U.S. patent application number 12/264648 was filed with the patent office on 2010-05-06 for data center cooling device and method.
Invention is credited to Richard Erwin Cockrell.
Application Number | 20100107658 12/264648 |
Document ID | / |
Family ID | 42129789 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100107658 |
Kind Code |
A1 |
Cockrell; Richard Erwin |
May 6, 2010 |
DATA CENTER COOLING DEVICE AND METHOD
Abstract
A cooling system and method for cooling devices housed in a data
center. A cabinet housing a set of condenser coils is located
within the data center positioned on its floor and including fans
for drawing air passed the condenser coils and exiting the device
angularly to the floor of the data center. The present invention
also contemplates the use of redundant compressors and condensers,
a system that includes a secondary evaporator coil and
configuration which enables the device, under certain conditions,
to bypass its compressor.
Inventors: |
Cockrell; Richard Erwin;
(Napa, CA) |
Correspondence
Address: |
Bay Area Technolgy Law Group PC
500 Sansome Street, Suite 404
San Francisco
CA
94111
US
|
Family ID: |
42129789 |
Appl. No.: |
12/264648 |
Filed: |
November 4, 2008 |
Current U.S.
Class: |
62/62 ; 62/208;
62/259.2; 62/498 |
Current CPC
Class: |
F25B 2400/0401 20130101;
F25B 2400/06 20130101; F25B 41/40 20210101; F25D 16/00 20130101;
H05K 7/20827 20130101; F25B 2700/2106 20130101 |
Class at
Publication: |
62/62 ; 62/259.2;
62/498; 62/208 |
International
Class: |
F25D 23/12 20060101
F25D023/12; F25B 1/00 20060101 F25B001/00 |
Claims
1. In a cooling system for cooling devices housed in a data center,
said device comprising a cabinet, a set of evaporator coils, an
inlet and outlet and at least one fan for drawing air from within
said data center through said inlet and outlet and for movement of
said air over said evaporator coils to a pleumum providing cooler
air to said data center, the improvement comprising angling the air
flow emanating from said cabinet proximate to the plane of said
flooring.
2. The cooling system of claim 1 wherein said at least one fan
comprises a prop or axial fan.
3. The cooling system of claim 2 wherein said at least one fan
comprises a fan having a blade diameter of approximately 24'' to
28''.
4. The cooling system of claim 2 wherein sufficient fans are
employed for maintaining static pressure and air flow within said
space and being capable of changing their output to maintain the
required static pressure via multiple static pressure sensors.
5. A cooling system for cooling a data center to a predetermined
temperature and humidity level, said cooling system comprising a
set of evaporator coils and at lease one fan for moving air within
said data center passed said set of evaporator coils, at least two
sets of compressors and two sets of condensers located external to
said data center, positioned in parallel to provide coolant to said
set of evaporator coils.
6. The cooling system of claim 5 wherein each of said compressors
and condensers operate at a load that is less than the load imposed
upon said cooling system if only a single compressor and single
condenser was used to operate said cooling system to maintain said
evaporator coils at a selected temperature difference between the
temperature of coolant passing within said evaporator coils and air
passing over said evaporator coils within said data center.
7. The cooling system of claim 6 wherein a single set comprising a
compressor and condenser, acting alone, is sized to enable them to
operate said evaporator coils at said predetermined temperature
difference.
8. In a cooling system comprising a compressor, a condenser,
coolant, pump and primary evaporator coil for cooling, the
improvement comprising a secondary evaporator coil in series with
said primary evaporator coil, said secondary evaporator coil being
a flooded coil directly piped to a flash vessel to ensure said
condenser only receives coolant in the appropriate state.
9. The cooling system of claim 8 further comprising a valve wherein
when said coolant temperature is lower than ambient room
temperature, said valve selectively allowing for introduction of
coolant into flooded secondary evaporator coil.
10. The cooling system of claim 9 wherein said coolant is returned
to said condenser, via the flash vessel from said flooded secondary
evaporator coil while bypassing said compressor.
11. In a cooling system comprising a compressor, condenser,
coolant, pump and evaporator coils, the improvement comprising a
measurement device and actuator wherein when said measurement
device measures a wet bulb temperature and when less than or equal
to a preselected value, said coolant is circulated by said pump
between said condenser and evaporator coils wherein thermo-siphon
automatically transfers coolant from said evaporator coils to said
condenser, via a flash vessel while bypassing said compressor.
