Abstract:
The invention provides a recirculating shower system comprising a showerhead and shower tray, a circuit configured to collect used water from the shower tray and to recirculate at least part of the used water to the showerhead for further use, the circuit including at least one heat pump to exchange heat between relatively hot water and relatively cold water.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates to a recirculating shower system. In particular the invention relates to a recirculating shower system in which energy is transferred in the recirculation circuit by one or more heat pumps. 
       BACKGROUND 
       [0002]    Water recirculating systems are known for many applications. For example, showers that are arranged to recirculate water within the shower and thereby use less water. Recirculating showers find application principally in portable and mobile applications such as boats and camping vans. For example U.S. Pat. No. 4,828,709 describes a recirculating shower system for use on boats and recreational vehicles. The recirculating water system, which operates with water from a non-mains water supply in the boat or vehicle, comprises filters, a water heater and fresh and used water storage tanks. 
         [0003]    In many parts of the world, fresh water is in short supply and measures are taken to preserve the water supply, and there are often incentives offered by governments for reducing water usage. 
         [0004]    One problem with the use of recirculating showers in domestic applications lies in regulations that require that any water mixed with mains water must meet water purity standards that the waste water from a shower does not meet. 
         [0005]    Domestic showers commonly in use are of two general types, namely electric showers and mixer showers. 
         [0006]    Typically, electric showers draw water solely from a cold mains supply and heat the water as necessary to the desired temperature. This type of shower therefore does not run out of hot water and is able to provide a stable water temperature. They also have the advantage that they are relatively simple to fit in that they require no special plumbing, only a cold water supply. 
         [0007]    The maximum power that can be drawn from a standard domestic electricity supply of 240 volts (for example in Australia and across Europe) is 7.5-11.5 kW, which limits the power that is available to heat up the water as it passes through the shower heater. To get a hot enough shower, it may be necessary to limit the flow rate of the water, typically to a maximum rate of 5-6 litres per minute. Obviously, a higher flow rate could be achieved but only at the expense of providing shower water at a lower temperature. In some parts of the world, this problem is made worse since the maximum power that can be drawn is lower than 7 kW, e.g. in some areas of China, the maximum power that can be drawn is 3 kW, which ultimately can make electric showers unusable due to the extremely low flow rate of heated water. 
         [0008]    Mixer showers achieve the desired water temperature by blending water taken from both hot and cold water supplies using a valve. Mixer showers require both hot and cold water supplies and so obviously require a source of hot water, e.g. a hot water tank or a combination boiler or a multipoint water heater. They therefore require more complicated plumbing than electric showers. In addition, if the water supply is not constant, e.g. because someone else is drawing hot water, the temperature of the shower can fluctuate. 
         [0009]    However, mixer showers can achieve a higher flow rate than electric showers and are cheaper than electric showers. 
         [0010]    Power showers are a variant of mixer showers and include a pump. WO 2006/131743 addresses some of the above issues by providing a recirculating shower system wherein the water within the shower is collected in the shower tray, recirculated via a pump and cleaned by a hydrocyclone, then filtered, pasteurised in an electricity-driven heater, mixed with cold fresh mains water, and delivered back to the showerhead, whereafter the cycle is repeated. 
         [0011]    However, whilst the system is up to 70% more energy and water efficient than a conventional shower, it has a number of weaknesses, including:
       The heater requires up to 9 kW of power to provide a shower with a flow rate of 10 litres per minute. In developed nations this will require a dedicated power supply of 240v and 40 Amps connected directly from the fuse/breaker box to the shower. This is expensive and disruptive to install. In developing nations this can be more power than is supplied to a house via domestic supply, making the shower system not viable in those countries.   The water recirculation percentage achieved by the system is dependent on the ambient water temperature of the cold water supplied; the warmer the cold water input, the less water can be recycled. In very warm countries in the summer, this will mean the recirculation percentage can fall from 70% to as little as 50%.       
 
         [0014]    Overcoming these weaknesses would make the original shower more water efficient, more energy efficient, cheaper and simpler to install, cheaper to run, and available to millions more people. 
