The present invention relates to a heat pump apparatus which performs a refrigeration cycle.
Airconditioners of the so-called multi type have been known in the prior art. Japanese Patent Kokai Gazette No. (1998)300292 discloses one such airconditioner that includes a single outdoor unit and a plurality of indoor units connected to the outdoor unit. In this airconditioner, the outdoor unit contains an outdoor circuit and each indoor unit contains an indoor circuit. The outdoor circuit of the outdoor unit includes a compressor, an outdoor heat exchanger, an outdoor expansion valve, a receiver, et cetera. On the other hand, the indoor circuit of each indoor unit includes an indoor heat exchanger and an indoor expansion valve. The indoor units are each connected in parallel to the outdoor unit to form a refrigerant circuit of the airconditioner.
The above-described airconditioner performs a refrigeration cycle by circulation of a refrigerant through the refrigerant circuit. Additionally, the airconditioner operates switchably between a cooling mode of operation and a heating mode of operation by reversing the circulation direction of refrigerant in the refrigerant circuit.
During the cooling mode of operation, a cooling operation, in which each indoor heat exchanger acts as an evaporator, is carried out. During the cooling mode of operation, a refrigerant discharged from the compressor is caused to condense by the outdoor heat exchanger. After passing through the receiver, the refrigerant is distributed to each indoor circuit. Thereafter, the refrigerant is depressurized by the indoor expansion valve, is caused to evaporate by the indoor heat exchanger, is brought back to the outdoor circuit, and is drawn into the compressor.
During the heating mode of operation, a heating operation (i.e., a heat pump operation), in which each indoor heat exchanger acts as a condenser, is carried out. During the heating mode of operation, a refrigerant discharged from the compressor is distributed to each indoor circuit and is caused to condense by the indoor heat exchanger. The refrigerant condensed is depressurized by the indoor expansion valve. Thereafter, the refrigerant is delivered to the outdoor circuit. And, after passing through the receiver, the refrigerant is further depressurized by the outdoor expansion valve. Thereafter, the refrigerant is caused to evaporate by the outdoor heat exchanger and is drawn into the compressor.
Installation of a multi type airconditioner in a building may result in a difference in installation height between indoor units. For example, when an outdoor unit is installed on the roof and indoor units are installed on the first floor and on the second floor, respectively, there is a difference in installation height between the indoor units. In this case, the refrigerant, while changing in phase, circulates between an outdoor circuit contained in the outdoor unit installed on the roof and each of indoor circuits contained in the indoor units installed on the first and second floors.
However, if the difference in installation height between the indoor units becomes greater, this causes the problem that the refrigerant flows only through the upper-situated indoor unit, in other words no refrigerant flows in the lower-situated indoor unit during the heating mode of operation of the airconditioner. As a result, the lower-situated indoor unit fails to provide sufficient heating. Consequently, conventional airconditioners are subject to many restrictions on the difference in installation height between indoor units and the degree of layout freedom at the time of installation in a building is little.
Referring to FIG. 4, such a drawback will be illustrated by an example case in which a first indoor unit (12) is installed lower than an outdoor unit (11) and a second indoor unit (13) is disposed lower than the first indoor unit (12). Here, the description will be made on the condition that there is an installation height difference of H1 between the second indoor unit (13) and the first indoor unit (12) and there is an installation height difference of H2 between the first indoor unit (12) and the outdoor unit (11) is (see FIG. 2).
FIG. 4 is a Mollier diagram (i.e., a pressure-enthalpy diagram) showing a typical refrigeration cycle performed in the refrigerant circuit of the airconditioner. During the heating mode of operation, a refrigerant condensed by an indoor heat exchanger of the first indoor unit (12) is depressurized by an indoor expansion valve of the first indoor unit (12) and, as a result, the pressure decreases by xcex94Pi1. On the other hand, a refrigerant condensed by an indoor heat exchanger of the second indoor unit (13) is depressurized by an indoor expansion valve of the second indoor unit (13) and, as a result, the refrigerant pressure decreases by xcex94Pi2. The refrigerant condensed in the second indoor unit (13) flows toward the outdoor unit (11) and the refrigerant pressure will have decreased by a liquid head difference xcex94h1 corresponding to the installation height difference H1 between the first indoor unit (12) and the second indoor unit (13) at the moment that the refrigerant reaches the height of the first indoor unit (12). Thereafter, the refrigerant from the first indoor unit and the refrigerant from the second indoor unit flow into each other and the refrigerant pressure decreases by a liquid head difference xcex94h2 corresponding to the installation height difference H2 between the first indoor unit (12) and the outdoor unit (11). And, the refrigerant flows into the receiver. The refrigerant, which has exited the receiver, is depressurized by the outdoor expansion valve and the refrigerant pressure decreases by xcex94P0. Then the refrigerant is caused to evaporate by the outdoor heat exchanger and is drawn into the compressor.
