The invention relates to a thermal energy recovery system, comprising a heat pump, and on a primary side of the heat pump an inlet for the wastewater entering the system and an outlet for the wastewater leaving the system, and on a secondary side of the heat pump an inlet for a cold fluid entering the system and an outlet for heated fluid leaving the system, wherein downstream the inlet for the wastewater into the system and upstream of the heat pump, a filter is applied for removal of solids from the wastewater prior to the wastewater entering a first storage or wastewater storage for filtered wastewater which is provided downstream the filter and upstream the primary side of the heat pump.

Such a thermal energy recovery system is described in Dutch patent application 2025464 in the name of the applicant.

DE 3119 809 A1 discloses a device for recovering heat from polluted waste water, with a heat exchanger, the primary part of which is switched into a waste water outlet and the secondary part of which is switched into a fresh water inlet, and with a pump and a filter in the waste water outlet, wherein the filter is divided into two filter parts, of which one is connected upstream of the primary part of the heat exchanger and the other is connected downstream, and wherein the filter parts can be switched in such a way that the filter part connected upstream of the heat exchanger will entertain a flow in a direction corresponding to the filter operation and the flow through the filter part connected downstream of the heat exchanger will entertain a flow in the direction corresponding to a flushing operation.

W02012/061891 teaches a process and apparatus for the recovery of heat energy from wastewater. Wastewater, for example grey water from a domestic residence, is introduced to a detention chamber, which provides effective decoupling between the introduction of new wastewater and the demand for heat energy from its ultimate application. A heat exchange surface, in contact with the wastewater on one side and a working fluid on the other, extracts heat from the detention chamber through thermal conduction and the working fluid is transferred, via a heat pump, to a second heat exchange surface. The second heat exchange surface, in contact with the working fluid on one side and heat energy storage media on the other, transfers heat energy to the storage media through conduction. Heat energy can then be extracted from the storage media for applications including heating of potable water, or provision of building heating.

DE 10 2015 224723 A1 discloses an apparatus for heat recovery from waste water of a device working with hot water, in particular a washing machine, dishwasher or disinfectant rinse, the apparatus comprising a connection for the supply of fresh water, a connection for the supply of the waste water, a connection for the discharge of fresh water and a connection for the discharge of the waste water, the apparatus having at least one waste water tank for the intermediate storage of the waste water and at least one fresh water tank for the intermediate storage of the fresh water, as well as a heat pump in order to extract residual heat from the waste water temporarily stored in the waste water tank and to further heat the fresh water temporarily stored in the fresh water tank to a preferably predeterminable maximum temperature, wherein a heat exchanger is provided to first heat the fresh water temporarily stored in the fresh water container by temperature equalization with the wastewater temporarily stored in the wastewater container, and that a separating container is provided for the intermediate storage of wastewater, the separating container being upstream of the at least one wastewater container, to only pass wastewater from the separating tank into the wastewater tank when the wastewater in the separating tank is warmer than the wastewater in the wastewater tank.

A disadvantage of many known thermal energy recovery systems for wastewater is that recovery of heat from the wastewater is closely intertwined with the simultaneous heating of tapwater to be taken from the system. Both processes of recovery of heat from wastewater, and heating of tapwater have to occur simultaneously.

Correspondingly to the simultaneous recovery of heat and the heating of tapwater in the prior art, a further disadvantage is that in many known systems not all available wastewater is effectively used for recovery of heat. Roughly 30% of the water used in a household is used for flushing toilets. This source of energy is however not effectively used in the prior art.

It is further known in the prior art to apply a wastewater storage for filtered wastewater, wherein the storage is provided downstream the filter and upstream the primary side of the heat pump.

The wastewater storage is required to be able to temporarily store the wastewater and gradually extract the heat by using the heat pump. The use of the known wastewater storage has several disadvantages for use in a domestic (inside a building) situation. In most (European) houses the sewage is placed under the ground floor in the so-called underfloor crawling or service space. This brings about several disadvantages .

A first disadvantage is that placement and accessibility of the wastewater storage is challenging. The access to the underfloor or crawling space is usually through a small (40x60cm) hatch, which prevents placement of a wastewater storage, usually a tank, and which requires therefore additional piping and costly installation to provide the wastewater storage elsewhere in the house. This reduces the available living space. Placement in the underfloor service space or outside of the house further requires drilling open the hatch or digging a sizeable hole outside. Both are very costly.

