U.S. patent number 3,653,221 [Application Number 05/055,686] was granted by the patent office on 1972-04-04 for latent storage air-conditioning system.
Invention is credited to Frank M. Angus.
United States Patent |
3,653,221 |
Angus |
April 4, 1972 |
LATENT STORAGE AIR-CONDITIONING SYSTEM
Abstract
An air-conditioning system for structures with widely
fluctuating loads includes a water storage and ice builder tank
from which chilled water is circulated to the room cooling units
located throughout the structure. Ice is produced in the storage
tank through a direct expansion refrigeration system using freon
R-12 as a refrigerant and including a compressor, a condenser, and
evaporator coils located within the storage tank. Individually
controlled evaporator coils are placed in serially connected
chambers within the storage tank through which the water flows, and
controls are provided for making the system completely automatic in
operation.
Inventors: |
Angus; Frank M. (Dallas,
TX) |
Family
ID: |
21999518 |
Appl.
No.: |
05/055,686 |
Filed: |
July 17, 1970 |
Current U.S.
Class: |
62/59; 62/139;
62/223 |
Current CPC
Class: |
F25D
17/02 (20130101); F25B 5/00 (20130101); F25B
49/02 (20130101); F24F 5/0017 (20130101); F25D
16/00 (20130101); Y02E 60/14 (20130101); Y02E
60/147 (20130101) |
Current International
Class: |
F24F
5/00 (20060101); F25D 17/00 (20060101); F25B
5/00 (20060101); F25D 17/02 (20060101); F25B
49/02 (20060101); F25D 16/00 (20060101); F25d
017/02 () |
Field of
Search: |
;62/201,223,225,59,131,139 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wayner; William E.
Claims
What is claimed is:
1. In a latent storage air-conditioning system including:
an ice building storage tank; and a refrigeration system including
a plurality of refrigerant evaporators in said tank, a compressor,
a condenser, and control means for the compressor responsive to the
compressor inlet pressure; the improvement comprising
a plurality of ice building chambers disposed in said tank for the
series flow of cooling liquid therethrough; an evaporator in each
tank chamber disposed to form an ice bank therein surrounding the
evaporator;
an expansion valve for each evaporator for expanding liquid
refrigerant therein; and the means associated with each expansion
valve responsive to a predetermined temperature rise through said
evaporator for controlling said expansion valve;
a control valve in the refrigerant supply line for selectively
controlling the flow of liquid refrigerant to the several
evaporator expansion valves;
and temperature responsive means mounted contiguous to one
evaporator coil, disposed in a tank chamber between the inlet and
outlet tank chambers; said temperature responsive means being
responsive to the temperature of the ice or water immediately
adjacent to said coil and to the temperature of refrigerant within
the coil, to selectively open and close said refrigerant control
valve.
2. An air-conditioning system as set forth in claim 1
including at least one fan means for flowing cooling air across
said condenser; and the means responsive to a predetermined high
pressure at the compressor inlet for shutting off one or more of
said fan means to reduce the flow of air over said condenser.
3. An air-conditioning system as set forth in claim 1
including a second temperature responsive means mounted contiguous
to one evaporator coil, disposed in a tank chamber between the
inlet and outlet tank chambers; said second temperature responsive
means being responsive to the temperature of the ice or water
immediately adjacent to its respective coil and to the temperature
of refrigerant within the coil, to selectively open and close the
refrigerant control valve; said first named and said second
temperature responsive means being responsive to different
preselected temperatures;
third temperature responsive means responsive to atmospheric
temperature; and control means operated by said third temperature
responsive means for alternatively connecting said first named and
said second temperature responsive means to operate said
refrigerant control valve.
4. An air-conditioning system as set forth in claim 1
wherein each of said expansion valves is a thermal expansion valve
having a temperature responsive power element; and wherein said
expansion valve temperature responsive means includes a temperature
sensing bulb mounted contiguous to its respective evaporator coil
adjacent to the suction end thereof.
5. An air-conditioning system as set forth in claim 1
a second control valve for selectively controlling the flow of
liquid refrigerant to a sub-group of expansion valves, less than
the total number of expansion valves, whereby refrigerant is
expanded through only a portion of the evaporator coils;
and pressure responsive control means, responsive to a
predetermined high suction pressure for closing said second control
valve, and responsive to a predetermined lower suction pressure for
reopening said second control valve.
6. In a method for cooling a building structure where cooling loads
fluctuate widely, including the steps:
providing a plurality of local cooling units in said structure;
providing a chilled water storage tank; circulating chilled water
between said tank and the several local cooling units in response
to demand from the respective local units; providing a
refrigeration system including a plurality of refrigerant
evaporators in said tank, a compressor, and a condenser for
building ice in said tank; and controlling the normal operation of
the refrigeration system compressor in response to the compressor
inlet pressure;
the improvement comprising:
providing a plurality of individual evaporator coils in said
storage tank;
placing said evaporators in serially connected flow chambers within
said storage tank;
providing a separate expansion valve for each of said evaporator
coils; controlling each expansion valve in response to the
temperature rise of the refrigerant flowing through its respective
evaporator coil;
and controlling the flow of refrigerant to the several evaporator
expansion valves in response to a control temperature which is a
function of the medium immediately surrounding one evaporator coil
in an intermediate one of said serially connected flow chambers and
of the suction pressure of said one evaporator coil.
