Operating Method for Refrigerating Machine

1. Field of the Invention

The present invention relates to an operating method for a refrigerating system and an air-conditioning system which are applicable for buildings and warehouses with refrigeration.

2. Description of the Prior Art

Generally, a refrigerating system and an air-conditioning system employ a refrigerating machine having a smaller capacity than the capacity corresponding to the maximum value of the load of the system for the purpose of reducing instollation and maintenance cost for the system. The refrigerating machine is operated in an operating method as shown in FIGS. 1 to 3. FIG. 1 shows a variation of the load of the system during the period from the start of air-conditioning operation to the end FIGS. 2 and 3 illustrate a variation of an amount of accumulated quantity of heat and a variation of the refrigerating machine's output during the operation of the refrigerating machine. As seen from the graph in FIG. 1, the load Q.sub.L takes place during the period between an air-conditioning start time T1 and the end time T2. And the maximum value of the load far exceeds the maximum value Q.sub.R Max of the refrigerating machine's output Q.sub.R. Therefore, if the refrigerating machine is started at the time T1, the air-conditioning energy is insufficient by the amount corresponding to the sum of the integrating values S1+S3-S2. In order to avoid this difficulty, the air-conditioning start time is set at time T1' which is earlier than the time T1, and the air-conditioning energy is accumulated in a heat storage tank by a predictive amount of the energy, as shown in FIGS. 2 and 3. In this case, if a refrigerating machine the maximum output Q.sub.R Max of which is used, the installation costs for the system may be saved but a large heat storage tank is required. Inversely, if a refrigerating machine having a large capacity is used, the heat storage tank is small but the system cost is expensive. It is a common practice, therefore, that the value of Q.sub.R Max is suitably selected as a compromise between the system cost and the capacity of the heat storage tank. In the operating method shown in FIGS. 1 to 3, the refrigerating machine must always be operated within the time period that the air-conditioning load takes place. Therefore, the refrigerating machine is operated at the maximum output thereof when the air-conditioning load is largest. In the cooling mode of the air-conditioning system, a time period that the air-conditioning load is high is coincident with one that an ambient temperature is high. For this, the refrigerating machine must be operated at the time that the temperature of cooling water of the refrigerating machine is high, that is, must be operated with a low coefficient of performance of the refrigerating machine. Thus, the conventional operating method of the refrigerating machine is disadvantageous in that the operating cost of the air-conditioning system increases.

A Japanese patent publication No. 46501/'72 discloses another type of refrigerating system in which the refrigerating machine is operated at night to accumulate a predetermined amount of heat and, at the same time, an amount of heat to be used on that day is predicted. When the predictive heat amount is larger than the accumulated heat amount, the refrigerating machine is operated by using surplus power in the day time to compensate for the insufficient amount of the heat.

An object of the invention is to provide a refrigerating system and an air-conditioning system which are operable at a low operating cost and free from the above-mentioned disadvantages of the conventional systems.

To achieve the above-mentioned object, in the present invention, the operating time period of a refrigerating machine is divided into a proper number of time intervals. Priority ranking is allotted or assigned to those respective intervals on the basis of a predictive variation pattern of ambient temperature. In accordance with the priority ranking, an output variation pattern of the refrigerating machine is determined is order that an integrating value of the refrigerating machine's output is equal to that of the air-conditioning load. The output variation pattern thus determined is used to control the operation of the refrigerating machine. With such a method, the operation cost of the refrigerating machine is minimized.

Other objects and features of the invention will be apparent from the following description taken in connection with the accompanying drawings, in which:

FIGS. 1 to 3 show graphs for explaining conventional operating methods of a refrigerating system and air-conditioning system, in which

FIG. 1 shows a load variation during the period from the air-conditioning start to the air-conditioning end,

FIG. 2 shows a variation of accumulated quantity of heat during the operating period of the refrigerating machine, and

FIG. 3 shows a refrigerating machine's output variation when the refrigerating machine is operated.

