Patent Description:
In HVAC installations, which are used for heating, cooling, air conditioning and venting of rooms and buildings, flow rates of fluids have to be permanently adapted to current requirements. The requirements depend on parameters determining the demand for heating, ventilation and air conditioning within the building, such as outside temperature, humidity, solar radiation, as well as the number of people or other organisms, machines and devices within the building, which may consume fresh air and emit energy. In particular fluid flow within heat exchangers as well as mergers and splitters has to be controlled for optimizing energy exchange between the fluids.

A method for operating a heat exchanger is disclosed in <CIT>. A heat transfer medium flows through the heat exchanger on a primary side. The heat transfer medium enters the heat exchanger with a first temperature and exits the heat exchanger with a second temperature, and emits on a secondary side a heat flow to a secondary medium flowing through the heat exchanger in the case of heating or, in case cooling, absorbs a heat flow from the secondary medium which enters the heat exchanger with third temperature and exits the heat exchanger again with a fourth temperature, wherein the heat exchanger is capable of transferring a maximum heat flow. In a control system at least three of the four temperatures are measured and the respective saturation level of the heat exchanger is determined from the measured temperatures and is used for controlling the operation of the heat exchanger.

<CIT> describes a method and device for determining the state of a heat transfer device through which at least two heat media flow and wherein heat is transferred between the at least two heat media in a heat transfer process. For this purpose, a) at least one physical measuring variable of at least one of the heat media is measured during heat transfer, and b) a value of at least one state variable depending on the measuring value(s) and characterizing the state of the heat transfer device is determined based on the measured values or measuring signals of the measured variable(s).

In HVAC installations, heat and/or cold are/is normally generated centrally in order to be led via a suitable heat transfer medium, e.g. water, to the respective premises where the heat and/or cold are/is emitted into the buildings or at least certain rooms thereof via local heat exchangers. The heat flow emitted or absorbed by the local heat exchanger, which is required for achieving a predetermined room temperature, is often controlled in such a manner that the mass flow on the primary side of the heat transfer medium is changed accordingly.

Alternatively, outside air can be centrally cooled and then led to the respective premises which may be single rooms or stories of buildings or entire buildings in networks for districts comprising several buildings (so-called district heating and/or district cooling networks). Especially within the latter, diameters of central air ducts leading to and away from a central heat exchanger, may be several meters wide in diameter. Due to boundary curve effects of the airflow inside such ducts with relatively large diameters, flow rates may not be measured accurately anymore by means of sensors only placed at the walls of the ducts.

Hence, according to the prior art, a plurality of flow sensors is placed within such ducts in order to provide a grid of sensors equally distributed along the cross-section of the duct in order to overcome the boundary curve effects. The sensors are usually arranged along several rods, which extend between opposing walls of the duct.

However, such arrangements of sensors according to the prior art have several disadvantages. First of all, by arranging the rods within the fluid flow, they become obstacles impairing flow characteristics. Flow resistance is increased and thus energy demands for pumps or fans moving the fluid rise. Moreover, the sensors as well as the rods carrying them are prone to fouling. Residues like dust or dirt may build up on the rods and sensors, which again impairs flow characteristics. On the other hand, measurement accuracy of the sensors may be decreased. Finally, installing, operating and maintaining sensor arrangements produce costs with a negative economic effect for the entire HVAC installation.

The same as outlined above for flow sensors may also hold for enthalpy sensors used for measuring the enthalpy of the first or second fluid, in order to derive therefrom an enthalpy difference and, thus, an amount of thermal energy exchanged between the fluids. Even though, their installation in relatively large ducts may be less problematic than for flow sensors, the enthalpy sensors remain still an important factor in assembly, operation and maintenance and, thus, the overall costs of the HVAC installation.

In view of the disadvantages of flow and enthalpy measurement arrangements known from the prior art as described above, it is an object of the present invention to provide a method and a system for determining flow rates and/or enthalpy differences in a heat exchanger of an HVAC installation, which method and system do not have at least some the disadvantages of the prior art. In particular, it is an object of the present invention to provide a method and a computer system for determining the flow rates and/or enthalpy differences in an HVAC installation with a reduced number of sensors.

According to the present invention, these objects are achieved through the features of the independent claims <NUM>, <NUM> and <NUM>. In addition, further advantageous embodiments follow from the dependent claims and the description.

In a method according to the present invention for operating an HVAC installation, a set of enthalpies and flow rates as variables of the HVAC installation is monitored and used for controlling the operation of said HVAC installation, comprising the steps of: (a) dividing said set of enthalpies and flow rates into a first and second subset; (b) measuring each variable of said first subset with a related sensor arranged in said HVAC installation; and (c) determining the variables of said second subset from the measured variables of said first subset by using a mathematical and/or empirical relationship between the variables of said first and second subset.

Thereby, the method according present invention has the decisive advantage over the prior art that at least one of the sensors for measuring the value of the flow rates or the value of the enthalpies may be omitted or replaced by an auxiliary, non-calibrated sensor. The omitted sensors are so to say virtualized. By providing virtual sensors in a method according to the present invention, the number of installed sensors is reduced in comparison to the prior art. Thereby, the present invention enables to reduce the number of sensors or use cheaper auxiliary sensors, maintain desired flow characteristics within the ducts or any fluid lines in general and helps to minimize the overall costs of HVAC installations.

In an embodiment of the invention, at least one non-calibrated auxiliary sensor is provided to measure one variable of said second subset, and said at least one non-calibrated auxiliary sensor is calibrated by using the respective determined variable of said second subset.

Such a way of calibrating a sensor enables to utilize sensors of a certain quality or arrange sensors in such a way, which helps to minimize costs and impacts on fluid lines.

In another embodiment of the invention, at least one of said variables of said first subset is kept constant. Thereby, the number of variables to be determined by actual measurements can be further reduced.

The actual value of said constant variable may be only once measured with a sensor.

The single measurement can be used for deriving at least one reference value therefrom.

