerant in the
refrigerant circuit (2) by the flow path switching unit (4) can
switch between heating operation and cooling operation.
[0024] According to such a configuration, the flow direction of the
refrigerant serving as the fluid to be heat-exchanged in the
refrigerant circuit (2) is switched by the flow path switching unit
(4), thereby allowing the underground heat exchanger (10) serving
as a heat-source heat exchanger to function as an evaporator or a
condenser. In such a configuration, the underground heat exchanger
(10) configured as the first through fifth aspects of the invention
can obtain effects that are substantially similar to those provided
by the first through fifth aspects of the invention. In the air
conditioning system (1) having the above configuration, therefore,
the underground heat exchanger (10) capable of efficiently
performing heat exchange between the refrigerant and soil in the
ground can also be obtained at low costs.
Advantages of the Invention
[0025] In the underground heat exchanger (10) of the first aspect
of the invention, the heat-transfer pipe (12) is formed inside the
outer pipe 11 so as to extend from a top portion of the outer pipe
(11) and to be bent at a bottom portion of the outer pipe (11) to
return to the top portion, and is arranged such that at least a
portion thereof contacts an inner circumferential surface of the
outer pipe (11). The heat-transfer pipe (12) has fluid to be
heat-exchanged flowing thereinside in opposite directions in
heating operation and cooling operation. Accordingly, one
heat-transfer pipe (12) allows the heat medium (13) to efficiently
circulate inside the outer pipe (11) in both heating and cooling
operations, and heat exchange is efficiently performed between the
fluid to be heat-exchanged and soil in the ground through the heat
medium (13). Therefore, heat exchange between the fluid to be
heat-exchanged and soil in the ground in both heating operation and
cooling operation can be efficiently performed with a low cost
configuration.
[0026] Such a configuration can allow the underground heat
exchanger (10) to be divided in a longitudinal direction into
units, or an inside of the underground heat exchanger (10) to be
divided into a plurality of spaces, thereby enhancing uniform
capability, manufacturing cost reduction, and simplification of
on-site construction operation of the underground heat exchanger
(10).
[0027] According to the second aspect of the invention, the
heat-transfer pipe (12) is provided such that at least one of the
first body portion (12d) provided from a top portion to a bottom
portion of the outer pipe (11) and the second body portion (12e)
provided from the bottom portion to the top portion is formed in a
helical shape, and the helical portion contacts an inner
circumferential surface of the outer pipe (11), thereby having a
larger heating surface area of the heat-transfer pipe (12) inside
the outer pipe (11). Thus, heat exchange can be efficiently
performed between fluid to be heat-exchanged and soil in the ground
in both heating operation and cooling operation.
[0028] According to the third aspect of the invention, an inner
circumferential surface of the outer pipe (11) includes the grooves
(11a) extending in a circumferential direction of the outer pipe
(11), so that the heat medium (13) is held in the inner
circumferential surface of the outer pipe (11) with more certainty.
Hence, heat exchange is more efficiently performed between fluid to
be heat-exchanged and soil in the ground through the heat medium
(13). Particularly, according to the forth aspect of the invention,
an outer circumferential surface of the heat-transfer pipe (12)
includes the grooves (12f) extending in a circumferential direction
of the heat-transfer pipe (12), so that the heat medium (13) is
held on the outer circumferential surface of the heat-transfer pipe
(12) with more certainty. Hence, heat exchange is more efficiently
performed between fluid to be heat-exchanged and soil in the ground
through the heat medium (13) by a combination with the
configuration of the third aspect of the invention.
[0029] According to the fifth aspect of the invention, the outer
pipe (11) is buried under the ground such that a longitudinal
direction thereof is in a vertical direction, and the grooves (11a,
12f) are formed so as to extend in a horizontal direction, thereby
reducing or preventing an occurrence of vertically flowing down of
the heat medium (13) condensed inside the outer pipe (11) with more
certainty.
