Heating system

Abstract

A heating system 1 for heating a building comprises a first container (e.g. hot water cylinder 10) defining a first interior space, heat source (e.g. heater 100) to heat a first fluid (e.g. water) con

Description

The present invention relates to a heating system. More particularly, the present invention relates to a heating system for heating a building. The present invention also relates to a method of heating a building. The term ‘building’ as used herein, refers to any temporary or permanent structure which may require heating or the regulation of temperature therein. For example, the term ‘building’ may refer to a habitable structure, for example domestic housing, including detached, semi-detached, or terraced housing, flats, and apartments. The term ‘building’ may also refer to communal spaces including leisure facilities such as sports centers, halls, gymnasiums, schools, places of worship, museums, and art galleries. The term ‘building’ may also refer to industrial facilities including factories and warehouses, and commercial properties including shops and offices. Most buildings in developed and developing countries include a water heating system for heating cold water, for example from a mains water supply, to provide a supply of hot or heated water for use within the building, for example to fixtures and fittings located or installed in the building such as taps / faucets or the hot water feed of appliances. Often, the water heating system is also used to heat the interior space of the building, for example by delivering hot water to radiators plumbed into a central heating system of the building. In many cases, water for the hot water supply and central heating system is heated by a single compact unit, commonly referred to as a ‘combination’ boiler. Combination boilers typically heat water rapidly on demand by burning fossil fuels such as oil or natural gas. Combustion of the fuel releases energy which is absorbed by cold water passed in close proximity to the burning fuel, for example along one or more pipes, to heat the water. The heated water is then delivered, as required, to the hot water supply and / or central heating system of a building. However, increasing financial and environmental pressures are driving consumers to move away from the consumption of fossil fuels, and to adopt alternative, preferably renewable, energy sources, such as electricity. Electricity can be generated from renewable sources, for example wind, solar, and hydroelectric power sources. The use of electric heating systems therefore offers an environmentally friendly alternative to fossil fuel heating systems. However, electric water heating systems can still be costly to run, and in many cases more expensive than fossil fuel alternatives. This problem is exacerbated by the comparative inefficiency of conventional electric heating systems. By way of example, immersion heaters may be used instead of oil or gas boilers to heat water using an electric heating element. The element is immersed in a volume of water contained within an insulated hot water cylinder. The volume of water is maintained at a constant temperature, for example 60°C, by a thermostat, and the heated water is drawn off when required to supply hot water to a building. However, residual hot water retained within the cylinder loses heat over time and energy is therefore wasted if the hot water is not used immediately. It also takes a comparatively long time to heat the volume of water within the cylinder, which means immersion heaters cannot meet the energy demand of central heating systems which may be required to operate continuously or for prolonged periods of time. Therefore, a separate oil or gas boiler is required to provide hot water to a central heating system alongside the immersion heater. Alternatively, a separate electric system may be employed to heat the interior of the building, such as one or more electric radiators. However, such systems are also costly to run. Various heating and hot water systems have been developed in recent years which attempt to address these problems to provide an energy-efficient and costefficient electric heating system capable of providing a hot water supply and central heating to a building. For example, United Kingdom Patent Application No. 1812128.5, published as GB 2577239 A discloses an electric water heater for domestic hot water or central heating including two hot water exchange units (referred to therein as ‘Pod T and ‘Pod 2’) which are stainless steel capped cylinders incorporating tubular inserts. Heat is obtained from stainless steel electrodes that each provide 300W of power which are placed into the tubular inserts. Each pod is serviced by a standard domestic water pump. The electrodes have direct contact with the flowing water to be heated, but are not immersed in the water. Pod 1 is for central heating and Pod 2 for hot water. The system is designed to be eco-friendly, safe, easy to install, and gives overall monetary savings. However, the system requires two hot water exchange units to heat water in separate hot water supply and central heating circuits, which increases the overall size of the system compared to traditional combination boilers. More recently, United Kingdom Patent No. GB 2592026 B and related divisional Patent No. GB 2592093 B disclose an electric boiler including a heating element and a thermally conductive inner container. The inner container surrounds the heating element to define an inner passage about the heating element and has an inlet and an outlet for a flow of water arranged such as to cause water received at the inner container inlet to flow along the inner passage in close proximity to a surface of the heating element to the inner container outlet. The boiler further includes an outer container in which the inner container is located, the outer container defining an outer passage about at least part of the inner container. The outer container has an inlet and an outlet for a flow of water. The outer container outlet is fluidly connected to, or forms, the inner container inlet. The outer container is arranged such as to cause water received at the outer container inlet to flow along the outer passage, in close proximity to a surface of the inner container, to the outer container outlet. The outer container may be a first outer container, the boiler further including a second outer container in which the first outer container is located. The second outer container has an inlet and an outlet to define a second outer container passage therebetween in fluid isolation from the passage of the first outer container and the inner container. In this manner, two fluidly isolated separate water supplies, or flow paths, may be heated to create a combination boiler with sanitary water being drawn through and heated in the first outer container and the inner container. Then, when 4 sanitary water is not being drawn through the boiler, this water in the boiler may be heated to transfer energy to the water of the central heating system passing through the second outer container. The electric boiler is therefore capable of providing an instantaneous hot water supply, suitable for sanitary hot water supply or for a central heating system. However, the boiler construction is complex, making installation and maintenance challenging. The boiler also, by virtue of its construction, draws heat from the central heating system when sanitary water flows through the first outer container, thus compromising the operation of the central heating system every time sanitary water is used. There therefore remains a need for a compact combination heating system which does not rely on the consumption of fossil fuels such as oil or natural gas, and which has a reduced energy consumption and operating cost without compromising on functionality. Accordingly, in a first aspect, the present invention provides a heating system for heating a building, the heating system comprising: a first container defining a first interior space; a heat source configured to heat a first fluid contained within the first interior space; a heat recovery means located within the first interior space; and at least one space heating apparatus; wherein the heat recovery means is configured to absorb thermal energy from the first fluid contained within the first interior space; and wherein the at least one space heating apparatus is configured to utilise thermal energy absorbed by the heat recovery means to heat a building. The heating system includes a first container. The first container defines a first interior space for containing a first fluid. Preferably the first fluid is a liquid, most preferably water. An ‘interior space’ of a container refers herein to a continuous void or cavity defined within the walls of the container. The first container may thus be any vessel defining a first interior space suitable for containing a first fluid. In particular, at least a portion of the first container is or can be rendered substantially gastight or watertight, so that one or more fluids contained therein cannot leak or otherwise escape from the first container, in use. The first container may have one or more outer walls defining any suitable shape. For example the first container may be substantially cuboidal, substantially cylindrical, or substantially spherical. Alternatively, the first container may be any other irregular or compound shape. One or more walls of the first container may be wholly or partially open. Preferably, however, the first container is substantially enclosed. Preferably, the first container is thermally insulated. For example, all or a portion of one or more walls of the first container may be formed from a thermally insulating material, including but not limited to fiberglass, polyurethane, or combinations thereof. In a particularly preferred embodiment, the first container is an insulated hot water cylinder, examples if which are known in the art and, in the