12. The cooling system of claim 11 further comprising two sensors,
one for wet bulb temperature and one for return air temperature,
the wet bulb temperature sensor being the primary trigger to
activate and deactivate the transferring of coolant from evaporator
to condenser, via said flash vessel through a bypass valve
bypassing said compressor, said compressor being deactivated
thereby.
13. The cooling system of claim 12 further comprising a return air
sensor such that if the return air temperature rises to a preset
level, said bypass valve is closed and said compressor is
reactivated.
14. A method for cooling devices housed in a data center comprising
positioning a set of evaporator coils on the floor of the data
center, drawing ambient air from within said data center passed
said set of evaporator coils and directing said air at an angle
proximate to the plane of said floor.
15. The method of claim 14 wherein said air is directed passed said
evaporator coils through the use of at least one prop or axial
fan.
16. The method of claim 15 wherein said at least one fan comprises
a fan having a blade diameter of approximately 24'' to 28''.
17. The method of claim 14 wherein said air emanating from said
evaporator coils is directed towards said devices in a space where
required static pressure is maintained via said at least one prop
or axial fan.
18. A method for cooling devices in a data center to a
predetermined temperature and humidity, said method comprising
providing a set of evaporator coils, a fan, two sets of compressors
and two sets of condensers located external to said data center
positioned in parallel, moving air within said data center passed
said set of evaporator coils and using said at least two sets of
compressors and two sets of condensers to provide coolant to said
set of evaporator coils.
19. The method of claim 18 wherein each of said compressors and
condensers are operated at a load that is less than the load
imposed upon said cooling system if only a single compressor and
single condenser was used to operate said cooling system to
maintain evaporator coils at a selected temperature difference
between the temperature of the coolant passing within said
evaporator coils and air passing over said evaporator coils for
said data center.
20. The method of claim 18 wherein a single set comprising a
compressor and condenser, acting alone, is sized to enable it to
operate said evaporator coils at said predetermined temperature
difference.
21. A method for cooling devices housed in a data center comprising
a cooling system of a compressor, condenser, coolant, pump and
primary evaporator coil for cooling, and further comprising a
secondary evaporator coil in series with said primary evaporator
coil wherein said secondary evaporator coil is flooded by being
directly piped to said condenser, via a flash vessel.
22. The method of claim 21 wherein when said coolant temperature is
lower than room air temperature, coolant is introduced into said
secondary evaporator coil.
23. The method of claim 22 wherein said coolant is returned to said
condenser from said secondary evaporative coil, via said flash
vessel while bypassing said compressor.
24. A method for cooling devices housed in a data center including
a device comprising a compressor, condenser, coolant, pump and
evaporator coils, wherein when the wet bulb temperature of outdoor
air is below a preset value, said coolant is circulated by said
pump between said condenser and evaporator coils, via a flash
vessel, while bypassing said compressor.
25. The method of claim 24 wherein when said coolant ceases to
travel from said condenser to said evaporator coils and back to
said condenser, said compressor is activated for compressing said
coolant.
26. In a cooling system comprising a compressor, condenser,
coolant, pump and evaporator coils, the improvement comprising
operating said compressor at compression ratios below approximately
1.5 and above 1.01 to 1.
27. The cooling system of claim 26 wherein condenser set points are
variable and float 7.degree. to 15.degree. F. above outdoor wet
bulb temperature.
28. The cooling system of claim 26 further comprising metering
devices whereby coolant pumps, through speed control, maintain the
selected pressure differentials and flow rates though said metering
devices.
29. The cooling system of claim 26 further comprising sensors for
controlling the speed of said compressor such that as the
compression ratios are reduced, mass flow rates of said compressor
is not exceeded beyond a preselected value.
Description
TECHNICAL FIELD
[0001] The present invention involves a cooling system and method
for its operation used for cooling devices in a data center. Data
centers are rooms that contain electronic systems generally
arranged on racks, the standard rack being defined by the EIA as an
enclosure approximately 78'' high, 24'' wide and 40'' deep. These
racks are employed to house printed circuit board-based devices
which, under normal operation, can generate significant amounts of
heat. For the proper operation of such devices and for maintaining
them throughout their normal life cycle, proper temperature and
humidity must be maintained.
