WO2001032007A1

WO2001032007A1 - Temperature control system

Info

Publication number: WO2001032007A1
Application number: PCT/GB2000/004169
Authority: WO
Inventors: Peter Mccallum Baxter; Iain Johnston
Original assignee: University Court Of The University Of St. Andrews
Priority date: 1999-10-30
Filing date: 2000-10-30
Publication date: 2001-05-10
Also published as: AU1044901A; GB9925714D0

Abstract

Apparatus for controlling the temperature of a liquid in at least one vessel (14) comprises first heat exchanger (11) located inside the vessel through which heating fluid is circulated and a second heat exchanger (9) located inside the vessel through which coolant fluid is circulated. The temperature of the liquid in the vessel (14) is monitored by a temperature sensor (21) located inside the vessel (14). Control means (23) are provided to respond to the temperature sensor (21) in order to control the circulation of heating and coolant fluid through the first (11) and second (9) heat exchangers to control the temperature of the liquid in the vessel (14). The apparatus may be adapted to provide independent temperature control of a number of vessels and is particularly applicable to aquaria.

Description

Temperature Control System

This invention relates to an apparatus for controlling the temperature of liquids or aqueous media in vessels. In particular the invention relates to temperature control in fresh or salt water aquaria.

A wide variety of aquaria are in use throughout the world. These range from small tanks of approximately 50 litres in size, used by private keepers of tropical fish and the like to very large tanks containing thousands of litres of water, used in research for the study of all manner of marine life. In all cases, it is important to control the temperature of the water in which the animals live. In doing so, the primary concern is to ensure that the temperature of the water is within a range so that the animals remain alive. In addition to this, research into the environmental conditions in which aquatic animals live provides important information on their physiology and can lead, for example, to the optimisation of fish hatching and growth conditions. A major requirement in determining these optimum conditions is the accurate control of water temperature .

Temperature control apparatus is, therefore, widely used. Currently, temperature control in aquaria is achieved mainly by use of at least one thermostatically controlled electrical heating/cooling element located inside the tank and automatically operated in response to changes in temperature detected by a temperature sensor. There are a number of problems associated with temperature control devices of this type. Firstly, they require the use of electricity in and in close proximity to water, thereby increasing the risk of electrocution. As a consequence, the electrical elements must be extremely well sealed to prevent contact with water.

Secondly, in conventional, prior art temperature control systems, faults occurring in the thermostat situated in the water and used to monitor water temperature can have a harmful effect on the animals in the tank. Any fault occurring in the thermostat can have one of two consequences. If the thermostat malfunction causes a false low reading to be recorded, this will result in the heating element increasing the amount of heat input to the tank. This will cause the water in the tank to overheat and if not corrected will result in the death of the animals. If the thermostat malfunction causes a false high reading to be recorded, the heating element will not be switched on and the tank temperature may drop below the temperature necessary to sustain life. Therefore the aquarium keeper must ensure that any thermostat used is reliable, robust and regularly tested, or risk losing fish.

The present invention seeks to provide apparatus which controls the temperature accurately and safely and ensures that the temperature in the tank cannot exceed predetermined maximum and minimum values .

In accordance with a first aspect of the invention, there is provided apparatus for controlling the temperature of a liquid in at least one vessel, the apparatus comprising: first and second heat exchange means adapted to be located in said vessel; heating means for circulating a heating fluid through said first heat exchange means; cooling means for circulating a coolant fluid through said second heat exchange means; and temperature sensing means located in said vessel; and control means for setting a desired temperature of liquid within said vessel and responsive to said temperature sensing means to control the circulation of heating and coolant fluid through said first and second heat exchange means so as to control the temperature of the liquid in said vessel .

Preferably, said heating means comprises a source of heating fluid comprising a fluid reservoir and a thermostatically controlled heater for heating said heating fluid to a first predetermined temperature, and flow and return piping connecting said reservoir to said first heat exchange means.

