Control method for heating and / or cooling system

Abstract

The present disclosure relates to a control method of controlling a heating and / or cooling system, optionally a heat pump system. The system comprises at least one primary P and at least one secondary fluid circuit S fluidly connected by a tank, optionally a decoupling tank. The primary fluid circuit P is configured for transfer of thermal energy via a fluid flow at a primary fluid flow rate Qp from a source, optionally an outdoor heat pump unit 3, to a secondary fluid circuit S. The secondary fluid circuit S is configured for transfer of thermal energy via the fluid flow at a secondary fluid flow rate Qs to a destination, optionally a heating / cooling circuit and / or a domestic hot water tank or buffer tank. The tank is in fluid connection with a primary fluid inlet Pin for supply of the tank with fluid, and a secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and in fluid connection with a secondary fluid inlet Sin for supply of the tank with fluid, and a primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P. The fluid has a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts_in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout.

Description

Technical field

[0001] The invention concerns a control method, a control unit and a heating and / or cooling system, in particular a heat pump system, comprising such control unit.Background

[0002] Heating or cooling installations (domestic heating / cooling systems) such as heat pump systems may comprise a (often so-called decoupling) tank which is used as a device that may make two fluid circuits hydraulically independent, e.g. the primary fluid circuit and the secondary fluid circuit of a heating or air-conditioning system. The primary fluid circuit directly or indirectly represents the energy production (generator) circuit, e.g. a boiler or a heat pump. The secondary fluid circuit is made up of emitters, fan convectors, radiators and underfloor heating, i.e. the heat consumption circuit. The primary and secondary fluid circuit are in fluidic communication thanks to the tank.

[0003] Such separation or decoupling of the primary and secondary fluid circuits is not physical, but the primary fluid circuit has its own pump and the secondary fluid circuit has one or more pumps, depending on the installation / configuration. The advantage of decoupling circuits is for instance to establish a hydraulic neutral point which allows for control of flow and pressure in the secondary fluid circuit, particularly when several secondary fluid circuits are operating independently of each other. Excessive differences in flow rate and / or pressure between the primary and secondary circuits may create disturbances that interfere during operation of the system.

[0004] The term "hydraulic neutral point" refers to a point in a heating or cooling system where the static pressures of the primary and secondary circuits are balanced. This means that at this point, there is no interactivity between the dynamic pressures induced by the different pumps; e.g. if the flow rates between the circuits are balanced (i.e. at the hydraulic neutral point), the hot water passes from the primary fluid circuit via the decoupling tank directly into the secondary fluid circuit without any significant mixing. Even if the flow rate in the secondary fluid circuit changes, thanks to the hydraulic neutral point, this does not affect the flow rate in the primary fluid circuit.

[0005] Improvements as to the efficiency (e.g. in terms of COP (coefficient of performance) of a heating and / or cooling system are desired against this background.Summary of the invention

[0006] The present invention relates to a control method of controlling a heating and / or cooling system, optionally a heat pump system. The system comprises at least one primary P and at least one secondary fluid circuit S fluidly connected by a tank, optionally a decoupling tank. The primary fluid circuit P is configured for transfer of thermal energy via a fluid flow at a primary fluid flow rate Qp from a source, optionally an outdoor heat pump unit 3, to a secondary fluid circuit S. The secondary fluid circuit S is configured for transfer of thermal energy via the fluid flow at a secondary fluid flow rate Qs to a destination, optionally a heating / cooling circuit and / or a domestic hot water tank or buffer tank. The tank is in fluid connection with a primary fluid inlet Pin for supply of the tank with fluid, and a secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and in fluid connection with a secondary fluid inlet Sin for supply of the tank with fluid, and a primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P. The fluid has a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts_in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout. The method comprises two alternative control approaches a) and b). According to (a), the following is performed: Setting and maintaining a primary temperature difference ΔTp between the temperatures Tp_in and Tp_out, by adjusting the primary fluid flow rate Qp accordingly. According to (b), the following is performed: Setting and maintaining the primary fluid flow rate Qp by adjusting the temperature difference ΔTp between the temperatures Tp_in and Tp_out accordingly. One of the following subsequent steps is performed: Adjusting the secondary temperature difference ΔTs between the temperatures Ts_in and Ts_out such that the secondary temperature difference ΔTs is lower than or equal to the primary temperature difference ΔTp, ΔTs ≤ ΔTp; or adjusting the secondary fluid flow rate Qs such that the secondary fluid flow rate Qs is lower than or equal to the primary flow rate Qp, Qs ≤ Qp.

[0007] Whether alternative (a) or (b) is used, may depend on the sensors which are available / present in the system, i.e. whether a control based on flow rate or based on temperature difference is used.

[0008] The requirement that the secondary fluid flow rate is equal to or smaller than the primary fluid flow rate has the effect that the heating losses in the decoupling tank are reduced, and so the overall thermal and energetic efficiency of the installation is improved. This is reflected in a better Coefficient of Performance (COP), which measures the ratio between the energy generated and the energy consumed by the system. At the same time, this solution ensures that the flow temperature is guaranteed, thereby meeting the customer's needs.

[0009] The idea underlying the invention is to improve the performance of a heating and / or cooling system by adjusting the temperature difference or flow rate in the primary fluid circuit, which transfers calories from the refrigerant circuit to the primary fluid circuit. It is desired to set the temperature of the primary fluid circuit such that heat exchange with the refrigerant is improved to the effect that the temperature range of the refrigerant is suitable in terms of the Carnot cycle. As an example, it was found that 8% in performance may be gained (better COP), compared to running the primary fluid circuit at a fixed flow rate.

[0010] Moreover, it was found expedient when a temperature difference ΔTp between the temperature at the inlet of the primary fluid circuit at the (decoupling) tank and the temperature at the outlet of the primary fluid circuit is held constant. The temperature difference at the inlet and outlet of the primary fluid circuit at the (decoupling) tank is similar to the temperature difference at the inlet and outlet of the heat generator (heat pump, boiler,...). To hold this temperature difference constant, the flow rate in the primary fluid circuit may be adjusted as needed for the constant temperature difference.

[0011] For such adjustment, the heat pump power needs to be adjusted and, hence, controlled. (The relation between the heat and the temperature is H = M*C*ΔT, wherein H: heat; M: Mass; c: specific heat; ΔT: change in temperature.) The (volumetric) fluid flow rate Q may be defined as the change of volume V per time Δt, namely Q = ΔV / Δt.

[0012] For example, the predetermined temperature difference between the temperature at the inlet of the primary fluid circuit at the (decoupling) tank and the temperature at the outlet of primary fluid circuit may be set as foiiows:10°C (if the destination is a high temperature radiator); 5°C (if the destination is underfloor heating or fan convector); 8°C (if the destination is a medium temperature radiator). For example, the installer / fitter may choose a ΔT suitable for the desired application during installation.

[0013] In use, fixing the temperature difference, i.e. defining the ΔT, means setting target temperature difference at least for a period of time, e.g. constant over time for a given use (underfloor heating, radiator,...) or a given mode. In other words, typically for the entire life of the heating product after its installation for a dedicated usage. It may not depend on the logic control. Rather, it is the zone in demand that imposes the temperature difference. Possibly, the temperature difference is programmed for it once and for all, e.g. the user having no access to the target temperature difference after the installation, except for massive modifications of the system (e.g. update of the emitters, circuit, insulation, etc.), ΔT is usually constant.

[0014] However, it is not excluded to change and adapt the target temperature difference, e.g. by a user or as variable parameter. For example, a time program is conceivable.

[0015] Accordingly, it is desired to improve the performance / efficiency of a heating / cooling system on the basis of a target ΔT or target flow rate Q achieved by adjusting the primary fluid flow rate or temperature difference, so as to comply with different heating / cooling demands. The invention proposes adjusting the secondary fluid flow rate or the secondary temperature difference such that the secondary fluid flow rate or secondary temperature difference is lower than or equal to the primary flow rate or secondary temperature difference, respectively.

[0016] This may be seen as controlling the secondary circuit according to the primary circuit. This may help to reduce undesired mixing of the primary and secondary fluid flows in the tank and, thus, thermal loss.

[0017] From another angle, the invention may be seen as forgoing a constant primary flow rate, but working on the basis of a target ΔTp (=Tp_in - Tp_out), so that the primary flow rate becomes variable. The secondary flow rate is adjusted as a function of the primary flow rate.

[0018] In general, a (decoupling) tank may be referred to as hydraulic separator, buffer tank or mixing tank, or simply as tank. It may serve for hydraulic separation of the primary and secondary fluid circuits. A (decoupling) tank of the invention may allow for mixing of fluid and as pressure balancer between the primary and secondary fluid circuits. Such tank may be seen as making the link between several circuits, such as a primary fluid circuit and a secondary fluid circuit. The tank has several connectors to pipes and, hence, pipes at each side. The primary fluid circuit corresponds to and is at the source side (i.e. the side of the heating device, such as the heat pump, where the fluid is heated / cooled by the heating device). The secondary fluid circuit corresponds to and is at the distribution side (i.e. the side of the radiators, floor heaters, fan coils).

[0019] By means of a (decoupling) tank between fluid circuits, the fluid flows and, hence, the fluid circuits are (remain) separated and do not conflict with the others. Each circuit may have its "own" flow. However, the tank allows for a balance between the primary and secondary fluid circuits, i.e. the demand and supply flows, so that the circuits may be in communication so as to allow for balanced heat, charge, recirculation etc.

