Fluid heating and/or cooling system and related methods

Abstract

A method of and system for heating and/or cooling a fluid, the method comprising moving the fluid through a secondary side of a heat exchanger and controlling the temperature of a primary side of the heat exchanger such that the temperature of the primary side of the heat exchanger is maintained substantially at a determined temperature interval from a reference temperature which is a function of at least one of: a temperature of an inlet to the secondary side and a temperature of an outlet of the secondary side.

Claims

1. A fluid heating and/or cooling system arranged to heat and/or cool a fluid to a desired temperature, the desired temperature being the temperature to which fluid within the fluid heating and/or cooling system is to be heated or cooled, the fluid heating and/or cooling system comprising: a heat pump comprising a compressor, an evaporator having an evaporating temperature at which refrigerant therein evaporates and a condenser having a condensing temperature at which refrigerant therein condenses, connected by a refrigerant pipe-work system arranged to carry a refrigerant; wherein one of the condenser and the evaporator provides a heat exchanger between the fluid and the refrigerant; the heat exchanger having: (i) a primary inlet arranged, in use, to receive the refrigerant; (ii) a secondary inlet arranged, in use, to receive the fluid; and (iii) a secondary outlet arranged, in use, to output the fluid; a fluid storage vessel arranged, in use, to allow fluid therefrom to be circulated through the heat exchanger via the secondary inlet, and to receive fluid returned from the secondary outlet, in a heating pipe-work system; at least one temperature sensor arranged to monitor a temperature of the fluid and to generate a temperature output; and a system controller arranged to have input thereto the at least one temperature output and to generate a reference temperature from the at least one temperature input thereto, wherein the reference temperature is a function of the temperature of at least one of a secondary inlet and outlet of the heat exchanger and the controller is further arranged to control a temperature of the primary side of the heat exchanger in response to the reference temperature such that the temperature of the primary side of the heat exchanger is repeatedly adjusted so as to remain substantially at a determined temperature interval from the reference temperature as the fluid approaches the desired temperature.

2. The fluid heating and/or cooling system of claim 1 wherein: (a) when the fluid is to be heated, the condenser provides the heat exchanger, the temperature of the primary side is the condensing temperature, and the controller is further arranged to control the condensing temperature in response to the reference temperature such that the condensing temperature is maintained substantially at a determined temperature interval above the reference temperature; and/or (b) when the fluid is to be cooled, the evaporator provides the heat exchanger, the temperature of the primary side is the evaporating temperature, and the controller is further arranged to control the evaporating temperature in response to the reference temperature such that the evaporating temperature is maintained substantially at a determined temperature interval below the reference temperature.

3. The system of claim 1 wherein the temperature sensor is located in a region of the secondary inlet of the heat exchanger such that the temperature of the secondary inlet can be determined.

4. The system of claim 1 wherein the temperature sensor is not located at the secondary inlet and wherein the controller is arranged to calculate the temperature of the fluid entering the secondary inlet using the temperature output.

5. The system of claim 1 in which there exists a known temperature gradient between the primary side of the heat exchanger through which refrigerant flows and a secondary side of the heat exchanger through which the fluid flows and the determined temperature interval substantially corresponds to the temperature gradient.

6. The system of claim 1 in which the controller is arranged to maintain at least one of the following: (i) the condensing temperature at a minimum whilst still ensuring that heat transfer occurs between the refrigerant and the fluid; and/or (ii) the evaporating temperature at a maximum whilst still ensuring that heat transfer occurs between the refrigerant and the fluid.

7. The system of claim 6 in which the minimum means a temperature difference of between 1 and 6 degrees centigrade between the condensing temperature and a temperature of the fluid at an outlet from a secondary side of the heat exchanger.

8. The system of claim 6 in which the maximum means a temperature difference of between 1 and 6 degrees centigrade between the evaporating temperature and a temperature of the fluid at the outlet from a secondary side of the heat exchanger.

9. The system of claim 1 wherein the heat pump is at least one of the following: (i) an air-source heat pump; (ii) a ground source heat pump; and (iii) a water source heat pump.

