U.S. patent application number 10/773016 was filed with the patent office on 2005-08-11 for thermal energy storage device and method.
Invention is credited to Anderson, R. David.
Application Number | 20050172660 10/773016 |
Document ID | / |
Family ID | 34826701 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050172660 |
Kind Code |
A1 |
Anderson, R. David |
August 11, 2005 |
Thermal energy storage device and method
Abstract
A thermal energy storage unit is provided for a conventional an
air conditioning system having a compressor, a condensing unit, an
expansion unit and an evaporator, all operative interconnected. The
thermal energy storage unit is located exterior to a structure to
be cooled and is connected solely to refrigerant lines running to
and from the compressor without altering the existing expansion
unit and evaporator unit located within the structure. The air
conditioning system is operated through at least two distinct
phases of operation, one phase of operation including the running
of the compressor to supply refrigerant to the expansion unit and
the evaporator unit to cool the indoor space inside the structure
and another distinct phase of operation being the operation of the
thermal energy storage unit to exactly simulate the running of the
compressor without powering the compressor.
Inventors: |
Anderson, R. David; (Wichita
Falls, TX) |
Correspondence
Address: |
WHITAKER, CHALK, SWINDLE & SAWYER, LLP
3500 CITY CENTER TOWER II
301 COMMERCE STREET
FORT WORTH
TX
76102-4186
US
|
Family ID: |
34826701 |
Appl. No.: |
10/773016 |
Filed: |
February 5, 2004 |
Current U.S.
Class: |
62/435 |
Current CPC
Class: |
F25D 16/00 20130101;
F25B 2400/16 20130101; F25B 2400/24 20130101; Y02E 60/14 20130101;
F24F 5/0017 20130101; Y02E 60/147 20130101 |
Class at
Publication: |
062/435 |
International
Class: |
F25D 017/02 |
Claims
What is claimed is:
1. An air conditioning system, comprising: a compressor for
compressing a refrigerant, the refrigerant being a compressible
phase change fluid; a condensing unit operatively connected to the
compressor; an evaporator unit and an associated expansion means
operatively interconnected to the condensing unit and to the
compressor, the evaporator unit being in heat exchange relationship
with a supply air stream for an indoor space inside a structure,
the compressor being operable to circulate the refrigerant between
the condensing unit and the evaporator unit to cool the supply air
stream; a thermal energy storage unit including a tank having a
thermal energy storage medium disposed therein and having an
associated heat exchanger, the heat exchanger being operably
connected to the compressor and evaporator; a refrigerant
circulating device for circulating refrigerant through the heat
exchanger in the tank and between the tank and the condenser and
evaporator; wherein the refrigerant circulating device includes a
prime mover and an auxiliary liquid which is acted upon by the
prime mover, the auxiliary liquid being coupled to the refrigerant,
whereby force exerted by the prime mover on the auxiliary liquid is
indirectly transferred to the refrigerant.
2. The air conditioning system of claim 1, wherein the auxiliary
liquid has a higher relative viscosity and a lower relative vapor
pressure than the refrigerant.
3. The air conditioning system of claim 1, wherein the refrigerant
is Freon.
4. The air conditioning system of claim 1, prime mover is a
positive displacement pump.
5. The air conditioning system of claim 1, wherein the prime mover
communicates with a pair of fluid cylinders containing oil as an
auxiliary fluid and wherein the prime mover exerts a motive power
upon pistons located within the fluid cylinders to thereby
mechanically couple the motive power of the prime mover to the
refrigerant being circulated in the system.
6. The air conditioning system of claim 1, wherein the prime mover
communicates with a pair of fluid cylinders containing the
auxiliary fluid and wherein the prime mover exerts a motive power
on a flexible bladder located within the each of the fluid
cylinders to thereby couple the motive power of the prime mover to
the refrigerant being circulated in the system.
7. The air conditioning system of claim 1, wherein the prime mover
is powered by a direct current motor and battery.
8. The air conditioning system of claim 1, wherein the storage
medium in the tank is water.
9. An air conditioning system, comprising: a compressor for
compressing a refrigerant, the refrigerant being a compressible
phase change fluid; a condensing unit operatively connected to the
compressor; an evaporator unit and an associated expansion means
operatively interconnected to the condensing unit and to the
compressor, the evaporator unit being in heat exchange relationship
with a supply air stream for an indoor space inside a structure,
the compressor being operable to circulate the refrigerant between
the condensing unit and the evaporator unit to cool the supply air
stream; a thermal energy storage unit including a tank having a
thermal energy storage medium disposed therein and having an
associated heat exchanger, the heat exchanger being operably
connected to the compressor and evaporator, the thermal energy
storage unit further including a temporary refrigerant storage
tank; a refrigerant circulating device for circulating refrigerant
through the heat exchanger in the tank and between the tank and the
condenser and evaporator; wherein the refrigerant circulating
device includes a prime mover and an auxiliary liquid which is
acted upon by the prime mover, the auxiliary liquid being coupled
to the refrigerant, whereby force exerted by the prime mover on the
auxiliary liquid is indirectly transferred to the refrigerant; a
valve system for controlling the flow of refrigerant through the
air conditioning system, the valve system being operative to
provide three distinct time periods of operation for the system, a
first time period which allows refrigerant to flow from the
condenser to the heat exchanger of the thermal energy storage unit
to freeze the medium in the tank and to then return to the
condenser without utilizing the evaporator, a second time period
which bypasses the condenser and circulates refrigerant through the
thermal storage unit and through the evaporator to thereby cool the
supply air inside the structure before returning to the thermal
storage unit, and a third time period which utilizes only the
temporary refrigerant storage vessel of the thermal storage unit
and which utilizes the condenser and evaporator to cool the supply
air inside the structure as if the thermal storage unit were not
present.
10. The air conditioning system of claim 9, wherein the auxiliary
liquid has a higher relative viscosity and a lower relative vapor
pressure than the refrigerant.
11. The air conditioning system of claim 9, wherein the prime mover
is a positive displacement pump.
12. The air conditioning system of claim 9, wherein the prime mover
communicates with a pair of fluid cylinders containing oil as an
auxiliary fluid and wherein the prime mover exerts a motive power
upon pistons located within the fluid cylinders to thereby
mechanically couple the motive power of the prime mover to the
refrigerant being circulated in the system.
13. The air conditioning system of claim 9, wherein the prime mover
communicates with a pair of fluid cylinders containing the
auxiliary fluid and wherein the prime mover exerts a motive power
on a flexible bladder located within the each of the fluid
cylinders to thereby couple the motive power of the prime mover to
the refrigerant being circulated in the system.
14. The air conditioning system of claim 9, wherein the prime mover
is powered by a direct current motor and battery.
15. The air conditioning system of claim 9, wherein the storage
medium in the tank is water.
16. A method of operating an air conditioning system having a
compressor, a condensing unit, an expansion unit and an evaporator,
all operative interconnected, the evaporator unit being in heat
exchange relationship with a supply air stream for an indoor space
inside a structure, the compressor being located exterior to the
structure and being operable to circulate refrigerant between the
condensing unit and the evaporator unit to cool the supply air
stream, the method comprising the steps of: locating a thermal
energy storage unit exterior to the structure to be cooled and
connecting the thermal storage unit solely to refrigerant lines
running to and from the compressor without altering the existing
expansion unit and evaporator unit; operating the air conditioning
system through at least two distinct phases of operation, one phase
of operation including the running of the compressor to supply
refrigerant to the expansion unit and the evaporator unit to cool
the indoor space inside the structure and another distinct phase of
operation being the operation of the thermal energy storage unit to
exactly simulate the running of the compressor without powering the
compressor.
