GB2528946A

GB2528946A - Improved heating system

Info

Publication number: GB2528946A
Application number: GB1413973.7A
Authority: GB
Inventors: Mike Kellett
Original assignee: HUSKY HEAT PUMPS Ltd
Current assignee: HUSKY HEAT PUMPS Ltd
Priority date: 2014-08-07
Filing date: 2014-08-07
Publication date: 2016-02-10
Also published as: GB201413973D0

Abstract

A heating system 300 comprises a pipework circuit containing water which can be pumped around the circuit and combined heating means and pump 310 for heating water in the circuit. Heat emitting means 303 are mounted in or adjacent a space to be heated 301 and connected to the circuit for heated water to flow through the circuit from the heating means and pump 310. A control unit 311 monitors the air temperature within the space to be heated 301 with a temperature sensor 312 to maintain a substantially constant air temperature in the space to be heated 301 by adjusting the temperature of water flowing out from the heating means while maintaining continuous operation of the pump. The combined heating means and pump 310 may be a heat pump, or the heating means may be a heat pump, boiler or furnace. A temperature sensor (515, Fig. 5) may be used to determine the temperature of water flowing out of the heating means, and a valve (513, Fig. 5) may be used to adjust the outflow temperature.

Description

Improved heating system

FIELD OF THE INVENTION

[0001] The present invention relates to healing systems, in particular to improving the operaling efficiency of hydronic cenlral heating syslems, which may also be referred to as wet central heating systems.

BACKGROUND

[0002] Central healing systems maintain the air temperature al an acceptable level wilhin a building by generating heat at one point and distributing it to multiple points. In the UK, a conventional central heating system generates heal by the combustion of fossil fuel, such as natural gas or propane, in a boiler. These systems are usually hydronic central heating systems, which may also be referred 10 as wet systems. In a hydronic syslem, the heat is transferred from the boiler into waler contained within the system as the water is circulated through pipes connecting the boiler to emitters, such as radiators, where the heat is subsequently lransferred into lhe air.

[0003] Heating controls are used to conlrol the operation of central healing systems in an effort to maintain a comfortable air temperature within a building. A programmable timer may be used to switch on and off the system depending on the time of day. Once the timer has switched on the system, a room thermostat measures the air temperature within a room and will cause the boiler to switch on if the air temperature is below a preselected value. A boiler thermostat sets the temperature at which the boiler then supplies heated water to the radiators, the water being circulated through the system by a pump which switches on and off with the boiler. The timer and room thermostat may be provided as a single unit. Heated water is supplied at constant temperature until the room thermostat is satisfied, i.e. until the air temperature within the room reaches the preselected value, which will cause the boiler and the pump to switch off. Alternatively, some heating systems select a water temperature depending on the temperature outside of the building. The room thermostat will continue to measure the air temperature within the room and will again cause the boiler and the pump to switch on if the air temperature cools such that it falls below the preselected value. This cyclic switching on and off of the boiler and the pump, resulting in cyclic heating and cooling the water within the heating system, will continue until the programmable timer deactivates the system.

[0004] The fuel used by a central heating system accounts for a substantial portion of a building's running costs and its carbon footprint. Improvement in the operation of heating systems is required to increase their efficiency so as to reduce fuel consumption, lessen the impact on the natural environment and lower the financial cost of operating a heating system.

An object of the present invention is to provide a heating system which can be operated at an improved efficiency, i.e. more economically by reducing running costs and fuel consumption.