7. The method set forth in claim 6, including the steps:
providing a first temperature responsive control for controlling
the flow of refrigerant to said expansion valves responsive to a
first predetermined control temperature spread at an evaporator
coil;
providing a second temperature responsive control for controlling
the flow of refrigerant to said expansion valves responsive to a
second predetermined control temperature spread at an evaporator
coil;
connecting said first and second temperature responsive controls
alternatively to a flow control valve actuated through an
alternating relay;
and controlling the condition of said alternating relay in response
to the temperature of the ambient atmosphere.
8. The method set forth in claim 6, including the steps:
shutting off the flow of refrigerant to a portion of said
evaporator coils in response to a predetermined pressure at the
compressor inlet which is above the normal inlet pressure range for
the compressor.
9. The method set forth in claim 6, including the steps:
flowing the refrigerant through a heat exhanger placed within the
water circulating in said storage tank prior to delivery to said
expansion valves.
10. The method set forth in claim 6, including the steps:
providing an air-cooled condenser;
providing at least one forced air means for effecting the flow of
air through said condenser;
and rendering inoperative at least one of said forced air means in
response to a predetermined compressor discharge pressure which is
below the normal discharge pressure range for the compressor.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to the air-conditioning of structures or
enclosures where loads fluctuate widely with infrequent peaks, and
more particularly to such a system controlled for automatic
operation where there is no engineer in charge.
Latent storage cooling systems are presently used in a number of
commercial applications where process cooling water is required.
These applications include the cooling of: concrete mixes, where
some specifications call for 35.degree. water; starch mixtures; ice
cream mix; pasteurized milk products; resin solutions; wax
emulsions; syrups; bread dough and mixer jackets; cooking oils;
dyes; eggs; raw potatoes, and similar products where quick cooling
vastly improves the product; beer; wort; and soft drinks. In these
and other commercial applications where the cooling system is
operated 8 hours daily for 5 days a week, this represents only a 24
percent load factor (based upon total KWH used per month compared
to the total KW demand multiplied by the number of hours in a
month).
In the air-conditioning of building structures or building
complexes such as churches, auditoriums, funeral homes, lodges,
assembly halls and other type structures where a large group of
people may assemble for relatively short and infrequent periods of
time, and when little or no air-conditioning is required for
intervening periods of time, a properly designed latent storage
air-conditioning system may often operate at approximately one-half
the electric power cost as that of a conventional air-conditioning
system.
Typical church operations with conventional air-conditioning
systems often operate on a load factor as low as 15 percent.
Obviously, if commercial plants can beneficially use latent storage
systems with a 24 percent load factor, a church installation with
only a 15 percent load factor is in a far better position to obtain
economic benefits from the installation of a latent storage
air-conditioning system.
Latent storage or ice bank systems are known to be economic systems
particularly for the high peak-intermittent load type applications
of which a church operation is a typical example. In a typical
latent storage air-conditioning system, a bank of ice is built up
in a storage tank, is melted off by the flow of circulating water
during the periods of cooling load, and is again built up during
periods of little or no cooling load. In such a system, the
capacity of the compressor-condenser refrigeration unit may be only
one-fifth or one-sixth of the size which might be required for a
conventional chilled water system or a direct expansion system of
equal cooling capacity. It is this factor primarily which results
in a much higher load factor in a church operation for a latent
storage system as compared with a conventional air-conditioning
system. For example, for a church operation with a conventional
system that operates on a 15 percent load factor, a conversion to a
latent storage system may result in a 38 percent load factor.
Compared in another way, the church may be cooled with a
conventional system at a cost of 3.75.cent. per KWH per ton of
air-conditioning, while the cost with a latent storage system may
be reduced to 1.82.cent. per KWH per ton of air-conditioning.
A difficulty with installations of this type is in maintaining
proper balance of the system under the varying load conditions. It
is particularly desirable that such systems be as completely
automatic as possible, particularly for nonindustrial applications
such as churches where the operation and regulation of the unit is
not under the control of an engineer. It is therefore desirable
that the system be provided with simple controls for substantially
complete automatic operation, that is be self-adjusting to the
fluctuating load demands and to the fluctuating ambient conditions,
and that it include safety shutdown features to prevent damage to
equipment under abnormal operation.
In some climates, such as in certain areas of Florida, Texas and
California, it is desirable that air-conditioning systems be
maintained operative throughout the year since even during the
winter months cooling may be desired or it may be desired to use
the system to reduce humidity. For such operation, it is again
desirable that suitable controls be provided for automatically
adapting the system for winter operation particularly where the
system is not under the control of an engineer.
A primary object of this invention is to provide an improved latent
storage air-conditioning system.
Another object of this invention is to provide an improved control
system for a latent storage air-conditioning system, which
maintains system balance for widely fluctuating cooling loads and
to provide an improved control system for a latent storage
air-conditioning system which adjusts to changes of the ambient
temperature conditions externally of the structure being
cooled.
A further object of this invention is to provide an improved
control system for a latent storage air-conditioning system which
is self-adjusting to overload conditions.
Still another object of this invention is to provide a latent
storage air-conditioning system with improved controls for
preventing freeze-up to the point of restricting or stopping water
flow even when the system is operated during the cooler months of
the year.
A still further object of this invention is to provide an efficient
self-regulating latent storage air-conditioning system for a high
peak-infrequent load church application, which may be operated at
approximately 50 percent of the cost of a comparable capacity
chilled water or direct expansion air-conditioning system.
Broadly, these objects are accomplished in apparatus according to
the invention which includes an ice building liquid storage tank
and a refrigeration system including a plurality of pipe-coil
refrigerant evaporators in the tank, a compressor, a condenser, and
control means for the compressor responsive to the compressor inlet
pressure. A plurality of ice building chambers are formed in the
tank with an evaporator in each tank chamber and each evaporator
includes an expansion valve, and control means associated with each
expansion valve responsive to the temperature rise through the
evaporator for regulating the refrigerant flow.
