Refrigeration – Automatic control – Refrigeration producer
Reexamination Certificate
2003-03-04
2004-06-01
Norman, Marc (Department: 3744)
Refrigeration
Automatic control
Refrigeration producer
C062S228500
Reexamination Certificate
active
06742348
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling a linear expansion valve so as to suitably control the flow rate of refrigerant circulating in an air conditioning system, and more particularly to a method for controlling the aperture ratio of a linear expansion valve of a heat-pump type air conditioning system using a plurality of compressors.
2. Description of the Related Art
A general air conditioning system includes a compressor, a condenser, a linear expansion valve, and an evaporator. The compressor converts a low temperature and low pressure gaseous refrigerant into a high temperature and high pressure gaseous refrigerant. The condenser converts the high temperature and high pressure gaseous refrigerant, converted by the compressor, into a mid-temperature and high pressure liquid refrigerant. The linear expansion valve converts the mid-temperature and high pressure liquid refrigerant, converted by the condenser, into a low temperature and low pressure liquid refrigerant. The evaporator converts the low temperature and low pressure liquid refrigerant into a gaseous refrigerant.
On the other hand, the heat-pump type air conditioning system is provided with a four-way valve which changes the flow-path size of the refrigerant according to heating and cooling modes, whereby the functions of indoor and outdoor heat exchangers are changed. Namely, the indoor and outdoor exchangers serve as a condenser and an evaporator, respectively, in the heating mode, whereas both exchangers serve as an evaporator and a condenser, respectively, in the cooling mode.
In recent times, a plurality of compressors having different capacities are used to change the compression capacity according to a heating or cooling load, so as to optimize cooling and heating efficiencies.
As shown in
FIG. 1
, a heat-pump type air conditioning system using a plurality of compressors according to the prior art includes a plurality of compressors
11
and
12
, an outdoor heat exchanger
14
, an outdoor fan
14
a
, an linear expansion valve
15
, an indoor heat exchanger
16
, an indoor fan
16
a
, and a four-way valve
13
. The compressors
11
and
12
compress refrigerant. The outdoor heat exchanger
14
allows heat exchange between the compressed refrigerant and outdoor air to condense the compresses refrigerant into a mid-temperature and high pressure liquid refrigerant. The outdoor fan
14
a
ventilates outdoor air toward the outdoor heat exchanger
14
. The linear expansion valve
15
decompresses the mid-temperature and high pressure refrigerant into a low temperature and low pressure refrigerant. The indoor heat exchanger
16
allows heat exchange of the refrigerant passing through the linear expansion valve
15
with indoor air to evaporate the refrigerant and refrigerate the indoor air. The indoor fan
16
a
ventilates the indoor air toward the indoor air. The four-way valve
13
changes the flow-path size of the refrigerant according to the cooling and heating modes.
Based on the difference between a desired heating/cooling preset temperature and actual indoor temperature T
4
, a controller
20
judges whether the cooling and heating loads are large or small and controls the operation of the compressors
11
and
12
so that either all or a part of the compressors are activated.
In addition, the controller
20
controls the four-way valve
13
to change the flow-path size of the refrigerant according to the cooling/heating mode, and detects pipe temperatures T
1
and T
2
of the indoor heat exchanger
16
and the outdoor heat exchanger
14
to control the operation of the indoor fan
16
a
and the outdoor fan
14
a.
Further, the controller
20
allows a suitable amount of refrigerant to be circuited according to the cooling and heating loads. The controller
20
also detects the pipe temperatures T
1
, T
2
and the inlet-side pipe temperature T
3
, and controls the aperture ratio of the linear expansion valve
15
so as to maintain a suitable superheat.
However, the heat-pump type air conditioning system of the prior art has the following problems. If a connection pipe of the outdoor and indoor heat exchanger
14
and
16
is composed of a long pipe, a pressure drop occurs while the refrigerant passes through the long pipe, reducing the inlet-side pipe temperature T
3
. This causes the current superheat to be significantly lower than the target superheat set at the time of designing the system. Accordingly, the controller
20
judges there to be a large amount of circulating refrigerant and thus reduces the aperture ratio of the linear expansion valve
15
so as to reduce the flow rate of refrigerant. Thereby, the flow rate of circulating refrigerant is sharply reduced, resulting in a shortage of the flow rate of refrigerant compared to the cooling load.
In addition, when the connection pipe of the indoor and outdoor heat is composed of a short pipe, or the flow rate of the circulating refrigerant is insufficient, the inlet pipe temperature T
3
becomes high, causing the current superheat to exceed the target superheat. This causes the controller
20
to control the linear expansion valve
15
to have a higher aperture ratio, thereby sharply increasing the flow rate of circulating refrigerant. This causes liquid refrigerant to flow into the compressors
11
and
12
.
Further, the controller
20
detects indoor temperature T
4
and outdoor temperature T
5
, and controls the operation of the indoor and outdoor fans
16
a
and
14
a
and the aperture ratio of the linear expansion valve according to the cooling and heating loads. However, if the cooling and heating loads increase, the aperture ratio of the linear expansion valve
15
sharply increases, and thus the amount of the circulating refrigerant sharply increases, consequently causing a problem in that liquid refrigerant flows into the compressors
11
and
12
.
Moreover, when the air volume of the indoor fan
16
a
decreases, or when the outdoor fan
14
a
is turned off in order to prevent heating overload under a condition of high outdoor temperature during the heating operation, refrigerant passing through the indoor heat exchanger
16
or the outdoor heat exchanger
14
is insufficiently evaporated, causing liquid refrigerant to flow into the compressors
11
and
12
.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for controlling a linear expansion valve of an air conditioning system, wherein the flow rate of circulating refrigerant is prevented from being deficient or excessive at any operation environment of the air conditioning system so that the refrigerant is always circulated at a suitable flow rate, thereby improving the air conditioning performance and also securing high reliability of the air conditioning system.
It is another object of the present invention to provide a method for controlling a linear expansion valve of an air conditioning system, wherein the aperture ratio of the linear expansion valve is controlled so that a suitable amount of refrigerant is circulated, irrespective of whether a connection pipe of indoor and outdoor heat exchangers is composed of a long pipe or a short pipe.
It is still another object of the present invention to provide a method for controlling a linear expansion valve in an air conditioning system using a plurality of compressors, wherein the aperture ratio of the linear expansion valve is controlled so that the liquid refrigerant is prevented from flowing into the compressors when the compression capacity of the refrigerant is changed according to cooling and heating loads.
It is yet another object of the present invention to provide a method for controlling a linear expansion valve of an air conditioning system, wherein the opening valve of the linear expansion valve is controlled according to the operation status of an indoor or outdoor fan so as to prevent the liquid refrigerant from flowing into the compresso
Choi Chang Min
Huh Deok
Hwang Yoon Jei
Kim Cheol Min
Lee Won Hee
LG Electronics Inc.
Norman Marc
LandOfFree
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