Heating installations, methods and systems

Abstract

A method of controlling a heating system 400 for premises 426 includes an air source heat pump 429, a premises heating installation 406 coupled to receive heated fluid from the air source heat pump, a

Description

Technical field The present disclosure variously relates to methods and apparatus, for installations including an in-building hot water supply system, that support reduced energy and water usage. Background Worldwide, there is a shortage of potable water. Water shortages are now commonly reported around the world, and although it might be thought that such issues only affect "hot" countries and continents, that is no longer the case. The European Environment Agency reports that water shortages or water stress is a problem that affects millions of people around the world, including over 100 Million people in Europe. About 88.2 % of Europe's freshwater use (drinking and other uses) comes from rivers and groundwater, while the rest comes from reservoirs (10.3 %) and lakes (1.5 %), which makes these sources extremely vulnerable to threats posed by over-exploitation, pollution and climate change. Consequently, there is an urgent need reduce domestic water usage. In Europe, on average, 144 litres of freshwater per person per day is supplied for household consumption, but much of this water is "wasted" through carelessness and poor choices of taps, showers, and appliances. Allied to the need to reduce water consumption is the need to reduce domestic energy consumption, particularly given that (at least in Europe) around 75% of heating and cooling is still generated from fossil fuels while only 22% is generated from renewable energy. According to Directive 2012 / 27 / EU buildings represent 40% of the final energy consumption and 36% of the CO2 emissions of the European Union. The EU Commission report of 2016 "Mapping and analyses of the current and future (2020 - 2030) heating / cooling fuel deployment (fossil / renewables)" concluded that in EU households, heating and hot water alone account for 79% of total final energy use (192.5 Mtoe). The EU Commission also report that, "according to 2019 figures from Eurostat, approximately 75% of heating and cooling is still generated from fossil fuels while only 22% is generated from renewable energy. To fulfil the EU's climate and energy goals, the heating and cooling sector must sharply reduce its energy consumption and cut its use of fossil fuels. Heat pumps (with energy drawn from the air, the ground or water) have been identified as potentially significant contributors in addressing this problem. In many countries, there are policies and pressures to reduce carbon footprint. For example, in the UK in 2020 the UK Government published a whitepaper on a Future Homes Standard, with proposals to reduce carbon emissions from new homes by 75 to 80% compared to existing levels by 2025. In addition, it was announced in early 2019 that there would be a ban on the fitment of gas boilers to new homes from 2025. It is reported that in the UK at the time of filing 78% of the total energy used for the heating of buildings comes from gas, while 12% comes from electricity. The UK has a large number of small, 2 -3 bedroom or less, properties with gas-fired central heating, and most of these properties use what are known as combination boilers, in which the boileracts as an instantaneous hot water heater, and asa boilerforcentral heating. Combination boilers are popular because they combine a small form factor, provide a more or less immediate source of "unlimited" hot water (with 20 to 35kW output), and do not require hot water storage. Such boilers can be purchased from reputable manufactures relatively inexpensively. The small form factor and the ability to do without a hot water storage tank mean that it is generally possible to accommodate such a boiler even in a small flat or house - often wall-mounted in the kitchen, and to install a new boiler with one man day's work. It is therefore possible to get a new combi gas boiler installed inexpensively. With the imminent ban on new gas boilers, alternative heat sources will need to be provided in place of gas combi boilers. In addition, previously fitted combi boilers will eventually need to be replaced with some alternative. Whether it is in a commercial or domestic setting, heated water is required throughout the day all year round. It goes without saying that the provision of heated water requires both clean water and a source of heat. To provide heated water, a heating system is provided to an often centralised water provision system to heat water up to a predetermined temperature e.g. set by a user, and the heat source used is conventionally one or more electric heating elements or burning of natural gas. Generally, during periods of high energy (e.g., gas or electricity) demand utilities providers would implement a peak tariff which increases the unit cost of energy, partly to cover the additional cost of having to purchase more energy to supply to customers and partly to discourage unnecessary energy usage. Then, during periods of low energy demand utilities providers would implement an off-peak tariff which lowers the unit cost of energy to incentivise customers to switch to using energy during these off-peak periods instead of peak periods to achieve an overall more balanced energy consumption over time. However, such strategies are only effective if customers are always aware of the changes in tariffs and in addition make a conscious effort to modify their energy consumption habits. Clean water as utility is currently receiving much attention. As clean water becoming scarcer, there has been much effort to educate the public on the conservation of clean water as well as development of systems and devices that reduce water consumption, such as aerated showers and taps to reduce water flow, showers and taps equipped with motion sensors that stop the flow of water when no motion is detected, etc. However, these systems and devices are restricted to a single specific use and only have limited impact on problematic water consumption habits. With growing concerns over the environmental impact of energy consumption, there has been a recent growing interest in the use of heat pump technologies as a way of providing domestic heated water. A heat pump is a device that transfers thermal energy from a source of heat to a thermal reservoir. Although a heat pump requires electricity to accomplish the work of transferring thermal energy from the heat source to the thermal reservoir, it is generally more efficient than electrical resistance heaters (electrical heating elements) as it typically has a coefficient of performance of at least 3 or 4. This means under equal electricity usage 3 or 4 times the amount of heat can be provided to users via heat pumps compared to electrical resistance heaters. The heat transfer medium that carries the thermal energy is known as a refrigerant. Thermal energy from the air (e.g. outside air, or air from a hot room in the house) or a ground source (e.g. ground loop or water filled borehole) is extracted by a receiving heat exchanger and transferred to a contained refrigerant. The now higher energy refrigerant is compressed, causing it to raise temperature considerably, where this now hot refrigerant exchanges thermal energy via a heat exchanger to a heating water loop. In the context of heated water provision, heat extracted by the heat pump can be transferred to a water in an insulated tank that acts as a thermal energy storage, and the heated water may be used at a later time when needed. The heated water may be diverted to one or more water outlets, e.g. a tap, a shower, a radiator, as required. However, a heat pump generally requires more time compared to electrical resistance heaters to get water up to the desired temperature, in part because heat pumps are typically slow to start up. A heat pump may comprise an outdoor unit with heat exchanger coils that extract heat from the air or ground outside and transfers it to an indoor unit either directly to the inside of a building to warm it or to a thermal energy storage medium to store it for use later. The process of extracting thermal energy from the outside air cools the heat exchanger coils in the outdoor unit, and moisture from the air condenses on the cool outdoor coils. In cold outdoor conditions, for example when the outside air is 5°C, the outdoor coils can cool below freezing, and frost can form on the outdoor coils. As frost accumulates on the outdoor coils, the heat pump becomes less efficient, requiring a greater temperature difference with the outside air to output the same power compared to frost-free coils. It is therefore desirable to operate a heat pump in a defrost cycle, regularly and when frost accumulates, to remove frost from the heat exchanger coils in the outdoor unit of the heat pump. A number of factors can influence when a heat pump requires a defrost cycle, for example outdoor temperature and humidity, the power output of the heat pump, and the condition of the heat pump (e.g. older system may be less efficient and requires more frequent defrosting). Generally, a heat pump operates a defrost cycle whenever frost forms on the outdoor heat exchanger coils. During a defrost cycle, a heat pump is operated in reverse, in that warm refrigerant is sent to the outdoor unit to thaw the heat exchanger coil. A heat pump may operate a defrost cycle until, for example, the coil reaches around 15°C. Once the heat exchanger coil is thawed, the heat pump can resume the normal heating cycle. Clearly, while a heat pump is operating a defrost cycle, it will not be able to performs its normal function of transferring heat to the indoor unit (e.g. into the thermal energy storage 150) until the defrost cycle is complete. It may therefore be desirable to prepare the building before a heat pump defrost cycle begins. It is therefore desirable to provide improved methods and systems for the control of heating installations for the provision of heated water. Summary According to a first aspect, there is provided method of controlling a heating system for premises as defined in claim 1 with optional features being defined in the dependent claims. According to a second aspect, there is provided a heating system for premises as defined in claim 17. According to a third aspect, there is provided a computer readable medium, as defined in claim 18. Some further optional features are described below. Preferably, the controller is configured to increase energy input into the heating arrangement in anticipation of a forecast fall in the temperature of the air from which the air source heat pump extracts energy. Preferably, the controller is configured to determine a start time and a duration of the defrost cycle of the air source heat pump based on a predicted likelihood that the premises heating arrangement will be activated or used or required during a forecast period of lowered