More particularly, apparatus according to the invention includes a
storage tank where the several ice building chambers are disposed
for serial flow of liquid through the chambers, and wherein a
control valve for supplying refrigerant to all of the expansion
valves is responsive to a control temperature at an evaporator
coil, which control temperature is a function of the temperature of
ice or water immediately surrounding the coil and the suction
pressure of the system.
The novel features of the invention, as well as additional objects
and the advantages thereof, will be understood more fully from the
following description when read in connection with the accompanying
drawings.
DRAWINGS
FIG. 1 is a diagrammatic view of the complete latent storage
air-conditioning system according to the invention.
FIG. 2 is a plan view, partially broken away and partially in
section, of the water storage and ice making tank and associated
components, and
FIG. 3 is a schematic diagram of the electric control circuit and
related components.
Referring particularly to FIG. 1 of the drawing, the
air-conditioning system for a building structure or building
complex includes local cooling or conditioning units 10, 11, 12 and
13 which would be located in respective rooms or spaces to be
cooled. The local cooling units are heat exchange units wherein the
conditioning liquid, chilled water in this case, is circulated
through coils in the units and the air in the room is circulated
over the coils by means of a suitable fan. The chilled water is
supplied to the cooling units from a central storage tank 14
through supply and return headers 15 and 16 respectively.
Where the same local conditioning units are used for the heating of
the rooms, the supply and return headers 15 and 16 may be connected
also to a source of warm water, such as the boiler 17 illustrated
diagrammatically in FIG. 1.
The water within the storage tank 14 is chilled by the formation of
ice banks, the ice bank being built up with a conventional
refrigeration system including evaporator coils, A1, A2, A3, B1, B2
and B3 positioned within the storage tank 14 and the compressor 19
and the condenser 20. The refrigeration system employs a suitable
refrigerant, such as freon R-12, for forming ice around the
evaporator coils. The water is caused to circulate within the
storage tank 14 to provide for the proper rate of heat transfer
between the ice banks formed on the coils and the circulating water
during the cooling period.
In the following description, all references to temperature are in
degrees Farenheit.
Now referring more particularly to the several components of the
above-described system, each of the local cooling units 10 through
13 may represent a plurality of such units disposed in a large
room, such as an auditorium, or in a plurality of rooms to be
cooled as a unit, with each plurality of units served by a common
circulating pump. Referring particularly to the local unit 10, for
example, this unit includes a housing 23 suitably mounted within
the enclosure space to be cooled, which houses a cooling coil
through which water is circulated through an inlet conduit 24 and
an outlet conduit 25, the inlet and outlet conduits being connected
respectively to the supply and return headers 15 and 16. An
electric motor driven fan 26 circulates the room air over the coils
for the desired conditioning. An electric motor driven pump 27
effects the flow of cooling water through the unit 10, and the
motors for the pump and fan are connected to a suitable source of
power through a switch 28 which may be a thermostatically
controlled switch responsive to the temperature within the
enclosure space being cooled.
Each of the cooling units 10 through 13 is similar in structure and
includes similar components and controls so that each enclosure
space is conditioned individually in response to its own
thermostatic control so long as an adequate supply of chilled (or
heated) water is available to the local units.
In the diagrammatic illustration of FIG. 1 each cooling unit
includes a single fan and a single pump and accordingly the fan and
pump motors are operated together through a common switch. As
mentioned above, a plurality of such cooling units usually is
supplied from a common pump to cool several "zones" and in this
event the several unit fan motors may be operated through
individual respective on-off switches each of which feeds back to a
holding coil to operate the associated pump. In this manner, when
any one unit is turned on, the pump is started; and when the last
unit is turned off, the pump is stopped. The temperature of each
zone is controlled by the conventional means available in water
circulation systems, such as: motor operated face and bypass
dampers; motor operated three-way mixing valves; and two-way
solenoid valves.
To illustrate the flexibility of this system for a church building
or complex for example: a first pump may be operating small room
consoles and offices and nurseries since they are often used daily;
a second pump may operate units in the church sanctuary, including
separate units in the balcony which is usually hotter, and separate
units in the choir loft so that choir practice may be held without
cooling the entire sanctuary; a third pump may be provided for a
chapel and fellowship hall for use for weddings and receptions, and
a fourth pump may be used to supply schoolrooms.
As shown in the drawings, the storage tank 14 is generally
rectangular in structure, including end walls 31 and 32 and side
walls 33 and 34, the end walls and side walls preferably being
fabricated of steel and being suitably insulated. The tank includes
internal vertical walls or partitions 35 and 36 which extend
parallel to the side walls and which divide the tank into six
side-by-side elongated chambers 37 through 42 progressing from the
side wall 33 toward the side wall 34. Three partitions 35 extend
from the inlet end wall 31 terminating short of the opposite end
wall 32 and two partitions 36 extend from the end wall 32 between
the partitions 35 terminating short of the inlet end wall 31,
whereby each pair of adjacent chambers are communicated at one end
of the tank. The chamber 37 adjacent to the side wall 33 is the
inlet or return chamber, and the chamber 42 adjacent to the side
wall 34 is the outlet or supply chamber. Tanks for typical
installations may include from four to 12 chambers.