If the installation height difference H1 between the indoor units (12, 13) is increased, then the liquid head difference xcex94h1 corresponding to the installation height difference H1 also increases. In this case, the valve travel of the indoor expansion valve (which has already been in a certain open state) of the second indoor unit (13) is increased to a further extent so as to reduce the differential pressure xcex94Pi2 between the inlet pressure and the outlet pressure of the indoor expansion valve, whereby the flow rate of refrigerant to the second indoor unit (13) is assured. However, even when the indoor expansion valve of the second indoor unit (13) is fully opened, it is impossible to reduce the differential pressure xcex94Pi2 to zero. Accordingly, if the installation height difference H1 between the indoor units (12, 13) becomes excessive, this makes it impossible to assure the flow rate of refrigerant to the second indoor unit (13) by adjustment of the valve travel of the indoor expansion valve of the second indoor unit (13). As a result, the flow rate of refrigerant to the second indoor unit (13) decreases. Therefore, severe restrictions have been imposed on the indoor unit installation height difference H1 in order to prevent occurrence of such a situation.
In consideration of the above-described inconvenience, the present invention was made. Accordingly, an object of the present invention is to relax restrictions on the installation of a heat pump apparatus including a plurality of utilization side circuits, thereby improving the freedom of installation thereof.
The present invention discloses a heat pump apparatus comprising a refrigerant circuit (15) in which a plurality of utilization side circuits (60, 65) having respective utilization side heat exchangers (61, 66) and utilization side expansion mechanisms (62, 67) are each connected in parallel to a heat source side circuit (20) having a compressor (41, 42), a heat source side expansion mechanism (24), and a receiver (23), and the heat pump apparatus performs at least a heating operation for allowing refrigerant, condensed by each of the utilization side heat exchangers (61, 66) in a refrigeration cycle in which refrigerant circulates in the refrigerant circuit (15), to flow into the receiver (23). And, the heat pump apparatus further comprises a communicating passageway (35) for directing gaseous refrigerant in the receiver (23) to a suction side of the compressor (41, 42), a switching mechanism (36) for establishing and interrupting flow of gaseous refrigerant in the communicating passageway (35), and a controlling means (90) for controlling the switching mechanism (36) so that gaseous refrigerant flows in the communicating passageway (35) in the heating operation.
In the refrigerant circuit (15) of the present heat pump apparatus, the utilization side circuits (60, 65) are each connected in parallel to the heat source side circuit (20). The heat source side circuit (20) includes the compressor (41, 42), the heat source side heat exchanger (22), the heat source side expansion mechanism (24), and the receiver (23). The utilization side circuit (60) includes the utilization side heat exchanger (61) and the utilization side expansion mechanism (62). The utilization side circuit (65) include the utilization side heat exchanger (66) and the utilization side expansion mechanism (67).
The heat pump apparatus performs a heating operation. At the time of performing a heating operation, the refrigerant, while changing in phase, circulates in the refrigerant circuit (15), whereby refrigeration cycles are performed. During the heating operation, refrigerant discharged from the compressor (41, 42) is delivered to the utilization side heat exchanger (61, 66) and is caused to condense by liberation of heat to objects. By virtue of such heat liberation, the objects are heated. The refrigerant condensed by the utilization side heat exchanger (61, 66) flows through the utilization side expansion mechanism (62, 67) and then flows into the receiver (23) of the heat source side circuit (20). Thereafter, the refrigerant in the receiver (23) flows through the heat source side expansion mechanism (24) and is caused to evaporate by heat absorption in the heat source side heat exchanger (22). Thereafter, the refrigerant is drawn into the compressor (41, 42). In this way, the refrigerant circulates in the refrigerant circuit (15).
The heat pump apparatus is provided with the communicating passageway (35) and the switching mechanism (36). The switching mechanism (36) is a mechanism capable of establishing and interrupting flow of gaseous refrigerant in the communicating passageway (35). When the switching mechanism (36) is open, gaseous refrigerant becomes circulatable in the communicating passageway (35), and gaseous refrigerant in the receiver (23) is delivered to the suction side of the compressor (41, 42). In other words, the compressor (41, 42) sucks in gaseous refrigerant from the receiver (23) and, as a result, the pressure of the receiver (23) decreases. On the other hand, when the switching mechanism (36) is closed, circulation of gaseous refrigerant in the communicating passageway (35) is prevented.
