GB2149083A

GB2149083A - Thermal storage system for heating and cooling

Info

Publication number: GB2149083A
Application number: GB08329514A
Authority: GB
Inventors: Robert Houston Stevenson; Adrian Arthur Beaulieu
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-11-04
Filing date: 1983-11-04
Publication date: 1985-06-05
Also published as: GB8329514D0

Abstract

A thermal storage system for heating and cooling includes a container (12) defining a reservoir of a thermal storage fluid (e.g. a water/glycol mixture), at least one electric resistance heating element (14) immersed in the thermal storage fluid in the container for heating the fluid, and a heat exchanger (46) in fluid communication with the container for passing the thermal storage fluid in heat exchange relationship with a water line (48) for carrying the heat or cold to the point of use. Conduits (30,32,34,38,40,42) connect the heat exchanger to the container, and pumps (26,28) are provided in the conduits to circulate the thermal storage fluid from the container to the heat exchanger and back. A refrigeration unit is selectively in communication with the pumps for receiving the thermal storage fluid from the container in the cooling mode of operation, and for returning chilled fluid in the form of slush to the container. <IMAGE>

Description

SPECIFICATION Thermal storage system for heating and cooling BACKGROUND OF THE INVENTION The cost of using electricity to provide space heating or hot water was formerly disproportionate to the cost of providing equivalent heating from other available energy sources. That is, although installation charges for the equipment required to provide electric space heating or hot water are comparable to or less than the installation cost of other heating devices, the unit charges incurred for electrical energy to operate the equipment have been considerably in excess of the cost of other fuels. As a consequence, the number of homes and institutions which use electrical heating is relatively small despite advantages, such as the safety and cleanliness of electrical heating.

In order to gain the advantages of electrical heating, while markedly reducing the costs of electrical heating, equipment has been devised which permits the purchase of electrical energy during periods that are known as offpeak periods and the storage of this energy for use during periods at which the demand for electrical energy is high, that is, peak periods. Electrical utilities experience periods during the day in which the demand for electricity is substantially above the requirements at other times. In order to satisfactorily fulfill their obligation to the communities which they serve, the utilities are required to predicate their power supply capacity on the highest demand for electrical energy that can be expected at any given time during the day.

However, this means that the utility must operate at less than full capacity for a substantial portion of each 24-hour period. Thus, during off-peak periods, excess energy is available. Accordingly, most major utilities have established unit charges for electricity which are lower during the off-peak period than in the period of high demand in order to encourage additional use during the off-peak period.

An example of such cost-reducing electrical heating apparatus is disclosed in U.S. Patent No. 3,422,248 to A.A. Beaulieu et al issued on January 14, 1 969. The Beaulieu et al device comprises an apparatus for accumulating energy and storing it in the form of high temperature water under pressure during offpeak periods and utilizing the stored energy to heat separate water for end use during both the peak and off-peak periods. Although the Beaulieu et al apparatus effectively reduces the cost of electrical energy necessary to provide space heating and domestic hot water, it has no provision for similarly reducing the cost of electrical energy for space cooling or air conditioning. Thus, in the summer months, the apparatus is employed only for domestic hot water uses, such as washing, or it is not used at all.In addition, separate equipment must be installed to provide air conditioning.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a thermal storage system which utilizes off-peak electrical energy, and the reduced rates associated therewith, to store not only a hot fluid for heating water for space heating, but also to store a chilled fluid for space cooling or air conditioning.

It is another object of the present invention to provide a combined heating and cooling thermal storage system which requires a single thermal storage container.

It is a further object of the present invention to provide a combined heating and cooling thermal storage system in which a common heat exchanger and associated conduits are utilized in both the heating and cooling mode to provide a fluid having the appropriate temperature for heating or cooling water destined for the point of use.

In order to fulfill these and other objects, the combined heating and cooling thermal storage system according to the present invention comprises a container defining a reservoir of a thermal storage fluid, at least one electric resistance heating element immersed in the thermal storage fluid in the container for heating the fluid, and a heat exchanger in fluid communication with the container for passing the thermal storage fluid in heat exchange relationship with a water line for carrying the heat or cold to the point of use.

Conduits connect the heat exchanger to the container, and pumps are provided in the conduits to circulate the thermal storage fluid from the container to the heat exchanger and back. A refrigeration unit is in communication with the conduits in the cooling mode of operation for receiving the thermal storage fluid from the container and for returning chilled fluid in the form of slush to the container.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of the combined heating and cooling thermal storage system according to the present invention; and Figure 2 is a schematic illustration of a control circuit for controlling the circulation of the thermal storage fluid in the system of Figure 1.

