Patent Description:
As people spend an estimated <NUM>% of their time indoors, Heating, Ventilating and Air Conditioning HVAC systems have become of great importance to everyday life and have a great impact on people's health and comfort. In the field of Heating, Ventilating and Air Conditioning, HVAC systems typically comprise a fluid transportation system connected to a heat exchanger arranged such as to be able to transfer thermal energy to or from the environment to be controlled (referred to hereafter as controlled environment) by means of a fluid circulating in said fluid transportation system.

Various thermal networks are known for enabling transfer of thermal energy from a (potentially shared) thermal energy source to one or more controlled environment(s), such as district heating, district cooling and low temperature networks. Alternatively, or additionally, thermal networks are known for enabling transfer of thermal energy from one or more controlled environment(s), whereby the controlled environment(s) act as an energy source, for example by capturing thermal energy as a by-product of an industrial process.

In thermal networks of the district heating type, the fluid circulating in the fluid transportation system is typically characterized by high supply temperatures (e.g. between <NUM> and <NUM>) from the thermal energy source, a thermal energy transfer device, such as a heat exchanger being arranged to decouple the district heating network from the thermal energy consumer (located or thermally coupled with the controlled environment).

In thermal networks of the district cooling type, the fluid circulating in the fluid transportation system is typically characterized by very low supply temperatures (e.g. between -<NUM> and <NUM>) from the thermal energy source, a thermal energy transfer device, such as a heat exchanger being arranged to decouple the district cooling network from the thermal energy consumer (located or thermally coupled with the controlled environment).

In thermal networks of the low temperature network type, also referred to as <NUM>th generation district heating, the fluid circulating in the fluid transportation system is typically characterized by moderate supply temperatures (e.g. between <NUM> and <NUM>) from the thermal energy source, a thermal energy transfer device, such as a heat pump being arranged to decouple the low temperature network from the thermal energy consumer (located or thermally coupled with the controlled environment). Furthermore, the thermal energy transfer device, such as a heat pump, is arranged to supplement the thermal energy provided by the thermal energy source, transferring the moderate temperature of the network to a higher or a lower temperature which can be used for heating, respectively cooling. Low temperature networks often incorporate renewable energy sources (e.g. ground heat) and can be used for both heating and cooling of buildings. In such networks, heat pumps are often used for space heating and domestic hot water, whereas in some cases cooling can be supplied directly using heat exchangers only.

<CIT> discloses a method of controlling an orifice of a valve in an HVAC system to regulate the flow of a fluid trough a thermal energy exchanger and adjust the energy transfer rate of the thermal energy exchanger in response to a demand value in view of efficiency constraints on an energy transfer rate.

<CIT> discloses a method and system for regulating the flow of a fluid trough a thermal energy exchanger by using an estimated energy transfer.

<CIT> discloses a method and system to regulate the flow of a fluid trough the thermal energy exchanger by determining an energy-per-flow gradient and controlling an opening of a valve depending on the determined energy-per-flow gradient.

However, it has been observed that known methods/ systems for operating HVAC systems comprising a thermal energy source and a thermal energy transfer device often operate sub-optimally, unreliably and/or are prone to failures.

It is an object of embodiments disclosed herein to at least partially overcome the disadvantages of known methods/ systems for operating HVAC systems comprising a thermal energy source and a thermal energy transfer device.

Applicant has observed that known methods/ systems for operating HVAC systems comprising a thermal energy source and a thermal energy transfer device often operate sub-optimally, unreliably and/or are prone to failures due to one or more of the following:.

Applicant has identified the cause of the above-mentioned issues as follows:.

Therefore, it is an object of the invention to provide a method/ system for operating HVAC systems comprising a thermal energy source and a thermal energy transfer device which enables optimal operation of the HVAC system, avoiding frequent interruptions in the operation of the energy transfer device; maximizing the transfer of thermal energy per unit of fluid flowing through the fluid transportation system; and avoiding breakdowns caused by freezing and/or condensation of the fluid in the energy transfer device and/or the fluid transportation system. According to the present invention, this object is achieved by the features of the independent claim <NUM>. In addition, further advantageous embodiments follow from the dependent claims and the description.

