CONTROL OF A DISTRICT HEATING SYSTEM

TECHNICAL FIELD

[0001] The present invention relates to a heating system comprising centralized and decentralized heating, and controlling the heating system. There is provided a system, a method, a computer program and a non-transitory computer means for controlling a heating system.

BACKGROUND

[0002] Energy production and emitted greenhouse gases into the atmosphere are global challenges. Current efforts include developing industrial processes in view of energy efficiency, as well as replacing fossil fuel combustion with renewables and nuclear power. De-carbonization is an aim in energy production, industrial processes, heating and transportation. Electrification is seen as an option to make heat production carbon free.

SUMMARY

[0003] Aim is to enable efficient control of a heating system.

[0004] The invention is defined by the features of the independent claims. Some embodiments are defined in the dependent claims.

[0005] According to a first aspect of the present invention, there is provided a method for controlling a district heating system comprising at least one centralized heating asset and decentralized heating assets, wherein the decentralized heating assets comprise electricity-driven heating assets connected to a power system. The method comprises controlling heat production of the centralized heating asset and the decentralized heating assets, at a time range, based on determined overall heat demand from the district heating system, at the time range, production capacity of heat by the centralized heating asset, at the time range, production capacity of heat by the decentralized heating assets, at the time range, and a state of the power system comprising overall demand and supply in the power system at the time range.

[0006] According to a second aspect of the present invention, there is provided a an apparatus for controlling, or an apparatus configured to control, a district heating system, wherein the district heating system comprises at least one centralized heating asset and decentralized heating assets. The decentralized heating assets comprise electricity-driven heating assets connected to a power system. The system comprises means for controlling, or a controller configured to control, heat production of the centralized heating asset and the decentralized heating assets, at a time range, based on determined overall heat demand of the district heating system, at the time range, production capacity of heat by the centralized heating asset, at the time range, production capacity of heat by the decentralized heating assets, at the time range, and a state of the power system comprising overall demand and supply in the power system at the time range.

[0007] According to a third aspect of the present invention, there is provided a computer program configured to cause a method in accordance with the first aspect to be performed.

[0008] According to a fourth aspect of the present invention, there is provided a non- transitory computer readable medium comprising program instructions that, when executed by at least one processor, cause at least to control a district heating system, which comprises at least one centralized heating asset and electricity driven decentralized heating assets connected to a power system, at a time range, based on determined overall heat demand of the district heating system, at the time range, production capacity of heat by the centralized heating asset, at the time range, production capacity of heat by the decentralized heating assets, at the time range, and a state of the power system comprising overall demand and supply in the power system at the time range. [0009] At least one or more embodiments may further comprise means or a method for dimensioning the decentralized heating assets for the district heating system, based on heat production capacity of the at least one central heating asset, heat production capacity of the decentralized heating assets and input power demand of the decentralized heating assets.

[0010] At least one or more embodiments may further comprise means or a method for controlling based on at least one of: history data, measured data, estimated data, calculated data and/or forecasted data. The decentralized heating assets may comprise electricity-driven, carrier media circulating assets; assets for heating and cooling; and/or heat pumps.

[0011] At least one or more embodiments may further comprise means or a method for connecting the decentralized heating assets to an electric power system, and means for operating the decentralized heating assets as part of the district heating system.

[0012] At least one or more embodiments may further comprise means or a method for determining the overall heat demand of the district heating system, which is dependent at least partly on outdoor temperature. Production capacity of the at least one centralized heating asset may be dependent at least on the overall heat demand, for example on heat transfer losses. In addition or alternatively, production capacity of the decentralized heating assets may be dependent on at least one of the following: a coefficient of performance of the decentralized heating assets; a heat production capacity of the at least one centralized heating asset; and an input power demand of the decentralized heating assets. The state of the power system may be dependent on a ratio of the overall demand and supply in the power system.

[0013] The power system may comprise an electric power system. The electric power system may supply energy to the decentralized heating assets. [0014] At least one or more embodiments may further comprise means or a method for controlling heat production of the at least one centralized heating asset and the decentralized heating assets in a stepless manner.

[0015] At least one or more embodiments may further comprise means or a method for adjusting heat production of the centralized heating asset and the decentralized heating assets. For example, means for adjusting a ratio between the decentralized heating assets and the at least one centralized heating from 35:65 to 75:25.

[0016] According to at least one or more embodiments the decentralized heating assets comprise means or a method for providing heat to a primary side of the district heating system including the at least one centralized heating asset; and/or means or a method for adjusting adjust according to a frequency reserve market of the power system, and means or a method for up-regulating and downregulating the decentralized heating assets.