According to the invention a set of values associated with a heat exchanger of the HVAC installation is determined, the set comprising: flow rates and enthalpy differences of a first fluid and a second fluid in a configuration for exchanging thermal energy between the fluids through the heat exchanger, the enthalpy differences each being a difference between a fluid inlet enthalpy and a fluid outlet enthalpy of the fluids when entering and exiting the heat exchanger, respectively, whereby a subset of values comprising at least two values of the flow rates and the enthalpy differences is measured; and the complete set of values is determined, using the measured subset of the values.

For example, the value of the second flow rate and the value of the second enthalpy difference may be acquired by means of one or more sensors. Then the value of the first flow rate may be calculated as a function of the value of the first enthalpy difference the value of the second enthalpy difference, and the value of the second flow rate. Alternatively or additionally, the value of the first enthalpy difference may be calculated as a function of the value of the first flow rate, the value of the second enthalpy difference, and the value of the second flow rate.

In another embodiment, a full or complete set of values of an energy balance equation set up with respect to an energy related envelope boundary of a heat exchanger may be determined. The envelope boundary delimits the heat exchanger as a thermodynamic system e. by walls, insulation, etc. Any space outside the boundary may be regarded as surroundings or environment of the heat exchanger.

In another embodiment, the energy balance equation comprises at least one efficiency factor representing a thermodynamic loss with respect to the respective envelope boundary. Thermodynamic loss may occur, when heat a transfers takes place across the boundary besides as through the fluids, such as by heat transmission through walls or insulation. Also dissipation of energy within the fluids when passing through the heat exchanger may be taken into account in the efficiency factor. Ideally, the efficiency factor would yield to having a value of one and may thus be omitted.

In just another embodiment of the invention, at least one of the values of the flow rates and the enthalpy differences is used for calibrating a non-calibrated auxiliary flow sensor or a non-calibrated auxiliary enthalpy sensor for acquiring the value of one of the flow rates or enthalpy differences, respectively.

In particular, at least one of the value of the first flow rate or the value of the second flow rate may be used for calibrating an auxiliary flow sensor which is used for acquiring the value of the first flow rate or the value of the second flow rate when the second fluid or the first fluid, respectively is essentially stationary within the heat exchanger. In other words, the calibrated auxiliary flow sensor may be used for acquiring the value of the first flow rate or the value of the second flow rate when the second fluid or first fluid, respectively, is essentially not flowing. This may be the case, when for example during periods where neither heating nor cooling is required, the first fluid travels through the heat exchanger to the respective premises where it is required while the second fluid is not being processed.

As an auxiliary flow sensor, a non-calibrated flow sensor may be used which is not arranged as the flow sensors according to the prior art described above. The auxiliary sensor may be designed such that it is of especially low-cost and does not protrude into the respective fluid line in an undesired way. In calibrating the auxiliary sensor during a cooling or heating period, correction factors for measurement signals gained by the auxiliary sensor may be determined which allow for acquiring the respective flow rate with sufficient accuracy.

In another embodiment of the invention, the non-calibrated auxiliary enthalpy sensor comprises a non-calibrated auxiliary temperature sensor and/or a non-calibrated auxiliary humidity sensor used in conjunction with a look up table or function for determining a value of at least one of said enthalpies.

In a further embodiment of the invention, at least one of the values of the flow rates is a predetermined constant value.

In particular, at least one of the value of the first flow rate and the value of the second flow rate may be a predetermined constant value. Some heat exchangers or HVAC installations work with constant flow rates. If the constant value of such a constant flow rate is known, the respective other flow rate can be calculated by using a transposed energy balance of the heat exchanger.

In another embodiment of the invention, the predetermined constant value is determined using a temporary flow sensor, temporarily placed for measuring the value of the respective flow rate.

The predetermined constant value may be acquired by means of the temporary sensor temporarily placed for measuring the value of the first flow rate or the value of the second flow rate, respectively.

The temporary sensor may be placed, for example, in the first fluid line or the second fluid line transporting the first and the second fluid, respectively. By means of the temporary sensor, a one-time measurement of at least one of the flow rates to be acquired may be carried out. Based on this measurement, the predetermined constant value may be set up.

In just another embodiment of the invention, at least one of the values of the flow rates is determined by means of an operational parameter of a pump, a fan, a valve and/or a damper configured to respectively move, direct, block, split or merge at least one of the fluids.

In particular, the value of the first flow rate and/or the value of the second flow rate may be determined by means of such an operational parameter, which may be a frequency, a current, a voltage, a pressure, a position or the like. The at least one pump or fan may be at least partly arranged within and/or connected to the first or second fluid line. By using the operational parameter, a flow sensor for measuring the flow rate of the respective fluid driven or moved by the pump or fan may be omitted. By omitting the flow sensor, the respective flow rate is determined by a virtual sensor.

The operational parameter may be a variable operational parameter of a drive of the pump, fan, valve or damper.

The operational parameter may be a variable frequency of a drive of the pump and/or fan. The variable frequency maybe a rotational speed of the drive or a shaft attached thereto for driving the pump or fan. Alternatively or additionally, other operational parameters of the pump, the fan and/or a respective drive, such as electrical currents, voltages and/or hydraulic pressures, may be used as required within a certain application for calculating the operational parameter from which at least one of the flow rates may be derived.

In another embodiment of the invention associated with a heat exchanger of the HVAC installation the method comprises the steps of: recording in a computer at least one measurement data set, which includes a plurality of data points representing measured values of at least one of the enthalpy differences in dependence of values of the respective flow rate; calculating by the computer a curve or lookup table of values of the enthalpy difference from the at least one measurement data set; and predicting the enthalpy difference or the respective flow rate by looking up a corresponding value of the respective flow rate or of the enthalpy difference, respectively, based on the curve or lookup table.

In other words, calculating the curve or lookup table may involve calculating a function of the second flow rate based on the at least one measurement dataset.

The calculation of the curve or lookup table may involve calculating based on the at least one measurement data set a function of an inlet enthalpy difference and/or an outlet enthalpy difference, the inlet enthalpy difference being a difference between a first fluid inlet enthalpy and a second fluid inlet enthalpy, and the outlet enthalpy difference being a difference between a first fluid outlet enthalpy and a second fluid outlet enthalpy.