interests of brevity, shall not be described in detail herein. The first interior space may have any suitable volume. For example, the first container may define a first interior space having a volume of at least 25 litres, preferably at least 50 litres, more preferably at least 75 litres, still more preferably at least 100 litres, most preferably at least 125 litres. The first container may define a first interior space having a volume of up to 1000 litres, preferably up to 900 litres, more preferably up to 800 litres, still more preferably up to 700 litres, more preferably still up to 600 litres, most preferably up to 500 litres. In preferred embodiments, the first container defines a first interior space having a volume of from 25 litres to 1000 litres, preferably from 50 litres to 800 litres, more preferably from 75 litres to 600 litres, most preferably from 100 litres to 400 litres. The first interior space is arranged to contain a volume of a first fluid, preferably a liquid, such as water. Preferably, the first container includes a first inlet in fluid communication with the first interior space. The first inlet is preferably configured for connection to a reserve of the first fluid, for example a supply of cold or unheated water, such as the mains or other cold water supply of a building. The terms ‘cold’ or ‘unheated’ fluid, as used herein, shall be understood, unless it is otherwise clear from the context, to refer to fluid that has not been acted upon by a component of the heating system to increase the temperature of the fluid or has not otherwise absorbed thermal energy within the heating system to raise the temperature of the fluid. The first inlet is preferably located in a wall of the first container to facilitate the passage of a first fluid from the exterior of the first container to the first interior space. The first inlet may be connected to a reserve of the first fluid by any suitable means, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. The heating system includes a heat source configured to heat the first fluid contained within the first interior space of the heating system. For example, the heat source may heat cold water received in the first interior space from a reserve of cold water, such as the mains water supply of a building. Preferably, the first container includes a first outlet in fluid communication with the first interior space. The first outlet is preferably configured to deliver a supply of the first fluid, as heated by the heat source, to a building, for example to one or more fixtures or fittings, such as taps / faucets, or appliances installed or located in the building. For example, the first outlet may be connected to the hot water feed of a domestic, commercial, or industrial building to provide hot water to taps / faucets or appliances located or installed in the building. The terms ‘hot’ or ‘heated’ fluid, as used herein, shall be understood, unless it is otherwise clear from the context, to refer to fluid that has been acted upon by a component of the heating system to increase the temperature of the fluid or has otherwise absorbed thermal energy within the heating system to raise the temperature of the fluid relative to that of cold or unheated fluid, as defined hereinbefore. The first outlet is preferably located in a wall of the first container to facilitate the passage of the first fluid from the first interior space to the exterior of the first container. The first outlet may deliver a supply of heated first fluid to one or more fixtures, fittings or appliances installed or located in a building by any suitable means, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. Any suitable heat source may be employed to heat the first fluid contained within the first interior space of the heating system. The heat source may be configured to heat the first fluid by the conversion of electric energy to thermal energy, by the combustion of a fuel, for example natural gas, or combinations thereof. For example, the heat source may be provided by an electric immersion heating element, or the heater coil of a boiler, for example a gas boiler, or combinations thereof. Preferably, the heat source is electric. Preferably, the heat source comprises a plurality of heating elements, for example a plurality of resistive electric heating elements such as cartridge heaters. Preferably the heat source has a power output of at least 0.5 kW, preferably at least 0.75 kW, more preferably at least 1kW, still more preferably at least 1.25 kW, most preferably at least 1.5 kW, for example at least 1.75 kW. Preferably the heat source has a power output of up to 5 kW, preferably up to 4 kW, more preferably up to 3 kW, most preferably up to 2 kW. In preferred embodiments, the heat source has a power output of from 0.5 to 5 kW, preferably from 0.75 to 4 kW, more preferably from 1 to 3 kW, still more preferably from 1.25 to 2 kW, most preferably 1.5 to 1.75 kW. The heat source may be located within the first interior space of the heating system. For example, the heat source may be located within the first interior space in a manner analogous to the heating element of conventional immersion heating systems known in the art. In a particularly preferred embodiment, however, the heating system includes a second container defining a second interior space in fluid communication with the first interior space, the heat source being located within the second interior space. The heat source may be housed within one or a plurality of tubular inserts extending within the second interior space, preferably stainless-steel inserts, to facilitate the transmission of thermal energy from the heat source to the first fluid without immersing the heat source directly in the first fluid. For example, where the heat source comprises a plurality of heating elements, each heating element may be housed in a respective one of the plurality of tubular inserts. The first container preferably includes a second inlet in fluid communication with the first interior space, and a second outlet in fluid communication with the first interior space. The second inlet and / or second outlet of the first container is preferably located in a wall of the first container to facilitate the passage of the first fluid between the first interior space and the exterior of the first container. The second container preferably includes a first inlet in fluid communication with the second interior space, and a first outlet in fluid communication with the second interior space. The first inlet and / or first outlet of the second container is preferably located in a wall of the second container to facilitate the passage of the first fluid between the second interior space and the exterior of the second container. The second outlet of the first container is preferably connected to the first inlet of the second container. For example, the second outlet of the first container may be connected to the first inlet of the second container via one or more lengths of pipe, tubing, or other suitable means for conveying a fluid. The second inlet of the first container is preferably connected to the first outlet of the second container. For example, the second inlet of the first container may be connected to the first outlet of the second container via one or more lengths of pipe, tubing, or other suitable means for conveying a fluid. Alternatively, one or more walls of the first container may be conterminous with one or more walls of the second container, such that the second inlet and second outlet of the first container may also form the respective first outlet and first inlet of the second container. In this manner the second inlet and / or second outlet of the first container open directly into the second interior space of the heating system. The first fluid contained within the first interior space is able to pass to the second interior space and vice versa, for example via the second inlet and / or second outlet of the first container, to be heated by the heat source located within the second interior space of the heating system. In this manner, the heat source is configured to heat the first fluid contained within the first interior space as it passes through the second interior space, where it absorbs thermal energy from the heat source, before returning to the first interior space. Preferably, the heating system includes means for circulating the first fluid between the first interior space and the second interior space of the heating system. This establishes a flow of the first fluid through the second interior space of the heating system which advantageously facilitates the rapid and efficient transfer of thermal energy from the heat source located in the second interior space to the first fluid. For example, the system may include a first pump fluidly connected to one of the second inlet and second outlet of the first container. The first pump is preferably operable to convey the first fluid from the first interior space to the second interior space, via the second outlet of the first container, and from the second interior space to the first interior space via the second inlet of the first container. The second container may have any suitable shape, configuration, and construction, for example as described hereinbefore with reference to the first container. Preferably, the second container is a stainless-steel capped cylinder. Similarly, the second container may define a second interior space having any suitable volume, as described hereinbefore with reference to the first interior space. However, in a particularly preferred embodiment, the second interior space has a smaller volume than the first interior space. For example, the ratio of the volume of the first interior space to the volume of the second interior space is preferably at least 10:1, more preferably at least 20:1, still more preferably at least 30:1, more preferably still at least 40:1, most preferably at least 50:1. In particularly preferred