In particular, the above-identified objectives are addressed according to the present invention by a method of operating an HVAC system using a flow regulating device arrangec to regulate a flow rate of a fluid between a thermal energy source and a thermal energy transfer device. According to embodiments disclosed herein, the fluid is a gaseous fluid, such as air and/or a liquid, such as water. The term thermal energy source is used in the context of the present invention to refer to a source of both heating and cooling energy source. Correspondingly, according to embodiments of the HVAC system, the thermal energy source is configured to supply heat to the thermal energy transfer device - referred to as heating. Alternatively, or additionally the thermal energy source is configured to extract heat from the thermal energy transfer device - referred to as cooling.

According to particular embodiments of the present invention, the thermal energy source is part of a thermal network such as a district heating/ cooling or low temperature network, while the thermal energy transfer device is a heat exchanger. Alternatively or additionally, the thermal energy transfer device comprises a heat pump configured to supplement the thermal energy provided by the thermal energy source.

In a first step of the method, a supply temperature; a return temperature and a flow rate of the fluid are determined (continuously, pseudo-continuously and/or at intervals during operation of the HVAC system). According to embodiments of the present invention, the supply temperature; the return temperature and/or the flow rate of the fluid are measured in a supply fluid transportation line and/or a return fluid transportation line of the fluid transportation system connecting the thermal energy source and the thermal energy transfer device. Alternatively, or additionally, the supply temperature is determined based on a measurement of the return temperature and data indicative of the relationship between the supply temperature and the return temperature as a function of the flow rate. Alternatively, or additionally, the return temperature is determined based on a measurement of the supply temperature and data indicative of the relationship between the supply temperature and the return temperature as a function of the flow rate.

Based on the determined supply temperature; return temperature and flow rate of the fluid, the flow rate of the fluid is regulated such as to maintain a target temperature difference between the supply temperature and the return temperature. According to embodiments of the present disclosure, regulating the flow rate of the fluid such as to maintain a target temperature difference comprises:.

The flow rate of the fluid is regulated such as to maintain a target temperature difference while ensuring that the return temperature is above a minimum return temperature threshold and that the flow rate is above an operational flow rate threshold of the thermal energy transfer device. Adherence to these two criteria addresses the aim to ensure that the HVAC system operates optimally, with less interruptions and less prone to errors. Ensuring that the return temperature is above a minimum return temperature threshold avoids the thermal energy transfer device and/or the fluid transportation system from being damaged due to freezing and/or condensation of the fluid. Ensuring that the flow rate is above an operational flow rate threshold of the thermal energy transfer device helps avoid unnecessary interruptions in the operation of the HVAC system due to the thermal energy transfer device being forced to shut down due to insufficient flow rate. Furthermore, ensuring that the flow rate is above an operational flow rate threshold of the thermal energy transfer device prevents unnecessary wear of the thermal energy transfer device due to operation near or below optimum parameters.

According to embodiments of the present invention, in order to prevent the return temperature from dropping below the minimum return temperature threshold, the method further comprises increasing the flow rate if the return temperature is equal to or less than the sum of the minimum return temperature threshold and a temperature safety margin.

If, despite the flow regulating device being fully open, the return temperature is equal to or less than the sum of the minimum return temperature threshold and the temperature safety margin, according to embodiments of the present invention, the flow regulating device is closed off, preventing the flow of fluid to and/or from the thermal energy source. The flow regulating device is closed off to avoid damage due to the return temperature dropping below the minimum return temperature threshold. Alternatively, or additionally, the flow regulating device is closed off, if the flow rate is equal to or less than the sum of the operational flow rate threshold and the flow safety margin despite the flow regulating device being fully open. According to further embodiments disclosed herein, the flow regulating device is closed off upon detection of a sudden change of the return temperature, a sudden change of the return temperature being indicative of a malfunction and/or deactivation of the thermal energy transfer device. Hence, the method/system of the present invention is able to react to unforeseen events, such as a malfunction of the thermal energy transfer device. The terms fully open and closed off as used herein with respect to the flow regulating device also comprise the flow regulating device being set to a (defined) maximum flow rate and a minimum flow rate respectively.

