NO326274B1 - Energy utilization system and method - Google Patents

Abstract

A system for utilization of renewable energy resources and / or energy recovery comprising a water heater (1) and a heat pump (2). The heat pump is designed to transfer heat and / or provide cooling to water in the water heater (1). The hot water heater comprises at least two tanks (3, 4) for the thermal storage of hot water and / or cold water and / or ice, which tanks (3, 4) are thermally insulated from each other, a first tank (4) having an inlet for cold water and is in fluid communication with a second tank (3) and the second tank (3) has an outlet for hot water. The first tank (4) is in heat exchanger relationship with the heat pump (2) at a first heat exchanger (10) having a first temperature level. The second tank (3) is in heat exchanger relationship with the heat pump (2) at a second heat exchanger (11) having a second temperature level, which is higher than the first temperature level.

Description

The present invention relates to a system for the utilization of renewable energy resources and/or recovery of energy comprising a multifunctional unit, which includes a water heater and a heat pump, the heat pump being designed to transfer heat and/or provide cooling to water in the water heater.

In recent years, heat pumps, and especially liquid-to-liquid heat pumps, have achieved a strong improvement in efficiency. It has also become common to connect the heat pump together with the system for supplying hot water for consumption. With regard to the latter, reference should be made to the following prior art: DE 2815974 describes a system in which a heat pump is used both to provide cooling to a cooling unit and heat to a hot water tank. Here, the coolant flow to the heat pump is led through an evaporator in the cooling unit and then through a condenser in the hot water tank. In this way, the heat absorbed by the refrigerant in the evaporator will be transferred to the hot water in the hot water tank.

This solution assumes that there is a need for both cooling and heating at all times. If you do not have a cooling system where heat can be extracted, this solution will be completely useless. In addition, the valuable overheating heat will not be used here, as all the heat from the heat pump is taken out in one place. It is therefore limited how hot one succeeds in getting the hot tap water.

NO 313062 describes a hot water tank which is connected to a heat exchanger. Water circulates from the lower part of the tank through the heat exchanger and back again to the tank a short distance above the outlet. Thereby, this water is heated to a temperature of around 40 °C. This water is further heated by means of an electric heating flask and circulates in the central part of the tank. A heat exchanger is located here, which extracts heat for heating the building. In the upper part of the tank, there is a further electric heating flask, which heats the water here to a sufficient temperature for consumption water.

It has been shown that this solution is not optimal. Even if a higher degree of efficiency is achieved, it has proven difficult to get the water in the hot water tank to circulate in its assigned zones in the tank. Attempts have been made to insert an insulating plate that would float in the separation between the two temperature zones in the tank, but this proved to be impossible to achieve.

JP 2003056905 describes a system for producing both hot tap water and water for heating. A heat pump and a storage tank for hot water are used here. This tank is in communication with an additional tank and supplies this additional tank with hot water. From the additional tank, hot water can be circulated to a yellow heating system.

Although two separate tanks are used here, the additional tank supplies both hot tap water and heat for heating. Since tap water has a significantly higher temperature than water for heating, this is not an optimal solution.

Heat pumps depend on an accumulator or buffer tank to achieve smooth operation. In order for the compressor to have a sufficient service life and to achieve the best efficiency possible, the temperature difference between the cooling/heating medium and the water in the tank should be as low as possible. The new CO2 heat pumps make this even more important, as the temperature difference between incoming and outgoing water is decisive for the operating result.

Other known solutions are described in US 4633676, US 2382368, EP 0240441, US 4364239 and GB 2064755.

According to the invention, a system for the utilization of renewable energy resources is achieved by a unit comprising at least two thermally insulated tanks for the thermal storage of hot water and/or cold water and/or ice, which tanks are also thermally insulated from each other, that the first of the tanks has a first heat exchanger that is in heat exchanger relationship with a second heat exchanger in a superheat unit in the heat pump, for heating water in the tank to a first high temperature level, that the second of the tanks has a third heat exchanger that is in heat exchanger relationship with a fourth heat exchanger in connection with a condenser in the heat pump, which is arranged to heat water in the second tank to a second temperature level lower than the first temperature level, or to cool or freeze water in the second tank and that the tanks have a supply of fresh water which is independent of the circuits comprising a first, second, third and fourth heat exchanger. Thereby, in a first operating mode, the first tank can be used to preheat water to be transferred to the second tank and in a second operating mode, the first tank can be used to provide cooling, while the second tank is used for heating hot tap water. This happens without there being any significant risk of dressing liquid contaminating the water in the first tank. Thereby, the water in the first tank can be used for hot tap water without further ado, for example for showering, washing up etc.