temperature. Optionally, the controller is configured to predict the likelihood based on past household behaviour of the premises, and / or on past behaviour of comparable households. Optionally, the controller may be configured to take account of occupancy or predicted occupancy of the premises in predicting the likelihood. Optionally, the controller is configured to take account of scheduled activity of occupants of the premises in predicting the likelihood. Optionally, the controller is configured to override a setting of the heating arrangement. Optionally, the determined start time and duration is adjusted based on sensed use of the heating arrangement. Brief description of the drawings Embodiments of various aspects of the disclosure will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematically an overview of a heating arrangement; Figure 2 corresponds generally to Figure 1, but includes more detail; Figure 3 shows schematically details of a hot water provisioning system that can be used in the system of Figure 2; Figure 4 schematically details of a system according to an aspect of the invention; and Figure 5 schematically shows exemplary data processing by an MLA to initiate a heat pump defrost cycle. Detailed description In a heating arrangement, cold and heated water may be provided by a centralized water provision system to a plurality of water outlets, including taps, showers, radiators, etc., for a building in a domestic or commercial setting. An exemplary water provisioning system is shown in Fig. 1. In this schematic system, the water provisioning system 100 comprises a control module 110, which may include one or more Machine Learning Algorithms 120. The control module 110 is communicatively coupled to, and configured to control, various elements of the water provision system, including flow control 130 for example in the form of one or more valves arranged to control the flow of water internal and external to the system, a (ground source or air source) heat pump 140 configured to extract heat from the surroundings and deposit the extracted heat in a thermal energy storage 150 to be used to heat water, and one or more electric heating elements 160 configured to directly heat cold water to a desired temperature by controlling the amount of energy supplied to the electric heating elements 160. Heated water, whether heated by the thermal energy storage 150 or heated by the electric heating elements 160, is then directed to one or more water outlets as and when needed. In embodiments, the heat pump 140 extracts heat from the surroundings into a thermal energy storage medium within the thermal energy storage 150. The thermal energy storage medium may in addition be heated by other sources. The thermal energy storage medium is heated until it reaches a desired operation temperature, then cold water e.g. from the mains can be heated by the thermal energy storage medium to the desired temperature. The heated water may then be supplied to various water outlets in the system. In the present schematic system, the control module 110 is configured to receive input from a plurality of sensors 170-1,170-2,170-3,..., 170-n. The plurality of sensors 170-1,170-2, 170-3, ..., 170-n may for example include one or more air temperature sensors disposed indoor and / or outdoor, one or more water temperature sensors, one or more water pressure sensors, one or more timers, one or more motion sensors, and may include other sensors not directly linked to the water provision system 100 such as a GPS signal receiver, calendar, weather forecasting app on e.g. a smartphone carried by an occupant and in communication with the control module via a communication channel. The control module 110 is configured, in the present embodiment, to use the received input to perform a variety of control functions, for example controlling the flow of water through the flow control 130 to the thermal energy storage 150 or electric heating elements 160 to heat water. A dotted line 180 Illustrates schematically an enclosure within which the components described above, other than the sensors 170-1,170-2,170-3,..., 170-n may be located. While a heat pump is generally more energy efficient for heating water compared to an electrical resistance heater, a heat pump requires time to start up as it performs various checks and cycles before reaching a normal operation state, and time to transfer sufficient amount of thermal energy into a thermal energy storage medium before reaching the desired operation temperature. On the other hand, an electrical resistance heater is generally able to provide heat more immediately. Thus, a heat pump can take longer to heat the same amount of water to the same temperature compared to an electrical resistance heater. Figure 2 shows a more detailed schematic diagram of an in-building hot water supply installation 200 having a plurality of controllable water outlets (various taps and showers that will be described more fully later), a supply of hot water 205 with at least one outlet having a controllable outflow temperature, and in a water flow path between the supply of water 205 and the plurality of controllable water outlets, at least one first temperature sensor 243 to detect the outflow temperature, at least one flow measurement device 210 and at least one flow regulator 215. A processor 240 is operatively connected to the at least one flow measurement device 210 and the at least one flow regulator 215. The illustrated water supply installation represents a dwelling with a master bathroom 221, a first en-suite shower room 222, a second en-suite shower room 223, a cloakroom 224, and a kitchen 225. The master bathroom 221 and the first en-suite shower room 222 may be on one floor of the dwelling, whereas the cloakroom 224, second en-suite 223 and kitchen 225 may be on another floor of the dwelling. In such a situation, it may be convenient to have, as shown, two separate circuits, 230 and 231, to supply water to the various outlets. The two circuits 230 and 231 may each be fed from a different outlet, the temperature of the two outlets being separately adjustable, and each outlet lhaving its own associated temperature sensor 243. The temperature of the water at the outlet (s) may be adjusted by mixing cold water with hot water from a source of fixed or variable temperature, or it may be adjusted by controlling the energy put into a heat source, such as an electric heating element or even a gas fired heater. Later we will describe hot water systems which include thermal energy storage arrangements, generally in combination with a heat pump, and in such systems generally the hot water supply temperature may be adjusted by mixing in different proportions of cold water from a cold-water supply. Sometimes such systems may include an instantaneous heat source (such as an electrical heating element) downstream of the thermal energy storage arrangement, controlled by a processor of the system, and in such installations control of hot water supply temperature may involve controlling the amount of energy supplied to the instantaneous water heater, as well possibly by mixing in different proportions of cold water from a cold-water supply. The master bathroom 221 is shown as including a shower outlet 235, a bath tap or faucet 236, and a tap 237 for a sink. The en-suite shower rooms 222 and 223 also include a shower outlet 235, and a tap 237 for a sink. Conversely, the cloakroom 224 contains just a W.C. (not shown) and a hand basin with a tap 238. Finally, the kitchen 235 has a sink with a tap 239. A processor, or system controller, 240, with an associated memory 241, is coupled to the at least one flow measurement device 210 and the at least one flow regulator 215. It will be appreciated that each of the two circuits 230 and 231 is provided with a respective flow measurement device 210 and flow regulator 215 The processor is also optionally connected to one or more temperature sensors 243, one for each of the circuits 230 and 231. This processor may be associated with an energy bank. The processor may also be coupled to an RF transceiver 242, which includes at least one RF transmitter and at least one RF receiver, for bidirectional communication via Wi-Fi, Bluetooth, or the like, and preferably also to the Internet 244 for connection to a server or central station 245, and optionally to a cellular radio network (such as LTE, UMTS, 4G, 5G, etc.). By means of the RF transceiver 242 and / or the connection to the Internet, the processor 240 is able to communicate with a mobile device 250, which may for example be a smart phone or tablet, for use by an installation engineer in configuring (and also optionally in mapping) the in-building water supply installation. The mobile device 250 includes software, such as a specific app, that co-operates with corresponding software in the system controller 240 and also potentially within server 245, to facilitate the configuring (and optionally mapping) methods according to embodiments of the invention, and in particular to synchronize actions taken by the engineer to a clock of the system controller 240 / server 245. The memory 241 contains code to enable the processor to perform a method of configuring (and optionally mapping) an in-building water supply installation processor, for example during a process of commissioning a new installation. During the commissioning process, in order to configure the hot-water supply installation 200, the engineer may be asked to setup a temperature sensor direct under a particular hot-water outlet, e.g., a specific tap or shower outlet, and to open the outlet fully at a specific moment. The system processor is configured to measure flow, the difference between both outflow and provided temperature, time delay and, preferably, outdoor temperature (data provided from an external temperature sensor). This will allow algorithms (e.g., MLAs) to calculate heat loss through the distribution system, distance between the outlet (tap or shower outlet) and the source of hot water, and finally, accurately adjust the outflow temperature to achieve the correct water temperature at the relevant controllable outlet (e.g., tap). For example, if the household includes children, then the maximum hot water temperature to every outlet other than, for example, the kitchen sink may be limited to 40C or41C, whereas if there are infants in the house, the maximum temperature may be limited to 37C. Even in the absence of children, the maximum temperature for all outlets other than the kitchen sink may be set at 43C, and possibly 41C for shower outlets. The system may also be set up to restrict the flow of hot water to some classes of water outlets, such as handbasins and sinks, and possibly showers, with different maximum flow rates being set for each class of outlet, and / or maximum specific flow rates may be set for specific outlets - so lower flow rates set for bathrooms and cloakrooms used by children, for example. The determination of maximum temperatures and flow rates may be