Alternatively or additionally, calculation of the curve or lookup table involves calculating based on the at least one measurement data set a function of an inlet temperature difference and/or an outlet temperature difference, the inlet temperature difference being a difference between a first fluid inlet temperature and a second fluid inlet temperature, and the outlet temperature difference being a difference between a first fluid outlet temperature and a second fluid outlet temperature.

Further, at least one of the values of the flow rates and the enthalpies may be temporarily measured by means of at least one of a temporarily placed flow sensor and a temporarily placed enthalpy sensor, respectively, preferably during a commissioning of the heat exchanger, for establishing a curve fit of the curve of values of the enthalpy difference with respect to the at least one measurement dataset.

Especially, establishing the curve fit may be based on at least one curve fit coefficient.

By measuring or determining the enthalpies of the first and of the second fluid and temporarily the second flow rate of the second fluid, the second enthalpy difference of the second fluid may be predicted by determining the curve fit based on the at least one curve fit coefficient. Once the relationship is established, it can be used to calculate the second flow rate when the temporary sensor is not present anymore.

With the calculated second flow rate, the first flow rate may be calculated.

The at least one curve fit coefficient may be derived from a power or a heat transfer fit function of the thermal energy exchanged dependent on the value of the respective flow rate.

Alternatively, the at least one curve fit coefficient may be derived from an enthalpy fit function of the value of the enthalpy difference dependent on the value of the respective flow rate.

Furthermore, the at least one curve fit coefficient may be derived from a temperature fit function of a value of a temperature difference dependent on the value of the respective flow rate, the temperature difference being a difference between an outlet temperature of the respective fluid exiting the heat exchanger and a fluid inlet temperature of the respective fluid entering the heat exchanger.

In another embodiment, a method according to the present invention further comprises normalizing at least one of the measurement data set, data point or any curve or lookup table derived therefrom in order to obtain at least one of a normalized data set, normalized data point, normalized curve or normalized lookup table. Normalization may not only be achieved by using an average, but alternatively e.g. simply a difference, or some other function of the fluid values.

In other words, though the curve fit and possibly normalization operations, only one of the value of the second flow rate or the value of the second enthalpy difference needs to be measured or otherwise determined in order to then look up the corresponding value not measured in the curve or normalized curve. The curve or normalized curve may therefore be used as or at least partly constitute a look up table for predicting enthalpy differences or flow rates. This helps to replace at least one sensor by a virtual sensor. When measuring a flow rate, the corresponding enthalpy difference may be predicted. Thus, two enthalpy sensors for measuring the respective enthalpy difference may be omitted. Alternatively, one of the enthalpy differences may be measured and a sensor for acquiring the corresponding flow rate may be omitted.

In another embodiment of the invention, at least one of the values of the flow rates or the enthalpies is derived from a corresponding value of a branch flow rate or a branch enthalpy of a partial fluid stream or flow of at least one of the fluids.

Hence, not for all of the branches or their combinations, respective flow rates and enthalpies have to be measured. By deriving at least some of the flow rates and enthalpies, at least one more sensor may be calibrated, normalized, parameterized, and/or virtualized.

The second fluid is a liquid or liquid mixture. In the HVAC installation, the gas is air and the liquid may be water, glycol or a mixture thereof.

In addition to a method of determining a set of values associated with a heat exchanger, the present invention also relates to an arrangement, in particular an HVAC installation or a heat exchanger network according to independent claim <NUM>.

In another embodiment of the inventive arrangement and according to another aspect which on its own can be regarded an independent solution of the above-mentioned objects underlying the present invention, the arrangement further comprises at least one of: a mixing unit and a splitting unit merging or diverging, respectively, a number m of fluids and partial fluids having a number of m respective flow rates and partial flow rates and a number of m respective enthalpies and partial enthalpies, wherein the system is configured to measure a number of maximally m - <NUM> of the flow rates, partial flow rates enthalpies and partial enthalpies, and configured to calculate from the measured maximally m - <NUM> flow rates, partial flow rates enthalpies, and partial enthalpies at least one of the flow rates, partial flow rates, enthalpies, and partial enthalpies.

Hence, for each and every merging and/or diverging of fluids, at least for one of the merged and/or diverged streams, respective flow rates, temperatures, humidities, and/or enthalpies may be calculated based on the measurements relating to the other streams. This helps to further omit sensors and/or to replace sensors according to the prior art with auxiliary sensors. Additionally or alternatively, at least one more sensor may be calibrated, normalized, parameterized, and/or virtualized.

In addition to a method and a system for determining a set of values associated with a heat exchanger, the present invention also relates to a computer program product according to independent claim <NUM>.

In further embodiments, the computer program code is configured to control the one or more processors of the computer such that the computer implements embodiments of the method described above.

The present invention will be explained in more detail, by way of example, with reference to the drawings in which:.

<FIG> shows a schematic diagram illustrating heat exchange between a first fluid <NUM> and a second fluid <NUM> in a system <NUM> according to the present invention. The system <NUM> comprises a firstfluid line <NUM> for guiding the first fluid <NUM> and a second fluid line for guiding the second fluid <NUM>. The first fluid line <NUM> and the second fluid line <NUM> are each connected to a heat exchanger <NUM>, wherein thermal energy is exchanged between the first fluid <NUM> and the second fluid <NUM>.

The first fluid line <NUM> and the second fluid line <NUM> each have an inlet section 101i, 102i, and an outlet section 101o, 102o, respectively. The inlet sections 101i, 102i lead to and the outlet sections 101o, 102o lead away from the heat exchanger <NUM> and can be at least partially integrated therein. The first fluid line <NUM> and the second fluid line <NUM> maybe each provided with enthalpy sensors <NUM>, such as a first enthalpy sensor <NUM> and a second enthalpy sensor <NUM>, respectively. In particular, the inlet sections 101i, 102i may be each provided with an inlet enthalpy sensor 111i and 112i, respectively. The outlet sections 101o, 102o may be each provided with an outlet enthalpy sensor 111o and 112o, respectively. The enthalpy sensors <NUM>, 111i, 111o, <NUM>, 112i, 112o may be located on an energy-related envelope boundary <NUM> of the heat exchanger <NUM> or at least in the vicinity of the envelope boundary <NUM> such that respective inlet and outlet enthalpies of the first fluid <NUM> and the second fluid <NUM> may be measured with a satisfying accuracy.