A second disadvantage when placement in the underfloor or crawling space is at all possible, is the requirement for venting of the wastewater storage to remove the associated smell. This occurs when a solid wastewater storage is placed, which is higher than the sewage pipe. The water needs to be actively pumped into this storage. Placement of a solid storage underneath the existing sewage is impractical and expensive, therefore venting and pumping is most often required. When the wastewater storage is filled with wastewater the air inside the storage needs to vented out and when the storage is emptied air needs to be supplied to the storage. The air from the wastewater storage needs to be vented far from the domestic area to prevent bad odours in the living environment. A third disadvantage is that measurement of the amount of wastewater inside the storage requires regular maintenance of the measurement devices. In a conventional wastewater storage tank, measurements can be performed using a floater, or other measuring techniques which require direct contact with the contaminated wastewater. This measurement method requires direct contact of the measuring equipment with the (black) wastewater which quickly leads to fouling and ineffective measurement results and thereby faulty control of the system.

The invention is aimed to overcome the difficulties of the prior art.

A first object of the invention is to make effective use of all available (domestic or office building) wastewater, including black wastewater, to recover as much thermal energy as possible.

A second object of the invention is to recover so much heat from the wastewater that it is possible to use the available heat not only for heating tapwater, but also for heating the spaces/rooms in the house where the system is employed.

A third object is to make the application of a thermal energy recovery system in a domestic environment feasible at low cost, and without notable restructuring of the house where the system will be installed.

These and other objects and advantages of the invention, which will become apparent from the following disclosure are provided by a thermal energy recovery system and by a house provided with such a thermal energy recovery system with the features of one or more of the appended claims.

In a first aspect of the invention the filter of the thermal energy recovery system is a passive non-pressurized flow filter which is embodied as a perforated tube with a closed bottom center and in the bottom half of the tube, immediately above the closed bottom center, radially sideways oriented filtration holes to enable waste water to pass through the filtration holes using gravity. Such a filter is able to process black water without clogging, since there are no perforation holes in the bottom centre of the tube, thus creating a flow area for solids (with a small amount of water) to pass along the filter. In a second aspect of the invention wherein the system is provided with one or more pumps for circulating the wastewater on the primary side of the heat pump and/or the (heated) fluid on the secondary side of the heat pump, and wherein a control system is provided to control operation of the one or more pumps based on measurements with one or more sensors, it is proposed that the wastewater storage is a flexible storage which is able to expand and retract to exactly follow and match the amount of filtered wastewater to be stored in the wastewater storage, and the one or more sensors comprise at least a first sensor for monitoring the amount of wastewater in the wastewater storage, which first sensor is positioned externally of the wastewater storage to monitor a parameter of the wastewater storage which is externally measurable, and said first sensor is one of an ultrasonic distance sensor, a laser distance sensor, a magnetic sensor cooperating with a metal attachment to the wastewater storage for measuring the volume content of the wastewater storage.

Since the proposed measurement is external from the wastewater storage and no contact with the wastewater in the wastewater storage is required, a reliable measurement of the amount of wastewater in the wastewater storage is securely available over a long period of time.

The use of the flexible bag brings about the following advantages .

Firstly the flexible wastewater storage can be folded and shaped to any size to fit the small access hatch to the underfloor service or crawling space. Furthermore the flexible wastewater storage can easily be placed on any soil or surface roughness without requirement of levelling the storage.

Secondly due to the flexible nature of the wastewater storage no venting is required. When the flexible storage fills up it can for instance increase in height and when the flexible storage is emptied it can decrease in height.

It is preferable that the wall of the flexible storage is impermeable for water and air, so that no air can escape from the flexible wastewater storage and therefore no venting is required. Thirdly the amount of water in the wastewater storage can be determined completely externally, for instance by measuring the distance between the top and bottom of the bag, or by measuring the height of the bag, or by measuring the distance between the top of the wastewater storage and a fixed reference object such as the underside of the ground floor. With an increasing amount of wastewater in the flexible wastewater storage, the distance between the top of the wastewater storage and the fixed ground floor decreases, and this can be simply used as an indication of the amount of wastewater that is in the wastewater storage.

With the system of the invention virtually all wastewater can be used for recovery of heat, not only the so- called grey wastewater, but also the black wastewater which would normally be directly disposed down the drain. Since in this manner also a higher level of heat can come available at the primary or entry side of the heat pump, the effectivity in the transfer of heat by the heat pump is also improved.