[0017] At least one or more embodiments comprise means or a method for feeding in energy to a frequency reserve market of the power system, and means or a method for receiving compensation from the frequency reserve market of the power system.

[0018] At least one or more embodiments comprise at least one or more of the following:

- means or a method for determining dimensioning of the decentralized heating assets,

- means for determining input power demand of the decentralized heating assets,

- means or a method for determining peak power of the centralized heating asset,

- means or a method for determining total electricity consumption,

- means or a method for determining total heat delivery of the centralized and decentralized heating assets,

- means or a method for determining a share of the decentralized heating assets in the total heat delivery,

- means or a method for determining number of frequency reserve hours of the decentralized heating assets, - means or a method for determining number of open central heating hours,

- means or a method for determining capacity fed-in to a frequency reserve market by the decentralized heating assets,

- means or a method for determining heat energy fed-in to open district heating market by the decentralized heating assets,

- means or a method for determining frequency reserve compensation, and/or

- means or a method for determining open district heating market compensation.

[0019] An apparatus according to the second aspect or any of the embodiments, may comprise the means comprising at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the performance of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the following embodiments are discussed in more detail with reference to the attached drawings, of which:

[0021] Figure 1 illustrates, by way of an example, a heating system according to an embodiment.

[0022] Figure 2 illustrates, by way of an example, an arrangement for controlling a heating system according to an embodiment.

[0023] Figure 3 illustrates, by way of an example, an apparatus according to an embodiment.

[0024] Figure 4 illustrates, by way of an example, a method according to an embodiment.

[0025] Figures are presented as illustrative examples and embodiments may not be limited solely to the illustrated parts, but modifications may be made under the scope as defined in the claims. Figures that may not fully present the claimed invention, aim to provide better understanding on the context and relating technical field. DESCRIPTION OF EMBODIMENTS

[0026] There is provided heating system including a centralized heating asset and decentralized heating assets. The centralized heating asset comprises district heating; and the decentralized heating assets comprise electricity-driven, carrier media circulating assets, like heat pumps. According to an aspect of the invention, integrating decentralized heating assets, like heat pumps, into a district heating system may lead to decrease in operating expenditure and/or carbon dioxide (CO2) emissions of the heating system. This may further result in savings in operation of the heating system. The heating system enables dimensioning and/or utilization of decentralized heating assets with the centralized heating asset(s) in an optimal manner. Decentralized heating assets and their use is properly planned and/or predicted. The centralized and decentralized heating assets are used in parallel by choosing an optimal heat production logic in a time range, e.g. hourly. The decentralized heating assets may provide heat energy to a primary side of the heating system, which comprises the centralized heating assets. According to an aspect of the invention, the decentralized heating assets may support a primary side of the heating system, when the use of decentralized assets is predictable. Predictability may include estimates based on collected history data and/or heating capacity of the decentralized assets. In addition, the decentralized heating assets may be utilized to provide ancillary services in the power system, for example to maintain the power system balance. Decentralized heating capacity may support the primary side of the heating system. In addition, the decentralized heating assets may receive compensation for feeding heat to the primary side of the heating system.

[0027] Figure 1 illustrates, by way of an example, a heating system according to an embodiment. The heating system of Fig. 1 comprises a primary side and a secondary side. The primary side corresponds to a centralized heating and the secondary side corresponds to a decentralized heating. The primary side comprises one or more production plant 101, optional one or more heat source 102, and a piping or tubing system 100. Piping or tubing system 100 is configured to distribute heat generated in the primary side. Thermal energy from a production plant 101, and optionally from other or additional heat sources 102, may be transmitted to the secondary side, e.g. to customers, via the piping or tubing system 100. A carrier media, like hot water, is transmitted via the piping or tubing system 100, which may comprise supply and return pipes. The heating system may be a district heating system, which comprises at least one production plant, production management system, heat exchangers, consumption end technologies and a network, or a district heating network. The district heating network comprises a physical network for enabling heat distribution. The network is configured to connect the entities and to enable heat transfer. The primary side comprises centralized heating asset, which may include one or more production plant 101 and/or one or more heat source 102. The centralized heating asset is configured to produce district heat in a large scale, to be transmitted to multiple buildings/consumers in a certain area, to a secondary side of the district heating system. District heat production of the centralized heating asset, like a production plant 101, may be based on fuel combustion. In addition, one or more heat source 102 may comprise a heat pump or other technology utilizing carrier media for distributing heat. District heat production may cause economic and environmental challenges. In order to reduce such challenges, decentralized heating assets of the secondary side are operationally combined with the centralized heating assets of the primary side. The heating system may utilize electricity-driven heat production technologies in the secondary side of the heating system. Examples of the decentralized heating assets include air source heat pumps, water source heat pumps, heat pumps in data centres, geothermal heat pumps and electric boilers.