10. The system of claim 1 wherein a target condensing temperature and/or evaporating temperature is calculated by the controller, wherein the calculation uses factors including one or more of the following: (i) type of heat exchanger; (ii) the fluid temperature at the secondary inlet; (iii) maximum and/or minimum condensing temperatures of the condenser; (iv) maximum and/or minimum evaporating temperatures of the evaporator; (v) losses in the fluid heating system; and (vi) a target fluid temperature of the fluid within the fluid storage vessel.

11. A control system arranged to control the heating and/or cooling of a volume of fluid contained within a fluid storage vessel to a desired temperature, the desired temperature being the temperature to which the volume of fluid is to be heated or cooled using a heat exchanger, the control system comprising: at least one input arranged to have input thereto the output of a temperature sensor arranged to monitor a temperature of the fluid to be heated or cooled; and wherein a controller is arranged to generate a reference temperature from the at least one temperature input thereto, wherein the reference temperature is a function of the temperature of at least one of a secondary inlet and outlet of the heat exchanger, through which the fluid flows, and the controller is further arranged to control a temperature of a primary side of the heat exchanger, through which refrigerant flows, in response to the reference temperature such that the temperature of the primary side of the heat exchanger is repeatedly adjusted so as to remain substantially at a determined temperature interval from the reference temperature as the fluid approaches the desired temperature.

12. The system of claim 11 in which, within the heat exchanger that the control systems is arranged to control, there exists a known temperature gradient between the primary side of the heat exchanger and the secondary side of the heat exchanger and the determined temperature interval substantially corresponds to the temperature gradient.

13. The system of claim 11 in which the controller is arranged to maintain the temperature of the primary side at a minimum whilst still ensuring that heat transfer occurs between the refrigerant and the fluid, when the system is arranged to heat the fluid.

14. The system of claim 11 in which the controller is arranged to maintain the temperature of the primary side at a maximum whilst still ensuring that heat transfer occurs between the refrigerant and the fluid, when the system is arranged to cool the fluid.

15. The system of claim 13 in which the minimum and/or maximum means a temperature difference between the temperature of the primary side and a temperature of the fluid at an outlet from a secondary side of the heat exchanger of between 1 and 7 degrees centigrade.

16. The system of claim 13 in which the minimum and/or maximum means a temperature difference between the temperature of the primary side and a temperature of the fluid at an outlet from a secondary side of the heat exchanger of between 1 and 4 degrees centigrade.

17. A method of heating and/or cooling a fluid within a fluid storage vessel to a desired temperature, the desired temperature being the temperature to which fluid within the fluid storage vessel is to be heated or cooled, the method comprising moving the fluid from the storage vessel through a secondary side of a heat exchanger and back to the fluid storage vessel, and controlling the temperature of a primary side of the heat exchanger such that the temperature of the primary side of the heat exchanger is repeatedly adjusted so as to remain substantially at a determined temperature interval from a reference temperature which is a function of at least one of a temperature of an inlet to the secondary side and a temperature of an outlet of the secondary side as the fluid approaches the desired temperature.

18. The method of claim 17 in which the primary side of the heat exchanger comprises a portion of a condenser within a refrigeration cycle.

19. The method of claim 17 in which the primary side of the heat exchanger comprises a portion of an evaporator within a refrigeration cycle.

Description

(1) There now follows by way of example only a detailed description of an embodiment of the present invention with reference to the accompanying drawings in which:

(2) FIG. 1 shows a schematic of an embodiment of the system in which an air source heat pump is used to heat water; and

(3) FIG. 2 shows a schematic of the controls of the embodiment of the invention shown in FIG. 1.

(4) For reasons of clarity, it is convenient to describe an embodiment in terms of a system arranged to heat a fluid, and in particular to heat water. However, the skilled person will appreciate that other embodiments may be arranged to heat and/or cool other fluids.