embodiments, the ratio of the volume of the first interior space to the volume of the second interior space is at least 100:1. The ratio of the volume of the first interior space to the volume of the second interior space may be up to 1000:1, preferably up to 800:1, more preferably up to 600:1, still more preferably up to 400:1, for example up to 200:1. Preferably the ratio of the volume of the first interior space to the volume of the second interior space is from 10:1 to 1000:1, more preferably from 20:1 to 800:1, still more preferably from 30:1 to 600:1, more preferably still from 40:1 to 400:1, most preferably from 50:1 to 200:1, for example from 100:1 to 200:1. Advantageously, this increases the surface area to volume ratio of the heat source and second interior space, as compared to the first interior space. Therefore, the heat source is able to more rapidly and efficiently transfer thermal energy to the first fluid to heat the first fluid to a desired temperature as it passes through the second interior space. For example, the second container may define a second interior space having a volume of at least 0.25 litres, preferably at least 0.5 litres, more preferably at least 0.75 litres, still more preferably at least 1 litre, most preferably at least 1.25 litres, for example at least 1.5 litres. The second container may define a second interior space having a volume of up to 10 litres, preferably up to 9 litres, more preferably up to 8 litres, still more preferably up to 7 litres, more preferably still up to 6 litres, most preferably up to 5 litres. In preferred embodiments, the second container defines a second interior space having a volume of from 0.25 litres to 10 litres, preferably from 0.5 litres to 8 litres, more preferably from 0.75 litres to 6 litres, most preferably from 1 litre to 4 litres, for example 2 litres. The flow of the first fluid through the second interior space may be laminar or turbulent. Preferably the flow of the first fluid through the second interior space is turbulent to promote mixing to aid in the efficient transfer of heat from the heat source to the first fluid. The heating system preferably includes an agitator. The agitator is preferably located within the second interior space to generate a turbulent flow of the first fluid within the second interior space. The heat source may be configured to heat the first fluid contained within the first interior space to any desired temperature. For example, the heat source may be configured to heat the first fluid to a temperature of at least 30°C, preferably at least 40°C, more preferably at least 50C, still more preferably at least 60°C, most preferably at least 70°C. The heat source may be configured to heat the first fluid to a temperature of up to 100°C, preferably up to 90°C, more preferably up to 80°C, most preferably up to 70°C. In preferred embodiments, the heat source may be configured to heat the first fluid to a temperature of from 30°C to 100°C, preferably from 40°C to 90°C, more preferably from 50°C to 80°C, most preferably from 60°C to 70°C. Preferably, the heating system includes a thermostat. The thermostat may be configured to control the operation of the heat source on the basis of a determination of the temperature of the first fluid contained within the first interior space. Additionally or alternatively, where the heating system includes a second container, as described hereinbefore, the thermostat may be configured to control the operation of means for circulating the first fluid between the first interior space and the second interior space on the basis of a determination of the temperature of the first fluid contained within the first interior space. Operation of one or both of the heat source and, if present, means for circulating the first fluid between the first interior space and the second interior space, such as a first pump, may be controlled by the thermostat to maintain the temperature of the first fluid contained within the first interior space at a desired level or set point. For example, the thermostat may control the operation of the heat source and / or first pump on the basis of a determination of the temperature of the first fluid contained within the first interior space. In particular, when the thermostat detects that the temperature of the first fluid contained within the first interior space has fallen below a predetermined set point, the thermostat may activate the heat source to raise the temperature of the first fluid contained within the first interior space. Similarly, where the heating system includes a first pump, when the thermostat detects that the temperature of the first fluid contained within the first interior space has fallen below a predetermined set point, the thermostat may activate the first pump to cause the first fluid to flow over and around the heat source, for example through the second interior space, to raise the temperature of the first fluid contained within the first interior space. Where the first container includes a first outlet for delivering a supply of the first fluid, as heated by the heat source, to a building, the temperature of the first fluid may be maintained at or below a temperature that is considered safe for use in the building, for example safe for delivery to one or more fixtures, fittings or appliances located or installed in the building. However, the temperature of the first fluid may be maintained above that which is considered safe for use in the building, for example to increase a reserve of thermal energy available for absorption by the heat recovery means, as described in more detail hereinbelow. Accordingly, the heating system preferably includes a blending valve. The blending valve may be connected to the first outlet of the first container to receive a supply of heated first fluid from the first interior space, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. The blending valve may be connected to a reserve of the first fluid, such as the mains or other cold water supply of a building, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. The blending valve is preferably configured to mix a supply of heated first fluid from the first interior space with a supply of unheated first fluid from the first fluid reserve, preferably to lower the temperature of the heated first fluid to a desired level, for example to a temperature considered safe for use in a building. The heating system further includes a heat recovery means located within the first interior space. The heat recovery means is configured to absorb thermal energy from the first fluid contained within the first interior space. Accordingly, the heat recovery means may be any means suitable for absorbing thermal energy from a fluid. For example, the heat recovery means may include a heat sink or heat pipe. Preferably, the heat recovery means defines a passage for conveying a second fluid within, and in fluid isolation from, the first interior space. For example, the heat recovery means may include a pipe, preferably a tortuous pipe, such as a helical or spirally wound heat exchange coil, for conveying the second fluid within the first interior space. The second fluid thus absorbs thermal energy from the first fluid as it passes through the heat recovery means. Preferably, the first container includes a third inlet. The third inlet is preferably located in a wall of the first container to provide access to the first interior space. The heat recovery means may extend from or through the third inlet within the first interior space. Preferably, the first container includes a third outlet. The third outlet is preferably located in a wall of the first container to provide access to the first interior space. The heat recovery means may extend from or through the third outlet within the first interior space. In a particularly preferred embodiment, the heat recovery means extends within the first interior space between the third inlet and the third outlet. Accordingly, where the heat recovery means includes a passage for conveying a second fluid within the first interior space, the second fluid may enter the first container via the third inlet, where it is conveyed through the heat recovery means in fluid isolation from the first interior space, to exit the first container via the third outlet. Accordingly, the heating system preferably includes means for circulating the second fluid through the heat recovery means. For example, the system may include a second pump fluidly connected to one of the third inlet and third outlet of the first container. The thermostat, if present, may be configured to control the operation of the means for circulating the second fluid through the heat recovery means on the basis of a determination of the temperature of the first fluid contained within the first interior space. For example, the thermostat may control the operation of the second pump on the basis of a determination of the temperature of the first fluid contained within the first interior space. In this manner, if the thermostat determines that the temperature of the heated first fluid within the first interior space has fallen below a temperature sufficient to maintain the absorption of thermal energy from first fluid by the heat recovery means at a desired rate, it may operate to increase the flow rate of the second fluid, under the action of the second pump, through the heat recovery means. By increasing the flow rate of the second fluid through the heat recovery means, the rate at which thermal energy is absorbed by the heat recovery means, and the second fluid conveyed therein, is increased. In a preferred embodiment, the flow rate of the second fluid through the heat recovery means is inversely proportional to the temperature of the first fluid. Preferably, the heat recovery means is configured to be wholly or partially submerged within the first fluid contained in the first interior space to facilitate the absorption of thermal energy from the first fluid by the