The envelope boundary <NUM> separates the heat exchanger <NUM> as a thermodynamic system from an environment <NUM> surrounding it. The envelope boundary <NUM> may comprise any kind of walls, isolation or alike. Any heat crossing the boundary of the heat exchanger other than through the fluids <NUM>, <NUM> and losses due to entropy generation within the heat exchanger <NUM> due to irreversibilities associated with heat transfer, fluid friction, and the maximum capacity rate of the heat exchanger limiting heat transfer between the fluids <NUM>, <NUM> is considered as a thermodynamic loss. Such losses are included in a respective efficiency factor η of the heat exchanger.

Flow sensors <NUM>, such as a first flow sensor <NUM> and a second flow sensor <NUM> may be at least partially placed within or connected to the first fluid line <NUM> and the second fluid line <NUM>, respectively, in such a way that a first flow rate ϕ<NUM> of the first fluid <NUM> and a second flow rate ϕ<NUM> of the second fluid may be measured. Additionally or alternatively, an auxiliary flow sensor <NUM><NUM>' maybe at least partially arranged within or connected to the first fluid line <NUM>, such that the auxiliary flow sensor <NUM>' may be calibrated for acquiring the value of the first flow rate ϕ<NUM>.

Pumps or fans <NUM>, such as a first pump or fan <NUM> and a second pump or fan <NUM> are partly arranged within the first fluid line <NUM> and the second fluid line <NUM> or connected thereto for moving the first fluid <NUM> and the second fluid <NUM> through the fluid lines <NUM>, <NUM>, respectively, and thus through the heat exchanger <NUM>. The first and the second pump or fan <NUM>, <NUM> may be driven by motors or drives <NUM>, such as a first motor or drive <NUM> and a second motor or drive <NUM>, respectively. The motors <NUM>, <NUM>, <NUM> may be provided with meters <NUM>, such as a first meter <NUM> and a second meter <NUM>, respectively, for measuring a variable frequency of the first drive <NUM> and/or the second drive <NUM> and/or the first pump or fan <NUM> and/or the second pump or fan <NUM>, respectively.

The system <NUM> further comprises transmission lines <NUM> for transmitting data and/or information between the enthalpy sensors <NUM>, <NUM>, <NUM>, flow sensors <NUM>, <NUM>'. <NUM>, <NUM>, meters <NUM>, <NUM>, <NUM> and a computer <NUM>. The computer <NUM> comprises and/or is connected to at least one processor <NUM> and can read from and/or write onto a computer-readable medium <NUM> for reading therefrom and/or storing thereon computer program code configured to control the one or more processors <NUM> of the computer <NUM>.

<FIG> shows an exemplary block diagram with steps S11 to S14 for determining the first flow rate ϕ<NUM> of the first fluid <NUM> in line with a method according to the present invention. In the first step S11, the value of the second flow rate ϕ<NUM> of the second fluid <NUM> is determined.

Therefore, the second flow rate may be either measured by means of the second flow sensor <NUM> and/or the second meter <NUM>. Alternatively or additionally, the value of the second flow rate ϕ<NUM> is predicted by looking up its value as described in detail reference to <FIG> further down below.

A function for calculating the value of the first rate ϕ<NUM> or the value of the first enthalpy difference ΔH<NUM>, respectively, may be derived from an energy balance equation set up with respect to the energy-related envelope boundary <NUM> of the heat exchanger <NUM>. The first fluid <NUM> and the second fluid <NUM> may be assigned to a primary or secondary side of the heat exchanger <NUM> which is configured to exchange energy between the primary side and the secondary side as desired. The energy balance equation is defined as follows: <MAT> wherein ϕ<NUM> is the flow rate of the first fluid, ϕ<NUM> is the flow rate of the second fluid, ΔH<NUM> a first enthalpy difference and ΔH<NUM> is a second enthalpy difference, Q is the exchanged amount of thermal energy, and η represents the efficiency factor of the heat exchanger.

The first enthalpy difference ΔH<NUM> is defined as the magnitude of the difference between the first fluid inlet enthalpy H<NUM>,i and the first fluid outlet enthalpy H<NUM>,o: <MAT>.

The second enthalpy difference ΔH<NUM> is defined as the magnitude of the difference between the second fluid inlet enthalpy H<NUM>,i and the second fluid outlet enthalpy H<NUM>,o: <MAT>.

The efficiency factor η is used as required in order to take into account any thermal losses occurring when exchanging thermal energy between the first fluid <NUM> and the second fluid <NUM> within the heat exchanger <NUM>. Such thermal losses would include any thermal energy crossing the boundary <NUM> (e.g. walls/insulation) surrounding the heat exchanger <NUM> other than through the fluids <NUM>, <NUM>.

In step S12, a value of the second enthalpy difference ΔH<NUM> of the second fluid <NUM> is determined by means of the second inlet enthalpy sensor 112i and the second outlet enthalpy sensor 112o. In step S13, the first enthalpy difference ΔH<NUM> of the first fluid <NUM> is measured by means or the first inlet enthalpy sensor 111i and the first outlet enthalpy sensor 111o. Alternatively or additionally, the second enthalpy difference ΔH<NUM> is predicted by looking up its value as described in detail with reference to <FIG> further down below.

In step S14, the first flow rate ϕ<NUM> is calculated by the computer <NUM> using the energy balance from equation (<NUM>) transposed as follows: <MAT>.

Hence, in the embodiment of the method according to the present invention illustrated in <FIG>, the auxiliary flow sensor <NUM>' may be only used in order to be able to determine the first flow rate ϕ<NUM> when the second flow rate ϕ<NUM> approximates zero, i.e. when the second fluid <NUM> becomes essentially stationary within the heat exchanger <NUM>. Therefore, the auxiliary flow sensor <NUM>' can be calibrated in that its output value is correlated by means of the computer <NUM> to the first flow rate ϕ<NUM> of the first fluid <NUM> as calculated in step S14 during times when the second fluid <NUM> is flowing through the heat exchanger with a second flow rate ϕ<NUM> which is sufficient for the calculation.