It is further preferable that at the secondary side of the heat pump a second storage for heated fluid is provided, which second storage is also a flexible storage which is able to expand and retract to exactly follow and match the amount of water to be stored. This brings about advantages as are already explained hereinabove with reference to the flexible first storage for wastewater.

The mentioned wastewater storage at the primary side and the second storage at the secondary side of the heat pump makes the operational processes of recovering heat from domestic wastewater, and providing the heated fluid at the secondary side of the heat pump independent from each other. Accordingly it is not only possible to use the system of the invention for heating tapwater from the energy available in (domestic or office building) wastewater, but also to use the recovered heat for space heating in a building.

Moreover the water storages at the primary side and secondary side of the heat pump also open the way to improve the working efficiency of the at least one heat pump, and to design it with a lower capacity than what would be required without storages. As a non-limiting example: When in an average Dutch household all the energy present in the wastewater during one day is spread out over 24 hours this results in a required thermal conversion power of only 0.8 kW. The wastewater stream is variable and therefore completely equalizing the thermal power over the course of 24 hours would require a too large storage volume. An optimum between the required storage volume and the heat pump thermal conversion power is reached at a thermal conversion power of 4 kW. Additional storage on the secondary side may be required to ensure both instant hot water and a sufficient flow of 8 1/s for comfortable showering and other tap water applications. The required primary side storage volume is ~ 200L and the secondary side storage volume ~200L.

To remove fouling of the filter, it is preferable that the filter is provided with a purging system. Purging can be done using for instance the water pressure in the public water supply network, or filtered water available in the system.

To counter fouling of the filter it is desirable that the filter is provided with an internal coating.

Another favorable aspect of the invention is that a third storage for water or another suitable fluid (for instance glycol) is provided that is arranged to collect energy from the environment. This third storage is equipped to connect to said one or more pumps for transferring the water or fluid from the third storage to the primary side of the heat pump. By placing this third storage in the crawling space of a house, the energy available in the crawling space environment can be collected and be made available for use in the house, for instance for tapwater heating or for space heating.

The invention is accordingly also embodied in a house or building provided with a foundation and a ground floor, wherein there is a crawling space below the ground floor, and wherein the house is provided with a thermal energy recovery system provided with one or more of the features specified in the claims.

In one embodiment of the house or building of the invention at least the wastewater storage for filtered wastewater is provided in the crawling space.

Preferably both the wastewater storage for filtered wastewater and the second (insulated) storage for heated fluid are provided in the crawling space. Preferably also the above- mentioned third storage for fluid, which is used to collect energy from the environment is also positioned in the crawling space of the house.

Another aspect of the invention is that space heaters of the house or building are connected to the thermal energy recovery system of the invention.

The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of a thermal energy recovery system according to the invention that is not limiting as to the appended claims.

In the drawing:

- figure 1 shows a PID diagram of the thermal energy recovery system of the invention;

- figure 2 is a detailed view at a flexible wastewater storage of the filtered wastewater together with a sensor to measure the amount of water contained in the wastewater storage; and

- figure 3 shows the filter which is embodied as a perforated tube with a closed bottom center and in the bottom half of the tube, immediately above the closed bottom center, radially sideways oriented filtration holes to enable waste water to pass through the filtration holes.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same or similar parts.

The core of the thermal energy recovery system for domestic wastewater according to the invention is the heat pump denoted with reference 1.

The system further has an inlet 3 for wastewater and an outlet 9 for wastewater that has passed the heat pump 1. Going from inlet 3 to outlet 9, the wastewater first passes a filter 5, and is thereafter channelled through duct 6 to a first storage for the filtered wastewater, which will be further referred to as the wastewater storage 7. The wastewater storage 7 is a flexible storage which is able to expand and retract to exactly follow and match the amount of filtered wastewater which is to be stored in the wastewater storage 7. The wall of the wastewater storage 7 is impermeable for water and air. Solid particles that the filter 5 has removed from the wastewater stream coming from the wastewater inlet 3, go directly through duct 8 to sewage outlet 9. Preferably the filter 5 is a passive non-pressurized flow filter which is embodied as a perforated tube with a closed bottom center and in the bottom half of the tube, immediately above the closed bottom center, radially sideways oriented filtration holes to enable waste water to pass through the filtration holes. This is shown in figure 3, which provides a view at the filter from below.

