Condensate tempering system for use with steam sterilizers

A steam condensate tempering system for a steam sterilizer uses a fast temperature sensor to measure the temperature of combined water and steam condensate from a sterilizer, and a controller for controlling the flow of cool water to mix with the steam condensate in response to the temperature sensed by the temperature sensor.

BACKGROUND OF THE INVENTION 
In steam sterilizers used in hospitals, universities, and other facilities 
in which it is necessary to sterilize equipment, steam can be used to 
perform the sterilization. One type of steam-based sterilizer has a 
sterilization chamber into which the components are put, and an outer 
jacket around the chamber for warming and insulating the sterilization 
chamber. Steam is introduced into the jacket to insulate and heat the 
chamber, and separately into the chamber to sterilize the components. The 
steam from the jacket and chamber is collected in steam traps that provide 
steam condensate toward a drain. 
Building codes typically specify that water provided from equipment to a 
drain not be hotter than a certain temperature, such as 140.degree. F., to 
minimize damage to the pipes and leaching of heavy metals. Consequently, 
the steam condensate must be cooled before it is provided down the drain. 
In typical sterilizers currently in use, the steam condensate provided 
from the steam traps is mixed with cooling water from a cool water line, 
typically a municipal water line. The combined cooling water and steam 
condensate is provided to a funnel that has an air gap to prevent drain 
water from mixing into lines in the sterilizer. The combined water is then 
provided down the drain. 
The cool water line is typically connected to provide cooling water 
continuously at a rate of 0.5 to 5 gallons per minute, depending on the 
particular sterilizer system. Furthermore, there is typically a separate 
municipal water line serving the jacket and the chamber steam condensate 
lines. Such a cooling system thus causes a very large amount of cool water 
to be provided down the drain, even if much of that cool water is 
excessive for meeting building code requirements. 
SUMMARY OF THE INVENTION 
The present invention includes a steam condensate tempering system for use 
with steam sterilizers and methods for controlling cooling water flow in 
connection with sterilizing components. The systems and methods herein 
substantially reduce the consumption of water compared to typical steam 
sterilizers currently in use. The system is particularly adapted, but not 
necessarily limited, to sterilizers that have a sterilizing chamber and an 
outer jacket, both of which receive steam over separate lines and provide 
steam condensate via separate steam traps. 
The present invention includes a method for retrofitting a steam sterilizer 
to provide significant water savings while not interfering with the 
sterilization process, and without effecting any change to the operation 
of the sterilizer itself. The method is used with a sterilizer that has at 
least a sterilizing chamber and typically a funnel that receives steam 
condensate from the chamber (via a steam trap) mixed with cooling water 
from a relatively cool water line, such as a municipal water line (or a 
private water line). The method includes providing a controllable valve in 
the cool water line, coupling the cool water line in the system so that 
cooling water mixes with the steam condensate from the chamber, providing 
a temperature sensor to monitor the temperature of the water to be 
provided to the drain, and providing a controller that is responsive to 
the sensed temperature to control the valve based on a relationship 
between the sensed temperature and a threshold temperature. 
According to another aspect, the present invention includes a system for 
cooling steam condensate from a steam sterilizer. The system has a valve 
in a relatively cool water line for controlling the flow of cooling water. 
A temperature sensor is provided in the drain line, and preferably in a 
mixing chamber that receives steam condensate and cooling water, to 
quickly sense the temperature of the water in the mixing chamber. A 
controller receives signals from the temperature sensor and controls the 
valve in response thereto. If the sensed temperature exceeds a threshold 
level, such as 120.degree. F., the controller actuates the valve so that 
more cooling water can be provided. If the temperature of the water in the 
mixing chamber is less than the threshold level, the valve for the cooling 
water is kept off. 
While sterilizers have been used for many years with a continuously running 
cool water line to cool the steam condensate provided to the drain, the 
present invention provides substantial savings in terms of water supply 
and consequently in cost to the institution with the sterilizer(s) while 
keeping the water sufficiently cool to meet the requirements of building 
codes. It has been found that the water savings for cooling the steam 
condensate from the chamber and jacket can be up to 90% with the system of 
the present invention compared to prior sterilizer designs. This 
efficiency represents a savings of about 500,000 gallons of water on 
average per sterilizer per year, which can be over 20,000,000 gallons of 
water per year in a single medical/research facility. In addition, the 
design according to the present invention allows changes to be made to an 
existing sterilizer without affecting the operation of the sterilizer or 
the sterilization process. Other features and advantages will become 
apparent from the following detailed description, drawings, and claims.