By having the first tank in liquid communication with the second tank so that partially heated water from the second tank can be transferred to the first tank for further heating, an efficient two-stage heating of hot water that can be used for tap water is achieved.

If the communication line between the first and the second tank is equipped with a shut-off valve and that each of the tanks includes separate inlets and outlets, so that they can function independently of each other, the tanks will easily be used for different purposes, for example one tank for hot water and one tank for cold water.

Preferably, the first tank is arranged to store hot tap water.

If the hot tap water is kept separate from the water that circulates in a building's heating or cooling circuit, the risk of contaminating the tap water with bacteria that might flourish in the heating or cooling circuit is reduced.

By the fact that the first tank's heat exchanger is arranged to receive hot or cold liquid from the heat pump and the heat exchanger is further connected to a heating/cooling system for heating or cooling a building, an efficient system for distributing heat/cooling is provided.

If the tanks are equipped with electric heating flasks for reheating water or a backup heat source, you will also be able to have hot water available at high consumption or at times when the heat pump is not efficient enough.

If the second tank is connected to a heating/cooling system for heating or cooling a building, the system can be used both for heating tap water and heating or cooling a building. Good energy utilization is thereby achieved.

By placing the first and second tanks in a common casing, a compact unit is provided which contains all central functions.

In a further embodiment, the system comprises an outlet from the second tank, for draining water, in particular for draining chilled drinking water. Thereby, cold drinking water can be provided in an energy-efficient way.

By having the water heater in a heat exchange relationship with waste water, especially gray water, possibly via a third tank that is in liquid communication with one of the water heater's other tanks, it will be possible to recover heat that would otherwise be wasted.

In a further embodiment, the system comprises a heat exchanger for heat transfer from waste water, especially gray water, to the external circuit of the heat pump. In this way, heat that would otherwise go to waste can also be recovered and possibly accumulated.

By the fact that the second tank contains liquid, for example water, and is arranged to provide cooling to the liquid for the accumulation of ice and/or chilled liquid, it becomes possible to accumulate ice or ice water which can function as a cold store.

In its simplest embodiment, the present invention comprises a two-part heating/cooling buffer or accumulator tank. In what follows, this will be called multicentre. The multi-central is necessary to achieve optimal operating efficiency for a heat pump. The heat pump can extract energy from air or water and transfer it to water. The multi-central unit is designed to supply the building, residential or commercial building, with heat and hot water and possibly with cooling and hot water, by the room thermostat automatically calling for heat or cold via the heat pump. In cooling mode, the multi-central unit can also provide chilled drinking water.

The invention will now be explained in more detail with reference to the accompanying figures, where: Figure 1 schematically shows the principles of the system according to the present invention,

Figure 2 shows details of the heat pump in Figure 1,

Figure 3 shows a combined heating, cooling system and heat recovery from waste water according to an alternative embodiment of the invention and Figure 4 shows yet another embodiment of the invention, where heat in waste water is recovered via the heat pump's primary circuit. Figure 5 shows a diagram of air temperature and borehole temperature during a year and

Figure 6 shows a Mollier diagram of a heat pump.

Figure 1 schematically shows a heat storage system according to the invention, comprising a multi-central 1 which includes a water heater and a heat pump 2. The multi-central 1 is equipped with two tanks, an upper tank 3 and a lower tank 4. The tanks 3 and 4 are insulated both from the surroundings and against each other.

Cold water is supplied to the lower part of the lower tank 4 through a cold water inlet 5. From the upper part of the lower tank 4, water can flow on to the lower part of the upper tank 3 via a transfer run 6. From the run 6 there is a branch 7 equipped with a shut-off valve 8 for draining chilled drinking water, as will be explained in more detail below. There is also a pipe 22 which connects the upper tank 3 with the cold water supply.

From the upper part of the upper tank 3 there is a hot water outlet 9.

In each of the tanks 3 and 4 there is arranged a heat exchanger 10 h.h.v. 11. The lower heat exchanger 10 is via an upper inlet 12 in connection with the heat pump 2 and via a lower outlet 13 in connection with a floor heating pipe 14.1 instead of or in addition to yellow heating pipe 14, you can also use so-called fan coils 21 (radiator with built-in fan) for heating or cooling the building. The heat exchanger in this case is an air to liquid heat exchanger. It can be configured to extract heat from exhaust air flowing out of the building.