BACKGROUND OF THE INVENTION
[0002] Historically, computer room air conditioning (CRAC) systems
were manufactured by those who supplied residential and commercial
air conditioning systems, generally. The design philosophy was to
build such systems at the lowest possible cost, that is, the cost
of manufacturing being more important than the operational cost of
the system. These CRAC systems were built to do as much work as
possible while occupying the smallest possible space within the
data center. Energy consumption in running these systems was less
of a consideration than the floor space that the units would occupy
in a typical data center location.
[0003] These design considerations have changed considerably over
time as computing systems of the type typically located within a
data center consume considerable amounts of energy while generating
heat necessitating CRAC systems of greater efficiency. With the
increasing popularity of the Internet, data centers are now
considered to be the number one energy consumer in the United
States.
[0004] There have been three fundamental CRAC system designs
referred to, for the sake of simplicity, as CRAC1, CRAC2 and
CRAC3.
[0005] CRAC1 is a split refrigeration system with outdoor air
cooled condensing. This system is characterized by having two main
components, namely, the CRAC unit itself located inside of the data
center and a condenser located external thereto. The indoor unit
houses the systems' compressors, evaporators, controls and cooling
fans. The outdoor unit houses the condenser and condenser fans
which inter-connect to the indoor unit with piping through which
the refrigerant travels.
[0006] The CRAC2 system also employs two main components, namely,
the CRAC units located within the data center and heat exchanger
components located external thereto. The indoor unit houses the
compressor, condenser, evaporator, system controls and cooling
fans. The outdoor unit is composed of a heat exchanger from which
heat from the system is rejected as well as pumps used to move heat
transfer fluid from the indoor to outdoor units. This design can
also have an optional heat exchanger located in series with the
indoor heat exchangers. When the fluid temperature from the outdoor
heat exchanger is below the return air temperature, a valve opens
allowing the heat transfer fluid to pass through the lead heat
exchanger. The fluid removes heat from the return air stream.
[0007] CRAC3 systems employ CRAC units located in the data center
and fluid chillers located external thereto. The indoor unit houses
the indoor heat exchanger, indoor fan systems and controls. The
outside unit is composed of either a self-contained refrigeration
system which chills the heat transfer fluid which is usually air
cooled or a split chiller system which is composed of a compressor,
evaporator, fluid cooled condenser and fluid cooled heat
exchanger.
[0008] Regardless of the system type, the design philosophy in
sizing and installing CRAC systems in a data center is quite
consistent from installation to installation. The typical
installation involves adding a sufficient number of units to meet
the anticipated heat load of the facility and one additional unit
for redundancy. Thus, as facilities grow, more indoor and outdoor
units are added to the system noting that, typically, each CRAC
unit operates independently of other units. Thus, the control
valves of each unit are turned on and off independently of other
units to meet and maintain building loads. Indoor fans never shut
off to maintain the load imposed upon the facility. Centrifugal
fans are commonly employed for supply side air. Small fans are
employed even though smaller fans are generally more inefficient
than those which are larger. Regardless of fan type, current CRAC
installations are based upon a "one load, one system" methodology.
Such installations exhibit the same efficiency when operating under
normal or emergency conditions. These systems do not integrate
redundancy in the form of additional heat exchange area in order to
make them more efficient. Parameters seldom change dramatically
unless loads change dramatically. The redundancy of this type of
system is based upon adding units which are brought on line as
needed.
[0009] It is quite apparent that previously suggested CRAC systems
made no attempt to maximize operating efficiencies as most prior
designs were created well before energy became as expensive as it
is today and before the explosive use of Internet-based
communications and information downloading created such a severe
impact upon energy usage and resultant heat generation.
[0010] Thus, it is an object of the present invention to provide
CRAC systems having several unique and innovative design criteria
to make such systems much more efficient to operate while
maximizing their ability to effectively cool a data center both
under ordinary conditions and when emergencies require supplemental
cooling capacity.
[0011] It is yet a further object of the present invention to
provide a data center cooling system which, depending upon
environmental conditions, can transfer coolant while bypassing the
systems' compressor.