DETAILED DESCRIPTION OF THE PRE FERRED EMBODIMENT In Fig. 1, the reference numeral 10 generally indicates the thermal storage system according to the present invention. The thermal storage system 10 includes a container in the form of a tank 1 2 defining a reservoir for storing a thermal storage fluid in a hot or cold state, depending on whether the system 10 is in a heating or cooling mode of operation.

The thermal storage fluid contemplated for use in the system is a 3-5% solution of glycol in water. Such a solution is preferred to plain water because the solution forms a slush rather than ice upon freezing, which is advantageous because slush can be pumped through the system, whereas ice tends to resist the flow of liquid and to clog conduits.

A plurality of electric resistance heating elements 14, one of which is illustrated, are immersed in the fluid in the tank 1 2 and are operative at off-peak hours to heat the fluid in the tank to a relatively high temperature, for example, on the order of 170OF to 280OF.

The tank 1 2 is closed to define a closed system so that pressure in the tank builds to a level in the range of approximately 30 psig to 60 psig depending on the temperature of the thermal storage fluid in the tank. Because the pressure in the tank 1 2 is proportional to the temperature, the control of the temperature in the tank 1 2 is achieved by pressure controllers 1 5 and 16, pressure controller 1 5 acting to connect the electric resistance heating elements 14 to a source of electricity when the pressure in the tank 1 2 falls below a predetermined level corresponding to a predetermined minimum temperature level, and pressure controller 1 6 acting to disconnect the electric resistance heating elements 14 from the source of electricity when the pressure in the tank 12 rises above a level corresponding to a predetermined maximum temperature level.

The tank 1 2 is also provided with a high temperature shut off control 1 7 which cuts off electricity to the heating elements 14 if the high pressure controller 1 6 should fail, and a high pressure relief valve 1 8 to protect against overpressurization of the tank 12 if the high temperature shut off control 1 7 should fail. In addition, a low fluid level cut off control 1 9 cuts off power to the heating elements 14 if the fluid in the tank 12 drops below a predetermined level. A drain 20 is also included.

An outlet pipe 21, having an array of perforations 22 at its top, extends from the bottom of the tank 1 2 to a level just below the surface of the fluid in the tank 12. A second array of perforations 24 is defined in the outlet pipe 21 near the bottom of the tank 1 2. The thermal storage fluid is drawn from the tank 12 through the outlet pipe 21 by one or both of a small pump 26 and a large pump 28, which are positioned in a flow line comprising a conduit 30 which connects the outlet pipe 21 with the inlets of the respective pumps 26 and 28, and conduits 32 and 34 which connect the outlets of the pumps 26 and 28 to the inlet 35 of a heat exchanger 36 for transferring heat between the thermal storage fluid and another fluid, such as water, which is circulated to the point of use, for example, to space heating units in various rooms of a residence or institution. The inlet 35 shown in Fig. 1 is the inlet to the shell side of the heat exchanger 36, which is of the shell and tube type. It is understood, however, that the thermal storage fluid from the tank 1 2 could be circulated through the tube side of the heat exchanger 36 and that other types of heat exchangers could be employed.

A check valve 37 is positioned in the conduit 34 to prevent back flow from the heat exchanger 36 to the pumps 26 and 28. A shell side outlet conduit 38 from the heat exchanger 36 is connected to the conduit 30, which receives flow from the outlet pipe 21, and to return conduits 40 and 42, which return fluid to the tank 1 2.

The connection among the conduits 30, 38 and 40 is controlled by a three-way valve 44, which controls the flow of fluid leaving the conduit 38 and determines the ratio of the amount of fluid which returns to the tank 1 2 through the conduits 40 and 42 to the amount of fluid which flows into the conduit 30 and is thereby recirculated by the pumps 26 and 28 through the conduits 32 and 34 to return to the heat exchanger 36. it can be seen that by controlling the position of the three-way valve 44, the temperature of the thermal storage fluid passing through the heat exchanger 36 can be controlled, since, for example, in the heating mode, the temperature of the fluid which has passed through the heat exchanger is less than the temperature of the fluid which has just been drawn from the tank 1 2. The position of the three-way valve 44 is determined in response to the temperature of the thermal storage fluid leaving the heat exchanger 36 through the shell side outlet conduit 38 and can be sensed by positioning a sensor 46 in the conduit 38. By thus controlling the position of the three-way valve 44, the temperature of the water circulated through the tube side of the heat exchanger 36 can be controlled. The three-way valve 44 illustrated is of the motorized type, but it is understood that a self-contained temperature-responsive valve can be used in which the sensor is contained within the valve unit.

