System and method of cooling apparatus

This invention intends to provide an apparatus-cooling system high in cooling efficiency and easy in maintenance as well as a method to cool an apparatus. The invention is characterized in that an apparatus-cooling water system comprising at least a water tank (1) for storing pure water, pipings (3), (5) for outwardly introducing pure water from the water tank and returning the water to the tank, respectively, and pump (2) for passing pure water through the pipings is provided with an ozonator (6) for supplying ozone into the pure water.

FIELD OF THE INVENTION 
The present invention relates to an apparatus cooling system for, for 
example, cleanrooms, and in particular to a system and method for cooling 
an apparatus which is easy to maintain. 
BACKGROUND OF THE INVENTION 
It is important to remove the heat generated by various apparatuses in the 
immediate vicinity of the apparatuses in order to minimize the power 
necessary to conduct air temperature regulation in a cleanroom, and in 
order to reduce the operating costs of the cleanroom. The main parts of a 
common apparatus cooling system are shown in FIG. 4; such a system 
comprises municipal water water tank 1, circulation pump 2, strainer 8, 
heat exchanger 7, and piping, and conducts the removal of heat from the 
apparatuses using municipal water at a temperature within a range of 
20.degree.-25.degree. C. 
However, because various substances are dissolved or dispersed in municipal 
water, when municipal water is used as cooling water, the following 
problems occur. For example, suspended matter contained in the municipal 
water, such as sand, dirt, silica, or the like accumulates in the piping, 
and may lead to the blockage of the piping. Accordingly, in order to 
remove the suspended matter present in the cooling water, a strainer 8 is 
attached upstream from the use point; however, it is impossible to remove 
all suspended matter, and thus very small suspended matter which is able 
to pass through the strainer accumulates steadily in the piping, and this 
finally leads to the blockage of the piping. 
On the other hand, Ca ions and the like are also dissolved in municipal 
water, and when this is heated at the use point, calcium carbonate, which 
is not readily soluble, is produced, and this is precipitated and adheres 
to the piping walls. Furthermore, dissolved silica components are also 
steadily precipitated and adhere to the inner walls of the piping. As a 
result, the cooling efficiency decreases markedly, and furthermore, water 
flow resistance increases. 
The problems stated above are present when municipal tap water is used in 
apparatus cooling systems, and thus in order to solve this problem, 
attempts have been made to use pure water from which all precipitated 
matter has been removed in place of the municipal water. However, in such 
cases, while obstructions occurring as the result of the precipitation of 
suspended matter or the accumulation of dirt or the like were eliminated, 
problems occurred in which bacterial strains appeared and multiplied 
within the apparatus cooling system. The bacteria which appeared were 
attached to the interior of the piping and the heat exchanger, in the same 
way as the suspended matter and the precipitated matter above, and thus 
the heat exchanging efficiency was reduced, and an increase in water flow 
resistance within the piping system was experienced, and blockage of the 
piping system eventually occurred. 
In light of the above circumstances, the present invention has an object 
thereof to provide an apparatus cooling system which utilizes pure water 
from which suspended matter and precipitated matter have been removed as 
the apparatus cooling water, and which suppresses the appearance of 
bacteria, has high cooling efficiency, and is easy to maintain. 
SUMMARY OF THE INVENTION 
The first essential feature of the present invention is that an apparatus 
cooling system is provided with a water tank for storing pure water, 
pipings for outwardly introducing pure water from said water tank and 
returning this water to the water tank, and a pump for passing pure water 
through the pipings, is provided with a mechanism for supplying ozone into 
the pure water. 
The second essential feature of the present invention is that a method for 
cooling apparatuses in which pure water is circulated and apparatuses are 
cooled is characterized in that pure water containing ozone is employed as 
the pure water. 
Embodiment Examples 
Hereinbelow, the apparatus cooling method and system of the present 
invention will be explained using diagrams. FIG. 1 is a concept diagram 
showing an example of the compositon of the system of the present 
invention. 
In FIG. 1, reference 1 indicates a water tank for pure water; pure water is 
supplied from a water purifying apparatus (not depicted in the diagram) 
via piping 9 which connects the pure water apparatus and the water tank 1. 
