WO2010087759A1 - District heating substation control - Google Patents

District heating substation control Download PDF

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Publication number
WO2010087759A1
WO2010087759A1 PCT/SE2010/050051 SE2010050051W WO2010087759A1 WO 2010087759 A1 WO2010087759 A1 WO 2010087759A1 SE 2010050051 W SE2010050051 W SE 2010050051W WO 2010087759 A1 WO2010087759 A1 WO 2010087759A1
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WIPO (PCT)
Prior art keywords
primary
supply temperature
temperature
district heating
heat
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Application number
PCT/SE2010/050051
Other languages
French (fr)
Inventor
Jerker Delsing
Jan Van Deventer
Jonas Gustafsson
Original Assignee
D-Con
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by D-Con filed Critical D-Con
Priority to EP10736098A priority Critical patent/EP2394099A1/en
Publication of WO2010087759A1 publication Critical patent/WO2010087759A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D10/00—District heating systems
    • F24D10/003—Domestic delivery stations having a heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
    • F24D19/00—Details
    • F24D19/10—Arrangement or mounting of control or safety devices
    • F24D19/1006—Arrangement or mounting of control or safety devices for water heating systems
    • F24D19/1009—Arrangement or mounting of control or safety devices for water heating systems for central heating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/17—District heating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/14—Combined heat and power generation [CHP]

Definitions

  • the present invention relates to control of a district heating substation having a primary supply line for receiving, from a district heating plant, a heat carrier having a primary supply temperature, and a primary return line for returning, to the district heating plant, the heat carrier with a primary return temperature, the substation comprising a heat exchanger having a primary side connected between the primary supply line and primary return line, and a secondary side connected to a heat distribution system.
  • a CHP plant connected to a district heating network utilizes the district heating system as big heat sink for the cooling water in the power production process. This is good way of creating a win-win situation as the excess heat produced in the power production can be sold as district heating, and concurrently decreases environmental effect when less amount of primary fuel is needed.
  • ⁇ T temperature drop
  • the ⁇ T also influences the electricity production in the CHP plant.
  • the returning district heating water condensate the hot steam after the electricity producing turbines in extraction condensing CHP, a lower returning district heating temperature (higher ⁇ T) will increase steam condensation capabilities. This result in a higher pressure drop across the turbine, that hence can turn faster and produce more electric power.
  • increased ⁇ T also contributes to decrease the pump power needed in the DH network, reduces distribution losses and enables more customers to connect to the available DH network.
  • a method for controlling a district heating substation comprising storing a relationship between primary supply temperature and desired secondary supply temperature, detecting a primary supply temperature, using said relationship to determine a set point value for secondary supply temperature based on the detected primary supply temperature, and controlling the secondary supply temperature according to said set point value, by regulating the primary side flow.
  • a district heating substation comprising a memory storing a relationship between primary supply temperature and desired secondary supply temperature, a sensor for detecting a primary supply temperature, a primary side control valve for regulating a primary flow through the primary side, and a controlled connected to said sensor and arranged to determine a set point value for secondary supply temperature based on the detected primary supply temperature and said relationship, and to control the secondary supply temperature according to said set point value, by actuating the primary side control valve.
  • the present invention is based on the realization that the secondary supply temperature is not subject to any significant variations due to realistic load variations with constant primary supply temperature. Therefore, the substation control may be based on primary supply temperature without negatively affecting the temperature drop ⁇ T.
  • the primary supply temperature depends non linearly on outdoor temperature.
  • One example is when many separate heat plants are connected to the same district heating network. At low system load (high outdoor temperature) it may then be sufficient to just utilize one plant, but when the system load increases over a certain level, an additional heat plant needs to be run. This can in many cases result in a "step" or other non linearity of the primary supply temperature.
  • the control system will not be optimal, as the primary temperature changes somewhat independent from the outdoor temperature.
  • a system according to the present invention will not suffer from the same drawbacks, as the radiator supply temperature will be correlated to primary supply temperature, thus avoiding the non-linearities between primary supply temperature and outdoor temperature.