FIGS. 4 to 10 illustrate an embodiment of an operating method for a refrigerating system and air-conditioning system according to the invention, in which

FIG. 4 shows a predictive load variation pattern from the air-conditioning start to the air-conditioning end on a prearranged day for a refrigerating operation,

FIG. 5 shows a predictive pattern of an ambient temperature variation within the operating period of a refrigerating machine on a prearranged date for the refrigerating operation,

FIG. 6 shows priority ranking allotted to the divided plural time intervals of an operating period of a refrigerating machine,

FIG. 7 shows a variation pattern of the output of a refrigerating machine within an operating period of the refrigerating machine,

FIGS. 8A to 8E illustrate how to determine a variation pattern of the output of the refrigerating machine shown in FIG. 7 on the basis of the priority ranking shown in FIG. 6,

FIG. 9 shows integrated curves when the air-conditioning load shown in FIG. 4 and the output of the refrigerating machine shown in FIG. 7 are respectively integrated from the end of the air-conditioning to the start of the air-conditioning in an opposite direction of the time evolution, and

FIG. 10 shows a flow chart useful for explaining the operating method of a refrigerating machine according to the invention.

An operating method of a refrigerating machine according to the present invention will be described with reference to FIGS. 4 through 10. Firstly, a start time T1 of air-conditioning, an end time T2 of air-conditioning and a time T1" for initializing the operation of the refrigerating machine, on a prearranged day for operating the refrigerating machine are set up. A variation pattern of the air-conditioning load Q.sub.L during the period from T1 to T2 is predictively set by using an air-conditioning load predictor, as shown in FIG. 4. Then, a variation pattern of ambient temperature during the period from times T1" to T2 is predictively set by using an ambient temperature predictor, as shown in FIG. 5. Following this, the time period between T1" and T2 is divided into a proper number of time intervals. And priority ranking is allotted or assigned to the respective time intervals divided on the basis of the variation pattern of the ambient temperature Twb, as shown in FIG. 6, the Y-coordinate axis indicates the priority ranking. In the present embodiment, the time period from T1" to T2 is divided into 12 time intervals (for example, if the time interval from T1" to T2 is 24 hours, each divided interval is 2 hours), the priority ranking is allotted to the divided segments in the order from a low ambient temperature to a high one. Alternatively, the allotment of the priority ranking may be made on depending on a coefficient of performance (i.e. efficiency) of the refrigerating machine which is calculated by using the ambient temperature Twb and the temperature of the water at the outlet of the refrigerating machine. As a third step of the methodological procedure, a variation pattern of the output Q.sub.R1 of the refrigerating machine is determined. In the embodiment, the refrigerating machine output Q.sub.R is produced, within the maximum output Q.sub.R Max, until an integrating value of the refrigerating machine output Q.sub.R becomes coincident with that of the load Q.sub.l. This output production of Q.sub.R is performed by the integration starting from the time interval with a high priority ranking to that of a low priority ranking. How to determine the variation pattern of the refrigerating machine output Q.sub.R1 in the embodiment will be described with reference to FIG. 8. At the first step, an integrated load S.sub.L is calculated by using the variation pattern of the air-conditioning load Q.sub.L, as shown in FIG. 8A. At the second step, the refrigerating system is so set that the refrigerating machine is operated at the maximum output during the interval with the highest priority ranking (the interval I.sub.5 in FIG. 6), as shown in FIG. 8B. At this time, the integrated output S.sub.R is given by S.sub.R =Q.sub.R Max .times.I.sub.5. Under this condition, however, since S.sub.R <S.sub.L in area, the refrigerating machine must be operated at the maximum output additionally during the segment with the first and second high priority ranking (I.sub.5 +I.sub.4 in FIG. 6), as shown in FIG. 8C. As a result, the integrated output S.sub.R is given by S.sub.R =Q.sub.R Max .times.I.sub.5 +Q.sub.R Max .times.I.sub.4. At this time, the area S.sub.R is still less than the area S.sub.L, i.e. S.sub.R <S.sub.L. Therefore, at the third step, the maximum output operation of the refrigerating machine is still continued to the third priority ranking segment (I.sub.3 shown in FIG. 6), as shown in FIG. 8D. As a result of this step, the integrated output S.sub.R is Q.sub.R Max .times.I.sub.5 +Q.sub.R Max .times.I.sub.4 +Q.sub.R Max .times.I.sub.3. The output S.sub.R is still less than S.sub.L. Accordingly, the maximum output operation of the refrigerating machine is further continued to the segments of the fourth and fifth and the succeeding priority ranking. With progression of the refrigerating machine operation, the refrigerating machine operates for the eighth priority ranking segment, in the maximum operation mode. At this stage, the integrated output S.sub.R is given by

