Cold water supply system

A cold water supply system includes an agitator tank in a cold water supply tank for receiving the cold water from a refrigerating units and a bypass pipe line for directing a calculated amount of return water from the load into the agitator tank. A temperature sensor for sensing the return water temperature is provided and another temperature sensor for sensing the refrigeration unit outlet temperature is provided for controlling regulating means in accordance with the sensed temperatures for automatically regulating the cold water temperature supplied into the agitator tank to a predetermined temperature.

BACKGROUND OF THE INVENTION 
This invention relates to cold water supply systems, and more particularly 
to cold water supply systems in which a computer is incorporated into a 
refrigeration plant and the optimum capacity control of the variable 
capacity refrigerator operation is directly controlled through the use of 
the DDC (Direct Digital Control) function. 
One typical conventional system of the type the present invention is 
concerned with is illustrated in FIGS. 1 and 2. In FIG. 1, in order to 
ensure that a necessary predetermined amount of cold water or brine at a 
constant predetermined temperature is always maintained in a supply tank 
10, the water level in the supply tank 10 is monitored by a level sensor 
12 which supplies a level signal to a computer 14. The computer 14, when a 
decrease of the cold water level is detected by the level signal from the 
level sensor 12, starts pumps 16, valves 18 and refrigerators 20 in 
sequence. At this time, the computer 14 determines and controls the number 
of the refrigerators 20 to be operated according to the cold water level 
and the cold water level change rate in the supply tank 10. The computer 
14 also automatically controls the pumps 16 and the valves 18 
correspondingly. A temperature sensor 26 is disposed in the tank 10 and a 
level sensor 28 is disposed in the tank 24. 
FIG. 2 illustrates the operation of the above described conventional supply 
system in a flow chart. In FIG. 2, it is seen that a function 101 
determines if the cold water level within the supply tank 10 is sufficient 
for the supply of the water to a load (not illustrated). If the water 
level is sufficiently high, the refrigeration units of the refrigeration 
system 20 are not started at all as shown in a function 102. If the water 
level is not sufficiently high, only one refrigerator 20 is started to 
operate as shown by a function 103, and the computer 14 calculates and 
determines in advance which of the two cold water supply amounts, from the 
refrigerator 20 to the supply tank 10 or the cold water discharge amount 
from the supply tank 10 to the unillustrated load, is larger from the 
level change rate as shown in a function 104. The level change rate used 
herein can be obtained based on the signal from the level sensor 12. When 
it is determined from the above level change rate that the water level in 
the supply tank 10 is being lowered, a function 105 determines whether or 
not the refrigeration system 20 should be stopped with the actual water 
level also taken into consideration. If the water level is being lowered, 
a function 106 determines whether or not one more refrigerator 20 of the 
refrigeration system should be started taking the actual water level also 
into consideration. 
Also, the refrigerating capacity of each of the refrigerators 20 can be 
changed by the automatic vane control function of turbo-refrigerators, and 
in order to maintain the cold water temperature constant, the computer 14 
automatically controls the refrigeration capacity of the refrigerators 20 
so that the cold water temperature at the outlet of the refrigerators 20 
is kept constant through the use of the difference between the return cold 
water temperature measured by a temperature measuring sensor 22 for 
sensing the temperature of the return water received in return water tank 
24 and the temperature of the supply cold water in the supply water tank 
10 which latter temperature is kept at a constant set value. 
Thus, the computer 14 functions to effect the start-stop control of the 
refrigeration system, i.e., how many of the pumps 16, the valves 18 and 
the refrigerators 20 are to be started or stopped by the detection of the 
level, namely the determination of the amount of the supply water by the 
level detection sensor 12, and the computer 14 also functions to control 
the refrigerating capacity of the refrigerators 20 that are actuated by 
the above start-stop control through the use of the temperature of the 
return cold water from the return water measuring temperature sensor 22. 
Since the conventional cold water supply system is constructed as described 
above, the number of the refrigerators that should be started up is 
determined according to the amount of the supply cold water, and the 
refrigeration capacity of the started refrigerator is automatically 
determined in accordance with the difference between the cold water 
temperature and the discharge set temperature (set value). Therefore, with 
the conventional cold water supply system, the refrigerators sometimes 
must be operated at a low load factor when the difference between the 
water temperatures is small which results in inefficient operation, and 
this is further aggravated when a plurality of refrigerators are started 
and operated in parallel. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the present invention is to provide a cold water 
supply system high in operating efficiency. 
With the above object in view, the present invention resides in a cold 
water supplying system which comprises an agitator tank within a cold 
water supply tank for receiving the cold water from a refrigerating 
system, a bypass piping means for directing a calculated amount of return 
cold water into the agitator tank, a temperature sensor for sensing the 
temperature of the return cold water, a second temperature sensor for 
detecting the water temperature discharged from the refrigerating system, 
and regulating means for automatically regulating the temperature of the 
cold water to be supplied into the agitator tank to a predetermined 
temperature. 
Thus, according to the present invention, a refrigeration plant employing 
variable capacity refrigerators is suitably controlled through the use of 
the operating function, forecasting function and DDC function to directly 
control the capacity of the refrigerators, thereby realizing optimum 
temperature control and high efficiency refrigerator operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 3 and 4 in which one embodiment of the present 
invention is illustrated, there is shown that the cold water supply system 
of the present invention comprises a cold water supply tank 50 connected 
for supplying cold water to a load (not shown). The supply tank 50 has 
formed therein an agitator tank 52 in which an agitator 54 is disposed. 