A supply conduit 43, passing through the inlet end wall 31
communicates the supply chamber 42 with the liquid supply header
15, and a service valve 44 is provided in this conduit adjacent to
the tank. A service valve 45 is also provided at the opposite end
of the supply header 15 for selectively closing this header from
the boiler 17. A return conduit 46 passing through the inlet end
wall 31 communicates the return header 16 with the inlet chamber
37, and a service valve 47 is provided adjacent to the tank for
selectively closing this conduit. A service valve 48 is provided at
the opposite end of the return header 16 for selectively closing
communication with the boiler 17. When cooling water is circulating
through the above-described system, the water circulates from the
return header 16 serially through the tank chambers 37 through 42
to the supply header 15.
Referring now to the refrigeration system as illustrated
diagrammatically in FIG. 1, the compressor-condenser unit is
enclosed in a suitable housing 51. Due to high building costs, the
storage tank 14, the condenser unit which is commonly an air cooled
condensing unit, the compressor 19 and associated apparatus are
mounted outside a building enclosure for all weather operation. It
is easy to "hide" the installation with shrubs or an inexpensive
wall matching the building. Often, the tank and compressor unit are
located in a basement or first floor space and the condenser
mounted on the roof with vertical discharge. In the illustrated
arrangement, the compressor 19 and an electric driving motor 52 are
mounted on a suitable base and the compressor is connected with the
evaporator coils in the cooling tank 14 by a suction conduit 53
which may include a suitable vibration absorber 54. The compressor
is connected to the condenser coil 20 through the compressor
discharge conduit 55 which may include a suitable pulsation damper
56.
The condenser coil 20 is suitably mounted adjacent to the top of
the housing 51 and a fan 57 driven by an electric motor 58 provides
for the forced flow of atmospheric air over the condenser coil.
While only a single fan 57 is shown in the diagrammatic
illustration, a plurality of fans are usually provided for
producing the desired air flow over the condenser coil, and for
producing variable air flow for better winter control of expansion
valves as will be described.
A condenser discharge conduit 59 connects the condenser coil with a
liquid receiver 60 for the storing of liquid refrigerant. A
refrigerant supply conduit 61 connects the receiver 60 with the
evaporator coils and associated components, and this liquid supply
conduit includes a solenoid controlled valve 62 for controlling the
flow of liquid refrigerant through this conduit.
The refrigeration system, as illustrated includes six individual
evaporator coils A1, A2, A3, B1, B2 and B3 which are positioned
respectively in the compartments 37, 38, 39, 40, 41 and 42. The
coils A1, A2, and A3 make up the A bank of three coils, and the
coils B1, B2 and B3 make up the B bank of three coils. As seen in
the drawings, each of the coils extends throughout its respective
compartment so that an ice bank will be formed which substantially
fills the compartment as will be presently described.
Referring particularly to FIG. 2 of the drawing, liquid refrigerant
is supplied to the evaporator coils through the refrigerant supply
conduit 61 which is connected to a heat exchanger 65 at the tank
14, the heat exchanger also being connected to the compressor
suction conduit 53. In the heat exchanger 65 the temperature of the
liquid refrigerant is reduced, and the liquid chamber of the heat
exchanger is connected by means of a conduit 66 to a subcooler coil
67 located below the water level in the tank 14 where the
refrigerant is further cooled. The subcooler coil 67 is connected
by a conduit 68 to the liquid header 69 which extends across the
tank adjacent to the end wall 32 and which supplies the liquid
refrigerant to each of the evaporator coils. Each of the six
evaporator coils is supplied from the header 69 by an individual
leader conduit 70 which includes a thermal expansion valve 71
isolated by service valves 72.
The liquid header 69 includes a solenoid actuated shut-off valve 75
which is positioned on the header between the leader conduits 70
for the respective evaporator coils A3 and B1. The shut-off valve
75 is provided for the purpose of selectively shutting off the flow
of liquid refrigerant to the B bank of evaporator coils, as will be
explained subsequently in connection with the operation of the
system.
As best seen in FIG. 1, the liquid refrigerant enters each
evaporator coil at the top thereof and the evaporated and partially
superheated refrigerant leaves the coil at the bottom thereof
through a riser conduit 76 where superheat continues. The riser
conduits for the coils A1, A2 and A3 are connected to a suction
header 77 and the riser conduits for the coils B1, B2 and B3 are
connected to a suction header 78. Each of the headers 77 and 78 is
connected to a conduit 79 through respective service valves 80, and
the conduit 79 is connected to the heat exchanger 65 for raising
the temperature of the gaseous refrigerant passing into the
compressor suction conduit 53.
Each of the thermal expansion valves 71 is controlled in the usual
manner through differential pressures acting across a diaphram or
other power element which regulates the valve opening. The pressure
acting on the power element to open the valve is provided by a
sealed system including temperature responsive bulb 83 connected
with one side of the power element through a capillary tube. The
pressure acting on the power element to close the valve is provided
jointly by the suction pressure of the refrigerant within the coil
and an adjustable spring. The control bulb 83 is mounted on the
riser conduit 76 for the respective evaporative coil at a point
below the water level in the tank 14. As best seen in FIG. 1, the
bulb is mounted on the riser at a point slightly below the water
level, and therefore near the top of the tank for convenience of
servicing.
The thermal expansion valves 71 are selected and adjusted to
produce a superheat of 10.degree. , for example, above the
temperature of the liquid refrigerant in the coil. When an
evaporator coil has no ice on it and is exposed to the circulating
water returning from the local cooling units 10 through 13, which
may have a temperature of 48.degree. for example, the refrigerant
will be fully evaporated and superheated within the coil to a
temperature well above the superheat setting so that the associated
valve is maintained full open.