[0030] The air conditioning system (1) of the sixth aspect of the
invention includes the refrigerant circuit (2) including: the
underground heat exchanger (10) described in any one of the first
through fifth aspects of the invention; the utilization side heat
exchanger (5); the compression mechanism (3); the expansion
mechanism (6); and the flow path switching unit (4) for switching a
flow direction of refrigerant serving as fluid to be
heat-exchanged. The air conditioning system (1) is configured such
that the flow path switching unit (4) can switch between heating
operation and cooling operation. Therefore, the air conditioning
system (1) can also obtain effects that are substantially similar
to those provided by the first through fifth aspects of the
invention.
BRIEF DESCRIPTION OF DRAWINGS
[0031] FIG. 1 is a schematic diagram illustrating an air
conditioning system including an underground heat exchanger
according to an embodiment of the present invention;
[0032] FIG. 2 is a longitudinal cross-section illustrating a
schematic configuration of the underground heat exchanger.
[0033] FIG. 3 is an enlarged partial perspective view illustrating
a schematic configuration of an outer pipe and a heat-transfer pipe
of the underground heat exchanger.
[0034] FIG. 4 is an enlarged partial cross-sectional view
illustrating a change in phase of carbon dioxide inside the
underground heat exchanger during heating operation.
[0035] FIG. 5 is a diagram, corresponding to FIG. 4, illustrating a
change in phase of carbon dioxide inside the underground heat
exchanger during cooling operation.
DESCRIPTION OF EMBODIMENTS
[0036] Embodiments of the present invention will be described
hereinafter with reference to the drawings. The following
description of the preferred embodiments is merely exemplary in
nature and is in no way intended to limit the invention, its
application, or uses.
[0037] An underground heat exchanger according to the embodiments
of the present invention is used in an air conditioning system
capable of performing heating operation and cooling operation. The
underground heat exchanger is configured to function as an
evaporator during heating operation to recover heat from soil in
the ground, whereas the underground heat exchanger functions as a
condenser during cooling operation to dissipate heat into soil in
the ground.
<Overall Configuration of Air Conditioning System>
[0038] FIG. 1 is a schematic diagram illustrating an air
conditioning system (1) including an underground heat exchanger
(10) according to an embodiment of the present invention. The air
conditioning system (1) includes a refrigerant circuit (2) to which
a compressor (3) (compression mechanism), a four-way valve (4)
(flow path switching unit), an indoor heat exchanger (5)
(utilization side heat exchanger), an expansion valve (6)
(expansion mechanism), and a plurality of underground heat
exchangers (10) buried under the ground are connected in sequence
through a refrigerant pipe. The refrigerant circuit (2) has
refrigerant (fluid to be heat-exchanged) sealed therein, and the
refrigerant circulates inside the refrigerant circuit (2), so that
the indoor heat exchanger (5) becomes a condenser and the
underground heat exchanger (10) becomes an evaporator during
heating operation, whereas the indoor heat exchanger (5) becomes an
evaporator and the underground heat exchanger becomes a condenser
during cooling operation, thereby performing a vapor compression
refrigeration cycle. In this embodiment, the plurality of
underground heat exchangers (10) are connected in parallel to the
refrigerant circuit (2), and each of the heat exchangers (10) is
configured to perform heat exchange with soil in the ground.
[0039] The compressor (3) includes, for example, a scroll
compressor, and is configured to suck refrigerant from a suction
port to compress and discharge the compressed refrigerant from a
discharge port. In the refrigerant circuit (2), the discharge port
of the compressor (3) is connected to a second port (P2) of the
four-way valve (4), and the suction port of the compressor (3) is
connected to a fourth port (P4) of the four-way valve (4).