Alternatively, or additionally, if the flow regulating device is fully open and the return temperature is equal to or less than the sum of the minimum return temperature threshold and the temperature safety margin, the flow regulating device is communicatively connected to the thermal energy transfer device to transmit a turn-off signal to the thermal energy transfer device to avoid damage due to risk of the return temperature dropping below the minimum return temperature threshold.

Alternatively, or additionally, if the flow regulating device is fully open and the flow rate is equal to or less than the sum of the operational flow rate threshold and the flow safety margin, the flow regulating device transmits a turn-off signal to the thermal energy transfer device to avoid damage due to risk of the flow rate below the operational flow rate threshold. In order to avoid unnecessary flow through the system, the flow regulating device is closed off after the thermal energy transfer device has been turned off.

To avoid the flow rate dropping below the operational flow rate threshold, operating the HVAC system according to embodiments of the present invention further comprises increasing the flow rate if the flow rate is equal to or less than the sum of the operational flow rate threshold and a flow safety margin.

According to further embodiments of the present invention, the flow regulating device is communicatively connected to the thermal energy transfer device to receive a signal indicative of a thermal energy demand thereof. In order to operate the HVAC system even more efficiently, the flow rate is regulated further as a function of the thermal energy demand. In particular, increasing the flow rate at predetermined time interval(s), in the presence of thermal energy demand - while maintaining the target temperature difference and ensuring that the return temperature is above a minimum return temperature threshold. Hence, if the flow rate has been previously reduced or if the flow regulating device has been previously closed off, the flow regulating device makes successive attempts to meet the energy demand (in the presence of an energy demand)- while meeting the safe conditions of minimum return temperature threshold and operational flow rate threshold. According to further embodiments, a time interval between successive attempts to meet the energy demand (by increasing the flow-rate) is gradually increased after each attempt, the time interval being reset to an initial value after a successful attempt.

It is an object of further embodiments of the present disclosure to operate the HVAC system in accordance with a secondary fluid circuit, that is the fluid circuit connecting the thermal energy transfer device with the thermal energy consumer. This further object is addressed by receiving, by the flow regulating device, data indicative of a secondary supply temperature and/or a secondary return temperature of a secondary fluid flowing between the thermal energy transfer device and the thermal energy consumer and regulating the flow rate of the fluid further as a function of the secondary supply temperature and/or the secondary return temperature. Alternatively, or additionally, this further object is addressed by receiving, by the flow regulating device, data indicative of an energy consumption of the thermal energy transfer device and regulating the flow rate of the fluid further as a function of the energy consumption of the thermal energy transfer device.

It is an object of further embodiments of the present invention to operate the HVAC system in accordance with the functioning of the thermal energy transfer device, in particular if the thermal energy transfer device is configured to supplement the thermal energy provided by the thermal energy source. This further object is addressed by receiving, by the flow regulating device, data indicative of internal state(s) of the thermal energy transfer device and regulating the flow rate of the fluid further as a function of the internal state(s) of the thermal energy transfer device and/or the thermal energy demand.

It is a further object of the present invention to provide a flow regulating valve which, if arranged to regulate a flow rate of a fluid between a thermal energy source and a thermal energy transfer device of an HVAC system, enable the operation of the HVAC system avoiding frequent interruptions in the operation of the energy transfer device; maximizing the transfer of thermal energy to/from per unit of fluid flowing through the fluid transportation system; and avoiding breakdowns caused by freezing of the fluid in the energy transfer device and/or the fluid transportation system. According to the present invention, this further object is achieved by the features of the independent claim <NUM>. In addition, further advantageous embodiments follow from the dependent claims and the description. In particular, this object is addressed by a flow regulating device comprising a valve and/or a damper configured to regulate a flow rate of a fluid between a thermal energy source and a thermal energy transfer device, the flow regulating device further comprising a processing unit configured to carry out the method according to one of the embodiments disclosed herein. Alternatively, or additionally, the flow regulating device comprises a pump (in case the fluid is a liquid) and/or a fan (in case the fluid is a gas) configured to regulate a flow rate of a fluid between a thermal energy source and a thermal energy transfer device.

