TECHNICAL FIELD

The present invention relates to thermal storage tanks for heat pump systems, and more particularly, but not exclusively, to thermal storage tanks for solar assisted heat pump systems.

BACKGROUND

Heat pump systems, such as solar assisted heat pump (SAHP) systems store thermal energy in liquid (e.g. water) within a large, single chamber thermal storage tank, from which heat is drawn off for space heating and hot water generation. Heat is transferred into the liquid, from the heat source (e.g. solar array) with a heat exchanger coil within the tank.

For thermal storage units installed within households, mornings are commonly a time of peak demand for both domestic space heating and domestic hot water generation. When solar radiation is not received by solar arrays (e.g. overnight), or where the rate of heat drawn off exceeds the rate at which heat is transferred into the tank, the temperature of the liquid within the tank may drop significantly, as heat may be drawn off and lost. The temperature of the liquid within the tank rises again when the received thermal radiation that is transferred to the liquid within the tank exceeds the rate at which any heat is drawn off and lost. Effective space heating (e.g. underfloor heating) typically requires the liquid within the thermal storage tank to have a temperature of at least 35°C. Effective generation of hot water typically requires the thermal storage liquid to have a temperature of at least 55°C (e.g. to kill legionella bacteria).

A larger thermal storage tank provides a higher thermal storage capacity, which can be used to provide a greater contribution to a household’s energy consumption from solar energy. A thermal storage tank may be at least large enough to store all of the output of the heat source during a day of maximum generation (e.g. generation by a thermal array during a day of full sunshine, during high summer). However, even when solar radiation is being received by a connected solar array and transferred to the liquid within the single chamber thermal storage tank, the large volume of liquid within the tank heats slowly (e.g. over a course of hours), due to the large thermal inertia of the liquid within the tank. This can result in a lower temperature of the liquid in the tank that is desirable, e.g. for space heating and hot water generation, in particular during times of peak morning demand. If space heating or hot water generation is required urgently, heat pumps are used, wasting electricity, which both increases costs (e.g. when electricity is used whilst priced above the minimum daily tariff, which commonly occurs overnight) and increases the household’s carbon emissions, relative to use of a solar array.

SUMMARY OF THE DISCLOSURE

According to a first aspect, there is provided a thermal storage tank divided into a first and second chamber by a partition, wherein the partition has a partition aperture for the flow of fluid from the first chamber to the second chamber, and wherein a heat exchanger is provided within the first chamber for transferring heat from a heat source to fluid within the first chamber, wherein the second chamber has a volume that is at least twice the volume of the first chamber, and wherein the first chamber contains one or more outlet ports and one or more inlet ports and the second chamber contains one or more outlet ports.

According to a second aspect, there is provided a thermal storage system comprising a thermal storage tank according to the first aspect and a solar thermal array having an inlet and outlet that are coupled to ports of the first chamber.

The first chamber may have a volume that is less than 25% of the volume of the second chamber.

The first chamber may have a volume that is less than 10% of the volume of the second chamber.

The partition may comprise a thermally insulating board.

The partition may be a plastic board.

The aperture may be provided with a one-way valve for permitting the flow of fluid through the aperture from the first chamber to the second chamber, and for preventing a flow of fluid through the aperture from the second chamber to the first chamber.

The aperture may be located proximate the edge of the partition.

The second chamber may have an outlet port remotely located from the aperture. The heat exchanger may be a coiled heat exchanger.

The thermal storage system may comprise a heat exchanger for heating potable water.

The heat exchanger for heating potable water may comprise a heat exchange coil within a tank for potable water, wherein the heat exchange coil is coupled to ports of the first chamber.

The thermal storage system may comprise a building heating system having an outlet coupled to an inlet port of the first chamber, and having an inlet coupled to a first valve, the first valve being coupled to receive inputs from an outlet port of the first chamber and an outlet port of the second chamber.