Another evaporator coil, the coil B3, in the outlet chamber 34 for
example, may have a substantial bank of ice insulating the coil
from the circulating water so that this coil will require much less
cooling; and the superheat setting will be reached relatively
quickly to effect a throttling and substantial closing of the
expansion valve for this coil. The intermediate coils between the
coils A1 and B3 may have varying amounts of insulating ice
surrounding the coils and will require varying amounts of cooling,
accordingly. Since each coil is controlled by an individual thermal
expansion valve 71, the valves for the coil requiring less cooling
will then be throttled down to reduce the demand for refrigerant at
these coils; and correspondingly, the valves of the coils requiring
more cooling will be opened to utilize a greater proportion of the
liquid refrigerant. In this manner, the ice banks on the coils tend
to build back evenly.
FIG. 3 of the drawing is a diagrammatically illustration of the
electric control circuit and associated control elements for the
air conditioning system.
The compressor motor 52 is connected to a suitable source of
electrical energy through a motor starter 85, and this starter is
energized through a series circuits including a start-stop switch
86 and a dual pressure control 87, which includes normally open
low-pressure contacts 88 and normally closed high-pressure contacts
89 which are connected in series. The control is set so that the
normally open low-pressure contacts will close when the pressure on
the suction side of the compressor rises to a value such as 20 psi,
to start the compressor, and the contacts will open when the
suction pressure drops to 5 psi, for example to stop the
compressor. The high-pressure contacts 89 function as a safety
cutoff designed to open the circuit when the compressor head or
discharge pressure reaches a value of 190 psi, for example, to shut
off the compressor before it is damaged due to excessive discharge
pressure, or before the compressor motor is damaged due to failure
of its overload protection devices.
The condenser fan motor 58 is also connected to a suitable power
source through a motor starter 91 which is connected in series with
an auxiliary contact 92 in the compressor motor starter 85, which
remains closed when the compressor is running, and with a reverse
acting high-pressure control 93 including normally closed contacts.
Through the auxiliary contact 92 then, the condenser fan motor 58
is normally energized and de-energized with the compressor motor
52.
The reverse acting high pressure control 93 is responsive to the
compressor head pressure and serves to shut off the condenser motor
when the head pressure is reduced below a predetermined value such
as 110 psi, for example. This control is necessary for proper
operation of the expansion valves which require a certain pressure
drop over the valve to give the proper tonnage. For example, with
120 psi head pressure a properly selected and adjusted thermal
expansion valve will maintain 20.degree. in the evaporator coil
with approximately 10.degree. superheat. However, if the ambient
outdoor temperature becomes quite low, 60.degree. for example, the
pressure drop over the expansion valve will become so low that it
will not feed the coil all the way through; and there is a
probability that only two-thirds of a full bank of ice will be
formed on the coil, and the oil in the refrigerant will not be
carried to the compressor to maintain oil balance. This is caused,
of course, by excessive cooling capacity to the condenser unit, due
to the lower ambient air temperature; and accordingly, when the
head pressure reduces to the predetermined value, the condenser fan
is shut off to reduce the cooling capacity. When the head pressure
again rises to another predetermined value, such as 130 psi, the
fan will again be operated. Usually, a condenser unit will be
provided with two or more fans which may be dropped of
progressively in accordance with a head pressure control 93, as
above.
The start-stop switch 86 in the compressor motor starter circuit
remains closed in normal operation of the unit and is used only for
shutting down the system for the purpose of maintenance for
example. As mentioned above, the compressor is controlled in
response to its inlet pressure, and this inlet or suction pressure
is determined by the temperature of the refrigerant gas in the
evaporator coils. The temperature of the refrigerant gas in the
coils is, of course, a function of the refrigeration cycle, and of
the temperature of the water flowing adjacent to the evaporator
coils, and of the thickness of ice around the coil.
The main control for the refrigeration system is the solenoid
controlled valve 62 which controls the flow of liquid refrigerant
from the receiver 60 to the evaporator coils. As seen in FIG. 3,
the solenoid valve 62 is connected to a source of electric power in
series with a thermostat 95, identified as a summer thermostat, and
with the normally closed contacts 98 of an automatic change-over
relay 97. The summer thermostat 95 controls the operation of the
system during the summer months or the normal cooling season, and
its temperature responsive bulb 96 is placed on one of the
evaporator coils as described below.
The summer thermostat and its associated bulb are illustrated in
both FIGS. 1 and 2 wherein it is seen that the thermostat control
95 is mounted on the tank end wall 32 and the bulb 96 is mounted on
the evaporator coil A3, in heat transfer relation with the coil
surface. This bulb is placed on one of the inner coils, the third
coil from the inlet side of the tank in the illustrated six-coil
installation, to detect an average temperature condition. Also, the
bulb is mounted near the top of the evaporator coil, but
sufficiently below the surface level of the tank water to be
removed from local surface conditions. The temperature detected by
the bulb is a function of the refrigerant temperature within the
coil and that of the ice or water surrounding the bulb. As will be
further described in connection with the operation of the system,
the thermostat 95 may be set to respond, for example, to a
4.degree. temperature range of 20.degree. to 24.degree. , that is,
when the detected bulb temperature rises to 24.degree., the
solenoid valve 62 will be opened to effect the flow of refrigerant
liquid to the several expansion valves 71, and when the detected
temperature falls to 20.degree. , the valve will be closed to shut
off the flow of refrigerant to the expansion valves.
The system also includes an automatic control for adjusting to
periods of the year other than the peak summer cooling season.