[0028] In the secondary side of the district heating system, decentralized heating assets 103 may be based on electricity-driven, water circulation technologies. The secondary side may comprise buildings and entities at a customer or end user side. The decentralized heating assets may comprise heat pumps. A heat pump is a device configured to transfer heat energy from a heat source for thermal use. A heat pump uses external power to accomplish the work of transferring energy from the heat source to the heat sink. This may be based on various different technologies and a heat pump may comprise air-to- air heat pumps, air-to-water heat pumps, ground-source heat pumps, water source heat pumps, exhaust air heat pumps and electrical resistance heaters. In secondary side of the district heating system, decentralized heat production is designed and operated from perspective of an individual building. Together the district heating system’s primary side and secondary side form a heating system, which is able to utilize both centralized 101,

102 and decentralized 103 heating assets and technologies. Decentralized heating assets

103 are added to the heating system and connected to a power system.

[0029] Fig. 2 illustrates, by way of an example, an arrangement for controlling a heating system according to an embodiment. A system, or a district heating system is controlled by jointly controlling use of centralized heating assets and decentralized heating assets. The primary side including the centralized heating assets may be able to control both the primary and the secondary sides. Controlling the secondary side may comprise a direct control and/or sending instructions or requests to the secondary side. Switching and adjusting between use of centralized and decentralized heating assets is enabled. A controller 200 may comprise a receiver or means for receiving data, and a processor configured to process data, like parameters. The controller 200 is configured to processes data, like parameters, in order to control heat production of the district heating system. The controller 200 may form a control logic for controlling the heat production. The control logic may include control instructions for both the centralized and the decentralized heating assets. Processing may include forming multiple alternative control logic, and selecting the used one, according to selected parameters, which may include current status of any of the heating assets, current resources, compensation from power system, or any alike, or a combination of parameters. Controlling is based on parameters, which are updated at intervals, typically constant intervals. An interval or a time range may be, for example, hourly, every second hour, every half hour, or any other time period. Parameters illustrate features that may be used for controlling, planning, dimensioning, adjusting and/or optimizing the heating system according to embodiments. The parameters include heat demand 201 of the system, a power system state 202, heat production capacity of centralized heating asset 203 and heat production capacity of decentralized heating assets 204. Outdoor temperature has effect on at least some parameters. For example, temporary, annual or average temperature may be set as a parameter. Temperature may be expressed in kelvin (K), degree Celsius (°C), or degree Fahrenheit (°F).

[0030] The heat demand 201 refers to total or overall heat demand from the district heating system. It is dependent at least partly on outdoor temperature. The heat demand 201 from the district heating system may be expressed as hourly value, in kilowatthours per hour, kWthh/h, wherein the lower index th refers to thermal energy. Overall heat demand may include demand for providing space heating and domestic hot water in the district, or for any other use or consumption of heat.

[0031] A power system state 202 includes overall demand and supply in the power system at a time range. The power system refers to an electric power system. Electricity demand relates to electricity consumption. Ratio of the overall demand and supply in the power system may be used for determining existing resources of the power system, which in turn may have effect on other parameters, for example to a state of the power system. Ratio of the overall power demand and supply may be balanced. Ratio has effect on frequency of the power grid. In case the overall demand exceeds supply, the frequency is decreased. In case supply exceeds the overall demand, the frequency is increased. A constant frequency, which is aimed to be maintained, may be 50 Hz. The ratio or balance may have effect on a need to increase or curtain demand (consumption), or on a need to provide further or less power, like electricity, from other sources. This in turn, has effect on performance of the power system, for example relating to capacity, resources, compensations, as well as costs. Performance of the power system may vary, for example hourly.

[0032] Production capacity of centralized heating asset 203 and decentralized heating assets 204 refers to total heating power output of the corresponding heating assets of the system. Centralized heating asset 203, like one or more power plants for providing district heating, may have district heat production capacity, which is assumed sufficient to meet the heat demand 201 at all times. With such assumption, peak power demand of the district heating is not a restricting parameter. Outdoor temperature may have effect on heat demand. Heat transfer losses may have effect on production capacity of the centralized heating assets 203. Heat transfer losses may be expressed as annual average, in percentages (%).