Preferably, said cooling means comprises a source of coolant fluid comprising a fluid reservoir and a thermostatically controlled cooler for cooling said coolant fluid to a second predetermined temperature, and flow and return piping connecting said reservoir to said second heat exchange means.

Preferably, the flow and return piping of said heating means comprises a main loop and flow and return branches connecting said main loop to said first heat exchange means.

Preferably the flow and return piping of cooling means comprises a main loop and flow and return branches connecting said main loop to said second heat exchange means.

Preferably, the flow and return branches connected to each heat exchange means are interconnected by by- pass valve means. Where the apparatus is adapted to control the temperature of a plurality of vessels, it is preferred that the respective heat exchange means of each vessel are connected in parallel to said main heating and cooling loops.

Preferably, said control means includes first valve means for controlling the flow of heating fluid through said first heat exchange means, second valve means for controlling the flow of coolant fluid through said second heat exchange means and a controller responsive to said temperature sensing means for controlling the operation of said first and second valve means .

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which:

Fig. 1 is a schematic diagram of an example of a temperature control system embodying the invention, for use in regulating the temperature of a single tank;

Fig. 2 is a schematic diagram showing how the system of Fig. 1 may be extended for use in regulating the temperature of two or more separate tanks;

Fig. 3 is a schematic diagram of a temperature control relay/flow regulation system for use in accordance with the invention; Fig. 4 is a block diagram of an example of a temperature control system embodying the invention, for use in regulating the temperature of a plurality of tanks; and

Fig. 5 shows an example of a coolant equilibrium chamber for use in accordance with the invention.

Figure 1 shows an example of a temperature regulation system in accordance with the present invention. The system comprises a source 5 of heating fluid (in this case water, preferably containing a cleaning fluid to prevent blockages in the pipe) comprising a first storage tank and a source 7 of coolant fluid (also water, preferably with a cleaning fluid and/or an antifreezing fluid added) comprising a second storage tank. Water from the respective sources 5 and 7 is pumped around a heating circuit 15 and a cooling circuit 17 by means of respective pumps (not shown) , one for each circuit, in order to regulate the temperature of water contained within a tank 14.

The heating fluid source 5 includes thermostatically controlled means for heating the water contained therein to a first predetermined temperature, greater than the maximum temperature required in the tank 14. The heating means can be of any suitable type, typically an electric heating element of the type used in central heating systems. The cooling fluid source 7 includes thermostatically controlled means for cooling the water contained therein to a second predetermined temperature, less than the minimum temperature required in the tank 14. The cooling means can be of any suitable type, such as an electric pumped cooling unit. One advantage of the present invention is that the temperature of the fluid in the sources 5 and 7 does not need to be controlled with a high degree of accuracy.

The heating and cooling circuits 15, 17 each comprise a network of pipes 15a, b,c and 17a, b,c, suitably rigid piping such as copper or plastic piping, preferably thermally insulated. Each of the circuits 15 and 17 comprises a main flow and return loop 15a, 17a connected to the respective storage tanks 5 and 7, a flow branch 15b, 17b connecting the flow side of the loops 15a, 17a to inlets of respective heat exchangers 9 and 11 located inside the tank 14, and a return branch 15c, 17c connecting outlets of the heat exchangers 9 and 11 to the return sides of the loops 15a, 17a. The cooling circuit 17 preferably also includes a coolant equilibrium chamber 18 in the return side of the loop 17a, used to cool coolant fluid returning from the heat exchanger 11 as will be described in greater detail below.

The cooling and heating circuits 15, 17 supply fluid to the respective heat exchangers 9 and 11. In this embodiment the heat exchangers 9 and 11 are each of the same design and consist of a welded box with flat top and side surfaces constructed from a stainless steel alloy and designed for use in fresh water and salt water tanks. Heat exchangers are generally well known and, for the purposes of the present invention, can have any of a variety of configurations; e.g. coil shaped or box-type with ribbed surfaces in order to improve heat transfer efficiency.