based on rules provided by the system supplier. Later we will discuss hot water supply systems which use heat pumps and thermal energy storage arrangements, and such systems benefit significantly from the imposition of temperature and flow rate control - since heat pumps sized according to the space heating need of a modestly sized 1 to 3-bedroom dwelling generally do not have the heating capacity to satisfy the instantaneous hot water demands of the household, without the provision of voluminous hot water storage tanks. By managing hot water flow and temperature, it may be possible to eliminate the need to provide hot water storage, while minimizing the size of the energy shortfall to be accommodated by other means. If the installation does include a thermal energy storage arrangement and a heat pump, the system supplier will typically pre-program the processor with suitable values for temperature and flow based on outlet type and household composition. A database of temperatures and optionally flow rates, based on outlet type and household composition may also be made available to the system controller over the internet, and updated from time to time. A user interface for the system controller may provide a means for occupiers and or service engineers to adjust the various settings according to changes in the household composition - for addition the arrival of guests with infants, children or elderly or infirm persons, of for example to allow users to set lower maximum temperatures and / or flow rates. Figure 3 shows, schematically, a heating system 300, showing some of the components that may be used in a system similar to that described above with reference to Figures 1 and 2 and flow paths between the components. As shown, heating system 300 includes a mains inlet of cold water 302 and a domestic hot water outlet 304, such as a tap or shower outlet and a domestic hot water heating appliance 310, such as a radiator. The system 300 further includes a heat pump 306, which may typically have a heating capacity of 3-12 kW, a heat exchanger 308, and a thermal storage appliance 342, such as a relatively small water tank holding approximately 15 litres of water. These components are connected by water flow pipes, with flow transducers, temperature transducers and valves that control the water flows though the pipes in a manner to be described below. The flow transducers and temperature transducers are all connected via signal lines to provide signals to a system controller 340, which controls the valves in order to control the system to operate in one of several operating modes as will be described below. One, some or all of the flow transducers may be replaced by pressure transducers that determine the pressure of the fluid in order to be able to determine the flow rate. Leading from the mains cold water inlet 302 a first flow path 312 leads to a first inlet HX1 of the heat exchanger 308. A temperature transducer TT01 and a flow transducer FT01 measure the temperature and the flow rate of the cold water at the mains cold water inlet 302. A temperature transducer TT02 and a flow transducer FT03 measure the temperature and the flow rate at the first inlet HX1 to the heat exchanger 308. A second flow path 314 leads from the first flow path 312 near the mains cold water inlet 302 towards the domestic hot water outlet 304. A first motorised valve MV01 is positioned in the second flow path 314 to regulate the water flow within the second flow path 314. A flow transducer FT02 measures the flow rate of the cold water passing through the first motorised valve MV01, from which it is selectively combined with water leaving a motorised three-way valve MV03 as will be further described below, towards the domestic hot water outlet 304 adjacent which a temperature transducer TT07 measures the temperature of the water leading to the domestic hot water outlet 304. A first part 316a of a third flow path 316 leads from the first flow path 312 nearer to the heat exchanger 308 than the second flow path 314. A second motorised valve MV02 is positioned in the first part 316a of the third flow path 316 to regulate the water flow within the first part 316a of the third flow path 316 leading to a lower part of the thermal storage appliance 342. A temperature transducer TT11 measures the temperature of the water at the lower part of the thermal storage appliance 342 and another temperature transducer TT10 measure the temperature of the water at an upper part of the thermal storage appliance 342. A second part 316b of the third flow path 316 leads from the upper part of the thermal storage appliance 342 to a second inlet B of a motorised three-way valve MV03, with a temperature transducer TT05 measuring the temperature of the water in the second part 316b of the third flow path 316. A return flow path 318 is provided to return water from an outlet of the motorised valve MV02 in the first part 316a of the third flow path 316 to an inlet of the motorised valve MV02 via a circulation pump 320 and a non-return valve 322. The heat exchanger 308 has a first outlet HX2 which is connecter to receive the water having entered the heat exchanger via first inlet HX1. A fourth flow path 324 leads from the first outlet HX2 of the heat exchanger to a first inlet A of the motorised three-way valve MV03, via an electric heater 326. A temperature transducer TT03 measures the temperature of the water leaving the first outlet HX2 of the heat exchanger 308 and a temperature transducer TT04 measures the temperature of the water leaving the electrical heater 326 and entering the first inlet A of the motorised three-way valve MV03. A fifth flow path 328 leads from the outlet AB of the motorised three-way valve MV03 towards the domestic hot water outlet 304, and combines with the first flow path 314 prior to reaching the domestic hot water outlet 304. A temperature transducer TT06 measures the temperature of the water leaving the outlet AB of the motorised three-way valve MV03 prior to being combined with water from the second flow path 314 and a temperature transducer TT07 measures the temperature of the water after it has been combined with water from the second flow path 314 as it enters the domestic hot water outlet 304. On the other side of the heat exchanger 308 from the first inlet HX1 and the first outlet HX2 are second inlet HX3 and second outlet HX4. The second inlet HX3 is fed by a sixth flow path 330 leading from an outlet of the heat pump 306 via a motorised three-way valve MV04, with a temperature of transducer TT08 measuring the temperature of the water at the second inlet HX3 of the heat exchanger 308. A seventh flow path 332 is coupled between the second outlet HX4 of the heat exchanger 308 and an inlet of the heat pump 306. As shown, the heat pump 306 includes a heat exchanger 334 and a circulating pump 336 to heat water received at the inlet and to output the heated water and the output. A temperature transducer TT09 measures the temperature of the water leaving the heat exchanger 308 and being passed into the inlet of the heat pump 306. Thus, the motorised three-way valve MV04 has a first inlet A coupled to the outlet of the heat pump 306, an outlet AB coupled to the second inlet HX3 of the heat exchanger 308. A second outlet B of the motorised three-way valve MV04 leads to an inlet of the domestic hot water heating appliance 310, whose outlet leads to the seventh flow path 332. A dotted line labelled 344 illustrates all the components of the system that can be included in a housing that may be made of a similar size and shape as to replace a combination boiler, although it will be appreciated by people skilled in the art that in some circumstances, the components may be otherwise arranged, inside or outside such a housing, which may not be needed at all in some circumstances. In particular, for example temperature transducer TT09 may be located within the housing 344 nearer the heat exchanger 308 or outside the housing 344 nearerthe domestic hot water heating appliance 310. Others of the temperature and flow transducers, such as, for example, flow transducer FT01 and / or temperature transducer TT01 may similarly be positioned inside or outside the housing, as desired. The heating system 300 may be operated in a number of modes of operation, which will now be briefly described. Although there are a number of differing operating modes, several may be interrelated and used in combination or separately. The modes are: Heat Exchanger Charging Mode in which the heat exchanger 308 is used to heat water that is used to fill (or charge) the thermal storage appliance 342; Electric Heater Charging Mode in which the electric heater 326 is used to heat water that is used to charge the thermal storage appliance 342; Initial Hot Water Mode, in which hot water provided to the domestic hot water outlet 304 is provided either by the thermal energy storage appliance 342, if it is charged with hot water, or is heated by the electric heater 326, or a combination of both, as required; Mixed Water Mode to decrease temperature of water from Mode 3 is mixed with cold water from the mains cold water inlet 302 to reduce the temperature of the water being provided to the domestic hot water outlet 304; Steady State Mode in which the heat pump 306 is used to heat water from the cold water from the mains cold water inlet 302 at the heat exchanger and to provide the heated water, optionally further heated by the electric heater 326, and mixed with cold water from the mains cold water inlet 302 to reduce the temperature of the water being provided to the domestic hot water outlet 304; Combined Mode, which is a combination of the Initial Hot Water Mode and the Steady State Mode; Heat Pump Defrost Mode; House Heating Mode; and Overall Mode, which is a combination of the Combined Mode and the House Heating Mode. In the Heat Pump Charging Mode the thermal storage appliance 342 is charged with hot water provided from the heat exchanger 308. In this mode of operation, the second motorised valve MV02 is closed and the circulation pump 320 in the return flow path 318 is turned on so that water is pumped from the thermal storage appliance 342 via the circulation pump 320, the non-return valve 322 and the first flow path 312 to the first inlet HX1 of the heat exchanger 308. Since the water is being pumped from the first part 316a of the third flow path 316 into the first flow path 312, water from the domestic cold water inlet 302 does not affect the flow. The water is heated in the heat exchanger 308 and is passed from the first outlet HX2 through fourth flow path 324 via the electric heater 326, which in this mode is turned off, to the motorised valve MV03 which is controlled to direct the water from port A to port B, so that the water returns to the thermal storage appliance 342. It will be apparent that the water can be so looped around more than once, if desired, until the water at the thermal storage appliance 342 reaches a predetermined temperature, as measured by temperature