Figure 1 further shows that the filter 5 is provided with a purging system 21 for cleansing the filter 5. Although not shown it is further possible that the filter 5 is provided with an internal coating.

At the primary side 2 of the heat pump 1 there is further a first fluid pump 10 with which filtered domestic wastewater is transported from the wastewater storage 7 into the heat pump 1 through a duct 11. Wastewater which leaves the heat pump 1 and from which the heat is recovered, is guided through duct 12 to the sewage outlet 9, or is re-cycled back to the wastewater storage using electric valve V3 .1 for further extraction of heat. This circulation process allows to extract all usable heat before the water is guided through duct 12 to the sewage outlet 9. In this way the wastewater can be gradually cooled down in cycles of small temperature difference, which increases the efficiency of the heat pump 1.

At the secondary side 13 of the heat pump 1 an inlet 14 for a cold fluid, usually water, and an outlet 15 for heated fluid is provided. The outlet 15 can be used for feeding hot tapwater outlets and/or for supplying heated fluid to a space heating system 23. The space heating system 23 may require the application of an additional heating system 24.

The fluid at the secondary side 13 of the pump 1 and that is to be heated is provided at the inlet 14 and transported by a second pump 17 through a duct 16 at the secondary side 13 of the heat pump 1. In the heat pump 1 the fluid is taking up the energy recovered from the wastewater which is provided at the primary side 2 of the heat pump 1. A return stream of heated fluid leaves the heat pump 1 through duct 15, so as to arrive at a second storage 19 for the heated fluid. Hot tapwater or heating fluid used for space heating is then taken from the second storage 19. Preferably the second storage 19 is a flexible storage which is able to expand and retract to exactly follow and match the amount of fluid to be stored.

As mentioned the system is provided with pumps 10, 17 for circulating the wastewater on the primary side 2 of the heat pump 1 and/or the (heated) fluid on the secondary side 13 of the heat pump 1. Further a (not shown) control system is provided to control operation of the pumps 10, 17 and the valves VI, V3.1, V3.2 and the space heating/hot tapwater valve based on measurements with one or more sensors, in particular measurements with at least a first sensor 22 for monitoring the amount of filtered wastewater stored in the wastewater storage 7.

Figure 1 further depicts that a third storage 25 for water or another suitable fluid is provided that is arranged to collect energy from the environment, which third storage 25 is equipped to connect to said one or more pumps 10 for transferring the fluid from the third storage 25 to the primary side 2 of the heat pump 1. This third storage 25 is always filled with (for instance 200-500L or more) water or another suitable fluid such as glycol. The moment there is a demand for heat in the house which cannot be gained from the wastewater storage 7, the 3-way valve V3.2 is switched by the (not shown) control system and to have the pump 10 supply water from the third storage 25 and circulate it through the heat pump 1. By the operation of the heat pump 1 the fluid in the third storage 25 slowly cools down. The heat regained with the heat pump 1 can be used to heat the tap water or the heating system of the house. When the fluid in the third storage 25 has cooled down to a certain setpoint (for example 3°C or lower if the used fluid permits) the heat pump 1 switches off and the circulation stops. The third storage 25 holding then 3°C fluid subsequently heats up to 10°C - 14°C due to the temperature of the soil and the environment in the crawl space. When the higher temperature of 10°C - 14°C is reached the third storage 25 is "available" again for the heat pump 1 to be used again for space heating or tapwater heating of the house. Figure 2 depicts that the first sensor 22 is positioned externally of the first storage 7 to monitor a parameter of the first storage 7 which is externally measurable, so as to derive therefrom the amount of wastewater stored in the first storage 7. It is preferred that the first sensor 22 is one of an ultrasonic distance sensor, a laser distance sensor, a magnetic sensor cooperating with a metal attachment to the first storage 7 for measuring the volume content of the flexible bag.

Figure 2 illustrates that the amount of water in the wastewater storage 7 can be determined by measuring the distance between the top of the wastewater storage 7 and a fixed reference object such as the underside of the ground floor, indicated by the dashed line. With an increasing amount of wastewater in the flexible wastewater storage 7, the distance between the top of the wastewater storage 7 and the fixed ground floor decreases, and this can be simply used as an indication of the amount of wastewater that is present in the wastewater storage 7.

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the thermal energy recovery system of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment.