Technical field

The present invention relates to a heat exchanger and a system for recovery 5 of thermal energy from waste water.

Background of the invention

With increasing demands for buildings that are energy efficient and resource efficient living, much has been done to improve buildings without negatively

10 affecting the quality of the indoor climate. Heat pumps, recovery systems for ventilation, new and better control systems for control and monitoring are installed for this purpose along with better construction materials and systems. In this way energy consumption due to transmission losses through the building envelope, ventilation losses (voluntary and involuntary), along with

15 other combined losses have been improved.

Consumption of water is a source of loss that is difficult to manage and previously has amounted to a negligible part of energy consumption. There is now, however, a need to reduce losses caused by water consumption.

Some progress has been made in this area in the form of low-flush

20 showers, faucets, and toilets along with insulation of installations etc. but the

remaining consumption is difficult to handle and requires some form of waste water recovery.

There are a number of solutions that have different problems either purely technically or as regards to efficiency. Heat exchangers located as a floor

25 in the shower where incoming water is exchanged with outgoing water is

problematical regarding installation and approval according to rules in the sector and, besides, water is recycled only when showering. There are upright exchangers but they have a design that either is not suitable for greater flows or have poor effectiveness. There is thus a need to reduce losses caused by water

30 consumption. Summary of the invention

With reference to the above, an object of the present invention is to provide for a heat exchanger and a system for recovery of thermal energy from waste water.

This and other objects, which will become apparent in the following description, are accomplished by means of a heat exchanger a system according to respective independent claims. Embodiments of the heat exchanger and the system are accomplished by the dependent patent claims and by the following description and drawings.

More specifically, a heat exchanger in accordance with the present invention for recovery of thermal energy from waste water is provided. Said heat exchanger comprises an outer tube, an inner tube for waste water, and a control element, wherein said inner tube is arranged inside said outer tube in such a way that a space is formed between said inner tube and said outer tube and wherein said control element is arranged in said space and is arranged to guide a medium in a helical movement around the inner tube so that thermal energy from said waste water is transferred to said medium.

The heat exchanger according to the invention ensures that thermal energy is emitted from the waste water to the medium with a high degree of efficiency. Since the medium has direct contact with the outside of the inner tube, heat transfer is very good. It is advantageous that the control element directs the medium in a helical movement, since the medium then is transported a long distance in the space between the inner and outer tube, which provides long contact time with the inner tube and thus increased efficiency. Furthermore, the heat exchanger according is advantageous with regards to the Coanda effect in that the waste water is evenly distributed over an internal surface of the inner tube which contributes to transfer of thermal energy. The heat exchanger according to the invention is flexible as regards to its length, connection dimensions, and variable flow characteristics in combination with low

maintenance costs, which makes it suitable for a number of applications. For example, the length of the heat exchanger, the spacing of the winding of the control element, and the spacing between the inner and outer tube can be varied and adjusted according to the waste water flow. A high efficiency can be achieved, since the heat exchanger can be adjusted so that very good conditions are obtained.

According to one embodiment said control element can be arranged to guide said medium in a space formed between the control element, an outside of the inner tube, and an inside of the outer tube.

In other words, there is a space outside of an outside of the control element and an outside of the inner tube and inside an inside of the outer tube, where said medium can be guided by the control element.

According to one embodiment, a portion of the outside of the control element is arranged to face towards said space that is formed between the control element, an outside of the inner tube, and an inside of the outer tube, and a portion of the outside of the control element is arranged to face toward the outside of the inner tube. The control element is thus arranged to guide said medium in a helical movement around the inner tube by at least a portion of the outside of said control element.

According to one embodiment, the flow path of said medium outside of the inner tube is helically shaped. In other words, said medium is guided in a spiral-formed track which is defined at least partly by the inside of the outer tube, the outside of the inner tube and the control element (as, for example, a portion of the outside of the control element). The outer tube, the inner tube, and the control element are thus arranged in such a way that a spiral-formed channel is formed in the space between said inner tube and said outer tube, where said medium is allowed to flow.

By guiding said medium by the control element in the above mentioned space, heat exchange will mainly occur from the waste water via the wall of the inner tube to said medium being guided in a helical movement around the inner tube. The heat exchanger can thus in an efficient way recover thermal energy from the waste water, since the heat exchange occurs directly between said medium and the waste water via the wall of the drain tube.