transducer TT10 or temperature transducer TT04. In order to provide the heat exchanger 308 with hot water from the heat pump, the motorized valve MV04 is controlled so that water in the sixth flow path 330 from the heat pump 306 passes through port A to port AB of the motorized valve MV04and hence to the second inlet HX3 of the heat exchanger 308. The water then returns from second outlet HX4 of the heat exchanger 308 to the heat pump 306. In this mode the heat pump power is modulated to transfer heat to the circulating hot water loop, charging the thermal energy storage appliance 342, for example a 15 litre tank, with continued operation of the circulation pump 320 on the hot water side. An example case would be if the circulation pump 320 runs at 6L / min, and the heat pump 306 is modulated to heat the water in the hot water loop to 55°C at the heat exchanger 308, the circulation pump 320 would run for approximately 6 minutes to charge the water in the thermal energy storage appliance 342 to 55°C in 2 passes through the loop. In the Electric Heater Charging Mode the thermal storage appliance 342 is charged with hot water heated by the electric heater 326. In this mode, similarly to the first mode, the second motorised valve MV02 is closed and the circulation pump 320 in the return flow path 318 is turned on so that water is pumped from the thermal storage appliance via the circulation pump 320, the non-return valve 322 and the first flow path 312 to the first inlet HX1 of the heat exchanger 308. The heat pump does not provide thermal energy to the heat exchanger in this mode, so the water is passed from the first outlet HX2 of the heat exchanger through fourth flow path 324 to the electric heater 326, which in this mode is actively controlled to heat the water. The hot water is then passed to the motorised valve MV03 which is controlled to direct the water from port A to port B, so that the hot water returns to the thermal storage appliance 342. It will be apparent that the water can be so looped around more than once, if desired, until the water at the thermal storage appliance 342 reaches a predetermined temperature, as measured by temperature transducer TT10 or temperature transducer TT04. In this mode the electric heater power is modulated to heat the circulating water on the hot water side to the desired temperature. An example case would be if the circulation pump 320 runs at 5L / min, and the electric heater 326 is modulated to heat the water in the hot water loop to 55°C as measured at temperature transducer TT04, the circulation pump 320 would run for 6 minutes to charge the water in the thermal energy storage appliance 342 to 55°C in 2 passes. The controller can therefore select which charging mode to use to charge the thermal energy storage appliance. This may depend on whetherthe heat pump is available and active. If it is active and hot fluid is already available at the heat exchanger then the Heat Pump Charging mode can be selected. If the heat pump is already active but motorised valve MV04 is not allowing the hot fluid to pass thorough to the heat exchanger, then the Heat Pump Charging mode may still be selected and the motorised valve MV04 is controlled, as mentioned above, so that the hot fluid passes from port A to port AB and hence to the second inlet HX3 of the heat exchanger. On the other hand, if the heat pump is not active, and given that, as described above, it takes some time for it to start to produce hot fluid, then the controller may select the Electric Heater Charging mode, so as to use the electric heater to heat the water to charge the thermal energy storage appliance. In the Initial Hot Water Mode hot water is provided to the domestic hot water outlet 304 either by the thermal energy storage appliance 342, if it is charged with hot water, or is heated by the electric heater 326, or a combination of both. If the thermal energy storage appliance 342 is charged full of hot water, then that can be used in preference to using the electric heater 326 to heat the water. To use hot water from the thermal energy storage appliance 342, the motorised valve is MV02 is open, so that the third flow path 316 is used to take cold water from the mains cold water inlet 302 to displace hot water from the thermal storage appliance 342. The hot water from the thermal storage appliance 342 passes through motorised valve MV03 from port B to port AB. As the temperature of the water from the thermal energy storage appliance 342 reduces (due to mixing with the cold water from the mains cold water inlet 302), the motorised valve MV03 is controlled to gradually open the pathway from port A to port AB, while gradually closing the pathway from port B to port AB. The flow rates across ports A-AB and ports B-AB are configured to be inversely proportional so that the flow of water out from port AB into the fifth flow path 328 leading to the domestic hot water outlet 304 remains constant. This is regulated according to the temperature sensed at temperature transducer TT06 depending on whether the sensed temperature is less than a desired temperature at temperature transducer TT06. Thus, if the temperature at temperature transducer TT06 is less than the desired temperature, the proportion of valve port B allowing fluid flow to port AB can be reduced from 100% to allow flow through port A, whilst reducing flow from port B. The now reduced flow from port B is therefore mixed with coming from port A. The water passing through port A of motorised valve MV03 comes from the fourth flow path 324 and via the electric heater 326 where it is heated, as necessary, to provide the hot water at port AB at the desired temperature, as sensed at temperature transducer TT06. Water in the fourth flow path 324 comes through the heat exchanger 308, having reached it via the first flow path 312 from the mains cold water inlet 302. This mode of operation relies on the thermal energy storage appliance 342 being pre-charged, for example by either of the first or second modes of operation. Typically, the water in the thermal energy storage appliance 342 is charged to 1.25 times the desired temperature as sensed at temperature transducer TT07 measured as temperatures at temperature transducers TT11 and TT10. When there is a secondary hot water demand of flow, as measured at flow transducer FT01, water flows through the third flow path 316 and into the thermal energy storage appliance 342. The thermal energy storage appliance 342 may be a stratified tank holding 15L, where 15L of water entering at a temperature measured by temperature transducer TT01, will displace 15L of preheated water. The depletion of the tank is measured by the read temperature at temperature transducers TT10 and TT11, and by knowing amount of water that has passed through the tank: V=t*(Q@ FT01-Q@ FT03-Q@ FT02) Where V is the depletion of the tank; t is time; Q@FTO1 is the flow measured at flow transducer FT01; Q@FT02 is the flow measured at flow transducer FT02; and Q@FTO3 is the flow measured at flow transducer FT03. As the water flows out of the tank and into port B of motorised valve MV03, if for whatever reason the temperature at temperature transducer TT05 is less than the desired temperature at temperature transducer TT07, the electric heater 326 can be used to top up the temperature of the water passing through the fourth flow path 324, where motorised valve MV03 is controlled to at least partially open port A to allow a at least a proportion of the flow measured at flow transducer FT01 through the fourth flow path 324 to the electric heater 326, where the bypassed proportion of flow of at flow transducer FT03 can be heated from the temperature at temperature transducer TT03 to a temperature at temperature transducer TT04 by controlling the electric heater 326. This is a useful mode to use when the heat pump 306 is not operational, or not yet fully operational, when it is not providing hot fluid to the heat exchanger 308. Of course, as the heat pump heats up, the fluid will start to get hotter, and may be provided to the heat exchanger 308, so that the water passing through it may start to increase in temperature, as measured by temperature transducer TT03, so that the heating provided by the electric heater 326 may be controlled to produce the appropriate desired temperature. In the Mixed Water Mode the temperature of the hot water from the thermal energy storage appliance 342 and / or from the electric heater 326 (provided as per the Initial Hot Water Mode of operation described above) or from the heat exchanger 308 if that is producing hot water as per the Steady State mode, is mixed with cold water from the mains cold water inlet 302 to reduce the temperature of the water being provided to the domestic hot water outlet 304. In this Mixed Water mode, whether the hot water leaving the port AB of the motorised three-way valve MV03 is provided via the heat exchanger 308 via the fourth flow path 324 (whether or not that water is heated by the electrical heater 326) or from the thermal storage appliance 342, the temperature of the hot water leaving the port AB of the motorised three-way valve MV03 is measured using the temperature transducer TT06. The temperature is signalled to the system controller 340 (not shown in Figures 4 to 12). The controller 340 then determines whether the temperature at temperature transducer TT06 is higher than the desired temperature for the hot water to be available at the domestic hot water outlet 304. If it is higher, then cold water from the second flow path 314 is mixed into the hot water leaving the port AB of the motorised three-way valve MV03 into the fifth flow path 328 by opening the motorised valve MV01 to allow cold water from the mains cold water inlet 302 to flow through the second flow path 314 to the fifth flow path 328. The amount by which the motorised valve MV01 is opened will depend on the temperature of the cold water from the mains inlet 302 as measured by the temperature transducer TT01 and the flow rate of the cold water from the mains inlet 302 as measured by the flow transducer FTO1 to produce the desired flow rate as measure by flow transducer FT02 in the second flow path 314 leading to the fifth flow path 328 so that the cold water from the second flow path 314 mixes with the hot water in the fifth flow path 328 to produce the desired temperature for the water to be available at the domestic hot water outlet 304, as measured by the temperature transducer TT07. A suitable control program executed by the controller will modulate this mixing in normal operation, preventing any overshoot from the desired temperature at the domestic hot water outlet 304. This firstly acts as a safety feature to prevent scalding of a user who doesn't have temperature safety valves installed on taps or faucets in the home. Secondly, the mixing allows the thermal storage appliance 342 to be charged to a higher temperature than that of the desired outlet temperature, so that when the system is run in a mode of operation