[0040] The four-way valve (4) includes: a first port (P1)
connecting to the indoor heat exchanger (5); the second port (P2)
connecting to the discharge port of the compressor (3); a third
port (P3) connecting to the underground heat exchanger (10); and
the fourth port (P4) connecting to the suction port of the
compressor (3). The four-way valve (4) can switch between a first
state (a state indicated by a solid line in FIG. 1) and a second
state (a state indicated by a dashed line in FIG. 1). The first
state is in which the first port (P1) and the second port (P2)
communicate with each other, and the third port (P3) and the fourth
port (P4) communicate with each other. The second state is in which
the first port (P1) and the fourth port (P4) communicate with each
other, and the second port (P2) and the third port (P3) communicate
with each other.
[0041] The indoor heat exchanger (5) is, for example, a cross-fin
type fin-and-tube heat exchanger, and serves as an air heat
exchanger for exchanging heat of refrigerant with indoor air. In
the air conditioning system (1), the indoor heat exchanger (5) is
installed in an indoor unit arranged in a room to be
air-conditioned. In the refrigerant circuit (2), one end of the
indoor heat exchanger (5) is connected to the expansion valve (6),
and another end is connected to the first port (P1) of the four-way
valve (4). In the vicinity of the indoor heat exchanger (5), an
indoor fan (7) for sending air subjected to heat exchange with the
indoor heat exchanger (5) into the room is provided.
[0042] The expansion valve (6) includes an electronic expansion
valve whose degree of opening is variable. A change in degree of
the opening of the expansion valve (6) leads to expansion of
refrigerant flowing from the indoor heat exchanger (5) or the
underground heat exchanger (10), thereby decompressing the
refrigerant to a predetermined pressure level.
[0043] The underground heat exchanger (10) has a substantially
cylindrical outer shape, and is configured to be buried under the
ground so as to extend in a longitudinal direction (vertical
direction) such that heat exchange is performed between refrigerant
flowing thereinside and soil. The underground heat exchanger (10)
includes: an outer pipe (11) having a closed-bottomed tubular
shape; a heat-transfer pipe (12), in which the refrigerant flows,
installed inside the outer pipe (11); and a heat medium (13) sealed
inside the outer pipe (11) each of which will be described in
detail later. The underground heat exchanger (10) is configured to
perform heat exchange between the refrigerant flowing inside the
heat-transfer pipe (12) and the soil outside the outer pipe (11)
through the heat medium (13).
[0044] In the air conditioning system (1), therefore, heating
operation is performed when the four-way valve (4) is in the first
state, and cooling operation is performed when the four-way valve
(4) is in the second state. That is, in heating operation, the
underground heat exchanger (10) functions as an evaporator and the
indoor heat exchanger (5) function as a condenser to perform a
vapor compression refrigeration cycle in the refrigerant circuit
(2). In the cooling operation, on the other hand, the underground
heat exchanger (10) functions as a condenser, and the indoor heat
exchanger (5) functions as an evaporator to perform a vapor
compression refrigeration cycle in the refrigerant circuit (2).
<Configuration of Underground Heat Exchanger>
[0045] A configuration of the underground heat exchanger (10) will
be described below with reference to FIG. 2.
[0046] The underground heat exchanger (10) includes the outer pipe
(11), the heat-transfer pipe (12) installed inside the outer pipe
(11), and the heat medium (13) sealed inside the outer pipe (11) as
described above.
[0047] The outer pipe (11) is a metal tubular member with both ends
closed with respective plate members made of metal, and has space
(S) thereinside. The outer pipe (11) has a closed structure capable
of sealing a predetermined amount of carbon dioxide (CO.sub.2)
serving as the heat medium (13) in the space (S) thereof. In the
space (S) of the outer pipe (11), the heat-transfer pipe (12), in
which refrigerant flows, is installed. The heat-transfer pipe (12)
is connected to a refrigerant pipe of the refrigerant circuit (2)
by penetrating through the plate member forming one of the end
surfaces (end surface on a ground surface side) of the outer pipe
(11). Here, the outer pipe (11) is vertically buried under the
ground such that a tubular axial direction thereof is in a
substantially vertical direction. Although the outer pipe (11) is
ideally buried under the ground in a substantially vertical
direction, a certain degree of inclination may be allowed.
