AU763394B2

AU763394B2 - Hot water system

Info

Publication number: AU763394B2
Application number: AU44396/02A
Authority: AU
Inventors: Ross Haysom; Ravindra Hiremath
Original assignee: Pump and Electrical Engineering Services Pty Ltd
Current assignee: Pump and Electrical Engineering Services Pty Ltd
Priority date: 2001-07-12
Filing date: 2002-05-24
Publication date: 2003-07-24
Anticipated expiration: 2022-05-24
Also published as: AU4439602A

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: PUMP ELECTRICAL ENGINEERING SERVICES PTY LTD A.C.N. 085 197 913 Invention Title: HOT WATER SYSTEM The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 HOT WATER SYSTEM This invention relates to a hot water system for supplying hot water (which term includes tempered and warm water) to a building in which-relatively large numbers of hot water takeoff points are required and which may be dispersed over a considerable distance.

Conventional hot water systems for domestic dwellings generally comprise either a hot water storage tank in which hot water is heated and stored for use or instantaneous heaters for heating water on demand. In domestic environments, the water is distributed to hot water outlets which are relatively close together.

In larger buildings such as apartment blocks, office buildings and the like, hot water outlets can be distributed over a considerable distance. Conventional systems for delivering hot water in these environments comprise a plurality of heaters which heat water and supply the water to a water storage vessel. Cold water is supplied to the heaters by a primary pump. The water storage vessel also includes a cold water inlet. Water is discharged from the hot water vessel and distributed to the outlets in the building by a circuit which may include secondary circulating pumps which return water to the hot water storage vessel. The reason for this is to maintain hot water in the circuit so that when a user turns on a tap which may be a considerable distance from the hot water storage vessel, hot water can be delivered almost instantaneously. If the water is not returned to the vessel so that hot water can be circulated then the water in the circuit will cool over time. When a hot water tap is turned on, cold water will be delivered and will flow for a considerable amount of time before hot water passes through the circuit from the hot water storage tank to the tap. This not only wastes time but also a considerable H:\ARymer\Keep\Speci\P46034.doc 24/05/02 3 amount of water.

In general, the temperature of water delivered from the hot water storage vessel is about 65 0 C. The primary pump which pumps the water through the heaters to the storage vessel, is controlled dependent on the temperature of water in the storage vessel. Water is pumped through the heaters when water is supplied from the vessel and the temperature of the hot water in the vessel drops due to addition of cold water to the vessel. Hot water is also circulated from the vessel through the heaters by the primary pump if the water temperature in the vessel drops due to cooling. In general, the pump capacity is chosen such that the pump supplies sufficient flow rate/pressure to meet maximum demand of the hot water system. Flow pressure is therefore controlled by the pump and also by the supply of cold water to the hot water storage vessel.

The present invention relates to an improvement to the conventional system described above.

The invention may be said to reside in a hot water system for a building, including: water heating means for heating water; a water supply circuit for supplying water to a plurality of water outlets in the building; a pump for pumping water through the water heating means and through the circuit; pressure monitoring means for monitoring the pressure of water in the circuit; and control means for controlling the speed of operation of the pump in accordance with the pressure monitored by the pressure monitoring means so that water is pumped through the water heating means and then through the circuit by the pump dependant on the pressure of the water in the circuit to maintain a substantially constant pressure in the circuit independent of flow rate of water H:\ARymer\Keep\Speci\P46034.doc 24/05/02 4 in the circuit.

The present invention has the advantage of therefore controlling the pressure of water in the circuit by control of the speed of the pump. The water storage vessel can therefore be done away with and the water still supplied at a constant water pressure by appropriate control of the speed of the pump.

In the preferred embodiment of the invention, the hot water circuit circulates water to the plurality of water outlets and then back to a suction side of the pump for recirculation by the pump through the water heating means and the circuit so as to maintain hot water in the circuit for delivery to the outlets when required.