where the thermal storage appliance 342 provides the hot water to be used from the domestic hot water outlet 304, the higher temperature water is mixed down with cold water from the mains cold water inlet, thereby producing a slower drain on the thermal storage appliance 342 and giving it a proportionally higher effective volume. After the Initial Hot Water mode of operation, in which the hot water is initially provided by the thermal energy storage appliance 342 of from the electric heater 326 (or a combination of both), once the heat pump has reached full operation and is providing hot fluid to the heat exchanger 308, the Steady State mode of operation may be instituted. In this Steady State Mode the motorised valve MV02 is shut so that there is no flow through the third flow path 316 and the thermal energy storage appliance 342. The electric heater 326 is active and controllable by the controller. The mixing control as described above with reference to the fourth mode is also active. Thus, motorised valve MV04 is controlled to pass water from port A to port AB. In this mode the heat pump 306 is actively providing heated fluid via the sixth flow path 330 and the motorised valve MV04 set to pass the fluid from port A to port AB to the heat exchanger 308 at a temperature determined by the measured flow rate of secondary hot water demand and set hot water temperature as measured a temperature transducer TT07. The water flow passing through the heat exchanger 308 is heated by the heat exchanger to a temperature measured by temperature transducer TT03. Thus, the flow measured at flow transducer FT03, the temperature measured by temperature transducer TT02, and the temperature measured by temperature transducer TT03 can be used to determine the amount of energy provided by the heat pump and subsequently provide feedback to the heat pump for power output adjustments. If the temperature measured by temperature transducer TT03 is determined to be less than the desired temperature at temperature transducer TT07, the electric heater 326 is controlled to heat the water to top the temperature of the water to the required temperature as measured at the temperature transducer TT04. It will be apparent that since the water is passing through the motorised valve MV03 from port Ato port AB, the temperature measured by temperature transducer TT04 will be the same as the temperature at temperature transducer TT06. If the temperature measured by temperature transducer TT06 is greater than desired temperature at temperature transducer TT07, cold water can be mixed with the hot water described for the fourth mode of operation, in which the temperature of the hot water is mixed with cold water from the mains cold water inlet 302 to reduce the temperature of the water being provided to the domestic hot water outlet 304. The Combined mode of operation is, essentially, a combination of the Initial Hot Water and the Steady State modes. The hot water is provided from the heat exchanger 308 or from the thermal storage appliance 342. The electric heater 326 can be used to top up the water temperature from the heat exchanger 308, if the water temperature measured at temperature transducer TT06 is lower than the desired water temperature at temperature transducer TT07. On the other hand, if the water temperature measured at temperature transducer TT06 is higher than the desired water temperature at temperature transducer TT07 cold water from the mains cold water inlet 302 via the second flow path 314 can be mixed into the hot water to reduce its temperature to the desired temperature. As mentioned above, there are occasions, especially in inclement weather, when the heat pump is at risk of freezing up. In such circumstances, whether to defrost a frozen heat pump, or to try to prevent the heat pump freezing if it is predicted that the temperature is likely to fall to below freezing, the controller may control the system to bring the Heat Pump Defrost Mode into operation. In this Heat Pump Defrost mode of operation the second motorised valve MV02 is closed and the circulation pump 320 in the return flow path 318 is turned on so that water is pumped from the thermal storage appliance 342 via the circulation pump 320, the non-return valve 322 and the first flow path 312 to the first inlet HX1 of the heat exchanger 308. Since the water is being pumped from the first part 316a of the third flow path 316 into the first flow path 312, water from the domestic cold water inlet 302 does not affect the flow. The water is passed from the first outlet HX2 through fourth flow path 324 via the electric heater 326 to the motorised valve MV03 which is controlled to direct the water from port A to port B, so that the water returns to the thermal storage appliance 342 and may circulate around again. The water entering at the first inlet HX1 of the heat exchanger 308 is controlled to be hot, either from the thermal storage apparatus, or, more likely, from being heated by the electric heater 326, or a combination of both, depending on the extent to which the thermal storage medium is charged with hot water. In this Heat Pump Defrost mode the electric heater may be active and may be modulated to transfer heat to the circulating hot water loop, passing through the thermal energy storage appliance 342. The motorized valve MV04 is controlled so that water in the sixth flow path 330 from the heat pump 306 passes through port Ato port AB of the motorized valve MV04 and hence to the second inlet HX3 of the heat exchanger 308. The water then returns from second outlet HX4 of the heat exchanger 308 to the heat pump 306. As the water passes from the second inlet HX3 to second outlet HX4 of the heat exchanger 308 it is heated by heat exchange with the hot water entering through the first inlet HX1 of the heat exchanger 308 to the first outlet HX1, as described above. The heated water returned to the heat pump 306 is then able to provide thermal energy to the refrigerant loop at the heat pump 306, which in turn is being circulated via the heat pump's compressor. The now hot refrigerant is then able to defrost the evaporator coils. The House Heating Mode assumes that no hot water is required at the domestic hot water outlet 304 (or any other hot water outlet, and this House Heating mode is therefore focussed exclusively on providing hot fluid, which may be water, for heating the domestic dwelling or other building, either through the use of radiators or a hot water underfloor heating system. In this House Heating mode, the heat pump is actively producing hot water which is directed through the motorised valve MV04 controlled to pass the hot water from port A to port B so that the hot water passes to the domestic hot water heating appliance 310, whose outlet leads back to the heat pump 306. The Overall Mode, which is a combination of the Combined Mode and the House Heating Mode is, therefore, a combination of the Initial Hot Water, Steady State and eighth House Heating modes so that all the various modes discussed above can be combined, as required. In this case, the electric heater 326 is active and modulable and all four motorised valves MV01, MV02, MV03 and MV04 are active and modulable. In this Overall mode the Heat Pump 306 can provide both heating (as per the House Heating mode discussed above) and thermal energy to heat or preheat hot water at the heat exchanger 308. As described above in relation to the Combination mode, the hot water is provided from the heat exchanger 308 or from the thermal storage appliance 342. The electric heater 326 can be used to top up the water temperature from the heat exchanger 308, if the water temperature measured at temperature transducer TT06 is lower than the desired water temperature at temperature transducer TT07. On the other hand, if the water temperature measured at temperature transducer TT06 is higher than the desired water temperature at temperature transducer TT07 cold water from the mains cold water inlet 302 via the second flow path 314 can be mixed into the hot water to reduce its temperature to the desired temperature. As mentioned above, most of the components of the system, excluding the heat pump 306, the domestic hot water outlet 304 and the domestic hot water heating appliance 310 are generally included within an enclosure (or housing) 344 that may be made of a similar size and shape as to replace a combination boiler. The enclosure 344 may include insulating material to mitigate against heat loss and it will be apparent that the differing operating modes, may be used in combination or separately, as desired and controlled by the controller. Figure 4 shows schematically an overview of a similar system 400 according to an aspect of the invention. The system includes a controller 402 having a memory 416, the controller 402 being coupled to an air source heat pump 409, a premises heating installation 406, and a local weather sensing arrangement 408. The controller 402 is configured to receive weather forecast data from an external source 410, for example via a wired or wireless connection 414, and local weather status information from the local weather sensing arrangement 408. The system also optionally includes an energy store 412 which is coupled to the air source heat pump 404, the controller 402, and the premises heating installation 406. The external source 410 of weather forecast data may be coupled to the internet 418 or other cloud based processing system, which may include a central station 420 for analysing data and providing information to the controller 402. Also shown in Figure 4 are a number of other premises heating installations 426, with associated air source heat pumps 429, which are located in the vicinity of the system 400, but are not part of it. The other premises heating installations 426, with associated air source heat pumps 429, may, for example be premises heating installations 426, with associated air source heat pumps 429 of neighbouring properties. They are connected, by a wired or wireless connection, to the internet 418, similarly to system 400. The vicinity of the system 400, i.e. the local heat pump 409 controlled by the controller 402, may be defined geographically, topographically, or in any other convenient way. For example, the other premises heating installations may be those within a certain distance of the system 400. That distance may be set depending on the number of other premises within that distance, for example, so that there are not too many, but not too few to provide a reasonable statistical sample. Alternatively, or additionally, the vicinity may be defined based on topographical features where the local system 400 is situated. For example, if it is at the bottom of a valley, other systems that may be close by in distance, may not be suitable if they are at the top of an adjoining hill, whereas further systems that are in the valley may be more suitable comparisons. In situations where the local system is in a densely populated area, for example in a block of