[0033] Energy storages may be part of the centralized heating assets 203 and have effect on production capacity of centralized heating assets 203. An energy storage may comprise a heat storage and/or an electric storage. In addition, possible waste heat may be utilized for heating. District heat demand is affected by outdoor temperature, solar radiation, precipitation, wind and timings of such, for example. Solar radiation may have heating effect and wind may have cooling effect to a temperature. Further, social load has effect on demand. Social load may comprise common social times of using heat or warm water, like shower times.

[0034] Decentralized heating assets 204, like heat pumps, may have restricted heating power output. Nominal output of decentralized heating assets may be set as a parameter. The decentralized heating assets’ nominal heating power output may be expressed in kilowatts, kWth, wherein the lower index th refers to thermal energy. In addition, parameters that may have effect on decentralized heating assets 204 comprise electricity peak power demand of the decentralized heating assets 204 (in kW _e i, where the lower index el refers to electric energy), coefficient of performance (COP) of the decentralized heating assets 204, and heat peak demand of the centralized heating assets 203.

[0035] Other parameters may be included. The parameters having effect to control of a heating system may comprise performance and/or cost related data. Values are case specific, depending for example on type, manufacturer and properties of the used heat pumps or -assets. When temperature of a heat source is constant, like for data centres, ground-source heat pumps and exhaust air heat pumps, the COP is constant, correspondingly, as long as a heated space has constant temperature. For air-to-water and other air-source heat pumps a COP may comprise a dynamic COP, which may be determined as a function of outdoor temperature. A power system state 202 may comprise an electricity power system, which may be economically controlled by costs regulations. Cost regulations may be used as parameters. Cost regulations may include timely varying component of total electricity cost of a market place, called a spot market; electricity distribution fee; taxes set for customers, like households, factories, data centres; and/or a fixed margin for electricity retailer. Cost regulations may be added as parameters for controlling a heating system. Costs may be expressed as cost units per megawatthour, like €/MWh, $/MWh, £/MWh, and so on. Similarly, centralized heating asset 203, like district heating, may include delivery costs, which may be used as parameters. Centralized heating asset 203 delivery costs may include fuel costs, fuel taxes, emission allowance costs, operations and maintenance costs, and/or income from power system spot market. In addition, some costs may be allocated to heat transfer losses. Costs may include fixed and/or variable components. Costs have a direct dependence on components, like capacity, resources, performance, efficiency, current demand, and so on.

[0036] Control of the centralized and decentralized heating assets, or adjusting those, may be implemented in a stepless manner. A response time of the system may be minimized. This enables adjusting according to determined need in real time. The centralized and decentralized heating assets are capable of operating with a partial load. The decision on usage of centralized or decentralized heating assets depends on various factors. The decision and at least some factors may be updated regularly, e.g. on hourly basis. Control and adjustment of usage between centralized and decentralized heating assets may vary during winter and summer time, being at least partly dependent on outdoor temperature. In an example, during a cold season use of the centralized heating asset is emphasized over the decentralized heating assets; and during a warm season use of the decentralized heating assets is emphasized over the centralized heating asset. Here emphasizing may relate to energy production or time of use, for example.

[0037] District heating refers to regional or local heating. District heating may cover relatively large area, e.g. a country, a province or a city; or a smaller sub-area, like a part of a municipality, a commune or a determined unity, like a building or a group of buildings. Size of a district is not limited, but may be freely selected. Number of heating assets may be scaled up or down, as desired. Total production capacity of central and decentral heating assets is considered instead of number of the heating assets. Reference to one or more central heating asset refers to one or more heating assets in the primary side. Reference to decentral heating assets refers to total of the heating assets in the secondary side.

[0038] In order to enable bi-directional energy transfer between the primary and secondary sides of the heating system, i.e. also from the secondary side to the primary side, those shall employ similar medium for carrying energy. Decentralized heating assets may comprise electricity-driven assets, which utilize water circulation. Example of such are heat pumps. Water circulation enables circulation of heat energy bi-directionally between the primary and secondary sides. Decentralized heating assets form part of local low- temperature district heating and cooling systems. Centralized heating assets may be used for covering consumption peaks. Initially, when planning a heating system, the heating assets to be employed are planned and selected. This includes dimensioning the system and the heating assets. Dimensioning the system may include dimensioning decentralized heating assets for a peak demand. Coefficient of performance (COP) of decentralized heating assets may be set.

[0039] As an example 1, minimum COP may be set as 1.2, when outdoor is at or below a set lower limit, which may be -30 °C. Maximum COP may be set as 4.2, when outdoor temperature is at or above a set upper limit, which may be +30 °C. Output heat temperature of the decentralized heating assets may be set to 50-70 °C, for example to 65 °C. A dynamic COP may be determined as a function of outdoor temperature.