  • Another positive aspect of primary temperature based control is limitation of sudden heat load peaks during e.g. a rain shower that decreases the outdoor temperature temporarily. Using traditional outdoor temperature dependent control methods this means that the primary flow will increase, even though there is no need for that as the building has a long thermal time constant. As a result, the primary temperature drop ⁇ T will decrease. In a system according to the present invention, where the primary flow is based on primary supply temperature, this effect is avoided as the primary supply temperature is controlled externally, by the energy company.
  • the relationship between primary supply temperature and secondary supply temperature may be formed by determining, for each primary supply temperature in a set of primary supply temperatures, a secondary supply temperature that minimizes the primary return temperature for this primary supply temperature.
  • the relationship should be determined from a "steady state” analysis, i.e. a situation where the outdoor temperature and primary supply temperature are assumed to be constant.
  • the primary return temperature can be significantly decreased, and the temperature drop ⁇ T at the substation can be increased. Compared to conventional heating system control, this more optimal control leads to an increased temperature drop over the heat distribution system.
  • a conventional system typically is dimensioned as a so called 60/40 system, radiator supply temperature 6O 0 C and radiator return temperature 4O 0 C at dimensioned minimal outdoor temperature
  • a system according to this embodiment of the invention typically leads to a corresponding 75/25 system. The exact temperatures will depend on the dimensioning of the heat distribution system, i.e. number of radiators, their convection capacity, etc.
  • radiator supply temperature will result in a decreased secondary side flow
  • heat distribution system can be referred to as a "low-flow high temperature" system.
  • Such a system has a large temperature drop at each radiator, which in turn enables a large temperature drop at the primary side.
  • the secondary supply temperature that minimizes the primary return temperature for a given primary supply temperature can advantageously be determined based on a simulation model of a building heated by the district heating substation. By simulating a gradual decrease of secondary side flow rate, while maintaining a constant power consumption, a local minimum of the primary return temperature can be localized, and the corresponding secondary supply temperature may be determined.
  • the heat distribution system comprises a plurality of radiators, and a secondary side flow is controlled using thermostatic valves adapted to regulate the flow through each radiator based on a desired indoor temperature.
  • Thermostatic valves can limit the flow in the radiator system to achieve an optimal flow without any interference from a circulation pump.
  • the secondary flow control means may include a constant speed pump or a variable speed pump. In the latter case, the secondary flow is preferably held at a constant differential pressure e.g. using a constant pressure circulation pump, in order to reduce noise caused by pressure variations.
  • a variable speed pump may also be controlled in different ways.
  • the primary supply temperature information can be received from a heat meter arranged to measure the heat consumption in the substation. This eliminates the need for an additional temperature sensor.
  • the senor forms part of a sensor network connected to the substation controller, the sensor network being arranged to collect information from both the primary and secondary side of the heat exchanger to be used in the control process.
  • FIG. 1 shows a district heating substation 10 according to an embodiment of the present invention.
  • the substation comprises a heat exchanger 11 , with a primary side 12 and a secondary side 13.
  • the primary side is connected between a primary supply line 14 receiving a heat carrier such as water from a district heating plant (not shown), and a primary return line 15 for returning the heat carrier to the district heating plant.
  • a control valve 16 is provided to control the flow through the primary side of the heat exchanger.
  • the secondary side is connected to a heat distribution system 17, here comprising one or several radiators 18 connected to each other with piping 19.
  • a circulation pump 9 for example a constant speed circulation pump, is arranged to control the flow of a heat carrier in the heat distribution system. In order to limit pressure variations, the pump can be a constant relative pressure circulation pump.
  • thermostatic valves 20 can be mounted in series with the radiators 18 to further improve the indoor comfort by regulating the radiator flow, and hence also the radiator heat transfer in dependence of the temperature in the radiator surroundings.
  • the substation 10 further typically comprises a second heat exchanger with a secondary side connected to a tap water distribution system. This is not relevant for the present invention, and will not be further described.
  • the substation 10 further comprises a controller 21 , arranged to actuate the control valve.
  • a temperature sensor 22 is arranged to detect the temperature of the heat carrier in the primary supply line, and to provide a value of the detected primary supply temperature to the controller 21.