During the fall and spring, for example, there is some demand for
cooling, but desirably some adjustment should be made to effect
better efficiency of the system. This control includes a winter
thermostat 100 which is connected in series with the solenoid
controlled valve 62 through the normally open contacts 99 of the
automatic change-over relay 97, and through which the solenoid is
connected to a source of electric power. The winter thermostat 100
includes a temperature responsive bulb 101 which is mounted on one
of the evaporator coils in the same manner as the summer thermostat
bulb 96. In FIG. 2, the winter thermostat control 100 is shown
mounted on a tank end wall 32 and its associated bulb 101 is
mounted on the evaporator coil B1 in the same relative location as
the bulb 96.
The contacts 98 and 99 of the change-over relay 97 are so operated
that when one contact is closed the other is open. In the normal
condition during summer operation as above described, the contacts
98 are closed and the contacts 99 are open; and accordingly the
solenoid valve 62 is controlled by the summer thermostat 95. The
change-over relay 97 is controlled by a third thermostat 103 having
a temperature responsive bulb 104 mounted to respond to and detect
the ambient outside temperature. This thermostat 103 may be set to
respond to an outside temperature of approximately 70.degree., for
example, wherein the change-over relay 97 is switched to the summer
condition when the outside temperature is above 70.degree. , and to
the winter condition when the temperature is below 70.degree.. In
the winter condition, of course, the contacts 99 would be closed
and the contacts 98 would be opened so that the solenoid valve 62
is controlled through the winter thermostat 100.
A further control for the system is provided to prevent overload of
the compressor during times of maximum demand for cooling of the
water. Such a situation would occur if the compressor was shut down
for an extended period due to an electrical or mechanical failure,
resulting in dissipation of all or substantially all of the ice in
the tank 14. This situation may arise from a transformer failure,
motor overload, or blown fuse not noticed by the custodian. In such
a situation, upon restarting the system the temperature of water
coming into the tank inlet chamber 37 would be higher than normal,
and the refrigeration compressor may be overloaded due to excessive
suction and head pressures.
To prevent the compressor from being cut off by the high-pressure
cut-off portion of the dual pressure control 87, the system
responds to an increase in the compressor suction pressure to
reduce the cooling demand for the refrigeration system and permit
the system to build back the ice bank under more normal load
conditions. This is accomplished by temporarily removing the B bank
of evaporator coils B1, B2 and B3 from the system by closing the
valve 75 in the liquid header 69 as seen in FIG. 2. In FIG. 3 this
solenoid controlled valve is shown connected to a suitable power
source in a series with a reverse acting low-pressure control 105.
The contacts of the low-pressure control are normally closed and
this control responds to an elevated suction pressure of 34 psi,
for example, to energize the solenoid control valve 75 to shut off
the flow of refrigerant to the B bank of coils. This will permit
the refrigeration system to build up the ice bank on the A bank of
coils under near normal conditions until such time as the
compressor suction pressure drops to about 28 psi, for example, at
which time the low-pressure control 105 will respond by opening the
solenoid control valve 75 to again bring the evaporator coils B1,
B2 and B3 into the system.
OPERATION
The operation of the above-described latent storage
air-conditioning system will now be described with reference to
assumed temperature conditions and design conditions of the system.
It is further assumed that the system is designed for a church
complex wherein certain offices, meeting rooms and school rooms are
used during the week and require cooling and wherein the peak
demand load is in a church auditorium on a Sunday.
During the week, the ice banks are replenished to maximum capacity
around the several coils in the respective tank chambers during the
night so that on a typical midweek morning maximum cooling capacity
will be available in the storage tank 14. Each of the tank chambers
37 through 42 will be desirably substantially filled with a slab of
ice which extends from a point near the bottom of the tank to a
point adjacent the water surface, which extends substantially the
length of the tank chambers, and which extends in width to leave a
flow passage between the respective ice banks and the partitions or
walls which are approximately 1 inch wide.
For example, if the chambers are approximately 18 inches wide, the
ice banks are desirably built up to a width of approximately 16
inches leaving 1 inch flow paths along either side of the ice bank.
Under these conditions, maximum surface of ice is presented to the
water flowing through the tank. Under average conditions, during
the flow of cooling water from the tank to the cooling units 10
through 13, the cooled water will leave the tank at about
40.degree. and return to the tank at about 48.degree. . When the
ice banks are at a maximum, however, the outlet temperature will
likely be less than 40.degree. and may be as low as 36.degree.
.
The availability of this initially cooler water is a particular
advantage where the system is applied to cool a church auditorium
or a similar load. This cool water removes the excess humidity of
the early morning "muggy" air, and also the excess humidity caused
by members of the congregation moving in from the outside and
giving off more heat and moisture than will be given off after the
congregation has settled down and quiet.
As the cooling units 10 through 13 are turned on in the morning,
through the local thermostat control switches 28, the pumps 27 will
cause circulation of the water from the tank 14, and the warm water
returned to the tank will enter the inlet side chamber 37 at
approximately 48.degree. . As the warm water flows through the tank
it affects a melting of the ice banks, with the ice bank in the
chamber 37 being depleted at a faster rate than the ice banks in
the succeeding chambers due to the greater temperature difference
between the water and the ice, and due to the temperature gradient
of the water as it flows through the tank, the temperature
differences in the succeeding chambers will diminish.
Under the above conditions, the bulb 96 of the summer thermostat
95, which is assumed to be controlling the system, will be covered
by the ice surrounding the evaporator coil A3. The bulb then is
insulated from the water by the thickness of the ice; and the
temperature of the bulb will be determined by the combination of
the temperature of the ice surrounding the bulb and the temperature
of the refrigerant gas in the coil. The temperature of the gas in
the coil is a function of the suction pressure, which is common to
all of the coils. Since the ice temperature at the coil will vary,
depending upon ice thickness and water temperature, and since the
refrigerant temperature will vary, depending on suction pressure,
the temperature at the bulb fluctuates in accordance with the needs
of the system.