According to embodiments of the present invention, the flow regulating device comprises a flow rate sensor device configured to determining the flow rate of the fluid to and/or from the thermal energy source and the thermal energy transfer device and a temperature sensor device configured to determine a supply temperature of the fluid and a return temperature of the fluid. According to embodiments of the flow regulating device, the temperature sensor device comprises a first temperature sensor configured to determine the supply temperature of the fluid to the thermal energy source and a second temperature sensor configured to determine the return temperature of the fluid from the thermal energy source. Alternatively, or additionally, the supply temperature is determined by the temperature sensor device based on a measurement of the return temperature by the second temperature sensor and data indicative of the relationship between the supply temperature and the return temperature as a function of the flow rate. Alternatively, or additionally, the return temperature is determined by the temperature sensor device based on a measurement of the supply temperature by the first temperature sensor and data indicative of the relationship between the supply temperature and the return temperature as a function of the flow rate.

In order to allow operation of the HVAC system in view of the energy demand of the thermal energy transfer device, according to embodiments, the flow regulating device further comprises (or is communicatively connected to) a secondary temperature sensor device configured to determine a secondary supply temperature and/or a secondary return temperature of a secondary fluid at a secondary fluid circuit of the thermal energy consumer, the flow regulating device being further configured to determine a thermal energy demand of the thermal energy transfer device based on the secondary supply temperature and/or the secondary return temperature. Alternatively, or additionally the flow regulating device comprises (or is communicatively connected to) a secondary flow rate sensor device configured to determine a secondary flow rate of the secondary fluid at the secondary fluid circuit of the thermal energy consumer, the flow regulating device being further configured to determine a thermal energy demand of the thermal energy transfer device based on the secondary flow rate.

It is a further object of the present disclosure to provide an HVAC system enabled to operate such as to avoid frequent interruptions in the operation of the energy transfer device; maximize the transfer of thermal energy per unit of fluid flowing through the fluid transportation system; and avoid breakdowns caused by freezing of the fluid in the energy transfer device and/or the fluid transportation system. According to the present invention, this further object is achieved by the features of claim <NUM>. In addition, further advantageous embodiments follow from the dependent claims and the description. In particular, this object is addressed by an HVAC system comprising a thermal energy source; a thermal energy transfer device; a fluid transportation system comprising a supply fluid transportation line arranged to transport a fluid from the thermal energy source to the thermal energy transfer device and a return fluid transportation line arranged to transport the fluid from the thermal energy transfer device to the thermal energy source. The HVAC system further comprising a flow regulating device according to one of the embodiments disclosed herein.

Embodiments of the HVAC system further comprise a thermal energy consumer, such as a heat exchanger, connected to the thermal energy transfer device <NUM> by a secondary supply fluid transportation line and a secondary return fluid transportation line of a secondary fluid transportation system for transporting a secondary fluid.

According to embodiments of the HVAC system, the thermal energy source is configured to supply heat to the thermal energy transfer device - referred to as heating. Alternatively, or additionally the thermal energy source is configured to extract heat from the thermal energy transfer device - referred to as cooling.

According to embodiments of the HVAC system, the thermal energy transfer device comprises a secondary thermal energy source configured to supplement the thermal energy provided by the thermal energy source, such as a heat pump, a combustion heater, an electric heater or chiller.

It is a further object of the present invention to provide a computer program product, comprising instructions, which - when executed by a processing unit of a flow regulating device enable the operation of an HVAC system such as to avoid frequent interruptions in the operation of the energy transfer device; maximize the transfer of thermal energy per unit of fluid flowing through the fluid transportation system; and avoid breakdowns caused by freezing of the fluid in the energy transfer device and/or the fluid transportation system. According to the present invention, this object is achieved by the features of the independent claim <NUM>. In addition, further advantageous embodiments follow from the dependent claims and the description. In particular, this further object is addressed by a computer program product comprising instructions, which - when executed by a processing unit of a flow regulating device, cause the flow regulating device to carry out the method of operating an HVAC system according to one of the embodiments disclosed herein.

It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the invention.

The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

The herein described disclosure will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be considered limiting to the invention defined in the appended claims. The drawings which show:.