[0048] The heat-transfer pipe (12) is made of copper and is a pipe
member, in which refrigerant flows, forming a portion of a flow
path of the refrigerant circuit (2). In this embodiment, the
heat-transfer pipe (12) is formed so as to extend from a top
portion to a bottom portion of the outer pipe (11) and to be bent
at the bottom portion to return to the top portion, and is
installed inside the outer pipe (11) such that both ends thereof
protrude outward by penetrating through the plate member forming
one of the end surfaces of the outer pipe (11). Specifically, the
heat-transfer pipe (12) includes: a first connection portion (12a)
that has one end side connecting to the expansion valve (6); a body
portion (12c) connecting to the other end side of the first
connection portion (12a); and a second connection portion (12b)
that has one end side connecting to the body portion (12c) and the
other end side connecting to the third port (P3) of the four-way
valve (4). These connection portions (12a, 12b) are provided so as
to penetrate through the plate member forming one of the end
surfaces (end surface on the ground surface side) of the outer pipe
(11), whereas the body portion (12c) is arranged along an inner
surface of the outer pipe (11).
[0049] The body portion (12c) includes: a first body portion (12d),
formed in a straight shape, connecting to the other end side of the
first connection portion (12a) and extending to the bottom portion
of the outer pipe (11); and a second body portion (12e), formed in
a helical shape, connecting to the first body portion (12d) and
extending to the top portion of the outer pipe (11). Such helical
formation of the second body portion (12e) can increase a surface
area in which heat is exchanged between refrigerant flowing inside
the second body portion (12e) and the carbon dioxide (13) sealed
inside the outer pipe (11). Accordingly, heat exchange is
efficiently performed between the refrigerant and the carbon
dioxide (13).
[0050] The helical second body portion (12e) is arranged so as to
contact an inner circumferential surface of the outer pipe (11),
and the first body portion (12d) is arranged on an inward side of
the helical second body portion (12e) so as to contact the second
body portion (12e). Accordingly, the second body portion (12e)
contacts the inner circumferential surface of the outer pipe (11),
so that the carbon dioxide (13) condensed on an outer
circumferential surface of the second body portion (12e) or the
inner circumferential surface of the outer pipe (11) is moved to
the inner circumferential surface of the outer pipe (11) or the
outer circumferential surface of the second body portion (12e),
thereby leading to evaporation of the carbon dioxide (13) on each
of such surfaces, as will be described later.
[0051] That is, as illustrated in FIG. 4, during heating operation
of the air conditioning system (1), low-pressure refrigerant that
has a saturation temperature lower than a temperature of soil in
the ground flows inside the heat-transfer pipe (12) of the
underground heat exchanger (10). Consequently, the carbon dioxide
(13), inside the outer pipe (11), that has a saturation temperature
lower than a temperature of the soil and higher than a temperature
of the low-pressure refrigerant is condensed on an outer surface of
the heat-transfer pipe (12). Herein, the refrigerant flowing inside
the second body portion (12e) of the heat-transfer pipe (12) is
evaporated by heat of condensation of the carbon dioxide (13), and
is sucked through the suction port of the condenser (3).
[0052] As described above, since the second body portion (12e) and
the inner circumferential surface of the outer pipe (11) contact
each other, the condensed carbon oxide (13) moves from the outer
circumferential surface of the second body portion (12e) to the
inner circumferential surface of the outer pipe (11) and is
evaporated on the inner circumferential surface by heat of the soil
in the ground. The evaporated carbon dioxide (13) is condensed
again when cooled by the second body portion (12e) of the
heat-transfer pipe (12).
[0053] On the other hand, as illustrated in FIG. 5, during cooling
operation of the air conditioning system (1), high-pressure
refrigerant that has a saturation temperature higher than a
temperature of soil in the ground flows inside the heat-transfer
pipe (12) of the underground heat exchanger (10). The carbon
dioxide (13), inside the outer pipe (11), has a saturation
temperature higher than a temperature of the soil and lower than a
temperature of the high-pressure refrigerant, thereby vaporizing on
the outer surface of the heat-transfer pipe (12) while condensing
on the inner circumferential surface of the outer pipe (11).
