EP3961127A1

EP3961127A1 - Air conditioning system and method for its control

Info

Publication number: EP3961127A1
Application number: EP20193681.2A
Authority: EP
Inventors: Duan WU; Georgeanna KAWALEY
Original assignee: Mitsubishi Electric Corp; Mitsubishi Electric R&D Centre Europe BV Netherlands
Current assignee: Mitsubishi Electric Corp; Mitsubishi Electric R&D Centre Europe BV Netherlands
Priority date: 2020-08-31
Filing date: 2020-08-31
Publication date: 2022-03-02

Abstract

An air conditioning system and a method for its control is provided. The air conditioning system comprises a heating and/or cooling part and a heat transfer circuit, wherein a first heat exchanger thermally connects the heating and/or cooling part with the heat transfer circuit. The heat transfer circuit comprises a pump configured to circulate a heat transfer medium in the heat transfer circuit, a second heat exchanger configured to transfer heat between the heat transfer medium of the heat transfer circuit and an indoor space, and a bypass line bypassing the second heat exchanger, wherein the bypass line comprises a bypass valve between a first and a second end of the bypass line, wherein the bypass valve is configured to control a flow through the bypass line and wherein the heat transfer circuit comprises a heat transfer medium containing a phase change material. A controller of the system is configured to control an opening degree of the bypass valve. The presented air conditioning system has an increased coefficient of performance.

Description

An air conditioning system and a method for its control is provided. The air conditioning system comprises a heating and/or cooling part and a heat transfer circuit, wherein a first heat exchanger thermally connects the heating and/or cooling part with the heat transfer circuit. The heat transfer circuit comprises a pump configured to circulate a heat transfer medium in the heat transfer circuit, a second heat exchanger configured to transfer heat between the heat transfer medium of the heat transfer circuit and an indoor space, and a bypass line bypassing the second heat exchanger, wherein the bypass line comprises a bypass valve between a first and a second end of the bypass line, wherein the bypass valve is configured to control a flow through the bypass line and wherein the heat transfer circuit comprises a heat transfer medium containing a phase change material. A controller of the system is configured to control an opening degree of the bypass valve. The presented air conditioning system has an increased coefficient of performance.
In conventional HVAC systems, water or refrigerant is used for transport heating or cooling to indoor unit for maintaining the indoor temperature or comfort. A slurry of a phase change material (PCM slurry) can be used to reduce the usage of refrigerant due to increased F-gas regulation to reduce greenhouse gas emission.
The main challenge for PCM slurry based systems to control the system operation is to guarantee the operation temperature range is suitable for specific PCM material and concentration as well as to deliver the correct amount of cooling capacity to the indoor space.
For a PCM slurry based system, the degree of freedom of the system is increased due to the phase change temperature variable which is related to the concentration of PCM. However, the problem with the prior art systems and methods is that the temperature of the medium containing a phase change material (PCM) cannot be controlled satisfactorily to be in the desired range around the phase change temperature of the PCM. Thus, in prior art systems and methods, the cooling capacity at an indoor unit can vary and a desired higher cooling capacity can often only be achieved by increasing the flow rate of the medium containing the PCM to very high flow rates, which consumes much electrical energy. Thus, there is a desire in the prior art to improve the coefficient of performance (COP) regarding these air conditioning systems and methods for controlling these air conditioning systems.
CN 104 673 191 A discloses a tetrabutylammonium bromide (TBAB) aqueous solution which is in heat exchange with the refrigerant and uses a cooled refrigerant to obtain a TBAB aqueous solution containing a TBAB hydrate slurry, wherein concentration of solid TBAB in the TBAB hydrate slurry and that of dissolved TBAB in the TBAB aqueous solution is the same.
US 6,237,346 B1 discloses a method for transporting cold latent-heat which is characterized in that a cold transporting medium for use in the method is a semi-clathrate hydrate (liquid-liquid clathrate) capable of crystallization when an onium salt having C₄H₉-group and iso-C₅H₁₁-group is included as a guest into basket-like clathrate lattices consisting of water molecules.
US 2017/0307263 A1 discloses a heat transfer system that includes a heat exchanger comprising an inlet, an outlet, and a flow path through the heat exchanger between the inlet and the outlet, wherein the system also includes a fluid circulation loop external to the heat exchanger connecting the outlet to the inlet, wherein a phase change composition is disposed in the system flowing through the fluid circulation loop and the flow path through the heat exchanger.
Starting from this prior art, it was the object of the present application to provide an air conditioning system and a method for controlling an air conditioning system which does not suffer the disadvantages of the prior art. Specifically, the system and method should be characterized by an increased COP compared to known systems and methods.
The object is solved by the air conditioning system according to claim 1 and the method for controlling an air conditioning system according to claim 11. The dependent claims illustrate advantageous embodiments of the invention.
According to the invention, an air conditioning system is provided which comprises
a heating and/or cooling part comprising a first part of a first heat exchanger, wherein the first heat exchanger comprises the first part and a second part and is configured to exchange heat between the first and second part,
a heat transfer circuit comprising the second part of the first heat exchanger and further comprising