<FIG> shows a highly schematic block diagram of an embodiment of the HVAC system <NUM> according to the present invention, comprising a thermal energy source <NUM> and a thermal energy transfer device <NUM> connected by a fluid transportation system <NUM>. The fluid transportation system <NUM> comprises a supply fluid transportation line <NUM> arranged to transport a fluid from the thermal energy source <NUM> to the thermal energy transfer device <NUM> and a return fluid transportation line <NUM> arranged to transport the fluid from the thermal energy transfer device <NUM> to the thermal energy source <NUM>. A pump/ fan <NUM> may be provided to induce the flow of fluid through the fluid transportation system <NUM>.

The thermal energy source <NUM> is configured to supply heating and cooling energy to the thermal energy transfer device <NUM> such as to supply/ extract heat to/from the thermal energy transfer device <NUM>. The thermal energy (heating / cooling) is supplied/ extracted by means of the fluid flowing through the fluid transportation system <NUM>.

According to particular embodiments - illustrated on <FIG> with dotted lines - the HVAC system <NUM> comprises a secondary fluid transportation system <NUM>, fluidly connecting the thermal energy transfer device <NUM> with an energy consumer <NUM>. The secondary fluid transportation system <NUM> comprises a secondary supply fluid transportation line <NUM> and a secondary return fluid transportation line <NUM> for transporting a secondary fluid between the thermal energy transfer device <NUM> and the thermal energy consumer <NUM>.

In order to transfer thermal energy (heating / cooling) between the fluid transportation system <NUM> and the secondary fluid transportation system <NUM>, the thermal energy transfer device <NUM> comprises a heat exchanger <NUM>, connected to both the fluid transportation system <NUM> and the secondary fluid transportation system <NUM> such as to enable thermal transfer there-between.

Additionally or alternatively, the thermal energy transfer device <NUM> comprises a secondary thermal energy source <NUM> such as a heat pump, a combustion heater, an electric heater or chiller or a combination thereof, configured to supplement the thermal energy provided by the thermal energy source <NUM>.

<FIG> shows a highly schematic block diagram of an embodiment of the flow regulating device <NUM> according to the present disclosure. The flow regulating device <NUM> comprises a valve V and/or a damper D configured to regulate the flow rate Φ of the fluid between the thermal energy source <NUM> and the thermal energy transfer device <NUM> through the supply fluid transportation line <NUM> and return fluid transportation line <NUM> of the fluid transportation system <NUM>. A motor M, in particular an electric motor, is provided to drive the valve V and/or a damper D.

The flow regulating device <NUM> further comprises a processing unit <NUM> configured to operate the HVAC system <NUM> according to any one of the embodiments of the method disclosed herein. Depending on the embodiment, the processing unit <NUM> comprises an electronic circuit implemented as programmed processors, including data and program memory, or another programmable logic unit, e.g. an application specific integrated circuit (ASIC).

Optionally, the flow regulating device <NUM> further comprises a communication module <NUM> configured for data communication with a remote computer or external controller, such as a Building Management System BMS. According to embodiments, the communication module of the flow regulating device <NUM> comprises a radio communication circuit, in particular a Wireless Local Area Network WLAN communication circuit; a Near Field Communication NFC, Ultra Wide Band UWB and/or a Bluetooth Low Energy BLE. According to further embodiments, the communication module of the flow regulating device <NUM> comprises a wired communication circuit, in particular an Ethernet communication circuit a BACnet, a ModBus and/or an MP-Bus communication circuit.

Optionally, the flow regulating device <NUM> further comprises a data store <NUM> for storing data content comprising configuration data of the flow regulating device <NUM>, and for operation-related data recorded by the flow regulating device <NUM>.

The flow regulating device <NUM>, in particular its processing unit <NUM>, motor M, and sensor device(s) <NUM>, <NUM>, is powered by a power supply comprising a power connector and/or an internal energy storage device, such as battery and/or a capacitor. According to particular embodiments, the power connector is connected to the wired communication circuit, the flow regulating device <NUM> being powered by a data line connection, such as Power over Ethernet PoE or Power over Data Line PoDL.