According to this embodiment, since the circuit delivers the water back to the suction side of the pump, only a single primary pump or primary pump system is required in order to circulate the water through the circuit.

Additional secondary pumps provided only for the purpose of circulating water through the circuit are therefore not required.

In another, less preferred, embodiment of the invention, rather than maintain the water in the circuit hot by recirculating the water by the pump through the water heating means, the circuit temperature is provided by other means independent of the pumped water heating, such as heat tracing (thermal wrapping incorporating electric heating) so that the water is maintained hot and can be delivered to the water outlets when required.

Preferably the water heating means comprises a plurality of instantaneous water heaters.

In one embodiment of the invention, the pump is provided H:\ARymer\Keep\Speci\P46034.doc 24/05/02 5 on an inlet side of the water heating means and pumps water through the water heating means by pushing the water through the water heating means.

In another embodiment, the pump is provided on an outlet side of the water heating means and pumps water through the water heating means by drawing the water through the water heating means.

In a still further embodiment of the invention, a water flow compensating means is provided between a cold water inlet to the system and the water supply circuit for supplying cold water into the water supply circuit when water flow requirements through the circuit exceed capability of supply through the water heating means.

In one embodiment, the flow compensating means is coupled in parallel to the pump so that cold water flows from the cold water inlet to the supply circuit without passing through the pump.

In another embodiment, when the pump is provided on the outlet side of the water heating means, the flow compensating means supplies water to an inlet side of the pump so that cold water is drawn by the pump together with hot water from the water heating means for supply to the supply circuit.

Preferably the compensating means comprises a non-return valve so that if the pressure in the supply circuit drops, the pressure difference between the pressure in the circuit and the cold water supply forces the non-return valve open to enable cold water to enter the circuit to increase the pressure in the circuit.

Most preferably each of the water heaters comprises a water heater made by Rinnai Australia Pty Ltd and sold H:\ARymer\Keep\Speci\P46034.doc 24/05/02 6 under the registered trade mark INFINITY.

A preferred embodiment of the invention will be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagram of a water heating system according to a preferred embodiment of the invention; Figure 2 is a block diagram of a control circuit according to the preferred embodiment of the invention; and Figure 3 is a diagram of a system according to a second embodiment of the invention.

With reference to Figure 1, a system 10 is shown which comprises a bank of instantaneous water heaters 12. The bank of heaters 12 in the preferred embodiment comprises five water heaters 12a to 12e.

Depending on the size of the building and the requirements for hot water, additional banks of heaters such as the bank 12' in Figure 1 could also be included. The bank of heaters 12' is identical to the bank 12 and therefore the following description will only include a complete description of the bank 12.

The heaters 12a are preferably instantaneous gas fired water heaters made by Rinnai Australia Pty Ltd and sold under the trade mark INFINITY. A gas supply pipe 14 connects to each of the heaters 12a to 12e by branch line 16 so that gas for combustion can be supplied to each of the heaters 12a to 12e. Cold water is supplied via conduit 20 which includes appropriate flow control devices and non-return valves exemplified by reference numeral 21.

The conduit 20 connects to pump 22 via valves 24 and 26 and then to conduits 28 which supply cold water to each of the heaters 12a to 12c via conduits 30. Hot water is supplied from each of the heaters 12a to 12e by conduits H:\ARymer\Keep\Speci\P46034.doc 24/05/02 7 32 which connect to a hot water supply circuit 34 which delivers hot water to the building so that water can be taken off from a plurality of water outlets collectively represented by reference numeral 36 in Figure i. The circuit 34 then returns through flow control valves 36a to the suction side of pump 22 by joining conduit 20 at point 38.

The circuit 34 includes a pressure monitor 40 for monitoring the pressure of water flowing through the circuit 34. The pressure monitor 40 is connected to a controller 50 which outputs electrical signal on line 52 to the pump 22 for controlling operation of the pump 22.