       SUMMARY OF THE INVENTION 
       [0015]    In one form, although it need not be the only or indeed the broadest form, the invention resides in a recirculating shower system comprising a showerhead and shower tray, a circuit configured to collect used water from the shower tray and to recirculate at least part of the used water to the showerhead for further use, the circuit including at least one heat pump to exchange heat between relatively hot water and relatively cold water. 
         [0016]    In a further form of the invention, there is provided recirculating shower system comprising a showerhead and shower tray, a circuit configured to collect used water from the shower tray and to recirculate at least part of the used water to the showerhead for further use, the circuit including: a hydrocyclone separator; a filter downstream of the separator; a heat exchanger downstream of the filter; at least one heat pump to exchange heat between relatively hot water and relatively cold water; a heating unit for holding the recirculating water when heated to a pasteurizing temperature; and a mixing tank for mixing relatively hot and relatively cold water upstream of the showerhead. 
         [0017]    Heat pump(s) used in the system of the invention are conventional heat pumps known in the art. Heat pumps are systems that transfer heat from one location to another. Two common examples of the use of heat pumps are fridges and air conditioners. Heat pumps work by pumping a gas around a sealed system through two locations. In the first location the gas is allowed to expand, which cools it and draws heat from whatever is around it. In the second location the gas is compressed which produces heat, which is then radiated into that location. The heat that is taken from the first location is therefore moved to the second location. The first location decreases in temperature and the second location increases in temperature. 
         [0018]    The energy required to power a heat pump is only required to compress and circulate the gas within the heat pump circuits. This makes heat pumps extremely efficient as, for each Joule of energy used to power the pump, the system will move between 3 and 6 Joules of heat from the first location to the second location. 
         [0019]    Therefore a heat pump system with a 3 Kilowatt input will actually move (output) between 9 kW and 18 kW of heat energy. 
         [0020]    The liquid used in the invention can be any liquid used in a recirculating manner where the liquid requires heating and/or cooling for use. 
         [0021]    Referring to the forms of the invention above, the energy recirculating system of the invention reduces energy requirements by efficiently transferring the existing energy within the system, resulting in a system which requires minimal, if any, additional heat energy to be input to the system. 
         [0022]    The heat pump(s) are configured in such a way as to have the cooling circuit within both a cold water input to the system and the waste water outflow from the system and the heating circuit in the location of the electric heater of the original design. 
         [0023]    The system thereby:
       Removes heat from the cold water input, controlling and reducing the temperature of the fresh cold water fed into the system and maximising the water recirculation percentage.   Removes energy from the waste water sent to the sewer reducing energy wastage.   Transfers the energy from the cold water input and the waste water output to the heating unit.       
 
         [0027]    In order that the invention may be more readily understood and put into practice, one or more preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWING 
         [0028]      FIG. 1  is a schematic of a recirculating shower system of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    A detailed, non-limiting example of the use of the invention in a recirculating shower system, such as that described in WO2006/131743 is provided. 
         [0030]    Referring to  FIG. 1 , in a shower system of the invention, the mains water ( 1 ) is introduced to the system via a water pipe ( 2 ) passing through a hydraulic jump ( 3 ), which prevents water passing back from the system into the mains water, and is pumped by a pump ( 4 ) through the cold water inlet ( 5 ) of a shower mixer ( 6 ). The mixer adjusts the relative cold and hot flows until the mixed flow is at the required temperature for the shower. This will be discussed in more detail below. 
         [0031]    The mixed water passes from the mixer to a bypass valve ( 7 ) which can direct the shower water to either:
       The showerhead ( 22 ) via a pipe or hose ( 21 ), or   To a bypass circuit ( 8 ).       
 
         [0034]    When the shower is turned on the bypass valve is set automatically to direct the water to the bypass circuit ( 8 ), diverting water away from the showerhead ( 22 ) so that no water is used until the preset temperature is reached and the user has pressed the start button. This prevents any wasted water during temperature setting, or if the user does not immediately use the shower after turning the shower on. 