The pure water of water tank 1 is pressurized by circulation pump 2, 
passes through water supply piping 3, and is sent to each apparatus 
cooling portion, represented by use points 4. The pure water which is sent 
to each apparatus cooling portion collects the heat which is generated by 
the apparatuses, passes through return piping 5, and is sent to heat 
exchanger 7; in heat exchanger 7, the heat, collected from the apparatuses 
is discharged. An ozone supplying apparatus 6 is connected to return 
piping 5 at a point downstream from heat exchanger 7; after ozone has been 
poured into the pure water from ozone supplying apparatus 6, the pure 
water is returned to water tank 1. Furthermore, in order to remove the 
dirt or dead bacteria present at the initiation of system operation, it is 
possible to provide a filter in the piping. 
It is preferable that the materials used for the members utilized in the 
apparatus cooling system be such that dirt or substances which will 
precipitate as a result of the heat of the apparatuses will not leach into 
the cooling water, and which are capable of withstanding pressure of 
approximately 10 kg/cm.sup.2 ; for example, stainless steel, hardened 
vinyl chloride, polyethylene lined cast iron pipe, or the like, may be 
employed. 
Water tank 1 generally comprises a container, a cooling water input port, 
an exit port, a pure water supply port, and a water gauge; when the water 
level within the container decreases, pure water is supplied from the pure 
water apparatus via piping 9, and thus the water level is maintained at a 
predetermined level. 
Any type of pump may be used as circulation pump 2, provided that this pump 
is capable of pressurizing the cooling water to a level of 5 kg/cm.sup.2 
or more; for example, a centrifugal pump or the like may be employed. 
The heat exchanger 7 should preferably be of a closed type in order to 
prevent the entry of bacteria; for example, a plate type heat exchanger 
may be employed. 
The ozone supplying apparatus 6 utilized in the present invention comprises 
an ozone generating portion and an ozone distributing portion. Any method 
may be used for the ozone generating method; for example, the silent 
discharge method, the photochemical reaction method, the electrolytic 
method, the radiation exposure method, or the high frequency electrolytic 
method or the like may be employed. Furthermore, any method may be 
employed as the ozone distributing method insofar as such a method is 
capable of supplying ozone generated by the ozone generating portion into 
the cooling water; for example, a method utilizing an ejector, a bubble 
tower, a rotary atomizer, a bubble agitation tank, or the like, may be 
employed. 
The ozone supplying apparatus 6 may be installed at any position along the 
cooling water piping system in the apparatus cooling system; however, it 
is preferable that this ozone supplying apparatus be provided immediately 
before the water tank, which is the position at which bacteria are most 
likely to appear, and the ozone supplying apparatus is not limited to one 
position, but may be installed at 2 or more positions. Furthermore, the 
supply of ozone may be conducted continuously or intermittently. 
An ozone concentration of several ppb in the cooling water of the present 
invention has exhibited some antibacterial effects; however, in order to 
completely prevent the appearance of bacteria, a concentration of 50 ppb 
or more at all points in the cooling water system is preferable. 
Furthermore, it is preferable that the upper limit of this ozone 
concentration be on the level of 1 ppm, from the point of view of the 
corrosion of the cooling system. 
As a result of autolysis, the ozone concentration even in pure water 
declines over time. Accordingly, in order to maintain an ozone 
concentration of 50 ppb at the position which is furthest removed from the 
supply point when the piping of the cooling water system is long, and in 
order to keep the ozone concentration at the supply point under 1 ppm, it 
is preferable that, rather than a single ozone supply point, a number of 
ozone supply points be provided. 
Furthermore, the pure water which is used in the present invention is water 
having a specific resistance of 1 M.OMEGA..cm or more, and which contains 
almost no suspended matter or ions or chemical compounds which are 
precipitated as a result of heating. This pure water may be obtained, for 
example, by first passing municipal water through a reverse osmosis 
apparatus, and then treating this water in an ion exchange column. 
Function 
In the cooling water piping system described above, an ozone supplying 
apparatus is provided, and the ozone concentration in the cooling water is 
constantly maintained at a level of 50 ppb or more, and thereby, it is 
possible to prevent the appearance of various bacteria, and it is possible 
to maintain the initial high cooling efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION 
Hereinbelow, the present invention will be explained in detail on the basis 
of embodiments; however, it is of course the case that the present 
invention is in no way limited to the embodiments described. 