[0012] Although the discussion which appears below reveals a unique
system capable, under certain conditions, to provide coolant to
condenser coils without use of a compressor, the present invention
is not the first instance in which compressor-free cooling has been
suggested. In this regard, reference is made to FIG. 1 representing
a schematic drawing of such a system commercially available from
Trane Co. Specifically, when water returning from cooling tower 11
is colder than the chilled water circulating through cooling load
12, refrigerant pressure within condenser 13 is slightly lower than
that in evaporator 14. This pressure differential drives the
refrigerant vapor "boiled off" in evaporator 14 to condenser 13,
where it condenses and flows by gravity back to evaporator 14. As
long as the proper pressure difference exists between evaporator 14
and condenser 13, refrigerant flow and consequent "free cooling"
continues. According to its manufacture, the system shown in FIG. 1
is capable of refrigerant-migration "free cooling" up to as much as
40% of the chiller's design tonnage. Since the chiller and "free
cooling" cycle cannot operate simultaneously, free cooling of this
type can only be used when the cooling capacity of water tower 11
is sufficient to meet the entire building load. As "free cooling"
capacity is available only when the ambient wet bulb temperature is
below 50 degrees F., accessories such as chilled water pumps,
condenser water pumps and cooling tower fans must continue to
operate in their conventional manner while the chiller operates in
the "free cooling mode." This minimizes the energy savings from
such a system which is realized only from its ability to bypass its
compressor.
SUMMARY OF THE INVENTION
[0013] As a first embodiment, the present invention involves a
cooling system for cooling devices housed in a data center, the
device comprising a cabinet, a set of evaporator coils, an inlet
and outlet and at least one fan for drawing air from within the
data center through said cabinet and for movement of the air over
said evaporator coils to the data center heat loads. The
improvement comprises angling the air flow emanating from the
cabinet proximate 45.degree. to 70.degree. to the plane of the
flooring.
[0014] As a second embodiment, the invention is directed to a
cooling system for cooling a data center to a predetermined
temperature and humidity, the cooling system comprising a set of
evaporator coils and a fan for moving air within the data center
passed the set of evaporator coils. At least two sets of
compressors, two sets of condensers and two independent control
systems are located external to the data center and positioned in
parallel to provide coolant to the set of evaporator coils.
[0015] The third embodiment involves a cooling system comprising a
compressor, a condenser, coolant, pump and primary evaporator coil
for cooling. The improvement comprises a secondary evaporator coil
in series with the primary evaporator coil, the secondary
evaporator coil being a flooded coil piped to the condenser.
[0016] As yet another embodiment, the invention involves a cooling
system comprising a compressor, condenser, condensable coolant,
pump and evaporator coils. The improvement comprises a measurement
device and actuator wherein when the measurement device measures
the wet-bulb temperature and when it is no greater than a
preselected value, the compressible coolant is circulated by the
pump between the condenser and evaporator coils while bypassing the
compressor.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 is a schematic depiction of a commercially available
chiller of the prior art.
[0018] FIG. 2 is a side view of a portion of the present invention
showing evaporator coils and fans to be housed in a cabinet used
for cooling an appropriate data center according to the present
invention.
[0019] FIG. 3 is a schematic view of a system according to the
present invention including two circuits provided for redundancy
and for increased efficiency.
[0020] FIG. 4 is a schematic view of a part time economizing system
using a scavenger coil in series with main evaporator coils to
increase efficiency of the present invention.
[0021] FIG. 5 is yet another schematic view of an economizing
circuit similar to that depicted in FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Turning first to FIG. 2, housing 20 is depicted with its
side walls removed for illustrative purposes. Frame members 21
support sets of evaporator coils 22 receiving coolant from
compressors and related hardware located external to the data
center being cooled.
[0023] In operation, ambient air within the data center is drawn
through open top 25 passed sets of evaporator coils 22 through the
use of prop or axial fans 23. Ideally, multiple fans are employed
sufficient to maintain a positive static pressure within a space
beneath the flooring. Although not shown, cool air created by
housing 20 is discharged proximate racks of circuit boards and
similar solid state devices through openings strategically located
proximate thereto.
