EP0077414B1

EP0077414B1 - Air temperature conditioning system

Info

Publication number: EP0077414B1
Application number: EP81108580A
Authority: EP
Inventors: Fumio C/O Mitsubischi Denki K. K. Matsuoka; Hitoshi C/O Mitsubischi Denki K. K. Iijima
Original assignee: Mitsubishi Electric Corp
Current assignee: OFFERTA DI LICENZA AL PUBBLICO
Priority date: 1981-10-20
Filing date: 1981-10-20
Publication date: 1987-01-14
Also published as: DE3175833D1; EP0077414A1; DE3177054D1

Description

The present invention relates to an air temperature conditioning system, comprising a compressor, a first heat exchanger, expansion means, and a second heat exchanger connected in series with each other; and means for repeatedly starting and stopping said compressor in response to room temperature sensing means.
Such a system is known from US-A-4017286.
The conventional refrigeration cycle apparatus includes a compressor, a condenser, an expansion device such as a capillary tube or an expansion valve, and an evaporator with these components sequentially coupled in series with each other. When the compressor is stopped, the pressure of the refrigerant on a high pressure side is balanced with the pressure of the refrigerant on the low pressure side. As the compressor is started, the difference between the pressures of the high pressure side and the low pressure side is gradually increased until the apparatus is brought to an ordinary operating state. When the compressor is accordingly repeatedly started and stopped, the high pressure side refrigerant is balanced in presence with the low pressure side refrigerant each time the apparatus is stopped. During these times, refrigerant liquid stored on the low pressure side in an evaporator is drawn into the compressor. The presence of the liquid refrigerant in the condenser increases the load on the compressor at the time of restarting the compressor. This lowers the coefficient of performance (hereinafter abbreviated as "COP") of the apparatus as compared with that during continuous operation.
The apparatus should retain refrigerant separately distributed on the high pressure side and low pressure side without mixture thereof when the compressor is stopped thus to eliminate a loss of energy produced at the time of restarting the compressor in the conventional apparatus and to thereby improve the efficiency thereof and to make it possible to attain an ordinary operating state in a short time after the compressor is restarted. A solution to this problem is suggested by CH-A-188 957. A valve is provided for isolating the high pressure side of the compressor from the low pressure side when the compressor is stopped.
When the above-described refrigeration cycle apparatus is used in an air temperature conditioning system capable of operating in both cooling and heating modes and the system is operated in the heating mode, the reversing capacity is utilised to drive the refrigerant in the reverse direction to perform defrosting. In this case, the outdoor side heat exchanger is used as a condenser and the indoor side heat exchanger is operated as an evaporator. Accordingly, the heating operation of the indoor side heat exchanger must be stopped during defrosting or a heater must be additionally provided. This is clearly disadvantageous for the user. Neither US-A-4 017 286 nor CH-A-1 88 957 suggests a solution to this problem.
An object of the invention is to provide an air temperature conditioning system which incorporates a series connection of a compressor, first and second heat exchangers, and an expansion device in which heating operation may be continued with one heat exchanger whilst performing the operation of defrosting the other heat exchanger.
According to the invention, there is provided an air temperature conditioning system comprising a compressor, a first heat exchanger, expansion means, and a second heat exchanger connected in series with each other; and means for repeatedly starting and stopping said compressor in response to room temperature sensing means; characterised by: means for isolating refrigerant on a high pressure side of said compressor from refrigerant on a lower pressure side of said compressor when said compressor is stopped; and diverting means for passing refrigerant from the compressor to the second heat exchanger for defrosting said second heat exchanger while continuing a heating operation with said first heat exchanger.
The foregoing object as well as the characteristic features of the invention will become more apparent and more readily understandable by the following description when read in conjunction with the accompanying drawing, in which the sole Figure is a schematic structural view of a preferred embodiment of an air temperature conditioning system according to the invention.
