The present invention relates to a complete integrated heating system for heating of residential buildings and, potentially, domestic hot water therefore.

Background of the invention

During the last decades, the focus on developing energy- efficient systems for heating and cooling of buildings has been constantly increasing and new heat energy sources, such as solar heating and geothermal heating, have been introduced. Even though these new sources have gradually reached a certain level of "maturity", typical heating systems known in the art still exhibit certain difficulties when it comes to integrating the different heat energy sources in common system in a truly energy- efficient and intelligent way.

Brief description of the invention

It is an object of the present invention to provide an integrated heating system, which overcomes the above-mentioned disadvantage of solutions known in the art.

The present invention relates to a heating system comprising a heat source, such as a heat pump, and an inner tank, which inner tank is arranged within an outer tank, wherein the inner tank comprises a Phase Change Material (PCM) in direct physical contact with a secondary heat-transferring medium and a diffuser unit arranged beneath the PCM, through which diffuser unit the secondary heat-transferring medium is brought into contact with the PCM, wherein the inner tank is surrounded by a fluid, preferably water, within the outer tank, which fluid can be brought into fluid connection with a fluid-based heating system, for instance a central heating system of a building, and wherein the heat source is arranged to circulate a primary heat-transferring medium, such as a hotgas, through the outer tank for supplying heat energy to the heating system, and a circulation pump is arranged to pump the secondary heat-transferring medium from above the PCM within the inner tank passing through the outer tank to the diffuser unit at the bottom of the inner tank, the piping for the circulating primary heat-transferring medium and the piping for the secondary heat-transferring medium within the outer tank being arranged in close vicinity to each other to allow heat energy to be exchanged between the primary heat-transferring medium and the secondary heat-transferring medium.

A heating system configured like this ensures an optimised heat exchange between the primary heat-transferring medium and the secondary heat-transferring medium in the outer tank due to the close vicinity of the relevant piping and between the secondary heat-transferring medium and the PCM in the inner tank due to the use of "Direct Heat Transfer" through the direct physical contact between the secondary heat-transferring medium and the PCM. In an embodiment of the invention, the diffuser unit comprises a perforated plate through the perforations of which the secondary heat-transferring medium is arranged to penetrate the PCM from the bottom and upwards.

The use of such a diffuser unit ensures an equally distributed and effective penetration of the PCM by the secondary heat-transferring medium.

In an embodiment of the invention, the perforated plate is a metal plate with at least 1000, preferably at least 5000, perforations, with diameters in the range from 1 mm to 5 mm, preferably around 2 mm.

The use of this number and dimensions of the perforations ensures and efficient penetration of the PCM by the secondary heat-transferring medium and prevents small flakes of solidified PCM from ending up under the perforated plate. In an embodiment of the invention, the PCM is sodium acetate trihydrate or another salt with similar latent heat properties. Sodium acetate trihydrate has proven to have latent heat properties very well suited for this purpose. In an embodiment of the invention, the secondary heat-transferring medium is a thermal oil.

In an embodiment of the invention, the heating system comprises a primary heat- transferring medium spiral pipe arranged around the inner tank for circulation of the primary heat-transferring medium within the outer tank, which primary heat- transferring medium spiral pipe is arranged within another spiral pipe with larger diameter, through which other spiral pipe the secondary heat-transferring medium flows on its way from the circulation pump to the diffuser unit, preferably in the opposite direction of the flow of the primary heat-transferring medium.

Letting the primary heat-transferring medium flow in a pipe within another pipe, in which the secondary heat-transferring medium flows in the opposite direction optimises the heat exchange between the two mediums. In an embodiment of the invention, the heating system comprises one or more primary heat-transferring medium spiral pipes arranged around the inner tank for circulation of the primary heat-transferring medium within the outer tank, which one or more primary heat-transferring medium spiral pipes are arranged within a casing around the inner tank, through which casing the secondary heat-transferring medium flows on its way from the circulation pump to the diffuser unit, preferably in the opposite direction of the flow of the primary heat-transferring medium.

The use of a casing around the inner tank for the secondary heat-transferring medium allows for splitting the circulation of primary heat-transferring medium within the outer tank into more than one spiral pipe, thereby reducing the pressure drop along the spiral pipes. In an embodiment of the invention, the primary heat-transferring medium flows through the primary heat-transferring medium spiral pipe in a downward direction, whereas the secondary heat-transferring medium flows through the other spiral pipe or the casing in an upward direction.