DETAILED DESCRIPTION 
Referring to FIG. 1, a sterilizing system 8 has a sterilizer 10 with a 
chamber 14 surrounded by a jacket 12. Steam is introduced into chamber 14 
to sterilize components 15, and into jacket 12 to insulate chamber 14. 
Jacket 12 is also used to heat chamber 14 during a drying cycle after 
sterilization. Steam condensate is provided from both chamber 14 and 
jacket 12 to a funnel 16 via separate steam traps 17, and thereafter to a 
drain line 18. Funnel 16 provides an air gap to prevent water in drain 
line 18 from mixing with lines in sterilizer 10. 
In prior systems, cool water would be continuously injected from a 
municipal water line to mix with the steam condensate before it reaches 
funnel 16. Funnel 16 would thus receive a mixture of steam condensate and 
relatively cool water. For convenience, in such prior systems (many of 
which are currently in operation), the cool water line was connected such 
that it provided cooling water continuously, 24 hours a day, at a rate of 
0.5 to 5 gallons per minute (GPM), depending on the system. Typically, 
there would be a separate cool water line for the jacket and the chamber. 
An example of such a sterilizer is an AMSCO Eagle series sterilizer, which 
is available from Steris Corporation, located in Mentor, Ohio. 
The condensate tempering system of the present invention provides 
substantial water savings by replacing the continuous flow of the cool 
water line with a controllable system. The system includes a mixing 
chamber 32 with an inlet 34 at a lower portion of mixing chamber 32, and 
an outlet 36 at an upper portion of mixing chamber 32. Inlet 34 is 
connected to drain line 18 from funnel 16, and is also in fluid 
communication with a relatively cool water line 40, typically from a 
municipal water supply. 
A fast response temperature probe 42, i.e., a temperature probe that can 
sense temperature in a short period of time (preferably in several 
seconds), is provided in mixing chamber 32 and provides to a controller 44 
signals indicating the temperature of the water in mixing chamber 32. 
Controller 44 compares the sensed temperature to a chosen threshold, such 
as 120.degree. F. If the temperature exceeds the threshold, the controller 
causes a valve 46, such as a solenoid valve, to open so that cooling water 
flows in line 40 to mixing chamber 32. The cooling water mixes with the 
steam condensate from funnel 16. Mixing chamber 32 also allows for some 
mixing before the resulting mixed water is provided to the drain. 
By using such a temperature probe, controller, and valve, it is not 
necessary to keep the cool water line running at all times. It has been 
found that the system of the present invention reduces the use of water by 
the sterilizer for cooling the steam condensate from the chamber and 
jacket by up to 90% while working with existing equipment. 
Assuming a maximum drain temperature of 140.degree. F., a threshold 
temperature of 120.degree. F. provides a significant buffer below a 
maximum temperature of 140.degree. F. Other settings, such as 130.degree. 
F., could be used, although it has been found that such a higher setting, 
while still keeping the water safely below 140.degree. F., does not result 
in significant additional savings in water. 
FIG. 2 shows a graph illustrating how the temperature of drain water 
remains below 122.degree. F. with a system such as that described above 
with a controller threshold of 120.degree. F. and a flow rate of 4 GPM. It 
has further been found that a desirable flow rate for the municipal water 
line is about 2 GPM when needed (compared to 0.5 to 5 GPM continuously in 
prior systems), although the flow could be still less, and savings can be 
realized with as low as 0.5 GPM while still sufficiently cooling the steam 
condensate. In FIG. 2, the temperature peaks and then declines from the 
five numbered peaks when the valve is opened to allow water to flow. 
Typically, the valve needs to be open only several seconds at a time, as 
the steam condensate is provided in small quantities at a time from the 
steam traps. For a 60-minute sterilization cycle, the total water usage 
can be on the order of only 2-4 gallons for cooling the steam condensate 
from the jacket and chamber. This water usage compares to 30-100 gallons 
for a typical steam sterilizer without the present invention. 
Another advantage of the approach described herein is that all of the 
components in the tempering system can be added to the drain and provided 
externally without making any change to the existing sterilizer chamber, 
jacket, or steam traps, and therefore not affect the actual sterilization 
and drying processes in the chamber. 
While the condensate tempering system of the present invention can be 
provided as part of a new sterilizer, it can also easily be retrofitted to 
an existing sterilizer. The present invention thus includes a method 
including providing a mixing chamber in the drain line, a valve in the 
cool water line, a temperature sensor in the mixing chamber, and a 
controller for controlling the valve to control the flow of water in the 
relatively cool water line. Note that this method of the present invention 
only changes the fluid flow after steam condensate is provided from the 
steam traps. Accordingly, the operation of the sterilizing components is 
not affected or altered at all. 
A new sterilization system could be constructed differently from a 
retrofitted system as described above; for example, the mixing chamber 
could be eliminated and a temperature probe could be provided in some 
other portion of the system between the chamber and the drain, e.g., in a 
lower portion of a funnel with an air gap and with the cooling water 
provided to the funnel. 
Having described an embodiment of the present invention, it should be 
apparent that modifications can be made without departing from the scope 
of the present invention. For example, the water lines could be arranged 
in different ways, such as coupling the cool water line directly to the 
mixing chamber. In any arrangement of water lines, the temperature of the 
steam condensate or steam condensate combined with cooling water should be 
sensed before the drain, and cool water should be fluidly coupled to 
combine with the steam condensate to reduce the temperature below a 
desired threshold before the water is provided down a drain. While 
separate traps are shown with a chamber and jacket, a single trap could be 
used. The temperature probe should be sufficiently fast so that there is 
sufficient time for the cooling water to be provided to reduce the 
temperature of the effluent in the lines below the desired threshold 
before going down the drain.