The heat exchangers 9 and 11 are connected by means of inlet and outlet connector pipes 13 to the respective branch pipes 15b, c and 17b, c. It is advantageous for these connector pipes 13 to be made of a flexible material such as rubber or the like with suitable connectors 13a so as to provide points in each circuit which allow easy access to the interiors of the circuits 15 and 17. Such access is required in order to check the pipes for blockages and for cleaning purposes. The connectors 13a may suitably be of the type employed for connecting washing machines and the like to domestic water supplies.

Each of the hot and cold circuits also includes a by- pass valve 19 interconnecting the flow and return branches 15b, c and 17b, c, enabling the respective heat exchangers 9 and 11 to be isolated from their associated circuits 15 and 17 and/or to enable the flow of fluid through the heat exchangers 9 and 11 to be regulated. The use of such by-pass valves is particularly preferred in cases where the system independently regulates the temperature of a plurality of tanks, as shall be described further below. In these cases, the by-pass valves 19 also provide a means of equalising pressure in the various heat exchangers associated with the different tanks regardless of their position in the circuit.

The by-pass valves may be manually or automatically controlled.

The heating and cooling circuits 15 and 17 further include zone valves 25 located in the flow branches 15b, 17b at positions downstream of the by-pass valves 19.

The temperature of the water in the tank 14 is monitored by a temperature sensor 21, which controls the operation of a temperature control relay (TCR) 23. The TCR 23 in turn controls the operation of the zone valves 25.

The system operates as follows. The heating and cooling fluid sources 5 and 7 maintain reservoirs of heating and cooling fluid at approximate temperatures which are respectively greater and lower than the maximum and minimum temperatures required for the water in the tank 14. The heating and cooling fluids are circulated continuously in the loops 15a and 17a. The desired temperature for the water in the tank 14 is set on the TCR 23. The actual temperature of the water in the tank 14 is monitored continuously by the sensor 21. In response to signals received from the sensor 21, the TCR 23 controls the operation of the zone valves 25 so as to control the flow of heating and cooling fluid through the heat exchangers 9 and 11, thereby adjusting the temperature of the water in the tank 14 towards the set temperature.

That is, if initially the temperature of water in the tank 14 is below the set temperature, the "hot" zone valve 25 is open and the "cold" zone valve 25 is closed, heating fluid will be circulated through the heat exchanger 9 whilst no cooling fluid circulates through the heat exchanger 11. The temperature of the water in the tank 14 will rise until the temperature exceeds the set temperature, at which point the TCR 23 will operate in response to the sensor 21 to close the hot zone valve 25 and open the cold zone valve 25, and will thereafter switch between the two zone valves 25 in order to balance the tank temperature at its set level. The TCR operates to open one zone valve 25 as the other zone valve 25 closes.

In this embodiment, the zone valves 25 are controlled so as to be fully open or fully closed, with either the hot or cold zone valve being open at any one time. This is a particularly simple control scheme. It will be understood that the zone valves could be operated in a more sophisticated manner if required, e.g. by being partially opened or closed. Figure 2 illustrates an embodiment of the present invention when employed to regulate the temperatures of two tanks 114 and 214.

The system of Fig. 2 can be seen to be similar to that of Fig. 1. First flow and return branches 115b, 115c and 117b, 117c connect the heat exchangers 9, 11 of the first tank 114 to the main heating and cooling loops 15a and 17a. Second flow and return branches 215b, 215c and 217b, 217c connect the heat exchangers 9, 11 of the second tank 214 to the main heating and cooling loops 15a and 17a, in parallel with the first branches 115b, 115c and 117b, 117c. Each tank 114, 214 has connector pipes 13, connectors 13a, by-pass valves 19, a temperature sensor 21, TCR 23 and zone valves 25 associated therewith. Accordingly, the temperature of each tank 114, 214 can be controlled independently of the other and either tank can be isolated from the heating and cooling circuits 15 and 17 whilst the system continues to regulate the temperature of the other tank. Different temperatures can be set for each of the tanks 114, 214.