[0054] That is, as described above, since the second body portion
(12e) and the inner circumferential surface of the outer pipe (11)
contact each other, the carbon dioxide (13) condensed on the inner
circumferential surface of the outer pipe (11) moves to the outer
circumferential surface of the second body portion (12e) and is
vaporized on the outer circumferential surface by heat of the
refrigerant. The vaporized carbon dioxide (13) is condensed again
when cooled by the inner circumferential surface of the outer pipe
(11). When the carbon dioxide (13) vaporizes on the outer surface
of the second body portion (12e) of the heat-transfer pipe (12),
heat of the refrigerant flowing inside the second body portion
(12c) is absorbed by evaporation of the carbon dioxide (13), so
that the refrigerant is condensed and flows into the expansion
valve (6).
[0055] In this embodiment, as illustrated in FIG. 3, the inner
circumferential surface of the outer pipe (11) has a plurality of
grooves (11a) that are formed alongside one another in a
longitudinal direction and extend horizontally in a circumferential
direction of the outer pipe (11). Moreover, the outer
circumferential surface of the second body portion (12e) of the
heat-transfer pipe (12) has a plurality of grooves (12f) that are
formed in a longitudinal direction of the heat-transfer pipe (12).
The grooves (12f) are parallel to the grooves (11a) on the inner
circumferential surface of the outer pipe (11) and extend
horizontally in a circumferential direction of the heat-transfer
pipe (12).
[0056] Accordingly, the inner circumferential surface of the outer
pipe (11) and the outer circumferential surface of the second body
portion (12e) of the heat-transfer pipe (12) have the respective
grooves (11a, 12f) formed thereon, so that the carbon dioxide (13)
condensed on the outer circumferential surface of the second body
portion (12e) during heating operation and the carbon dioxide (13)
condensed on the inner circumferential surface of the outer pipe
(11) during cooling operation are held inside the respective
grooves (11a, 12f), thereby reducing or preventing an occurrence of
flowing down of the carbon dioxide (13) to a lower portion of the
outer pipe (11). As described above, since the grooves (11a, 12f)
are respectively arranged on the inner circumferential surface of
the outer pipe (11) and the outer circumferential of the second
body portion (12e) of the heat-transfer pipe (12) in the
circumferential direction and extend horizontally, the condensed
carbon dioxide (13) can spread in the circumferential direction
(horizontal direction) on the outer circumferential surface of the
second body portion (12e) of the heat-transfer pipe (12) or the
inner circumferential surface of the outer pipe (11) (see FIGS. 4
and 5). Consequently, heat exchange of the carbon dioxide (13) is
performed with the refrigerant and soil. Thus, such an arrangement
of the grooves (11a, 12f) can reduce or prevent an occurrence of
vertically flowing down of the condensed carbon dioxide (13) in the
outer pipe (11) with more certainty, and heat exchange is
effectively performed between the refrigerant inside the
heat-transfer pipe (12) and the soil outside the outer pipe (11)
through the carbon dioxide (13).
[0057] In this embodiment, the grooves (11a) on the inner
circumferential surface of the outer pipe (11) and the grooves
(12f) on the outer circumferential surface of the heat-transfer
pipe (12) are formed in substantially parallel, but not limited
thereto. The grooves (11a, 12f) may cross each other, or the
grooves (11a, 12f) may be slightly inclined up and down relative to
a horizontal direction.
--Operation--
[0058] Next, operation of the air conditioning system (1) having
the above configurations will be described with reference to FIGS.
1, 4 and 5.
(Heating Operation)
[0059] As illustrated in FIG. 1, the four-way valve (4) is switched
to a first state at the beginning of heating operation.
Subsequently, when the compressor (3) comes into operation,
compressed high-pressure refrigerant (gas refrigerant) is
discharged from a discharge port of the compressor (3) and flows
into the indoor heat exchanger (5) through the four-way valve (4).