The flow regulating device comprises a flow rate sensor device <NUM> configured to determining the flow rate Φ of the fluid to and/or from the thermal energy source <NUM> and the thermal energy transfer device <NUM> and a temperature sensor device <NUM> configured to determine a supply temperature Ts of the fluid and a return temperature Tr of the fluid.

In order to allow operation of the HVAC system <NUM> in view of the energy demand of the thermal energy transfer device <NUM>, the flow regulating device <NUM> is communicatively connected to a secondary temperature sensor device <NUM>' configured to determine a secondary supply temperature Ts2 and/or a secondary return temperature Tr2 of the secondary fluid transportation system <NUM> connecting the thermal energy consumer <NUM>. Furthermore, the flow regulating device <NUM> is optionally communicatively connected to a secondary flow rate sensor device <NUM>' configured to determine a secondary flow rate Φ2 of the secondary fluid at the secondary fluid transportation system <NUM>.

Optionally, according to further embodiments, the flow regulating device <NUM> is communicatively connected to the thermal energy transfer device <NUM> using a corresponding interface <NUM> to receive a signal indicative of a thermal energy demand thereof.

<FIG> shows a highly schematic diagram of an embodiment of the flow regulating device <NUM>, illustrating the installation of the flow regulating device <NUM> in the fluid transportation system <NUM> between the thermal energy source <NUM> and the thermal energy transfer device <NUM>. As shown on this figure, the valve V / damper D of the flow regulating device <NUM> is arranged on the return fluid transportation line <NUM> of the fluid transportation system <NUM>. The temperature sensor device <NUM> comprises a first temperature sensor S1 configured to determine the supply temperature Ts of the fluid to the thermal energy source <NUM> and a second temperature sensor S2 configured to determine the return temperature Tr of the fluid from the thermal energy source <NUM>.

According to various embodiments, the flow regulating device <NUM> may be arranged within a single housing or distributed amongst various housings. In particular, the sensor devices (flow rate sensor device <NUM>, secondary flow rate sensor device <NUM>', the temperature sensor device <NUM> and/or the secondary temperature sensor device <NUM>') may be arranged in housings separate from the housing accommodating the processing unit <NUM>, the communication module <NUM>, the data store <NUM> and/or the interface to thermal energy transfer device <NUM>.

Turning now to <FIG>, embodiments of the method of operating the HVAC system <NUM> shall be described in detail.

<FIG> shows a flowchart illustrating steps of an embodiment of the method of operating an HVAC system <NUM> comprising a thermal energy source <NUM> and a thermal energy transfer device <NUM>. In a first, preparatory step S10, a flow regulating device <NUM> is arranged between the thermal energy source <NUM> and the thermal energy transfer device <NUM> such as to be able to regulate a flow rate Φ of a fluid between the thermal energy source <NUM> and the thermal energy transfer device <NUM>. According to various embodiments, the flow regulating device <NUM> regulates the flow rate Φ of the fluid using a valve V / damper D arranged in the supply fluid transportation line <NUM> and/or the return fluid transportation line <NUM> of the fluid transportation system <NUM> connecting the thermal energy source <NUM> and the thermal energy transfer device <NUM>.

Thereafter, in steps S20, S30 and S40, supply temperature Ts; return temperature Tr respectively flow rate Φ of the fluid are determined (continuously, pseudo-continuously and/or at intervals during operation of the HVAC system).

Based on the determined supply temperature Ts; return temperature Tr and flow rate Φ of the fluid, in step S50, the flow rate (Φ) of the fluid is controlled such as to maintain a target temperature difference dTt between the supply temperature Ts and the return temperature Tr.

According to embodiments of the present invention, regulating the flow rate (Φ) of the fluid such as to maintain a target temperature difference dTt comprises:.