  • a feedback path 23 is arranged to provide the controller 21 with the temperature of the heat carrier in the secondary supply, i.e. the radiator supply temperature.
  • the temperature sensor 22 is here illustrated as the heat meter of the district heating system, otherwise used to measure power consumption in the substation for billing purposes.
  • the sensor may also form part of a more complex sensor network, where a plurality of sensor devices communicate using a suitable communication protocol.
  • the sensor devices can be arranged to collect information from both the primary side and a secondary side of the heat exchanger, which information can be used by the controller.
  • the communication in the sensor network can be performed using a standardized protocol, such as TCP/IP.
  • the sensor network can use Service Oriented Architecture protocols to automatically integrate data from connected devices into a sensor network control loop. It may also use wireless communication.
  • the primary supply delivers hot heat carrier to the primary side of the heat exchanger, where heat is transferred to the heat carrier circulated in the heat distribution system.
  • the primary return returns cooled heat carrier to the heat plant. After being heated the secondary side heat carrier is circulated in the heat distribution system, and is cooled off in the radiators 18 by heat convection.
  • the secondary side supply temperature, or radiator supply temperature is controlled by the controller 21 by actuating the control valve 16.
  • a radiator supply temperature set point, T rs se tpomt
  • T ps the detected primary supply temperature
  • the controller applies a feedback control, for example a negative feedback wherein a feedback temperature Trs.feedback from the feedback path 23 is subtracted from the temperature set point Trs setpoint, and the control valve 16 is actuated based on the resulting difference.
  • the relationship between primary supply temperature and radiator supply temperature can be determined in different ways. According to one approach, the relationship is established by selecting a desired radiator supply temperature (e.g. 6O 0 C) at a given outdoor temperature (e.g. -3O 0 C). Although often practical, this approach does not provide an optimal control in terms of temperature drop at the secondary side, and, more importantly, at the primary side. To achieve a higher primary side ⁇ T a low-flow high temperature system is preferred.
  • the relationship between primary supply temperature and secondary side temperature is determined by finding, for a given primary supply temperature, the radiator supply temperature that minimizes the primary return temperature.
  • Such a relationship can be determined using a simulation model as described in "Thermodynamic simulation of a detached house with district heating subcentral", by J. Gustafsson, J. van Deventer, and J. Delsing, IEEE, 2:nd annual Systems Conference, Montreal, April 2008.
  • the model simulates the main parts of a building connected to a district heating system, and includes: • Thermodynamic building with separate settings for floor, walls, roof and windows. The thermal inertia of the building, and air exchange rate are also simulated.
  • Supply information which includes, outdoor temperature, primary supply temperature, and primary pressure.
  • the simulation is performed as follows. At steady state conditions, i.e. constant outdoor temperature and primary supply temperature, the power consumption R, n , t of the radiator system is recorded. A slowly continuously decreasing radiator system flow rate ⁇ r is now simulated. To keep the power consumption at a constant level, the primary flow m p through the heat exchanger is adjusted according to
  • T ps and T pr are the primary supply and return temperatures
  • cp is the constant pressure heat capacity for water
  • Figure 2 shows curves for T pr , T r8 , TM r and m p simulated at an outdoor temperature of -10 0 C.
  • the optimal control conditions are met when the primary return temperature Tpr has a local minimum. This is easily located by d ⁇ pr determining when its time derivative, — — .equals zero. In fig. 2 this occurs at approximately 19:15.
  • Figure 3 shows a resulting control curve 31.
  • figure 3 also shows a conventional 60/40 control curve 32 for the simulated system. It is clear that the optimized control curve in this case has resulted in a higher radiator supply temperature.
  • a relationship must be determined between primary supply temperature and radiator supply temperature.
  • a relationship between outdoor temperature and primary supply temperature (curve 33 in figure 3) is used, and the resulting primary supply based control curve 34 is shown in figure 4. This control curve 34 may be applied in the controller in figure 1 , to be used in the control described above.
  • a control strategy according to this embodiment of the present invention has been compared with traditional control methods for two different supply temperature schemes. Simulations of three identical houses with three different control methods were conducted.