17. The method of claim 16, wherein the thermal storage unit
includes a tank, a storage medium within the tank, and a heat
exchanger located in the tank.
18. The method of claim 17, wherein the system is further provided
with a refrigerant circulating device for circulating refrigerant
through the heat exchanger in the tank and between the tank and the
condenser and evaporator unit; wherein the refrigerant circulating
device includes a prime mover and an auxiliary liquid which is
acted upon by the prime mover, the auxiliary liquid being coupled
to the refrigerant, whereby force exerted by the prime mover on the
auxiliary liquid is indirectly transferred to the refrigerant.
19. The method of claim 18, wherein the auxiliary liquid has a
higher relative viscosity and a lower relative vapor pressure than
the refrigerant.
20. The method of claim 18, wherein the prime mover is a positive
displacement pump.
21. The method of claim 18, wherein the prime mover communicates
with a pair of fluid cylinders containing oil as an auxiliary fluid
and wherein the prime mover exerts a motive power upon pistons
located within the fluid cylinders to thereby mechanically couple
the motive power of the prime mover to the refrigerant being
circulated in the system.
22. The method of claim 18, wherein the prime mover communicates
with a pair of fluid cylinders containing the auxiliary fluid and
wherein the prime mover exerts a motive power on a flexible bladder
located within the each of the fluid cylinders to thereby couple
the motive power of the prime mover to the refrigerant being
circulated in the system.
23. The method of claim 18, wherein the prime mover is powered by a
direct current motor which is connected to a battery as an energy
source.
24. A method of operating an air conditioning system having a
compressor, a condensing unit, an expansion unit and an evaporator,
all operative interconnected, the evaporator unit being in heat
exchange relationship with a supply air stream for an indoor space
inside a structure, the compressor being located exterior to the
structure and being operable to circulate refrigerant between the
condensing unit and the evaporator unit to cool the supply air
stream, the method comprising the steps of: locating a thermal
energy storage unit exterior to the structure to be cooled and
connecting the thermal storage unit solely to refrigerant lines
running to and from the compressor without altering the existing
expansion unit and evaporator unit; providing control means for
controlling the flow of refrigerant through the air conditioning
system, control means being operative to provide three distinct
time periods of operation for the system, a first time period which
allows refrigerant to flow from the condenser to the heat exchanger
of the thermal energy storage unit to freeze the medium in the tank
and to then return to the condensing unit without utilizing the
evaporating unit, a second time period which bypasses the
condensing unit and circulates refrigerant through the thermal
storage unit and through the evaporating unit to thereby cool the
supply air inside the structure before returning to the thermal
storage unit, and a third time period which utilizes only the
temporary refrigerant storage vessel of the thermal storage unit
and which utilizes the condensing unit and evaporating unit to cool
the supply air inside the structure as if the thermal storage unit
were not present.
25. The method of claim 24, wherein a refrigerant circulating
device is provided for circulating refrigerant through the heat
exchanger in the tank and between the tank and the condensing unit
and evaporating unit; wherein the refrigerant circulating device
includes a prime mover and an auxiliary liquid which is acted upon
by the prime mover, the auxiliary liquid being coupled to the
refrigerant, whereby force exerted by the prime mover on the
auxiliary liquid is indirectly transferred to the refrigerant.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an energy storage device
that can easily be added to an existing Freon compression
air-conditioning system commonly used in residential and small
commercial applications. The method of the invention allows the
addition of a single thermal energy storage unit which will
replicate the operation of a conventional condensing unit while
using only energy that was previously stored in the existing system
without any change or alteration of existing equipment.
[0003] 2. Description of the Prior Art
[0004] As a result of the growing popularity of air-conditioning,
electrical demands have increased drastically in certain areas. A
particular problem exists because of the common demand for
air-conditioning power during the hottest portion of the day. Such
demands tax electrical generation plants and the electrical
distribution systems presently in place. In order to counter this
common demand, electric utilities currently offer incentives
including significantly reduced rates for electricity used during
off peak hours.
[0005] For example, it has become common for the consumer to be
offered a two-tiered electrical pricing structure. Available
incentives for the consumer include a lower price for electricity
when used at low demand times (off peak time) and a higher price
for high demand time use (peak time). These incentives are an
effort to more efficiently utilize existing electrical facilities
(power plants, power lines, etc.) and to defer the need for
additional facilities and equipment to provide the capacity to meet
the peak time demand. Significantly, the peak time demand hours
currently represent only about 8% of the total available hours in a
year.
[0006] As a typical example, a consumer who has been paying a
uniform ten cents per kilowatt hour of electrical use might only
pay three cents per kilowatt hour for the same amount of power
during off peak times while paying fifteen cents during peak times.
The definition of "peak time" varies according to a number of
variables including the geographic location, the particular
generation stations involved, the distribution methods utilized,
the local population etc. Generally, the peak time hours are from
noon until sundown during the summer months with other times being
defined as off peak. As should be apparent from the foregoing
discussion, it has become economically advantageous for the
consumer to buy and store energy during the off peak times and to
use the stored energy during peak times.
[0007] In order to take advantage of existing incentives offered by
the electrical utilities, larger commercial users of electricity
have found it feasible to shift their electric use to off peak
hours by using any of several different methods. These existing
methods have included: (1) using multiple air conditioners and
scheduling building use such that all of the space cooling
equipment does not operate at the same time; (2) shifting the
operation schedule of equipment that can be operated during
off-peak hours by operating such equipment on a timer without
supervision where the operation requires no longer than 16 hours to
complete its process; (3) changing the operating hours of employees
to off-peak hours, including offering shift premiums for employees
willing to cooperate; and (4) installing a thermal storage system
for space cooling needs which stores energy during off-peak hours
and then utilizes the stored energy during peak hours.
[0008] The thermal storage method listed as (4) above is
particularly pertinent to the improvement offered by the method and
device of the present invention. The existing thermal storage
systems include:
[0009] 1. Cooling large volumes of water during off-peak hours and
then circulating the cooled water through the structure to be
cooled during peak hours.
[0010] 2. Freezing a smaller volume of water to ice, followed by
circulating a liquid through the ice for cooling and by then
flowing the liquid inside the structure where it cools the air and
then returns to the ice bank to once again be cooled. Such systems
take advantage of the greater energy storing capacity which occurs
with the phase change of water from a liquid to solid. Using water
as the storage media, 144 BTU of heat can be transferred to the ice
per pound before the ice completely melts.
[0011] 3. Freezing a volume of water to ice where the ice is
located in a tank which surrounds a coil containing a refrigerant
(typically R-22, Freon) used in the conventional cooling process
during the off-peak hours with a conventional condensing unit.
During peak hours the Freon refrigerant condenses to near 100%
liquid in the ice tank and is then is circulated with conventional
pumping equipment to an evaporative coil located inside the
structure. The Freon in the evaporative coil removes heat from the
structure by evaporating the Freon to near its gaseous state.
Because the pressure in the evaporative coil is only slightly
higher than in the condensing coil of the ice tank (the difference
is the pressure drop in the line and any elevation difference), the
vaporizing temperature of the Freon in the evaporative coil is only
slightly higher than the condensing temperature in the ice tank
condensing coil. By this means, heat is transferred from inside the
structure to the ice tank until the ice is melted.