a pump configured to circulate a heat transfer medium in the heat transfer circuit,
a second heat exchanger configured to transfer heat between the heat transfer medium and an indoor space, and
a bypass line bypassing the second heat exchanger, wherein the bypass line comprises a bypass valve between a first and a second end of the bypass line, the bypass valve being configured to control a flow through the bypass line, wherein the heat transfer circuit comprises a heat transfer medium, which is configured to be circulated in the heat transfer circuit, wherein the heat transfer medium contains a phase change material; and

The advantage of the air conditioning system according to the invention is that it is has an increased coefficient of performance (COP) compared to known air conditioning systems. This advantage is achieved by the controller of the system which is configured to control an opening degree of the bypass valve. Thus, the controller can ensure that the temperature of the heat transfer medium, which comprises the phase change material (PCM), is essentially identical to the phase change temperature of the PCM, which is related to the concentration of PCM. This allows to achieve a minimum flow rate in the heat transfer circuit (slurry circuit) and energy efficiency to be improved. In comparison with a water based cooling system, the present system and method achieves a COP which is 4.5% higher which is mainly due to the pumping power reduction in the slurry circuit.
The air conditioning system can be characterized in that the heating and/or cooling part is a refrigerant circuit comprising a compressor, a condenser, an expansion device, a liquid separator and a refrigerant.
The bypass line of the system can branch off from a main circuit of the heat transfer circuit between the pump and the second heat exchanger on its first end and branches of the main circuit between the second part of the first heat exchanger and the second heat exchanger on its second end.
The heat transfer circuit can further comprise a third heat exchanger which is configured to transfer heat between the heat transfer medium and an indoor space. Furthermore, the heat transfer circuit can further comprise a storage device for storing the phase change material.
The heat transfer medium can contain the phase change material in the form of a dispersion of solid phase change material in a liquid, preferably in the form of a slurry. Furthermore, the heat transfer medium can contain the phase change material in a concentration of 5 to 20 wt.-%, preferably 7 to 15 wt.-%, more preferably 8 to 12 wt.-%, especially 10 wt.-%, relative to the total weight of the heat transfer medium. Moreover, the heat transfer medium can contain a phase change material which has a phase change temperature in the range of -5 °C to 5 °C.
The heat transfer circuit can comprise a temperature sensor at a first end of the second part of the first heat exchanger. Furthermore, the heat transfer circuit can comprise a (further) temperature sensor at a second end of the second part of the first heat exchanger. Moreover, the refrigerant circuit can comprise a temperature sensor and a pressure sensor at the discharge line of a compressor of the refrigerant circuit.
The controller can be configured to control an opening degree of an expansion device of the heating and/or cooling part based on a degree of superheat determined from a temperature sensor and a pressure sensor at the discharge line of a compressor of the refrigerant circuit. The control is preferably such that if the determined degree of superheat is higher than a predetermined value, the opening degree of the expansion device is increased and/or if the determined degree of superheat is lower than a predetermined value, the opening degree of the expansion device is decreased.
Moreover, the controller can be configured to control the speed of a compressor of the system based on the temperature of the heat transfer medium. The control is preferably such that the speed of the compressor is increased if the temperature of the phase change material is higher than the phase change temperature of the phase change material and/or the speed of the compressor is decreased if the temperature of the phase change material is lower than the phase change temperature of the phase change material. The temperature of the phase change material is preferably obtained from a temperature sensor at an inlet of the first heat exchanger.
Furthermore, the controller can be configured to control the opening degree of the bypass valve based on a differential temperature of the heat transfer medium between an inlet of the first heat exchanger and an outlet of the first heat exchanger. The control is preferably such that the opening degree of the bypass valve is increased if the differential temperature is lower than a predetermined set point and/or the opening degree of the bypass valve is decreased if the differential temperature is higher than a predetermined set point. The differential temperature is preferably calculated from a temperature obtained from a temperature sensor at an inlet of the first heat exchanger and from a temperature obtained from a temperature sensor at an outlet of the first heat exchanger.