  • the first house (H1 ) is equipped with an optimal traditional control system with 60 0 C radiator supply temperature at an outdoor temperature of -30 0 C (curve 32 in figure 3).
  • the second house (H2) uses the optimized control curve (curve 31 in figure 3).
  • the third house (H3) uses the optimal control curve correlated to the primary supply temperature (curve 34 in fig. 4).
  • Simulation B uses a linear supply temperature scheme, shown as curve 36 in figure 6, whereas Simulation B uses a non-linear supply temperature variant, shown as curve 35 in figure 6.
  • the outdoor temperature included a daily variation term and a slow variation term.
  • the outdoor climate was identical for all simulation runs. Both simulation were run for a time period of 3 days.
  • Table Primary return temperature and primary flow rate in three different houses.

Abstract

A method and a system for control of a district heating substation (10) having a primary supply line (14) for receiving, from a district heating plant, a heat carrier having a primary supply temperature, and a primary return line (15) for returning, to the district heating plant, the heat carrier with a primary return temperature, the substation comprising a heat exchanger (11 ) having a primary side (12) connected between the primary supply line and primary return line, and a secondary side (13) connected to a heat distribution system. A relationship between primary supply temperature and desired secondary supply temperature is stored, a set point value for secondary supply temperature is determined based on a detected primary supply temperature, and the secondary supply temperature is controlled according to said set point value, by regulating the primary side flow. The present invention is based on the realization that the secondary supply temperature is not subject to any significant variations due to realistic load variations with constant primary supply temperature. Therefore, the substation control may be based on primary supply temperature without negatively affecting the temperature drop ΔT.

Description

DISTRICT HEATING SUBSTATION CONTROL
Field of the invention
The present invention relates to control of a district heating substation having a primary supply line for receiving, from a district heating plant, a heat carrier having a primary supply temperature, and a primary return line for returning, to the district heating plant, the heat carrier with a primary return temperature, the substation comprising a heat exchanger having a primary side connected between the primary supply line and primary return line, and a secondary side connected to a heat distribution system.
Background of the Invention
District heating has been commercially used since the early twentieth century. Today, district heating networks can be found almost all over the northern hemisphere, albeit most common in the eastern, central and northern parts of Europe. By centralizing and combining heat and power production in a combined heat and power (CHP) plant, the overall fuel efficiency will be increased. In traditional fossil fuel fired electricity producing power plants, the fuel efficiency rarely exceeds 50%, the rest of the fuel becomes heat that is lost or wasted. In a CHP plant most of the 'waste' heat can be captured and used in e.g. a district heating system. By doing this, the overall fuel efficiency can reach over 90%.
A CHP plant connected to a district heating network utilizes the district heating system as big heat sink for the cooling water in the power production process. This is good way of creating a win-win situation as the excess heat produced in the power production can be sold as district heating, and concurrently decreases environmental effect when less amount of primary fuel is needed.
To maximize the fuel efficiency in a district heating system it is of great importance to have a large temperature drop (ΔT) in the district heating network. By maintaining a large ΔT, more energy per volume unit will be utilized. If the district heating network is powered by an extraction condensing CHP plant, the ΔT also influences the electricity production in the CHP plant. As the returning district heating water is used condensate the hot steam after the electricity producing turbines in extraction condensing CHP, a lower returning district heating temperature (higher ΔT) will increase steam condensation capabilities. This result in a higher pressure drop across the turbine, that hence can turn faster and produce more electric power. Beside these objectives, increased ΔT also contributes to decrease the pump power needed in the DH network, reduces distribution losses and enables more customers to connect to the available DH network.
An increase of system ΔT with 10 degrees C will result in a 55% reduction of pump power. Depending on heat production method, the total primary fuel source savings varies between 0.1 and 14%. This verifies that there is a large interest in ΔT optimization within the district heating industry. As the energy companies only can invoice for energy utilized by a customer, and not for energy lost in the distribution network, the majority of the total ΔT must be dropped over the customer's district heating substation.
However, currently available systems for district heating substation control do not provide satisfactory control of the temperature drop at the substation.
