Field of the Invention

This invention relates to water heating and in one application a heat recovery system for use in a shower. In particular this invention relates to a heat recovery system for installing in a shower in a new installation or a retro-fit installation.

Background Art

A very large amount of energy in the form of hot water is lost to the environment when showering. Whilst the shower water itself is generally not considered re- useable, the heat energy contained in the water can be recovered and used to heat up the incoming cold water. Shower water is comfortable at about 40 to 45°C. The water which goes to the drain at the base of the shower is only a few degrees cooler than that. An efficient heat exchanger can heat up the incoming cold water so that only a very small flow of hot water from the hot water tap is required. Devices exist which recover heat energy from the drainpipe itself and return warm water to the hot water storage system or to the inlet side of an instantaneous water heat system. Such devices require major alterations to the plumbing if not installed during construction. They are also limited in size and hence efficiency by the size of drainpipe that is available or accessible.

The invention described allows much simpler installation and can use the recovered heat energy immediately thus reducing losses considerably.

The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or elsewhere as at the priority date of the application.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to

imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention

In accordance with the invention there is provided a method of recovering heat from water going to drain in a shower or hot water rinsing facility, said method comprising providing heat recovery system comprising a cold water flow pathway on a first floor of said shower or facility, said cold water flow pathway being enclosed by a wall or walls providing a heat transfer surface, and having two end portions being an inlet for receiving cold water and an outlet for exiting heated water, one said end portion in use being located by said drain in said first floor; said method including providing a second floor located above said first floor and having a drain hole serving as a drain inlet to said heat recovery system said drain inlet being located in proximity to the other said end portion of said cold water flow pathway, the wall or walls of said cold water flow pathway defining an external flow pathway for water going to drain from said drain inlet.

Preferably said cold water flow pathway is of substantially planar configuration.

Preferably said cold water flow pathway is formed in a spiral shape.

The first floor may be provided by the existing floor of the shower or facility, in which case the cold water flow pathway is located directly on the existing floor.

Alternatively the first floor comprises a flat panel having sides, in which the cold water flow pathway is located. In this arrangement, an aperture is formed in said first floor to align with said drain.

Preferably the cold water flow pathway is formed of circular cross-section metal pipe. It is convenient to use copper pipe, as is common in domestic applications.

Preferably said cold water flow pathway is bonded intermittently to said first floor, the external wall of said cold water flow pathway and said first floor thereby forming said external flow pathway for water going to said drain.

Preferably said cold water flow pathway is bonded continuously to said first floor, the external wall of said cold water flow pathway and said first floor thereby forming said external flow pathway for water going to said drain.

Preferably said inlet connects to said end portion located in proximity to said drain and said outlet connects to said end portion located in proximity to said drain inlet.

Also in accordance with the invention there is provided a heat recovery system for a shower or hot water rinse facility having a cold water flow pathway having two end portions serving as an inlet and an outlet, said cold water flow pathway being enclosed by a wall or walls providing a heat transfer surface; said heat recovery system having a floor panel located above said cold water flow pathway, said floor panel having a drain hole serving as a drain inlet to said heat recovery system said drain inlet being located in proximity to one of said end portions; the wall or walls of said cold water flow pathway defining an external flow pathway for water going to drain from said drain inlet.

Preferably said heat recovery system includes a base comprising a tray in which said cold water flow pathway is mounted. An aperture is formed in said base to align with the existing shower drain.

Preferably said cold water flow pathway is of substantially planar configuration.

Preferably said cold water flow pathway is formed in a spiral shape.

Preferably said cold water flow pathway is formed of circular cross-section pipe.

Preferably said cold water flow pathway is bonded continuously to said base, the external wall of said cold water flow pathway and said base bounded thereby forming said external flow pathway.

- A - Brief Description of the Drawings

Referring to the drawings, a number of preferred embodiments will now be described. In the drawings:

Figure 1 is a diagrammatic representation in above plan view, of a first configuration of an embodiment of the invention;

Figure 2 is a diagrammatic representation in above plan view, of a second configuration of an embodiment of the invention; and

Figure 3 is an exploded perspective view of the most preferred embodiment of the invention; and

Figure 4 is an exploded perspective view of an alternative embodiment of the invention.

Best Mode(s) for Carrying Out the Invention

All embodiments are heat recovery systems 11 for a shower. Both configurations comprise a cold water flow pathway in the form of a flat spiral of copper pipe 13 (standard plumbing grade). The spiral of copper pipe 13 has two end portions 15 and 17 the end portion 17, leading to the centre 19 overlaying the spiral.

In both configurations the spiral 13 lies directly on a base 21 or first floor and is bonded continuously thereto.

The first configuration shown in Figure 1 has the end portion 17 being the cold water inlet, communicating within the centre 19 of the spiral of copper pipe 13 located adjacent to the existing drain 23 in the shower. An aperture 25 provides a drain inlet to the heat recovery system 11 from the shower cubical. The aperture is located in proximity to the outer periphery 27 of the spiral of copper pipe 13.

The heated cold water exiting the end portion 15 is directed to the cold water inlet of the shower mixer, or alternatively to the cold water inlet of a hot water storage

heater. This configuration is intended for use in a shower cubical having an existing centrally located drain 23.

The second configuration shown in Figure 2 has the end portion 15 being the cold water inlet, communicating with the outer periphery 27 of the spiral of copper pipe. The aperture 25 providing the drain inlet from the shower cubical receives hot water from the shower and directs it at the centre 19 of the spiral of copper pipe

13. The heated cold water existing the end portion 17 is directed to the cold water inlet of the shower mixer or the cold water inlet of the hot water storage heater.