[0040] Dimensioning decentralized heating assets of a district may be based on coverage of a peak heat demand. The decentralized heating assets may be dimensioned between 0 kWth and peak heat demand, which is greater than 0 kWth (the lower index th refers to thermal energy). The decentralised heating assets may be dimensioned over the peak heat demand, for example to prepare for future needs of enlarged heat demand. Dimensioning of decentralized heating assets may be related to electricity peak power demand and coefficient of performance (COP) of the decentralized heating assets for the considered buildings. A COP may be presented as heat demand weighted average, which takes into account time of use of the decentralized heating assets: if it is used mainly during cold hours the weighted COP decreases compared to average COP. The centralized heating asset may be dimensioned to cover the whole heat demand in peak hours, even though decentralized heating assets are also dimensioned to match the peak heat demand. In buildings, electricity peak power demand caused by the decentralized heating assets, like heat pumps, may be taken into account, in addition to COP of the decentralized heating assets, and district heat peak demand of the centralized heating asset.

[0041] Dimensioning of decentralized heating assets according to 100% of peak, when used with centralized heating asset, may provide an optimal solution. Basic operation refers to situation, where the decentralized heating assets are used only to cover heat demand in the district/area (or included buildings). It is enabled to utilize both a centralized heating asset, like district heating, and decentralized heating assets, like heat pumps, together as a district heating system. This enables optimization of the district heating system and use of energy based on temporal parameters. This enables to operate in combination in open district heating markets. In addition, this opens opportunity to provide flexibility or balancing services to the power system through electrical load management. This may refer to operating in combination with a frequency reserve of the power system, to which the decentralized heating assets are connected. Frequency reserve refers to frequency restoration and to frequency containment of the power system. Frequency reserve may relate to frequency containment reserve (FCR) or frequency restoration reserve (FRR), for example. Frequency of a power system is kept constant, for example in 50 Hz, while variation from a constant value may not exceed ±0,1 Hz. When demand varies, for example devices connected to the power system are powered on or off, some peaks may be caused. Utilizing decentralized heating assets in frequency reserve market and in an open centralized heating market improves overall performance of system compared to situation where decentralized heating assets are used only to meet buildingspecific heat demand. The latter may cause disadvantages and/or undesired effects for the system via building-specific electricity consumption peaks, which will have effect on use and pricing of resources. In order to enable taking part on frequency reserve market, decentralized heating assets are adjustable such that those can be up-regulated and down- regulated. Up-regulation is implemented by adding production or reducing consumption. Down-regulation is implemented by cutting down production or adding consumption. For example ramping up a factory may cause an electricity consumption peak, which may be compensated by controlling decentralized heating assets such that those are up-regulated.

[0042] Planning and designing a heating system may include dimensioning. For dimensioning, heating durations at the selected area, or in the buildings at the area, are considered. Typically, different years differ in curve shape. However, the minimum and maximum heating power demand may be similar or almost equal each year. Maximum heating power demand is one parameter in dimensioning the hybrid heating system. Maximum heating power is dependent on the area, climate and outdoor temperature. It may be in order to megawatts, for example 2.0-3.5 MWth. Minimum heating power may be 0 MWth. Heating demand may include annual heat consumption and/or hourly aggregated heat demand, which may include heating the space and domestic hot water. In consideration of dimensioning, annual average performance of heating assets may be taken into account.

[0043] Annual weighted average heat delivery performance for the decentralized heating assets in a year is dependent on outdoor temperature. In addition, the decentralized heating assets’ annual weighted average heat delivery performance may depend on at least one of: hourly electricity spot resources, a fixed margin for an electricity retailer, variable and fixed electricity distribution resources, electricity taxes, hourly coefficient of performance (COP) for the decentralized heating assets system, the decentralized heating assets system operation and maintenance resources, and hourly heat production of the decentralized heating assets system, which may include space heating, domestic water heating and possible feed-in into the open centralized heating asset(s) system. At least some or all of the mentioned parameters concerning the district in question may be investigated in order to dimension the heating system.

[0044] Annual weighted average delivery costs for the centralized heating assets in a year are dependent on at least one of: the delivery resources (e.g. as weighted annual average), hourly total fuel resourcing and taxes, hourly emission allowances, hourly compensation from power market (e.g. electricity spot market), centralized (district) heating system operations and maintenance resourcing, hourly centralized (district) heat production and heat transfer losses of the centralized heating asset (e.g. as annual average, %). At least some or all of the mentioned parameters concerning the district may be investigated in order to dimension the heating system.