General disclosure of the invention
It is therefore an object of the present invention to provide an improved district heating substation control. According to a first aspect of the present invention, this and other objects is achieved by a method for controlling a district heating substation comprising storing a relationship between primary supply temperature and desired secondary supply temperature, detecting a primary supply temperature, using said relationship to determine a set point value for secondary supply temperature based on the detected primary supply temperature, and controlling the secondary supply temperature according to said set point value, by regulating the primary side flow. According to a second aspect of the present invention, this and other objects is achieved by a district heating substation comprising a memory storing a relationship between primary supply temperature and desired secondary supply temperature, a sensor for detecting a primary supply temperature, a primary side control valve for regulating a primary flow through the primary side, and a controlled connected to said sensor and arranged to determine a set point value for secondary supply temperature based on the detected primary supply temperature and said relationship, and to control the secondary supply temperature according to said set point value, by actuating the primary side control valve.
The present invention is based on the realization that the secondary supply temperature is not subject to any significant variations due to realistic load variations with constant primary supply temperature. Therefore, the substation control may be based on primary supply temperature without negatively affecting the temperature drop ΔT.
In many situations, the primary supply temperature depends non linearly on outdoor temperature. One example is when many separate heat plants are connected to the same district heating network. At low system load (high outdoor temperature) it may then be sufficient to just utilize one plant, but when the system load increases over a certain level, an additional heat plant needs to be run. This can in many cases result in a "step" or other non linearity of the primary supply temperature. In a conventional system, where the substation control is based on outdoor temperature, the control system will not be optimal, as the primary temperature changes somewhat independent from the outdoor temperature. A system according to the present invention will not suffer from the same drawbacks, as the radiator supply temperature will be correlated to primary supply temperature, thus avoiding the non-linearities between primary supply temperature and outdoor temperature. Another positive aspect of primary temperature based control is limitation of sudden heat load peaks during e.g. a rain shower that decreases the outdoor temperature temporarily. Using traditional outdoor temperature dependent control methods this means that the primary flow will increase, even though there is no need for that as the building has a long thermal time constant. As a result, the primary temperature drop ΔT will decrease. In a system according to the present invention, where the primary flow is based on primary supply temperature, this effect is avoided as the primary supply temperature is controlled externally, by the energy company.
The relationship between primary supply temperature and secondary supply temperature may be formed by determining, for each primary supply temperature in a set of primary supply temperatures, a secondary supply temperature that minimizes the primary return temperature for this primary supply temperature. The relationship should be determined from a "steady state" analysis, i.e. a situation where the outdoor temperature and primary supply temperature are assumed to be constant.
By using such a relationship, the primary return temperature can be significantly decreased, and the temperature drop ΔT at the substation can be increased. Compared to conventional heating system control, this more optimal control leads to an increased temperature drop over the heat distribution system. While a conventional system typically is dimensioned as a so called 60/40 system, radiator supply temperature 6O0C and radiator return temperature 4O0C at dimensioned minimal outdoor temperature, a system according to this embodiment of the invention typically leads to a corresponding 75/25 system. The exact temperatures will depend on the dimensioning of the heat distribution system, i.e. number of radiators, their convection capacity, etc. This increase of radiator supply temperature will result in a decreased secondary side flow, and the heat distribution system can be referred to as a "low-flow high temperature" system. Such a system has a large temperature drop at each radiator, which in turn enables a large temperature drop at the primary side.
The secondary supply temperature that minimizes the primary return temperature for a given primary supply temperature, can advantageously be determined based on a simulation model of a building heated by the district heating substation. By simulating a gradual decrease of secondary side flow rate, while maintaining a constant power consumption, a local minimum of the primary return temperature can be localized, and the corresponding secondary supply temperature may be determined.