heat recovery means and, if present, a second fluid conveyed by the heat recovery means. The heating system preferably includes at least one space heating apparatus. The at least one space heating apparatus is configured to utilise thermal energy absorbed by the heat recovery means to heat a building. Accordingly, the at least one space heating apparatus refers to any apparatus suitable for emitting heat to heat a building, preferably the interior space of a building. For example, the at least one space heating apparatus may include at least one radiator, such as the radiator of a central heating system, or the pipes of an underfloor heating system. Thermal energy absorbed by the heat recovery means from a first fluid contained within the first interior space is utilised by the at least one space heating apparatus. Preferably, thermal energy absorbed by the heat recovery means from the first fluid contained within the first interior space is transmitted to the at least one space heating apparatus where it is emitted by the at least one space heating apparatus to heat a building. Accordingly, the heating system preferably includes means for transmitting thermal energy from the heat recovery means to the at least one space heating apparatus. Thermal energy may be transmitted from the heat recovery means to the at least one space heating apparatus by any suitable means. For example, the heat recovery means may be connected to the at least one space heating apparatus by a thermally conductive material, including but not limited to a metal or alloy such as copper, iron, steel, or combinations thereof. Where thermal energy is absorbed from the first fluid by a second fluid conveyed within the first interior space by the heat recovery means, the heat recovery means may be in fluid communication with the at least one space heating apparatus. For example, the third inlet of the first container, if present, is preferably connected to a return of the at least one space heating apparatus, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. The third outlet of the first container, if present, is preferably connected to a feed of the at least one space heating apparatus, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. In this manner, the second fluid may be circulated, for example under the action of the second pump, if present, through the at least one space heating apparatus, for example through at least one radiator of a central heating system, to transmit thermal energy absorbed by the heat recovery means to the at least one space heating apparatus. The thermal energy transmitted by the second fluid is then emitted by the at least one space heating apparatus to heat a building. In a particularly preferred embodiment, however, the at least one space heating apparatus is fluidly decoupled from the heat recovery means. For example, the means for transmitting thermal energy from the heat recovery means to the at least one space heating apparatus preferably includes a heat exchanger. Any suitable heat exchanger may be employed, including but not limited to a plate heat exchanger. The heat exchanger includes a ‘hot side’ in thermal communication with a ‘cold side’. Thermal energy is transferred from the hot side to the cold side by maintaining a thermal gradient between the two (i.e. maintaining the temperature of the hot side above that of the cold side). This is preferably achieved by passing fluids at different temperatures respectively through the hot and cold side of the heat exchanger, without allowing them to mix. For example, the hot side of the heat exchanger preferably includes a hot side feed and a hot side return for conveying a fluid through the hot side of heat exchanger. Similarly, the cold side of the heat exchanger preferably includes a cold side feed and a cold side return for conveying a fluid through the cold side of the heat exchanger. In this manner, thermal energy is transferred from fluid passing through the hot side of the heat exchanger to fluid passing through the cold side. The heat recovery means may provide or may be connected to the hot side of the heat exchanger. For example, where the heat recovery means includes a heat sink or heat pipe, the heat recovery means may extend from the first interior space, for example via the third outlet of the first container, to provide the hot side of the heat exchanger external to the first container. Preferably, the heat recovery means is in fluid communication with the heat exchanger, most preferably the hot side of the heat exchanger. For example, the third inlet of the first container, if present, may be connected to a hot side return of the heat exchanger, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. Similarly, the third outlet of the first container, if present, may be connected to a hot side feed of the heat exchanger, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. The heating system preferably includes means for circulating the second fluid through the heat exchanger, preferably the hot side of the heat exchanger. The means for circulating the second fluid through the heat exchanger is preferably provided by the second pump, if present. The second pump, if present, is preferably operable to convey a second fluid through the heat recovery means via the third inlet and third outlet of the first container, where thermal energy is absorbed by the second fluid from the heated first fluid contained within the first interior space of the heating system, to raise the temperature of the second fluid. The second fluid is then conveyed, under the action of the second pump, through the hot side of the heat exchanger via the hot side feed and hot side return of the heat exchanger. Preferably, the at least one space heating apparatus is in fluid communication with the heat exchanger, most preferably the cold side of the heat exchanger. For example, a cold side feed of the heat exchanger is preferably connected to a return of the at least one space heating apparatus, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. A cold side return of the heat exchanger is preferably connected to a feed of the at least one space heating apparatus, for example via one or more lengths of pipe, tubing, or other means for conveying a fluid. Thus, a third fluid, for example water or oil, may be conveyed through the cold side of the heat exchanger via the cold side feed and cold side return, where thermal energy is absorbed from the hot side of the heat exchanger, for example from the second fluid flowing through the hot side of the heat exchanger. The third fluid is then preferably conveyed through the at least one space heating apparatus via the at least one space heating apparatus feed and return, where the thermal energy absorbed by the third fluid is emitted as heat from the one or more space heating apparatus to heat a building. Accordingly, the heating system preferably includes means for circulating the third fluid through the cold side of the heat exchanger and the at least one space heating apparatus. For example, the system may include a third pump fluidly connected between cold side feed of the heat exchanger and the return of the at least one space heating apparatus, or between the cold side return of the heat exchanger and the feed of the at least one space heating apparatus. In some embodiments, the heat source is a primary heat source, and the heating system further includes a secondary or ‘auxiliary’ heat source configured to provide supplemental thermal energy to the at least one space heating apparatus. 23 For example, the auxiliary heat source may provide supplemental energy in times of particularly high demand on the heating system, such as during exceptionally cold weather. The auxiliary heat source may be of any suitable type, construction, or arrangement, as described hereinbefore with reference to the, now primary, heat source. The auxiliary heat source may be provided at any suitable location within the heating system. The auxiliary heat source may have any suitable power output, for example as described hereinbefore with reference to the, now primary, heat source. In a particularly preferred embodiment, the heating system includes a third container defining a third interior space, the auxiliary heat source being located within the third interior space. The third container may have any suitable shape, configuration, and construction, for example as described hereinbefore with reference to the first container and / or second container. Similarly, the third container may define a third interior space having any suitable volume, as described hereinbefore with reference to the first interior space and / or second interior space. The third container preferably includes a first inlet in fluid communication with the third interior space, and a first outlet in fluid communication with the third interior space. The first inlet and / or first outlet of the third container is preferably located in a wall of the third container to facilitate the passage of a fluid through the third interior space. The auxiliary heat source may be located between the heat recovery means and the at least one space heating apparatus. Preferably, where the heating system includes a heat exchanger in fluid communication with the heat recovery means, as described hereinbefore, the auxiliary heat source is connected in-line between the hot side return of the heat exchanger and the third inlet of the first container. For example, where the auxiliary heat source is located within the third interior space defined by a third container of the heating system, the hot side return of the heat exchanger may be connected to the first inlet of the third container, and the first outlet of the third container may be connected to the third inlet of the first container. In this manner, the second fluid may be circulated, for example under the action of the second pump, if present, through the heat recovery means, the hot side of the heat exchanger, and the