<FIG> shows a schematic block diagram of another embodiment of a method according to the present invention comprising steps S21 to S24. In steps S21 and S22, in line with steps S11 and S12 described with reference to <FIG> above, the value of the second flow rate ϕ<NUM> and the value of the second enthalpy difference ΔH<NUM>, respectively, are determined.

In step <NUM>, the first flow rate ϕ<NUM> of the first fluid <NUM> is measured by means of the first flow sensor <NUM> or the auxiliary flow sensor <NUM>'. In step S24, the first enthalpy difference ΔH<NUM> of the first fluid <NUM> is calculated by the computer <NUM> based on the energy balance from equation (<NUM>) transposed as follows: <MAT>.

<FIG> shows a schematic block diagram of an embodiment of a method according to the present invention for predicting the second flow rate ϕ<NUM> as mentioned above with reference to <FIG> and <FIG>. In a step S31, a measurement dataset <NUM> is recorded which includes a plurality of data points <NUM> representing measured second values of the second enthalpy difference ΔH<NUM> in dependence of values of the second flow rate ϕ<NUM>.

<FIG> shows an exemplary schematic diagram of the dataset <NUM> with the plurality of data points <NUM>. A curve <NUM> may represent a respective average or trend of the data points <NUM>.

In step S <NUM> illustrated in <FIG>, the computer <NUM> is used for normalising the measurement dataset so that the measurement data set <NUM> with the data points <NUM> becomes a normalized data set 200n with data points 202n as shown in <FIG>. Normalization of the least one measurement dataset <NUM> is for example carried out by using a function of an inlet enthalpy difference ΔHin and/or an outlet enthalpy difference ΔHout. Such a function may be e.g. a logarithmic mean enthalpy difference (LMED): <MAT> wherein the inlet enthalpy difference ΔHin is a magnitude of the difference between a first fluid inlet enthalpy H<NUM>,i and a second fluid inlet enthalpy H<NUM>,i: <MAT>and wherein the outlet enthalpy difference ΔHout is a magnitude of the difference between a first fluid outlet enthalpy H<NUM>,o and a second fluid outlet enthalpy H<NUM>,o: <MAT>.

When using LMED as an example for calculating a logarithmic average of the second enthalpy difference ΔH<NUM> from the at least one measurement dataset, the function of the second flow rate ϕ<NUM> could be defined as: <MAT>.

In a step <NUM>, a curve fit is established by the computer <NUM> for creating a normalized curve 212n of second enthalpy differences ΔH<NUM> as shown in <FIG>. Based on the normalized curve 212n, the second flow rate ϕ<NUM> may be predicted. Once the relationship is established, it can be used to calculate the second flow rate ϕ<NUM> when a temporarily placed auxiliary flow sensor <NUM>' is not present anymore, i.e. it may be omitted because of being virtualized.

For example, the normalized curve 212n may established by determining an e.g. two-parameter curve fit based on two curve fit coefficients k<NUM>, k<NUM>. The second flow rate ϕ<NUM> is then determined based on the established normalized curve 212n according to: <MAT>.

For example, when using the two-parameter curve fit, the power or heat transfer Q would be calculated as: <MAT>.

In the alternative or additionally, the at least one curve fit coefficient k<NUM>, k<NUM> may be derived from an enthalpy fit function of the value of the enthalpy difference ΔH<NUM> dependent on the value of the respective flow rate ϕ<NUM>, ϕ<NUM>. For example, when using the two-parameter curve fit, the second enthalpy difference ΔH<NUM> would be calculated as: <MAT>.

In another alternative or further additionally, the at least one curve fit coefficient k<NUM>, k<NUM> may be derived from a temperature fit function of a value of a temperature difference ΔT<NUM>, ΔT<NUM> dependent on the value of the respective flow rate ϕ<NUM>, ϕ<NUM>. For example, when using the two-parameter curve fit, the temperature difference ΔT<NUM> would be calculated as: <MAT> wherein the second temperature difference ΔT<NUM>, ΔT<NUM> is the difference between an outlet temperature T<NUM>,o, T<NUM>,o of the respective fluid exiting the heat exchanger and a second fluid inlet temperature T<NUM>,i, T<NUM>,i of the respective fluid entering heat exchanger: <MAT>.

Finally, in a step <NUM>, a first flow rate ϕ<NUM> is calculated by means of the second flow rate ϕ<NUM> based on the transposed energy balance according to equation (4a) defined above.

Alternatively or additionally to the determination of the normalized curve 212n as explained above with reference to <FIG>, the curve <NUM> or normalized curve 212n may also be determined based on measured temperatures T<NUM>,i, T<NUM>,o, T<NUM>,i, T<NUM>,o, and temperature differences ΔT<NUM>, ΔT<NUM>, respectively. Therefore a characteristic heat transfer Qchar could be calculated as: <MAT> wherein Qchar is the exchanged amount of thermal energy already denoted in equation (<NUM>) above, and ΔTin is an inlet temperature difference calculated as: <MAT>.

Then a characteristic enthalpy difference ΔH<NUM>, char of the second fluid <NUM> could be calculated as: <MAT> wherein the second enthalpy difference ΔH<NUM> could be calculated as: <MAT> wherein cp,<NUM> is the specific heat constant of the second fluid <NUM>, and ΔT<NUM> is the second temperature difference of the second fluid <NUM> as calculated in equation (<NUM>) above.

As another example, if it is further assumed that fluid <NUM> is a liquid, such as water, glycol, or a mixture thereof, and fluid <NUM> is air, when no dehumidification takes place, Qchar could be calculated by: <MAT> <MAT> wherein the constant K includes the unchanging humidity and specific characteristics of an HVAV installation, in particular the heat exchanger <NUM> thereof.