The upper heat exchanger 11 is connected to the heat pump 2 via an upper inlet 15 and a lower outlet 16.

Multisentralen 1 is also equipped with an electric heating flask 19,20 in each of the tanks. These can be used as additional energy supply or as backup heating should the heat pump fail.

Reference should now be made to Figure 2, which shows the principles of a heat pump according to the present invention. The circuit that includes underfloor heating and fan coils is omitted in this figure, but can of course be present.

The heat pump 2 has secondary circuits. The first circuit is a superheating circuit which comprises a unit 17, which extracts an amount of energy from hot steam and lowers its temperature. From this unit, water (or any other suitable liquid which can transport heat energy) circulates through the heat exchanger 11. The second circuit is a heating circuit comprising a condenser 18, in which the steam condenses. From here, water circulates through the heat exchanger 10. The heat pump further comprises a compressor 22, which compresses hot steam. Furthermore, it comprises an evaporator 23, which extracts thermal energy from either a borehole 35 or air (represented by arrow 24). The heat pump thus comprises two primary circuits: a first primary circuit which is designed to collect thermal energy from air and a second primary circuit which is designed to collect thermal energy from the ground or possibly from water. A control device is connected to the heat pump which determines which of the two primary circuits will supply energy to the secondary circuits based on temperature measurements in the ground/water and air. The rest of the heat pump's structure is, in and of itself, well known to a specialist in the field and is therefore not to be explained in more detail here. However, with the heat pump, efforts have been made to reduce the filling amount of heating/cooling medium, for example CO2, as much as possible. Therefore, this is only used in the circuits in the central unit 2 itself, but a mixture of water and alcohol is used for the transfer of heat/cold to boreholes, the water heater, underfloor heating etc. This saves the environment from burdens should a leak occur.

The operation of the system in Figures 1 and 2 will now be explained. As mentioned, the multi-central 1 has a lower stainless pressure tank 4 with a stainless heat exchanger 10, which either preheats the cold water or cools it depending on the heat pump 2's setting. From the heat exchanger 10, the circuit 13 is continued to the yellow heater tubes 15 (or convectors) for heating or cooling needs, respectively. In cooling mode, chilled drinking water is also produced from the tap 8.

The upper pressure tank 3 with reheat exchanger 11 from the heat pump's superheating circuit 17 provides such a high hot water temperature that electrical reheating is not necessary.

As there are two tanks that are completely isolated from each other, both heat and hot tap water, or cooling and hot tap water, can be accumulated in the multi-central.

In a specific operating mode, cold water with a temperature of approx. 10 °C flow in through the cold water inlet 5 from the water supply network. Water with a temperature of around 48 °C from the heat pump's condenser 18 is circulated through the heat exchanger 10 and heats the cold water in the lower tank 4 to a temperature of approx. 45 °C. The water from the heat pump 2 is further circulated out of the heat exchanger 10 to a yellow heating pipe 14. The heating liquid now maintains a temperature of between 25 and 35 °C, which is an ideal temperature range for underfloor heating. Appropriately, a conventional temperature regulator and thermostat is connected to the yellow heating pipe, so that the temperature in the building can be regulated and set to the desired temperature.

The heating liquid flows back to the heat pump and is reheated to approx. 48 °C.

The water in the lower tank 4 will, as hot water is drawn from the upper tank 3,

flow as preheated cold water through the transfer chute 6 and into the upper tank 3. Here the water will be reheated by the heat exchanger 11. The heat exchanger is supplied with water from the superheating circuit 17 to the heat pump 2 with a temperature of approx. 90 °C. Finally, hot tap water with a temperature of between 60 and 80 °C can be drawn out through the hot water outlet 9. The total temperature difference of between 60 and 80 °C is very favorable for the efficiency of, among other things, a CO2 heat pump.

If there is a need for cooling (especially in summer, but also for larger buildings with a large total heat production), the heat pump can be reversed, so that cold liquid is circulated through the heat exchanger 10 and further into the underfloor heating system 14 to cool the rooms. Thereby, the cold water in the lower tank 4 will be cooled. Via branch 7, this water can be drained off as cold drinking water.

The heat energy extracted from the water in the cooled lower tank 4 will be able to be used in the heat pump to heat the water supplied to the heat exchanger 11. The heat exchanger 11 will thus still be supplied with hot water from the heat pump 2's superheating circuit 17, as in the case above, and the hot water in the upper tank 3 is heated approximately as much as in the first case above.