In the indoor heat exchanger (5), the high-pressure refrigerant
dissipates heat to indoor air and is condensed. The indoor air is
heated by heat of condensation, and indoor heating is performed.
The refrigerant condensed in the indoor heat exchanger (5) flows
out of the indoor heat exchanger (5), is then decompressed by the
expansion valve (6), and flows into the underground heat exchanger
(10) (a solid line arrow in FIG. 1). In the expansion valve (6),
the refrigerant is decompressed such that a saturation temperature
thereof is lower than a temperature of soil in the ground.
[0060] The low-pressure refrigerant flowing into the underground
heat exchanger (10) absorbs heat of the ground through the carbon
dioxide (13) in the outer pipe (11) and is evaporated. The
evaporated refrigerant flows out of the underground heat exchanger
(10), and is sucked again into the compressor (3) through the
four-way valve (4). Then, the refrigerant is compressed to a
predetermined pressure level and is discharged.
[0061] Accordingly, the refrigerant circulates inside the
refrigerant circuit (2) to perform a vapor compression
refrigeration cycle, and indoor heating is performed.
[0062] Next, a change in the state of the refrigerant and the
carbon dioxide (13) in the underground heat exchanger (10) will be
described.
[0063] As described above, when the low-pressure refrigerant having
a saturation temperature lower than a temperature of the soil in
the ground flows into the body portion (12c) of the heat-transfer
pipe (12) in the underground heat exchanger (10), the carbon
dioxide (13) being sealed inside the outer pipe (11) of the
underground heat exchanger (10) and having a saturation temperature
higher than a temperature of the refrigerant is condensed on the
body portion (12c) of the heat-transfer pipe (12) as illustrated in
FIG. 4. Then, the refrigerant inside the heat-transfer pipe (12) is
evaporated by heat of condensation of the carbon dioxide (13), and
is sucked into the compressor (3) after flowing out of the
underground heat exchanger (10).
[0064] On the other hand, in the outer pipe (11) of the underground
heat exchanger (10), the condensed carbon dioxide (13) moves
horizontally along the outer circumferential surface of the helical
second body portion (12e) of the heat-transfer pipe (12) to the
inner circumferential surface of the outer pipe (11), the inner
circumferential surface being in contact with the second body
portion (12e). On the outer circumferential surface of the outer
pipe (11), the carbon dioxide (13) is vaporized by heat of the soil
in the ground, and the vaporized carbon dioxide (13) is condensed
again by the refrigerant flowing in the second portion (12e) of the
heat-transfer pipe (12).
(Cooling Operation)
[0065] First, the four-way valve (4) is switched to a second state
at the beginning of cooling operation. Subsequently, when the
compressor (3) starts operation, compressed high-pressure
refrigerant is discharged from a discharge port of the compressor
(3), and flows into the underground heat exchanger (10) through the
four-way valve (4) (a dashed line arrow in FIG. 1). The
high-pressure refrigerant flowing into the underground heat
exchanger (10) dissipates heat to soil in the ground through the
carbon dioxide (13) inside the outer pipe (11), and condenses. The
condensed refrigerant flows out of the underground heat exchanger
(10), is then decompressed by the expansion valve (6), and is
injected into the indoor heat exchanger (5). In the expansion valve
(6), the refrigerant is decompressed such that a saturation
temperature thereof is lower than an indoor temperature.
[0066] The low-pressure refrigerant flowing into the indoor heat
exchanger (5) absorbs heat of indoor air, and is evaporated. The
evaporated refrigerant flows out of the indoor heat exchanger (5),
and is sucked again into the compressor (3) through the four-way
valve (4). Then, the refrigerant is compressed to a predetermined
pressure level and is discharged.
[0067] In this manner, the refrigerant circulates inside the
refrigerant circuit (2) to perform a vapor compression
refrigeration cycle, and indoor cooling is performed.