[0020] The (decoupling) tank allows for impact on the thermal transfer of heat in the system. For example, a (decoupling) tank allows fluid from the primary fluid circuit to enter the tank and leave the tank into the secondary fluid circuit, as if a "main flow" of fluid crosses the tank as if the tank were a simple, connecting tube. If the fluid flow (in terms of the volumetric flow rate) differs between the primary and the secondary fluid circuits, i.e. at different sides of the (decoupling) tank, a part of the fluid flow entering the tank on one side may exit the tank on the same side, at another pipe at another height. Such fluid paths imply mixing of fluids having different temperatures.

[0021] The control method of the invention may aim at avoiding mixing of the primary and secondary fluid flows in the tank. The control method of the invention may be seen as aiming at balancing of primary and secondary fluid flow rates. If the primary fluid flow rate is dominant in that it exceeds the secondary fluid flow rate, the temperature or fluid flow rate in the primary fluid circuit may actively be controlled, in line with claim 1.

[0022] According to (a), the primary temperature difference is the target and is set and maintained, while the primary fluid flow rate is adjusted so as to meet the targeted primary temperature difference. E.g. as a function of the primary fluid flow rate, the secondary fluid flow rate may be adjusted, e.g. by adjusting the pump speed of a secondary pump accordingly.

[0023] According to (b), the primary fluid flow rate is the target and is set and maintained, while the primary temperature difference is adjusted so as to meet the targeted primary fluid flow rate. E.g. as a function of the primary temperature difference, the secondary temperature difference may be adjusted, e.g. by adjusting the pump speed of a secondary pump accordingly

[0024] Example controls may be as follows to set the secondary fluid flow rate Qs: Measurement of the secondary fluid flow rate Qs and adjustment thereof based on the primary fluid flow rate Qp, i.e. Qs = f(Qp). Measurement of at least two temperatures in secondary fluid circuit, namely Ts_in and Ts_out, and adjustment of the secondary fluid flow rate Qs such that ΔTs is constant.

[0025] The system may have to get access to the value of Qp, via a speed modulating pump with a communication protocol (for instance a LIN pump) or a flowmeter and / or temperatures probes (or equivalent servo control means) in the secondary fluid circuit, preferably in the indoor unit (IDU). Accordingly, the secondary temperature difference may be adjusted by means of an update of the secondary flow (thanks to pump control), which implies an update of the temperature in the secondary flow circuit.

[0026] The step of maintaining a temperature difference ΔTp may be controlled by an outdoor unit (ODU) of the heat pump system, e.g. in case of a monobloc unit, or an indoor unit (IDU) in case of split outdoor units.

[0027] ΔTp, i.e. the temperature difference, is maintained constant when the heat pump is working. Hence, the time period during which ΔTp is constant corresponds to the usage of the heat pump.

[0028] The meaning of "modular" may be as not a ON / OFF parameter. but as a parameter for which it is possible to vary different levels between maximum speed and standstill. In particular, the speed can be evaluated more or less progressively, with a limited number of speeds (for example 2 to 5) or with a non-finite number (function-based control). For example, it may be a case of controlling the power supply and therefore the speed according to a very variable number of possibilities. This is the case with Pulse Width Modulation (PWM) type control, for which it is possible to synthesise pseudo analogue signals. For example, according to prior art controls, Qp was forced to be e.g. 40l / min. So it was not possible to reduce this value to adapt the control to the external temperature for instance.

[0029] A flow and / or temperature determination device may be used to control the temperature or flow rate in the first and / or second fluid circuits.

[0030] A temperature difference ΔTp_s between Tp_in and Ts_out and / or a temperature difference ΔTs between Ts in and Tp_out may be less than 10, optionally less than 6°C.

[0031] A servo-control may refer to the constellation that the secondary pump looks for information of the primary fluid circuit and will adapt its speed according to value from the primary fluid circuit.

[0032] The parameter K depends on the tank that is used, in particular its geometry. For each tank, the parameter K may be pre-defined.

[0033] The destination may be an emitter, and may be, in general, e.g. a heating / cooling circuit, radiator, emitter, or domestic hot water tank or buffer tank.

[0034] There may be at least one (e.g. one or two) primary fluid circuits one or two secondary fluid circuits, or even more corresponding circuits. Each of the primary and secondary fluid circuits have their individual fluid circuit and individual fluid temperature etc., thus representing actually independent fluid circuits, which are, however, fluidly coupled via the common (decoupling) tank. In case of more than a single primary / secondary flow circuit, the total sum of the primary fluid circuits may be referred to as "the" primary flow rate, and the total sum of the secondary fluid circuits may be referred to as "the" secondary flow rate.

[0035] The fluid in the primary and secondary fluid circuit(s) is optionally water-based. More specifically, the fluid may be pure water or water mixed with additives, such as glycol for anti-freeze purposes.

[0036] The physical principle underling a (decoupling) tank accommodating fluid at different temperatures is stratification: The coldest fluid will, in theory, be at the lowest level (close to the bottom of the tank) and the hottest fluid will be at the highest level (close to the top of the tank). Such theoretical distribution may be compromised by perturbations, such as flow or a mixing element. Presently, flow differences between inlet(s) / outlet(s), may lead to less "ideal" thermal stratification. Nevertheless, by means of a tank, it is possible to manage different outlet temperatures (for the secondary fluid circuit(s)) with a single inlet tube (providing fluid at a single temperature from the primary fluid circuit). For example, the secondary fluid circuit which requires the highest fluid temperature may be connected to the highest outlet tube, for example for radiators (as the fluid temperature of fluid for radiation heating is higher than the temperature of fluid for floor heating).

[0037] The upper region may be regarded as a hot or warm zone of the tank, as it usually comprises the warmer part of the fluid in the tank. The lower region may be regarded as a cold zone of the tank, as it usually comprises the colder part of the fluid in the tank. A continuous decrease of the temperature of the fluid in the tank from top to bottom of the tank, when installed on site, is the usual configuration.

[0038] Optionally, the secondary fluid flow rate Qs is set to Qs = K x Qp, the parameter K: 0 < K ≤ 1, more preferably 0.3 < K ≤ 1. Alternatively, optionally, the secondary temperature difference ΔTs is set to ΔTs = a x ΔTp, the parameter a: 0 < a ≤ 1, more preferably 0.3 < a ≤ 1. This may help to efficiently implement the control of the invention.

[0039] The secondary fluid circuit may comprise one or more secondary fluid (sub)circuits. Optionally, the secondary fluid circuit S comprises at least a first secondary fluid circuit S-1 and optionally a second S-2, further optionally a third circuit S-3. Optionally, in case of multiple secondary fluid circuits, the sum of the respective parameters K or per secondary fluid circuit is equal to or below 1. Hence, if three secondary (sub)circuits are provided, the sum of K of all three circuits is below 1. For example, 0.1 ≤ K_1, 2, 3 ≤ 0.3 as K-value per (sub)circuit may be a suitable value. This may represent an efficient control.

[0040] Optionally, the secondary flow fluid rate Qs is adjusted by adjusting the rotational speed of at least one secondary pump in the secondary fluid circuit. The speed may refer to the rotational speed, power and / or frequency. Reference to a PWM (pulse width modulation) of the signal / current is made. This may efficiently implement a control of the invention.

[0041] More optionally, the speed of the secondary pump is determined based on the secondary fluid flow rate Qs, even more optionally measured by a secondary flow determination device arranged in the secondary fluid circuit S. This may help to control the secondary flow rate accordingly.

[0042] Even more optionally, the secondary flow determination device is a speed modulated pump with a communication protocol, preferably a local Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors. A LIN bus communication protocol to communicate data on the status of at least one of the elements may be used to control the flow and / or temperature of the primary and / or secondary fluid circuit. This may support implementation of the control of the invention.

[0043] Optionally, the modification of the speed of the secondary pump is determined to maintain a temperature difference ΔTs between the temperatures Ts in and Ts_out, of the secondary fluid circuit substantially constant, optionally equal to a temperature difference ΔTp between the temperatures Tp_in and Tp_out. In toher words, ΔTs between the temperatures Ts in and Ts_out of the secondary fluid circuit is maintained substantially constant, optionally ΔTs = ΔTp. This may allow for efficient control.

[0044] Optionally, the temperature difference ΔTs between the temperatures Ts_in and Ts_out is measured by at least one temperature-determination sensors at each of the secondary fluid inlet Sin and the secondary fluid outlet Sout, respectively, for determination of the temperatures Ts_in and Ts,_out respectively. This may allow for efficient control.

[0045] The invention is also direction to a control unit configured to carry out the method of the invention.

[0046] The invention is also directed to a heating / cooling system comprising the control unit of the invention. Specifically, the system of the invention comprises a primary and secondary fluid circuits and further comprises a control unit of the invention.

[0047] The invention, in general, refers to any kind of heat pump system, including at least one ground source (water)- and / or air source-heat pump unit. The heat pump units may have an indoor and / or outdoor units. A heat pump unit of the heat pump system may be a split unit or a monobloc unit. The heat pump system may be configured to heat and / or cool air or water (of a closed loop or of an open loop, such as domestic hot water).

