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1. (WO2018226706) RECIRCULATING FLUID HEATING SYSTEMS
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CLAIMS

1. A liquid heating system comprising:

(a) a reservoir;

(b) a cold liquid supply communicating with the reservoir;

(c) a heater having an inlet connected to the reservoir and an outlet connected to one or more fixtures;

(d) a heated liquid return connection connected between the outlet of the heater and the reservoir;

(e) a pump connected in series with the heater, whereby the pump can draw liquid from the reservoir and impel the liquid in a predetermined downstream direction through the heater and through the return connection to the reservoir;

and

(f) a controller operable to actuate the heater to supply heat to liquid passing from the inlet to the outlet so as to bring the liquid at the outlet to a setpoint temperature, the return connection and pump being constructed and arranged to permit liquid flow from the outlet of the heater to the reservoir but prevent liquid flow from the reservoir to the fixtures through the return connection.

2. A system as claimed in claim 1 wherein the return connection includes a check valve.

3. A system as claimed in claim 2 wherein the reservoir is closed and the cold liquid supply is arranged to supply the cold liquid under pressure so as to maintain liquid in the reservoir under superatmospheric pressure.

4. A system as claimed in claim 1 wherein the reservoir is open to the atmosphere, so that liquid in the reservoir is under atmospheric pressure.

5. A system as claimed in claim 4, wherein the pump is operable to drive liquid through the heater to the one or more fixtures.

6. A system as claimed in claim 5, further comprising a demand sensor operative to detect operation of one or more of the fixtures to draw liquid from the outlet of the heater, wherein the controller is operative to actuate the circulating pump at a first pumping power to impel liquid through the heater when none of the fixtures is in operation and to a second pumping power higher than the first pumping power when one or more of the fixtures is in operation.

7. A system as claimed in claim 1 wherein the reservoir is unfired.

8. A system as claimed in claim 7 wherein the reservoir is selected from the group consisting of stackable reservoirs, collapsible reservoirs, and reservoirs constructed on site.

9. A system as claimed in claim 1 wherein the control system is operable to vary the amount of heat supplied to the liquid by the heater within a range of non-zero heating rates responsive to the temperature detected by the sensor.

10. A system as claimed in claim 9 further comprising a cold liquid intake connection connected between the source of cold liquid and the inlet of the heater, the controller being operative to actuate the cold liquid inlet connection to provide cold liquid flow through the intake connection so that a combination of cold liquid and liquid from the reservoir is supplied to the inlet of the heater.

11. A system as claimed in claim 10 wherein the controller is operative to control a ratio of (i) cold liquid from the cold liquid intake connection to (ii) liquid from the reservoir supplied to the inlet of the heater and thereby maintain the heater at a heating rate at or near a setpoint heating rate while maintaining liquid discharged from the heater at or near the setpoint temperature.

12. A system as claimed in claim 11 further comprising a temperature sensor operative to detect the temperature of liquid passing out of the outlet of the heater, wherein the controller is operative to adjust the heating rate applied by the heater so as to maintain the temperature at the setpoint temperature, and to control the ratio responsive to the heating rate applied by the heater.

13. A system as claimed in claim 1 wherein the control system is operative to vary the setpoint temperature responsive to a control input representing a condition prevailing at one or more of the fixtures.

14. A system as claimed in claim 1 wherein the control system is operative to vary the setpoint temperature responsive to a control input representing operation of different ones of the fixtures to draw liquid from the outlet of the heater.

15. A system as claimed in claim 1 further comprising a temperature sensor operative to detect a temperature of liquid passing out of the heater, and wherein the control system is operative to deactivate the pump and the heater when the temperature detected by the sensor is at or approximates the setpoint temperature and the heater is not supplying heat

16. A system as claimed in claim 1 further comprising a temperature sensor is operative to detect the temperature of liquid passing from the reservoir to the heater and wherein the control system is

operative to deactivate the pump and the heater when the temperature detected by the sensor is at or approximates the setpoint temperature.

17 A system as claimed in claim 15 or claim 16 wherein the control system is operative to reactivate the pump after a period of deactivation regardless of the temperature detected by the sensor, and then, responsive to the temperature detected by the sensor, either (i) maintain the pump in operation and activate the heater or (ii) deactivate the pump again.

18. A system as claimed in claim 1 further comprising a demand sensor operative to detect operation of one or more of the fixtures to draw liquid from the outlet of the heater, and to raise the setpoint temperature responsive to detection of demand, so that the heater supplies the heated liquid to the fixtures at a temperature higher than a temperature of liquid stored in the tank.

19. A heating unit for use in a liquid heating system comprising:

(a) a frame;

(b) components mounted to the frame including:

(i) a heater having an inlet and an outlet;

(ii) an outlet end connection connected to the outlet of the heater, the outlet end connection assembly including a reservoir return connection point and a fixture connection point,;

(iii) an inlet end connection defining a reservoir draw connection point communicating with the inlet of the heater;

(iv) a pump connected in series with the heater, the pump being operable to impel liquid from the inlet end connection to the outlet end connection through the heater, the outlet end connection assembly being arranged to allow liquid flow from the outlet of the heater to the reservoir return connection point but prevent liquid flow from the reservoir return connection point to the outlet of the heater and the fixture connection point; and

(vi) a controller operable to actuate the heater to supply heat to liquid passing from the inlet to the outlet so as to maintain the liquid passing out of the outlet at a setpoint temperature.

20. A unit as claimed in claim 19 wherein the outlet end connection includes a check valve between the outlet of the heater and the reservoir return connection point.

21. A unit as claimed in claim 19 or claim 20 wherein the frame defines an enclosure, the heater and pump being disposed within the enclosure, the connection points being accessible from outside of the enclosure.

22. A method of constructing a heated liquid supply system comprising connecting the reservoir return connection point and reservoir draw connection points of a unit as claimed in claim 19 to a

reservoir formed separately from the unit, connecting the fixture connection point of the unit to one or more fixtures adapted to use the heated liquid.