According to one embodiment said control element can be wound around said inner tube.

According to one embodiment, the space between the control element, an outside of the inner tube, and an inside of the outer tube, where said medium is guided, can be varied by changing the spacing of the winding of said control element. Hereby, the capacity of the heat exchanger can be altered and adjusted in order to optimize the flow for the heat exchanger.

According to one embodiment, said control element may be soldered onto said inner tube.

Such an embodiment is advantageous since the control element has a strengthening/supporting function on the inner tube. Said medium directed in said space can exert a large pressure on the inner tube (the pressure may be as high as around 16 bar), and the strengthening/supporting function may thus contribute to that the inner tube can better resist this pressure.

According to one embodiment, said control element may be a tube that is filled, or almost filled, with a material such as some sort of filling mass, for example cement or silicon. In other words, a cross-section of said control element is filled with some material. According to one embodiment said control element may be compact or solid. In other words, said control element has a cross- section that is compact or solid.

In this way, the tube does not have a through channel where air or liquid can flow. Such an embodiment is advantageous since the strengthening or supporting function of the control element is improved.

According to one embodiment, said inner tube and said outer tube can be mounted parallel with the vertical plane.

Such an embodiment is advantageous since the waste water then flows in parallel with the vertical plane.

According to one embodiment, said inner tube can be arranged centrally in said outer tube. This is advantageous since it contributes to good efficiency as the waste water flows centrally in the inner tube.

According to one embodiment, said outer tube may have an inlet for said medium in a lower portion of said outer tube and an outlet for said medium in an upper portion of said outer tube. This is advantageous since a counter flow heat exchanger then is formed, which has high efficiency.

According to one embodiment the inlet is provided to lead said medium to the space between the control element, an outside of the inner tube and an inside of the outer tube. According to one embodiment, said inner tube may have an inlet for said waste water in an upper portion of said inner tube and an outlet for said waste water in a lower portion of said inner tube. This is advantageous since a counter flow heat exchanger is formed, which has high efficiency.

According to one embodiment, the edge of said inlet and/or outlet of said inner tube comprises at least one projection arranged in a direction of flow in said inner tube. The projection contributes to that a slit is formed between the drain tube and the heat exchanger. This is advantageous because it

compensates for small discrepancies caused by that the drain tube is not mounted vertically, and also contributes to quickly and evenly distribute the waste water over the surface when it reaches the slit.

According to one embodiment, said inner tube may be made of copper. This is advantageous since heat transfer in copper is very good. Copper also counteracts the ability for diatoms and similar to become attached and thereby degrading heat transfer over time. This contributes to low maintenance costs.

According to one embodiment said outer tube can be at least one of copper, steel, or stainless steel. Steel and stainless steel have the advantage that they are inexpensive.

According to one embodiment said control element can be a tube.

Such embodiment is advantageous since the control element can be shaped in a helical track around the inner tube relatively simply.

According to one embodiment, said control element can be a tube wound around said inner tube. This is advantageous since the drain heat exchanger can be assembled by soldering the tube to the inner tube and thereafter pushing the outer tube into place over the inner tube and the tube wound and soldered onto the inner tube. By soldering the control element to the inner tube the construction is made even more stable.

In spite of the relatively large force needed to push the outer tube into place, the tube should probably remain in its position.

According to one embodiment, said control element can be at least one of copper, aluminum, or stainless steel. Said control element can also be of a material which withstands fresh water. According to one embodiment said medium can be water. This is advantageous since water has many applications.

According to one embodiment the temperature of said medium when it leaves said outlet for said medium may be in the range of 8-50°C. This is advantageous since the medium can be pre-heated by the invention before it is used for various applications.

A system for recovery of thermal energy from waste water in accordance with the present invention is provided. Said system comprising a heat exchanger according to the any one of the above embodiments and at least one of a water closet, a hot water dispenser arranged to heat liquid to a predetermined

temperature, and shower mixer, a kitchen mixer or a bathroom mixer, wherein said medium is water. This is advantageous since the heat exchanger can provide the water closet, the hot water dispenser, and the shower, kitchen, and bathroom mixers with heated water.

According to one embodiment the system can comprise a conduit for leading water from said heat exchanger to said hot water dispenser. This is advantageous since the hot water dispenser does not need to work as much, because the water is already heated by the heat exchanger.