Water from a domestic water line 48 flows into an inlet 50 to the tube side of the shell and tube heat exchanger 36, and an outlet 52 from the tube side returns heated water to the domestic line 48. The domestic line 48 includes a bypass section 53 through which water may flow to return to the point of use without passing through the heat exchanger 36. A mixing valve 54 can be positioned at the connection between the tube side outlet 52 and the bypass section 53 of the domestic water line 48 to mix the water which passes through the heat exchanger 36 with the water which bypasses the heat exchanger 36 in order to control the temperature of the water flowing in the domestic water line 48 to the point of use.

In order to provide air conditioning capability for the thermal storage system, a refrigeration system, which is generally designated by the reference numeral 56, is provided which includes a compressor 58 and a slush producing chamber 60. An inlet connection 62 is provided between the slush producing chamber 60 and the conduit 32, and an outlet connection 64 is provided between the slush producing chamber 60 and the return conduit 42. Thus, the thermal storage fluid is circulated through the slush producing chamber 60 by the pumps 26 and 28 so that, as slush is produced, it is moved into the tank 1 2. An electrically operated valve 66 is provided in the inlet connection 62 to control the flow of thermal storage fluid into the slush producing chamber 60.Thus, when no further slush is required in the tank 1 2 or when the system is operating in the heating mode, the valve 66 will prevent any flow into the slush producing chamber 60. However, when slush is being produced, a portion of the flow through the conduit 32 is allowed to flow into the slush producing chamber 60, while the remainder of the flow continues through the conduit 32 and circulates through the heat exchanger 36.

A control circuit for controlling the circulation of the thermal storage fluid through the thermal storage system 10 is illustrated in Fig.

2. The pumps 26 and 28 are connected in parallel to a power supply 68 through an onoff switch 70 and a conventional fuse 72, as well as through a summer-winter switch 74 and a temperature control switch 76 arranged in series. The summer-winter switch 74 includes a contact arm 78 connected to the small pump 26 and a contact arm 80 connected to the large pump 28. The contact arms 78 and 80 are connected to one another for movement together between two positions, in which the contact arm 78 contacts either a first terminal 82a or a second terminal 83a and the contact arm 80 contacts either a first terminal 84a or a second terminal 85a. The summer-winter switch 74 also includes a contact arm 86 which is either closed or open for controlling the flow of electricity to the compressor 58.In Fig. 2 the summer-winter 74 switch is in its summer position, corresponding to the cooling mode of operation, in which the contact arms 78 and 80 contact the terminals 83a and 85a, respectively, and the compressor contact arm 86 is closed so that the compressor 58 can operate. A slush volume switch 88, which is mounted at the bottom of the tank 12, is connected in series with the compressor contact arm 86 and includes a contact arm 90, which is in the closed position when the tank 1 2 is less than full of slush and in the open position when the tank 1 2 is full of slush. Thus, when the tank is full of slush, the compressor 58 does not operate.The electrically operated valve 66 is connected in series with the compressor contact arm 86 and the slush volume switch 88, whereby the valve 66 allows thermal storage fluid to flow into the slush producing chamber 60 only when the compressor 58 is operating.

The temperature control switch 76 is connected to the summer-winter switch 74 through terminals 82b, 83b, 84b and 85b, which are connected with terminals 82a, 83a, 84a and 85a, respectively. The temperature control switch 92 is a snap-acting temperature-responsive switch having a pair of contact arms 94 and 96 which are movable between the terminals 82b and 83b, and 84b and 85b, respectively. The contact arms 94 and 96 are also connected to one another for limited movement relative to one another so that, in response to rising temperature, the contact arm 94 moves from the terminal 82b to the terminal 83b before the contact arm 96 moves from the terminal 84b to the terminal 85b. The temperature control switch 92 is connected to a temperature sensor 98 mounted on the tube side outlet 52 of the heat exchanger 36.