Reference is now made to the drawing showing a preferred embodiment of the refrigeration cycle apparatus, constructed as an air temperature regulating system according to the invention, in the heating mode. Reference numeral 1 designates generally a compressor. A refrigerant gas compressed at high temperature and high pressure by the compressor 1 is fed through a check valve 2 and a four-way valve 3 into a condenser 7. The refrigerant dissipates heat in the condenser 7 and is condensed to a high temperature and high pressure liquid. The refrigerant liquid is then passed through an expansion valve 6 where the refrigerant becomes a low temperature, low pressure liquid and a solenoid valve 5, which acts as a switching valve, and from there is introduced into an evaporator 4. The low temperature and low pressure refrigerant liquid in the evaporator 4 absorbs heat and thus evaporates to a gas. This refrigerant gas is again fed through the four-way valve 3 into an accumulator 8 which isolates the refrigerant liquid which cannot be evaporated in the evaporator 4 and is retained in the liquid state and which returns only the refrigerant gas again to the compressor 1. While the compressor 1 is operating, the apparatus continuously performs the refrigeration cycle.
Reference numeral 10 illustrates a fan for the condenser 7 and 9 a fan for the evaporator 4. The four-way valve 3 is a change-over or switching valve which operates so that the condenser 7 can be used as an evaporator and the evaporator 4 used as a condenser.
When this refrigeration cycle apparatus is used in a room airtemperature conditioning system,the evaporator 4 is used as an outdoor side heat exchanger, and the condenser 7 is used as an indoor side heat exchanger. In the cooling mode, the apparatus is operated in a refrigeration cycle in which the four-way valve 3 is switched so that the outdoor side heat exchanger is used as a condenser and the indoor side heat exchanger is used as an evaporator.
The air temperature conditioning system operates to detect the temperature in the room by a temperature detector or thermostat (not shown) and to start or stop the compressor 1 so as to maintain the room temperature at a set temperature by operating or stopping the refrigeration cycle apparatus.
The solenoid valve 5, which isolates the compressor 1, is constructed so as to open when the compressor 1 is started and to close when the compressor 1 is stopped. The solenoid valve 5 and the check valve 2 function to isolate high pressure side refrigerant and low pressure side refrigerant when the compressor 1 is stopped.
In this refrigeration cycle apparatus used in an air temperature conditioning system as described above, when the compressor 1 is repeatedly started and stopped to maintain the room temperature at a set value, the solenoid valve 5 is simultaneously opened and closed. Since the valve 5 is closed when the compressor 1 is stopped, the high temperature and high pressure refrigerant liquid in the condenser 7 does not flow into the evaporator 4. On the other hand, since the check valve 2 is provided at the exhaust side of the compressor 1, the refrigerant gas in the condenser 7 and the condensed refrigerant liquid cannot return to the compressor 1.
When the compressor 1 is restarted, the high pressure side refrigerant in the refrigeration cycle is isolated from the low pressure side refrigerant. Since the solenoid valve 5 is only then opened, a desired pressure difference between the high and low pressure side refrigerant can be attained in short time and the apparatus can reach the ordinary operating state in short time.
A conventional refrigerant cycle not incorporating such an isolating device requires about five minutes to reach the ordinary operation state after restarting. On the other hand, the refrigeration cycle apparatus of the invention requires only about one minute and twenty seconds to make the transition.
It is noted that the aforesaid switching element is not limited to the solenoid valve 5 but may also be another type of switching valve and may be any type which closes when the compressor 1 is stopped and opens when the compressor 1 is started.
The four-way valve 3 is, as illustrated, positioned to connect the indoor heat exchanger 7 as a condenser and the outdoor heat exchanger 4 as an evaporator. Further, there is provided a refrigerant bypass tube 21 extending between the outlet of the compressor 1 and the inlet of the outdoor side heat exchanger 4. A second solenoid valve 22 is disposed in the bypass tube 21 for opening or closing the bypass tube 21. The second solenoid valve 22 is operated to be open during the starting of the defrosting operation of the outdoor side heat exchanger and to close at the end of the defrosting operation of the outdoor side heat exchanger in the heating mode.
In the apparatus thus constructed the second solenoid valve 22 provided in the bypass passage 21 is normally closed in the heating mode, and the high temperature and high pressure refrigerant gas compressed by the compressor 1 passes through the check valve 2 and is introduced from the four-way valve 3 into the indoor side heat exchanger 7 which dissipates heat to the atmosphere to condense the refrigerant gas and to a high pressure and high temperature refrigerant liquid. The refrigerant liquid becomes low pressure and lowtemperature refrigerant at the expansion valve 6 and is introduced through the solenoid valve 5 into the outdoor side heat exchanger 4 which absorbs heat from the atmosphere to evaporate the refrigerant liquid. The refrigerant gas thus evaporated is again introduced through the four-way valve 3 and the accumulator 8 into the compressor 1 to complete one cycle. The same cycle is continuously repeated.