According to one embodiment the system can comprise a conduit for leading water from said heat exchanger to said water closet. This is

advantageous when the outdoor temperature is low and the building that the water closet is in should be heated. Incoming cold water is preheated by outgoing waste water, which means that energy is saved because the need for extra energy for heating the water in the water closet is reduced.

According to one embodiment, the system may comprise a conduit for leading water from said heat exchanger to said shower mixer, wherein said shower mixer is arranged to mix said water with water from said hot water dispenser.

According to one embodiment the system can comprise a conduit for leading water from said hot water dispenser to said shower mixer, said kitchen mixer or said bathroom mixer, wherein said shower mixer, said kitchen mixer or said bathroom mixer is arranged to mix water with water from said heat exchanger. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc.]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps in any of the method disclosed herein need not to be performed in the exactly disclosed manner, unless explicitly stated otherwise.

Brief description of the drawings

Embodiments of the present invention will hereafter be described in exemplified manner, with reference to the illustrative appended drawings, wherein:

Fig. 1 shows a cross-section of the heat exchanger according to the invention.

Fig. 2 shows a schematic view of a system for recovery of thermal energy from waste water according to the invention.

Detailed description

The heat exchanger according to the invention is based on the idea of saving energy by using thermal energy in the waste water to preheat water for use in, for example, bath, shower, dishwashing, clothes washing, and flushing toilets.

In order to reach the desired temperature the preheated water sometimes needs to be mixed with water of an even higher temperature. This water with an even higher temperature can be heated by, for example, a hot water dispenser. Water heated by the hot water dispenser can be water preheated by the heat exchanger which, is then further heated by the hot water dispenser.

Fig. 1 shows a cross-section of the heat exchanger according to the invention. Heat exchanger 100 has an inner tube 1 10 and an outer tube 120. The inner tube 1 10 is arranged centrally in the outer tube 120. The inner tube 1 10 is arranged for leading waste water. Waste water is directed downwards in the figure and flows by means of gravitation. A space 130 is formed between the inner tube and the outer tube. A control element 140 extends inside the space 130. The control element is arranged to guide said medium in a helical movement around the inner tube. When a medium is led around the inner tube and waste water flows in the inner tube, thermal energy from the waste water can be transferred to the medium.

The medium is preferably water. The water can be cold water intended for bath, shower, dish washing, clothes washing, flushing toilets, and watering.

An inlet 1 12 for waste water is arranged in an upper portion of the inner tube 1 10, and an outlet 1 14 for waste water is arranged in a lower portion of the inner tube 1 10 for waste water. In an embodiment, such as shown in Fig. 1 , the outer tube 120 does not fully encompass the inner tube 1 10. This is advantageous since it simplifies connecting the heat exchanger 100 with an existing drain tube.

The edge of inlet 1 12 and/or of the outlet 1 14 has a projection 1 16. The projection 1 16 protrudes parallel with the center line of the inner tube. The projection 1 16 simplifies assembling of the heat exchanger 100 since it

compensates for any unevenness from sawing the existing drain tube in two. This also creates a slit that facilitates quick distribution of waste water over the internal surface. The slit facilitates quick distribution of waste water over the internal surface. The slit that is created also provides a certain leeway to compensate for assembling of the heat exchanger vertically. The slit is like a slot through which the water may run, and quickly be distributed in and, since the heat exchanger must be assembled vertically, the water will then run over the edge evenly over the tube.

In one embodiment, the heat exchanger does not comprise a projection.

The heat exchanger is instead assembled so that a slit is made when the heat exchanger is assembled vertically.

When the heat exchanger 100 according to the invention is to be assembled, a portion of an existing drain pipe is sawed off. The inlet 1 12 and outlet 1 14 of the inner tube 1 10 is brought into contact with the edges of the existing drain tube. Since it is difficult to saw the existing drain tube exactly evenly, projection 1 16 compensates for this so that it is possible to turn the heat exchanger 100 so that it is arranged parallel with the vertical plane and the gravitational field. Two seals (not shown) can then be assembled over the edges of the existing drain tube and the inlet 1 12 and outlet 1 14 of inner tube 1 10. These seals can, for example, be a coarse piece of tubing or rubber that is pressed into place with hose clamps.

The outer tube 120 has an inlet 122 in its lower portion and an outlet 124 in its upper portion. The inlet 122 leads into a space formed between control element 140, the outside of inner tube 1 10, and the inside of outer tube 120. Inlet 122 and outlet 124 can, for example, be tubular. Inlet 122 is arranged to lead the medium that is to be heated into the heat exchanger.