         [0035]    When the bypass valve .is set to direct water to the showerhead, the shower water is collected in a shower tray ( 23 ) incorporating an inlet nozzle ( 24 ) connected to a water pipe ( 25 ) which connects to the recirculation circuit pump ( 27 ) via a water pipe ( 26 ). In order to prevent the recirculation circuit from blocking, the inlet ( 24 ) to the recirculation circuit is covered by a strainer or mesh of a similar design to that used in a spa bath. 
         [0036]    When the bypass valve is set to bypass, the water is passed to the recirculation pump ( 27 ) via water pipes ( 8 ) and ( 26 ). 
         [0037]    The recirculation pump ( 27 ) pumps the water to a hydrocyclone ( 10 ) via a water pipe ( 9 ). The purpose of the hydrocyclone is two-fold: 
         [0038]    It removes suspended solids smaller than 2 mm from the shower water which extends the life of the filter ( 14 ). A hydrocyclone works by spinning the water; any particles that are heavier than the water are forced to the outside of the hydrocyclone where they fall to the bottom and are carried away by the underflow ( 11 ); the outlet at the bottom of the hydrocyclone. The cleaner water is forced upwards through the vortex finder at the top of the hydrocyclone to the overflow ( 13 ). The hydrocyclone generally sends 30% of the water to the underflow and 70% to the overflow. 
         [0039]    By reducing the recirculation volume by 30%, the hydrocyclone necessitates the re-introduction of new mains cold water. The introduction of the cold water allows the recirculated water to be heated, higher than the temperature required for showering, as the cold water will reduce the temperature of the hot water within the mixer. This therefore allows the recirculated water to be ‘overheated’ to a pasteurisation temperature of 72° C. which is sufficient to kill Legionella and other pathogens. 
         [0040]    From the hydrocyclone overflow ( 13 ) the water enters a filter ( 14 ) which removes chlorine, any residual particulate matter not already removed and any shampoo and soap within the water. 
         [0041]    From the filter ( 14 ) the water enters a heat exchanger ( 16 ) via a water pipe ( 15 ). The heat exchanger comprises two circuits:
       a ‘cold’ circuit passing from the filter ( 14 ) to the temperature regulator ( 17 ) and heating unit ( 18 ), and   a ‘hot’ circuit passing from the heating unit ( 18 ) and temperature regulator ( 17 ) back to the shower mixer ( 6 ) via a water pipe ( 19 ).       
 
         [0044]    The function of the heat exchanger is to increase the temperature of the water travelling towards the heating unit, which reduces the workload of a heater which may be in the heating unit, and to reduce the temperature of the water flowing to the mixer to a temperature closer to a temperature suitable for showering. 
         [0045]    From the heat exchanger ( 16 ), the water passes through a temperature and flow regulator ( 17 ) which monitors the temperature and flow of the water to insure that the temperatures reached by the heating unit are at least enough to pasteurise the water (72° C.) but below a level which would cause excessive pressure within the heating unit. 
         [0046]    In WO2006/131743 the heating unit includes an electric thermal resistance heater. In the invention this is replaced, or supplemented, by the hot circuit of heat pump A ( 32 ) and heat pump B ( 31 ). The vessel and the two hot circuits combine to create the heat transfer point ( 34 ) where the heat energy collected by heat pumps A &amp; B at heat collection point ( 30 ) on the cold inlet circuit, and heat collection point ( 33 ) on the hydrocyclone underflow ( 11 ) are transferred to the recirculated shower water to increase the water temperature to 72° C. 
         [0047]    From the heating unit/heat transfer point, the hot recirculated shower water passes back through the hot circuit of the heat exchanger ( 16 ) to the hot inlet ( 20 ) of the shower mixer ( 6 ) via water pipe ( 19 ). Within the mixer ( 6 ) the temperature sensor(s) ( 29 ) monitor the temperatures of the cold inlet ( 5 ) and the hot inlet ( 20 ) sending the information to a central processing unit ( 28 ) which adjusts the flow volumes to provide water at the required shower temperature at the showerhead ( 22 ). 