The thermal storage system may comprise a heat pump that is an air source heat pump or a ground source heat pump, the heat pump having an outlet coupled to an inlet port of the first chamber, and having an inlet coupled to a second valve, the second valve being coupled to receive inputs from an outlet port of the first chamber and an outlet port of the second chamber.

The thermal storage tank or the thermal storage system may comprise a controller configured to control operation of one or more circulation pumps selected from the group consisting of: a circulation pump for circulating fluid between the thermal storage tank and a potable water heat exchanger; a circulation pump for circulating fluid between the thermal storage tank and a solar water heater; a circulation pump for circulating fluid between the thermal storage tank and a building heating system; and a circulation pump for circulating fluid between the thermal storage tank and a heat pump that is an air source heat pump or a ground source heat pump.

DESCRIPTION OF THE DRAWINGS

Examples are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates a thermal storage tank with a heat exchanger coil; Figure 2 shows the heat exchanger coil of Figure 1; and • Figure 3 schematically illustrates a thermal storage system, comprising the thermal storage tank of Figure 1.

DETAILED DESCRIPTION

In the described examples, like features have been identified with like numerals.

Figure 1 schematically illustrates a thermal storage tank 100 for a thermal storage fluid (e.g. liquid). The tank 100 has a first chamber 102 and a second chamber 104 separated by a partition 110. The partition 110 is provided with a partition aperture 112 for fluid to flow from the first chamber 102 to the second chamber 104. A heat exchange coil 130 is provided within the first chamber 102 for a heating fluid to be circulated through, to heat fluid within the first chamber.

The partition aperture 112 in the illustrated thermal storage tank 100 is spaced apart from the centre of the partition 110. The aperture 112 may be spaced apart from the edge of the partition 110 by a distance D2 that is less than half of the width D1 of the partition 110, and may be spaced apart from the edge of the partition by a distance D2 that is less than a quarter of the width D1 of the partition.

The illustrated partition 110 is a partition board. The partition may be formed from a thermally insulating material. The partition may be a plastic partition board, e.g. polyethylene. The illustrated partition 110 is 5mm thick. The partition 110 inhibits free mixing of liquids in the first and second chambers 102, 104, enabling liquids of different temperatures to be maintained within the first and second chambers.

In the illustrated thermal storage tank 100, the aperture 112 is provided with a one-way partition valve V0, for permitting fluid to flow from the first chamber 102 to the second chamber 104, and for preventing fluid flow from the second chamber 104 to the first chamber 102. The illustrated one-way partition valve V0 is a passive valve, which opens under fluid pressure from one side, and closes under fluid pressure from the opposite side. The illustrated partition valve V0 closes under its own weight when there is no fluid flow through the aperture 112, or it may be biased into a closed configuration (e.g. by closure spring, not shown). Alternatively, the one-way partition valve may be actively controlled, e.g. by the controller C.

The thermal storage tank 100 is provided with ports 120A, 120B, 120C for the inlet and outlet of fluid, in use, i.e. the second chamber 104 having one or more outlet ports 120A, and the first chamber 102 having one or more inlet and one or more outlet ports 120B, 120C. In use, the thermal storage tank 100 may contain a liquid L, e.g. water that may contain chemicals to reduce one or more of corrosion and deposition of limescale.

The thermal storage chamber 100 may be installed with the second chamber 104 above the first chamber 102. The illustrated thermal storage tank 100 is substantially cylindrical, with a circular cross-sectional shape parallel to the partition 110.

In the illustrated thermal storage chamber 100, the first chamber 102 has a dimension D3 of approximately 150mm perpendicular to the partition 110, and the second chamber 104 has a dimension D4 of approximately 1400mm perpendicular to the partition 110. A fill-restrictor (not shown) may limit the depth to which the second chamber 104 fills with liquid L, e.g. limits the depth to approximately 1100mm. The internal diameter D1 of the first and second chambers 102, 104 is approximately 1240mm.