[0048] Specifically, the invention is also directed to a heating and / or cooling system, optionally a heat pump system. The system comprises at least one primary P and at least one secondary fluid circuit S fluidly connected by a tank, optionally a decoupling tank, the primary fluid circuit P for transfer of thermal energy via fluid at a primary fluid flow rate Qp from a source, optionally an outdoor unit 3, to fluid in a secondary fluid circuit S, the secondary fluid circuit S for transfer of thermal energy at a secondary fluid flow rate Qs to a destination / emitter 5, optionally a heating / cooling circuit and / or a domestic hot water tank or buffer tank. The tank comprises a primary fluid inlet Pin, a primary fluid outlet Pout, a secondary fluid inlet Sin, and a secondary fluid outlet Sout, wherein the tank is configured to establish fluid communication with the primary fluid inlet Pin for supply of the tank with fluid, and the secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and with the secondary fluid inlet Sin for supply of the tank with fluid, and the primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P, the fluid having a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout. The system further comprises at least one primary pump 6 configured for variable speed for adjusting the primary flow rate Qp, and at least one secondary pump 7 configured for variable speed for adjusting the secondary flow rate Qs, and the control unit of the invention.

[0049] Optionally, the secondary pump is a speed modulated pump with an Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors. This may allow for efficient measurement. The measurement may be direct or indirect (contact or not), more optionally without direct contact between sensor and the fluid.

[0050] Detailed embodiments and further advantages and features related to the present invention are described in the following, wherein these examples shall not be regarded as limiting the invention.Brief description of the drawings

[0051] Fig. 1 schematically shows in Fig. 1(a) and 1(b) steps of a control method according to an embodiment of the invention. Fig. 2 schematically shows in Fig. 2(a) a situation in which the secondary fluid flow rate is too high, Qp < Qs; and in Fig. 2(b) a situation in which the secondary fluid flow rate and the primary fluid flow rate are balanced, namely equal, according to an embodiment of the invention, Qs = K x Qp, K = 1. Fig. 3 schematically shows in Fig. 3(a) a situation in which Qs is adjusted as a function of Qp, and Fig. 3(b) shows a situation in which Qs is adjusted based on a temperature difference in the primary fluid circuit. Fig. 4 schematically shows in Fig. 4(a) a heating and / or cooling system according to an embodiment of the invention, in which a secondary pump is provided outside the indoor unit; and in Fig. 4(b) a heating and / or cooling system according to an embodiment of the invention, in which a secondary pump is provided inside the indoor unit. Fig. 5 schematically shows in Fig. 5(a) a heating and / or cooling system according to an embodiment of the invention, in which a single secondary fluid circuit is provided; in Fig. 5(b) a heating and / or cooling system according to an embodiment of the invention, in which two secondary fluid circuits are provided; and in Fig. 5(c) a heating and / or cooling system according to an embodiment of the invention, in which three secondary fluid circuits are provided. Fig. 6 schematically shows in Fig. 6(a) and 6(b) systems of an embodiment of the invention. Detailed description

[0052] Fig. 1(a) shows method steps according to alternative (a), according to which the primary temperature difference is the target. In step 1, ΔTp is set as the target. In step 2, the primary fluid flow rate Qp is varied and is adjusted, so as to continue to meet the requirement of step 1. In step 3, the secondary fluid flow rate Qs is set accordingly, wherein it is checked that Qs ≤ Qp.

[0053] As to step 4, either step 4a or step 4b is performed, namely either, according to step 4a, the secondary fluid flow rate Qs is determined as a function of the primary fluid flow rate Qp or, according to step 4b, the secondary temperature difference ΔTs is set to be constant, optionally almost equal to the primary temperature difference ΔTp. In step 4a, a speed modulating pump with a communication protocol, such as a LIN pump, needs to be present in the secondary fluid circuit S. For step 4b, temperature sensors 9 need to be present in the secondary fluid circuit(s) S. In step 5, the secondary fluid flow rate Qs is adjusted and set accordingly.

[0054] The method shown in Fig.1(b) differs from the steps in Fig. 1(a) in that, in step 1, the primary fluid flow rate is set as the target. In step 2, ΔTp is varied and adjusted.

[0055] The embodiments of Fig. 1(a) and 1(b) reflect an implementation of the method of the invention. The fluid has a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts_in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout. Based on at least some of these values, the method comprises, in more general, the following steps: (a) Setting and maintaining the primary temperature difference ΔTp between the temperatures Tp_in and Tp_out, by adjusting the primary fluid flow rate Qp accordingly, or (b) setting and maintaining the primary fluid flow rate Qp by adjusting the primary temperature difference ΔTp between the temperatures Tp_in and Tp_out accordingly.

[0056] These steps are implemented by adjusting the secondary temperature difference ΔTs between the temperatures Ts in and Ts_out such that the secondary temperature difference ΔTs is lower than or equal to the primary temperature difference ΔTp, namely ΔTs ≤ ΔTp; or by adjusting the secondary fluid flow rate Qs such that the secondary fluid flow rate Qs is lower than or equal to the primary flow rate Qp, namely Qs ≤ Qp.

[0057] Turning to Fig. (2), more specifically Fig. 2(a) and 2(b), the decoupling tank 2 has, on one side, here at the left side, an inlet Pin and an outlet Pout for the primary fluid circuit P. At the opposite side of the tank 2, here at the right side, an inlet Sin and an outlet Sout for the secondary fluid circuit S are provided. More specifically, the primary inlet Pin is located opposite to the secondary outlet Sout, and the secondary inlet Sin is located opposite to the primary outlet Pout. The tank 2 is in fluid connection with a primary fluid inlet Pin for supply of the tank 2 with fluid, and a secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and in fluid connection with a secondary fluid inlet Sin for supply of the tank 2 with fluid, and a primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P.

[0058] Fig. 2(a) schematically shows a situation in which the secondary fluid flow rate Qs is too high, namely higher than the primary flow rate Qp, so that Qp < Qs. The consequence is that that destination fluid of the second fluid circuit S is returned into the secondary fluid circuit S by cooling the secondary fluid circuit S. The primary temperature difference ΔTp is 5°C (35°C - 30°C), wherein the secondary temperature difference ΔTs is only 1°C (30°C - 29°C). Hence, the temperature difference ΔTs in secondary fluid circuit is too small and the heating performance by means of the secondary flow circuit S is, thus, compromised.

[0059] Fig. 2(b) schematically shows a situation in which the secondary fluid flow rate Qs and the primary fluid flow rate Qp are balanced, namely equal, according to an embodiment of the invention, Qs = K x Qp, K = 1. The consequence is that fluid in the primary and secondary flow circuits Qp, Qs basically do not mix. Accordingly, the temperatures of both circuits remain substantially constant. Also, the primary temperature difference ΔTp between the primary fluid inlet and the primary fluid outlet, on the one hand, and the secondary temperature difference ΔTs between the secondary fluid inlet and the secondary fluid outlet, on the other hand, are basically identical. The primary temperature difference ΔTp is 5°C (35°C-30°C), and the secondary temperature difference ΔTs is also 5°C (34°C - 29°C).

[0060] Fig. 3(a) schematically shows a situation in which Qs is adjusted as a function of Qp, namely Qs = f(Qp). Fig. 3(b) shows a situation in which Qs is adjusted based on the temperature difference in the primary fluid circuit, namely such that ΔTp = ΔTs = constant.

[0061] Fig. 4(a) schematically shows a heating and / or cooling system 1 according to an embodiment of the invention, in which a secondary pump 7 is provided outside the indoor unit 4. A primary pump 6 is provided in the primary fluid circuit P connecting to the outdoor unit 3. The indoor unit 4 includes the tank 2. The secondary fluid circuit S as connects from the indoor unit 4 to the destination, namely the radiator 5, and includes the secondary pump 7 outside the indoor unit 4. Fig. 4(b) shows a heating and / or cooling system 1 according to an embodiment of the invention, in which the secondary pump 7 is provided inside the indoor unit 4. Other than that, the embodiment of Fig. 4(b) corresponds to the embodiment of Fig. 4(a).

[0062] The systems as shown in Fig. 4(a) and 4(b) comprises a primary P and a secondary fluid circuit S fluidly connected by the tank 2. The primary fluid circuit P is configured for transfer of thermal energy via a fluid flow at a primary fluid flow rate Qp from the source, namely an outdoor heat pump unit 3, to the secondary fluid circuit S, which is configured for transfer of thermal energy via the fluid flow at a secondary fluid flow rate Qs to a destination, here a radiator 5.

[0063] Fig. 5(a) schematically shows a heating and / or cooling system 1 according to an embodiment of the invention, in which a single secondary fluid circuit S is provided. Fig. 5(b) shows a heating and / or cooling system 1 according to an embodiment of the invention, in which two secondary fluid circuits S-1, S-2 are provided. Each of the secondary fluid circuits S-1, S-2 originate from the indoor unit 4. The indoor unit 4 also includes the tank 2. Fig. 5(c) shows a heating and / or cooling system 1 according to an embodiment of the invention, in which three secondary fluid circuits S-1, S-2, S-3 are provided. A secondary fluid circuit connects to the tank 2 and to an optional buffer tank 10, wherein the buffer tank 10 connects to three secondary fluid circuits S-1, S-2, S-3. The optional buffer tank 10 may be a storage tank for hot water (for instance, defining a volume of 1000 l). In case of multiple secondary fluid circuits, such as in the embodiment of Fig. 5(b) and 5(c), the sum of the respective parameters K, i.e. K per secondary fluid circuit, is equal to or below 1.