         [0048]    The hydrocyclone ( 10 ) removes heavier particles from the water and splits the flow so that about 30% leaves through the underflow ( 11 ) carrying the majority of undissolved solids. This portion of the water still retains energy in the form of heat from the original shower. In general, the temperature of this water is about 40° C. This water is fed into heat recovery tank A ( 33 ). Heat pump A ( 32 ) transfers the residual energy in the water in heat recovery tank A ( 33 ) to the pasteurisation unit ( 34 ). Once energy has been recovered, the cooled water from heat recovery tank A ( 33 ) exits to the drains ( 12 ). 
         [0049]    The balance of water from the hydocyclone ( 10 ), which is now clean, exits through the top of the hydrocyclone overflow ( 13 ). 
         [0050]    The clean water is then carried to the filter ( 14 ) where it becomes visually clean and chlorine is removed. 
         [0051]    The water is now visually clear, but must be sterilised at 72° C. for 15 seconds. 
         [0052]    After the carbon filter ( 14 ) the water therefore enters a heat exchanger ( 16 ). The heat exchanger raises the temperature of the water from about 41° C. to about 55° C. This reduces the energy input required to reach pasteurisation temperature and increases the efficiency of the shower. 
         [0053]    Simultaneously, fresh cold water is pumped into heat recovery tank B ( 30 ). Energy recovered from this tank by heat pump B ( 31 ) is also fed into the pasteurisation unit ( 34 ). The energy provided to the pasteurisation unit ( 34 ) by the heat pumps A ( 32 ) and B ( 31 ) should be sufficient energy in most circumstances to obviate the need for a heating element in the pasteurisation unit ( 34 ). This is a large and significant energy and cost saving aspect of the invention. 
         [0054]    In the system of the invention, heat pumps A and B can be replaced with a single heat pump having 2 circuits. 
         [0055]    In the mixer unit ( 6 ) the recirculated hot water and cold fresh mains water are mixed to provide a shower of the required temperature. The fresh water also replaces the volume of water lost from the underflow ( 11 ) of the hydrocyclone ( 10 ). 
         [0056]    After passing through the mixer unit ( 6 ), the water passes the bypass valve where it is either diverted around the shower (pause mode) or to the showerhead ( 22 ), and the energy and water cycles of the system of the invention continue as described above. 
         [0057]    Having broadly described the invention with reference to  FIG. 1 , more detail on some of the energy calculation aspects of this embodiment of the invention will be discussed. 
       Thermodynamic and Energy Calculations 
       [0058]    With regard to heat recovery tank A ( 33 ) for the hydrocyclone underflow and to heat recovery tank B ( 30 ) for the inlet cold water, the cold water inlet water and the underflow water must be able to flow, but their temperature can be reduced to very close to freezing. Therefore any heat in excess of 1° C. in either of these tanks can be considered as ‘surplus’ heat. 
         [0059]    The energy content of that ‘surplus’ heat will depend on the ambient temperature of the water, but assuming that the shower is inside a house, the ambient water temperature should be similar to that of the house itself and will therefore be around 20° C. when the shower is first activated. 
         [0060]    If the tanks each hold 5 L, this means that each litre of water in the heat .recovery tanks has a ‘spare’ 19° C. of heat energy. The specific heat of water is 4.2 kJ/L, which means that each 5 L heat recovery tank contains 399 kJ of ‘spare’ energy. Combined, both heat recovery tanks therefore hold a total of 798 kJ of energy that could be recovered by a heat pump system. 
         [0061]    Turning to the pasteurisation requirements of the recycled water, as the water in the pasteurisation unit needs to be held at 72° C. for 15 seconds, the size of the pasteurisation tank has to be one quarter of the flow rate of 1 minute (15 seconds being one quarter of a minute). The flow rate will be 7 L/min (assuming a flow rate at the showerhead of 10 L/min and a recirculation fraction of 70%). Therefore, the pasteurisation unit ( 34 ) will need to hold at least 1.75 L. For illustrative purposes, this has been increased to 2 L. 