third interior space. The auxiliary heat source is thereby operable to pre-heat the second fluid as it passes through the third interior space, and before it passes through the heat recovery means. In this manner, the auxiliary heat source may increase or ‘boost’ the temperature of the second fluid in times of particularly high demand on the at least one space heating apparatus, when thermal energy absorbed by the heat recovery means and second fluid alone may be insufficient to maintain the operation of the at least one space heating apparatus at a desired level. It will be understood that the auxiliary heat source may be connected in an analogous manner between the third outlet of the first container and the hot side feed 25 of the heat exchanger, between the cold side return of the heat exchanger and the feed of the at least one space heating apparatus, or between the return of the at least one space heating apparatus and the cold side feed of the heat exchanger. The thermostat, if present, may be configured to control the operation of the auxiliary heat source on the basis of a determination of the temperature of the first fluid contained within the first interior space. For example, when the thermostat detects that the temperature of the first fluid contained within the first interior space has fallen below a predetermined set point or minimum level sufficient to maintain the absorption of thermal energy from the first fluid by the heat recovery means at a desired rate (for example at a rate sufficient to maintain the operation of the at least one space heating apparatus), the thermostat may activate the auxiliary heat source to provide supplemental thermal energy to the at least one space heating apparatus. Heating systems according to the first aspect may be used to heat a building. Accordingly, in a second aspect, the present invention provides a method of heating a building, the method comprising: providing a heating system according to the first aspect; operating the heat source to heat a first fluid contained within the first interior space; operating the heat recovery means to absorb thermal energy from the first fluid; and operating the at least one space heating apparatus to utilise the thermal energy absorbed by the heat recovery means to heat the building. Preferably, the method further includes transmitting the thermal energy absorbed by the heat recovery means to the at least one space heating apparatus. Preferably, the method further includes providing a supply of the heated first fluid to the building, for example to one or more fixtures, fittings or appliances installed or located in the building. Preferably the method further includes conveying a second fluid within and in fluid isolation from the first interior space, via the heat recovery means, to absorb thermal energy from the first fluid. The second fluid may be conveyed through the at least one space heating apparatus where the thermal energy is emitted to heat the building. Preferably, however, the method further includes conveying the second fluid through the hot side of a heat exchanger, if present, to transmit thermal energy absorbed by the heat recovery means to a third fluid conveyed through a cold side of the heat exchanger. Preferably, the method further includes conveying the third fluid through the at least one space heating apparatus where the thermal energy is emitted to heat the building. Further aspects of methods of heating a building, including operating a heating system according to the first aspect, are as described hereinbefore with reference to the first aspect and, in the interests of conciseness, shall not be repeated here. Advantageously, the heating system is operable to heat and retain a volume of the first fluid within the first interior space at a desired temperate to be provided on demand to supply a building with the heated first fluid. By retaining a volume of the first fluid at a desired temperature to be drawn off on demand, the required power output of the heat source can be reduced, as compared to systems in which a supply of cold fluid is to be heated instantaneously for immediate consumption, for example in the case of conventional gas or electric combination boilers. This reduces the energy consumption and operating cost of the heating system. Over time, the temperature of the first fluid contained within the first interior space will nevertheless decrease as thermal energy is lost to the ambient environment. Advantageously, however, the heating system is operable to absorb thermal energy from the first fluid contained within the first interior space, at least a portion of which would otherwise be lost to the ambient environment, and to utilise this thermal energy to heat a building using the one or more space heating apparatus. Accordingly thermal energy provided to the first fluid by the heat source is utilised, even when there is no demand for a supply of the heated first fluid, to heat the building. This increases the energy efficiency of the system, for example as compared to traditional immersion heating systems, in which there is no recovery of 28 energy, whilst providing a combination heating system operable with a single, preferably electric, heat source. Significantly, and most advantageously, the operation of the at least one space heating apparatus, for example the radiators of a central heating system, is not compromised by, or otherwise impacted, when the heated first fluid contained within the first interior space is supplied to the building. In particular, when there is demand for a supply of the heated first fluid, it is drawn from the first interior space, for example via the first outlet of the first container. However, this volume of the first fluid may be immediately replaced by a supply of the first fluid, for example from the mains supply of the building. This supply of the first fluid is either diluted by the volume of heated first fluid remaining within the first interior space, so as to not appreciably lower the temperature of the first fluid below a desired set point, or, if the temperature of the first fluid does fall below a desired set point, rapidly heated by the heat source to maintain the temperature of the heated first fluid contained within the first interior volume. Accordingly, absorption of thermal energy by the heat recovery means is not substantially affected, as a desired thermal gradient between the first fluid and the heat recovery means is maintained or rapidly restored, even when a volume of the first fluid is supplied to the building. Embodiments of the present invention will now be described by way of example only, having reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a first embodiment of a heating system; Figure 2 is a schematic representation of a heater for inclusion in the heating system of Figure 1; Figure 3 is a schematic representation of a second embodiment of a heating system; Figure 4 is a schematic representation of a third embodiment of a heating system; and Figure 5 is a schematic representation of an auxiliary heater for inclusion in the heating system of Figure 4. For ease of explanation, like numbers have been used throughout the Figures to indicate analogous features of each embodiment. Turning first to Figure 1, there is shown a schematic representation of a first embodiment of a heating system, indicated generally as 1, for heating a building. The heating system 1 includes a first container 10 in the form of a vessel, for example an insulated hot water cylinder, defining a first interior space 15 for retaining a first fluid, in particular water. The vessel 10 includes a first inlet 22 connected to a reserve of the first fluid 70, in this case cold water, for example the mains water supply of the building. In this manner the first inlet 22 provides a cold water inlet. The heating system 1 includes a heater 100, described in more detail hereinbelow with reference to Figure 2, for heating the first fluid contained in the first interior space 15 to a desired temperature. 30 The vessel 10 further includes a first outlet 24 for delivering a supply of the heated first fluid, in particular a hot water supply, to one or more fixtures, fittings or appliances 80 installed or located in the building. In this manner the first outlet 24 provides a hot water outlet. The vessel 10 optionally includes a drain valve 26 and / or pressure and temperature relief valve 28. Drain valves, pressure and temperature relief valves, and their use are known in the art and, in the interests of brevity, shall not be described in detail herein. The vessel 10 includes a second inlet 32 and a second outlet 34 fluidly connected respectively to an output 114 and an input 112 of the heater 100. In this manner, the first interior space 15 of the heating system 1 is in fluid communication with the heater 100. A first pump 52 is operable to convey the first fluid from the first interior space 15 to the input 112 of the heater 100 via the second outlet 34, through the heater 100, and from the output 114 of the heater 100 to the first interior space 15 via the second inlet 32. The vessel 10, first pump 52, and heater 100, are thereby connected to form a heating circuit for heating the first fluid contained within the first interior space 15 defined by the vessel 10. Turning now to Figure 2, there is shown a schematic representation of a heater, indicated generally as 100, for inclusion in the heating system 1 of Figure 1. The heater 100 includes a second container 110 in the form of an enclosed chamber, for example a stainless-steel capped cylinder. The chamber 110 defines a second interior space 115. The chamber 110 includes a first inlet 112 providing an input of 31 the heater 100, as described hereinbefore with reference to Figure 1. The chamber 110 further includes a first outlet 114 providing an output of the heater 100, as described hereinbefore with reference to Figure 1. The input 112 and output 114 of the heater 100 are in fluid