[0012] Thermal storage devices of this last type have had some
success in new construction, but have had very limited use in
existing structures because of the initial expense and
inconvenience of installation. Approximately 85% of the presently
existing office space in this country was constructed prior to
1990. As a result, for any significant shift in the amount of
electrical demand to off-peak hours to occur, a thermal storage
system must be provided which is not only low in initial cost but
which can also be installed with a minimum of effort and
inconvenience. One limitation on the use of existing technology has
been the requirement that the existing equipment be greatly
modified, including modification of the evaporative coil or related
equipment already located within the interior of the structure
being cooled.
[0013] Another principal limitation on the use of the third type of
thermal energy storage system described above relates to the
various difficulties that are encountered in pumping liquid Freon
which is condensed in the ice tank. An important part of any
thermal energy storage device is the ability to cool the structure
in the event the energy storage medium is depleted. With the first
two types of systems described above, this task is easily
accomplished because there are two coils in the storage medium. One
of the coils is for cooling the medium with conventional methods
while the other coil contains the coolant that is circulated
through the structure. In the event of energy depletion of the
storage medium, it is an easy matter to cool the energy storage
medium with conventional means, which in turn cools the circulating
fluid.
[0014] With the third type of device there is one coil in the
storage medium which serves multiple purposes. In one time frame a
conventional condensing unit is employed for (1) freezing the
storage medium with compression of the refrigerant vapor; (2)
condensing the vapor to its liquid state in a condensing coil; (3)
holding back pressure on the Freon with an expansion device so that
condensing can take place at the ambient temperature of the
condensing coil; and (4) freezing the storage medium after
expansion of the liquid to the suction pressure of the compressor
inside the single coil in the storage medium.
[0015] In a second time frame, the coil in the storage medium is
used to condense the Freon returning from the structure. After the
Freon is condensed to near 100% liquid, it is then pumped to an
evaporative coil inside the structure. The refrigerant is vaporized
in the evaporative coil due to the heat absorbed inside the
evaporative coil and is then returned to the storage medium coil
for condensing. It is then again pumped into the structure. An
expansion device is not needed in this second time period because
both the condensing coil and the evaporative coil operate at
essentially the same pressure.
[0016] A third time period occurs in the case of the energy storage
being depleted or cooling being needed in the structure during
off-peak periods. During this third time period many different
techniques have been employed to cool the structure. A basic
problem exists with respect to all of the existing methods,
however, because cooling of the structure with a conventional
condensing unit requires an expansion device to hold back pressure
on the cooling coil to enable the hot high pressure Freon leaving
the compressor to condense to a liquid at a temperature that is
close to ambient. This back pressure for R-22 is in excess of 200
psig, causing a differential pressure of over 100 psig between the
suction and discharge of the compressor. This pressure differential
is easily provided by the compressor but has not been achieved by
the liquid pump required in the second time period because of the
characteristic properties of the liquid Freon present in the ice
tank summarized above. The following patents represent the current
state of the art in attempting to solve this problem:
[0017] In U.S. Pat. No. 4,735,064, issued Apr. 5, 1988, to Fischer,
the approach described moved the expansion device outside the
structure in the vicinity of the ice tank where it served a dual
purpose. In the first time period, the expansion device is used to
make ice. In the third time period, the expansion device holds back
pressure on the conventional condensing coil and allows the liquid
to flash to low pressure before the evaporative coil inside the
structure. Because the expansion device is located outside the
structure, this method requires a new large and insulated line to
be run inside the structure to the evaporative coil. This is
costly, inconvenient, and impractical in most cases.
[0018] In U.S. Pat. No. 5,211,029, to Dean et al., issued May 18,
1993, the approach was to leave the expansion device inside the
structure near the evaporative coil and to bypass the device during
time period two operations. This arrangement works adequately in
the time period three, but requires an additional line to be run
into the structure for time period two operation when the pump is
running because the pump can't overcome the high pressure which is
present. Again this new line is costly, inconvenient, and
impractical in most cases. This patent does contain a very brief
comment that the pump could be discharged upstream of the expansion
device, but it does not present any plan for getting around the
pumping problems.
[0019] U.S. Pat. No. 4,916,916, to Fischer, issued Apr. 17, 1990
substitutes two volume tanks described as self pumpers for the
liquid pump. This method requires the compressor to run during the
second time period using the vapor high pressure discharge from the
compressor to pressurize first one and then the other volume tank,
thereby building up enough pressure to force the liquid Freon
condensed by the ice tank inside the structure and through the
expansion device. To save energy the patent proposes to replace the
conventional compressor with a two-speed compressor. One speed
would be used for time periods one and three and a reduced speed
would be used for time period two. This method is costly,
inconvenient, impractical but does demonstrate the problems
involved in pumping the liquid refrigerant.
[0020] U.S. Pat. No. 5,255,526, to Fischer, issued Oct. 26, 1993,
once again utilizes a liquid pump, leaves the expansion device
inside the structure near the evaporative coil, and adds a
refrigerant storage tank inside the structure. A bypass around the
expansion device is provided inside the storage tank. This method
requires a new line to be run from the pump into the structure to
the storage tank and the installation of a storage tank inside the
structure.
[0021] U.S. Pat. No. 5,647,225, to Fischer, issued Jul. 15, 1997,
uses a liquid pump and adds an additional evaporator without an
expansion device inside the structure. This new evaporator is used
in conjunction with the pump during time period two. This method
requires that two new lines be run into the structure and the
addition of a second evaporative coil.
[0022] U.S. Pat. No. 5,467,812, issued Nov. 21, 1995, to Dean et
al., is a means of both heating and cooling a structure with stored
energy. For the cooling phase a second evaporative coil is added
inside the structure, without an expansion device, to be used with
a refrigerant pump. This requires two new lines to be run into the
structure and the addition of another evaporative coil.
[0023] U.S. Pat. No. 5,678,626, issued Oct. 21, 1997, to Dean, is
similar in scope to the previous Dean patent with the additional
benefit of simultaneous cooling with both evaporative coils. This
requires that both the pump and the compressor be running at the
same time, however. Since there are two evaporative coils now
inside the structure, they both can be used at the same time.
However, the original coil requires the compressor to be running.
The time period in which both coils are likely to be required to
operate simultaneously will most probably be the time of the
highest electrical demand. However, from an economic view point,
this is precisely the time that the compressor should not be
running. This solution also requires two new lines to be run into
the structure and the addition of another evaporative coil.
[0024] U.S. Pat. No. 5,682,752, issued Nov. 4, 1997, to Dean,
abandons the concept of adding a second evaporative coil and
describes a refrigerant pump that pumps liquid Freon into an
expansion device. That device is described as a conventional
thermal expansion valve having a sensor for appropriately
controlling the flow of refrigerant to the evaporator. This type of
expansion device is rarely used in residential and small commercial
systems because of the attendant cost. As a result, it must be
added in most installations. The problems of pumping the low
viscosity liquid refrigerant are not discussed even though a gear
pump is cited as the preferred type of pump to be used. The patent
also teaches that proportional-integral control loop is required to
insure proper refrigerant flow when using the added thermal
expansion valve. This computer controlled proportional integral
loop adjusts the pump speed as a function of the refrigerant
temperature in the suction line. As slippage increases, the pump
speed increases.
[0025] The problem of transferring refrigerant to the suction of
the pump to raise the net positive suction pressure of the liquid
in an effort to reduce cavitation is not addressed. The '752 patent
does go on to describe a storage module, a first transitory mode, a
second transitory mode, and accompanying computer logic. This
described method also includes the use of a refrigerant storage
module commonly known as a "liquid receiver" in conjunction with a
pump down cycle. Such a cycle and receiver are described in a
number of presently available refrigeration textbooks, e.g.,
"Heating and Cooling Essentials", by Killinger, The
Goodheart-Willcox Company Inc., 1993 & 1999; "Modern
Refrigeration and Air Conditioning" by Althouse, Turnquist, and
Bracciano, The Goodheart-Willcox Company Inc., 1996, etc. By
computer controlling the speed of the pump to compensate for
slippage and by changing the expansion device from the common
metering orifice/capillary tube type of expansion device to a
thermally controlled expansion valve, a workable system may result.