Furthermore, it is also possible (especially in countries with a large cooling demand) to use the lower tank 4 for the accumulation of ice. In this case, it will be appropriate to supply the upper tank 3 with cold water directly from the network via the pipe 22 instead of from the lower tank 4.1 areas where you can buy cheap electricity at night, it will thus be possible to accumulate ice in the lower tank 4 if at night and extract cooling from this during the day. A quantity of 100-150 liters of ice will correspond to a power consumption of 70-80 kWh, which will be enough to cool a home for 12-14 hours. Furthermore, due to lower outside temperature at night, it will be easier to get rid of excess heat, which must then be led out via the evaporator 23.1 hot areas, the cooling requirement will be so great that you will get excess heat anyway and thereby get plenty of hot water in the tank 3.

Figure 6 shows a simple Mollier diagram of a heat pump, where the numbers in circles correspond to corresponding numbers in Figures 1 and 2. The number 1 represents the energy extraction from the ground or air. The number 3 is withdrawal of high-quality overheating heat. The number 2 is the withdrawal of heat from the condenser 18. The number 4 is the sum of the heat from the overheating circuit 17 and the condenser 18. Curve 45 is the vapor pressure curve for the heating medium. Thermal energy is supplied to the heating medium along line 40 so that the temperature and thus the energy increases. At the same time, the heating medium evaporates under constant pressure. The gas is then compressed along line 41. This increases the pressure. At the same time, the temperature also increases somewhat. The gas is now superheated. In the first part of the line 42, until the line 42 hits the vapor pressure line 45, the superheating heat is extracted from the gas in the superheating circuit 17. After the line 42 has passed the curve 45, the condenser 18 will extract most of the heat. To the left of curve 45, the heating medium will be subcooled liquid, which then expands under approximately constant pressure along line 43 until the liquid begins to evaporate.

By controlling the heat pump's energy output alternately between the air and the ground/water, you will always be able to obtain energy from where it is most obtainable. Figure 5 shows a diagram of daily average air temperatures (curve L) over a typical one-year cycle somewhere in Norway. The figure also shows a curve of the temperature in a borehole (curve B) which is used for energy extraction for a heat pump. As you can see from this, the temperature in the borehole drops rapidly throughout the autumn and around New Year it drops below zero. The energy output from the borehole is then significantly reduced. This coincides with the coldest time of the year. The temperature in the borehole does not go above zero again until early summer.

Curve B' shows the temperature in the borehole when this is connected to a heat pump that alternates between extracting energy from air and boreholes. When the temperature in the air is above a predetermined value, all energy extraction will take place from the air. The air temperature will drop throughout the autumn, but will still largely remain above this value. You will therefore not extract significant amounts of energy from the ground. When the temperature in the air drops below the predetermined value (in Figure 5 this happens in December), energy will instead be extracted from the borehole. The temperature in the borehole will then start to drop. Throughout the winter, the heat exchanger will alternately extract energy from air and boreholes depending on the temperature. Thereby, the temperature in the borehole will constantly stay above the temperature in the borehole for case B with only withdrawals from boreholes and will only fall below zero for short periods of time. In this way, the efficiency of the heat pump will be increased significantly compared to heat pumps that only use one energy source.

The predetermined value at which one switches from extracting energy from air to borehole or vice versa will in a simple embodiment of the invention be a non-constant value. However, it is more appropriate that the value is made dependent on the difference in temperature between air and borehole, but also take into account the time of year, i.e. date and local conditions.

An example of criteria for determining which energy source is to be used: If the air temperature is higher in the air than in the borehole, the air will be used as the energy source. If the temperature in the air is lower than in the borehole, the control system will check the date (for example the month) and look up a table showing how much lower than the borehole temperature the air temperature can be allowed to be. This table is adapted to the local conditions, but in principle it is laid out as follows: When you approach the cold season, you will try to save energy in the borehole. Energy will therefore be extracted from the air even if the temperature in the air is somewhat lower than in the borehole. The table thus indicates how big the temperature difference must be before moving on to extracting energy from the borehole. When you have passed a selected date in the cold season, you will start extracting energy from the borehole as long as the temperature is above the temperature of the air. It is then expected that the energy in the borehole will be high enough to last through the cold season.

In this way, you will avoid lowering the temperature in the borehole to a temperature that gives little energy yield during the cold season.