According to a preferred embodiment, the heat distribution system comprises a plurality of radiators, and a secondary side flow is controlled using thermostatic valves adapted to regulate the flow through each radiator based on a desired indoor temperature. Thermostatic valves can limit the flow in the radiator system to achieve an optimal flow without any interference from a circulation pump. The secondary flow control means may include a constant speed pump or a variable speed pump. In the latter case, the secondary flow is preferably held at a constant differential pressure e.g. using a constant pressure circulation pump, in order to reduce noise caused by pressure variations. Of course, a variable speed pump may also be controlled in different ways. The primary supply temperature information can be received from a heat meter arranged to measure the heat consumption in the substation. This eliminates the need for an additional temperature sensor. In this case, no additional sensors are required to implement primary supply temperature based control according to the present invention. According to one embodiment, the sensor forms part of a sensor network connected to the substation controller, the sensor network being arranged to collect information from both the primary and secondary side of the heat exchanger to be used in the control process.
Detailed description
Figure 1 shows a district heating substation 10 according to an embodiment of the present invention. The substation comprises a heat exchanger 11 , with a primary side 12 and a secondary side 13. The primary side is connected between a primary supply line 14 receiving a heat carrier such as water from a district heating plant (not shown), and a primary return line 15 for returning the heat carrier to the district heating plant. A control valve 16 is provided to control the flow through the primary side of the heat exchanger. The secondary side is connected to a heat distribution system 17, here comprising one or several radiators 18 connected to each other with piping 19. A circulation pump 9, for example a constant speed circulation pump, is arranged to control the flow of a heat carrier in the heat distribution system. In order to limit pressure variations, the pump can be a constant relative pressure circulation pump. Additionally, thermostatic valves 20 can be mounted in series with the radiators 18 to further improve the indoor comfort by regulating the radiator flow, and hence also the radiator heat transfer in dependence of the temperature in the radiator surroundings.
The substation 10 further typically comprises a second heat exchanger with a secondary side connected to a tap water distribution system. This is not relevant for the present invention, and will not be further described.
The substation 10 further comprises a controller 21 , arranged to actuate the control valve. A temperature sensor 22 is arranged to detect the temperature of the heat carrier in the primary supply line, and to provide a value of the detected primary supply temperature to the controller 21. A feedback path 23 is arranged to provide the controller 21 with the temperature of the heat carrier in the secondary supply, i.e. the radiator supply temperature.
The temperature sensor 22 is here illustrated as the heat meter of the district heating system, otherwise used to measure power consumption in the substation for billing purposes. The sensor may also form part of a more complex sensor network, where a plurality of sensor devices communicate using a suitable communication protocol. The sensor devices can be arranged to collect information from both the primary side and a secondary side of the heat exchanger, which information can be used by the controller.
The communication in the sensor network can be performed using a standardized protocol, such as TCP/IP. The sensor network can use Service Oriented Architecture protocols to automatically integrate data from connected devices into a sensor network control loop. It may also use wireless communication.
In use, the primary supply delivers hot heat carrier to the primary side of the heat exchanger, where heat is transferred to the heat carrier circulated in the heat distribution system. The primary return returns cooled heat carrier to the heat plant. After being heated the secondary side heat carrier is circulated in the heat distribution system, and is cooled off in the radiators 18 by heat convection.
The secondary side supply temperature, or radiator supply temperature, is controlled by the controller 21 by actuating the control valve 16. First, a radiator supply temperature set point, Trs,setpomt, is determined based on the detected primary supply temperature, Tps, received from the sensor 22 and a relationship between the primary supply temperature and desired radiator supply temperature. Then, the controller applies a feedback control, for example a negative feedback wherein a feedback temperature Trs.feedback from the feedback path 23 is subtracted from the temperature set point Trs setpoint, and the control valve 16 is actuated based on the resulting difference.
The relationship between primary supply temperature and radiator supply temperature, also referred to as the control curve, can be determined in different ways. According to one approach, the relationship is established by selecting a desired radiator supply temperature (e.g. 6O0C) at a given outdoor temperature (e.g. -3O0C). Although often practical, this approach does not provide an optimal control in terms of temperature drop at the secondary side, and, more importantly, at the primary side. To achieve a higher primary side ΔT a low-flow high temperature system is preferred.
According to one embodiment of the present invention, the relationship between primary supply temperature and secondary side temperature is determined by finding, for a given primary supply temperature, the radiator supply temperature that minimizes the primary return temperature.