[0064] The heating and / or cooling system is a heat pump system 1 and comprises a (single) primary P and at least one secondary fluid circuit S fluidly connected by the tank 2. The system 1 comprises at least one primary pump 6 configured for variable speed for adjusting the primary flow rate Qp, and at least one secondary pump 7 configured for variable speed for adjusting the secondary flow rate Qs. The system 1 further comprises the control unit 8. The secondary pump 7 is a speed modulated pump with an Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors.

[0065] Fig. 6(a) schematically shows a system 1 of an embodiment of the invention. The primary fluid circuit P includes a flow meter 11 for measurement of the primary flow rate Qp, and the secondary fluid circuit S includes a flow meter 11 for measurement of the secondary flow rate Qs. The secondary fluid circuit S also includes a secondary pump 6 and allows for adjustment of the secondary flow rate Qs such that Qs equal to or smaller than Qp.

[0066] Fig. 6(b) schematically shows a system 1 of an embodiment of the invention. Compared to the system shown in Fig. 6(a), no flowmeters 11 are provided, but temperature sensors 9. The primary fluid circuit P has a temperature sensor 9 for determination of the temperature at the inlet of the primary fluid circuit Tp_in, and a temperature sensor 9 for determination of the temperature at the outlet of the primary fluid circuit Tp_out. On this basis, the primary temperature difference ΔTp is calculated. The secondary fluid circuit S has a temperature sensor 9 for determination of the temperature at the outlet of the secondary fluid circuit Ts_out, and a temperature sensor 9 for determination of the temperature at the inlet of the secondary fluid circuit Ts_in. On this basis, the secondary temperature difference ΔTs is calculated and can be adjusted.

[0067] The secondary fluid flow rate Qs is set to Qs= K x Qp, the parameter K: 0 < K ≤ 1, more preferably 0.3 < K ≤ 1, according to the control of Fig. 6(a).The secondary temperature difference ΔTs is set to ΔTs = a x ΔTp, the parameter a: 0 < a ≤ 1, more preferably 0.3 < a ≤ 1, according to the control of Fig. 6(b).

[0068] According to Fig. 6(a), the secondary flow fluid rate Qs is adjusted by adjusting the rotational speed of at least one secondary pump 7 in the secondary fluid circuit S.

[0069] The speed of the secondary pump 7 is determined based on the secondary fluid flow rate Qs, here measured by a secondary flow determination device arranged in the secondary fluid circuit S. The secondary flow determination device 7 is a speed modulated pump with a communication protocol, preferably a local Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors.

[0070] According, to Fig. 6(b), the modification of the speed of the secondary pump 7 is determined to maintain a temperature difference ΔTs between the temperatures Ts in and Ts_out, of the secondary fluid circuit S substantially constant, optionally equal to a temperature difference ΔTp between the temperatures Tp_in and Tp_out. The temperature difference ΔTs between the temperatures Ts in and Ts_out is measured by the temperature-determination sensors 9 at each of the secondary fluid inlet Sin and the secondary fluid outlet Sout, respectively, for determination of the temperatures Ts_in and Ts,_out respectively.Examples:Alternative (a): ΔT s = const = ΔT p

[0071] The temperature difference ΔTp is held constant by adjusting the primary fluid flow rate, and so is ΔTs. At the same time, ΔTs ≤ ΔTp.

[0072] To do this, departure and return temperatures (Ts_out and Ts_in, respectively) of the secondary fluid circuit S, need to be determined via, for example, a temperature sensor 9 at the departure site and a temperature sensor 9 at the return site (these sensors may be on each circuit or directly at the outlet / inlet of the decoupling tank 2 on double, quatruple, etc.inlets / outlets connections). To obtain a suitable ΔTs, pump flow rates are adjusted knowing the ODU power. An advantage may be that the secondary flow rate Qs does not need to be known. A speed modulated pump 7, e.g. with no communication protocol with the primary fluid circuit P (PWM pump, e.g. with no LIN protocol for instance) can therefore be used in the secondary fluid circuit S, instead for a flow determination device.Alternative (b): Os = f(Qp)

[0073] Select ΔTp (5 K), but offset for 0,8 Pmax < P < Pmax Choice of a flow rate ratio: Qs / Qp = 0,8, i.e. K = 0.8 At Pmax: Qp = 1,38 m3h-1 ; ΔTp = 6,2 K Qs = 1,1 m3h-1; ΔTs = 7,8 K At Pmin: Qp = 0,34 m3h-1 ; ΔTp = 5 K Q = 0,27 m3h-1; ΔTs = 6,4 ΔT may go from 5 to 10 K and sometimes P=Pmax, depending on the type of emitter. E.g. the IDU sends the ODU the ΔTs to be kept constant, from 5° to 10°C depending on the type of heating emitters (for example 5°C for underfloor heating & fan coil, or 8°C for radiators) to guarantee maximum heat pump performance.

[0074] The detailed description of the invention is provided with respect to the embodiments depicted in the drawings. Obvious variations and alternatives may occur to the skilled person, based on the summary of the invention. These variations and alternatives are part of the invention in so far they are covered by the appended claims.Reference signs

[0075] 1heat pump system 2(decoupling) tank 3outdoor unit (ODU) 4indoor unit (IDU) 5destination (heating / cooling circuit, radiator, emitter, domestic fluid tank) 6primary pump 7secondary pump 8control unit 9temperature sensor 10buffer tank 11flow meter Pprimary fluid circuit Ssecondary fluid circuit S-1first secondary fluid circuit S-2second secondary fluid circuit S-3third secondary fluid circuit Qpprimary fluid flow rate Qssecondary fluid flow rate Pin / Poutprimary fluid inlet / outlet Sin / Soutsecondary fluid inlet / outlet Tp_intemperature at inlet of primary fluid circuit Tp_outtemperature at outlet of primary fluid circuit Ts_intemperature at inlet of secondary fluid circuit Ts_outtemperature at outlet of secondary fluid circuit

Examples

Embodiment Construction

[0052]Fig. 1(a) shows method steps according to alternative (a), according to which the primary temperature difference is the target. In step 1, ΔTp is set as the target. In step 2, the primary fluid flow rate Qp is varied and is adjusted, so as to continue to meet the requirement of step 1. In step 3, the secondary fluid flow rate Qs is set accordingly, wherein it is checked that Qs ≤ Qp.

[0053]As to step 4, either step 4a or step 4b is performed, namely either, according to step 4a, the secondary fluid flow rate Qs is determined as a function of the primary fluid flow rate Qp or, according to step 4b, the secondary temperature difference ΔTs is set to be constant, optionally almost equal to the primary temperature difference ΔTp. In step 4a, a speed modulating pump with a communication protocol, such as a LIN pump, needs to be present in the secondary fluid circuit S. For step 4b, temperature sensors 9 need to be present in the secondary fluid circuit(s) S. In step 5, the secondary...

Technical field

[0001] The invention concerns a control method, a control unit and a heating and / or cooling system, in particular a heat pump system, comprising such control unit.Background

[0002] Heating or cooling installations (domestic heating / cooling systems) such as heat pump systems may comprise a (often so-called decoupling) tank which is used as a device that may make two fluid circuits hydraulically independent, e.g. the primary fluid circuit and the secondary fluid circuit of a heating or air-conditioning system. The primary fluid circuit directly or indirectly represents the energy production (generator) circuit, e.g. a boiler or a heat pump. The secondary fluid circuit is made up of emitters, fan convectors, radiators and underfloor heating, i.e. the heat consumption circuit. The primary and secondary fluid circuit are in fluidic communication thanks to the tank.

[0003] Such separation or decoupling of the primary and secondary fluid circuits is not physical, but the primary fluid circuit has its own pump and the secondary fluid circuit has one or more pumps, depending on the installation / configuration. The advantage of decoupling circuits is for instance to establish a hydraulic neutral point which allows for control of flow and pressure in the secondary fluid circuit, particularly when several secondary fluid circuits are operating independently of each other. Excessive differences in flow rate and / or pressure between the primary and secondary circuits may create disturbances that interfere during operation of the system.

[0004] The term "hydraulic neutral point" refers to a point in a heating or cooling system where the static pressures of the primary and secondary circuits are balanced. This means that at this point, there is no interactivity between the dynamic pressures induced by the different pumps; e.g. if the flow rates between the circuits are balanced (i.e. at the hydraulic neutral point), the hot water passes from the primary fluid circuit via the decoupling tank directly into the secondary fluid circuit without any significant mixing. Even if the flow rate in the secondary fluid circuit changes, thanks to the hydraulic neutral point, this does not affect the flow rate in the primary fluid circuit.