Using the apparatus cooling system having the construction depicted in FIG. 
1, the antibacterial effects of the present invention were investigated. 
The pure water which is used as the cooling water is produced by treating 
municipal water in a reverse osmosis apparatus, an ion exchanging column, 
and ultrafiltration apparatus, in that order. The specific resistance of 
the pure water thus obtained was 3M.OMEGA..cm. 
An apparatus comprising the silent discharge type ozone generator 10 and an 
injector shown in FIG. 3 is employed as the ozone supplying apparatus 6; 
this apparatus is attached to the piping between the heat exchanger 7 and 
water tank 1. A mixture of air and the ozone generated by means of the 
silent discharge of air is ejected from the nozzle portion of injector 11, 
as shown in FIG. 3, and ozone is dissolved in the cooling water at various 
concentrations. Furthermore, the air which is ejected together with the 
ozone is discharged externally downstream from the throat portion. The 
ozone concentration in the circulating cooling water is controlled by 
means of the adjustment of the amount of ozone generated by ozone 
generator 10. 
The cooling water is sampled at the exit port of the water tank 1 and a 
measurement of the ozone concentration and bacterial count in the cooling 
water is conducted. Here, the measurement of the ozone concentration is 
carried out using an ozone meter 27501 made by Orbis Fayer. Furthermore, 
the bacteria count is carried out by filtering 1 liter of the cooling 
water with a 0.45 .mu.m membrane filter, immersing this filter in a 
culture liquid, allowing this to stand for a period of 24 hours in an 
incubator at a temperature of 35.degree. C., and counting the number of 
colonies which appear. 
The results obtained are shown in FIG. 2. The figure shows the change over 
time in the number of bacteria in cooling water prior to ozone supply and 
after the initiation of ozone supply. The bacterial amount present in the 
cooling water prior to ozone supply was approximately 60 CFU/l (CFU: 
Colony Formation Unit); however, as a result of supplying ozone, the 
number of bacteria decreased rapidly, and this decrease was more rapid as 
the ozone concentration rose. At a concentration of 20 ppb, the bacterial 
count decreased; however, it was impossible to completely remove the 
bacteria, and they remained essentially stable at a level of 20 CFU/l. At 
ozone concentrations greater than 50 ppb, the number of bacteria decreased 
rapidly as a result of ozone supply, and at 2 hours after the initiation 
of ozone supply, the number of living bacteria reached 0. This indicated 
that if ozone were supplied at concentrations greater than 50 ppb, it 
would be possible to completely prevent the appearance of bacteria in the 
cooling water. 
Next, in order to investigate the antibacterial effects of ozone with 
respect to various types of living bacteria, ozone concentrations were 
found which killed 99% of living bacteria within a period of 10 minutes, 
with respect to the bacteria shown in Table 1. The results are shown in 
column 2 of Table 1. 
TABLE 1 
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Bacterium C99 (ppb) 
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Escherichia coli 1.0 
Streptococcus fecalis 
1.5 
Mycobacterium tuberculosis 
50.0 
Poliovirus 10.0 
Endomocba hisdytica 
30.0 
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C99: Concentration necessary to kill 99% of bacteria within 10 minutes 
Table 1 shows that the ozone concentration necessary for the killing of 
bacteria by ozone differed among the various types of bacteria; it was 
determined that even in the case of the bacteria requiring the highest 
ozone concentration, Mycobacterium tuberculosis, an ozone concentration of 
50 ppb exhibited sufficient antibacterial activity. 
The results given above showed that if ozone was supplied in such a manner 
that the ozone concentration in the cooling water was always at a level of 
50 ppb, it would be possible to completely prevent the appearance of 
bacteria, and furthermore, even if bacteria entered the system externally, 
they could be immediately killed, so that the decrease in heat exchanging 
efficiency of the cooling water piping system, and the increase in 
pressure loss resulting from the increase in bacteria could be prevented. 
Industrial Applicability 
By means of the present invention, the appearance of bacteria within the 
system can be prevented, so that the decrease in the heat exchanging 
efficiency of the piping system, the increase in water flow resistance, 
and the blockage of the piping system can be prevented. As a result, it is 
possible to provide an apparatus cooling system which is capable of stably 
maintaining a high cooling efficiency.