Figure 3 shows a further embodiment of the invention. Here, the water heater 1 has three tanks 3, 4 and 30 which are thermally isolated from each other. The tanks are connected to each other via transfer pipes 6, 31. The bottom tank 30 is supplied with cold water from the cold water network via a cold water inlet 33 and is equipped with a heat exchanger 32, which is supplied with waste water (so-called gray water) with a temperature which will naturally vary but which will always be above the cold water temperature. Thereby, the cold water is preheated in a first step.

The two other tanks in the water heater function in the same way as in the embodiment in Figure 1 and therefore do not need to be described further.

Figure 4 shows yet another embodiment of the invention. This includes a water heater 1 and a heat pump 2. These units function largely as explained in connection with Figure 1 and therefore do not need to be described in more detail. In addition, the system has a heat exchanger 33 for waste water. The heat exchanger is placed inside a buffer tank 34 for the heat pump's 2 cooling/heating medium. The cooling/heating medium is led through the buffer tank 34 and down into a borehole 35. With the help of this system, heat can be extracted from the waste water in the summer and stored in the borehole 35. At the start of the cold period in winter, the ground around the borehole 35 will thus have a somewhat higher temperature than would otherwise be the case and the heat can thereby be extracted again using the heat pump. In winter, the waste water will also make a positive contribution to heat supply.

Although it is an advantage to assemble the tanks together in one unit, as shown in the figures, it is of course also possible to realize the invention with tanks which are arranged in separate units, but which are functionally linked together. However, the tanks should be placed in terms of height so that the tank for the hottest water is higher than the tank for the coldest water.

Claims (12)

1. System for the utilization of renewable energy resources and/or recovery of energy, comprising a multifunctional unit, which includes a water heater (1) and a heat pump (2), the heat pump being arranged to transfer heat and/or provide cooling to water in the water heater ( 1), characterized in that the unit comprises at least two thermally insulated tanks (3, 4) for thermal storage of hot water and/or cold water and/or ice, which tanks (3, 4) are also thermally insulated from each other, that the first of the tanks (3) have a first heat exchanger which is in a heat exchanger relationship with a second heat exchanger in a superheating unit (17) in the heat pump, for heating water in the tank (3) to a first high temperature level, that the second of the tanks (4) has a third heat exchanger which is in heat exchanger relationship with a fourth heat exchanger adjacent to a condenser (18,23) in the heat pump, which is arranged to heat water in the second tank (4) to a second temperature level which is lower e than the first temperature level, or to cool down or freeze water in the second tank (4) and that the tanks have a supply of fresh water which is independent of the circuits comprising a first, second, third and fourth heat exchanger. 2. System according to claim 1, characterized in that the first tank (3) is in liquid communication with the second tank (4) so that partially heated water from the second tank (4) can be transferred to the first tank (3) for further heating. 3. System according to claim 2, characterized in that the communication line between the first and the second tank (3,4) is equipped with a shut-off valve and that each of the tanks (3,4) comprises separate inlets (5,22) and outlets (7, 9 ), so that they can function independently of each other. 4. System according to claim 1, 2 or 3, characterized in that the first tank (3) is designed to store hot tap water. 5. System according to claim 4, characterized in that the hot tap water is kept separate from the water that circulates in a building's heating or cooling circuit. 6. System according to claim 1, 2, 3, 4 or 5, characterized in that the tanks (3, 4) are equipped with electric heating flasks (19, 20) for reheating water or reserve heat source. 7. System according to claim 1, characterized in that the second tank (4) is connected to a heating/cooling system (14, 21) for heating or cooling a building. 8. System according to one of the preceding claims, characterized in that the first and second tanks (3,4) are placed in a common casing (1). 9. System according to one of the preceding claims, characterized in that it comprises an outlet (7) from the second tank (4), for draining water, in particular for draining chilled drinking water. 10. System according to one of the preceding claims, characterized in that the water heater (1) is in a heat exchange relationship with waste water, especially greywater, possibly via a third tank (30) which is in liquid communication with one of the water heater's other tanks (4). 11. System according to one of the preceding claims, characterized in that it comprises a heat exchanger (33) for heat transfer from waste water, especially gray water, to the external circuit of the heat pump (2). 12. System according to one of the preceding claims, characterized in that the second tank (4) contains liquid, for example water, and is designed to provide cooling to the liquid for the accumulation of ice and/or chilled liquid.