[0005] Improvements as to the efficiency (e.g. in terms of COP (coefficient of performance) of a heating and / or cooling system are desired against this background.Summary of the invention

[0006] The present invention relates to a control method of controlling a heating and / or cooling system, optionally a heat pump system. The system comprises at least one primary P and at least one secondary fluid circuit S fluidly connected by a tank, optionally a decoupling tank. The primary fluid circuit P is configured for transfer of thermal energy via a fluid flow at a primary fluid flow rate Qp from a source, optionally an outdoor heat pump unit 3, to a secondary fluid circuit S. The secondary fluid circuit S is configured for transfer of thermal energy via the fluid flow at a secondary fluid flow rate Qs to a destination, optionally a heating / cooling circuit and / or a domestic hot water tank or buffer tank. The tank is in fluid connection with a primary fluid inlet Pin for supply of the tank with fluid, and a secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and in fluid connection with a secondary fluid inlet Sin for supply of the tank with fluid, and a primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P. The fluid has a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts_in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout. The method comprises two alternative control approaches a) and b). According to (a), the following is performed: Setting and maintaining a primary temperature difference ΔTp between the temperatures Tp_in and Tp_out, by adjusting the primary fluid flow rate Qp accordingly. According to (b), the following is performed: Setting and maintaining the primary fluid flow rate Qp by adjusting the temperature difference ΔTp between the temperatures Tp_in and Tp_out accordingly. One of the following subsequent steps is performed: Adjusting the secondary temperature difference ΔTs between the temperatures Ts_in and Ts_out such that the secondary temperature difference ΔTs is lower than or equal to the primary temperature difference ΔTp, ΔTs ≤ ΔTp; or adjusting the secondary fluid flow rate Qs such that the secondary fluid flow rate Qs is lower than or equal to the primary flow rate Qp, Qs ≤ Qp.

[0007] Whether alternative (a) or (b) is used, may depend on the sensors which are available / present in the system, i.e. whether a control based on flow rate or based on temperature difference is used.

[0008] The requirement that the secondary fluid flow rate is equal to or smaller than the primary fluid flow rate has the effect that the heating losses in the decoupling tank are reduced, and so the overall thermal and energetic efficiency of the installation is improved. This is reflected in a better Coefficient of Performance (COP), which measures the ratio between the energy generated and the energy consumed by the system. At the same time, this solution ensures that the flow temperature is guaranteed, thereby meeting the customer's needs.

[0009] The idea underlying the invention is to improve the performance of a heating and / or cooling system by adjusting the temperature difference or flow rate in the primary fluid circuit, which transfers calories from the refrigerant circuit to the primary fluid circuit. It is desired to set the temperature of the primary fluid circuit such that heat exchange with the refrigerant is improved to the effect that the temperature range of the refrigerant is suitable in terms of the Carnot cycle. As an example, it was found that 8% in performance may be gained (better COP), compared to running the primary fluid circuit at a fixed flow rate.

[0010] Moreover, it was found expedient when a temperature difference ΔTp between the temperature at the inlet of the primary fluid circuit at the (decoupling) tank and the temperature at the outlet of the primary fluid circuit is held constant. The temperature difference at the inlet and outlet of the primary fluid circuit at the (decoupling) tank is similar to the temperature difference at the inlet and outlet of the heat generator (heat pump, boiler,...). To hold this temperature difference constant, the flow rate in the primary fluid circuit may be adjusted as needed for the constant temperature difference.

[0011] For such adjustment, the heat pump power needs to be adjusted and, hence, controlled. (The relation between the heat and the temperature is H = M*C*ΔT, wherein H: heat; M: Mass; c: specific heat; ΔT: change in temperature.) The (volumetric) fluid flow rate Q may be defined as the change of volume V per time Δt, namely Q = ΔV / Δt.

[0012] For example, the predetermined temperature difference between the temperature at the inlet of the primary fluid circuit at the (decoupling) tank and the temperature at the outlet of primary fluid circuit may be set as foiiows:10°C (if the destination is a high temperature radiator); 5°C (if the destination is underfloor heating or fan convector); 8°C (if the destination is a medium temperature radiator). For example, the installer / fitter may choose a ΔT suitable for the desired application during installation.

[0013] In use, fixing the temperature difference, i.e. defining the ΔT, means setting target temperature difference at least for a period of time, e.g. constant over time for a given use (underfloor heating, radiator,...) or a given mode. In other words, typically for the entire life of the heating product after its installation for a dedicated usage. It may not depend on the logic control. Rather, it is the zone in demand that imposes the temperature difference. Possibly, the temperature difference is programmed for it once and for all, e.g. the user having no access to the target temperature difference after the installation, except for massive modifications of the system (e.g. update of the emitters, circuit, insulation, etc.), ΔT is usually constant.

[0014] However, it is not excluded to change and adapt the target temperature difference, e.g. by a user or as variable parameter. For example, a time program is conceivable.

[0015] Accordingly, it is desired to improve the performance / efficiency of a heating / cooling system on the basis of a target ΔT or target flow rate Q achieved by adjusting the primary fluid flow rate or temperature difference, so as to comply with different heating / cooling demands. The invention proposes adjusting the secondary fluid flow rate or the secondary temperature difference such that the secondary fluid flow rate or secondary temperature difference is lower than or equal to the primary flow rate or secondary temperature difference, respectively.

[0016] This may be seen as controlling the secondary circuit according to the primary circuit. This may help to reduce undesired mixing of the primary and secondary fluid flows in the tank and, thus, thermal loss.

[0017] From another angle, the invention may be seen as forgoing a constant primary flow rate, but working on the basis of a target ΔTp (=Tp_in - Tp_out), so that the primary flow rate becomes variable. The secondary flow rate is adjusted as a function of the primary flow rate.

[0018] In general, a (decoupling) tank may be referred to as hydraulic separator, buffer tank or mixing tank, or simply as tank. It may serve for hydraulic separation of the primary and secondary fluid circuits. A (decoupling) tank of the invention may allow for mixing of fluid and as pressure balancer between the primary and secondary fluid circuits. Such tank may be seen as making the link between several circuits, such as a primary fluid circuit and a secondary fluid circuit. The tank has several connectors to pipes and, hence, pipes at each side. The primary fluid circuit corresponds to and is at the source side (i.e. the side of the heating device, such as the heat pump, where the fluid is heated / cooled by the heating device). The secondary fluid circuit corresponds to and is at the distribution side (i.e. the side of the radiators, floor heaters, fan coils).

[0019] By means of a (decoupling) tank between fluid circuits, the fluid flows and, hence, the fluid circuits are (remain) separated and do not conflict with the others. Each circuit may have its "own" flow. However, the tank allows for a balance between the primary and secondary fluid circuits, i.e. the demand and supply flows, so that the circuits may be in communication so as to allow for balanced heat, charge, recirculation etc.

[0020] The (decoupling) tank allows for impact on the thermal transfer of heat in the system. For example, a (decoupling) tank allows fluid from the primary fluid circuit to enter the tank and leave the tank into the secondary fluid circuit, as if a "main flow" of fluid crosses the tank as if the tank were a simple, connecting tube. If the fluid flow (in terms of the volumetric flow rate) differs between the primary and the secondary fluid circuits, i.e. at different sides of the (decoupling) tank, a part of the fluid flow entering the tank on one side may exit the tank on the same side, at another pipe at another height. Such fluid paths imply mixing of fluids having different temperatures.

[0021] The control method of the invention may aim at avoiding mixing of the primary and secondary fluid flows in the tank. The control method of the invention may be seen as aiming at balancing of primary and secondary fluid flow rates. If the primary fluid flow rate is dominant in that it exceeds the secondary fluid flow rate, the temperature or fluid flow rate in the primary fluid circuit may actively be controlled, in line with claim 1.

[0022] According to (a), the primary temperature difference is the target and is set and maintained, while the primary fluid flow rate is adjusted so as to meet the targeted primary temperature difference. E.g. as a function of the primary fluid flow rate, the secondary fluid flow rate may be adjusted, e.g. by adjusting the pump speed of a secondary pump accordingly.

[0023] According to (b), the primary fluid flow rate is the target and is set and maintained, while the primary temperature difference is adjusted so as to meet the targeted primary fluid flow rate. E.g. as a function of the primary temperature difference, the secondary temperature difference may be adjusted, e.g. by adjusting the pump speed of a secondary pump accordingly

[0024] Example controls may be as follows to set the secondary fluid flow rate Qs: Measurement of the secondary fluid flow rate Qs and adjustment thereof based on the primary fluid flow rate Qp, i.e. Qs = f(Qp). Measurement of at least two temperatures in secondary fluid circuit, namely Ts_in and Ts_out, and adjustment of the secondary fluid flow rate Qs such that ΔTs is constant.

[0025] The system may have to get access to the value of Qp, via a speed modulating pump with a communication protocol (for instance a LIN pump) or a flowmeter and / or temperatures probes (or equivalent servo control means) in the secondary fluid circuit, preferably in the indoor unit (IDU). Accordingly, the secondary temperature difference may be adjusted by means of an update of the secondary flow (thanks to pump control), which implies an update of the temperature in the secondary flow circuit.

[0026] The step of maintaining a temperature difference ΔTp may be controlled by an outdoor unit (ODU) of the heat pump system, e.g. in case of a monobloc unit, or an indoor unit (IDU) in case of split outdoor units.

[0027] ΔTp, i.e. the temperature difference, is maintained constant when the heat pump is working. Hence, the time period during which ΔTp is constant corresponds to the usage of the heat pump.

[0028] The meaning of "modular" may be as not a ON / OFF parameter. but as a parameter for which it is possible to vary different levels between maximum speed and standstill. In particular, the speed can be evaluated more or less progressively, with a limited number of speeds (for example 2 to 5) or with a non-finite number (function-based control). For example, it may be a case of controlling the power supply and therefore the speed according to a very variable number of possibilities. This is the case with Pulse Width Modulation (PWM) type control, for which it is possible to synthesise pseudo analogue signals. For example, according to prior art controls, Qp was forced to be e.g. 40l / min. So it was not possible to reduce this value to adapt the control to the external temperature for instance.