         [0062]    On start-up of the system, the temperature of the water in the pasteurisation unit is also assumed to be 20° C. and, in order to reach pasteurisation temperature, will need to be raised to 72° C.: an increase of 52° C./L. The energy required to do that will be 2.0 L×4.2 kJ/L×52° C.=436.8 kJ. Comparing this figure to the ‘surplus’ energy in the heat recovery tanks A ( 30 ) and B ( 33 ), the, ‘surplus’ energy is more than enough to raise the temperature of the pasteurisation unit to 72° C. 
         [0063]    With regard to heat pumps A ( 31 ) and B ( 32 ), In order to maintain the pasteurisation unit ( 34 ) at 72° C. during operation, the heat pumps A ( 31 ) and B ( 32 ) need to be capable of transferring enough energy to the pasteurisation unit ( 34 ) to maintain its flow at 72° C. The flow rate is 7.0 L/min and the maximum increase in temperature that is needed is 20° C. This requires a constant input of 7.0 L/min×20° C.×4.2 kJ/L=588 kJ/min. This converts to 35,280 kJ/h or 9.8 Kilowatt hours. With a CoP of 3.0, this requires energy inputs of about 3.3 Kilowatts in the heat pumps to sustain the operation of the shower. 
         [0064]    On start-up, the energy transfer from the heat recovery tanks A ( 33 ) and B ( 30 ) to the pasteurisation unit ( 34 ) is 436.8 kJ, to reach 72° C. This requires a transfer of 218.4 kJ from each of the heat recovery tanks. This will reduce the temperature in each tank by 10.4° C. If the heat output from the heat pumps at maximum is 9.8 Kilowatts, or 588 kJ per minute, it takes 436.8 kJ/588 kJ of a minute, or 45 seconds, to reach pasteurisation temperature. 
         [0065]    Assuming that the ambient water temperature at the start is 20° C. each heat recovery tank has a temperature of 10° C. when the shower is started. During operation, the flow through each heat recovery tank is 3 L. This assumes a 10 litre flow at the showerhead and a 70% recirculation fraction. The flow through each heat recovery tank is equal, because the water flowing in from the mains must equal that sent to the sewer via the hydrocyclone underflow. 
         [0066]    To maintain the cold water inflow at 10° C. during shower operation, the heat&#39; energy drawn from heat recovery tank B ( 30 ) must equals the heat energy input to the tank by the fresh mains water. Assuming that the ambient water temperature is 20° C., each litre of water introduces 42 kJ to the tank (1 L×10° C.×4.2 kJ/° C./L). As the flow through the tank is 3 L/min, the input will be 126 kJ/min and this is transferred to the pasteurisation unit ( 34 ) to maintain the input temperature from heat recovery tank B ( 30 ) to the mixer unit ( 6 ) at 10° C. 
         [0067]    Assuming that the .heat pumps will be working at maximum during steady state operation then the heat pumps transfer 588 kJ/min to the pasteurisation unit ( 34 ). If 126 kJ is coming from the heat recovery tank B ( 30 ), the balance of 462 kJ/min will be drawn from heat recovery tank A ( 33 ). 
         [0068]    The water entering the heat recovery tank A ( 33 ) will have a temperature of 41° C. (45° C. being the shower temperature in this example and 4° C. being the known temperature loss in a shower) and will be flowing at a rate of 3 litres per minute. Drawing 462 kJ/min from this tank will therefore reduce the temperature by (462 kJ/min/3.0 L/min/4.2 kJ/° C./L)=36.6° C. and the water in heat recovery tank A ( 33 ) will therefore be reduced to 5° C. 
         [0069]    It is clear from the above that the introduction of heat pumps obviates the use of an electric element to heat the used water to pasteurisation temperature. This is highly advantageous because energy consumption needed for a shower of the invention is reduced by a further 65% compared to the recirculating showers currently available. This results in a shower that uses less than 10% of the energy of a conventional shower. In addition, the heat pumps allow control of the ambient water temperature which maximises the amount of water that can be recirculated, even in hotter climates. Also, the pumps allow waste heat to be scavenged from the waste water to be discarded without reintroducing that water. 
         [0070]    Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. 
         [0071]    Throughout this specification, unless the context requires otherwise, the word “comprises”, and variations such as “comprise” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not to the exclusion of any other integer or group of integers.