SUMMARY OF THE INVENTION

[0005] A heating system comprising: a pipework circuit containing water which can be pumped around the circuit; heating means operative to heat the water in the circuit; heat emitting means which is mounted in or adjacent a space to be heated and which is connected into the circuit for water to flow there through; a pump operative to pump water around the circuit so as to supply water from the heating means to the heat emitting means; a temperature sensor operative to determine the air temperature within the space to be heated; and a control unit having a programmable processor, the control unit being in operative communication with the heating means, the pump and the temperature sensor, and the programmable processor being configured to control the operation of the heating system in a manner which achieves and maintains a substantially constant air temperature at a value selected by input to the control unit in that it: (1) monitors the air temperature within the space to be heated from measurements obtained by the temperature sensor; (2) controls on the heating means and the pump to provide a continuous flow of heated water through the circuit, including to the heat emitting means; (3) controls the temperature of water supplied from the heating means to the heat emitting means by raising it until the air temperature within the space reaches the selected value; (4) once the selected value has been reached, adjusts the temperature of water supplied from the heating means to the heat emitting means by reducing it until a state of equilibrium is achieved in which the temperature of the water supplied to the emitting means serves to maintain substantially constant air temperature at the selected value; and (5) continues to control the temperature of water supplied to the heat emitting means, while maintaining continuous operation of the pump, so as to maintain the state of equilibrium.

[0006] The heating means may be provided as a boiler, a heat pump or a furnace. In some embodiments, the healing means may have a variable outflow temperature, variable by the programmable processer, to control the temperature of the water supplied to the emitting means. In alternative embodiments, the outflow temperature of the heating means may be constant and the temperature of the water supplied to the emitting means may be controlled by at least one valve operable by the programmable processor to selectively isolate the healing means from the circuil or to mix water healed by the heating means with waler wilhiri the circuit. In some further embodiments, the heating means may have a variable outflow temperature, variable by the programmable processer, in combination with at least one valve operable by the programmable processor.

[0007] The heat emitting means are typically in the form of radiators, but could be provided in other forms, such as underfloor heating apparatus. The heating means and the pump may be provided separately or in combination, e.g. when proved in the form of a heat pump.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a conventional hydronic central heating system Figure 2 is a chart showing the air temperature of a space to be heated over time for the heating system of Figure 1; Figure 3 is a schematic diagram of a preferred practical embodiment of a hydronic central heating system in accordance with the present invention; Figure 4 is a chart showing the air temperature of a space to be heated over time for the heating system of Figure 3; and Figure 5 is a schematic diagram of an alternalive praclical embodiment of a hydronic central heating system in accordance with the present invention;

DETAILED DESCRIPTION

[0009] Referring to Figure 1, a conventional hydronic central heating system 100 is provided for heating a space 101 within a building 102. The system 100 comprises a pipework circuit, a plurality of emitters, which are depicted as radiators 103, a boiler 104 and a pump 105. The pipework circuit includes a supply pipe 106 and a return pipe 107 which are connected to the radiators 103, the boiler 104 and the pump 105. The pump 105 circulates the water contained with the circuit in the direction indicated by arrows in Figure 1. The system 100 is operated by a programmable timer 108, a room thermostat 109 and a boiler thermostat (not shown) in a conventional manner as previously described.

[0010] Figure 2 is a chart illustrating a typical air temperature profile 200 within the space 101, i.e. the change in air temperature over time, over a period of time wherein the system is active. Air temperature is plotted against a vertical axis 201 and time plotted against a horizontal axis 202. Prior to activation of the system 100, the air temperature in the space 101 is at an initial temperature 203 lower than a target temperature 204, i.e. lower than a desired air temperature set by the user. Typically, the target temperature 204 is set between a minimum comfortable temperature 205 and a maximum comfortable temperature 206.

Upon activation of the system the boiler 104 and pump 105 switch on, heated water flows around the circuit and heat is transferred into the space 101. When the rate of heat transfer from the radiators 103 into the space 101 exceeds the rate at which heat is lost from the space 101, e.g. by conduction and air leakage through the walls of the building 102, the air temperature will rise. The boiler 204 gradually raises the water temperature of the water supplied to the radiators 103 to a value set by the boiler thermostat, for example 60°C, which is then maintained by the boiler 104 as the temperature within the space 101 rises. The pump 104 continues to circulate heated water around the circuit while the boiler 104 is switched on.