communication with the second interior space 115. The first fluid may therefore enter the chamber 110 via the input 112, for example under the action of the first pump 52 of the heating system 1 of Figure 1, and flow through the second interior space 115 to exit the chamber 110 via the output 114. The heater 100 includes a heat source comprising a plurality of heating elements 120. The heating elements 120 are preferably electric heating elements, for example resistive heating elements such as cartridge heaters. At least a portion of each heating element 120 is located within the second interior space 115 such that the first fluid flowing from the heater input 112 to the heater output 114 passes over and / or around the heating elements 120. Thermal energy generated by the heating elements 120 is absorbed by the flowing first fluid to raise the temperature of the first fluid. Preferably, the output 114 is located at the top of the chamber 110, in use, as shown in Figure 2. This allows temperature and pressure generated by the heating elements 120 to vent via the output 114 within the heating system 1, in the event of failure or shutdown of the first pump 52, thereby omitting the need to include a pressure and temperature relief valve in a wall of the chamber 110. As shown in Figure 2, the heating elements 120 are arranged so that a flow of the first fluid from the input 112 to the output 114 is substantially parallel to a longitudinal axis of each heating element 120. This increases the length of time the 32 first fluid is in contact with each heating element 120 to maximise transmission of thermal energy from the heat source to the first fluid. Returning now to Figure 1, the heating system 1 optionally includes a thermostat 60 operable to control the temperature of the first fluid contained within the first interior space 15 of the heating system 1. For example, the thermostat 60 may control the operation of the heater 100 and / or first pump 52 on the basis of a determination of the temperature of the first fluid contained within the first interior space 15. In particular, when the thermostat detects that the temperature of the first fluid contained within the first interior space 15 has fallen below a predetermined set point, the thermostat may activate one or both of the first pump 52 and heating elements 120 of the heater 100 to raise the temperature of the first fluid contained within the first interior space 15 by circulating the first fluid through the second interior space 115 where it absorbs thermal energy from the heating elements 120 before being returned to the first interior space 15. Heated first fluid, in particular hot water, contained within the first interior space 15 of the heating system 1 may be drawn off via the first outlet 24 to provide a supply of the heated first fluid, in particular a hot water supply, to fixtures, fittings or appliances 80 installed or located in the building. The first fluid contained within the first interior space 15 may be held by the thermostat 60 at a set point temperature, for example at least 30°C, preferably at least 40°C, more preferably at least 50°C, most preferably at least 60°C, for example at least 70°C. Where the temperature of the first fluid is held above that which is considered safe for use within the building (for example 60°C in the case of a domestic hot water supply), it may be mixed with an (unheated) supply of the first fluid drawn directly from the reserve of the fluid 70 to lower the temperature of the heated first fluid to a desired safe temperature. Accordingly, the heating system 1 optionally includes a blending valve 65 connected to the first outlet 24 of the vessel 10 and reserve of the first fluid 70. The blending valve receives heated first fluid from the first outlet 24 of the vessel 10, and unheated first fluid from the reserve 70, and is operable to mix the two flows as required to output a supply of heated first fluid to fixtures, fittings or appliances 80 of the building at a desired temperature. The vessel 10 further includes a third inlet 42 and a third outlet 44. A heat recovery means 46, for example a heat exchange coil in the form of a helical pipe, is located and extends within the first interior space 15 between the third inlet 42 and third outlet 44. The heat recovery means 46 defines a passage that is fluidly isolated from the first interior space 15 for conveying a second fluid, for example water or oil, within the first interior space 15 from the third inlet 42 to the third outlet 44. In this manner, the third inlet 42 is in fluid communication with the third outlet 44 to permit a flow of the second fluid between the third inlet 42 and third outlet 44 via the heat recovery means 46, within and fluidly isolated from the first interior space 15. The heat recovery means 46 is connected, via the third inlet 42 and third outlet 44, to a heat exchanger 200, for example a plate heat exchanger. The third inlet 42 of the vessel 10 is connected to a hot side return 214 of the heat exchanger 200, optionally via a second pump 54. Similarly, the third outlet 44 of the vessel 10 is connected to a hot side feed 212 of the heat exchanger 200. The second pump 54 is operable to convey the second fluid through the heat recovery means 46 via the third inlet 42 and third outlet 44, where thermal energy is absorbed by the second fluid from the volume of heated first fluid contained within the first interior space 15 of the heating system 1, to raise the temperature of the second fluid. The second fluid is then conveyed, under the action of the second pump 54, through the hot side of the heat exchanger 200 via the hot side feed 212 and hot side return 214 of the heat exchanger 200. A cold side feed 222 of the heat exchanger 200 is connected, optionally via a third pump 56, to the return 314 of at least one space heating apparatus 300, for example the radiators of a central heating system of the building. A cold side return 224 of the heat exchanger 200 is connected to a feed 312 of the at least one space heating apparatus 300. The third pump 56 is operable to convey a third fluid, for example water or oil, through the cold side of the heat exchanger 200 via the cold side feed 222 and cold side return 224, where thermal energy is absorbed from the second fluid flowing through the hot side of the heat exchanger 200, as described hereinbefore. The third fluid is then conveyed, under the action of the third pump 56, through the at least one space heating apparatus 300 via the feed 312 and return 314 of the at least one space heating apparatus 300, where thermal energy is emitted to heat the building. The heating system 1 is operable to heat a building as described in more detail hereinbelow. In a first method of heating a building, the heating system 1 is provided and installed in the building. For example, the first inlet 22 is connected to a mains water supply 70 of the building, and the first outlet 24 is connected to one or more fixtures, fittings or appliances 80 installed or located in the building. The heating elements 120 of the heater 100, thermostat 60, first pump 52, second pump 54, and third pump 56 are connected to a power supply, for example the mains electricity supply of the building. A supply of a first fluid, in this case cold water, is received within the first interior volume 15 of the heating system 1 from the mains water supply 70 to wholly or partially fill the vessel 10 with water. Heating elements 120 are operated to heat the water contained within the first interior space 15 defined by the vessel 10. In particular, water contained within the first interior space 15 is circulated through the heater 100 under the action of the first pump 52 where it absorbs thermal energy from the heating elements 120, before being returned to the first interior space 15. The temperature of heated water contained within the first interior space 15 may be maintained at a desired level or set point under the action of the thermostat 60. For example, the thermostat 60 may monitor, either continuously or at periodic intervals, the temperature of water within the first interior space 15 of the heating system 1. If the temperature of the water, as determined by the thermostat 60, falls below the set point, the thermostat 60 is operated to switch on one or both of the first pump 52 and heating elements 120 to circulate water from the first interior space 15 through the heater 100 and raise the temperature of the water contained in the first interior space 15 until it reaches or exceeds the set point, at which point the thermostat 60 is operated to switch off one or both of the first pump 52 and heating elements 120. This process is repeated as necessary to maintain the temperature of the water contained within the first interior space 15 at the set point. The heat recovery means 46 is operated to absorb thermal energy from the water contained within the first interior space 15 of the heating system 1. For example, the second pump 54 may be operated to circulate a second fluid, for example water or oil, through a passage defined by the heat recovery means 46, where it absorbs thermal energy from the heated water contained in the first interior space 15, and through the hot side of the heat exchanger 200. The third pump 56 may be operated to circulate a third fluid, for example water or oil, through the cold side of the heat exchanger 200 where it absorbs thermal energy from the second fluid passing through the hot side of the heat exchanger 200, and through the at least one space heating apparatus 300, for example the radiators of a central heating system of the building. Accordingly, the second pump 54, third pump 56, and heat exchanger 200 are operated to transmit thermal energy absorbed by the heat recovery means 46 to the at least one space heating apparatus 300. The at least one space heating apparatus 300 is operated to utilise the thermal energy, originally absorbed by the heat recovery means 46, to heat the building, for