The pump 22 draws water through the line 20 and supplies the water to the heaters 12a to 12e via the line 28 and branch lines 30. Water is then supplied to the circuit 34 from the conduits 32 and circulated via the pump 22 so as to return to the point 38 and then again through the water heaters to thereby maintain circulating hot water in the circuit 34.

When water is taken off from the water outlets 36, the pressure of the water in the circuit 34 will drop and this drop in pressure will be measured by the pressure monitor The controller 50 will therefore operate the pump 22 to increase the speed of the pump 22 so that more water is pumped through the heaters 12 to restore the pressure in the circuit 34 to the required pressure. Thus, in order to maintain a constant pressure of water in the circuit 34 the pressure is continuously monitored by the monitor and the pump 22 is controlled in speed so as to pump more water through the heaters and the circuit 34 to maintain the pressure in the circuit 34 at the required level regardless of the number of water outlets 36 which may be opened to supply hot water.

H:\ARymer\Keep\Speci\P46034 .doc 24/05/02 8 The controller 50 is shown in Figure 2. The pressure monitor 40 outputs a current signal to a comparator which is usually in the range from 4 to 20mA. The comparator 60 is provided with a reference current 62 and produces an output 64 indicative of the different between the reference current 62 and the current supplied by the pressure monitor 40. The controller includes processing means 66 for determining a pressure calculation based on the different signal 64 and a reference signal 69 is supplied to an inverter 70 which in turn produces a variable frequency control signal 72 for controlling the pump 22. Thus, the control signal 72 will be dependent on the signal supplied from the pressure monitor 40 and the speed of operation of the pump 22 will vary depending on the signal 72 so as to maintain a constant pressure of water in the circuit 34 regardless of the off-take of water from the outlets 36. The speed of operation of the pump will generally be at minimum speed when no water outlets are open so that water is circulated through the circuit 34 and the heaters 12 to maintain a supply of hot water in the circuit 34. When one of the water outlets 36 is open to supply water thereby causing a drop in pressure in the circuit 34, the drop in pressure is measured by the monitor 40 and the speed of the pump 22 is increased by changing the frequency signal 72 supplied to the pump 22 so that more water is pumped from the cold water inlet conduit 20 through the heaters 12c to maintain the required pressure in the circuit 34.

A flow compensating device 80 is located between the water inlet 20 and the circuit 34. The device 80 is provided in cold water line 81 which extends from the cold water inlet to join branch line 34a on the inlet side of the pump 22 via flow controller If the demand for water in the circuit 34 exceeds the amount which can be supplied through the heaters 12, the H:\ARymer\Keep\Speci\P46034.doc 24/05/02 9 device 80 allows cold water to pass from the inlet through the line 81 to the circuit 34 to increase the pressure in the circuit 34 to meet the required demand.

Thus, this embodiment of the invention automatically provides additional water flow should the demand for heated water exceed the system capability.

The device 80 is preferably in the form of a non-return valve which includes a valve element (not shown) and a spring for biasing the valve element into a closed position to prevent flow of water from the circuit 34 back into the line 20. However, if the pressure in the circuit 34 drops, the pressure in the line 20 opens the non-return valve 80 so that cold water can flow through the valve into the circuit 34 to thereby increase the pressure and flow in the circuit 34 to meet the required demand for supply of hot water.

Thus, according to the preferred embodiment of the invention, the system is capable of supplying hot water at a predetermined pressure regardless of the flow rate of water through the circuit 34 (and which is dependent on the amount of water taken off from the water outlets 36).

The pressure of the heated water leaving the heaters 12 is therefore continuously monitored to provide a positive reference of actual pressure which is compared to the set pressure reference and this comparison determines the water pump rate of charge into the circuit 34 and which is dependent on the flow requirements created by usage. The control of the pump dependent on pressure in the circuit 34 also overcomes friction losses inherent in the heaters 12 and may also provide an adjustable flow rate for the circulation of water through the circuit 34, thus maintaining a constancy of temperature in the circuit 34.