This configuration is intended for use in a shower having a drain 23 located offset from centre.

The shower water in both configurations flows into the aperture 25, and flows around the spiral (the drain pathway) formed by adjacent- pipes of the spiral of copper pipe 13, and flows out of the drain 23. As if flows, heat in the shower water is transferred to cold water within the spiral of pipe.

To ensure that water follows the drain pathway, the spiral of pipe 13 is bonded to the lower part of the base formed by a tray 29. The tray 29 is formed with sides 31 extending upwardly so that water entering via the aperture 25 is contained.

A second floor is provided in the form of a cover 33, having downward extending sides 35 so as to fit over the tray 29. The cover 33 is pressed along lines 37 lending to the aperture 25, to depress the top of the cover 33 to direct water from the shower into the aperture.

The cover 33 may include spiral vanes on the underside, aligned with the spiral of pipe 13 to assist in minimising overflow of water from the spiral, between the aperture 23 and drain 25. An alternative method of minimising overflow my be to provide a close fitting gasket between the cover 33 and the spiral of copper pipe 13.

The heat recovery system comprising the tray 29 and cover 33 occupies most or all of the entire shower floor. The cover 33 is designed so that water from the

shower runs toward the aperture 25 and enters the interior of the tray 29. The water then travels along the drain pathway in a spiral manner to the centre of the tray 29 and then through the drain 23 and onto the original floor and into the original drain. The incoming cold water pipe travels in a counter flow manner to the outgoing hot water thus picking up the heat energy from the outgoing water. The incoming water pipe forms the spiral for the shower water to flow around. The heated water then continues to the normal shower mixer where hot water is added to reach the desired temperature.

Modifications to existing plumbing can be avoided by using a dual outlet tap on the shower mixer or obtaining the cold water from another outlet such as the bath tap. The warmed water from the base can be added to the shower by means of a simple tee piece after the mixer. -

The recovery of most of the heat energy from the shower opens up further options for the hot water system employed. Since the power consumption for heating a constant flow of cold water is directly proportional to the temperature change required, the power consumption in this instance would be reduced by the same ratio as the reduction in temperature change. For example a cold water temperature of 15°C requires a temperature change of 30° whereas that cold water could theoretically be preheated to say 40° by the above invention thus requiring only about a 5° change or about one sixth of the heat energy. A very small instantaneous heater or storage heater could be installed very close to the shower itself. A heat pump could effectively be used as an instantaneous heater. Heat exchanger efficiencies can be close to 95% depending on design.

Tests conducted directly on a shower floor indicate efficiency gains as follows.

A spirally wound coil of half inch copper tube was placed on the floor of the shower recess and the inner end connected by a plastic hose to the cold water tap. The outer end of the spiral was connected by a plastic hose to a tee piece in the shower hose. A plastic floor was placed on top of the copper coil so the warm water from the shower would run off the perimeter. This water had to flow throughout the length of but beside the spiral copper tube to get to the drain.

The prototype model worked reasonably well given its crude method of construction. The incoming water at 18 degrees Celsius was heated to 33 degrees by the heat exchanger. The hot water supply was at 57 degrees and the shower head water at a comfortable 41 degrees Celsius. Assuming the total shower water output to be the same as when the cold side was connected to the cold water tap some calculations as to hot water saving can be made. The heat gained by the cold water in to the shower head must equal the heat lost from the hot water in to the shower head. Heat gained = mass (water in) x specific heat x temp change equals mass x specific heat times temp change for hot water in. hence the water flows are inversely proportional to the magnitude of the temp changes. Therefore the ratio of hot water required to warm water required changes in favour of less hot water as the temperature of the warm water from the heat exchanger rises. Put differently, since the volume and temperature of water down the drain remains constant, the volume of water used per second remains constant, then less hot water is required to maintain the shower at required temperature.

In practice, this balance might be better maintained by thermal sensors and appropriate valves in order to save gradual adjustment of the taps until equilibrium is reached.

An alternative method would be to return the warmed water to the cold inlet of the hot water system irrespective of type (storage or instantaneous).

An alternative embodiment is shown in Figure 4 when parallel walls 39, 41 laid out in a spiralling manner, welded to the first floor 29, form the cold water flow pathway and the drain pathway. The cold water flow pathway can be discerned between the walls 39, 41 from the pipe portion 15 from which warmed water exits the heat recovery system, spiralling inwards to meet the pipe portion 17 through which cold water enters the heat recovery system. The pipe 17 passes through the walls 39 and 41 and is sealed thereagainst to prevent leakage, to reach the inner position in the spiral formed by the walls 39, 41. The inner position is in close proximity to the position of the drain .23. In this manner, the cold water flowing in the cold water flow pathway from the pipe 17 to the pipe portion 15 will

flow counter-flow to the heated waste water which enters via aperture 25 in the cover 33 and exits via drain 23 in the base 21.

The cover 33 is secured to the tray 29 by screws 43 which extend through o-rings 45 and countersunk apertures 47 in the cover 33 into threaded studs 49 located in the tray 29. The screws and studs are provided spaced from each other a sufficient distance to allow the cold water flow pathway to be pressurised without water loss. A gasket 51 is also provided between the cover 33 and tray 29, to seal between the tops of the parallel walls 39, 41 , and the cover 33 to isolate the cold water flow pathway and the drain pathway from each other. A suitable sealing compound may be used between the gasket 51 and the tops of the parallel walls 39, 41 , in order to prevent leakage of water from the cold water flow pathway, where it is pressurised.

It should be appreciated that the scope of the invention is not limited to the particular embodiment described herein, and that changes may be made without departing from the spirit and scope of the invention.