[0029] A flow and / or temperature determination device may be used to control the temperature or flow rate in the first and / or second fluid circuits.

[0030] A temperature difference ΔTp_s between Tp_in and Ts_out and / or a temperature difference ΔTs between Ts in and Tp_out may be less than 10, optionally less than 6°C.

[0031] A servo-control may refer to the constellation that the secondary pump looks for information of the primary fluid circuit and will adapt its speed according to value from the primary fluid circuit.

[0032] The parameter K depends on the tank that is used, in particular its geometry. For each tank, the parameter K may be pre-defined.

[0033] The destination may be an emitter, and may be, in general, e.g. a heating / cooling circuit, radiator, emitter, or domestic hot water tank or buffer tank.

[0034] There may be at least one (e.g. one or two) primary fluid circuits one or two secondary fluid circuits, or even more corresponding circuits. Each of the primary and secondary fluid circuits have their individual fluid circuit and individual fluid temperature etc., thus representing actually independent fluid circuits, which are, however, fluidly coupled via the common (decoupling) tank. In case of more than a single primary / secondary flow circuit, the total sum of the primary fluid circuits may be referred to as "the" primary flow rate, and the total sum of the secondary fluid circuits may be referred to as "the" secondary flow rate.

[0035] The fluid in the primary and secondary fluid circuit(s) is optionally water-based. More specifically, the fluid may be pure water or water mixed with additives, such as glycol for anti-freeze purposes.

[0036] The physical principle underling a (decoupling) tank accommodating fluid at different temperatures is stratification: The coldest fluid will, in theory, be at the lowest level (close to the bottom of the tank) and the hottest fluid will be at the highest level (close to the top of the tank). Such theoretical distribution may be compromised by perturbations, such as flow or a mixing element. Presently, flow differences between inlet(s) / outlet(s), may lead to less "ideal" thermal stratification. Nevertheless, by means of a tank, it is possible to manage different outlet temperatures (for the secondary fluid circuit(s)) with a single inlet tube (providing fluid at a single temperature from the primary fluid circuit). For example, the secondary fluid circuit which requires the highest fluid temperature may be connected to the highest outlet tube, for example for radiators (as the fluid temperature of fluid for radiation heating is higher than the temperature of fluid for floor heating).

[0037] The upper region may be regarded as a hot or warm zone of the tank, as it usually comprises the warmer part of the fluid in the tank. The lower region may be regarded as a cold zone of the tank, as it usually comprises the colder part of the fluid in the tank. A continuous decrease of the temperature of the fluid in the tank from top to bottom of the tank, when installed on site, is the usual configuration.

[0038] Optionally, the secondary fluid flow rate Qs is set to Qs = K x Qp, the parameter K: 0 < K ≤ 1, more preferably 0.3 < K ≤ 1. Alternatively, optionally, the secondary temperature difference ΔTs is set to ΔTs = a x ΔTp, the parameter a: 0 < a ≤ 1, more preferably 0.3 < a ≤ 1. This may help to efficiently implement the control of the invention.

[0039] The secondary fluid circuit may comprise one or more secondary fluid (sub)circuits. Optionally, the secondary fluid circuit S comprises at least a first secondary fluid circuit S-1 and optionally a second S-2, further optionally a third circuit S-3. Optionally, in case of multiple secondary fluid circuits, the sum of the respective parameters K or per secondary fluid circuit is equal to or below 1. Hence, if three secondary (sub)circuits are provided, the sum of K of all three circuits is below 1. For example, 0.1 ≤ K_1, 2, 3 ≤ 0.3 as K-value per (sub)circuit may be a suitable value. This may represent an efficient control.

[0040] Optionally, the secondary flow fluid rate Qs is adjusted by adjusting the rotational speed of at least one secondary pump in the secondary fluid circuit. The speed may refer to the rotational speed, power and / or frequency. Reference to a PWM (pulse width modulation) of the signal / current is made. This may efficiently implement a control of the invention.

[0041] More optionally, the speed of the secondary pump is determined based on the secondary fluid flow rate Qs, even more optionally measured by a secondary flow determination device arranged in the secondary fluid circuit S. This may help to control the secondary flow rate accordingly.

[0042] Even more optionally, the secondary flow determination device is a speed modulated pump with a communication protocol, preferably a local Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors. A LIN bus communication protocol to communicate data on the status of at least one of the elements may be used to control the flow and / or temperature of the primary and / or secondary fluid circuit. This may support implementation of the control of the invention.

[0043] Optionally, the modification of the speed of the secondary pump is determined to maintain a temperature difference ΔTs between the temperatures Ts in and Ts_out, of the secondary fluid circuit substantially constant, optionally equal to a temperature difference ΔTp between the temperatures Tp_in and Tp_out. In toher words, ΔTs between the temperatures Ts in and Ts_out of the secondary fluid circuit is maintained substantially constant, optionally ΔTs = ΔTp. This may allow for efficient control.

[0044] Optionally, the temperature difference ΔTs between the temperatures Ts_in and Ts_out is measured by at least one temperature-determination sensors at each of the secondary fluid inlet Sin and the secondary fluid outlet Sout, respectively, for determination of the temperatures Ts_in and Ts,_out respectively. This may allow for efficient control.

[0045] The invention is also direction to a control unit configured to carry out the method of the invention.

[0046] The invention is also directed to a heating / cooling system comprising the control unit of the invention. Specifically, the system of the invention comprises a primary and secondary fluid circuits and further comprises a control unit of the invention.

[0047] The invention, in general, refers to any kind of heat pump system, including at least one ground source (water)- and / or air source-heat pump unit. The heat pump units may have an indoor and / or outdoor units. A heat pump unit of the heat pump system may be a split unit or a monobloc unit. The heat pump system may be configured to heat and / or cool air or water (of a closed loop or of an open loop, such as domestic hot water).

[0048] Specifically, the invention is also directed to a heating and / or cooling system, optionally a heat pump system. The system comprises at least one primary P and at least one secondary fluid circuit S fluidly connected by a tank, optionally a decoupling tank, the primary fluid circuit P for transfer of thermal energy via fluid at a primary fluid flow rate Qp from a source, optionally an outdoor unit 3, to fluid in a secondary fluid circuit S, the secondary fluid circuit S for transfer of thermal energy at a secondary fluid flow rate Qs to a destination / emitter 5, optionally a heating / cooling circuit and / or a domestic hot water tank or buffer tank. The tank comprises a primary fluid inlet Pin, a primary fluid outlet Pout, a secondary fluid inlet Sin, and a secondary fluid outlet Sout, wherein the tank is configured to establish fluid communication with the primary fluid inlet Pin for supply of the tank with fluid, and the secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and with the secondary fluid inlet Sin for supply of the tank with fluid, and the primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P, the fluid having a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout. The system further comprises at least one primary pump 6 configured for variable speed for adjusting the primary flow rate Qp, and at least one secondary pump 7 configured for variable speed for adjusting the secondary flow rate Qs, and the control unit of the invention.

[0049] Optionally, the secondary pump is a speed modulated pump with an Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors. This may allow for efficient measurement. The measurement may be direct or indirect (contact or not), more optionally without direct contact between sensor and the fluid.

[0050] Detailed embodiments and further advantages and features related to the present invention are described in the following, wherein these examples shall not be regarded as limiting the invention.Brief description of the drawings

[0051] Fig. 1 schematically shows in Fig. 1(a) and 1(b) steps of a control method according to an embodiment of the invention. Fig. 2 schematically shows in Fig. 2(a) a situation in which the secondary fluid flow rate is too high, Qp < Qs; and in Fig. 2(b) a situation in which the secondary fluid flow rate and the primary fluid flow rate are balanced, namely equal, according to an embodiment of the invention, Qs = K x Qp, K = 1. Fig. 3 schematically shows in Fig. 3(a) a situation in which Qs is adjusted as a function of Qp, and Fig. 3(b) shows a situation in which Qs is adjusted based on a temperature difference in the primary fluid circuit. Fig. 4 schematically shows in Fig. 4(a) a heating and / or cooling system according to an embodiment of the invention, in which a secondary pump is provided outside the indoor unit; and in Fig. 4(b) a heating and / or cooling system according to an embodiment of the invention, in which a secondary pump is provided inside the indoor unit. Fig. 5 schematically shows in Fig. 5(a) a heating and / or cooling system according to an embodiment of the invention, in which a single secondary fluid circuit is provided; in Fig. 5(b) a heating and / or cooling system according to an embodiment of the invention, in which two secondary fluid circuits are provided; and in Fig. 5(c) a heating and / or cooling system according to an embodiment of the invention, in which three secondary fluid circuits are provided. Fig. 6 schematically shows in Fig. 6(a) and 6(b) systems of an embodiment of the invention. Detailed description

[0052] Fig. 1(a) shows method steps according to alternative (a), according to which the primary temperature difference is the target. In step 1, ΔTp is set as the target. In step 2, the primary fluid flow rate Qp is varied and is adjusted, so as to continue to meet the requirement of step 1. In step 3, the secondary fluid flow rate Qs is set accordingly, wherein it is checked that Qs ≤ Qp.