[0011] Once the target temperature 204 within the space 101 is achieved, the boiler 104 and the pump 105 switch off. The air temperature in the space 101 continues to rise (as illustrated in Figure 2) immediately following the switching off of the boiler 104, as heated water remains in the circuit and continues to transfer heat into the space 101. This represents wasted fuel. The air temperature within the space 101 eventually cools as the water within the circuit cools and the rate of heat loss exceeds the rate of heat transfer into the space 101. Once the air temperature cools to below the target temperature 204 the boiler 104 and the pump 105 switch back on. Water circulation is resumed and the water supplied to the radiators 103 is reheated to the temperature set by the boiler thermostat. The air temperature within the room 100 does not begin to rise immediately following the switching on of the boiler 104, rather it continues to cool (as illustrated in Figure 2) until the water is heated sufficiently to return the rate of heat transfer into the space 101 to a rate higher than that which heat is being lost. This can result in the air temperature within the space 101 cooling to a temperature lower than the minimum comfortable temperature 205 before the air temperature again begins to rise. Plainly, this is undesirable effect for an occupant of the space 101. The air temperature profile 200 illustrates the cyclic heating and cooling of the space 101 overtime as the room thermostat 109 switches the boiler 104 and the pump 105 on and off.

[0012] Referring now to Figure 3, a preferred practical embodiment of hydronic central heating system 300 in accordance with the present invention is provided for heating a space 301 within a building 302. The system 300 comprises a pipework circuit, a plurality of emitters, which are depicted as radiators 303, and combined heating means and pump in the form of a heat pump 310. The pipework circuit includes a supply pipe 306 and a return pipe 307 which are connected to the radiators 303 and the heat pump 310. The heat pump 310 is located outside of the building 302 where it absorbs heat from the air at low temperature into a fluid which is then compressed by a compressor within the heat pump 310. Compression of the fluid increases its temperature so that heat in the fluid may then be transferred from the heat pump 310 into water contained within the circuit via a heat exchanger within the heat pump 310. The heat pump 310 also circulates the water contained with the circuit in the direction indicated by arrows in Figure 3. The system 300 is operated by a control unit 311 which is provided for convenience within the space 301 and communicates with the heat pump 310 via a wired connection. In alternative embodiments, the control unit 311 could be provided in alternative locations, such as on the heat pump 310, and could alternatively communicate with the heat pump 310 by wireless means. The control unit 311 has a programmable processor (not shown), programmable by a user to activate and deactivate the system 300, e.g. under timer control, and set a target air temperature 404 (see Figure 4) for within the space 301. The programmable processor is also configured to control the rate of heat transfer from the heat pump 310 into the water.

The rate of heat transfer, and thus the outflow temperature of the heat pump 310, may be controlled by various means, for example by switching the compressor within the heat pump 310 on and off. Alternatively, the rate of heat transfer may be controlled by modulating the rate at which the compressor within the pump 310 compresses the fluid. A temperature sensor 312 is provided within the space 301 for measuring the air temperature therein and communicates with the control unit 311 via a wired connection. In alternative embodiments, the control unit 310 and temperature sensor 312 could also communicate by wireless means.

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[0013] Figure 4 illustrates a typical air temperature profile 400 within the space 301 over a period of time wherein the system 300 is active. Air temperature is plotted against a vertical axis 401 and time plotted against a horizontal axis 402. Prior to activation of the system 300, the air temperature within the space 301 is at an initial temperature 403 lower than the target temperature 404. Typically, the target temperature 404 is set between a minimum comfortable temperature 405 and a maximum comfortable temperature 406. For example, the user may set a target temperature 404 of 21°C to fall between a minimum comfortable temperature 405 of 20°C and a maximum comfortable temperature 406 of 23.5°C. When the system 300 is brought into operation, e.g. under the control of a timer in the control unit 311, the heat pump 310 switches on under the control of the control unit 311. Heated water then flows around the circuit, flowing from the heat pump 310 through the supply pipe 306 to supply the radiators 303 where the heat in the water is transferred into the space 301. Water returns to the heat pump 310 from the radiators 303 through the return pipe 307. The control unit 311 controls the rate of heat transfer from the heat pump 310 into the water so as to gradually raise the water temperature to a maximum value, for example 55°C. The maximum value of water temperature is then maintained by the heat pump 310, under the control of the control unit 311, by adjusting the rate of heat transfer from the heat pump 310 into the water. As the water temperature rises, the rate of heat transfer from the radiators 303 into the space 301 increases and eventually exceeds the rate at which heat is lost from the space 301, thus causing the air temperature to rise.