[0024] A feature of the present invention is the orientation of
fans 23 in directing cooled air in the direction of arrows 24. CRAC
units of the prior art generally employ centrifugal fans that blow
air directly at the floor. This increases the static pressure load
on the fans as the air is forced to change direction by 90 degrees
upon impacting the floor. The present invention employs prop or
axial fans 23 directing air discharge as shown by arrows 24 by
mounting the fans at a 20 to 45 degree angle from vertical or 45 to
70 degree angle proximate to the plane of the floor. This provides
a much improved approach angle of the cold air discharge relative
to the floor and reduces the pressure drop characterized by prior
systems. All such expedients are considered to be embraced within
the present invention. Sufficient fans are employed for maintaining
static pressure and air flow within the space noting that output
can be varied to maintain the required static pressure via static
pressure sensors.
[0025] Yet a further embodiment of the present invention can be
appreciated by reference to FIG. 3. In its basic terms, system 30
is composed of two simple circuits, operating in parallel.
Specifically, parallel condensers 31A and 31B as well as parallel
compressors 34A and 34B operate externally to the data center each
set operating in conjunction with pumps 35A and 35B, respectively,
to supply coolant to expansion valves 36 and onto evaporators
32A/32B and 33A/33B, located within the data center. Redundant
condensers and evaporators are operated together at part load while
increasing the heat exchange surface area resulting in a decrease
in the temperature differences within the system; that is, the
temperature difference between the coolant temperature and the air
temperature flowing over the coil. By decreasing this temperature
difference, pressures are generally higher on the evaporator side
and lower on the condenser side of the system thereby decreasing
the compression ratio of the coolant and reducing the energy the
compressors consume to compress the coolant gas.
[0026] A main function of the present system is that it allows for
reduced compression operation. Compression ratio is a reference to
the difference between the suction and the discharge pressures
measured in absolute pressure. There are several main reasons why
the present invention can accomplish reduced compression where
others cannot.
[0027] As background, typical systems compression ratios are
derived by the use and control of the condensing pressure. Typical
systems control the condensing pressure buy either staging the
condenser fans off and on to meet a set point of condensing
pressure or speed control fans to meet that specific point. The
present system utilizes a unique form of control to allow for
reduced compression. Instead of turning fans on and off or slowing
them down to meet a specific point, the present system utilizes a
variable set point. Ideally, this set point establishes a
condensing temperature that is 8 degrees F. higher than the wet
bulb temperature. Condensers are controlled to match loads in ton
and to match a true constant set point.
[0028] It should be noted that every major compressor manufacturer
establishes proper operational conditions for its products. It is
common for manufacturers to state that a compression ratio of 1.5
to 1 is the lowest allowable compression ratio as anything less is
not warrantable. Increased mass flow rate is the main reason
manufacturers do not want lower compression rations. As compression
ratios decrease, a machine's capability of pumping refrigerant
increases. As an example, at a 2 to 1 compression ratio, a machine
may be capable of pumping 50 tons of coolant while at a 1.5 to 1
compression ratio a machine may be capable of pumping 75 tons of
coolant and at 1.05 to 1, that same machine may be capable of
pumping 100 tons of coolant. As the mass flow rates increase thru
the compressor restriction, friction increases as well, as much as
double in some cases. This causes a higher amount of wear and tear
on machine parts as gas flows thru the compressor ports, pipe and
valves.
[0029] The present system commonly operates at compression ratios
of 1.05 to 1-1.51 to 1 and in most cases it operates well under a
manufacture's published allowable compression ratio for long
periods of time. This is done by not exceeding the machine's
designed mass flow rate rather than compression ratio. This is
achieved by reducing the speed of the compressor to only allow the
machine to pump coolant to match its maximum mass flow rate.
[0030] To enable the present system to perform at reduced
compression levels, it must be able to compensate for what normal
systems cannot do. Low compression ratios create lower flow rates
through typical metering devices. Every metering device is rated
based on pressure differential across its valve. For example, a
common metering device may be rated at 15 tons under common
conditions, but as a system's compression ratio or pressure
differential drops, that same valve may be only rated for 5 to 10
tons.
[0031] Ideally, metering valves used herein are rated and designed
at a 1.3 to 1 compression ratio. These metering valves are provided
with a constant pressure differential by amplifying liquid pressure
entering the valve with the use of a liquid coolant pump and speed
control. Pump speed is varied to maintain a constant pressure drop
across the metering devices.
[0032] Yet a further embodiment of the present invention can be
appreciated by reference to FIG. 4. Specifically, system 40 is
depicted whereby coolant from pump 42 located externally to the
data center urges coolant through a separate evaporator coil 44
which is called a "scavenger coil." The scavenger coil is located
in series with main evaporator coils 43 through which air flows in
the direction of arrows 45 for cooling the data center. Vapor
condenser 41 is also located externally to the data center to
complete the circuit.