This configuration optimises the heat exchange, because the heat energy is transferred from the hotter primary heat-transferring medium to the cooler secondary heat-transferring medium.

In an embodiment of the invention, the inner tank is pressurised and further comprises a gas, preferably C0 ₂ or N ₂ , and is provided with a safety valve for letting out gas if the pressure within the inner tank exceeds a predefined limit and with a pressure gauge for measuring the pressure of the gas within the inner tank.

This means that the charge level of the heat storage can be estimated very accurately simply by measuring the pressure within the inner tank.

In an embodiment of the invention, the heating system further comprises a service pipe for giving access to the internal parts of the inner tank and means for plugging the service pipe hermetically during operation of the system.

This enables, for instance, for taking samples of the PCM within the inner tank, when the heating system is not in operation.

In an embodiment of the invention, the heating system further comprises a controller, which is connected, for instance wirelessly via the internet, to a central server, which central server is arranged to monitor and control one or more such heating systems in such a way that the heat production of each of the one or more such heating systems is optimised with respect to economic operation of the heating system. In an embodiment of the invention, when planning the heat production of a given heating system, the central server is arranged to take into consideration one or more of the following parameters:

~ vital operational data from the given heating system reported to the central server from the controller of that heating system

» information from electricity networks about actual loads and electricity prices ~ meteorological information such as local weather forecasts for the location of the given heating system

~ registered consumption patterns of the given heating system.

The use of such a controller connected to a central server makes it possible to obtain an optimised heat production and operation of the heating system.

The drawings

In the following, a few exemplary embodiments of the invention are described in further detail with reference to the drawings, of which

Fig. 1 is a schematic diagram of the general configuration of a heating system according to an embodiment of the invention,

Fig. 2 is a cross-sectional view of the tanks and piping of a heating system according to a first embodiment of the invention, and

Fig. 3 is a cross-sectional view of the tanks and piping of a heating system according to a second embodiment of the invention. Detailed description of the invention

Fig. 1 is a schematic diagram of the general configuration of a heating system 1 according to an embodiment of the invention. It illustrates how the heating system 1 basically consists of an inner tank 2 arranged within an outer tank 3, a circulation pump 7, a diffuser unit 11, a heat pump 12 and some piping.

The inner tank 2 comprises a Phase Change Material (PCM) 19, which is not shown in this figure. In preferred embodiments of the invention, the PCM 19 is sodium acetate trihydrate, which is a salt having its melting point at 58° C. In the melting process, this salt accumulates large amounts of thermal energy, which is gradually released again as the salt solidifies. Thus, the salt works as a heat storage, in which heat energy is stored when the salt melts and "withdrawn" when the salt solidifies. Three fluids circulate in the heating system 1, namely a primary heat-transferring medium, a secondary heat-transferring medium and a fluid surrounding the inner tank 2.

The circulation of the secondary heat-transferring medium, which in this case is a thermal oil 20, is controlled by the circulation pump 7. The thermal oil 20 is sucked from above the PCM within the inner tank 2 through a thermal oil suction pipe 6 and forwarded under pressure through a thermal oil pressurised pipe 8 to the bottom of the outer tank 3. This thermal oil pressurised pipe 8 is shown outside the outer tank 3 in Fig. 1, but it can pass through the outer tank 3 or the inner tank 2 on its way to the bottom of the outer tank 3 as can be seen in the embodiments illustrated in Figs. 2 and 3, which are described below.

From the bottom of the outer tank 3, the thermal oil 20 moves upward around the inner tank 2, for instance through a thermal oil spiral pipe 9 as illustrated in Figs. 1 and 2 or through a thermal oil casing 23 as illustrated in Fig. 3. Having reached its uppermost point after this upward motion, the thermal oil 20 is lead down to the diffuser unit 11 at the bottom of the inner tank 2 through a thermal oil diffuser pipe 10. In Fig. 1, this thermal oil diffuser pipe 10 is drawn inside the outer tank, but in other embodiments, such as the ones illustrated in Figs. 2 and 3, it passes through the inner tank 2 down to the diffuser unit 11.

In preferred embodiments of the invention, the main part of this diffuser unit 11 is a micro-perforated plate, typically a metal plate perforated with a large number of perforations with diameters in the range from 1 mm to 5 mm. The micro-perforated plate ensures that the thermal oil 20 under it is equally distributed across the bottom of inner tank 2, from where it penetrates the PCM 19 through the perforations from the bottom and upwards back to the original position on top of PCM 19. The direct physical contact between the thermal oil 20 and the PCM 19 ensures an optimal heat transfer between the two substances.