[0014] Once the target temperature 404 within the space 301 is achieved, as measured by the temperature sensor 312, the control unit 311 will begin to regulate the temperature of the water supplied to the radiators 303 by reducing the rate of heat transfer from the heat pump 310 into the water. This action lowers the temperature of the water supplied to the radiators 303. The heat pump 310 remains switched on whilst the system 300 is active and will continue to pump water around the circuit. The air temperature within the space 301 continues to rise immediately following the reduction in heat transferred into the water (as illustrated in Figure 4) until the water cools such that the rate of heat loss from the space 301 exceeds the rate of heat transfer from the radiators 303. As the temperature within the space 301 cools, the control unit 312 will continue to reduce the temperature of the water within the system until the target temperature 404 is reached. At this point the rate of heat transfer from the radiators 303 into the space 301 is equal to the rate of heat lost from the space 301 for the target temperature 404. The control unit 312 then continues to adjust the heat transferred from the heat pump 310 into the water supplied to the radiators 303 in order to maintain the target temperature 404 until the system 300 is deactivated by the control unit 311. The air temperature profile 200 illustrates that a substantially constant air temperature is maintained within a range of comfortable temperatures defined by the maximum and minimum comfortable air temperatures 405, 406. The control unit 311 will continue to adjust the temperature of the water supplied to the radiators 303 to account for changes in the rate of heat loss from the space 301, e.g. as the result of changes in the air temperature outside of the building 302. The system 300 may also include a further temperature sensor (not shown) for measuring the water temperature of the circulating water. This may be located within the heat pump 310. The further sensor improves the precision of the adjustments as the control unit 311 does not have to rely upon feedback from the sensor 312 within the space 301 as to changes in air temperature resulting from adjustment of the water temperature. A target water temperature, variable with changes in the rate of heat loss, may also be established by the control unit 311 for maintaining the target air temperature 404.

By not cyclically heating and cooling the water within the circuit, the heating system 300 performs more efficiently in comparison with the conventional system 100.

[0015] An alternative practical embodiment in accordance with the present invention is illustrated in Figure 5. A hydronic central heating system 500 is provided for heating a space 501 within a building 502. The system 500 comprises a pipework circuit, a plurality of emitters, which are depicted as radiators 503, a boiler 504 and a pump 505. The pipework circuit includes a supply pipe 506 and a return pipe 507 which are connected to the radiators 503, the boiler 504 and the pump 505. The pump 505 circulates the water contained with the circuit in the direction indicated by arrows in Figure 5. The system 500 is operated by a boiler thermostat (not shown) and a control unit 511 provided for convenience within the space 501 and communicates with the boiler 504 and the pump 505 via a wired connection.

The control unit 511 has a programmable processor (not shown), programmable by a user to activate and deactivate the system 500 and set a target air temperature for within the space 501. A first temperature sensor 512 is provided within the space 501 for measuring the air temperature therein and communicates with the control unit 511 via a wired connection. The system 500 further comprises first and second valves 513, 514 and a second temperature sensor 515 which are connected in the circuit. The first and second valves 513, 514 are operable to isolate the boiler 504 from the circuit and the temperature sensor 515 measures the water temperature of the circulating water. The valves 513, 514 and the sensor 515 also communicate with the control unit 511 via a wired connection. In alternative embodiments, communication between the features of the system 500 could be by wireless means. Valves 513, 514 could be substituted by a single mixing valve.