The system of the preferred embodiment therefore has the advantage that hot water can be supplied at a set H:\ARymer\Keep\Speci\P46034.doc 24/05/02 10 temperature in relation to a specified flow rate, a constant pressure of water can be supplied over the specific flow rates required and circulation of water through the circuit 34 and back to the heaters 12 ensures consistency of temperature throughout the circuit 34.

Furthermore, sincewater is only heated as it is pumped through the heaters 12 and hot water is not stored, water is only heated as per usage (with the exception of circulated water) and therefore no energy is consumed by the need to store a large volume of hot water in a hot water storage vessel.

Figure 3 shows a second embodiment of the invention in which like reference numerals indicate like parts to those described with reference to Figures 1 and 2.

In the embodiment of Figure 1, the pump 22 is provided on the inlet side of the water heaters 12 and pumps water through the water heaters 12 by pushing the water through the water heaters 12.

In the embodiment of Figure 3, the pump 22 is provided on the outlet side of the water heaters 12 and draws water from the cold water inlet 20 through the heaters 12 and then through the hot water outlet lines 32 to line 34 and then through the pump 22.

In the embodiment of Figure 3 and the embodiment of Figure 1, an emergency bypass 51 is provided in the event of pump failure so that water can bypass the pump 22.

In the embodiment of Figure 3, the compensating device in the form of a non-return valve is provided on the inlet side of the pump and in series with the pump so that when the pressure in the line 34 drops, the non-return valve is opened in the same manner as previously described to enable water to flow from the cold water inlet 20 into the H: \ARymer\Keep\Speci\P46034 .doc 24/05/02 11 circuit 34 to meet the required demand. In this embodiment, the line 81 may include a flow restrictor for limiting the flow of water through the non-return valve 80 to the pump 22.

The embodiment of Figure 3 operates in exactly the same manner as the embodiment of Figure 1, with the pressure monitor 40 performing the same function to enable control of the speed of the motor 22 to supply water at the required pressure in the circuit 34.

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.

H:\ARymer\Keep\Speci\P46034.doc 24/05/02

Claims

2. The system of claim 1 wherein, the hot water circuit circulates water to the plurality of water outlets and then back to a suction side of the pump for recirculation by the pump through the water heating means and the circuit so as to maintain hot water in the circuit for delivery to the outlets when required.
3. The system of claim 1 or 2 wherein, the water heating means comprises a plurality of instantaneous water heaters.
4. The system of any one of claims 1 to 3 wherein, the pump is provided on an inlet side of the water heating means and pumps water through the water heating means by pushing the water through the water heating means. The system of any one of claims 1 to 3 wherein, the pump is provided on an outlet side of the water H:\ARymer\Keep\Speci\P46034.doc 24/05/02 13 heating means and pumps water through the water heating means by drawing the water through the water heating means.
6. The system of any one of claims 1 to 5 wherein, a water flow compensating means is provided between a cold water inlet to the system and the water supply circuit for supplying cold water into the water supply circuit when water flow requirements through the circuit exceed capability of supply through the water heating means.
7. The system of claim 6 wherein, the flow compensating means is coupled in parallel to the pump so that cold water flows from the cold water inlet to the supply circuit without passing through the pump.
8. The system of claim 6 when appended to claim wherein, the flow compensating means supplies water to an inlet side of the pump so that cold water is drawn by the pump together with hot water from the water heating means for supply to the supply circuit.
9. The system of claim 6, 7 or 8 wherein, the compensating means comprises a non-return valve so that if the pressure in the supply circuit drops, the pressure difference between the pressure in the circuit and the cold water supply forces the non-return valve open to enable cold water to enter the circuit to increase the pressure in the circuit. A hot water system for building substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings. H: \ARymer\Keep\Speci\P46034.doc 24/05/02