[0033] Again referring to FIG. 4, scavenger coil 44 is a flooded
coil that is piped directly back to condenser 41. When the coolant
temperature is lower than the return air temperature, bypass valve
47 opens allowing coolant into the scavenger coil where it removes
heat from the data center. The coolant then returns directly back
to condenser 41, via flash vessel 33 without moving through a
compressor, thus enhancing system efficiency. As condenser 41 still
uses energy to remove heat and pumps use energy to pump coolant,
some energy is still employed to operate system 40. However, energy
usage is far more efficient than in a typical vapor compressor
cycle.
[0034] As is quite apparent, coolant from the pump goes through an
entirely separate cooling coil called the scavenger coil (SC) in
series with the main evaporator coils. This SC coil is a flooded
coil that is direct piped back to the condenser. When the
condensing liquid temperature is lower than the return air
temperature a valve opens allowing refrigerant into the scavenger
coil where it removes heat and goes directly back to the condenser
to extract the heat from the room. If, for example, the return air
temperature is 68.degree. F. and the condensing liquid temperature
is 65.degree. F., heat from the return air is absorbed into the
refrigerant (hot goes to cold). The larger the differential is
between the return air temperature and the refrigerant temperature,
the more energy is removed with this coil. Since a BTU is a BTU the
condensers still use energy to remove the heat and the pumps use
energy to pump the refrigerant there still is energy used. This
energy usage is far more efficient than a typical vapor compressor
cycle.
[0035] To summarize, coolant pump 42 pumps liquid refrigerant to
feed devices 49 and into the scavenger coils 44. Inside the
scavenger coils, the liquid refrigerant removes heat while still in
a semi liquid form. Liquid refrigerant leaves the scavenger coils
and flows to flash vessel 46. Vapor leaves flash vessel 46 and
enters the condenser 41 to be condensed. Flash vessels 46 level is
approximately 2 feet below condenser 41 outlet for purposes of
maintaining a proper liquid trap. Flash vessel 46 maintains a
liquid level based on the weight of the refrigerant and acts as an
expansion tank.
[0036] The present system is also designed, under certain
conditions, to allow for "free cooling." This means that the system
operates under the physics of a thermo-siphon or through migration
cooling as was suggested when discussing FIG. 1. However, in this
instance, when the wet bulb temperature is less than approximately
41-45 degrees F., the "free cooling" cycle operates. Instead of
operating with gravity controlling the flow rate as in the prior
art, the present system employs a pump to ensure there is enough of
a pressure difference to allow the coolant to flow through the
metering valve and the evaporator where it is boiled off and routed
through a motorized valve to the condenser where it condenses
without moving through a compression cycle. If the system detects a
lack of movement of the coolant or if a pulse is detected
indicating a break in natural migration from the condenser to the
evaporator, the compressor is activated by a sensor enabling the
system to operate normally.
[0037] To fully appreciate the system architecture of the present
invention, as its preferred embodiment, reference is made to FIG.
5. It is noted that system 50 is, in effect, one system having two
circuits. Multiple evaporator coils 51 and 52 are located within
the data center to be cooled. A first circuit comprised of
compressor 53, condenser 54, expansion receiver 55, pump 56 and
metering valves 57 is employed in conjunction with parallel
elements comprised of compressor 58, condenser 59, expansion
receiver 60, pump 61 and metering valves 62. Both circuits work
together but are capable of working independently in case of system
failures or emergencies. Each air handling unit has both circuits
operating in parallel comprised of the same components as in any
typical refrigeration system. The systems can be expanded to meet
growing loads. Indoor and outdoor units can be added as demand or
as planned expansion requires. Further, through the use of pumps 56
and 61 together with metering valves 57 and 62, economizing can be
carried out as explained above, by circulating coolant without use
of compressors 53 and 58 if outdoor wet bulb temperatures so
dictate.
[0038] What was discussed above represents examples of various
embodiments of the present invention. It is assumed that other
embodiments will be readily apparent to those skilled in the art.
It is intended that the specification is to be considered
illustrative of the present invention, the scope of which is to be
limited only by the claims.
* * * * *