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.

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.

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.