When the compressor 1 is started and stopped repeatedly to control the temperature in the room the solenoid valve 5 opens when the compressor 1 is started and closes when the compressor 1 is stopped, as mentioned above, to thus isolate the high pressure side refrigerant and the lower pressure side refrigerant. Accordingly, the COP of the compressor 1 is improved.
When frost accumulates on the outdoor side heat exchanger 4 reducing the heat exchange rate thereof, the COP of the compressor is lowered and hence a defrosting operation must be carried out to remove the frost.
In one embodiment of the invention, the solenoid valve 5 may be closed by a defrost operation command signal while simultaneously the second solenoid valve 22 in the bypass passage 21 is opened. The high temperature and high pressure refrigerant gas in the indoor side heat exchanger 7 continues to condense to become high temperature and high pressure refrigerant liquid while dissipating heat. On the other hand, the high temperature and high pressure refrigerant gas compressed by the compressor 1 is introduced into the outdoor side heat exchanger 4through the bypass tube 21 to thereby defrost the outdoor side heat exchanger by applying heat thereto to melt the frost. The refrigerant is then introduced through the four-way valve 3 from the accumulator 8 again into the compressor 1 and is again compressed by the compressor 1 to high temperature and high pressure gas which is then introduced through the bypass tube 21 into the outdoor side heat exchanger 4.
Since, in the conventional apparatus, in the defrosting cycle the four-way valve 3 is switched to the state in which the outdoor side heat exchanger 4 is used as a condenser and the indoor side heat exchanger 7 is used as an evaporator, the refrigerant gas exhausted from the outdoor side heat exchanger 4 is introduced through the indoor side heat exchanger 7 into the compressor 1 in one cycle. Accordingly, the heating operation cannot be performed during the defrosting operation.
But, with this embodiment of the invention, the two operations can be performed simultaneously since heating can be effected by utilizing the high temperature and high pressure refrigerant gas accumulated in the indoor side heat exchanger 7, the refrigerant heat in the indoor side heat exchanger 7 being utilized. Further, the defrosting operation can be executed without switching the four-way valve 3 in this embodiment.
The compressor 1 repeats starting and stopping operations in order to control the temperature in the room in heating operation.
In a further embodiment of the invention, defrosting of the evaporator can be effected by opening and closing of the second solenoid valve 22 in synchronism with the starting and stopping operations of the compressor 1, i.e. switching operation of the compressor 1 may be continued during defrosting.
When the compressor 1 is stopped and valve 5 closed in the apparatus thus constructed, the second solenoid valve 22 will open, the outlet side refrigerant from the compressor 1 is accordingly introduced through the bypass tube 21 into the outdoor side heat exchanger 4, and the outlet side pressure of the compressor 1 is thus lowered to balance with the inlet side pressure. Accordingly, since there is no pressure difference between the inlet side and the outlet side of the compressor when the compressor 1 is restarted, the starting torque is low and the electric power consumption is thus reduced compared with the prior art apparatus. In addition, since the starting torque of the compressor 1 is low, the size and capacity of the compressor may be reduced advantageously.
It is noted that even if the amount of refrigerant between the outlet side and the inlet side of the compressor 1 is small and the solenoid valve 5 is closed, as the check valve 2 is provided, the pressure in the outdoor side heat exchanger 4 will not increase even if the outlet refrigerant from the compressor 1 flows into the outdoor side heat exchanger 4.
The second solenoid valve 22 is operated to open when the compressor 1 is stopped and to close a predetermined time, in the heating mode, after the compressor 1 is started. The second solenoid valve 22 thus operated feeds some of the refrigerant, instead of through the check valve 2 into the high pressure side, into the lower pressure side, and accordingly decreases the starting torque of the compressor 1.
The second solenoid valve 22 provided in the bypass passage 21 is opened a short predetermined time before a defrosting operation is started and closed before the expiry of a predetermined short time after completion of the defrosting operation performed in the heating mode. The second solenoid valve 22 receives a control signal from a frost detector (not shown) provided at the outdoor side heat exchanger 4.
Since the second solenoid valve 22 thus constructed introduces rapidly the high temperature and high pressure refrigerant gas into the outdoor side heat exchanger 4 in the defrosting operation, the defrosting time is short. When the second solenoid valve 22 is closed before completion of the defrosting operation, the refrigerant in the outdoor side heat exchanger 4 is used until the defrosting operation is completed. The function of the outdoor heat exchanger 4 as the evaporator is quickly recovered when the operating mode is subsequently switched to the normal mode.