However, the system would be costly and have limited pump life.
[0026] In spite of the above advances in thermal energy storage
systems, a need exists for a workable system which is simple in
design and economical to install and which can be installed outside
the existing structure to be cooled without the necessity of
altering the existing equipment inside the structure.
SUMMARY OF THE INVENTION
[0027] The present invention provides a novel energy storage device
or system which can easily be added by retrofit to an existing
Freon compression air-conditioning system of the type commonly used
in residential and small commercial structures. The system of the
invention is also easily incorporated into new construction with
relatively little additional expense. The method and device of the
invention allow the addition of a single "package" to a new or
existing air conditioning system that totally simulates the
operation of the conventional condensing unit. The system of the
invention uses only energy that was previously stored by the system
and does not require any change or alteration of existing equipment
inside the structure. The add-on package of the invention creates a
new system that stores energy in a first time period, utilizes this
stored energy during a second time period to cool the structure,
and possesses the capacity to be able to cool the structure in a
third time period without utilizing stored energy.
[0028] In addition to providing an add-on package which can be
easily installed outside the structure, two distinct problems are
solved by the improved system of the invention. The problem of
pumping a low viscosity and easily vaporized liquid such as Freon
is solved. Additionally, the problem of controlling the Freon flow
and charge in each time period is solved without dependence upon
the particular type of system which existed initially and was
retrofitted.
[0029] The air conditioning system of the invention includes a
compressor for compressing a refrigerant, the refrigerant being a
compressible phase change fluid and a condensing unit operatively
connected to the compressor. An evaporator unit and an associated
expansion means are operatively interconnected to the condensing
unit and to the compressor, the evaporator unit being in heat
exchange relationship with a supply air stream for an indoor space
inside a structure. The compressor is operable to circulate the
refrigerant between the condensing unit and the evaporator unit to
cool the supply air stream.
[0030] The air conditioning system of the invention is also
comprised of a thermal energy storage unit including a tank having
a thermal energy storage medium disposed therein and having an
associated heat exchanger. The heat exchanger is operably connected
to the compressor and evaporator. The thermal energy storage unit
may further including a temporary refrigerant storage tank.
[0031] A refrigerant circulating device is provided for circulating
refrigerant through the heat exchanger in the tank and between the
tank and the condenser and evaporator. Preferably, the refrigerant
circulating device includes a prime mover and an auxiliary liquid
which is acted upon by the prime mover, the auxiliary liquid being
coupled to the refrigerant, whereby force exerted by the prime
mover on the auxiliary liquid is indirectly transferred to the
refrigerant.
[0032] A valve system is also provided for controlling the flow of
refrigerant through the air conditioning system. The valve system
is operative to provide three distinct time periods of operation
for the system. A first time period allows refrigerant to flow from
the condenser to the heat exchanger of the thermal energy storage
unit to freeze the medium in the tank and to then return to the
condenser without utilizing the evaporator. The second time period
bypasses the condenser and circulates refrigerant through the
thermal storage unit and through the evaporator to thereby cool the
supply air inside the structure before returning to the thermal
storage unit. The third time period utilizes only the temporary
refrigerant storage vessel of the thermal storage unit and utilizes
the condenser and evaporator of the air conditioning system to cool
the supply air inside the structure as if the thermal storage unit
were not present.
[0033] In a particularly preferred system of the invention, the
prime mover is a positive displacement pump which communicates with
a pair of fluid cylinders containing oil as an auxiliary fluid. The
prime mover exerts a motive power upon pistons located within the
fluid cylinders to thereby mechanically couple the motive power of
the prime mover to the refrigerant being circulated in the system.
The auxiliary liquid chosen, whether oil or another liquid, has a
higher relative viscosity and a lower relative vapor pressure than
the conventional Freon refrigerant. The preferred prime mover of
the invention can be powered by a direct current motor and
battery.
[0034] Additional objects, features and advantages will be apparent
in the written description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a simplified schematic diagram representing the
working of a gear type, positive displacement pump.
[0036] FIG. 2 is a simplified schematic diagram which illustrates
the problem of pumping liquid refrigerant in an air conditioning
system of the type under consideration.
[0037] FIG. 3 is a simplified schematic diagram of a conventional
air conditioning system illustrating the inside and outside
components thereof.
[0038] FIG. 4 is a simplified schematic, similar to FIG. 3, of
another conventional type air conditioning system.
[0039] FIG. 5 is a simplified schematic diagram of a pump unit used
in the method of the invention.
[0040] FIG. 6 is another embodiment of the pump unit which is used
in the method of the invention.
[0041] FIG. 7 is a simplified schematic diagram of one embodiment
of the device and method of the invention.
[0042] FIG. 8 is a simplified diagram, similar to FIG. 7, showing
another embodiment of the device and method of the invention.
[0043] FIG. 9 is a simplified diagram, similar to FIG. 8, showing
the system of the invention installed within the inside and outside
equipment of a conventional air conditioning system.
DETAILED DESCRIPTION OF THE INVENTION
[0044] The improvements represented by the present invention can
perhaps best be understood if two of the principal problems to be
overcome in the third type of thermal energy storage system
described above are first explained. These problems relate to (1)
the nature of the Freon refrigerant being pumped; and (2) flow
control problems related to pumping the Freon refrigerant. These
problems will be discussed in turn.
[0045] Problems with Pumping Freon:
[0046] Turning first to FIG. 2, the problems associated with
pumping condensed Freon are illustrated in schematic fashion. Coil
11 in FIG. 2 is intended to represent a coil located within an ice
tank and coil 14 is the conventional evaporative coil located
inside the structure to be cooled. Because the coils 11 and 14
communicate through top conduit 13, they are both at the same
approximate pressure. If the condensing coil 11 is made much larger
than the evaporative coil 14, the pressure of the two would be
controlled by the ice tank condensing coil and would be the
condensing pressure at the temperature of the Freon in the ice
tank. However, if the evaporative coil was made much larger than
the condensing coil, the pressure of the two would be controlled by
the evaporative coil and would be the evaporative pressure at the
evaporative Freon temperature. In reality, this pressure is
somewhere in between the two depending upon such factors as the
flow rate and temperature of the air across the evaporative coil,
the size of the two coils, and the heat transfer rate from the
condensing coil into the ice tank.
[0047] After the system reaches equilibrium, the Freon in the
condensing coil 11 is at saturation with some but not all of the
Freon in the liquid form. If the pump 12 and the expansion device
15 were eliminated and if pressure drops associated with line
friction were eliminated as well as any elevation differences, a
natural circulation would develop in the system. In reality this
doesn't occur because of pressure drops and elevation differences.
In a well designed system, designed for this type of operation, it
is possible to pump the liquid because there is very little
pressure drop and the elevation differences can be minimized. In
such a situation, the pump is merely required to develop enough of
a pressure differential to overcome these relatively small
resistances. It is evident from the above discussion that any
reduction in pressure at the suction of the pump would result in
the flashing of the liquid Freon to the gaseous state. This type of
flashing results in a reduction of pump capacity and a new
equilibrium results with the new and slower circulation rate.