Such a relationship can be determined using a simulation model as described in "Thermodynamic simulation of a detached house with district heating subcentral", by J. Gustafsson, J. van Deventer, and J. Delsing, IEEE, 2:nd annual Systems Conference, Montreal, April 2008. The model simulates the main parts of a building connected to a district heating system, and includes: • Thermodynamic building with separate settings for floor, walls, roof and windows. The thermal inertia of the building, and air exchange rate are also simulated.
• Substation with parallel coupled heat exchangers and control system.
• Radiator system that includes thermostatic valves.
• Supply information, which includes, outdoor temperature, primary supply temperature, and primary pressure.
The simulation is performed as follows. At steady state conditions, i.e. constant outdoor temperature and primary supply temperature, the power consumption R,n,t of the radiator system is recorded. A slowly continuously decreasing radiator system flow rate ώ r is now simulated. To keep the power consumption at a constant level, the primary flow m p through the heat exchanger is adjusted according to
< = cp (T —ps - Tpr ) where Tps and Tpr are the primary supply and return temperatures, and cp is the constant pressure heat capacity for water.
Figure 2 shows curves for Tpr, Tr8, ™ r and m p simulated at an outdoor temperature of -100C. The optimal control conditions are met when the primary return temperature Tpr has a local minimum. This is easily located by dτpr determining when its time derivative, — — .equals zero. In fig. 2 this occurs at approximately 19:15.
To find a complete optimal control curve with maximized ΔT, independent of external parameters, several optimization simulation, for different outdoor temperatures, has to be conducted with varying outdoor and primary supply temperatures. Figure 3 shows a resulting control curve 31. As a comparison, figure 3 also shows a conventional 60/40 control curve 32 for the simulated system. It is clear that the optimized control curve in this case has resulted in a higher radiator supply temperature. In order to apply the optimal control curve in the control system described in relation to figure 1 , a relationship must be determined between primary supply temperature and radiator supply temperature. For this purpose, a relationship between outdoor temperature and primary supply temperature (curve 33 in figure 3) is used, and the resulting primary supply based control curve 34 is shown in figure 4. This control curve 34 may be applied in the controller in figure 1 , to be used in the control described above.
Depending on additional heat contribution from non district heating related devices such as, fire places, electrical appliances and humans, the heat need for a building can change even though the outdoor temperature are constant. With varying load, the new optimal control curves might not be optimal any more. To investigate this, additional simulations were carried out with additional indoors heat sources to see how the control curve were subject to change. It was found that the supply temperature to the radiator system were kept at a reasonable constant level with varying load, see Trs in fig. 5. The variations in required heat power were hence controlled by the radiator thermostats, which adjusted the radiator system flow, see ^ r in fig.
5.
A control strategy according to this embodiment of the present invention has been compared with traditional control methods for two different supply temperature schemes. Simulations of three identical houses with three different control methods were conducted. The first house (H1 ) is equipped with an optimal traditional control system with 600C radiator supply temperature at an outdoor temperature of -300C (curve 32 in figure 3). The second house (H2) uses the optimized control curve (curve 31 in figure 3).
The third house (H3) uses the optimal control curve correlated to the primary supply temperature (curve 34 in fig. 4).
To compare ΔT as result of different primary supply temperature schemes, all control methods (H1 , H2 and H3), were run with two separate primary supply temperature schemes, referred two as Simulation A and
Simulation B. Simulation A uses a linear supply temperature scheme, shown as curve 36 in figure 6, whereas Simulation B uses a non-linear supply temperature variant, shown as curve 35 in figure 6.
The outdoor temperature included a daily variation term and a slow variation term. The outdoor climate was identical for all simulation runs. Both simulation were run for a time period of 3 days.
By comparing the primary return temperature and primary flow through the heat exchanger, it can be seen that the improved control curve, used in House 2 (H2), lowered the primary return temperature in both supply temperature schemes. Also the primary flow was decreased. The heat meter based control in house 3 (H3) resulted in similar results as using the optimal control curve based on outdoor temperature (H2).
In simulation B, where the supply temperature did not change linearly with outdoor temperature, we find an even further decreased primary return temperature in the third house (H3) which uses a primary supply temperature based control.
Table: Primary return temperature and primary flow rate in three different houses.