[0016] When the system 500 is brought into operation, the boiler 504 and the pump 505 switch on under the control of the control unit 511. The first valve 513 is placed in an open condition and the second valve 514 in a closed condition so that heated water flows around

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the circuit, flowing from the boiler 504 through the supply pipe 506 to supply the radiators 503 where the heat in the water is transferred into the space 501. Water returns to the boiler 510 from the radiators 503 through the return pipe 507. The boiler 504 gradually raises the water temperature of the water circulating within the circuit to a value set by the boiler thermostat, for example 55°C, which is then maintained by the boiler 504 causing the air temperature within the space 501 to rise.

[0017] Once the target temperature within the space 501 is achieved, as measured by the temperature sensor 512, the first valve 513 will close and the second valve 514 will open under the control of the control unit 511, thus isolating the boiler 504 from the circuit. This action cools the temperature of the water supplied to the radiators 503. The pump 505 is not isolated from the circuit and remains switched on while the system 500 is in operation, thus continuing to pump water around the circuit. As in the previously described embodiment, the water supplied to the radiators 503 eventually cools such that the rate of heat loss from the space 501 exceeds the rate of heat transfer from the radiators 503. As the temperature with the space 501 cools, the control unit 512 will begin to adjust the temperature of the water supplied to the radiators 503, as measured by the second sensor 515, by opening and closing the first and second valves 513, 514. The second sensor 515 improves the precision of the adjustments as the control unit 511 does not have to rely upon feedback from the sensor 512 within the space 501 as to changes in air temperature resulting from adjustment of the water temperature. A target water temperature, variable with changes in the rate of heat loss, may also be established by the control unit 511 for maintaining the target air temperature. With the first valve 513 in the open position and the second valve 514 in the closed position, water heated to the temperature set by the boiler thermostat is added to the circuit. The control unit 512 continues to cause a gradual reduction of the water temperature by selectively opening and closing the valves 513, 514 until the target temperature of the air within the space 501 is reached. The control unit 511 then adjusts the water temperature supplied to the radiators 503 until the system 500 is deactivated, maintaining a substantially constant air temperature. By opening and closing the first and second valves 513. 514, the control unit 511 will continue to adjust the temperature of the water within the circuit to account for changes in the rate of heat loss from the space 501. By not cyclically heating and cooling the water within the circuit, the heating system 500 performs more efficiently in comparison with the conventional system 100. The alternative embodiment demonstrates how the invention can be implemented retrospectively in an existing heating system.

EXAMPLE

[0018] Continuous operation of a heating system, i.e. maintaining the pumped circulation of heated water throughout the operation, is counter intuitive as typical central heating systems switch boilers, heat pumps, etc. on and off in an effort maintain a comfortable air temperature whilst not wasting heat and fuel. To demonstrate the improved efficiency of a system operated in accordance with the present invention a field trial which has been conducted will now be described.

[0019] A typical stone build domestic property having a hydronic heating system was provided with a propriety heat pump, specifically a Husky (RIM) PWR 16 heat pump. The heat pump could be set up to operate in two ways: Set up A heat pump is operated in a conventional manner, switching on and off under the control of a control unit in an effort to maintain a comfortable air temperature which is approximately equal to a target temperature by cyclic heating and cooling of the water supplied to emitters which is circulated only when the heat pump is on; or Set up B heat pump is operated in a manner in accordance with the present invention, heated water supplied to the emitters is continuously circulated and the water temperature adjusted by a control unit to maintain equilibrium of the rate of heat transfer from the emitters and the rate of heat lost from the space so as to maintain a target temperature.