[0048] No matter which type of pump is selected, it will tend to
have a reduced pressure zone at the pump suction. This pressure
reduction zone can be controlled somewhat by slower pump speeds,
proper piping configuration, etc. but cannot be eliminated
entirely. A sufficient column of liquid above the pump can overcome
this low-pressure zone. Columns of this type, commonly referred to
as a "suction head" must produce enough additional pressure at the
suction of the pump from the hydrostatic forces produced by gravity
to overcome the low-pressure zone for proper pumping operation. A
suction head of this type does exist in the ice tank but is
constantly changing because of the constantly changing load on the
evaporative coil resulting in changing pressures on the condensing
coil. The amount of liquid in the condensing coil changes
constantly because of the constant change in load on the
evaporative coil. As a result, this type of hydrostatic head is
unreliable and can't be counted upon to be consistently stable.
[0049] A further complication to the system is the viscosity of the
liquid Freon. At the condensing pressure and temperature, the Freon
viscosity is only about 15% that of water. Any increased
backpressure on the pump discharge results in slippage of the
liquid back through the pump from the discharge to the suction.
This slippage greatly affects the capacity of the pump and causes
eddy currents in the fluid. These eddy currents cause additional
low pressure zones that cause additional flashing of the liquid to
its gaseous state. Traditionally, designers have utilized increased
speed of the pump, tighter clearances of the internal pump parts,
and special designs of the pump to control this slippage. However,
these attempted solutions cause the pump price to increase
dramatically and the problems are not eliminated but merely
reduced. The low viscosity also affects the required seal design of
the pump. Generally speaking, a sealless pump design is preferred
in order to avoid problems, such as a magnetically driven pump. The
requirement of a magnetically driven pump also increases the cost
of the installation, however.
[0050] When the expansion valve is considered on the discharge of
the pump, a back pressure of over 100 psi is induced. This back
pressure is considerately higher than any pressure drops associated
with line sizes or with respect to the pressure considered with
elevation changes. Slippage and low pressure zones increase
dramatically, resulting in system failure. In order to insure
system integrity, a pump design must be provided which effectively
prevents any slippage.
[0051] At the condensing temperature in the ice tank, the viscosity
of the liquid Freon is only about 15% that of water at the same
temperature (0.553 lb/ft-h compared to 3.690 lb/ft-h). This
extremely low viscosity causes a variety of pump problems,
especially when trying to pump the liquid to significantly higher
pressures. These problems include extreme slippage and the need for
expensive shaft seal designs negatively affecting the pumping
efficiency and pump cost.
[0052] These problems can easily visualized by referring to FIG. 1
of the drawings. Because of the need to develop a significant
pressure differential across the pump, a positive displacement pump
is preferred. In FIG. 1, a gear pump is shown, although the same
problems will apply to any pump, whether or not the pump is a
positive displacement pump. The particular pump illustrated in FIG.
1 has a housing 21 that contains a chamber that has a driven gear
25, driven by a shaft 26, through a seal and bearing (not shown).
This driven gear 25 meshes and turns a mating idler gear 22 that
rotates on a shaft 10 resting in a bearing 23. In the drawing, the
driven gear 25 is rotated clockwise and the idle gear 22 is rotated
counter clockwise. With this rotational direction, a low-pressure
zone is developed at an intake zone 18. The liquid the is forced to
flow around the gears (clockwise around the driven gear 25 and
counterclockwise around the idler gear 22).
[0053] If the viscosity of the liquid is high enough, and if the
clearance between the gears and the housing is small enough, a
large volume of liquid is transferred from the low pressure zone 18
to the opposite side of the housing 21 to a discharge zone 20
causing an increase of pressure in zone 20 relative to zone 18. The
liquid in the high pressure discharge zone 20 is retarded from
flowing between the gears 22 and 25 to the low pressure zone 18
because of the meshing of the gears. If the mesh is tight enough
and the viscosity is high enough, very little leakage occurs. A
tight clearance between the gear faces and the housing will retard
flow from the high-pressure zone to the low-pressure zone if the
viscosity is high enough. The low-pressure zone 18 is connected to
the outside of the housing to serve as the "suction" of the pump
through the inlet chamber 24. The high-pressure zone 20 is
connected to the outside of the chamber with discharge chamber 27
serving as the pump "discharge".
[0054] Again with reference to FIG. 1, if the fluid being pumped
has a very low viscosity, an excess of liquid volume will tend to
flow from the high-pressure zone 20 to the low pressure zone 18.
This reverse flow of fluid is known as "slippage". Slippage
requires that additional speed be employed to turn the gears 22, 25
in order to maintain the desired volume flow rate needed to develop
a given pressure differential. Lower viscosity fluids being pumped,
higher pressure differentials and greater clearances between the
gears all increase slippage. Another problem arises due to the
natural lubrication properties of the fluid being pumped since the
fluid being pumped normally provides lubrication for operation of
the pump. A low viscosity liquid "washes" any lubrication
properties of the liquid away from the rotating gear surfaces. This
action results in accelerated wear of the bearings and seals
utilized in the pump mechanism.
[0055] The lowest system pressure of the liquid being pumped occurs
at the low-pressure zone 18. If the system pressure was lower
anywhere else in the system, the liquid would flow to that zone
instead of flowing to the pump suction. If this low-pressure zone
falls below the liquid's vapor pressure at operating temperature,
vaporization of the liquid will occur. This transformation of the
liquid to its vapor state is known as "cavitation" and greatly
reduces the volume flow rate of the pump. Experience teaches that
cavitation causes excessive pump wear, increases the power needed
to achieve volume flow required volume flow rates, as well as
producing unpleasant noises.
[0056] It can easily be shown that the presence of low viscosity
fluids coupled with poor lubrication of the pump gears results in
increased leakage around the drive shaft seal. When pumping a
liquid that is destructive to the environment leakage of this seal
is unacceptable. Because of the low viscosity and lubrication
properties of water, this type of pump has been found to be unfit
for use with water in most circumstances, resulting in increased
power use and premature mechanical failure. Trying to pump a liquid
with a viscosity much lower than water predictably results in
system failure.
[0057] Problems Associated with Flow Control of the Freon
Refrigerant:
[0058] Another problem associated with the third type of thermal
energy storage system described above can be seen with reference to
FIG. 3 of the drawings. FIG. 3 is a simplified schematic which is
intended to represent a basic refrigeration system of the type
found in most presently existing residential and small commercial
building structures. The particular structure to be cooled is
indicated generally as 31. Inside structure 31 is a coil type
evaporator, referred to as 32. Evaporator coil 32 is usually made
up of several coils that operate in parallel, as illustrated in the
drawing. Freon flow entering the evaporator coil 32 is split into
equal flows through each of the parallel coils in order to achieve
proper heat exchange efficiency. An air blower 34 is provided to
move internal structure supply source air across the evaporator
coil 32 with heat from the moving air being transferred to the
Freon in the coils 32.
[0059] A large diameter conduit 35 carries heat laden Freon vapor
through the structure wall and outside to the condensing unit 36.
The condensing unit 36 consists of a compressor 37 that compresses
the Freon vapor to an elevated pressure, a condensing coil 38 that
allows the high pressure Freon vapor to change to a liquid state as
it loses heat, and an air blower 39 that moves outside air past the
condensing coil to carry the heat away from the Freon that was
gained inside the structure and was added during compression.
[0060] A small diameter conduit 30 carries the high-pressure liquid
Freon back through the structure wall to an expansion device 40.
The expansion device 40 used in most existing installations
consists of two essential components. The first is a metering
orifice 44 that has a fixed orifice size to restrict Freon flow.