[0053] As to step 4, either step 4a or step 4b is performed, namely either, according to step 4a, the secondary fluid flow rate Qs is determined as a function of the primary fluid flow rate Qp or, according to step 4b, the secondary temperature difference ΔTs is set to be constant, optionally almost equal to the primary temperature difference ΔTp. In step 4a, a speed modulating pump with a communication protocol, such as a LIN pump, needs to be present in the secondary fluid circuit S. For step 4b, temperature sensors 9 need to be present in the secondary fluid circuit(s) S. In step 5, the secondary fluid flow rate Qs is adjusted and set accordingly.

[0054] The method shown in Fig.1(b) differs from the steps in Fig. 1(a) in that, in step 1, the primary fluid flow rate is set as the target. In step 2, ΔTp is varied and adjusted.

[0055] The embodiments of Fig. 1(a) and 1(b) reflect an implementation of the method of the invention. The fluid has a temperature Tp_in at the primary fluid inlet Pin, a temperature Tp_out at the primary fluid outlet Pout, a temperature Ts_in at the secondary fluid inlet Sin, and a temperature Ts_out at the secondary fluid outlet Sout. Based on at least some of these values, the method comprises, in more general, the following steps: (a) Setting and maintaining the primary temperature difference ΔTp between the temperatures Tp_in and Tp_out, by adjusting the primary fluid flow rate Qp accordingly, or (b) setting and maintaining the primary fluid flow rate Qp by adjusting the primary temperature difference ΔTp between the temperatures Tp_in and Tp_out accordingly.

[0056] These steps are implemented by adjusting the secondary temperature difference ΔTs between the temperatures Ts in and Ts_out such that the secondary temperature difference ΔTs is lower than or equal to the primary temperature difference ΔTp, namely ΔTs ≤ ΔTp; or by adjusting the secondary fluid flow rate Qs such that the secondary fluid flow rate Qs is lower than or equal to the primary flow rate Qp, namely Qs ≤ Qp.

[0057] Turning to Fig. (2), more specifically Fig. 2(a) and 2(b), the decoupling tank 2 has, on one side, here at the left side, an inlet Pin and an outlet Pout for the primary fluid circuit P. At the opposite side of the tank 2, here at the right side, an inlet Sin and an outlet Sout for the secondary fluid circuit S are provided. More specifically, the primary inlet Pin is located opposite to the secondary outlet Sout, and the secondary inlet Sin is located opposite to the primary outlet Pout. The tank 2 is in fluid connection with a primary fluid inlet Pin for supply of the tank 2 with fluid, and a secondary fluid outlet Sout for discharge of fluid into the secondary fluid circuit S; and in fluid connection with a secondary fluid inlet Sin for supply of the tank 2 with fluid, and a primary fluid outlet Pout for discharge of fluid into the primary fluid circuit P.

[0058] Fig. 2(a) schematically shows a situation in which the secondary fluid flow rate Qs is too high, namely higher than the primary flow rate Qp, so that Qp < Qs. The consequence is that that destination fluid of the second fluid circuit S is returned into the secondary fluid circuit S by cooling the secondary fluid circuit S. The primary temperature difference ΔTp is 5°C (35°C - 30°C), wherein the secondary temperature difference ΔTs is only 1°C (30°C - 29°C). Hence, the temperature difference ΔTs in secondary fluid circuit is too small and the heating performance by means of the secondary flow circuit S is, thus, compromised.

[0059] Fig. 2(b) schematically shows a situation in which the secondary fluid flow rate Qs and the primary fluid flow rate Qp are balanced, namely equal, according to an embodiment of the invention, Qs = K x Qp, K = 1. The consequence is that fluid in the primary and secondary flow circuits Qp, Qs basically do not mix. Accordingly, the temperatures of both circuits remain substantially constant. Also, the primary temperature difference ΔTp between the primary fluid inlet and the primary fluid outlet, on the one hand, and the secondary temperature difference ΔTs between the secondary fluid inlet and the secondary fluid outlet, on the other hand, are basically identical. The primary temperature difference ΔTp is 5°C (35°C-30°C), and the secondary temperature difference ΔTs is also 5°C (34°C - 29°C).

[0060] Fig. 3(a) schematically shows a situation in which Qs is adjusted as a function of Qp, namely Qs = f(Qp). Fig. 3(b) shows a situation in which Qs is adjusted based on the temperature difference in the primary fluid circuit, namely such that ΔTp = ΔTs = constant.

[0061] Fig. 4(a) schematically shows a heating and / or cooling system 1 according to an embodiment of the invention, in which a secondary pump 7 is provided outside the indoor unit 4. A primary pump 6 is provided in the primary fluid circuit P connecting to the outdoor unit 3. The indoor unit 4 includes the tank 2. The secondary fluid circuit S as connects from the indoor unit 4 to the destination, namely the radiator 5, and includes the secondary pump 7 outside the indoor unit 4. Fig. 4(b) shows a heating and / or cooling system 1 according to an embodiment of the invention, in which the secondary pump 7 is provided inside the indoor unit 4. Other than that, the embodiment of Fig. 4(b) corresponds to the embodiment of Fig. 4(a).

[0062] The systems as shown in Fig. 4(a) and 4(b) comprises a primary P and a secondary fluid circuit S fluidly connected by the tank 2. The primary fluid circuit P is configured for transfer of thermal energy via a fluid flow at a primary fluid flow rate Qp from the source, namely an outdoor heat pump unit 3, to the secondary fluid circuit S, which is configured for transfer of thermal energy via the fluid flow at a secondary fluid flow rate Qs to a destination, here a radiator 5.

[0063] Fig. 5(a) schematically shows a heating and / or cooling system 1 according to an embodiment of the invention, in which a single secondary fluid circuit S is provided. Fig. 5(b) shows a heating and / or cooling system 1 according to an embodiment of the invention, in which two secondary fluid circuits S-1, S-2 are provided. Each of the secondary fluid circuits S-1, S-2 originate from the indoor unit 4. The indoor unit 4 also includes the tank 2. Fig. 5(c) shows a heating and / or cooling system 1 according to an embodiment of the invention, in which three secondary fluid circuits S-1, S-2, S-3 are provided. A secondary fluid circuit connects to the tank 2 and to an optional buffer tank 10, wherein the buffer tank 10 connects to three secondary fluid circuits S-1, S-2, S-3. The optional buffer tank 10 may be a storage tank for hot water (for instance, defining a volume of 1000 l). In case of multiple secondary fluid circuits, such as in the embodiment of Fig. 5(b) and 5(c), the sum of the respective parameters K, i.e. K per secondary fluid circuit, is equal to or below 1.

[0064] The heating and / or cooling system is a heat pump system 1 and comprises a (single) primary P and at least one secondary fluid circuit S fluidly connected by the tank 2. The system 1 comprises at least one primary pump 6 configured for variable speed for adjusting the primary flow rate Qp, and at least one secondary pump 7 configured for variable speed for adjusting the secondary flow rate Qs. The system 1 further comprises the control unit 8. The secondary pump 7 is a speed modulated pump with an Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors.

[0065] Fig. 6(a) schematically shows a system 1 of an embodiment of the invention. The primary fluid circuit P includes a flow meter 11 for measurement of the primary flow rate Qp, and the secondary fluid circuit S includes a flow meter 11 for measurement of the secondary flow rate Qs. The secondary fluid circuit S also includes a secondary pump 6 and allows for adjustment of the secondary flow rate Qs such that Qs equal to or smaller than Qp.

[0066] Fig. 6(b) schematically shows a system 1 of an embodiment of the invention. Compared to the system shown in Fig. 6(a), no flowmeters 11 are provided, but temperature sensors 9. The primary fluid circuit P has a temperature sensor 9 for determination of the temperature at the inlet of the primary fluid circuit Tp_in, and a temperature sensor 9 for determination of the temperature at the outlet of the primary fluid circuit Tp_out. On this basis, the primary temperature difference ΔTp is calculated. The secondary fluid circuit S has a temperature sensor 9 for determination of the temperature at the outlet of the secondary fluid circuit Ts_out, and a temperature sensor 9 for determination of the temperature at the inlet of the secondary fluid circuit Ts_in. On this basis, the secondary temperature difference ΔTs is calculated and can be adjusted.

[0067] The secondary fluid flow rate Qs is set to Qs= K x Qp, the parameter K: 0 < K ≤ 1, more preferably 0.3 < K ≤ 1, according to the control of Fig. 6(a).The secondary temperature difference ΔTs is set to ΔTs = a x ΔTp, the parameter a: 0 < a ≤ 1, more preferably 0.3 < a ≤ 1, according to the control of Fig. 6(b).

[0068] According to Fig. 6(a), the secondary flow fluid rate Qs is adjusted by adjusting the rotational speed of at least one secondary pump 7 in the secondary fluid circuit S.

[0069] The speed of the secondary pump 7 is determined based on the secondary fluid flow rate Qs, here measured by a secondary flow determination device arranged in the secondary fluid circuit S. The secondary flow determination device 7 is a speed modulated pump with a communication protocol, preferably a local Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors.

[0070] According, to Fig. 6(b), the modification of the speed of the secondary pump 7 is determined to maintain a temperature difference ΔTs between the temperatures Ts in and Ts_out, of the secondary fluid circuit S substantially constant, optionally equal to a temperature difference ΔTp between the temperatures Tp_in and Tp_out. The temperature difference ΔTs between the temperatures Ts in and Ts_out is measured by the temperature-determination sensors 9 at each of the secondary fluid inlet Sin and the secondary fluid outlet Sout, respectively, for determination of the temperatures Ts_in and Ts,_out respectively.Examples:Alternative (a): ΔT s = const = ΔT p

[0071] The temperature difference ΔTp is held constant by adjusting the primary fluid flow rate, and so is ΔTs. At the same time, ΔTs ≤ ΔTp.