Claims

1. An air temperature conditioning system comprising a compressor (1), a first heat exchanger (7), expansion means (6), and a second heat exchanger (4) connected in series with each other; and means for repeatedly starting and stopping said compressor in response to room temperature sensing means; characterised by: means (2,5) for isolating refrigerant on a high pressure side of said compressor from refrigerant on a lower pressure side of said compressor when said compressor is stopped; and diverting means (21,22) for passing refrigerant from the compressor (1) to the second heat exchanger (4) for defrosting said second heat exchanger (4) while continuing a heating operation with said first heat exchanger (7).

2. A system as claimed in claim 1, wherein said isolating means comprises a check valve (2) provided between an outlet of said compressor (1) and an inlet of said first heat exchanger (7), and a first solenoid valve (5) provided between an outlet of said first heat exchanger (7) and an inlet of said second heat exchanger (4), wherein a branch tube for refrigerant is provided between said outlet of said compressor (1) and said check valve (2), wherein said diverting means has a second solenoid valve (22) and a bypass (21) for communicating one end of said branch tube with said refrigerant tube between said first solenoid valve (5) and said second heat exchanger (4) through said second solenoid valve (22), and wherein means are provided for closing said first solenoid valve (5) and for opening said second solenoid valve (22) when said defrosting operation is performed in said heating mode.

3. A system as claimed in claim 2, wherein means are provided for closing said first solenoid valve (5), for opening said second solenoid valve (22) when said compressor (1) is stopped in said heating mode, and for opening said first solenoid valve (5) and for closing said second solenoid valve (22) when said compressor (1) is started.

4. A system as claimed in claim 2, wherein means are provided for closing said first solenoid valve (5) and for opening said second solenoid valve (22) when said compressor (1) is stopped, for opening said first solenoid valve (5) when said compressor is started, and for closing said second solenoid valve (22) a predetermined time after said compressor (1) is started.

5. A system as claimed in claim 2, wherein means are provided for operating, when a defrosting operation is performed in a heating mode, to open said second solenoid valve (22), to close said first solenoid valve (5) a predetermined time after opening of said second solenoid valve (22), to close said second solenoid valve (22) a predetermined time before said defrosting operation is completed, and to open said first valve (5) when said defrosting operation is completed.

6. A system as claimed in any one of claims 1 to 5 wherein said first heat exchanger (7) is an indoor side heat exchanger and said second heat exchanger (4) is an outdoor side heat exchanger.

7. A system as claimed in any one of claims 1 to 6 wherein the first and second heat exchangers are operable selectively as condenser and evaporator and a reversing valve (3) is provided for reversing the direction of refrigerant flow through the heat exchangers.