The second essential component of the expansion device is the
presence of one very small tube 46 leading from the metering
orifice 44 to each coil in the evaporator unit. The purpose of
these small tubes is to split the Freon flow evenly into each coil
section. This system has proven to be the most economical system
that can be installed at the present time that also yields
dependable service. As a result it is the most common system in
use.
[0061] It should also be noted that the metering orifice 44 and the
small tubes 46 make up a performing unit which must meet the
capacity of the condensing unit with small changes being made by
changing the orifice size of the metering orifice 44. Although the
above described system offers cost advantages, there is a slow
equalization of the Freon pressure across the expansion device 40
when the compressor is not running. This pressure equalization is
sometimes referred to as "bleed over" and allows the compressor to
restart without a large load across it, thereby reducing the
compressor load on the compressor drive motor and allowing the use
of the smallest feasible motor.
[0062] A disadvantage of the above described existing system is the
critical need to have the proper amount of Freon in the system at
all times. The amount of Freon in the system, referred to in the
industry as the "charge", is critical down to the one-half ounce.
Overcharging or undercharging the system will greatly affect
operation. An overcharge causes a high head pressure because excess
liquid accumulates in the condenser. This accumulation will disable
that portion of the condenser coil, thereby increasing the load on
the remaining parts of the coil. This raises the temperature of the
Freon in the condenser coil and raises the condensing pressure. An
undercharge of Freon results in low head pressure because the
condenser is, in effect, oversized. Since not enough liquid is
being pushed through the expansion device and a low head pressure
causes low suction pressure. Vapor tends to bubble in the expansion
device because the bubbles further increase flow resistance.
[0063] A more expensive and thus less commonly used conventional
air conditioning system is illustrated in FIG. 4. In the system
shown in FIG. 4, a thermostatic expansion valve 54 is substituted
for the metering orifice of FIG. 3. This substitution eliminates
most of the problems associated with the requirements for a
critical Freon charge. The thermostatic expansion valve 54 opens
and closes depending upon the exiting evaporator Freon temperature.
A temperature-sensing bulb 51 mounted on the discharge line 55 of
the evaporator 50 controls the thermostatic expansion valve 54.
With the expansion valve 54 in place, a liquid storage tank or
"receiver" 52 can be used between the condensing unit 556 and the
expansion device 50. As a result of the presence of these
additional components, the Freon charge is not as critical as in
the system of FIG. 3.
[0064] Although the system of FIG. 4 is more expensive than the
system of FIG. 3, it is more versatile under changing load
conditions. One disadvantage of the system of FIG. 4 is that bleed
over cannot be used, as described with respect to FIG. 3, because
of the possibility of the suction line filling with liquid rather
than vapor due to the presence of excess Freon stored in the
receiver 52. Liquid of this type present in the compressor suction
could result in the destruction of the compressor since it cannot
compress liquids. Without bleed over, a larger start up load is
present on the compressor, resulting in more expense being required
in designing an acceptable compressor drive.
[0065] Because of the changes in the Freon system charge from one
time period to the next, all of the prior art systems described in
the background discussion above utilized the thermostatic expansion
valve 54 (FIG. 4) to replace the metering orifice (44 in FIG. 3).
Because of the need to make this and other replacements, the
addition of thermal storage to most residential and small
commercial systems requires equipment changes inside the building
structure as a part of the retrofit installation.
[0066] Because of the above described pumping problems, all the
prior art systems described in the background discussion except for
U.S. Pat. No. 5,682,752 (Dean) bypass the thermostatic expansion
valve during use of the energy storage tank. Although the '752 Dean
patent doesn't address the above described pumping problems, the
metering orifice is replaced with a thermostatic expansion valve
which is not bypassed. If this described method manages to pump the
liquid to the required pressure and volume flow rate, change to the
evaporative coil and change to the compressor drive limit the
method to new systems rather than a simple addition to an existing
system.
DESCRIPTION OF THE INVENTION
[0067] The thermal storage system of the invention can be added to
an existing Freon compression air-conditioning system such as is
commonly found in residential and small commercial structures.
These types of systems were described with respect to FIG. 3 above.
A single retrofit package totally simulates the operation of the
conventional condensing unit, using only energy that was previously
stored, without any change or alteration of the existing equipment.
The method and device of the invention create a new system that
stores energy in a first time period, uses this stored energy
during a second time period to cool the structure, and possesses
the capacity to be able to cool the structure in a third time
period without stored energy. Two distinct problems are solved to
accomplish these objectives of the invention as described in the
discussion which follows.
[0068] The Pumping Solution:
[0069] The device and method of the invention create a "second time
period" when the system uses stored energy to cool the associated
building structure. When the second time period arrives in the new
system, Freon that was condensed from the vapor state to the liquid
state is required to be pumped at a pressure that will be high
enough to simulate the running of the compressor in time period
three described above. With R-22 Freon (the normally used
refrigerant) this pressure has been defined to be above 200 psi by
the air conditioning industry. This pressure has been defined for
operation when the outside air temperature is too low to maintain
the condensing pressure required to maintain proper flow rates
through the expansion device. In the new system of the invention,
this pressure can be lower or higher but is used only as a guide
for purposes of the present discussion. The problems associated
with pumping liquid Freon have been described in some detail. The
characteristic properties of the liquid Freon, at the point in the
refrigeration cycle where pumping is required, are such that the
liquid Freon is difficult to reliably pump. Applicant has
discovered that the difficulties associated with pumping liquid
Freon at this point in the refrigeration cycle can be overcome by
pumping an auxiliary liquid that has the proper properties for pump
operation and by then mechanically coupling or transferring the
pressure and flow rate of the pumped auxiliary liquid to the liquid
Freon.
[0070] The auxiliary liquid which is selected will have a much
higher viscosity than the conventional liquid Freon present in the
system. The auxiliary liquid will also have a lower vaporization
pressure than the liquid Freon, will have the required lubrication
properties, and will not be dangerous to the environment should it
leak around the drive shaft of the pump. Several liquids have such
properties and can be used with conventional lubricating oil being
one example for purposes of the present discussion. Pumping such an
auxiliary liquid results in less energy use because of reduced
slippage in the pump, increased longevity of the pump because of
its lubrication properties and reduced cavitation.
[0071] The mechanical transfer or coupling of the pump pressure and
volume flow rate from the pumped auxiliary liquid to the liquid
Freon can be accomplished by several methods. The preferred methods
discussed below are intended to be illustrative of the principles
of the invention without being limiting.
[0072] FIG. 5 is a simplified schematic of one pumping system which
can be used in the practice of the invention. In the device and
system of FIG. 5, two cylinders 59, 63 each contain a piston 64,
65. The lower face 61, 62 of each piston 64, 65 is coupled a port
of a pump 67 by means of a conduit 66, 68, respectively. The
pumpable auxiliary liquid is contained in each cylinder below the
pistons in a chamber, such as chamber 70, in the pump conduits 66,
68, and in the pump 67. Dynamic seals on the pistons 64, 65 contain
the pumpable auxiliary liquid as the pistons move up and down. The
upper or top faces 72, 73 of the pistons 64, 65 in the cylinders
are exposed to chambers 66, 67 and communicate with check valve
arrangements 69, 70 that allow low pressure Freon in the pump
system entrance conduit 71 to enter the cylinder when the piston is
moving down and at the same time prevent high pressure Freon from
entering the cylinder. When the piston is moving up, the valve
arrangements reverse causing the low pressure Freon entrance 71 to
be blocked. and the exiting high pressure Freon to flow to the pump
system exit conduit 75. The valve arrangements are shown using
check valves that allow flow in one direction only. Other valves
could be used including individual electrical or pneumatically
operated valves, four way valves, shuttle valves, etc.