flats, then limiting the other systems to only those in that block of flats may be appropriate. The controller 402 is configured to set a control algorithm 403 for triggering a defrost cycle of the air source heat pump 409 based on information and / or predictions regarding defrost cycles of the other air source heat pumps 429 and their associated premises heating installations 426. The control algorithm of the controller 402 may also use the weather forecast data and the local weather status information, and may also use information and / or predictions regarding a status of the air source heat pump 409, energy usage of the premises heating installation, energy supply information and / or other information that may impact when and for how long a defrost cycle of the air source heat pump 409 may be triggered. The information or predictions about the defrost cycles peer air source heat pumps in the vicinity of the premises are analysed by a remote processor, for example in the central station 420, with the results of that analysis being provided to the controller 402. The result provided by the central station 420 may include information on frequency and / or timings of the defrost cycles of the peer air pumps, based, for example, on statistical analysis. Predictions may also be made by the central station 420 and information regarding the prediction may be provided to the controller 402. The controller 402 may also monitor the status of the heat pump and use monitored heat pump parameters to determine likely defrost need when determining when to trigger a defrost cycle. The status of the heat pump may be based on data inferring a heat pump state based on energy supply information. For example, a measure of energy availability may be determined based on applicable energy tariffs. Other data that the controller 402 can receive includes information of the local weather from the local weather sensing arrangement 408. This local weather information may be used to adjust any predictions of when to trigger a defrost cycle, based on local variations. The controller 402 may also receive a prediction of likely heat demand by the premises heating installation, which may be used to affect the determination of the triggering of the defrost cycle, so that a defrost cycle is not triggered when a high energy demand in likely. Knowledge of surplus energy availability in the premises heating system may also be used, since, that may be utilised in the defrost cycle. The received data is based on signals received from controllers of the peer air source heat pumps Thus, the triggering can be based on logic in the controller 402 determining standalone triggering for the heat pump, which can modify a triggering decision based on the received data. The logic can be arranged to determine pro-actively a time to defrost in advance of a hard requirement to defrost and the logic can be arranged to adjust the determined pro-active time based on actual defrost activity of other air source heat pumps in the vicinity of the premises. The triggering of the defrost cycle of the air source heat pump can be co-ordinated with triggering of defrost cycles of the other air source heat pumps in the vicinity of the premises to even supply fluctuations or energy demand. The co-ordinating can be inferred by the controller 402 based on the information regarding defrost cycles of peer air source heat pumps in the vicinity of the premises. The co-ordinating may be centrally controlled by the remote processor in the central station, and used by the controller 402 to trigger the defrost cycle of its heat pump 409. Furthermore, the central station 420 may be used for carrying out further analysis of the air source heat pump. For example, by storing a number and / or frequency of defrost 22 cycles of the air source heat pump, the central station 420 can compare the stored values to a number and / or frequency of defrost cycles of other peer air source heat pumps in the vicinity of the premises. If the number and / or frequency of defrost cycles of the air source heat pump 409 is found to be different, whether higher or lower, by more than a threshold number, to the number and / or frequency of defrost cycles of the peer air source heat pumps, the central station 420 can infer that there may be a fault with the air source heat pump 409, or, possibly, with the control algorithm 403. In such a case, the central station 420 can signal such a potential error or fault condition either to the controller 402, or to an appropriate interface at the central station 420, or both. It will thus be seen that a standard intrinsic prediction of a required defrost cycle of the air source heat pump can be enhanced by data regarding other heat pump behaviour in the local neighbourhood. The controller 402 may adjust the control algorithm 403, if necessary, based on local weather status information from the local weather sensing arrangement 408. The control algorithm 403 is operated with a view to using energy that is available currently, or that is predicted to become available, prior to a local change in the weather which is forecast to reduce the amount of energy available from the air source heat pump 409. For example, if the local air temperature is predicted to drop, and / or the relative humidity is predicted to drop, the control algorithm may be used to extract energy, and supply this to the premises heating installation, and / or the thermal energy store, in anticipation that this extracted energy will be useful later. A forecast for air temperature may make it more likely that occupants of the premises will start to use the heating installation, and / or increase its temperature setting, to offset the effect of the forecast fall in air temperature. Thus, the controller may be configured to control the supply of energy based on a predicted likelihood that the premises heating arrangement will be activated / used / required during a forecast period of lowered temperature. The controller 402 may be configured to predict the likelihood based on past household behaviour of the premises, and / or on past behaviour of comparable households. The controller 402 may be configured to use a machine-learning algorithm to learn occupant behaviour from the settings and operation of, inter alia, a premises heating arrangement. The controller may also be provided with data on the behaviour of comparable households, either provided on installation / initial configuration of the system or provided or updated from a supplier or operator server in the cloud, for example. The controller 402 is also preferably configured to take account of occupancy, or predicted occupants of the premises, in predicting the likelihood. To do this, the controller 402 may be configured to take account of schedule activity of occupants of the premises in predicting the likelihood - the controller 402 having, optionally, access to schedules, calendars, and / or appointment details of occupants of the premises respect, the controller 402 may operate in "smart home" mode. The controller 402 may also be supplied with information from presence detectors, for example movement sensors (e.g., PIR sensors) and or door sensors which may be provided as part of a security monitoring system, as well as, or instead of, being supplied with information from the electrical system of the premises strike that which may provide information on the activation of, for example, lighting circuits and the like in the premises. The use of a local weather sensing arrangement 408 enables more accurate prediction and detection of weather events affecting the premises, increasing the ability to achieve energy savings in the running of the system. The controller 402 may be configured to run a machine learning algorithm which is configured to learn how the weather experienced by the premises, as detected by the local weather sensing arrangement, differs from the weather forecast data received, for example in terms of time delay and, optionally, severity. Using such a machine learning algorithm, the controller 102 may be able to make better predictions of when it may be beneficial to increase a supply of energy from the green energy source to a local energy sink and / or energy store. The local weather sensing arrangement 408 is preferably arranged to sense air temperature, the humidity of the air, and barometric pressure. The arrangement 408 may include separate sensors to detect each of these variables, but preferably the arrangement 408 is based upon an integrated weather sensing device, for example a weather sensing chip. Such a chip is available as the Bosch Sensortec BME280 integrated environmental unit which provides a humidity sensor measuring relative humidity, barometric pressure and ambient temperature, all to a high degree of accuracy: the humidity sensor is accurate to ± 3% relative humidity, the pressure sensor is accurate to ± 0.25%, and the temperature sensor is accurate to ± 1°C over the range 0-65°C. The BME280 has a weather monitoring mode which provides pressure temperature and humidity readings once a minute, which is frequent enough for our purposes. Additionally, the local weather sensing arrangement 108 may include a wind speed sensor and wind direction detector, since wind direction and speed can be very useful indicators of current and likely imminent weather conditions - such as indicating the possible arrival, passage, and passing of cold weather fronts, etc. Although the above description was considered with respect to determining when to trigger a defrost cycle of the air source heat pump, it should be apparent that other types of status and changes of status may be similarly determined and triggered. For example, one type of status may be servicing. Just as the controller, with input from the central station determines when best to trigger a defrost cycle in the air source heat pump, it could similarly determine when best to take the air source heat pump out of service for other purposes, for example to allow servicing of the heat pump. It will be apparent that some other criteria may then also be used, such as time of day, or week, but other criteria, such as weather, likely needed use, etc, would still be relevant in making that determination. A determination that a number of nearby systems in the vicinity that have similar use patterns may that have planned imminent servicing may provide an indication, when properly analysed by the central station, that the particular local system may also require servicing. Thus, the status of other systems in the vicinity, may be considered and analysed by the central station, which may then send information to the local system to instruct, or to guide the local system to consider updating or changing its status in a similar manner to some, ora majority, or all, of those other local systems. That status change may, as explained above, be triggering a defrost cycle, bringing the air source heat pump out of service, whether for servicing or because some unusual fault or