[0045] Dimensioning the decentralized heating assets between 50% and 100% may not have significant impact on heat production performance and efficiency of the decentralized heating assets, as peak heating demand hours may be rare. This indicates that upscaling the decentralized heating assets may have diminishing marginal utility. In cases where decentralized heating assets are dimensioned under peak demand and heat demand exceeds output of the decentralized heating assets, the remaining heat may demand be produced by central heating assets and/or directly by an electric power system, using direct electric heating or resistance thermal elements.

[0046] Parameters may be used for modelling and optimization of selected properties, dimensioning the system, as well as for controlling the system. Parameters may be called system parameters and comprise at least some of the following: dimensioning of the decentralized heating assets, a peak power input of the decentralized heating assets, a peak power of the centralized heating asset, electricity consumption, the total heat delivery of the centralized and decentralized heating assets, a share of the decentralized heating assets in the total heat delivery, a number of frequency reserve hours, a number of open central heating hours, capacity sold to the frequency reserve market, heat energy sold to the open central (district) heating market, a frequency reserve compensation, and an open central heating market compensation. Outdoor temperature and set temperature of the circulated hot water (e.g. 65 °C) have effect on the controlling and dimensioning the system. The system parameters have effect on overall performance, or production efficiency, of the system. In addition, the system parameters may have effect, or dependence, on each others. Further, the system parameters have effect on production and consumption, demand and supply, as well as selection of used assets, which may vary in the course of time. The used assets, and the overall demand and supply may provide feedback for the system parameters, and vice versa.

[0047] Temperature of water in the secondary side shall exceed temperature of water in the primary side, in case heat is to be transferred from the secondary side to the primary side, and vice versa. [0048] The selection of the used assets may depend on certain parameters, for example prices, discharge or emission levels, prioritized assets or resources, or any other parameter, or a combination of such. The certain parameters may be mutually dependent and have priorities or different weights in relation to each other. The parameters or their priorities or weights may vary over time. A collected history data may be utilized. History data may comprise any parameter, as previously received, determined, collected or processed. Examples of history data may include usage of electricity, prices of electricity and heat, external temperatures. History data may be used for making predictions and estimates on upcoming parameter values. Predictions may aid future selections for use of assets.

[0049] System parameters are mutually dependent on each other. This applies to an area of a district heating system, and the assets used therein. According to an embodiment, a current outdoor temperature has effect on heat demand of the buildings of the district heating system; to an efficiency of decentralized heating assets (for example heat pumps of the buildings); and to a compensation (for example a price or a benefit) obtained from feeding heat into a district heating system. The heat demand in the buildings of the district heating system is covered with the centralized and decentralized heat production. The most suitable production logic may be selected for a time period, for example on hourly basis, based on parameters (as described in the previous, for example), which have effect on overall heat delivery situation, like use of resources, performance, effectivity, and/or costs. District heating production parameters (for example fuel costs and/or discharge/emission levels) have effect on the selection of the centralized heat production. Electricity system related parameters (for example, a price, a compensation and/or a heat pump efficiency, like COP) have effect on the selection of the decentralized heat production. In an embodiment, if the electricity price is low and/or the efficiency of the heat pump (COP) is high, then a selection may be made to use the heat pumps for heating the buildings of the district heating system. In an alternative, there may be a situation, that the price of feeding heat into the district heating system and the price obtained from the frequency reserve market is concluded to make it more profitable to use the heat pumps for these markets. In this case, the heat pumps may be controlled to feed the heat to the district heating system, instead of using the produced heat for heating the buildings, and/or to offer capacity of the decentralized heating assets, like heat pump capacity, to the frequency reserve market. In such cases, the buildings may be heated, at least partially, using the centralized district heating assets.

[0050] Shares of used centralized and decentralized heating assets are controlled during use. Shares of used heating assets between the decentralized and centralized may have a ratio (decentralized:centralized) from 0:100 to 100:0, for example from 35:65 to 75:25. On hourly basis, the decision to use the decentralized or centralized heating assets depends on various factors. For example, during a cold season, it may be efficient to use the centralized heating asset more often than the decentralized heating assets. According to an example, a heat production peak of the decentralized assets is a result of increase of frequency reserve market value, which make it profitable to use decentralized heating assets in order to produce heat to open centralized heating system, and to participate in frequency reserve market. A high compensation or a revenue is gained for providing heat to the centralized heating system and/or for participating to the frequency reserve market using the decentralized heating assets. In such case, heat is not provided locally by decentralized heating assets, i.e. for buildings including the decentralized heating assets. For example, during a warm season decentralized heating assets may be used more often than the centralized heating asset. Heat production peaks of the decentralized heating assets may be caused by use of the decentralized heating assets to cover corresponding local heat demand (for example of a building), and rest of their capacity is directed to open central (district) heating market and/or to frequency reserve market. This improves performance and overall efficiency of the system in long term. Compensation is based on demand, and a good compensation may be received from the open district heating market and from frequency reserve market during high demand/frequency of those. The raised compensation may raise production of heat to the open centralized heating system, until the demand is decreased. Compensation follows and decreases along with the demand, thereby decreasing production of heat to the open centralized heating system.