[0068] Next, a change in the state of the refrigerant and the
carbon dioxide (13) in the underground heat exchanger (10) will be
described. As illustrated in FIG. 5, during the cooling operation
described above, the carbon dioxide (13), being sealed inside the
outer pipe (11) of the underground heat exchanger (10) and having a
saturation temperature lower than a temperature of the refrigerant
and a saturation temperature higher than a temperature of soil in
the ground, is condensed on the inner circumferential surface of
the outer pipe (11) by geothermal heat. The condensed carbon
dioxide (13) moves horizontally along the inner circumferential
surface of the outer pipe (11) to the outer circumferential surface
of the second body portion (12e) of the heat-transfer pipe (12),
the outer circumferential surface being in contact with the inner
circumferential of the outer pipe (11). Since the high-pressure
refrigerant having a temperature higher than a saturation
temperature of the carbon dioxide (13) flows inside the
heat-transfer pipe (12), the carbon dioxide (13) vaporizes on the
outer circumferential surface of the second body portion (12e) of
the heat-transfer pipe (12). Herein, the heat of the refrigerant in
the heat-transfer pipe (12) is absorbed by the carbon dioxide (13),
so that the refrigerant is condensed and flows into the expansion
valve (6) from the underground heat exchanger (10).
[0069] On the other hand, the carbon dioxide (13) evaporated on the
outer circumferential surface of the second body portion (12e) of
the heat-transfer pipe (12) is condensed again on the inner
circumferential surface of the outer pipe (11).
--Advantages of Embodiment--
[0070] According to the embodiment, the underground heat exchanger
(10) includes the outer pipe (11) vertically buried under the
ground, and the outer pipe (11) includes the heat-transfer pipe
(12), in which fluid to be heat-exchanged flows, inserted
thereinside and the carbon dioxide (13) serving as a heat medium
sealed thereinside. In the underground heat exchanger (10), the
second body portion (12e) of the heat-transfer pipe (12) extending
from a top portion to a bottom portion of the outer pipe (11) is
formed in a helical shape, and the heat-transfer pipe (12) is
arranged such that the second body portion (12e) contacts an inner
circumferential surface of the outer pipe (11), so that a phase of
the carbon dioxide (13) is efficiently changed between the second
body portion (12e) and the inner circumferential surface of the
outer pipe (11) during both heating operation and cooling
operation. Consequently, heat exchange is performed between
refrigerant and soil in the ground through the carbon dioxide (13).
Thus, a switch in a flow direction of the refrigerant inside one
heat-transfer pipe (12) leads to heat exchange between the
refrigerant and soil in the ground during both heating operation
and cooling operation. Hence, the underground heat exchanger (10)
having good heat exchange efficiency is obtained with a low cost
configuration.
[0071] Moreover, the inner circumferential surface of the outer
pipe (11) and the outer circumferential surface of the second body
portion (12e) of the heat-transfer pipe (12) have a plurality of
respective grooves (11a, 12f) each of which is formed in a
circumferential direction and extends horizontally. The grooves
(11a) of the outer pipe (11) reduce or prevent an occurrence of
vertically flowing down of the carbon dioxide (13) condensed on the
outer circumferential surface of the second body portion (12e) of
the heat-transfer pipe (12) during heating operation, and the
grooves (12f) of the heat-transfer pipe (12) reduce or prevent an
occurrence of flowing down of the carbon dioxide (13) condensed on
the inner circumferential surface of the outer pipe (11) during
cooling operation. That is, the condensed carbon dioxide (13) moves
inside the grooves (11a, 12f) in the circumferential direction
(horizontal direction), so that the carbon dioxide (13) is
vaporized in a wider area of the circumferential direction, thereby
efficiently exchanging heat between refrigerant and soil in the
ground through the carbon dioxide (13).
