Patent Application
20210215372
s The present invention relates to a method and a control system for controlling energy transfer of a thermal energy exchanger. Specifically, the present invention relates to a method and a control system for controlling energy transfer of a thermal energy exchanger of an HVAC system.
By regulating the flow of fluid through a thermal energy exchanger of an HVAC system, it is possible to adjust the amount of energy transferred by the thermal energy exchanger to a secondary side of the thermal energy exchanger. For example, the energy exchange or the power transfer, correspondingly, is adjusted by regulating the amount of energy delivered by the heat exchanger to heat or cool a room in a building, or by regulating the amount of energy is drawn by a chiller for cooling purposes. While the fluid transport through the fluid circuit of the HVAC system is driven by one or more pumps or fans, the flow is typically regulated by varying the orifice (opening) or position of valves, e.g. manually or by way of actuators. The efficiency of thermal energy exchangers is reduced at high flow rates where the fluid rushes at an increased rate through the thermal energy exchangers, without resulting in a significant increase in energy exchange. Moreover, the actual energy transfer characteristics of thermal energy exchangers in an HVAC system depend on building or plant characteristics and various environmental conditions such as temperature, humidity, etc. Basically, the energy transfer Q of a thermal energy exchanger can be calculated on the basis of the flow of fluid OD through the thermal energy exchanger (flow rate) and the temperature differential ΔT over the energy exchanger, i.e. the difference between the inlet temperature Tin of the fluid entering and the outlet temperature Tor the fluid exiting the thermal energy exchanger. In stable/static scenarios, calculating of the energy transfer q≈Φ·ΔT is sufficiently accurate for controlling the energy transfer. However, in an HVAC system and scenario with numerous transient events and processes, e.g. frequently changing flow rates and temperature differentials ΔT, this basic calculation of energy transfer Q≈Φ·ΔT alone is often not sufficient for accurate control of energy transfer.
WO 2017/036674 describes a method of operating a thermal energy exchanger by recording measurement data sets with time-specific data values defining a normalized energy transfer which represents the thermal energy transferred in the thermal energy exchanger from thermal transfer fluid to air, normalized by at least one air side variable; calculating for the measurement data sets normalized data points defined by the normalized energy transfer; determining for the thermal energy exchanger a characteristic energy transfer curve which fits the normalized data points and which indicates an expected energy transfer in the thermal energy exchanger from the thermal transfer fluid to the air; and operating the thermal energy exchanger on the characteristic energy transfer curve.
US 2015/153119 describes a method for operating a heat exchanger by measuring at least three of the four temperatures at the entries and exits of the heat exchanger's primary and secondary sides; determining a saturation level of the heat exchanger from the measured temperatures; and controlling the operation of the heat exchanger, using the saturation level.
US 2014/222218 describes a method for operating an HVAC system by determining empirically for an energy consumer of the HVAC system the dependence of the flow of energy and/or the temperature differential ΔT, between the supply temperature and the return temperature, on the volumetric flow rate through the energy consumer; and operating the HVAC system in accordance with the determined dependence(s).
WO 2015/171196 describes a method for determining the thermal energy flow in an HVAC system by measuring one or more variables of the HVAC system, e.g. an entry and/or exit temperature of the HVAC system; inputting the measured variables into a virtual fluid flow system to determine the fluid flow of the HVAC system, using a mathematical or physical model; and determining the thermal energy flow using the fluid flow determined by the virtual fluid flow system and a sensed temperature.
It is an object of this invention to provide a method and a control system for controlling energy transfer of a thermal energy exchanger of an HVAC system, which method and control system do not have at least some of the disadvantages of the prior art. In particular, it is an object of the present invention to provide a method and a control system for controlling energy transfer of a thermal energy exchanger of an HVAC system with numerous transient events and processes.
According to the present invention, these objectives are achieved through the features of the independent claims. In addition, further advantageous embodiments follow from the dependent claims and the description.
According to the present invention, the above-mentioned objects are particularly achieved in that for controlling energy transfer of a thermal energy exchanger of an HVAC system, a flow sensor measures the flow of fluid through the thermal energy exchanger. A first temperature sensor measures a supply temperature of the fluid in a supply pipe connected to an entry of the thermal energy exchanger, and a second temperature sensor measures a return temperature of the fluid in a return pipe connected to an exit of the thermal energy exchanger. A control system determines flow-dependent model parameters for modelling performance of the thermal energy exchanger, using one or more measurement data sets, whereby each measurement data set includes for a respective measurement time a value of the measured flow of fluid, a value of the measured supply temperature of the fluid, and a value of the measured return temperature of the fluid. Using the flow-dependent model parameters, the control system calculates an estimated energy transfer of the thermal energy exchanger, and controls the energy transfer of the thermal energy exchanger by regulating the flow of fluid through the thermal energy exchanger, using the estimated energy transfer.