Simulation A Simulation B
House
Figure imgf000011_0001
s] s]
H1 48.20 33.76 0.03007 66.32 33.67 0.02182
H2 51 .47 30.49 0.02819 71 .04 28.96 0.02039
H3 51 .52 30.43 0.02815 71 .84 28.16 0.02018
The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

1. A method for controlling a district heating substation having a primary supply line for receiving, from a district heating production plant, a heat carrier having a primary supply temperature, and a primary return line for returning, to the district heating production plant, the heat carrier with a primary return temperature, said substation comprising a heat exchanger having a primary side connected between the primary supply line and primary return line, and a secondary side connected to a heat distribution system, said method comprising: storing a relationship between primary supply temperature and desired secondary supply temperature, detecting a primary supply temperature, using said relationship to determine a set point value for secondary supply temperature based on the detected primary supply temperature, and controlling the secondary supply temperature according to said set point value, by regulating the primary side flow.
2. The method according to claim 1 , wherein said relationship is formed by determining, for each primary supply temperature in a set of primary supply temperatures, a secondary supply temperature that minimizes the primary return temperature for this primary supply temperature.
3. The method according to claim 2, wherein the secondary supply temperature that minimizes the primary return temperature for a given primary supply temperature is determined based on a simulation model of a building heated by the district heating substation.
4. The method according to any one of the preceding claims, wherein said heat distribution system comprises a plurality of radiators, and wherein a secondary flow is controlled using thermostatic valves adapted to control the flow through each radiator based on a desired indoor temperature.
5. A district heating substation comprising: a primary supply line for receiving, from a district heating plant, a heat carrier having a primary supply temperature, a primary return line for returning, to the district heating plant, the heat carrier with a primary return temperature, a heat exchanger having a primary side connected between the primary supply line and the primary return line and a secondary side connected to a heat distribution system, a memory storing a relationship between primary supply temperature and desired secondary supply temperature, a sensor for detecting a primary supply temperature, a primary side control valve for regulating a primary flow through the primary side, and a controlled connected to said sensor and arranged to determine a set point value for secondary supply temperature based on the detected primary supply temperature and said relationship, and to control the secondary supply temperature according to said set point value, by actuating the primary side control valve.
6. The heating substation according to claim 5, wherein the heat distribution system includes: a plurality of radiators, and thermostatic valves adapted to regulate the flow through each radiator based on a desired indoor temperature.
7. The heating substation according to claim 5 or 6, said secondary flow control means including a variable speed pump.
8. The heating substation according to claim 7, wherein the variable speed pump is a constant differential pressure circulation pump.
9. The heating substation according to one of claims 5 - 8, wherein said sensor is adapted to receive temperature information from a heat meter connected to the primary supply line.
PCT/SE2010/050051 2009-01-30 2010-01-20 District heating substation control WO2010087759A1 (en)

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FR3012873A1 (en) * 2013-11-04 2015-05-08 Collard & Trolart Thermique METHOD AND DEVICE FOR TRANSFERRING THERMAL ENERGY IN THE URBAN ENVIRONMENT
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CN108463672A (en) * 2015-11-09 2018-08-28 威乐欧洲股份公司 Method for controlling centrifugal pump and relevant pumping system
CN108463672B (en) * 2015-11-09 2021-03-02 威乐欧洲股份公司 Method for controlling a centrifugal pump and associated pump system
WO2018015508A1 (en) 2016-07-20 2018-01-25 Vito Nv Reduction of the return temperature in district heating and increasing of the return temperature in district cooling
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KR20210004945A (en) * 2017-12-27 2021-01-13 이엠지 에너지몬타게그루펜 에이비 Responsive power steering and redundancy
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RU183885U1 (en) * 2018-06-06 2018-10-08 Федеральное государственное бюджетное образовательное учреждение высшего образования "Национальный исследовательский Мордовский государственный университет им. Н.П. Огарёва" Individual heat point with diaphragm pump
JP7369190B2 (en) 2018-11-22 2023-10-25 ストックホルム エクサージ アーべー Method and system for equilibrating mass flow during outage or malfunction of heat generation in district heating networks
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