As mentioned above, the temperature of the heating and cooling fluids in the sources 5 and 7 is set to be respectively higher and lower than the maximum and minimum acceptable temperatures required in any of the tanks regulated by the system. Typically, the temperature of the source of heating water for the heating circuit is set on the thermostat of the source at a temperature in the range 5°C to 20°C above the temperature of the highest desired tank temperature. Similarly, the temperature of the source of coolant water for the cooling circuit is set on the thermostat of the source at a temperature in the range 5°C to 20°C below the temperature of the coolest desired tank temperature.

The extent to which the temperature of the heating water source 5 is set to exceed that of the warmest tank temperature and the temperature of the cooling water source 7 is set to be below that of the coolest tank temperature depends on factors including the thermal transfer properties of the heat exchangers 9, 11, the level of insulation on the pipes, the speed with which system temperatures are to be equalised to the desired temperatures and the pressure of water through the heat exchangers. Accordingly, suitable set temperatures for the heating and cooling sources 5 and 7 will depend on the details of the particular system.

In tank systems containing live fish any equalisation or change of temperature should occur slowly in order to avoid shock to the fish's metabolism. In addition, the use of a hot water source set at a temperature a few degrees above the highest desired temperature and a cold water source set at a temperature a few degrees below the lowest desired tank temperature gives the present invention a highly advantageous fail-safe mechanism. Fig. 3 illustrates in greater detail the electrical connections of the TCR 23 and associated components as employed in the embodiments of Figs. 1 and 2. Power is supplied to each TCR 23 from a main power supply 50, via a spur switch 52, which allows the TCR etc. of any individual tank to be switched on and off. The TCR 23 is in turn connected to the hot and cold zone valves 25 and temperature sensor 21.

Figure 4 illustrates the application of the present to a system controlling an arbitrary number of tanks 14, seven tanks in this example. This is a simplified diagram showing the basic arrangement by which the heat exchangers 9 and 11 of a plurality of tanks may be connected in parallel to the main heating and cooling loops 15a and 17a. It will be understood that each tank 14 and its associated heating and cooling branches will include the various branch pipes, connectors, by-pass and zone valves, temperature sensor, TCR etc. as illustrated in detail in Figs. 1 and 2.

Since the present invention allows the temperature of each of the tanks 14 to be set individually within maximum and minimum values determined by the temperatures of the heating and cooling sources 5 and 7, it allows the study of fish and other marine life in different tanks at a range of different temperatures without the need to have a separate heating and cooling source for each of the tanks. Prior art systems which require the use of separate heating and cooling systems have the problem that this additional equipment is bulky, expensive to buy and run, as well as increasing the ambient temperature of the surroundings .

Fig. 5 illustrates the coolant equilibrium chamber 18 as used in the coolant circuit 17 of the previously described embodiments. In these embodiments the heating and coolant fluids continuously circulate through their respective heating and coolant circuits 15 and 17. In the case of the coolant circuit 17, the temperature of the coolant fluid rises after having passed through the heat exchanger 11. The cooling unit of the cooling fluid source 9, being thermostatically controlled, is sensitive to sudden influxes of warm water, which can cause the cooling unit to be switched on and off rapidly, possibly damaging the cooling compressor in the cooling unit. The present invention therefore preferably includes the coolant equilibrium chamber 18 located on the coolant return side of the main coolant loop 17a downstream of the heat exchangers 11. The coolant equilibrium chamber 18 in effect creates a buffer zone which smooths out any sudden or localised high coolant temperatures which can result from the passage of the coolant fluid through the heat exchanger. The coolant equilibrium chamber 18 can be a tank or a similar chamber in which the coolant fluid may circulate in order to allow its temperature to equalise. In Fig. 5, the chamber 18 comprises a sealed cylindrical casing 46 containing apertures for an inlet pipe 42 and an outlet pipe 44 connecting the interior of the casing 46 in series with the main coolant loop 17a. The casing 46 has a larger cross sectional area and therefore a larger volume per unit length than either the inlet pipe 42 or outlet pipe 44. The chamber 40 is connected to the inlet pipe and outlet pipe such that it is arranged vertically in relation thereto. The inlet pipe 42 extends to a point close to the bottom of the casing 46 whilst the outlet pipe 44 terminates close to the top of the casing 46. The volume of water enclosed within the casing 46 allows excessively hot water entering the casing via the pipe 42 to be cooled as it circulates through the chamber 18 prior to passing through the outlet 44 and back to the cooling source 7.