(5) The hot water heating system 100 shown in FIG. 1 is based on the use of an Air Source Heat Pump (ASHP) 110. The heating system 100 includes a compressor 102, condenser heat exchanger 104 and evaporator 106 each of which are linked by a refrigerant pipe-work system 108 and arranged to provide a refrigeration cycle. An evaporating control valve 112 is provided within the refrigerant pipe-work system 108 between the condenser 104 and the evaporator 106. The refrigerant pipe-work system 108 is arranged to conduct a refrigerant through a primary side 104a of the condenser heat exchanger 104.

(6) The refrigerant flows within the refrigerant pipe-work system 108, from the evaporator 106 to the compressor 102. The gas in this pipe section is at low pressure and temperature; the compressor 102 increases the temperature and pressure, and the heated, pressurised refrigerant then flows to a primary side 104a of the condenser heat exchanger 104, entering via a primary inlet 124a, which condenses the fluid within the refrigerant pipe system 108 to a high pressure, moderate temperature, liquid, which then exits via a primary outlet 124b. The condenser heat exchanger 104 allows heat to be transferred from the refrigerant to the fluid. The lower temperature refrigerant is then returned, via the evaporating control valve 112, to the evaporator 106, which extracts heat from the heat source, which in this case is outside air 132. The evaporating control valve 112 (which may be thought of as an expansion control means) lets the high pressure liquid expand into the evaporator 106 to a low pressure, cool, gas.

(7) The passage of refrigerant around the refrigerant pipe-work system 108 has been described in relative terms, such as low, medium, high. The skilled person will appreciate that these terms are described with reference to other parts of the refrigerant pipe-work system 108.

(8) The system 100 includes a hot water storage vessel 114, a heating pipework system 116a, 116b and at least two pumps 118, 120. Cold water enters the hot water storage vessel 114 via the cold feed 122 at a bottom region of the vessel 114. The cold water entering the vessel 114 here replaces the water leaving the vessel 114 via water pipe-work system 116b to be used for hot water services 126 such as washing, showers, baths and the like.

(9) At the same time, in order to heat the water for washing, the water pipework system 116a circulates cold water from the bottom region of the tank to a secondary side 104b of the condenser heat exchanger 104. The water flowing into the secondary side 104b is heated with heat from the primary side 104a of the condenser heat exchanger 104 and returned to the vessel 114.

(10) Hot water in the vessel 114 stratifies so that hot water can be stored for use in the top of the vessel, while colder water enters and is heated at lower levels in the vessel.

(11) The temperature sensor 130 measures the temperature of the water in a region of the secondary inlet 128a of the condenser heat exchanger 104.

(12) In alternative embodiments, the temperature sensor 130 is located elsewhere on the pipework loop 116a or within the vessel 114, near the entrance to pipework loop 116a. In such embodiments, the skilled person will appreciate that there is typically a known temperature drop around points of the heating pipe-work system and the temperature of the water at the secondary inlet 128a can be determined from other points of the heating pipe-work system.

(13) The temperature sensor 130 provides a temperature output.

(14) In alternative or additional embodiments, the system further comprises additional temperature and/or temperature/pressure sensors. Advantageously, such sensors are positioned at the inlet and/or outlet of the compressor 102 and/or evaporator 106 and at one or more positions in or near the fluid storage vessel 114.

(15) In addition to the valve 112 the refrigerant pipe work system also comprises a further valve 222 arranged to control the rate at which refrigerant can pass.

(16) FIG. 2 shows a control system 200 of the embodiment described above. In particular, a controller 202 is provided to accept inputs, as described below, and process those inputs to control the system described in relation to FIG. 1.

(17) Conveniently, the controller 202 comprises a processor. The processor may be any suitable processor such as Intel i3, i5, i7 or the like; an AMD Fusion processor; and Apple A7 processor.

(18) This temperature output from the temperature sensor 130 is provided as an input to the control system controller 202. The controller 202 controls the condensing temperature of condenser heat exchanger 104 in response to the temperature output such that the condensing temperature is a determined temperature interval above a reference temperature generated from the temperature of the water entering the secondary inlet 128a.