[0073] Because the effective area of the top surface 72, 73 of each
piston is the same as the bottom surface 61, 62, the pressure of
the liquid above the piston is the same as the liquid below the
piston with the exception of any drag that is associated with the
dynamic movement of the piston seals (which is small with proper
design). Because the exposed piston area are effectively identical,
a change in liquid volume below the piston causes the piston to
move creating an equal change in volume above the piston. By the
same reasoning, if pistons are selected such that the pistons in
each cylinder have different effective areas, the pumped pressure
will be different than the Freon pressure and a different volume
change will result. This might be considered an advantage in some
circumstances of pump design. Also, while a gear pump 67 is
illustrated, any of a variety of pump designs could be utilized, as
will be appreciated by those skilled in the relevant arts.
[0074] In the particular embodiment of the pump illustrated in FIG.
5, with the pump turning in the direction shown, the left piston 65
is traveling up while the right piston 64 is traveling down. As a
result of the described pump direction and the resulting piston
movement, low-pressure Freon is entering the top of the right
cylinder chamber 66 and the high-pressure Freon is exiting the left
cylinder chamber 70. In this illustration, the pump 67 reverses
direction when the piston 64 in the right cylinder 66 approaches
the bottom of the cylinder chamber 66. The location of piston 64
could conveniently be sensed by a transducer (not shown) that
senses the piston location and which operates magnetically,
optically, or mechanically, or by sensing the pressure of the
pumpable liquid between the piston and the pump. When the pump
reverses its rotation, the direction of the piston movement
reverses causing low-pressure Freon to enter the left cylinder and
high-pressure Freon to exit the right cylinder. By selecting the
proper design criteria, the volume of the pumpable liquid in the
two cylinders, the pump, and pump lines can be designed such that
when one piston is at the bottom of its stroke, the piston in the
other respective cylinder would be at the top of its stroke. Pump
capacity will be determined by selecting the diameter and the
length of the cylinders, the speed of each piston in its movement
within the respective cylinders, and the duration of each pump
rotation.
[0075] By purposely providing slow and long relative piston
movement and stroke, any low-pressure Freon in its vapor state can
enter the cylinders 59, 63 without causing harm since it would
quickly change to its liquid state with increasing pressure.
Instead of a single pump being used, a pump for each cylinder with
a volume tank could also be used. This type pumping system has been
used by Applicant on a three-ton air conditioning system with the
pump consuming less than 1/2 horsepower with a cycle time of about
40 seconds. Experiments have shown that the pump consumes 1/2
horsepower when it attempts to pump liquid Freon to the same
pressure and same volume flow rate. The greatly reduced power
consumption is due to the slippage and cavitation problems
described above.
[0076] The reduced power consumption which is achieved in the above
example is important for purposes of the invention because it
allows, for example, a battery (150 in FIG. 8) to be used as a
power source for the pump rather than a conventional AC power
outlet. A wet cell battery, for example, represents a much smaller
capacity and much less recharging energy, allowing it to be
recharged by solar panels, or the like. Because of the lubrication
properties of the pumped liquid and the absence of cavitation, the
life of the pump of the invention, as well as the pumping cost, are
greatly reduced.
[0077] FIG. 6 is another embodiment of the pump which can be used
in the practice of the invention to achieve the necessary energy
transfer. In the embodiment of FIG. 6, inflatable bladders 82, 84
are substituted in each of the cylinders 86, 88 in place of the
pistons described in FIG. 5. Each bladder 82, 84 separates the
pumpable auxiliary liquid from the Freon while maintaining equal
pressure on either side of the Freon. This system works essentially
the same as the piston method with the advantage of the elimination
of piston drag. Likewise, a number of component substitutions can
be visualized, as described with respect to FIG. 5.
[0078] While the invention has been described with respect to the
two embodiments of the pump illustrated in FIGS. 5 and 6, it is not
intended to be thus limited and a number of additional embodiments
utilizing the principles of the invention can easily be visualized.
For example, another example of pumping energy transfer could be
achieved by utilizing an auxiliary liquid which is non-mixable with
Freon. Such a non-mixable but otherwise compatible liquid could
conceivably be used without the further requirement of pistons or
bladders to separate the auxiliary liquid from the Freon.
[0079] Another example of pumping energy transfer could be achieved
by using one pump and one cylinder in conjunction with a surge
chamber providing pressure and volume to the high-pressure Freon
side of the system while the pump and pump and cylinder were taking
in low pressure Freon.
[0080] Another example of pumping energy transfer is illustrated in
FIG. 7 in which the pumping energy transfer system is insulated to
prevent additional vaporization of the liquid Freon as a result of
the Freon gaining heat. In the system illustrated in FIG. 7, the
energy transfer cylinders 92, 94 are located within, or at least
partly within, the energy storage tank 96.
[0081] The Freon Flow Control Solution:
[0082] The control of the flow of Freon through the three time
frames described above is a critical component of the successful
working of the method and device of the invention. In the first
time frame, the condensing unit is running and freezing the liquid
in the energy storage tank. In the second time frame, the
condensing unit is not running and cooling inside the structure is
being provided by the operation of the newly added thermal energy
storage unit. In a third time frame, the condensing unit is running
to cool the structure as if the new thermal energy storage unit
were not present. For the energy storage unit to be added to an
existing unit without any change to the existing unit, the added
unit must allow the operation of all three described time frame
operations in transparent fashion. For this type transparent
operation to be achieved, it is necessary that no liquid Freon be
allowed to accumulate in the condensing coil of the condensing unit
as a result of excess Freon in the system. Any accumulation of
liquid Freon in the condensing coil would result in an elevated
head pressure as has previously been described.
[0083] Another important feature for the proper operation of the
system of the invention is to preserve the previously described
bleed over advantage offered by the metering orifice expansion
device. This advantage should be preserved in order to avoid the
possibility of loading the evaporator coil with liquid Freon. Such
loading could very likely cause damage to the compressor upon start
up. The control of the Freon flow in the system to achieve these
goals is described by viewing FIG. 8.
[0084] FIG. 8 shows a thermal energy storage system of the
invention which can be added to an existing Freon compression
air-conditioning system without any major change to the existing
system. The system of the invention illustrated in FIG. 8 includes
an insulated storage tank 132 that houses an energy storage coil
134. The system further includes a liquid Freon pump system 67 as
described with respect to FIG. 5. The pump system 67 is powered by
a battery 150 that is recharged during time period one operations.
The system also includes a Freon liquid storage device or
"receiver" 143 of the type commonly used in the air-conditioning
industry, as well as volume tank called an expansion tank 144. Also
shown is an expansion device 135 for the energy storage coil as
well as a heat exchanger 136. Seven electrically operated control
valves (illustrated as 133, 137, 138, 139, 140, 142 and 145 in FIG.
8) are utilized. The unit is installed on the existing air
conditioning system by attaching line 148 to the large suction line
present in the existing system. The small liquid line of the
existing system is interrupted and attached to lines 146 and 147 of
the energy storage unit with line 146 being attached to the section
that leads to the condensing unit and line 147 being attached to
the section going inside the structure to the existing expansion
device.
[0085] The operation of the thermal energy storage system of FIG. 8
will now be described. The receiver 143 is a pressure-containing
vessel that has one opening 154 in the top thereof that receives
liquid Freon. A line 156 exits the top of the receiver 143 and also
extends in close proximity to the bottom surface 158 of the vessel
to allow exiting of the liquid Freon. Freon is taken from the
bottom of the vessel 143 in order to insure that liquid Freon
leaves the vessel, if the vessel contains any liquid. The expansion
tank 144 is a pressure containing vessel that simply provides
volume for expansion of any liquids that might "slug" into the
compression suction line. A conventional absorber has long had
common use in the industry and could be used.