As one skilled in the art will understand, the term “flow” as used herein also refers to “flow rate”, accordingly, the flow of fluid measured by a flow sensor relates to the flow rate of fluid measured by the flow sensor, for example. Likewise, the term “energy transfer” as used herein also refers to “energy transfer rate”, accordingly, the energy transfer of a thermal energy exchanger relates to the energy transfer rate of the thermal energy exchanger, for example.
In an embodiment, determining the flow-dependent model parameters comprises the control system determining a delay time in the supply pipe for the fluid to move from the first temperature sensor to the thermal energy exchanger, and determining a delay time in the return pipe for the fluid to move from the thermal energy exchanger to the second temperature sensor.
In a further embodiment, determining the flow-dependent model parameters comprises the control system determining an energy transfer coefficient for the thermal energy exchanger.
In an embodiment, determining the flow-dependent model parameters comprises the control system determining a secondary temperature associated with a secondary side of the thermal energy exchanger.
In an embodiment, determining the flow-dependent model parameters comprises the control system determining an exchange time for the fluid to replace the total fluid content of the thermal energy exchanger.
In a further embodiment, determining the flow-dependent model parameters comprises the s control system determining an estimated return temperature of the fluid in the return pipe, and setting the flow-dependent model parameters such as to minimize a difference between the estimated return temperature and the measured return temperature.
In an embodiment, calculating the estimated energy transfer comprises the control system determining an estimated energy transport extracted in the thermal energy exchanger from the fluid, determining an energy content stored in the thermal energy exchanger, and calculating the estimated energy transfer as a difference from the energy transport and the energy content.
In a further embodiment, determining the estimated energy transport comprises the control system determining an input temperature of the thermal energy exchanger, using the is measured supply temperature and a delay time in the supply pipe for the fluid to move from the first temperature sensor to the thermal energy exchanger, determining an output temperature of the thermal energy exchanger, using the measured return temperature and a delay time in the return pipe for the fluid to move from the thermal energy exchanger to the second temperature sensor, and calculating the estimated energy transport from the measured flow of fluid, the determined input temperature of the thermal energy exchanger, and the determined output temperature of the thermal energy exchanger.
In an embodiment, the control system receives a target energy transfer and controls the energy transfer by regulating the flow of fluid through the thermal energy exchanger based on a comparison of the target energy transfer and the estimated energy transfer.
In a further embodiment, regulating the flow of fluid through the thermal energy exchanger comprises the control system determining a target flow based on the comparison of the target energy transfer and the estimated energy transfer, and regulating the flow of fluid through the thermal energy exchanger based on a comparison of the target flow and the measured flow of fluid.
In addition to a method of controlling energy transfer of a thermal energy exchanger 1n an HVAC system, the present invention also relates to a control system for controlling energy transfer of a thermal energy exchanger of an HVAC system. The control system comprises at least one processor configured to obtain from a flow sensor, a measured flow of fluid through the thermal energy exchanger; obtain from a first temperature sensor, a supply temperature of the fluid in a supply pipe connected to an entry of the thermal energy exchanger; obtain from a second temperature sensor, a return temperature of the fluid in a return pipe connected to an exit of the thermal energy exchanger; determine flow-dependent model parameters for modelling performance of the thermal energy exchanger, using one or more measurement data sets, each measurement data set including for a respective measurement time a value of the measured flow of fluid, a value of the measured supply temperature of the fluid, and a value of the measured return temperature of the fluid; calculate an estimated energy transfer of the thermal energy exchanger, using the flow-dependent model parameters; and control the energy transfer of the thermal energy exchanger by regulating the flow of fluid through the thermal energy exchanger, using the estimated energy transfer.
In an embodiment, the processor is further configured to determine with the flow-dependent model parameters a delay time in the supply pipe for the fluid to move from the first temperature sensor to the thermal energy exchanger, and a delay time in the return pipe for the fluid to move from the thermal energy exchanger to the second temperature sensor.
In an embodiment, the processor is further configured to determine with the flow-dependent model parameters an energy transfer coefficient for the thermal energy exchanger.
In an embodiment, the processor is further configured to determine with the flow-dependent model parameters a secondary temperature associated with a secondary side of the thermal s energy exchanger.
In an embodiment, the processor is further configured to determine with the flow-dependent model parameters an exchange time for the fluid to replace the total fluid content of the thermal energy exchanger.
In an embodiment, the processor is further configured to determine the flow-dependent model parameters by determining an estimated return temperature of the fluid in the return pipe, and setting the flow-dependent model parameters such as to minimize a difference between the estimated return temperature and the measured return temperature.
In an embodiment, the processor is further configured to calculate the estimated energy transfer by determining an estimated energy transport, extracted in the thermal energy exchanger from the fluid, determining an energy content stored in the thermal energy exchanger, and calculating the estimated energy transfer as a difference from the energy transport and the energy content.