activity has been noted in the other systems, for example, power surges. Other status changes may include bringing the whole system out of service, for any of the above reasons, or for other reasons. The thermal energy store may, in some implementations, include a phase change material whose phase change is used to store energy as latent heat. One suitable class of phase change materials are paraffin waxes which have a solid-liquid phase change at temperatures of interest for domestic hot water supplies and for use in combination with heat pumps. Of particular interest are paraffin waxes that melt at temperatures in the range 40 to 60 Celsius, and within this range waxes can be found that melt at different temperatures to suit specific applications. Typical latent heat capacity is between about 180kJ / kg and 230kJ / kg and a specific heat capacity of perhaps 2.27Jg-1K1 in the liquid phase, and 2.1Jg1 in the solid phase. It can be seen that very considerable amounts of energy can be stored taking using the latent heat of fusion. More energy can also be stored by heating the phase change liquid above its melting point. For example, when electricity costs are relatively low and it can be predicted that there will shortly be a need for hot water (at a time when electricity is likely to, or known to be going to, cost more perhaps), then it can make sense to run the heat pump at a higher-than-normal temperature to "overheat" the thermal energy store. A suitable choice of wax may be one with a melting point at around 48 Celsius, such as n-tricosane C23, or paraffin C20-C33. Applying the standard 3K temperature difference across the heat exchanger (between the liquid supplied by the heat pump and the phase change material in the heat exchanger) gives a heat pump liquid temperature of around 51 Celsius. And similarly on the output side, allowing a 3K temperature drop, we arrive at a water temperature of 45 Celsius which is satisfactory for general domestic hot water - hot enough for kitchen taps, but potentially a little high for shower / bathroom taps - but obviously cold water can always be added to a flow to reduce water temperature. Of course, if the household are trained to accept lower hot water temperatures, or if they are acceptable for some other reason, then potentially a phase change material with a lower melting point may be considered, but generally a phase transition temperature in the range 45 to 50 is likely to be a good choice. Obviously, we will want to take into account the risk of Legionella from storing water at such a temperature, and the previously described disinfection techniques provide a means by which this risk may be managed. Heat pumps (for example ground source or air source heat pumps) have operating temperatures of up to 60 Celsius (although by using propane as a refrigerant, operating temperatures of up to 72 Celsius are possible), but their efficiencies tend to be much higher when run at temperatures in the range of 45 to 50 Celsius. So, our 51 Celsius, from a phase transition temperature of 48 Celsius is likely to be satisfactory. Consideration also needs to be given to the temperature performance of the heat pump. Generally, the maximum AT (the difference between the input and output temperature of the fluid heated by the heat pump) is preferably kept in the range of 5 to 7 Celsius, although it can be as high as 10 Celsius. Although paraffin waxes are a preferred material for use as the energy storage medium, they are not the only suitable materials. Salt hydrates are also suitable for latent heat energy storage systems such as the present ones. Salt hydrates in this context are mixtures of inorganic salts and water, with the phase change involving the loss of all or much of their water. At the phase transition, the hydrate crystals are divided into anhydrous (or less aqueous) salt and water. Advantages of salt hydrates are that they have much higher thermal conductivities than paraffin waxes (between 2 to 5 times higher), and a much smaller volume change with phase transition. A suitable salt hydrate for the current application is Na2S2O3.5H2O, which has a melting point around 48 to 49 Celsius, and latent heat of 200 / 220 kJ / kg. In terms simply of energy storage, consideration can also be given to using PCMs with phase transition temperatures that are significantly above the 40-50 Celsius range. For example, a paraffin wax, waxes being available with a wide range of melting points: n-henicosane C24 which has a melting point around 40 Celsius; n-docosane C21 which has a melting point around 44.5 Celsius; n-tetracosane C23 which has a melting point around 52 Celsius; n-pentacosane C25 which has a melting point around 54 Celsius; n-hexacosane C26 which has a melting point around 56.5 Celsius; n-heptacosane C27 which has a melting point around 59 Celsius; n-octacosane C28 which has a melting point around 64.5 Celsius; n-nonacosane C29 which has a melting point around 65 Celsius; n-triacosane C30 which has a melting point around 66 Celsius; n-hentriacosane C31 which has a melting point around 67 Celsius; n-dotriacosane C32 which has a melting point around 69 Celsius; n-triatriacosane C33 which has a melting point around 71 Celsius; paraffin C22-C45 which has a melting point around 58 to 60 Celsius; paraffin C21-C50 which has a melting point around 66 to 68 Celsius; RT 70 HC which has a melting point around 69 to 71 Celsius. Alternatively, a salt hydrate such as CH3COONa.3H2O - which has a melting point around 58 Celsius, and latent heat of 226 / 265 kJ / kg. Fig. 5 schematically shows an embodiment of an Machine Learning Algorithm 6200 executing on a control module (e.g. the controller 402) processing a set of input data to predict the next defrost cycle of a heat pump (e.g. the heat pump 409). The MLA 6200 receives input data specific to the house, through the control module, from a plurality of inputs, including one or more sensors disposed around the house, one or more user interfaces (e.g. control panels around the house in communication with the control module, smart devices, personal computers, etc.), one or more software program, one or more public and private databases, etc. During a training phase, the MLA 6200 may be trained to recognise when a defrost cycle is required, and establish a timescale and an average energy requirement for operating the heat pump in a defrost cycle, based for example on weather forecasts, current weather conditions, indoor temperatures and data collected from previous defrost cycle(s), with knowledge of the performance of the heat pump (e.g. an average thermal energy output of the heat pump, a heat pump efficiency or coefficient of performance, and any other information or quantities relating to the performance of the heat pump). In the present embodiment, the MLA 6200 receives inputs of weather forecast 6101 e.g. obtained from the public domain or a weather app on a smart device registered on the control module, current weather condition 6102 such as temperature and humidity e.g. obtained from the public domain or one or more sensors disposed around the house, indoor temperature 6103 e.g. obtained from one or more temperature sensors disposed inside the house, and data relating to the last defrost cycle(s) 6104 when the heat pump was last defrosted. The MLA 6200 also received information regarding defrost cycles of peer air source heat pumps, in the vicinity Based on the peer defrost cycles, weather forecast, the current weather conditions and the indoor temperature, the M LA 6200 can predict when the next defrost cycle may be expected 6301, e.g. when there is a long period of low temperature and high humidity a defrost cycle may be needed sooner, and may estimate a length of time required to defrost the heat pump. Information regarding peer defrost cycles provides information to enable enhanced predictions, using the knowledge of when and for how long peer air source heat pumps require defrosting. Moreover, using the established utility usage pattern 2300 and an occupancy prediction 3300, the MLA 6200 can estimate an expected energy and heated water demand during the time when a defrost cycle is predicted, and can prepare the water provision system in anticipation of the predicted defrost cycle 6302, for example by storing additional thermal energy in the thermal energy storage (by storing energy as sensible heat in addition to latent heat in the PCM), heating the house to a temperature higher than the pre-set temperature, etc. Additionally or alternatively, the MLA 6200 may moreover anticipate when demands for energy and heated water (e.g. for taps, showers and / or central heating) are low, and determine an appropriate timing for defrosting the heat pump that is e.g. less disruptive to the provision of heated water to the occupants. Using the inputs, the MLA 6200 can determine a time period when water and energy demands are low (e.g. overnight) and / or when occupancy is low (e.g. during school and working hours), and adjust the expected start time of the next defrost cycle to the determined low-demand time and / or low-occupancy time. The MLA 6200 may then instruct the control module to operate the heat pump to begin a defrost cycle 6301 at the adjusted start time. For example, if the MLA 6200 predicts a defrost cycle may be needed in the early evening when energy and heated water demands are expected to be high, the MLA 6200 may pre-charge the thermal energy storage medium by operating the heat pump to store more heat, e.g. by raising the temperature of the thermal energy storage medium to a higher operating temperature, as well as diverting some of the heat to warm up the building before the predicted defrost cycle, and / or the MLA 6200 may adjust the defrost cycle start time to later in the evening when demands are expected to be lower,. In another example, if a defrost cycle is expected during the day, the MLA 6200 may determine, based on an occupancy prediction and / or the usage pattern, that the next defrost cycle is during a period of time when energy and heated water demands are low e.g. when occupancy is expected to be low or zero, and determine that no preparation or adjustment is required. By predicting the next defrost cycle for the heat pump and predictively preparing the water provision system before the defrost cycle begins, based e.g. on the performance of the heat pump, peer defrost cycles, weather forecasts, current weather conditions, current indoor temperature, expected occupancy and demands for heated water, the present embodiment allows necessary heat pump defrost cycles to be performed in a manner that is less disruptive to the provision of heated water and thereby enables a heat pump to be utilised as an effective way of providing heated water. Similarly, by predicting other status changes, based on peer system status changes, as well as other data, the status changes may be performed in a manner that is less disruptive, or, in extreme circumstances, that may save the system or components thereof from damage.