As shown on the flowchart of <FIG>, the flow rate (Φ) of the fluid is regulated such as to maintain a target temperature difference dTt while ensuring - in substep S52 that the return temperature Tr is above a minimum return temperature threshold Trmin and ensuring - in substep S54 - that the flow rate Φ is above an operational flow rate threshold Φmin of the thermal energy transfer device <NUM>. Adherence to these two criteria addresses the aim to ensure that the HVAC system <NUM> operates optimally, with less interruptions and less prone to errors. Ensuring that the return temperature Tr is above a minimum return temperature threshold Trmin avoids the thermal energy transfer device <NUM> and/or the fluid transportation system <NUM> from being damaged due to freezing and/or condensation of the fluid. Ensuring that the flow rate Φ is above an operational flow rate threshold Φmin of the thermal energy transfer device <NUM> helps avoid unnecessary interruptions in the operation of the HVAC system <NUM> due to the thermal energy transfer device <NUM> being forced to shut down due to insufficient flow rate. Furthermore, ensuring that the flow rate Φ is above an operational flow rate threshold Φmin of the thermal energy transfer device <NUM> prevents unnecessary wear of the thermal energy transfer device <NUM> due to operation near or below its optimum parameters.

As illustrated on the flowchart of <FIG>, in order to prevent the return temperature Tr from dropping below the minimum return temperature threshold Trmin, the method further comprises - in a step S60 - increasing the flow rate Φ if the return temperature Tr is equal to or less than the sum of the minimum return temperature threshold Trmin and a temperature safety margin Tx. If, despite the flow regulating device <NUM> being fully open, the return temperature Tr is equal to or less than the sum of the minimum return temperature threshold Trmin and the temperature safety margin Tx, in a step S56, the flow regulating device <NUM> is closed off, preventing the flow of fluid to and/or from the thermal energy source <NUM>. The flow regulating device <NUM> is closed off to avoid damage due to the return temperature Tr dropping below the minimum return temperature threshold Trmin. Furthermore, the flow regulating device <NUM> is closed off, if the flow rate Φ is equal to or less than the sum of the operational flow rate threshold Φmin and the flow safety margin Φx despite the flow regulating device <NUM> being fully open.

Furthermore, if the flow regulating device <NUM> is fully open and the return temperature Tr is equal to or less than the sum of the minimum return temperature threshold Trmin and the temperature safety margin Tx, in step S58, the flow regulating device <NUM> transmits a turn-off signal to the thermal energy transfer device <NUM> to avoid damage due to risk of the return temperature Tr dropping below the minimum return temperature threshold Trmin.

To avoid the flow rate Φ dropping below the operational flow rate threshold Φmin, in step S60', the flow rate Φ is also increased if the flow rate Φ is equal to or less than the sum of the operational flow rate threshold Φmin and a flow safety margin Φx. Correspondingly, to avoid damage due to risk of the flow rate Φ below the operational flow rate threshold Φmin, the flow regulating device <NUM> also transmits - in step S58 - a turn-off signal to the thermal energy transfer device <NUM> if the flow regulating device <NUM> is fully open and the flow rate Φ is equal to or less than the sum of the operational flow rate threshold Φmin and the flow safety margin Φx.

As shown on the flowchart of <FIG>, in order to allow the HVAC system <NUM> to be operated further as a function of a demand of thermal energy and hence to operate the HVAC system <NUM> even more efficiently, in step S62, the flow rate Φ is increased at predetermined time interval(s) dt in the presence of thermal energy demand. Hence, if the flow rate Φ has been previously reduced (e.g. to ensure a safe return temperature) or if the flow regulating device <NUM> has been previously closed off, the flow regulating device <NUM> makes successive attempts to meet the energy demand - while meeting the safe conditions of minimum return temperature threshold Trmin and operational flow rate threshold Φmin.

Claim 1:
A method of operating an HVAC system (<NUM>), comprising a thermal energy source (<NUM>) and a thermal energy transfer device (<NUM>), using a flow regulating device (<NUM>) arranged to regulate a flow rate (Φ) of a fluid between the thermal energy source (<NUM>) and the thermal energy transfer device (<NUM>), the method comprising:
- determining a supply temperature (Ts) of the fluid;
- determining a return temperature (Tr) of the fluid;
- determining the flow rate (Φ) of the fluid; and
- regulating the flow rate (Φ) of the fluid such as to maintain a target temperature difference (dTt) between the supply temperature (Ts) and the return temperature (Tr), while ensuring that:
- the return temperature (Tr) is above a minimum return temperature threshold (Trmin); and
- the flow rate (Φ) is above an operational flow rate threshold (Φmin) of the thermal energy transfer device (<NUM>).