<FIG> shows a schematic diagram illustrating an arrangement <NUM>, such as an HVAC installation, according to an embodiment of the present invention. The arrangement <NUM> comprises the system <NUM> similar to <FIG> as well as a zone <NUM>, a plant <NUM> and a mixing unit <NUM>. The system <NUM> in this context may be e.g. an air handling unit (AHU). The zone <NUM> may be e.g. a zone in a building or an area to be provided with processed fluids, such as fresh or warm air, as the first fluid <NUM>. The plant <NUM> may e.g. provide a stream of cool or hot liquid which is fed to the system <NUM> as the second fluid <NUM> on a primary side in order to cool or heat the first fluid <NUM>, e.g. air.

The first outlet fluid <NUM>o exiting the system <NUM> enters the zone <NUM> and is there used and/or processed. After usage and/or processing, the first fluid <NUM> exits the zone <NUM> as a partial fluid 1b, which is then fed, into the mixing unit <NUM>. In the mixing unit <NUM>, the partial fluid 1b is mixed with another partial fluid 1a. From mixing the partial fluids 1a and 1b in a desired mixing ratio, the first inlet fluid <NUM>i entering the system <NUM> is obtained. The partial fluid 1a may be e.g. air used in the zone <NUM>. The other partial fluid 1b may be e.g. outside or outdoor air. Hence, the partial fluid 1b could be regarded as a recycled air stream.

<FIG> shows a schematic illustration of the mixing unit <NUM> depicted in <FIG>. In the mixing unit <NUM>, two branch fluid lines, a branch fluid line 101a, and another branch fluid line 101b, both leading into the first fluid line <NUM>, in particular the inlet section of the first fluid line <NUM>i, which may therefore be regarded as a main fluid line. The branch fluid line 1a and the first fluid line <NUM> are each provided with an enthalpy sensor <NUM> and a flow sensor <NUM>. The other branch fluid line 101b is provided with a valve or flap <NUM> driven by the motor or drive <NUM> provided with a meter <NUM>.

By measuring a flow rate ϕ1a of the partial fluid 1a and a flow rate ϕ<NUM>,i of the first inlet fluid <NUM>i, a flow rate ϕ1b of the partial fluid 1a may be calculated. Ideally, the flow rates ϕ and branch flow rate ϕj of each of the branches a to N may be calculated by: <MAT>.

As an ideal mixture, the enthalpy H<NUM>,i of the first inlet fluid <NUM>i could then be derived. Ideally, the enthalpies H and branch enthalpies of each of the branches a to N may be calculated by: <MAT>.

Hence, any enthalpy sensors <NUM> or flow sensors <NUM> associated to the branch fluid line 101b for measuring the enthalpy or mass flow of the partial fluid 1b could be omitted Not for all of the branches or their combinations, respective flow rates and enthalpies have to be measured. By deriving at least some of the flow rates and enthalpies from equations (<NUM>) and (<NUM>) above, at least one more sensor may be calibrated, normalized, parameterized, and/or virtualized.

In turn, alternatively and/or additionally, the other branch fluid line 101b is provided with the valve or flap <NUM> for regulating the mixing process through the flow rate ϕ1b of the other partial fluid 1b. Similarly as with any pump or fan <NUM>, the flow rate ϕ1b of the other partial fluid 1b may be determined through an operational parameter, such as a position of the valve or flap <NUM>, the motor <NUM>, which may be obtained with the meter <NUM> as described above with reference to the system <NUM> and related sequences of steps shown in <FIG>.

<FIG> shows a diagram illustrating another arrangement <NUM>, such as a heat exchanger network, according to an embodiment of the present invention. The arrangement <NUM> comprises the system <NUM> similar to <FIG> with the heat exchanger <NUM>, and corresponding systems <NUM> comprising the further heat exchanger <NUM> and the auxiliary heat exchanger <NUM>, respectively. Moreover, the arrangement <NUM> comprises a further mixing unit <NUM> and a splitting unit <NUM>. In a similar manner as described with reference to <FIG> above, a further envelope boundary <NUM> and an auxiliary envelope boundary <NUM> may be defined for the further heat exchanger <NUM> and the auxiliary heat exchanger <NUM>, respectively.

The fluids <NUM>, <NUM> may diverge into partial fluids 1a, 1b, 1c, 1d, 1e, such as partial flows and streams, or merged therefrom in any desired number and configuration and involving respective branch fluid lines 101a, 101b, 101c, 101d, 101e. Further fluids <NUM> and additional fluids <NUM> may be used in configurations to exchange thermal energy with the fluid <NUM> in at least one further heat exchanger <NUM> and auxiliary heat exchanger <NUM>, respectively. A skilled person will understand that principles underlying embodiments of the present invention described with reference to <FIG> above, may be expanded to more complex setups as illustrated in <FIG> involving said partial fluids 1a, 1b, 1c, 1d, 1e, further fluids <NUM>, additional fluids <NUM>, and respective further and auxiliary heat exchangers <NUM>, <NUM> associated to any desired number of the systems <NUM>.

Within the further mixing unit <NUM> , three partial fluids 1a, 1b, 1c are mixed with each other in a desired mixing ration in order to obtain the first inlet fluid <NUM>i, <NUM> entering the heat exchanger or the respective envelope boundary <NUM>. Within the heat exchanger <NUM>, the first fluid <NUM> and the second fluid <NUM> may exchange thermal energy between each other as described above with reference to the system <NUM> and related sequences of steps shown in <FIG>. When exiting the heat exchanger <NUM> or the respective envelope boundary <NUM> as first outlet fluid <NUM>o,<NUM>, the first fluid <NUM> becomes a further first inlet fluid <NUM>i,<NUM> entering the further heat exchanger <NUM> or the respective envelope boundary <NUM>.

Within the further heat exchanger <NUM> or the respective further envelope boundary <NUM> of the further system <NUM>, the first fluid <NUM> and the further fluid <NUM> may exchange thermal energy between each other in a similar manner as described above with reference to the system <NUM> and related sequences of steps shown in <FIG>. The further fluid <NUM> enters the further heat exchanger <NUM> or the respective envelope boundary <NUM> as a further inlet fluid <NUM>i through a further fluid line <NUM>, in particular a further inlet fluid line <NUM>i. The further fluid <NUM> exits the further heat exchanger <NUM> or the respective envelope boundary <NUM> as a further outlet fluid <NUM>o through the further fluid line <NUM>, in particular a further inlet fluid line <NUM><NUM>. The first fluid <NUM> exits the further heat exchanger <NUM> as a further first outlet fluid <NUM>i,<NUM> and enters the splitting unit <NUM>.