Claims

1. A method of controlling a heating system for premises, the heating system comprising:a controller, and coupled to the controller:an air source heat pump having at least an active mode of operation and a defrost mode of operation; anda premises heating installation coupled to receive heated fluid from the air source heat pump when the air source heat pump is in the active mode of operation; wherein the method comprises using the controller to:receive data, the data comprising results of an analysis bya remote processor of status of a plurality other heating systems comprising air source heat pumps in the vicinity of the premises;triggering a change of status of the heating system based on the received data and the status of the heating system.

2. The method of claim 1, wherein triggering a change of status of the heating system comprises triggering a change of status of the air source heat pump.

3. The method of claim 2, wherein the triggering a change of status of the air source heat pump is a triggering of a defrost cycle of the air source heat pump.

4. The method of claim 3, wherein the triggering a defrost cycle of the air source heat pump is further based on a determination of likely defrost needs based on heat pump parameters.

5. The method of either claim 3 or claim 4, wherein the triggering a defrost cycle of the air source heat pump is further based on data inferring a heat pump state based on energy supply information.

6. The method of any preceding claim, wherein the received data further includes one or more of:a measure of local weather;a prediction of likely heat demand by the premises heating installation; and surplus energy availability in the premises heating system.

7. The method of any preceding claim, wherein the triggering is based on logic determining stand-alone triggering for the heating system, wherein the logic is arranged to modify a triggering decision based on said received data.

8. The method of claim 7, wherein the logic is arranged to determine pro-actively a time to change the status in advance of a hard requirement to change the status and wherein the logic is arranged to adjust the determined pro-active time based on actual status activity of other heating systems in the vicinity of the premises.

9. The method of any preceding claim, wherein the received data is received from a central station comprising the remote processor, which collects data from controllers of the other heating systems.

10. The method of any preceding claim, wherein the triggering of the status change is coordinated with triggering of status changes of the other heating systems in the vicinity of the premises to even supply fluctuations or energy demand.

11. The method of claim 10, wherein the co-ordinating is centrally controlled by the remote processor instructing the controller and the controllers of one or more of the other heating systems.

12. The method of any preceding claim, wherein the controller uses a Machine Learning Algorithm (MLA) to determine a start time for the triggering of the status change.

13. The method of claim 12, wherein the MLA is used to predict an optimum start time and duration of the status change.

14. The method of any preceding claim, wherein the data further comprises one or more off:weather forecast data from an external source; andlocal weather status information from a local weather sensing arrangement, and wherein the triggering is adjusted based on the local weather status information.

15. The method of any preceding claim, wherein the vicinity is defined based on one or more of:number of other heating systems;geographical distance;topographical features.

16. The method of any preceding claim, wherein the remote processor stores a number and / or frequency of status changes of the heating system and compares to a number and / or frequency of status changes of the other heating systems in the vicinity of the premises, and if the number and / or frequency of status changes of the heating system is different by more than a threshold to the number and / or frequency of status changes of the other heating systems in the vicinity of the premises, signalling a potential error or fault condition.

17. A heating system for premises, the heating system comprising:an air source heat pump having at least an active mode of operation and a defrost mode of operation;a premises heating installation coupled to receive heated fluid from the air source heat pump when the air source heat pump is in the active mode of operation; anda controller coupled to the air source heat pump and to the premises heating installation, wherein the controller is configured to perform the method of any one of claims Ito 15.

18. A heating system for premises according to claim 17, further comprising a central station comprising the remote processor, the central station being configured to collect data from controllers of other heating systems in the vicinity of the premises, to analyse the data and to send results of the analysis to the controller of the heating system.

19. A heating system for premises according to claim 18, wherein the remote processor is further configured to perform the method of claim 16.5 20. A non-transitory computer readable medium storing computer readable instructions,wherein the computer readable instructions, when executed by one or more processors of a controller of a heating system for premises, cause the one or more processors to cause the controller to perform the method of any one of claims 1 to 15.34

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