[0020] The property had a maximum heat demand of 8.5 kilowatts for a target temperature of 21°C at an outside air temperature of -3°C. The estimated kilowatt usage of the property using a conventional system, i.e. set up A, was 41.6 kilowatts for a 24 hour period. The system was operated over a 24 hour period in a conventional manner and over a subsequent 24 hour period in a manner in accordance with the present invention. Measurements of the system's performance are summarised in the table below and it is evident that set up B performed more efficiently than set up A. For set up B, the improved system, the actual kilowatt usage was approximately half that of set up A. An advantage of reducing the temperature of the water supplied to the emitters is a consequent reduction in the heat losses from the building. This occurs as the improved system does not cyclically overshoot the target air temperature at which a greater rate of heat loss will be experienced when compared the rate of heat loss at the target air temperature. Furthermore, maintaining the target air temperature results in less air movement within the property when compared to temperatures over the target temperature. This effect also reduces heat losses.

SETUPA SETUPB

Average external temperature (°C) 6.3 5.8 Range of external temperature (°C) 2.1 to 10.3 1.9 to 9.8 Target temperature (°C) 21.0 21.0 Average temperature of water (°C) 37.3 28.2 Range of water temperature (°C) 35.0 to 41.0 35.0 to 40.0 Kilowatt usage (kW) 40.6 19.4 [0021] The invention is not restricted to the details of any forgoing embodiments and other embodiments are possible. Although a heat pump has been described as a preferred choice of heating means for a system in which the heating means has a variable outflow temperature, it should be appreciated that alternative heating means could be used, such as a conventional boiler or furnace. A heat pump is a preferable choice of heating means as the lower the water temperature produced the more efficiently the heat pump will operate.

Other variations are possible with respect to other features of the described embodiments, for example it is obvious that the invention could be used in combination with underfloor heating, open vented systems, sealed systems, ground source heat pump or air source heat pumps. The invention could also be implemented in combination with a hot water system.

[0022] Throughout the description and claims of this specification, the words comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Claims

CLAIMS1. A heating system comprising: a pipework circuit containing water which can be pumped around the circuit; heating means operative to heat the water in the circuit; heat emitting means which is mounted in or adjacent a space to be heated and which is connected into the circuit for water to flow there through; a pump operative to pump water around the circuit so as to supply water from the heating means to the heat emitting means; a temperature sensor operative to determine the air temperature within the space to be heated; and a control unit having a programmable processor, the control unit being in operative communication with the heating means, the pump and the temperature sensor, and the programmable processor being configured to control the operation of the heating system in a manner which achieves and maintains a substantially constant air temperature at a value selected by input to the control unit in that it: (1) monitors the air temperature within the space to be heated from measurements obtained by the temperature sensor; (2) controls on the heating means and the pump to provide a continuous flow of heated water through the circuit, including to the heat emitting means; (3) controls the temperature of water supplied from the heating means to the heat emitting means by raising it until the air temperature within the space reaches the selected value; (4) once the selected value has been reached, adjusts the temperature of water supplied from the heating means to the heat emitting means by reducing it until a state of equilibrium is achieved in which the temperature of the water supplied to the emitting means serves to maintain substantially constant air temperature at the selected value; and (5) continues to control the temperature of water supplied to the heat emitting means, while maintaining continuous operation of the pump, so as to maintain the state of eq u i Ii bri u m.
2. A heating system according to claim 1, wherein the heating means comprises a heat pump or a boiler or a furnace.
3. A heating system according to claim 1, wherein a heat pump provides the heating means and the pump.
4. A heating system according to claim 1, 2 or 3, wherein the heating means has a variable outflow temperature, variable by the programmable processor.
5. A heating system according to any preceding claim, further comprising at least one valve operable by the programmable processor to adjust the temperature of the water supplied to the heat emitting means.
6. A heating system according to any preceding claim, further comprising a temperature sensor operative to determine the water temperature within circuit.
7. A heating system substantially as hereinbefore described with reference to and as illustrated in figures 3 orb of the accompanying drawings.