In the cooling mode of operation, the domestic water line 48 is connected to one or more heating/air conditioning units in a building to be cooled. Chilled water is drawn into the domestic line 48 from the tube side outlet 52 of the heat exchanger 36 and is mixed with water from the bypass section 53 to obtain chilled water having the desired temperature. If no water is being demanded by the heating/air conditioning units, the temperature at the tube side outlet 52 of the heat exchanger 36 will be relatively cold due to the increased time for heat to transfer between the water in the tube side and the cold thermal storage fluid in the shell side. This cold temperature is sensed by the sensor 68, so that the contact arm 94 of the temperature control switch engages terminal 82b and contact arm 96 engages terminal 84b.Thus, neither of the pumps 26 and 28 operate, and no thermal storage fluid flows through the tube side of the heat exchanger 36. When cold water is demanded by the heating/air conditioning units, the temperature of the water in the tube side outlet 52 rises due to the flow of water in the tube side. The sensor 68 detects the rise and signals the temperature control valve, so that the contact arm 94 moves from terminal 82b to 83b, as is shown in Fig. 2.Thus, the small pump 26 operates to draw thermal storage fluid from the tank 1 2 through the outlet pipe 21 and the conduit 30 and pump it through the conduits 32 and 34, the shell side inlet 35, the heat exchanger 36, the shell side outlet conduit 38, the diverter valve 44 and the conduits 40 and 42, and back to the tank 1 2. In the heat exchanger 36, the thermal storage fluid cools the domestic water on the tube side by absorbing its heat, and flows back to the tank 1 2. if only a low amount of cooling is required, a portion of the relatively warm thermal storage fluid flowing from the shell side outlet conduit 38 is diverted by the diverter valve 44 to the conduit 30 to temper the cold thermal storage fluid being drawn through the outlet pipe 21, so that the thermal storage fluid circulating through the heat exchanger 36 provides only the mount of heat transfer demanded. If greater cooling capacity is required, the diverter valve 44 returns all of the fluid from the shell side outlet conduit 38 to the tank 1 2 and does not temper the fluid being pumped to the heat exchanger 36.If still greater cooling capacity is required, the temperature of the water at the tube side outlet 52 will rise further and cause the contact arm 96 of the temperature control switch to move to terminal 85b, thereby placing the large pump 28 in operation.

In order to charge the tank 1 2 with a supply of cold thermal storage fluid, which is done during the off-peak hours of the electric utility, the pumps 26 and 28 operate to circulate fluid from the tank 1 2 through the slush producing chamber 60 and back to the tank through the conduits 64 and 42. This flow circulation pattern is enabled by the electrically operated valve 66, which opens in the charging condition to allow some of the fluid from the conduit 32 to enter the slush producing chamber 60. The compressor 58 operates to produce the slush, which flows with liquid phase thermal storage fluid through the conduits 64 and 42.The slush enters the tank 12 and rises to the top, so that as additional slush is produced, the mass of slush in the tank increases downwardly until it engages a slush volume switch 88 at the bottom of the tank to end the charging operation. The terminals of the slush volume switch 88 are connected in series with the compressor contact arm 86, and the slush volume switch 88 is closed when additional slush is required to complete a full charge of cold thermal fluid in the tank 12, so that the compressor can operate. However, when a complete charge of slush is attained, the slush will actuate the slush volume switch 88, opening the contact arm and preventing the compressor from operating. The fact that the thermal storage fluid forms slush instead of ice allows the remaining thermal storage fluid in the tank, in the liquid phase, to be drawn through the slush to the outlet pipe 21.

In the winter position, the contact arms 78 and 80 of the summer-winter switch 74 contact the terminals 82a and 84a, respectively, which are connected to the terminals 82b and 84b, respectively, of the temperature control switch 92. Thus, in the heating mode, which corresponds to the winter position, as the temperature of the welter at the tube side outlet 52 rises, the pumps 26 and 28 will cease to operate. Conversely, as the temperature falls, the pumps will be actuated to circulate the thermal storage fluid, which in this mode is hot, through the heat exchanger 36.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

Claims

1. A thermal storage apparatus comprising: a container defining a reservoir of fluid; means for heating the fluid; means for cooling the fluid; a heat exchanger for passing the fluid in heat exchange relationship with another fluid; and control means for selectively activating the heating means and the cooling means.

2. The apparatus of claim 1 wherein the heating means comprises at least one electric resistance heating element.

3. The apparatus of claim 1 wherein the fluid is a solution of water and glycol.

4. The apparatus of claim 3 wherein the cooling means comprises refrigeration means for transforming the solution to slush.

5. The apparatus of claim 4, further comprising means for moving the slush from the refrigeration means to the container.

6. The apparatus of claim 5, further comprising valve means for selectively placing the refrigeration means in communication with the slush moving means.

7. The apparatus of claim 1 further including means for circulating the fluid from the container to the heat exchanger and back to the container.

8. The apparatus of claim 5 further including means for circulating the fluid from the container to the heat exchanger and back to the container.

9. The apparatus of claim 8 wherein the slush moving means and the circulating means comprise the same pump.

10. The apparatus of claim 8 wherein the slush moving means and the circulating means comprise the same set of pumps.

11. The apparatus of claim 5 wherein the cooling means further comprises a slush producing chamber connected in fluid communication between the slush moving means and the container.

1 2. A thermal storage apparatus substantially as hereinbefore described with reference to the accompanying drawings.