Within the splitting unit <NUM>, the first fluid <NUM> as the further first outlet fluid <NUM>i,<NUM> from the fluid line <NUM>, in particular a further first outlet fluid line <NUM><NUM>,<NUM>, is split into a partial fluid 1d and a partial fluid 1e flowing through a branch fluid line 101d and a branch fluid line 101e, respectively. The partial fluid 1d may be handled in a desired manner, e.g. recycled, discharged, etc. The partial fluid 1e enters the auxiliary heat exchanger <NUM> as an auxiliary first inlet fluid <NUM>i,<NUM> through the branch fluid line 101e, in particular an auxiliary first inlet fluid line <NUM>i,<NUM>.

Within the auxiliary heat exchanger <NUM> or the respective auxiliary envelope boundary <NUM> of the auxiliary system <NUM>, the first fluid <NUM>, in particular the partial fluid 1e, and the auxiliary fluid <NUM> may exchange thermal energy between each other in a similar manner as described above with reference to the system <NUM> and related sequences of steps shown in <FIG>. The auxiliary fluid <NUM> enters the auxiliary heat exchanger <NUM> or the respective envelope boundary <NUM> as an auxiliary inlet fluid <NUM>i through an auxiliary fluid line <NUM>, in particular an auxiliary inlet fluid line <NUM>i. The auxiliary fluid <NUM> exits the auxiliary heat exchanger <NUM> or the respective envelope boundary <NUM> as an auxiliary outlet fluid <NUM>o through the auxiliary fluid line <NUM>, in particular an auxiliary outlet fluid line <NUM><NUM>. The partial fluid 1e exits the auxiliary heat exchanger <NUM> as an auxiliary first outlet fluid <NUM>o,<NUM>.

The fluid lines <NUM>, 101a-e, <NUM>i,<NUM>, <NUM>o,<NUM>, <NUM>i,<NUM>, <NUM>o,<NUM>, <NUM>i,<NUM>, <NUM>i,<NUM>, <NUM>o,<NUM>, <NUM>, <NUM>i, <NUM>o, <NUM>, <NUM>i, <NUM>o, <NUM>, <NUM>i, <NUM>o are provided with the enthalpy sensors <NUM> and/or the flow sensors <NUM> as required in a manner to calibrate, normalize, parameterize, and/or virtualize at least some of the sensors <NUM>, <NUM>, 111i, 111o, <NUM>, 112i, 112o, <NUM>, <NUM>', <NUM>, <NUM>, drives or motors <NUM>, <NUM>, <NUM>, meters <NUM>, <NUM>, <NUM>, and/or valves or dampers <NUM> in the sense of the present invention. Hence, at least one of the enthalpy sensors <NUM> and/or the flow sensors <NUM> may be omitted as described above with reference to the system <NUM> and related sequences of steps shown in <FIG>.

Deviations from the above-described examples are possible without departing from the inventive idea. A skilled person will understand without any difficulties that the first fluid <NUM> and the second fluid <NUM> may be any kind of combination of fluids, between which an exchange of thermal energy should be carried out. However, the present invention may be especially useful if the first fluid <NUM> is air flowing in the first fluid line <NUM> having a relatively large diameter, and the second fluid <NUM> is a liquid, such as water. The further fluid <NUM> and the auxiliary fluid may also be chosen or determined by whatever liquids or gasses are desired to be used in a heat exchange process, in particular for economizing, pre-heating, additional heating and/or super heating purposes as required.

The system <NUM> may comprise first fluid lines <NUM> with inlet sections 101i and outlet sections 100o as well as second fluid lines <NUM> with inlet sections 102i and outlet sections 100o, branch fluid lines 101a-e,further fluid lines <NUM>, further inlet fluid lines <NUM>i, further outlet fluid lines <NUM>o, auxiliary fluid lines <NUM>, auxiliary inlet fluid lines <NUM>i, auxiliary outlet fluid lines <NUM>o in whatever number and form desired, e.g. as ducts, tubes, pipes, hoses or alike, for leading the fluids <NUM>, <NUM>, <NUM>, <NUM> to the heat exchangers <NUM>, <NUM>, <NUM> and away therefrom. The heat exchangers <NUM>, <NUM>, <NUM> may be and/or comprise any kind of thermal heat exchanging devices designed according to the specifically desired requirements.

For measuring enthalpies, any desired number of enthalpy sensors <NUM>, first enthalpy sensors <NUM>, 111i, 111o and second enthalpy sensors <NUM>, 112i, 112o may be used at preferred positions along the envelope boundaries <NUM>, <NUM>, <NUM> of the heat exchangers <NUM>, <NUM>, <NUM>. The enthalpy sensors <NUM>, <NUM>, 111i, 111o, <NUM>, 112i, 112o may be combined temperature and humidity sensors which may comprise separated temperature and humidity sensors in whatever number and form required for measuring temperature and humidity of a gaseous fluid. If a humidity measurement is not required when handling a liquid fluid, such as water, the enthalpy sensors <NUM>, <NUM>, 111i, 111o, <NUM>, 112i, 112o may only comprise temperature sensors for measuring respective temperatures of the liquid fluids.

The flow sensors <NUM>, <NUM>', <NUM>, <NUM> may be any kind of flow sensor desired for measuring a volumetric flow and/or mass flow of the respective fluid <NUM>, <NUM>, <NUM>, <NUM> and deriving therefrom a mass flow. Therefore, the flow sensors <NUM>, <NUM>', <NUM>, <NUM>' <NUM> may comprise pressure sensors in any number and form required.