As indicated above, the summer thermostat may be set to respond to
a temperature range of 20.degree. to 24.degree. , acting to open
the main control valve 62 when the bulb temperature rises to
24.degree. and to close this valve when the bulb temperature drops
to 20.degree.. The refrigeration system is designed so that the
freon R-12 drops below 20.degree. as it expands into the evaporator
coil. With the warm water flowing through the tank 14, there will
be some melting of the surface of the ice bank surrounding the
evaporator A3. The surface temperature of the ice is always, of
course, 32.degree. ; while the temperature of the ice adjacent to
the coil will be lower, due to the temperature gradient across the
thickness of the ice. When the ice temperature at the bulb 96 rises
to 24.degree. or higher, the thermostat 95 will respond to effect
the opening of the valve 62 to supply liquid refrigerant to the
several expansion valves 71, under the extant pressure at the
high-pressure side of the system which may be from 130 to 160 psi,
for example. When the average pressure within the evaporator coils
builds up, through expansion, to a pressure of about 20 psi, for
example, which is reflected at the compressor inlet, the contacts
88 of the dual pressure control 87 will close to start the
compressor and the condenser fan substantially simultaneously. The
valve 62 will remain open until the temperature at the bulb lowers
to 20.degree. due to expansion of refrigerant through the
evaporator coil A3.
If it is assumed that the average cooling load demanded by the
units 10 through 13 throughout the day is greater than the capacity
of the compressor refrigeration system, the compressor will run
substantially continuously with the additional required cooling
capacity provided by the melting of of the ice from the ice banks.
The banks in the chambers near the inlet side of the tank will be
depleted more rapidly than the banks near the outlet side. Under
these conditions the temperature of the ice adjacent to the coils
will tend to stay above 24.degree. , with these ice temperatures
being higher in the chambers adjacent the inlet side since the
insulating ice banks are depleting faster. Because of the
individual expansion valve and the super heat control for each of
the evaporator coils, the refrigerant is boiling off faster in the
warmer coils and slower in the cooler coils, with the warmer coils
thereby demanding more of the refrigerant capacity. The evaporator
coil A3 for example will be demanding less refrigerant than the
evaporator coil A1; and the flow of refrigerant to the coil A3 may
be throttled down and substantially cut off from time to time by
its associated expansion valve superheat control, while refrigerant
is demanded by other coils particularly the warmer coils A1 and A2.
For this reason, as long as there is a substantial demand for
cooling capacity in any of the coils, the temperature at the coil
A3 and the bulb 96 will likely not drop to the temperature of
20.degree. required to effect closing of the refrigerant control
valve 62.
In the evening and during the night, when there is little or no
demand for cooling and some or all of the local units 10 through 13
are shut off, the cooling load will be much less than the capacity
of the refrigeration system and the system will act to rebuild the
ice banks on the several evaporator coils. Since the coils whose
ice banks have been most depleted will be warmer, these coils will
demand more of the refrigerant and accordingly the associated banks
will be built up faster. Correspondingly, the coils having the
heavier ice banks will require less refrigerant and the superheat
control will act to throttle down and to substantially close the
expansion valves for these coils from time to time while
refrigerant continues to be expended through the warmer coils.
During this period of ice bank buildup, the freezing up of any tank
chamber, to the extent that it impedes the flow of circulating
water through the tank, is prevented through the individual control
of each evaporator coil through its associated thermal expansion
valve. When a particular coil has a full bank of ice, should the
expansion valve open to expand refrigerant to the coil, there will
be little boiling of the refrigerant due to the low temperature of
the coil and the superheat control quickly effects the throttling
or closing of the respective expansion valves to prevent further
increase of the ice bank in this particular tank chamber. While the
compressor continues to run, and assuming there is some circulation
of water through the tank, the temperature at the associated valve
control bulb 83 may increase to a value of above 30.degree. ,
wherein the expansion valve would be opened somewhat to expand a
small amount of refrigerant to the associated coil. Since there
will be little or no boiling of the refrigerant as it flows through
the coil, the temperature of the coil riser at the bulb 83 will be
quickly reduced to a value below the superheat setting of
30.degree. and thereby again cut off the expansion valve.
In this manner the ice banks for each of the several coils are
built up toward their maximum values; and as this condition is
approached, the average temperatures at the coils will be
approaching 20.degree. and when this temperature is detected by the
thermostat bulb 96 the thermostat control will effect the closing
of the solenoid operated refrigerant control valve 62. When this
occurs, the compressor will continue to run until the suction
pressure decreases to a low value such as 5 psi for example at
which time the dual pressure control 87 will shut off the
compressor with corresponding shut off of the condenser fan.
On a Sunday, when the peak cooling demand is required in the church
auditorium, the system will function in the same way except that a
substantial portion of the ice from the ice banks will be melted
during the day to provide the desired cooling capacity. It may be
that several nights will be required to completely replenish the
ice banks to full capacity; however, sufficient ice will be built
up during the Sunday night to provide the necessary reserve for
cooling capacity for the following day. Of course, if the average
cooling load during the weekday is about equal to the refrigeration
capacity, the ice banks will remain substantially static during the
day and will be further replenished on the succeeding night.
The winter thermostat 100 and associated controls are provided for
adjusting the system to the cooler ambient temperatures where the
condenser has greater cooling capacity. The winter thermostat may
be adjusted to respond to a temperature range for example of
23.degree. to 27.degree. whereby the refrigerant control valve 62
will be opened when the respective bulb temperature rises to
27.degree. and closed when the bulb temperature decreases to
23.degree. . During these times, of course, the need for reserve
ice capacity is not as great and the recovery rate of reserve ice
will be greater because of the greater condenser capacity.