In the illustrated thermal storage tank 100, the second chamber 104 has a volume that is at least twice the volume of the first chamber 102. For example, the second chamber 104 may have a volume that is at least three times the volume of the first chamber 102. The second chamber 104 may have a volume that is at least four times the volume of the first chamber 102. The second chamber 104 may have a volume that is at least five times the volume of the first chamber 102. The second chamber 104 may have a volume that is at least ten times the volume of the first chamber 102. The provision of the heat exchanger 130 within a first chamber 102, which has a significantly smaller than the second chamber 104, enables rapid heating of the smaller volume of hot water within the first chamber, e.g. for drawing-off to the potable water heat exchanger tank PWHX, for heating potable water to supply demand DEM for showering or hand-washing. Additionally, if the temperature of the water within the second chamber 104 is insufficient for space heating (spatial heating), water may also be drawn-off directly from the first chamber 102 to the space heater U for space heating.

The illustrated first chamber 102 is shallow, having a dimension D3 perpendicular to the partition 110 that is smaller than the diameter D1 of the first chamber, and may be less than half the diameter D1 of the first chamber. Having a smaller dimension D3 perpendicular to the partition 100 enhances the flow speed across the heat exchange coil 130 and mixing of fluid with the first chamber 102, when fluid is circulated through a coupled fluid circuit, and is input into the first chamber. Figure 2 illustrates a heat exchange coil 130 for use in the first chamber 102 of the thermal heat storage tank 100. The heat exchange coil 130 is formed from a tube substantially arranged in a flat spiral. An inlet and an outlet of the heat exchange coil 130 are coupled to (i.e. in fluid communication with) respective ports 120B, 120C of the first chamber 102.

Figure 3 illustrates a thermal storage system 150 in which the thermal storage tank 100 of Figure 1 is installed (e.g. in a building), coupled into respective fluid circuits with other elements, S, U, PWHX and HP for supplying or drawing-off heat from the thermal storage tank. Fluid flow through one or more of the fluid circuits may be controlled by a controller C (or by respective controllers).

The first chamber 102 of the thermal storage tank 100 is coupled in a fluid circuit to a solar thermal array S. When the temperature of fluid in the solar thermal array S is higher than the temperature of fluid in the first chamber 102, a pump (not shown) can circulate fluid out of an outlet port of the first chamber, through the solar thermal array, and back in through an inlet port of the first chamber.

The inlet and outlet ports of the first chamber 102, which are coupled to the same fluid circuit (e.g. the solar thermal array S), may be on opposed locations of the first chamber, to enhance fluid flow and fluid mixing with the first chamber. The outlet port(s) of the second chamber 104 are remotely located from the partition aperture 110, e.g. located diagonally across the chamber, on the opposite side from the aperture and spaced remotely from the partition.

The thermal storage tank 100 is coupled in a fluid circuit to an air source or ground source heat pump HP, and a respective valve V2.

When it is required to increase the fluid temperature in the first chamber 102 rapidly, the valve V2 switches for circulating fluid through an outlet of the first chamber 102, through the heat pump HP, and back in through an inlet port of the first chamber, e.g. substantially without flow of fluid through partition valve V0, which may remain closed. The heat pump HP may be operated to supplement heat being transferred into the first chamber 102 from the solar thermal array S, or when heat is not being transferred into the first chamber 102 from the solar thermal array (e.g. at night).

When it is required to transfer heat from the first chamber 102 to the second chamber 104, the heat pump valve V2 switches for circulating fluid through an outlet of the second chamber 102, through the heat pump HP, and back in through the inlet port of the first chamber, causing the partition valve VO to open, and for fluid to flow from the first chamber into the second chamber. The heat pump HP may pump the circulating fluid without heating it. Alternatively, the heat pump HP may additionally heat the circulating fluid.