example by emitting the thermal energy to heat the space within one or more rooms of the building. Hot water contained within the first interior space 15 may also be supplied to one or more fixtures, fittings, or appliances 80 installed or located in the building via the first outlet 24. When a volume of hot water is drawn off via the first outlet 24, it is 37 replaced by a corresponding volume of cold water from the mains supply 70. This cold water mixes with and is diluted by heated water contained within the first interior space 15, and if necessary heated under the action of the thermostat 60, first pump 52, and heater 100, as described hereinbefore, to maintain the temperature of the water within the first interior space 15 at the desired set point. Thus, the absorption of thermal energy by the heat recovery means 46, transmission of the absorbed thermal via the heat exchanger 200, and utilisation of the absorbed energy by the at least one space heating apparatus 300 may remain uninterrupted, even when demand for hot water (i.e. the heated first fluid contained within he first interior space 15) by the one or more fixtures, fittings or appliances 80 installed or located in the building is high. If the thermostat 60 determines that the temperature of the heated water within the first interior space 15 has fallen below a temperature sufficient to maintain the absorption of thermal energy, from the first fluid, by the heat recovery means 46 at a desired rate, it may optionally operate to increase the flow rate of the second fluid, under the action of the second pump 54, from the hot side return 214 of the heat exchanger 200 and through the heat recovery means 46. By increasing the flow rate of the second fluid through the heat recovery means 46, a sufficient thermal gradient is maintained between the first and second fluids to thus maintain the absorption of thermal energy by the heat recovery means 46 at a desired rate. This in turn maintains the transmission of thermal energy via the heat exchanger 200 to prevent an interruption or reduction in the operation of the one or more space heating apparatus 300, while the temperature of the first fluid within the first interior space 15 recovers to the desired set point under the action of the thermostat. In a preferred embodiment, the flow rate of the second fluid is inversely proportional to the temperature of the first fluid. The heat exchanger 200 fluidly decouples the heat recovery means 46 from the at least one space heating apparatus 300, whilst still allowing the transmission of thermal energy from the former to the latter. This is advantageous, at is allows the flow rate of a comparatively small volume of the second fluid to be increased under the action of the second pump 54 to maintain absorption of thermal energy by the heat recovery means 46 for utilisation by the at least one space heating apparatus 300, without increasing the flow rate of a comparatively large volume of the third fluid through the at least one space heating apparatus 300, which would place a far greater burden on the third pump 56. This reduces the net energy consumption of the heating system 1, whilst maintaining the operation of the at least one space heating apparatus 300 during times of high demand for hot water (i.e. the heated first fluid contained within the first interior space 15) by the one or more fixtures, fittings or appliances 80 installed or located in the building. However, in a second embodiment the heat exchanger 200 may be omitted, for example when the volume of fluid to be circulated through the at least one space heating apparatus 300 is relatively modest. This might be the case when the building to be heated is small, requiring only one or a small number of space heating apparatus 300. Turning now to Figure 3, there is shown a schematic representation of a second embodiment of a heating system, indicated generally as 2. It is to be understood that like numbers have been used to indicate features of the second embodiment analogous to those of the first embodiment of a heating system 1 shown in Figures 1 and 2. A detailed discussion of these features is provided hereinbefore 39 with reference to Figures 1 and 2 and, in the interests of conciseness, shall not be repeated with reference to Figure 3. As can be seen from Figure 3, in the heating system 2, the at least one space heating apparatus 300 is in fluid communication with the heat recovery means 46. In particular, the return 314 of the at least one space heating apparatus 300 is connected to the third inlet 42 of the vessel 10. Similarly, the feed 312 of the at least one space heating apparatus 300 is connected to the third outlet 44 of the vessel 10. In this manner, the second fluid conveyed by the heat recovery means 46 is circulated, under the action of the second pump 54 through the at least one space heating apparatus 300. Thermal energy absorbed by the second fluid from the first fluid, as described hereinbefore, is transmitted to the at least one space heating apparatus 300 by a flow of the second fluid through the at least one space heating apparatus 300, where it is emitted to heat a building. In a third embodiment of a heating system, the heater 100 may be a primary heater, and an auxiliary heater may be included to provide additional thermal energy to the at least one space heating apparatus 300. This might be required, for example, in times of particularly high demand on the heating system, for example during exceptionally cold weather. Turning now to Figure 4, there is shown a schematic representation of a third embodiment of a heating system, indicated generally as 3. It is to be understood that like numbers have been used to indicate features of the third embodiment analogous to those of the first embodiment of a heating system 1 shown in Figures 1 and 2. A detailed discussion of these features is provided hereinbefore with reference to Figures 1 and 2 and, in the interests of conciseness, shall not be repeated with reference to Figure 4. As can be seen from Figure 4, the heating system 3 includes an auxiliary heater 400, described in more detail hereinbelow with reference to Figure 5. The third inlet of the vessel 42 is connected to an output 414 of the auxiliary heater 400. In this manner, the heat recovery means 46 is in fluid communication with the auxiliary heater 400. The hot side return 214 of the heat exchanger 200 is connected to an input 412 of the auxiliary heater 400 via the second pump 54. In this manner, the hot side of the heat exchanger 200 is in fluid communication with the auxiliary heater 400. The second pump 54 is operable to circulate the second fluid through the heat recovery means 46, the hot side of the heat exchanger 200, and the auxiliary heater 400. The auxiliary heater 400 is operable to pre-heat to the second fluid before it passes through the heat recovery means 46. In this manner, the auxiliary heater 400 may increase or ‘boost’ the temperature of the second fluid in times of particularly high demand on the at least one space heating apparatus 300, when thermal energy absorbed by the heat recovery means 46 alone may be insufficient to maintain the operation of the at least one space heating apparatus 300 at a desired level. Turning now to Figure 5, there is shown a schematic representation of an auxiliary heater, indicated generally as 400, for inclusion in the heating system 3 of 41 Figure 4. The auxiliary heater 400 includes a third container 410 in the form of an enclosed chamber. The chamber 410 defines a third interior space 415. The chamber 410 includes a first inlet 412 providing an input of the auxiliary heater 400, as described hereinbefore with reference to Figure 4. The chamber 412 further includes a first outlet 414 providing an output of the auxiliary heater 400, as described hereinbefore with reference to Figure 4. The second fluid may therefore enter the chamber 410 via the input 412, for example under the action of the second pump 54 of the heating system 3 of Figure 4, and flow through the third interior space 415 to exit the chamber 410 via the output 414. The auxiliary heater 400 includes an auxiliary heat source comprising a plurality of auxiliary heating elements 420. The auxiliary heating elements 420 are preferably electric heating elements, for example resistive heating elements such as cartridge heaters. At least a portion of each auxiliary heating element 420 is located within the third interior space 415 such that the second fluid flowing from the auxiliary heater input 412 to the auxiliary heater output 414 passes over and / or around the auxiliary heating elements 420. Thermal energy generated by the auxiliary heating elements 420 is absorbed by the flowing second fluid to raise the temperature of the second fluid. As shown in Figure 5, the auxiliary heating elements 420 are arranged so that a flow of the second fluid from the auxiliary heater input 412 to the auxiliary heater output 414 is substantially perpendicular to a longitudinal axis of each auxiliary heating element 420. This arrangement minimises the size of the chamber 412 and promotes maximum heat exchange to the second fluid over a short flow path. Thus the overall size increase of the heating system 3 to accommodate the auxiliary heater 400 is minimised. Returning now to Figure 4, it will be understood that the auxiliary heater 400 5 could be located at any position between the heat recovery means 46 and the at least one space heating apparatus 300, to provide additional thermal energy to the at least one space heating apparatus 300. For example, the auxiliary heater 400 could be connected in-line between the third outlet 44 of the vessel 10 and hot side feed 212 of the heat exchanger 200, between the cold side return 224 of the heat 10 exchanger 200 and the feed 312 of the at least one space heating apparatus 300, or between the return 314 of the at least one space heating apparatus 300 and the cold side feed 222 of the heat exchanger 200.