The perforations of the diffuser unit 11 also function as a sieve ensuring that small flakes of solidified PCM 19 do not end up under the micro-perforated plate if the thermal oil 2 is pressed back through the micro-perforated plate due to the higher density of the PCM 19. Such flakes of PCM 19 under the micro-perforated plate would be disruptive for the equal distribution of thermal oil 20.

A reason for choosing a thermal oil 20 as the secondary heat-transferring medium is that sodium acetate trihydrate is soluble in water. Thus, if the PCM 19 is diluted with water, its latent heat capacity will be reduced significantly.

The "heat battery" formed by the PCM 19 is "charged" by the heat pump 12, which circulates the primary heat-transferring medium, typically a hotgas, through a hotgas inlet pipe 13, downwards through a hotgas spiral pipe 14 arranged within the outer tank 3 around the inner tank 2 and back to the heat pump 12 through a hotgas outlet pipe 14. On its way down through the hotgas spiral pipe 14, which is in close contact with the thermal oil 20 moving upwards through the outer tank 3 as described above, heat energy from the hot circulated hotgas is transferred to the cooler thermal oil 20. Also, some heat energy is transferred from the hotgas spiral pipe 14 to the fluid surrounding the inner tank 2 and to the inner tank 2 through radiation. When the thermal oil 20 has been heated, preferably to a temperature 3-5 °C above the melting point of the PCM 19, it is pumped to the diffuser unit 11 below the PCM 19. Due to the lower density of the thermal oil 20 than of the PCM 19, the thermal oil 20 will ascend through the PCM 19 and heat energy will be transferred from the thermal oil 20 to the cooler PCM 19 as the thermal oil 20 passes through. When the PCM 19 reaches its melting temperature, it will absorb large amounts of heat energy and melt. The thermal oil 20 reaching the top of the PCM layer 19 can then be sucked up by the circulation pump 7 and the process can be repeated.

The third fluid circulating in the heating system 1 is the fluid surrounding the inner tank 2 within the outer tank 3. Typically, this fluid is central heating water, which can be in fluid communication with a central heating system through a hot water forward pipe 4 and a cold-water return pipe 5.

The "heat battery" is "discharged" by drawing off hot water from the top of the outer tank 3 through the hot water forward pipe 4 and returning colder water to the bottom of the outer tank 3 through the cold water return pipe 5, the water having given off some of its heat energy on its way through a central heating unit (not shown) or the like. The cold water entering the outer tank 3 at the bottom thereof receives heat energy from the outer surface of the inner tank 2 and ascends towards the top of the outer tank 3 (so-called stratification).

In this case, heat energy is drawn from the PCM 19 in the inner tank 2, because the thermal oil 20 passing through the diffuser unit 11 and the PCM 19 will have been cooled down by the colder water in the outer tank 3, typically to a temperature below the temperature of the PCM 19. Thus, on its way up through the PCM 19, the thermal oil 20 receives heat energy from the PCM 19, which energy in turn will be transferred to the water in the outer tank 3 during the next passing thereof by the thermal oil.

The use of the latent heat of fusion from a PCM 19, such as sodium acetate trihydrate, makes it possible to obtain a very large heat storage capacity within a limited physical volume. Thus, a typical heating system 1 according to the present invention can deliver the necessary heat energy for the central heating system of a building (radiators, floor heating and/or caloriferes) as well as for domestic hot water at 50° C for a normal private household.

Figs. 2 and 3 are cross-sectional views of the tanks and piping of a heating system 1 according to a first and a second specific embodiment of the invention, respectively.

Both of the figures show how the thermal oil pressurised pipe 8 from the circulation pump 7 (not shown om these figures) to the bottom of the outer tank 3 and the thermal oil diffuser pipe 10 leading the thermal oil 20 down to the diffuser unit 11 both extend through the inner tank 2.

In both of these two embodiments, the inner tank 2 is pressurised and comprises an amount of pressurised gas 21, preferably C0 ₂ or N ₂ , forming a third layer above the PCM 19 and the thermal oil 20 on top thereof. A safety valve (not shown) ensures that gas 21 is let out of the heating system if the pressure therein exceeds a predefined limit. Furthermore, a pressure gauge (not shown) is provided for measuring the pressure of the gas 21 within the inner tank 2.