At this stage, S.sub.R =S.sub.L is not yet attained and therefore the insufficient amount of S.sub.L -S.sub.R is allotted to the time interval with the ninth priority ranking (I.sub.11 of FIG. 6). In other words, for the time interval having the ninth priority ranking, the refrigerating machine operates at the output Q.sub.R '=(S.sub.L -S.sub.R)/I.sub.11 but at the maximum output. At the fourth step, a variation of the load Q.sub.L shown in FIG. 4 and a variation of the output Q.sub.R1 shown in FIG. 7 are respectively integrated from time T2 to time T1" in the inverse direction of time evolution, as shown in FIG. 9. Then, the results .SIGMA.R and .SIGMA.L of the integrations are compared with each other. Here, in the period from time T1 to time T2, the relationship of .SIGMA.R.ltoreq..SIGMA.L indicates that the refrigerating machine output Q.sub.R1 is produced prior to the air-conditioning load Q.sub.L. The relationship of .SIGMA.L<.SIGMA.R indicates the air-conditioning load Q.sub.L is produced prior to the refrigerating machine output Q.sub.R1. In other words, this indicates that insufficiency of the accumulated quantity of heat temporarily takes place in the system. The consistency in time for the air-conditioning load Q.sub.L and the refrigerating machine output Q.sub.R1 may thus be judged by calculating those values .SIGMA.L and .SIGMA.R. If the relationship of .SIGMA.R.ltoreq..SIGMA.L always holds between T1 and T2, the Q.sub.R1 is directly used as the variation pattern of the refrigerating machine output. When .SIGMA.L.ltoreq..SIGMA.R, the refrigerating machine output Q.sub.R1 is modified in the following manner obtaining a modified refrigerating machine output Q.sub.R2. Firstly, the integrated values .SIGMA.L and .SIGMA.R during the final time interval I.sub.12 are compared. If .SIGMA.R.ltoreq..SIGMA.L, the output Q.sub.R1 of the refrigerating machine directly used as the modified refrigerating machine output. If .SIGMA.L.ltoreq..SIGMA.R, the Q.sub.R1 during the final time segment I.sub.12 is descreased until the relation of .SIGMA.R.ltoreq..SIGMA.L is obtained, thereby to obtain the modified output Q.sub.R2 and then a difference between Q.sub.R1 and Q.sub.R2, i.e. Q.sub.R1 -Q.sub.R2, is allotted to the time interval having a higher priority ranking, within the Q.sub.R Max. A similar operating method is made for the time segments of I.sub.11 and I.sub.10. A variation pattern thus formed of the modified refrigerating machine output Q.sub.R2 provides a refrigerating machine operating schedule which permits the refrigerating machine to operate at the lowest operating cost against the air-conditioning load occurring between time T1 and time T2.

FIG. 10 shows a flow chart illustrating how the operating method for refrigerating machines according to the invention is executed.

As described above, according to the operating method of refrigerating machines of the invention, the operating time period of the refrigerating machine is so selected as to provide the lowest operating cost. Therefore, the refrigerating system and air-conditioning system may be operated at a low maintenance cost.