[0086] The insulated storage tank 132 contains a liquid storage
medium that stores cooling energy. In the preferred case, this
medium is water. In the first time period heat is removed from the
liquid through the coil 134 housed within the tank 132. In most
cases heat is removed until the liquid changes state to its solid
form. If the liquid being utilized is fresh water, the heat removal
required for changing phase to ice would be 144 BTU per pound of
water after the liquid dropped to 32 degrees F. In the second time
period heat is added to the solid until it changes state back to a
liquid. This heat is added through the same coil 134 that extracted
the heat in the first time period. Each pound of ice would
theoretically absorb 144 BTU of heat before changing phase back to
water. The heat exchanger 136 simply pre-cools the warm liquid
Freon going to the expansion device 135 with cool Freon vapor
leaving the coil before it returns to the compressor. The expansion
device could be of various types, but a thermal expansion valve as
described above would provide the best service. The control valves
are either in the open or closed position depending upon the
control signal going to the valve.
[0087] Time Period One
[0088] With valves 137, 140, 142 and 145 in their open position and
the remaining valves closed, the unit would be in the energy
storage mode. Liquid Freon under pressure would be entering the
unit through line 146 from the condensing unit, passing through
valve 145. The liquid would enter the receiver 143 and exit as a
liquid. The liquid would then travel through valves 142 and 140
through the heat exchanger 136 to the expansion device. Flow
through the expansion device would result in a much lower pressure
upon passage through the device. The Freon would change states to
its vapor state as it passes through the low-pressure area and
would simultaneously extract heat from the liquid surrounding the
coil 134. The vaporized Freon would travel through the heat
exchanger 136, valve 137, and then exit the unit through line 148.
The line 148 returns the Freon to the condensing unit where it is
compressed to a hot high pressure vapor and then condensed to a
high pressure liquid in the condensing coil. This process would
continue for the duration of time period one or until all the
liquid in the storage tank changed to its solid state, at which
time the condensing unit would stop running. More Freon is in the
system than is required for this mode of operation and collects in
the receiver. The pump battery 150 is fully charged during this
time period.
[0089] Time Period Two
[0090] This time period requires the structure to be cooled with
energy that was stored during time period one. As will be
explained, this requires utilization of all of the Freon contained
in the system. This mode is operated with valves 133, 137 and 139
in the open position. The pump system is in operation as described
above. All the liquid Freon in the receiver 143 leaves the high
pressure warm receiver through valve 133 to the suction of the
pumping system at a faster rate than it can be pumped. The excess
flow goes into the energy storage coil 134 where it provides the
required net positive suction head for the pumping system. After a
sufficient time for the receiver 143 to empty, valve 133 closes.
The pumping system pumps the liquid to a pressure and flow rate to
simulate the running of the condensing unit. The liquid leaves the
pump system 67 and passes through valve 139 and leaves the unit
through line 147. The liquid then travels inside the structure to
the expansion device 135 with the same flow rate and pressure as it
would have as if the compressor were running.
[0091] The Freon then vaporizes in the evaporator coils 134 gaining
heat from the structure. It then travels through the existing line
through the structure and then into line 148 where it passes
through valve 137 into coil 134. When the Freon enters the coil 134
submerged in the cool liquid, it condenses to its liquid state and
passes the heat gained inside the structure to the cool liquid.
After the Freon condenses to its liquid state, it enters the
suction of the pumping system. As long as the pump system is
running and the liquid in the energy storage coil condenses the
Freon to its liquid state, the second time period exists. The
pumping system is turned on and off in the same manner as the
compressor would be turned on and off if it were in operation. This
action controls the temperature of the air inside the structure the
same as if the compressor were active. All of the Freon is in
circulation in this time period. At the end of this time period or
in the event the energy storage properties of the liquid in the
energy storage tank is depleted, the bulk of the Freon is
transferred back into the receiver.
[0092] This last action is accomplished by an industry standard
method called a "pump down" cycle in which all of the valves except
valves 137 and 145 are closed and the condensing unit is turned on.
Freon is pulled into the compressor as a vapor and compressed. The
compressed Freon flows into the receiver 143 where pressure is
increased until it liquefies. Any liquid that might flow into line
148 during the pump down cycle falls into the expansion tank 144
where it expands to its vapor state, thus protecting the
compressor. This continues until the pressure inside the energy
storage coil decreases to a preset level (that corresponds to a
temperature much lower than it would be if the storage liquid were
in its solid state). A pressure switch (not shown) senses this
pressure. When the pressure is decreased to the preset level, the
compressor is turned off and valves 137 and 145 are closed.
[0093] Third Time Period
[0094] This time period requires the condensing unit to run and
transfer heat from the structure to the outside as if the energy
storage unit were not present. Time period three operations occur
if cooling is required inside the structure during the first time
period or if the energy storage properties are depleted during time
period two. This is accomplished by the compressor coming on as
normal and valves 139, 142 and 145 being in the open position with
the remaining valves being closed. The liquid Freon from the
condensing unit flows into the new system through line 146, through
valve 145, and into and out of the receiver 143. Liquid Freon then
flows through valves 142 and 139 to the inside of the structure to
the expansion device. Then vaporizing Freon in the evaporator coils
gains heat and then travels to the compressor suction where it is
compressed and then condensed to a liquid in the condensing coil.
The Freon then flows back to line 146. This is the same path with
the same pressures and flow rates that the Freon would be taking
and would encounter if the new energy storage device were not
present with the exception of flowing through the receiver.
[0095] The purpose of receiver 143 in this time period is the
prevention of the excess Freon in the system from collecting in the
condenser coil where it would cause increased head pressure. Excess
Freon is accumulated in the condenser without affecting the
operation of the system. When the compressor goes off because the
air becomes cooled inside the structure bleed over would normally
occur as described above. This is achieved by the opening of valve
138 in conjunction with closing of valves 139, 142 and 145. When
these valves shift, the suction and discharge of the compressor is
equalized and is restarted with the same ease as before the energy
storage device was installed. These valves stay in this position
until the compressor comes back on, at which point they return to
normal third period operation.
[0096] FIG. 9 illustrates the unit described in FIG. 8 but with the
unit installed in the existing system as described in FIG. 3. It
should also be noted that, if the existing system were the more
expensive system containing a thermal controlled expansion valve
and a compressor not requiring bleed over, the thermal energy
system of the invention could be utilized in that type system as
well with similar results.
[0097] An invention has been provided with several advantages. The
thermal energy storage system of the invention can easily be added
to an existing Freon compression air-conditioning system commonly
used in residential and small commercial applications. The system
of the invention is also easily incorporated into new construction
with relatively little additional expense. The method and device of
the invention allow the addition of a single "package" to a new or
existing air conditioning system that totally simulates the
operation of the conventional condensing unit. The system of the
invention uses only energy that was previously stored by the system
and does not require any change or alteration of existing equipment
inside the structure. The add-on package of the invention creates a
new system that stores energy in a first time period, utilizes this
stored energy during a second time period to cool the structure,
and possesses the capacity to be able to cool the structure in a
third time period without utilizing stored energy.
[0098] In addition to providing an add-on package which can be
easily installed outside the structure, two distinct problems are
solved by the improved system of the invention. The problem of
pumping a low viscosity and easily vaporized liquid such as Freon
is solved. Additionally, the problem of controlling the Freon flow
and charge in each time period is solved without dependence upon
the particular type of system which existed initially and was
retrofitted.
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