[0051] Decentralized heating assets may offer their capacity for frequency reserve market, like hourly frequency reserve market, when for example at least 100-200 kW _ei electric compressor power is available, after capacity has been allocated to cover the overall heat demand, like heating spaces and domestic hot water (the lower index el refers to electric energy). The capacity may originate from one decentralized heating asset, or it may be aggregated capacity from more than one decentralized heating assets. There may be a minimum size, a minimum bid size, which may be offered for frequency reserve market. A minimum bid size for frequency reserve market may be 50-150 kW _e i, for example 100kW _e i, of electric power. Frequency reserve market functions symmetrically such that the minimum available up-regulation and down -regulation potential should be equal. For example, when at least 200 kWei electric compressor power is available, the decentralized heating assets can be operated with 50% load. In this case, the decentralized heating assets have minimum of 100 kWei available for both up- and down-regulation. Smaller loads may be utilized in frequency reserve market, although it such case the reserve resources may be aggregated in order to reach the minimum bid size. Probability of up-regulation and down-regulation may be equal. When power is offered to the frequency reserve market, the decentralized heating assets generate heat to open centralized (district) heating system using 50% of the available heating power. At the same time the decentralized heating assets receive compensation from the frequency reserve market due to offering 50% of the available compressor output power to the frequency reserve market. If available compressor output power is less than determined minimum, e.g. 200kW _e i, or offered capacity less than determined minimum, e.g. 100 kWei, then power is not offered to the frequency reserve market, nor is heat generated to the centralized (district) heating system by the decentralized heating assets. The decision on offering or not is based on available output and offered capacity of the decentralized heating assets, resources required for producing heat by the decentralized heating assets and possible compensation from the open centralized heating assets system and frequency reserve market.

[0052] Figure 3 illustrates, by way of an example, an apparatus according to embodiments. The apparatus 300 may be a controller configured to control a district heating system comprising centralized and decentralized heating assets, wherein the decentralized heating assets are connected to a power system. The apparatus 300 comprises a memory 301 for storing information, like executable instructions and data. Memory 301 may comprise different memory blocks and different kind of memories, like randomaccess memory, permanent memory, solid-state, magnetic, optic, holographic memory, for example. The apparatus 300 comprises a processor 303. The processor 303 may comprise circuitry, digital signal processor, single- or multi-core processor, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), a processing core, or a controller part. The processor 303 is configured to execute computer instructions and cause performance of actions in accordance to executable instructions. Memory 301 comprises computer instructions, or executable instructions, that the processor 303 is configured to execute. The memory 301 may store executable instructions, which are configured the cause certain actions, when executed by the processor 303. The apparatus 300 comprises a transmitter and/or a receiver 302. The transmitter and/or receiver 302 is configured to transmit and/or receive information, correspondingly. Transmitter and/or receiver 302 may operate in accordance with at least one of wireless technology standards and/or near-filed communication (NFC) technologies. Alternatively, or in addition, the transmitter and/or receiver 302 may comprise means for fixed coupling, like a connector, connecting terminal or adaptor. The apparatus 300, as well as the memory 301, the transmitter/receiver 302 and the processor 303, may be implemented using hardware and/or software. In addition, the apparatus 300 may comprise an interface for inputting and outputting information. The apparatus 300 may comprise compact structure with local parts, or at least some parts may be distributed and remotely accessed.

[0053] Figure 4 illustrates, by way of an example, a method according to embodiments. The method for controlling a district heating system comprising at least one centralized heating asset and decentralized heating assets, wherein the decentralized heating assets comprise electric heating assets connected to a power system. The method comprises controlling heat production of the centralized heating asset and the decentralized heating assets, at a time range, in phase 401. The controlling, in phase 401, being based on determined overall heat demand, 402, from the district heating system, at the time range; state of the power system, 403, including overall demand and supply in the power system at the time range; production capacity of heat by the centralized heating asset, 404, at the time range, and production capacity of heat by the decentralized heating assets, 405, at the time range.