In an embodiment, the processor is further configured to determine the estimated energy transport by determining an input temperature of the thermal energy exchanger, using the measured supply temperature and a delay time in the supply pipe for the fluid to move from the first temperature sensor to the thermal energy exchanger, determining an output temperature of the thermal energy exchanger, using the measured return temperature and a delay time in the return pipe for the fluid to move from the thermal energy exchanger to the second temperature sensor, and calculating the estimated energy transport from the measured flow of fluid, the input temperature of the thermal energy exchanger, and the output temperature of the thermal energy exchanger.
In an embodiment, the processor is further configured to receive a target energy transfer, and s control the energy transfer by regulating the flow of fluid through the thermal energy exchanger based on a comparison of the target energy transfer and the estimated energy transfer.
In an embodiment, the processor is further configured to regulate the flow of fluid through the thermal energy exchanger by determining a target flow based on the comparison of the target energy transfer and the estimated energy transfer, and regulate the flow of fluid through the thermal energy exchanger based on a comparison of the target flow and the measured flow of fluid.
In addition to a method and a control system for controlling energy transfer of a thermal energy exchanger 1n an HVAC system, the present invention also relates to a computer program product comprising a non-transient computer-readable medium having stored thereon computer program code configured to control a processor of a control system for controlling energy transfer of a thermal energy exchanger of an HVAC system. The computer program code is configured to control the processor such that the processor performs the following steps: obtaining from a flow sensor, a measured flow of fluid through the thermal energy exchanger; obtaining from a first temperature sensor, a supply temperature of the fluid in a supply pipe connected to an entry of the thermal energy exchanger; obtaining from a second temperature sensor, a return temperature of the fluid in a return pipe connected to an exit of the thermal energy exchanger; determining flow-dependent model parameters for modelling performance of the thermal energy exchanger, using one or more measurement data sets, each measurement data set including for a respective measurement time a value of the measured flow of fluid, a value of the measured supply temperature of the fluid, and a value of the measured return temperature of the fluid; calculating an estimated energy transfer of the thermal energy exchanger, using the flow-dependent model parameters; and controlling the energy transfer of the thermal energy exchanger by regulating the flow of fluid through the thermal energy exchanger, using the estimated energy transfer.
In an embodiment, the computer program code is further configured to control the processor such that the processor performs steps of the method of controlling opening of a valve in an HVAC system, as outlined above.
The present invention will be explained in more detail, by way of example, with reference to the drawings in which:
In
As illustrated in
The controller 200 is configured to control the opening of the valve 204 in response to a setpoint received from a building control system or a user terminal, for example, a setpoint Qref for thermal energy (or power) to be transferred to a secondary side 3 of the thermal energy exchanger 1, specifically to a fluid oi the secondary side, e.g. to the air that is moved into a room. For the purpose of controlling the energy transfer Q, the controller 200 generates a control signal for the valve 204 or its actuator 24, respectively, based and depending on the received setpoint Qref, as will be described below in more detail.
In the following paragraphs, described with reference to
As indicated schematically in
As illustrated in
As illustrated in
In step S2, the control system 40, i.e. the computer system 4 or the controller 200, respectively, determines flow-dependent model parameters M for modelling the thermal energy exchanger 1, specifically, for modelling the performance of the thermal energy exchanger 1. The flow-dependent model parameters M are determined based on the recorded measurement data sets. As illustrated in
In an embodiment where the diameter D1 of the supply pipe 21 or at least the distance d1 between the first temperature sensor 201 aid the entry 11 of the thermal energy exchanger 1 are known, an initial value for the delay time tsup_delay associated with the supply pipe 21 is defined based on said distance d1 and diameter D1. Likewise, in an embodiment where the diameter D2 of the return pipe 22 or at least the distance d2 between the exit 12 of the thermal energy exchanger 1 and the second temperature sensor 202 are known, an initial value for the delay time tret_delay associated with the return pipe 22 is defined based on said distance d2 and diameter D2. Vice versa, the distances d1 and d2, between the first temperature sensor 201 and the entry 11 of the thermal energy exchanger 1 or between the exit 12 of the thermal energy exchanger 1 and the second temperature sensor 202, respectively, can be estimated from derived values of the delay time tsup_delay associated with the supply pipe 21 or the delay time tret_delay associated with the return pipe 22, respectively, if the diameter D1 of the supply pipe 21 and/or the diameter D2 of the return pipe 22 (or a corresponding size of the valve 204) is/are known.