When the PCM 19 is heated, its volume expands and, vice versa, when the PCM 19 is cooled, its volume reduces. Thus, when the heating system 1 is fully "charged" with heat energy for the first time, gas will be forced out through the safety valve until the expansion of the volume of the PCM 19 ends, and the pressure inside the inner tank 2 will equal the pressure limit of the safety valve, for instance 1 bar. If the heating system 1 is subsequently completely "discharged", the pressure inside the inner tank 2 corresponding to this situation can be measured using the pressure gauge. Experiments have shown that there is an almost linear correlation between the "charge level" of the heating system 1 and the pressure within the inner tank 2. Thus, knowing the pressures corresponding to "fully charged" and "completely

discharged", respectively, the actual "charge level" can easily be estimated by simply reading the pressure gauge.

Also, both of these two embodiments comprise a service pipe 22 arranged at the top of the heating system 1, through which service pipe 22 access can be obtained to the inside of the inner tank 2 when the heating system 1 is not in operation, for instance for taking test samples of the PCM 19.

The difference between the two embodiments shown in Figs. 2 and 3, respectively, is to be found in the outer tank 3 outside the inner tank 2. In the embodiment shown in Fig. 2, the hotgas spiral pipe 14, in which hotgas flows downwards through the outer tank 3, is arranged within a thermal oil spiral pipe 9 with larger diameter, in which the thermal oil 20 flows upwards, i.e. in the opposite direction. This configuration constitutes a very efficient heat exchanger for transferring heat energy between the two substances.

In Fig. 3, on the other hand, the thermal oil spiral pipe 9 has been replaced by a thermal oil casing 23, in which the thermal oil 20 flows upwards through the outer tank 3 and around the inner tank 2. This allows for a split of the hotgas spiral pipe 14 into more branches. In Fig. 3, an upper connection part 24 splits up the flow of hotgas from the hotgas inlet pipe 13 into two hotgas spiral pipes 14 at the top of the thermal oil casing 23, whereas a lower connection part 25 collects the flow of hotgas from these two hotgas spiral pipes 14 into a common flow leaving the outer tank 3 through a hotgas outlet pipe 15 after having circulated a few times in a sub-cooler spiral 16 around the lowermost part of the inner tank 2. The use of more than one hotgas spiral pipe 14, reduces the pressure drop along the hotgas spiral pipes 14 and, thus, the pressure resistance seen into by the heat pump 12. A Smart Grid Controller can be connected to a central server via the internet for controlling the heating system 1. Thus, it can be ensured that heat energy is produced under optimal meteorological and economic conditions and with the highest possible Coefficient of Performance (COP) taking into account the consumption levels and patterns of the house.

The controller collects all vital operational data from the heating system 1 and reports to the central server, from where the operation of a large number of installed heating systems 1 can be monitored and controlled. The central server is also arranged to collect information from electricity networks about actual loads and electricity prices as well as meteorological information such as local weather forecasts. Furthermore, the central server is arranged to adapt to the different consumers' individual consumption patterns taking the weekly cycle into consideration when planning the heat production of the individual heating systems 1 monitored and controlled by the server. Being dependent on internet access, the controller is equipped with an internet connection (for instance Ethernet, WiFi or 3G). In case the controller loses the connection to the central server, a thermostatic control will take over and ensure that the consumer does not experience any lack of heat or hot water. Thus, the heating system 1 according to the present invention constitutes a complete integrated heating system 1 for heating and, potentially, domestic hot water of residential buildings. The system is especially developed in order to offer a direct substitution for oil, gas or pellet furnaces in the older part of the housing stock. However, the system is also suitable for substitution of other heat sources and in modern buildings. List of reference numbers

1. Heating system

2. Inner tank

3. Outer tank

4. Hot water forward pipe

5. Cold water return pipe

6. Thermal oil suction pipe

7. Circulation pump

8. Thermal oil pressurised pipe

9. Thermal oil spiral pipe

10. Thermal oil diffuser pipe

1 1. Diffuser unit

12. Heat pump

13. Hotgas inlet pipe

14. Hotgas spiral pipe

15. Hotgas outlet pipe

16. Sub-cooler spiral

77. Not used

18. Not used

19. Phase change material

20. Thermal Oil

21. Pressurised gas

22. Service pipe

23. Thermal oil casing

24. Upper connection part for hotgas spiral pipes

25. Lower connection part for hotgas spiral pipes