[0072] In addition, the above configuration can simplify an
internal structure of the underground heat exchanger (10) and
obtain heat exchange capability that is substantially the same in
any position in a longitudinal direction of the underground heat
exchanger (10). Accordingly, the underground heat exchanger (10)
may be divided in a longitudinal direction into units, or an inside
of the underground heat exchanger (10) may be divided into a
plurality of spaces. Such a configuration can enhance uniform
capability, manufacturing cost reduction, and simplification of
on-site construction operation of the underground heat exchanger
(10).
<<Other Embodiments>>
[0073] The foregoing embodiment may be configured as follows.
[0074] In the foregoing embodiment, only the second body portion
(12e) of the heat-transfer pipe (12) is formed in a helical shape
and has the grooves (12f) on the outer surface thereof, but not
limited thereto. The first body portion (12d) may be formed in a
helical shape and have grooves on an outer circumferential surface
thereof. In such a case, the helical first body portion (12d) is
also arranged so as to contact an inner circumferential surface of
the outer pipe (11). Moreover, a portion of each of the first body
portion (12d) and the second body portion (12e) may be formed in a
helix shape. In addition, a non-helical portion of the
heat-transfer pipe (12) may contact the inner circumferential
surface of the outer pipe (11), and grooves may be formed on the
outer circumferential surface of the heat-transfer pipe (12), the
outer circumferential surface being in contact with the inner
circumferential surface of the outer pipe (11). Moreover, the inner
circumferential surface of the outer pipe (11) or the outer
circumferential surface of the heat-transfer pipe (12) may be
configured not to have grooves.
[0075] In the foregoing embodiment, the second body portion (12e)
of the heat-transfer pipe (12) is formed in a helical shape, but
not limited thereto. The second body portion (12e) may be formed in
any shape as long as heat exchange efficiency is not affected by a
pressure loss between an inlet side and an outlet side of the
heat-transfer pipe (12).
[0076] In the foregoing embodiment, moreover, the carbon dioxide
(13) is used as a heat medium inside the outer pipe (11), but not
limited thereto. Any medium which undergoes a phase change between
-10.degree. C. and 40.degree. C. may be used.
[0077] Moreover, in the foregoing embodiment, the underground heat
exchanger (10) is configured to have one heat-transfer pipe (12)
which is installed inside one outer pipe (11), but not limited
thereto. The underground heat exchanger (10) may be configured to
have a combination of the outer pipe that is divided in a
longitudinal direction thereof and the heat-transfer pipe that is
divided with division of the outer pipe. In the foregoing
embodiment, a plurality of the underground heat exchangers (10) are
connected in parallel, but not limited thereto. A portion or all of
the plural underground heat exchangers (10) may be connected in
series. In the foregoing embodiment, the heat-transfer pipe (12)
inserted inside the outer pipe (11) is made of copper, but not
limited thereto. The heat-transfer pipe (12) may be made of any
material having good heat conductivity or corrosion resistance such
as aluminum, aluminum alloy, iron, or a composite material.
[0078] In the foregoing embodiment, the four-way valve (4) is
configured to switch a flow direction of the refrigerant in the
refrigerant circuit (2) in the air conditioning system (1), but not
limited thereto. Any configuration may be employed as long as the
flow direction of the refrigerant is switchable.
INDUSTRIAL APPLICABILITY
[0079] The present invention is useful particularly for an
underground heat exchanger for exchanging heat between refrigerant
and soil in the ground.
DESCRIPTION OF REFERENCE CHARACTERS
[0080] 1 air conditioning system [0081] 2 refrigerant circuit
[0082] 3 compressor (compression mechanism) [0083] 4 four-way valve
(flow path switching unit) [0084] 5 indoor heat exchanger
(utilization side heat exchanger) [0085] 6 expansion valve
(expansion mechanism) [0086] 7 indoor fan [0087] 10 underground
heat exchanger [0088] 11 outer pipe [0089] 11a grooves [0090] 12
heat-transfer pipe [0091] 12a first connection portion [0092] 12b
second connection portion [0093] 12c body portion [0094] 12d first
body portion [0095] 12e second body portion [0096] 12f grooves
[0097] 13 carbon dioxide (heat medium) [0098] S space
* * * * *