As shown the waste water is intended to be guided parallel with the gravitation and downwards in Fig. 1 , see arrows 150 and 151 . The medium to be preheated is arranged to be guided upwards in Fig. 1 in a helical movement, see arrows 160 and 165 that show when the medium is guided into and out of the heat exchanger. In this way a counter flow heat exchanger is formed.

The control element 140, as shown in Fig. 1 , can be a tube that is wound around the inner tube 1 10. The control element is, for example, soldered to the inner tube. The outer tube is then mounted around the inner tube. The outer tube is, for example, pulled outside of the inner tube and the control element. The outer tube can alternately be divided into two parts that are arranged around the inner tube and control element and which is then welded together.

In one embodiment, the control element is formed as an I-beam in miniature that is wound around the inner tube. This embodiment saves materials and can be made by assembling the outer tube in two halves that are welded together with longitudinal seams in the direction of flow.

The heat exchanger according to the invention is intended to be assembled in some form of household. It can, for example, be in a multi-family house, an office property, a single-family house, a row house, or a link house. The heat exchanger could also be installed in a boat, house trailer, or recreational vehicle. Since the heat exchanger uses waste water, it needs to be located under the drain inlet in the household. The heat exchanger is thus preferably located under inhabited space, in a cellar or shaft. In multi-family households, for example in apartment houses, one or more heat exchangers according to the invention can be installed. The medium that is brought from the heat exchanger according to the invention is sometimes referred to as preheated water here.

Fig. 2 shows a schematic view of a system according to the invention for recovery of thermal energy from waste water. System 200 comprises the heat exchanger 100 according to the invention. Fig. 2 shows in more detail a suggested fitting for a bathroom. Heat exchanger 100 is connected so that waste water 151 flows into the top of the heat exchanger 100 and flows out at the bottom of heat exchanger 100. Waste water 150 that flows out of heat exchanger 100 is cool in comparison with waste water 151 that flows into heat exchanger 100.

Cold water 160 is guided into the heat exchanger 100 and is preheated by the heat exchanger 100 by means of heat exchange with the waste water.

Preheated cold water 165 is guided further to hot water dispenser 210, to water closet 220, to shower and bath 230, as well as to bathroom mixer 240. The preheated cold water 165 maintains a temperature in the range of approx. 8-50 °C. The temperature of the preheated cold water 165 depends on the extent to which it has been heated in the heat exchanger 100. How much the cold water 160 is heated in the heat exchanger 100 depends in turn on how much waste water 151 is led into the heat exchanger 100 and the temperature of waste water 151 .

The preheated cold water 165 in the hot water dispenser 210 is further heated until it reaches a predetermined temperature. The predetermined temperature can, for example, be 55 °C. The water warmed to a

predetermined temperature is designated here as hot water 170. Hot water 170 is led to shower mixer 230 and bathroom mixer 240. Shower mixer 230 can, for example, be provided in a bathtub or in a shower. Bathroom mixer 240 can, for example, be provided in a sink in the bathroom.

Shower mixer 230 mixes hot water 170 with the preheated cold water 165 in accordance with what is determined by the user. If, for example, the preheated cold water 165 maintains a temperature in the upper part of the range, then a smaller amount of hot water 170 is added.

Bathroom mixer 240 mixes hot water 170 with the preheated cold water

165 in accordance with what is determined by the user. If, for example, the preheated cold water 165 maintains a temperature in the upper part of the range, then a smaller amount of hot water 170 is added. In one embodiment the bathroom mixer 240 also comprises a connection for cold water. This is advantageous since the user may, for example, want to have drinking water or water for brushing teeth. In one embodiment instead of a connection for cold water, the sink has a separate faucet for cold water.

If, for example, someone takes a shower, the water flows out in the bathroom drain and is led to the heat exchanger 100. The water in the heat exchanger 100 heats cold water 160 that is led up to the shower mixer 230. The longer time the person showers, the less hot water 170 needs to be added.

It should be noted that central preparation of hot water can be done, for example, by a remote heat exchanger as an alternative to the hot water dispensers.

It should be understood that the present invention is not limited to the embodiments described herein. Several modifications and variations are conceivable, for which reason the scope of the invention is exclusively defined by the accompanying claims.