The supply tank 50 also has a level sensor 56. The cold water supplied 
into the supply tank 50 is provided from a return water tank 58 connected 
to a return line (not shown) for receiving return water from the load. The 
return water in the return water tank 58 is supplied to the supply tank 50 
through a supply line 60 including a plurality of pumps 62, valves 64 and 
refrigerators 66. The pumps 62 and series connections of the valves 64 and 
the refrigerators 66 are connected in parallel, and these parallel 
connections are connected in series. A temperature sensor 68 is disposed 
at the discharge end of the refrigerators 66. Another temperature sensor 
70 and a level sensor 72 are disposed in the cold water return tank 58. 
It is seen that the return tank 58 and the supply tank 50 are also 
connected by a bypass line 74 parallel to the supply line 60. The bypass 
line 74 connects both the tanks 58 and 50 so that a controlled amount of 
cold return water is supplied to the agitator tank 52 of the supply tank 
50, and the bypass line 74 includes a pump 76 and a three-way valve 78 
which is controllable to regulate the flow rate of the cold water toward 
the supply tank 50. 
The cold water supply system of the present invention also comprises a 
computer 80 for regulating and controlling the operation of the cold water 
supply system. The computer 80 receives signals from various sensors such 
as the level sensor 56 in the supply tank 50, the temperature sensor 68 in 
the supply line 60, the level sensor 72 and the temperature sensor 70 in 
the cold water return tank 58. The computer 80 processes the received 
signals and provides various commands to the pumps 62, the valves 64 and 
the refrigerators 66 in the supply line 60, the agitator 54 in the supply 
tank 50, and the pump 76 and the three-way valve 78 in the bypass line 74. 
The flow of these sensor output signals and the computer commands are 
shown by arrows in dash line. 
The operation of the cold water supply system of the present invention is 
illustrated in the flow chart of FIG. 4. The water level in the supply 
tank 50 is first determined by a function 201 if it is higher or lower 
than the level necessary for supplying cold water to the load. If the 
level is determined to be higher, the refrigerators 66 are all stopped as 
shown in function 202, and if the level is lower than the necessary level, 
only one of the refrigerators 66 in the refrigerating system is started up 
as shown in function 203 and at the same time the bypass line 74 including 
the pump 76 and the three-way valve 78 is started up as shown in function 
204. The refrigerator 66 starts up at 100% of its refrigeration capacity, 
and the refrigerator discharge temperature measured by the temperature 
sensor 68 and the relatively hot water temperature measured by the 
temperature sensor 70, i.e., the temperature of the water that is to be 
supplied from the return tank 58 to the supply tank 50 through the bypass 
line 74. Then, a calorific calculation is carried-out based on the 
capacity of the pump 62 and the refrigerator discharge temperature 
measured by the temperature sensor 68 to calculate the flow rate of the 
relatively hot water that should be shifted from the return tank 58 to the 
agitator tank 52 in the supply tank 50 in order that the water temperature 
in the agitator tank becomes a predetermined constant temperature. This 
calculated flow rate is given as a command set value to the regulating 
three-way valve 78. 
In the event that the water temperature in the supply tank 50 is not 
expected to become the set value even when the three-way valve 78 is 
opened by 100%, the refrigerators 66 are controlled such that their 
capacity is decreased or, more particularly, the computer 80 calculates 
the necessary capacity percentage of the refrigerators 66 to obtain the 
required discharge temperature and supplies it to the refrigerators 66 as 
capacity control commands as shown in a function 205. 
Thus, the agitator tank 52 is supplied with cold water which is a sum of 
the flow from the refrigerators 66 and the flow from the bypass line 74 
according to the temperature measured by the temperature sensor 70 in the 
return water tank 58. Therefore the water level in the supply tank 50 
changes according to the difference between the above sum supply amount 
and the water flow from the supply tank 50 to the load. The computer 80, 
receiving the signal from the level sensor 56 in the supply tank 50 
representative of the water level change rate in the supply tank 50, 
predicts the relative sizes between the in-flow and the out-flow amounts 
of the supply tank 50 as shown in function 206. When it is determined from 
this level change rate that the water level within the supply tank 50 is 
increasing, function 207 taking the actual water level in the supply tank 
also into consideration determines if the refrigerators 66 should be shut 
down. When it is determined from the level changing rate that the water 
level in the supply tank 50 is decreasing, function 208 taking the actual 
water level in the supply tank also into consideration determines if one 
more additional refrigerator 66 should be started up. When an additional 
refrigerator 66 is started up, the load control by the calorific 
calculation and the flow rate calculation similar to those carried out in 
the function 205 for a plurality of refrigerators is carried out. 
The present invention has been described in conjunction with a single 
preferred embodiment, but various changes and modifications can be 
effected. For example, instead of the bypass line including the pump and 
the controllable three-way valve, a bypass line including a variable speed 
pump employing a variable voltage, variable frequency power source may be 
used with a computer controlled speed setting to control flow rate in the 
bypass line, enabling further saving in energy consumption. Also the 
present invention is equally applicable to a cold water supply system 
having a plurality of variable capacity refrigerators such as turbo or 
screw refrigerators. 
As apparent from the foregoing description, the present invention increases 
the operating efficiency of the refrigeration units.