[0072] To do this, departure and return temperatures (Ts_out and Ts_in, respectively) of the secondary fluid circuit S, need to be determined via, for example, a temperature sensor 9 at the departure site and a temperature sensor 9 at the return site (these sensors may be on each circuit or directly at the outlet / inlet of the decoupling tank 2 on double, quatruple, etc.inlets / outlets connections). To obtain a suitable ΔTs, pump flow rates are adjusted knowing the ODU power. An advantage may be that the secondary flow rate Qs does not need to be known. A speed modulated pump 7, e.g. with no communication protocol with the primary fluid circuit P (PWM pump, e.g. with no LIN protocol for instance) can therefore be used in the secondary fluid circuit S, instead for a flow determination device.Alternative (b): Os = f(Qp)

[0073] Select ΔTp (5 K), but offset for 0,8 Pmax < P < Pmax Choice of a flow rate ratio: Qs / Qp = 0,8, i.e. K = 0.8 At Pmax: Qp = 1,38 m3h-1 ; ΔTp = 6,2 K Qs = 1,1 m3h-1; ΔTs = 7,8 K At Pmin: Qp = 0,34 m3h-1 ; ΔTp = 5 K Q = 0,27 m3h-1; ΔTs = 6,4 ΔT may go from 5 to 10 K and sometimes P=Pmax, depending on the type of emitter. E.g. the IDU sends the ODU the ΔTs to be kept constant, from 5° to 10°C depending on the type of heating emitters (for example 5°C for underfloor heating & fan coil, or 8°C for radiators) to guarantee maximum heat pump performance.

[0074] The detailed description of the invention is provided with respect to the embodiments depicted in the drawings. Obvious variations and alternatives may occur to the skilled person, based on the summary of the invention. These variations and alternatives are part of the invention in so far they are covered by the appended claims.Reference signs

[0075] 1heat pump system 2(decoupling) tank 3outdoor unit (ODU) 4indoor unit (IDU) 5destination (heating / cooling circuit, radiator, emitter, domestic fluid tank) 6primary pump 7secondary pump 8control unit 9temperature sensor 10buffer tank 11flow meter Pprimary fluid circuit Ssecondary fluid circuit S-1first secondary fluid circuit S-2second secondary fluid circuit S-3third secondary fluid circuit Qpprimary fluid flow rate Qssecondary fluid flow rate Pin / Poutprimary fluid inlet / outlet Sin / Soutsecondary fluid inlet / outlet Tp_intemperature at inlet of primary fluid circuit Tp_outtemperature at outlet of primary fluid circuit Ts_intemperature at inlet of secondary fluid circuit Ts_outtemperature at outlet of secondary fluid circuit

Examples

Embodiment Construction

[0052]Fig. 1(a) shows method steps according to alternative (a), according to which the primary temperature difference is the target. In step 1, ΔTp is set as the target. In step 2, the primary fluid flow rate Qp is varied and is adjusted, so as to continue to meet the requirement of step 1. In step 3, the secondary fluid flow rate Qs is set accordingly, wherein it is checked that Qs ≤ Qp.

[0053]As to step 4, either step 4a or step 4b is performed, namely either, according to step 4a, the secondary fluid flow rate Qs is determined as a function of the primary fluid flow rate Qp or, according to step 4b, the secondary temperature difference ΔTs is set to be constant, optionally almost equal to the primary temperature difference ΔTp. In step 4a, a speed modulating pump with a communication protocol, such as a LIN pump, needs to be present in the secondary fluid circuit S. For step 4b, temperature sensors 9 need to be present in the secondary fluid circuit(s) S. In step 5, the secondary...

Claims

1. A control method of controlling a heating and / or cooling system, optionally a heat pump system (1), the system comprising at least one primary (P) and at least one secondary fluid circuit (S) fluidly connected by a tank (2), optionally a decoupling tank, the primary fluid circuit (P) for transfer of thermal energy via a fluid flow at a primary fluid flow rate (Qp) from a source, optionally an outdoor heat pump unit (3), to a secondary fluid circuit (S), the secondary fluid circuit (S) for transfer of thermal energy via the fluid flow at a secondary fluid flow rate (Qs) to a destination, optionally a heating / cooling circuit and / or a domestic hot water tank or buffer tank, wherein the tank (2) is in fluid connection with a primary fluid inlet (Pin) for supply of the tank (2) with fluid, and a secondary fluid outlet (Sout) for discharge of fluid into the secondary fluid circuit (S); and in fluid connection with a secondary fluid inlet (Sin) for supply of the tank (2) with fluid, and a primary fluid outlet (Pout) for discharge of fluid into the primary fluid circuit (P), the fluid having a temperature Tp_in at the primary fluid inlet (Pin), a temperature Tp_out at the primary fluid outlet (Pout), a temperature Ts_in at the secondary fluid inlet (Sin), and a temperature Ts_out at the secondary fluid outlet (Sout), the method comprising: (a) setting and maintaining a primary temperature difference ΔTp between the temperatures Tp_in and Tp_out, by adjusting the primary fluid flow rate Qp accordingly, or (b) setting and maintaining the primary fluid flow rate Qp by adjusting the primary temperature difference ΔTp between the temperatures Tp_in and Tp_out accordingly, and adjusting the secondary temperature difference ΔTs between the temperatures Ts in and Ts_out such that the secondary temperature difference ΔTs is lower than or equal to the primary temperature difference ΔTp, ΔTs ≤ ΔTp; or adjusting the secondary fluid flow rate (Qs) such that the secondary fluid flow rate (Qs) is lower than or equal to the primary flow rate (Qp), Qs ≤ Qp.

2. Method of claim 1, wherein the secondary fluid flow rate Qs is set to Qs = K x Qp, the parameter K: 0 < K ≤ 1, more preferably 0.3 < K ≤ 1, or the secondary temperature difference ΔTs is set to ΔTs = a x ΔTp, the parameter a: 0 < a ≤ 1, more preferably 0.3 < a ≤ 1.

3. Method of claim 2, wherein, in case of multiple secondary fluid circuits and respective parameters K, the sum of the respective parameters K is equal to or below 1.

4. Method of any of the preceding claims, wherein the secondary flow fluid rate (Qs) is adjusted by adjusting the rotational speed of at least one secondary pump (7) in the secondary fluid circuit (S).

5. Method of claim 4, wherein the speed of the secondary pump (6) is determined based on the secondary fluid flow rate (Qs), optionally measured by a secondary flow determination device (6, 11) arranged in the secondary fluid circuit (S).

6. Method of claim 5, wherein the secondary flow determination device (6, 11) is a speed modulated pump with a communication protocol, preferably a local Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors.

7. Method of any of the preceding claims, wherein the modification of the speed of the secondary pump (7) is determined to maintain a temperature difference ΔTs between the temperatures Ts_in and Ts_out, of the secondary fluid circuit (S) substantially constant, optionally equal to a temperature difference ΔTp between the temperatures Tp_in and Tp_out.

8. Method of any of the preceding claims, wherein the temperature difference ΔTs between the temperatures Ts_in and Ts_out is measured by at least one temperature-determination sensor (9) at each of the secondary fluid inlet (Sin) and the secondary fluid outlet (Sout), respectively, for determination of the temperatures Ts in and Ts,_out respectively.

9. Control unit configured to carry out the method of any of the preceding claims 1 to 8.

10. Heating and / or cooling system, optionally a heat pump system (1), the system comprising at least one primary (P) and at least one secondary fluid circuit (S) fluidly connected by a tank (2), optionally a decoupling tank, the primary fluid circuit (P) for transfer of thermal energy via fluid at a primary fluid flow rate (Qp) from a source, optionally an outdoor unit (3), to fluid in a secondary fluid circuit (S), the secondary fluid circuit (S) for transfer of thermal energy at a secondary fluid flow rate (Qs) to a destination / emitter (5), optionally a heating / cooling circuit and / or domestic hot water tank or buffer tank, wherein the tank (2) comprises a primary fluid inlet (Pin), a primary fluid outlet (Pout), a secondary fluid inlet (Sin), and a secondary fluid outlet (Sout), wherein the tank (2) is configured to establish fluid communication with the primary fluid inlet (Pin) for supply of the tank (2) with fluid, and the secondary fluid outlet (Sout) for discharge of fluid into the secondary fluid circuit (S); and with the secondary fluid inlet (Sin) for supply of the tank (2) with fluid, and the primary fluid outlet (Pout) for discharge of fluid into the primary fluid circuit (P), the fluid having a temperature Tp_in at the primary fluid inlet (Pin), a temperature Tp_out at the primary fluid outlet (Pout), a temperature Ts in at the secondary fluid inlet (Sin), and a temperature Ts_out at the secondary fluid outlet (Sout), the system further comprising at least one primary pump (6) configured for variable speed for adjusting the primary flow rate (Qp), and at least one secondary pump (7) configured for variable speed for adjusting the secondary flow rate (Qs), and the control unit (8) of claim 9.

11. System of claim 10, wherein the secondary pump (7) is a speed modulated pump with an Interconnect Network pump (LIN) pump, a speed modulated pump coupled with a flowmeter, and / or a speed modulated pump having at least two temperature sensors.

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