Further, the heat pump apparatus is provided with the controlling means (90). The controlling means (90) controls the switching mechanism (36) in the heating operation so that gaseous refrigerant in the receiver (23) is delivered, through the communicating passageway (35), to the compressor (41, 42). The controlling means (90) may be implemented by a controlling means which controls the switching mechanism (36) so that gaseous refrigerant in the receiver (23) is constantly delivered to the compressor (41, 42) for example during the heating operation. Alternatively, the controlling means (90) may be implemented by a controlling means which controls the switching mechanism (36) so that gaseous refrigerant in the receiver (23) is delivered to the compressor (41, 42) only when predetermined conditions are met during the heating operation.
Further, in the heat pump apparatus of the present invention, preferably the heat source side circuit (20) is connected, through interconnecting lines (16, 17), to the utilization side circuits (60, 65) disposed lower than the heat source side circuit (20), and at least one of the utilization side circuits (60, 65) is disposed at a different height from that of the other utilization side circuit (60).
In this heat pump apparatus, the heat source side circuit (20) is connected to the utilization side circuits (60, 65) by the interconnecting lines (16, 17). Stated another way, the heat source side circuit (20), the utilization side circuits (60, 65), and the interconnecting lines (16, 17) together constitute the refrigerant circuit (15) which is a closed circuit.
In the refrigerant circuit (15), the utilization side circuits (60, 65) are disposed lower than the heat source side circuit (20). Additionally, the utilization side circuits (60, 65) are installed at different heights, for example when the number of utilization side circuits is three and the three utilization side circuits are installed on the first floor, on the second floor, and on the third floor, respectively, or two of the three utilization side circuits are installed on the second floor and the remaining utilization side circuit is installed on the first floor.
Further, in the heat pump apparatus of the present invention, preferably the controlling means (90) controls the switching mechanism (36) so that gaseous refrigerant constantly flows through the communicating passageway (35) during the heating operation.
In this heat pump apparatus, the controlling means (90) controls the switching mechanism (36) so that gaseous refrigerant in the receiver (23) is constantly delivered, through the communicating passageway (35), to the compressor (41, 42) during the heating operation. In other words, gaseous refrigerant in the receiver (23) is drawn into the compressor (41, 42) during the heating operation, thereby constantly holding the pressure of the receiver (23) at low level.
In accordance with the present invention, gaseous refrigerant is withdrawn from the receiver (23) in the heating operation, whereby the pressure of the receiver (23) is reduced. Stated another way, it is possible to gain, in the heating operation, a sufficient pressure difference between the inflow side of the heat source side circuit (20) and the outflow side of each of the utilization side circuits (60, 65), thereby ensuring that refrigerant condensed by each of the utilization side heat exchangers (61, 66) is delivered to the receiver (23).
As a result of such arrangement, even when the utilization side circuits (60, 65) are installed at different heights thereby producing a difference in installation height between the utilization side circuits (60, 65), it is ensured that refrigerant condensed by each of the utilization side heat exchangers (61, 66) flows into the receiver (23). Therefore it is possible to secure a sufficient flow rate of the refrigerant in each of the utilization side circuits (60, 65). Accordingly, in accordance with the present invention, it is possible to relax restrictions on the difference in installation height between the utilization side circuits (60, 65) at the time of installation of the heat pump apparatus, thereby improving the freedom of installation thereof.
Further, the present invention provides the following effects. These effects will be described below.
Liquid refrigerant and gaseous refrigerant coexist in the inside of the receiver (23). When the gaseous refrigerant is pumped out of the receiver (23) and, as a result, the pressure of the receiver (23) decreases, a part of the liquid refrigerant held in the receiver (23) is caused to evaporate, thereby robbing evaporation heat from the remaining liquid refrigerant. Consequently, the specific enthalpy of the liquid refrigerant held in the receiver (23) decreases. In other words, the specific enthalpy of the liquid refrigerant that is delivered from the receiver (23) to the heat source side heat exchanger (22) serving as an evaporator drops. Accordingly, it is possible to gain, by just that much, an enthalpy difference between the inlet and the outlet of the heat source side heat exchanger (22). As a result, it is possible to increase the refrigerant evaporation pressure in the heat source side heat exchanger (22) while securing the refrigerant heat absorption amount in the heat source side heat exchanger (22). As a result of this, the compression ratio of the compressor (41, 42) is reduced while maintaining the amount of heat liberation in the utilization side heat exchangers (61, 66), and it becomes possible to improve the COP (coefficient of performance) of heat pump apparatus.