The outlet of the second chamber 104, to which the heat pump HP is connected, is located remotely from the partition aperture 112, to enhance the mixing within the second chamber 104 of fluid entering the second chamber through the partition valve V0. For example, the outlet of the second chamber 104 to the heat pump HP may be on the opposite side of the second chamber from the partition valve V0.

The first chamber 102 of the thermal storage tank 100 is coupled to a further heat exchanger, in a potable water heat exchanger tank PWHX, for heating potable water. When demand DEM for heated potable water PW is sensed (e.g. by the controller C), a pump circulates fluid out of an outlet port of the first chamber 102, through the further heat exchanger in the potable water heat exchanger tank PWHX, and back into the first chamber through an inlet port of the first chamber.

The thermal storage tank 100 is coupled in a fluid circuit to a space heater U (e.g. underfloor domestic heating) and a respective space heater valve V1. When the fluid temperature in the second chamber 104 is relatively high, the space heater valve V1 is switched for a pump to circulate fluid out of the second chamber, through the space heater U, and back into the first chamber 102 through an inlet port. When the fluid temperature in the second chamber 104 is relatively low, the space heater valve V1 is switched for the pump to circulate fluid out of the first chamber 102, through the space heater U, and back into the first chamber 102 through an inlet port.

A controller C may control operation of pumps for circulating fluid through respective fluid circuits to one or more of the solar thermal array S, the potable water heat exchanger PWHX, the heat pump HP, and the space heater U. The controller C may control operation of one or both of the heat pump valve V2 and the space heater valve V2 in correspondence with the relative temperatures of the fluids in the first and second chambers 102, 104.

By way of examples, operation of the thermal storage system 150 is described for four particular modes of operation: In a first mode of operation, heat supplied by the solar thermal array S to the fluid circulated from an outlet of the first chamber 102, through the solar thermal array S and passed back into the first chamber 102, is less than or equal to the heat drawn off by one or both of the further heat exchanger in the potable water heat exchanger tank PWHX and the space heater U. The heat pump HP may be used as an auxiliary supplier of heat, with the heat pump valve V2 switched to circulate fluid from an outlet of the first chamber 102, through the heat pump HP and back in through an inlet of the first chamber. Because the volume of the first chamber 102 is substantially smaller than the combined volume of the thermal storage tank 100, the thermal storage system 150 can respond to the user’s demands more rapidly and efficiently than for a single chamber thermal storage tank with the combined volume. For example, for the illustrated thermal storage tank 100 with the dimensions described previously, the fluid temperature within the first chamber 102 may increase from 35°C to 55°C in approximately two or three minutes, when heat is transferred from a commonly sized domestic solar array S receiving solar radiation at a rate of 500W/m ² .

In a second mode of operation, heat supplied by the solar thermal array S to the fluid circulated from an outlet of the first chamber 102, through the solar thermal array, and passed back into the first chamber, is greater than the heat drawn off by a user. To enable heat to be transferred to the fluid within the second chamber 104, the circulation pump of the heat pump HP is operated to draw fluid out of an outlet of the second chamber 104, and return it back into an inlet of the first chamber 102, causing hotter fluid to flow from the first chamber to the second chamber, through the partition valve V0.

In a third mode of operation, heat may be stored in the thermal storage system 150 by operation of the heat pump HP (e.g. using low priced electricity, such as overnight) to circulate fluid from an outlet of the second chamber 104, through the heat pump, and back in to the first chamber 102, causing hotter fluid to flow from the first chamber to the second chamber, through the partition valve V0.

In a fourth mode of operation, when the fluid temperature in the second chamber 104 is relatively high, space heating can be provided by circulating fluid from an outlet of the second chamber, through the space heater U, and back into an inlet of the first chamber 102.

The fluid (e.g. liquid) within the thermal storage system may be substantially water, e.g. with one or more of anticorrosion additives and antifreeze. The figures provided herein are schematic and not to scale.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.