As illustrated in
Q=Q
transport
−Q
content (1)
The energy transport Qtransport extracted in the thermal energy exchanger 1 from the fluid depends on the actual flow Φact, the input temperature Tin at the entry 11 of the thermal energy exchanger 1, and the exit temperature Tout at the exit 12 of the thermal energy exchanger 1, cp being a specific heat constant of the fluid and p being a density of the fluid:
Q
transport=Φact·ΔT=Φact·cp·p·(Tin−Tout) (2)
The input temperature Tin is defined by the supply temperature Tsup measured in the supply pipe 21 and the delay time tsup_delay for the fluid to move from the first temperature sensor 201 to the entry 11 of the thermal energy exchanger 1, whereby the value of Tin corresponds to the value of the supply temperature Tsup measured previously with a delay of delay time tsup_delay:
T
in
=f(Tsup, tsup_delay). (2.1)
The output temperature Tout is defined by the return temperature Tret measured in the return pipe 22 and the delay time tret_delay for the fluid to move from the exit 12 of the thermal energy exchanger 1 to the second temperature sensor 202, whereby the measured value of the return3 temperature Tret corresponds to the preceding value of the output temperature Tout at the time t=t−tret_delay in the past:
T
out
=f(Tret, tret_delay). (2.2)
The energy content Qcontent stored in the thermal energy exchanger 1 is defined by a volume V (content) of the thermal energy exchanger 1 and a primary temperature Tprimary of the thermal energy exchanger 1, cp being the specific heat constant of the fluid and p being the density of the fluid:
Q
content
=V·c
p
·p·T
primary. (3)
The primary temperature Tprimary of the thermal energy exchanger 1 is calculated as an average value from the input temperature Tin and the exit temperature Tout of the thermal energy exchanger 1:
T
primary=1/2(Tin+Tout). (2.1)
The volume V (content) of the thermal energy exchanger 1 is defined by the exchange time texchange of the thermal energy exchanger land the actual flow Φact:
V=t
exchange·Φact (3.2)
The energy transfer Q (Qest) from the thermal energy exchanger 1 to its secondary side 3 is defined by the primary temperature Tprimary of the thermal energy exchanger 1, the secondary temperature Tsecondary of the thermal energy exchanger 1, and the energy transfer coefficient Ctrans for the thermal energy exchanger 1:
Q=C
trans·(Tprimary−Tsecondary) (4)
Using relations (1)-(4), the control system 40, i.e. the computer system 4 or the controller zoo, respectively, determines the flow-dependent model parameters M, including supply delay time tsup_delay, return delay time tret_delay, energy transfer coefficient Ctrans, secondary temperature Tsecondary, and exchange time texchange, from the recorded data sets with the measured operating parameters, including flow Φact, supply temperature Tsup, and return temperature Tret. Using a plurality of data sets with the measured operating parameters, the control system 40, i.e. the computer system 4 or the controller 200, respectively, defines a set of equations for the relations (1)-(4) for determining the flow-dependent model parameters M. Specifically, the control system 40, i.e. the computer system 4 or the controller 200, respectively, uses initial estimated values for the flow-dependent model parameters M to determine an estimated value for the return temperature Tret_estimated and iteratively improves the flow-dependent model parameters M by applying an optimization function to minimize the error (e.g. mean squared error, MSE) or difference (e.g. mean square difference, MSD) between the estimated return temperature Tret_estimated and the actually measured return temperature Tret.
In accordance with the configuration and/or mode for recording the measurement data sets and determining the model parameters M in off-line batch processing, on-line calibration phase, and/or on an ongoing basis, in step S3, the control system 40, i.e. the computer system 4 or the controller 200, respectively, uses the (current) model parameters M to calculate an estimated value of the energy transfer Qest.
In step S4, the controller zoo determines a target flow Φref based on a comparison of the setpoint Qref for thermal energy (or power) to be transferred and the currently estimated value of the energy transfer Qest.
In step S5, the controller zoo controls the flow through thermal energy exchanger 1 by adjusting the opening (i.e. the orifice) of the valve 204 to regulate the flow Φ of the fluid through the thermal energy exchanger 1 based on a comparison of the determined target flow Φref and the currently measured actual flow Φact.
As indicated schematically, in step S6, the control system 40, i.e. the computer system 4 or the controller 200, respectively, continues processing in step S1 or step S3, respectively. As depicted by step S6″, in the on-line mode of operation with continuous recording of measurement data sets, processing is continued in step S1 by performing the steps S1 and S2 of block B1 for determining the model parameters M; whereas in the off-line batch processing or on-line calibration phase modes, processing continues in step S3 by performing steps S3 and S4 of block B2 for controlling the energy transfer. One skilled in the art will understand that block B1 for determining the model parameters M may be executed periodically, on request, and/or depending on defined system criteria.
It should be noted that, in the description, the sequence of the steps has been presented in a specific order, one skilled in the art will understand, however, that the order of at least some of the steps could be altered, without deviating from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 00750/18 | Jun 2018 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/065124 | 6/11/2019 | WO | 00 |