A regular flow of coolant is maintained through the system simply by use of the pump which circulates the coolant fluid in the rest of the circuit.

The present invention may be used to control the temperature in tanks of any size. In cases where a large tank is used it is important to ensure that the temperature of the liquid in the tank is accurately determined and that the heat exchanger can evenly exchange heat through the tank so as to avoid the tank containing local regions of higher or lower temperature. This can be achieved by the inclusion of a number of temperature sensors at different positions around the tank and similarly by providing more than one heating heat exchanger and more than one cooling heat exchanger. In this way, the temperature sensors can be used to provide an average tank temperature and the heat exchangers can improve the consistency of temperature through the volume of the tank.

The present invention has further advantages over the prior art. Where a fault occurs in the temperature sensor 21 which causes excessive heating or cooling of the tank, the system will fail safe since the temperature of the tanks cannot be heated to a temperature higher than that set as the maximum temperature of the heating source 5 or cooled to a temperature below that set as the lowest temperature of the coolant source 7.

Improvements and modifications may be incorporated without departing from the scope of this invention.

Claims

1. Apparatus for controlling the temperature of a liquid in at least one vessel, the apparatus comprising: first and second heat exchange means adapted to be located in said vessel; heating means for circulating a heating fluid through said first heat exchange means; cooling means for circulating a coolant fluid through said second heat exchange means; and temperature sensing means located in said vessel; and control means for setting a desired temperature of liquid within said vessel and responsive to said temperature sensing means to control the circulation of heating and coolant fluid through said first and second heat exchange means so as to control the temperature of the liquid in said vessel.

2. Apparatus as claimed in Claim 1 wherein said heating means comprises a source of heating fluid comprising a fluid reservoir and a thermostatically controlled heater for heating said heating fluid to a first predetermined temperature, and flow and return piping connecting said reservoir to said first heat exchange means.

3. Apparatus as claimed in Claim 1 or Claim 2 wherein said cooling means comprises a source of coolant fluid comprising a fluid reservoir and a thermostatically controlled cooler for cooling said coolant fluid to a second predetermined temperature, and flow and return piping connecting said reservoir to said second heat exchange means .

4. Apparatus as claimed in any preceding Claim wherein the flow and return piping of said heating means comprises a main loop and flow and return branches connecting said main loop to said first heat exchange means.

5. Apparatus as claimed in any preceding Claim wherein the flow and return piping of said cooling means comprises a main loop and flow and return branches connecting said main loop to said second heat exchange means.

6. Apparatus as claimed in Claim 4 or Claim 5 wherein the flow and return branches connected to each heat exchange means are interconnected by by- pass valve means.

7. Apparatus as claimed in any preceding Claim, wherein the apparatus is adapted to control the temperature of a plurality of vessels.

8. Apparatus as claimed in claim 7 when dependent on any of Claims 4 to 6, wherein the respective heat exchange means of each vessel are connected in parallel to said main heating and cooling loops.

9. Apparatus as claimed in any preceding claim wherein said control means includes first valve means for controlling the flow of heating fluid through said first heat exchange means, second valve means for controlling the flow of coolant fluid through said second heat exchange means and a controller responsive to said temperature sensing means for controlling the operation of said first and second valve means.