(19) In this embodiment, the temperature output represents the temperature of the water entering the secondary inlet 128a. In alternative or additional embodiments, the temperature sensor 130 is located at or near the secondary outlet 128b and the temperature output represents the temperature of the water leaving the secondary outlet 128b. The reference temperature is then generated by the controller 202 using the temperature output.

(20) In additional or alternative embodiments, the temperature sensor 130 is not located at the secondary inlet 128a or outlet 128b and is instead located elsewhere in the region of pipework 116a; the temperature of the fluid entering the secondary inlet 128a or leaving the secondary outlet 128b is calculable using the temperature output and other factors such as heat loss from pipes and temperature difference between the secondary inlet 128a and the secondary outlet 128b. The temperature output is therefore a known function of the temperature of the water entering the secondary inlet 128a and/or the temperature of the water leaving the secondary outlet 128b. The reference temperature is then generated from the temperature output by the controller 202.

(21) There is a temperature gradient across the secondary side 104b of the condenser heat exchanger 104 and the reference temperature is some function based upon at least one temperature within the secondary side 104b. In some embodiments, the reference temperature is the average temperature between the secondary inlet 128a and the secondary outlet 128b.

(22) In the present embodiment, the determined temperature interval is pre-set by a user or by software provided with the condenser heat exchanger 104. In other embodiments, controller 202 calculates the temperature interval to use based upon factors including one or more of the following: (i) the type of heat exchanger; (ii) the water temperature at the secondary inlet; (iii) maximum and minimum condensing temperatures of the condenser; (iv) the reference temperature; and (v) the desired hot water temperature; i.e. the temperature to which fluid within the fluid storage vessel is to be heated.

(23) The controller 202 then causes the compressor 102 and/or the evaporator control valve 112 to regulate the flow rate and/or pressure and temperature of the refrigerant, within the refrigerant pipe-work so as to reduce or increase the condensing temperature within the condenser heat exchanger 104 so that the condensing temperature is, or is close to, the reference temperature plus the determined temperature difference.

(24) In the description below, the connections between the controller 202 and the various components are described as wired connections. These connections may operate over any suitable protocol, such as RS232; RS485; TCP/IP; USB; Firewire; or the like; or a proprietary protocol. However, in other embodiments, it is also possible for the connections to be wireless in which case protocols such as Bluetooth; WIFI; or a proprietary protocol may also be suitable.

(25) In the embodiment shown in FIG. 2, the controller 202 communicates with the compressor 102 and the temperature sensor 130 electronically via wired communication channels 210b and 210i respectively. The controller 202 controls the compressor 102 to modulate the compressor 102 so as to allow adjustment of the condensing temperature.

(26) In some embodiments, the controller 202 also communicates with one or more of valves 112, 222 on the primary and secondary sides of the compressor 102, so as to regulate flow through the compressor 102 and hence adjust the condensing temperature.

(27) In alternative or additional embodiments, the controller 202 communicates with further temperature sensors such as the below to provide additional data/feedback. Thus, each of the following temperature sensors is arranged to generate a temperature output which is input to the controller 202: 230a in a region of the secondary outlet 128b of the heat pump condenser 104; 230b in a region of the lower level of the fluid storage vessel 114; 230c in a region of the higher level of the fluid storage vessel 114; and 230d in a region of the outlet of the evaporator 106.

(28) In alternative or additional embodiments, the controller 202 communicates with pressure/temperature sensors 232a, 232b in a region of the primary condenser inlet 124a and/or in a region of the evaporator 106 inlet.

(29) Advantageously, embodiments that utilise temperature sensors in addition to temperature sensor 103 increase the accuracy of the reference temperature and/or temperature interval calculation and/or to further optimise the heating system.

(30) The controller 202 also communicates with some or all of output control mechanisms 220, 112 and 222. The controller 202 can modulate the output of the compressor 102 by means of the compressor motor controller 220. Additionally or alternatively, the controller 202 can cause the evaporator expansion valve 112 and the condenser control valve 222 to be opened or closed or adjusted between the two extreme positions. Additionally or alternatively, the controller 102 can regulate the evaporator fan motor 240 and the condenser secondary pump 118.