[0054] Based on parameters and optimization, controlling the use of centralized and decentralized heating assets may include: using the centralized heating asset only, or using the decentralized heating assets only. The decentralized heating assets are electricity- driven, connected to electric power system, and employ water circulation technology. Water circulation enables transfer of heat between the primary side and the secondary side of the heating system. Control of the heating assets or a heating logic to be employed, may include at least one of the following: If building’s heating power demand exceeds nominal output of the decentralized heating asset(s) of the building, electricity may be used to cover the shortage. In alternative, if building’s heating power demand exceeds nominal output of the decentralized heating asset(s) of the building, the central heating asset may be used to cover the shortage. The decentralized heating assets may be used to produce heat to primary side of the open heating system (network), while not providing heat directly to the building. The decentralized heating assets may be used only to produce heat to primary side of the open district heating system and to participate in frequency reserve market, and not to provide heat directly to the building. The decentralized heating assets may be used primarily for directly heating the buildings and in case there is heating capacity left after building’s heating power demand is met, the decentralized heating assets is used to produce heat to primary side of the open heating system (network). If building’s heating demand exceeds nominal output of the decentralized heating assets, electricity power system or centralized heating asset of the primary side may be used to cover the shortage. The decentralized heating assets may be used primarily for directly heating the buildings. In case there is heating capacity left after building’s heating power demand is fulfilled, the decentralized heating assets may be used to produce heat to the primary side of the open district heating system, and to participate in frequency reserve market of the power system (for example electricity network). If building’s heating power demand exceeds nominal output of the decentralized heating assets, the primary side centralized heating asset may be used to cover the shortage. Open district heating system enables receiving heat from third parties, which may be external to the (open) district heating system. When a primary side is accessible such that heat may be fed from decentralized assets of a secondary side to the primary side, the primary side may be called an open network system. Throughout the description, the term (district) heating network covers both an open and a closed type of heating network systems.

[0055] The previously mentioned operations may form at least some optional heat delivery logics. The parameters may be used for selecting among optional heat delivery logics. Desired objective may be adjusted, e.g. effective heat delivery, best performing logic, hourly optimum delivery logic, resource optimum delivery logic, delivery logic of minimum emission(s), or alike or any combination of such. In addition, output may include peak power of the centralized heating asset, peak power input of the decentralized heating assets, frequency reserve active hours, frequency reserve capacity provided, frequency reserve compensation, hours of feeding in heat to the primary side, energy fed-in to the primary side, compensation from the primary side feed- in, and heat production of the decentralized heating assets. The parameters may be used for optimizing the current and/or future control and/or dimensioning of the heating system according to embodiments. [0056] The previous description and figures present adding secondary side decentralized heating assets in operational combination with the centralized, district heating system. This enables to increase the heat delivery operating performance/efficiency of the hybrid heating system. The centralized and decentralized heating assets may be used in parallel by controlling optimal production logic at a time range, e.g. hour by hour, from various available production logics. In order to capture full value of the heating system, the decentralized heating assets, which function with the centralized heating asset, are connected to a power system. The decentralized heating assets may be utilized in both a frequency reserve market of the power system, and in open central, district heating markets. Dimensioning of the decentralized heating assets system is based on peak heat demand of the heating system (network), which may form the highest accepted dimensioning. Results are sensitive to various parameters, for example power system resources and availability, central (district) heating delivery requirements and/or compensation, and use of decentralized heating assets in the hybrid heating system.

[0057] In order to make the heating system suitable for operation and use, dimensioning of the system is planned and implemented before operation. Automated hybrid heating system control is enabled during operations, taking into account resources of the power system (network), to which the decentralized heating assets are connected. The presented embodiments enable real-time control of the hybrid heating system, e.g. use between the centralized and decentralized heating assets. An operator of a hybrid heating system may be able to operate both primary and secondary side of the district heating system.

[0058] Combining decentralized heating assets into a centralized district heating system increases power (electricity) peak demand. The heating system is scalable, and it may cover an area, a municipality, a country or alike area or sub-area. Alternative technologies may be used as heat pump technologies, storage technologies and for heat demand response. Input parameters may be based on history data, determined, calculated or estimated data, and/or on forecast data, as input parameters. The embodiments enables for example minimizing emissions, for example carbon dioxide emissions, in the heating system by including emission data and/or factors as input parameters, and by setting emission reduction as a goal. An optimization program or model may be used for achieving desired constructions and/or settings with desired properties. Environmental sustainability of a heating system may be improved with electrification. [0059] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or parameters disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0060] The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the previous description, numerous specific details are provided, such as examples of structures, or values, to provide a thorough understanding of embodiments of the invention.

[0061] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0062] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.