As a further control of excessive condenser capacity, the
high-pressure control 93 serves to cut off all or some of condenser
fans to reduce cooling air flow over the condenser coil when the
compressor discharge pressure falls to a value where it is not
sufficient to properly operate the expansion valves. The control 93
then reduces the condenser capacity until such time as the head
pressure increases to the normal value at which time the operation
of the condenser fans will be restored.
Should there be an excessive demand on the refrigeration system
resulting from an elevated inlet water temperature to the tank 14,
this excessive demand will be reflected in higher compressor
suction pressure. The low-pressure control 105 reacts to a
predetermined high value of suction pressure, such as 38 psi, for
example, to close the solenoid actuated valve 75 thereby shutting
off the flow of liquid refrigerant to the B bank of the
refrigerator coils. This valve will remain closed until the
compressor suction pressure reduces to a more normal value of 28
psi, for example, at which time the B bank of coils will again be
connected into the refrigeration system.
To improve the efficiency of the refrigeration system, the
refrigerant liquid flowing from the receiver 60 flows successively
through the heat exchanger 65 and the subcooler 67 before being
delivered to the liquid header 69. Under typical design conditions,
the refrigerant gas may leave the compressor at approximately
120.degree. to be condensed and cooled to approximately 110.degree.
in the condenser coil 20. In the heat exchanger 65, the temperature
of the liquid refrigerant may be reduced from 110.degree. to
80.degree. , for example, with the heat being utilized to increase
the temperature of the refrigerant gas from 30.degree. to
35.degree. at the suction headers to approximately 55.degree. at
the compressor inlet. The temperature of the liquid refrigerant is
further reduced in the subcooler 67 to a temperature of 45.degree.
, for example, so that a temperature reduction of only about
25.degree. is required through the expansion valves to the desired
evaporator coil temperature of about 20.degree. . It has been
observed that, with the use of the subcooler 67, a 5 percent
greater refrigeration capacity is achieved. Also, by subcooling at
this low temperature, it is assured that no gas remains in the
liquid to possibly damage the needle type thermal expansion
valves.
Where the local heating units 10 to 13 are used for heating during
periods of cooler weather as well as for cooling, it will be
necessary for the custodian or other maintenance personnel to
manually change the valves associated with the liquid supply and
return headers 15 and 16. To change from cooling to heating, for
example, it will be necessary to close the valves 44 and 47 which
connect the headers, respectively, to the storage tank 14, and to
open the valves 45 and 48 which connect the supply and return
headers, respectively, to the boiler 17.
What has been described is an improved latent storage
air-conditioning system which is particularly adapted for the
cooling of structures where the cooling loads fluctuate widely with
infrequent peaks, the system having improved controls for
maintaining the system in balance at all times for all cooling load
demands from little or no load to the maximum peak load. The system
and controls are designed for automatic operation with little or no
requirements for adjustment due to fluctuations in the outside
temperature. Such automated controls are particularly desirable in
installations such as churches and lodges, for example, for which
this system is particularly adapted, where it is not feasible to
have a qualified air-conditioning engineer on hand to oversee the
operation of the system.
A particular feature of the system is the provisions of a plurality
of evaporators which are individually controlled and which are
positioned in individual, serially connected chambers within the
storage tank. With this arrangement the circulating water flows
over each evaporator or the ice bank built up around the evaporator
in sequence. An individual control is provided for each evaporator
to prevent over-cooling in a particular chamber which would tend to
freeze up or block the chamber, and therefore the flow of water
through the tank.
The individual evaporator controls, acting with the common
refrigerant flow control to all of the evaporators in response to
an average coil temperature condition within the storage tank,
serves to balance the system at all times, to produce and maintain
the ice banks necessary for the peak demands on the system, and to
efficiently utilize the compressor capacity to rebuild the ice
banks uniformly during periods when the cooling load is less than
that of the refrigeration system, and to eliminate freeze up of any
ice bank chamber.
Safety controls are provided to shut down the compressor in the
event of overload, to prevent damage thereto. Other controls are
provided to reduce the load on the system in the event of abnormal
demands in order to keep the system operating at a reduced capacity
rather than to shut down the system completely. This type of
control is particularly desirable in the above-mentioned church or
lodge situation where the qualified air-conditioning engineer is
not readily available.
Another feature of the invention is the seasonal control switch
which automatically adjusts the system to ambient temperature
conditions to provide for greater economy of operation during the
cooler months of the year. During the cooler months of the year,
less reserve ice capacity is necessary because of lower cooling
loads; and accordingly, the system automatically adjusts itself to
reduce the size of the ice banks built up in the several tank
chambers. This, or course, reduces the operating time of the
compressor and refrigeration system, and yet the system will build
back the several ice banks evenly, as described for normal summer
operation.
A particular advantage of the system is the arrangement of controls
which prevents the freeze up of any ice bank chamber while building
up all of the ice banks to full capacity during the periods of
little or no cooling demand, namely during the night. An ancilliary
advantage is that this buildup occurs principally during the cooler
night hours when the refrigeration system condenser is operating at
better efficiency. Another ancilliary advantage of this system
which obviates freeze up is that it is not necessary that water be
circulated through the tank, which condition would possibly occur
during the night when no local units are turned on.
While the preferred embodiment of the invention has been
illustrated and described, it will be understood by those skilled
in the art that changes and modifications may be resorted to
without departing from the spirit and scope of the invention.
* * * * *