Claims

1. A heating system for heating a building, the heating system comprising:a first container defining a first interior space;a heat source configured to heat a first fluid contained within the first interior space;a heat recovery means located within the first interior space; andat least one space heating apparatus;wherein the heat recovery means is configured to absorb thermal energy from the first fluid contained within the first interior space; andwherein the at least one space heating apparatus is configured to utilise thermal energy absorbed by the heat recovery means to heat a building.

2. The heating system according to claim 1, wherein the first container includes a first inlet in fluid communication with the first interior space for connection to a reserve of the first fluid.

3. The heating system according to claim 1 or claim 2, wherein the first container includes a first outlet in fluid communication with the first interior space, configured to deliver a supply of the first fluid heated by the heat source to a building.

4. The heating system according to claim 3, further comprising a blending valve connected to the first outlet.

5. The heating system according to any preceding claim, wherein the heat source comprises a plurality of heating elements.

6. The heating system according to any preceding claim, further comprising a second container defining a second interior space in fluid communication with the first interior space;wherein the heat source is located within the second interior space.

7. The heating system according to claim 6, further comprising means for circulating the first fluid between the first interior space and the second interior space.

8. The heating system according to claim 6 or claim 7, wherein the second interior space has a smaller volume than the first interior space.

9. The heating system according to claim 8, wherein the ratio of the volume of the first interior space to the volume of the second interior space is at least 10:1, preferably at least 20:1, more preferably at least 30:1, still more preferably at least 40:1, most preferably at least 50:

110. The heating system according to any preceding claim, wherein the heat recovery means defines a passage for conveying a second fluid within, and in fluid isolation from, the first interior space.

11. The heating system according to claim 10 further comprising means for circulating the second fluid through the heat recovery means.

12. The heating system according to any preceding claim further comprising means for transmitting thermal energy from the heat recovery means to the at least one space heating apparatus.

13. The heating system according to claim 12, wherein the means for transmitting thermal energy from the heat recovery means to the at least one space heating apparatus comprises a heat exchanger.

14. The heating system according to claim 13, wherein the heat recovery means is in fluid communication with the heat exchanger.

15. The heating system according to claim 14, when dependent on at least claim 10, further comprising means for circulating the second fluid through the heat exchanger.

16. The heating system according to any of claims 13 to 15, wherein the at least one space heating apparatus is in fluid communication with the heat exchanger.

17. The heating system according to claim 16 further comprising means for circulating a third fluid through the at least one space heating apparatus and the heat exchanger.

18. The heating system according to any preceding claim further comprising a thermostat.

19. The heating system according to claim 18, wherein the thermostat is configured to control the operation of the heat source on the basis of a determination of the temperature of the first fluid contained within the first interior space.

20. The heating system according to claim 18 or claim 19, when dependent on at least claim 7, wherein the thermostat is configured to control the operation of the means for circulating the first fluid between the first interior space and the second interior space on the basis of a determination of the temperature of the first fluid contained within the first interior space.

21. The heating system according to any of claims 18 to 20, when dependent on at least claim 11, wherein the thermostat is configured to control the operation of the means for circulating the second fluid through the heat recovery means on the basis of a determination of the temperature of the first fluid contained within the first interior space.

22. The heating system according to any preceding claim, wherein the heat source is a primary heat source, the heating system further comprising a secondary heat source configured to provide supplemental thermal energy to the at least one space heating apparatus.

23. A method of heating a building, the method comprising:providing a heating system according to any preceding claim;operating the heat source to heat a first fluid contained within the first interior space;operating the heat recovery means to absorb thermal energy from the first fluid; andoperating the at least one space heating apparatus to utilise the thermal energy absorbed by the heat recovery means to heat the building.

24. The method according to claim 23, further comprising providing a supply of the heated first fluid to the building.

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