The pumps or fans <NUM>, <NUM>, <NUM> may be pumps or fans in any number and form required for moving the first fluid <NUM>, the second fluid <NUM>, the further fluid <NUM> and the auxiliary fluid <NUM>, respectively. Therefore, the pumps and fans <NUM>, <NUM>, <NUM> may comprise drives <NUM>, <NUM>, <NUM> in any number and form required for driving the pumps or fans <NUM>, <NUM>, <NUM>. The drives <NUM>, <NUM>, <NUM> may comprise motors, gears and transmission devices in whatever number and form required for driving the pumps or fans <NUM>, <NUM>, <NUM>. The pumps or fans <NUM>, <NUM>, <NUM> and/or the drives <NUM>, <NUM>, <NUM> may be provided with meters <NUM>, first meters <NUM> and/or second meters <NUM>, respectively, in whatever number and form desired for measuring an operational parameter of the pumps or fans <NUM>, <NUM> and/or the drives <NUM>, <NUM>, such as a frequency, current, voltage, pressure, position or alike.

The data transmission lines <NUM> may comprise any kind of wired or wireless connections allowing for exchanging analogue and/or digital information between all sensors <NUM>, <NUM>, 111i, 111o, <NUM>, 112i, 112o, <NUM>, <NUM>', <NUM>, <NUM>, drives or motors <NUM>, <NUM>, <NUM>, meters <NUM>, <NUM>, <NUM> and the computer <NUM> with its processor <NUM> may be any kind of local or distributed computer system. A skilled person will understand without difficulties that the computer <NUM> may comprise interfaces and converters in whatever number and form required for conditioning data or voltages received over the transmission lines <NUM> in such a way that the data or voltages can be computed by the processor <NUM> when carrying out instructions.

The instructions may be stored on the computer readable medium <NUM> in whatever number and form desired. The computer readable medium <NUM> maybe any kind of volatile and non-volatile storage means, which may be built into the computer, may be accessed by the computer through a public or private network, and/or maybe a portable storage medium such as a portable flash storage, optical data carrier, magnetic data carrier, or alike.

The measurement dataset <NUM> may comprise data points <NUM> in whatever number and form desired for generating curves <NUM>, normalized data points 202n and normalized curves 212n. Hence, data points <NUM> may comprise measured values in whatever number and form desired. Normalized data points 202n may be based on data points <NUM> in whatever number and form desired.

The arrangements <NUM>, <NUM> may be HVAC installations, heat exchanger networks, power plants, chemical facilities, pharmaceutical facilities, refineries or alike comprising systems <NUM>, zones <NUM>, plants, mixing units <NUM>, valves or dampers <NUM>, further mixing units <NUM>, splitting units <NUM>, further fluid lines <NUM> and/or auxiliary fluid lines <NUM> in whatever number and form required for a certain application. The zones <NUM>, plants, mixing units <NUM>, valves or dampers <NUM>, further mixing units <NUM>, splitting units <NUM>, further fluid lines <NUM> and/or auxiliary fluid lines <NUM> may be connected to each other, merged or split as required by a certain application.

The first fluid lines <NUM> with inlet sections 101i and outlet sections 100o as well as second fluid lines <NUM> with inlet sections 102i and outlet sections 100o, branch fluid lines 101a-e, further fluid lines <NUM>, further inlet fluid lines <NUM>i, further outlet fluid lines 403o, auxiliary fluid lines <NUM>, auxiliary inlet fluid lines <NUM>i, and/or auxiliary outlet fluid lines <NUM>o may be provided with sensors <NUM>, <NUM>, 111i, 111o, <NUM>, 112i, 112o, <NUM>, <NUM>', <NUM>, <NUM>, drives or motors <NUM>, <NUM>, <NUM>, meters <NUM>, <NUM>, <NUM>, and/or valves or dampers <NUM> in whatever number and form desired for measuring, determining, and/or controlling properties and operational parameters of the fluids <NUM>, <NUM>, <NUM>, <NUM>. The sensors <NUM>, <NUM>, 111i, 111o, <NUM>, 112i, 112o, <NUM>, <NUM>', <NUM>, <NUM>, drives or motors <NUM>, <NUM>, <NUM>, meters <NUM>, <NUM>, <NUM>, and/or valves or dampers <NUM> may be connected to each other, to the computer <NUM> and/or the processor <NUM> via data transmission lines <NUM> which may comprise any kind of wired or wireless connections allowing for exchanging analogue and/or digital information.

Claim 1:
A method for operating an HVAC installation (<NUM>, <NUM>), wherein a set of values associated with a heat exchanger (<NUM>) of the HVAC installation (<NUM>) as variables of the HVAC installation (<NUM>, <NUM>) is monitored and used for controlling the operation of said HVAC installation (<NUM>, <NUM>), the set of values comprising: flow rates (φ1, φ2) and enthalpy differences (ΔH1, ΔH2) of a first fluid (<NUM>) and a second fluid (<NUM>) in a configuration for exchanging thermal energy (Q) between the fluids (<NUM>, <NUM>) through the heat exchanger (<NUM>), the enthalpy differences (ΔH1,ΔH2) each being a difference between a fluid inlet enthalpy (H1,i, H2,i) and a fluid outlet enthalpy (H1o, H2,o) of the fluids (<NUM>, <NUM>) when entering and exiting the heat exchanger (<NUM>), respectively,
wherein the first fluid (<NUM>) is air, and the second fluid (<NUM>) is a liquid or liquid mixture, especially water, glycol or a mixture thereof,
the method comprising the steps of:
a. dividing said set of values of flow rates (φ1, φ2) and enthalpy differences (ΔH1, ΔH2) into a first and second subset;
b. measuring each variable of said first subset, comprising at least two values of: the flow rates (ϕ<NUM>, ϕ<NUM>) and the enthalpy differences (ΔH<NUM>, ΔH<NUM>), with a related sensor (<NUM>, <NUM>) arranged in said HVAC installation (<NUM>, <NUM>), comprising a first inlet enthalpy sensor (111i) and a first outlet enthalpy sensor (111o) for the measurement of the first enthalpy difference (ΔH<NUM>), the first inlet enthalpy sensor (111i) and the first outlet enthalpy sensor (111o) being configured for measuring temperature and humidity of the first fluid; and
c. determining the variables of said second subset from the measured variables of said first subset by using a mathematical and/or empirical relationship between the variables of said first and second subset.