Besides, the controller can be configured to control the conveying speed of the pump based on a cooling capacity determined from the current flow rate of the heat transfer medium and determined from a differential temperature of the heat transfer medium between an inlet of the first heat exchanger and an outlet of the first heat exchanger. The control is preferably such that the conveying speed of the pump is increased if the cooling capacity is lower than a predetermined set point and/or the conveying speed of the pump (P) is decreased if the cooling capacity is higher than a predetermined set point. The current flow of the heat transfer medium is preferably obtained from the pump and the differential temperature is preferably calculated from a temperature obtained from a temperature sensor at an inlet of the first heat exchanger and from a temperature obtained from a temperature sensor at an outlet of the first heat exchanger.
According to the invention, a method is provided for controlling an air conditioning system according to the invention, wherein the method comprises a step of controlling an opening degree of the bypass valve based on a differential temperature of the heat transfer medium between an inlet of the first heat exchanger and an outlet of the first heat exchanger.
The method can be characterized in that an opening degree of an expansion device of the heating and/or cooling part is controlled based on a degree of superheat determined from a temperature sensor and a pressure sensor at the discharge line of a compressor of the refrigerant circuit. The control is preferably such that if the determined degree of superheat is higher than a predetermined value, the opening degree of the expansion device is increased and/or if the determined degree of superheat is lower than a predetermined value, the opening degree of the expansion device is decreased.
In the method, the speed of a compressor of the system can be controlled based on the temperature of the heat transfer medium. The control is preferably such that the speed of the compressor is increased if the temperature of the phase change material is higher than the phase change temperature of the phase change material and/or the speed of the compressor is decreased if the temperature of the phase change material is lower than the phase change temperature of the phase change material. The temperature of the phase change material is preferably obtained from a temperature sensor at an inlet of the first heat exchanger.
Furthermore, in the method, the opening degree of the bypass valve can be controlled based on a differential temperature of the heat transfer medium between an inlet of the first heat exchanger and an outlet of the first heat exchanger. The control is preferably such that the opening degree of the bypass valve is increased if the differential temperature is lower than a predetermined set point and/or the opening degree of the bypass valve is decreased if the differential temperature is higher than a predetermined set point. The differential temperature is preferably calculated from a temperature obtained from a temperature sensor at an inlet of the first heat exchanger and from a temperature obtained from a temperature sensor at an outlet of the first heat exchanger.
Moreover, in the method, a conveying speed of the pump can be controlled based on a cooling capacity determined from the current flow rate of the heat transfer medium and determined from a differential temperature of the heat transfer medium between an inlet of the first heat exchanger and an outlet of the first heat exchanger. The control is preferably such that the conveying speed of the pump is increased if the cooling capacity is lower than a predetermined set point and/or the conveying speed of the pump (P) is decreased if the cooling capacity is higher than a predetermined set point. The current flow of the heat transfer medium is preferably obtained from the pump and the differential temperature is preferably calculated from a temperature obtained from a temperature sensor at an inlet of the first heat exchanger and from a temperature obtained from a temperature sensor at an outlet of the first heat exchanger.
With reference to the following Figures and Example, the subject according to the invention is intended to be explained in more detail without wishing to restrict said subject to the special embodiments shown here.

Figure 1 shows a schematic drawing of an air conditioning system according to the invention. The refrigerant circuit RC comprises a compressor Comp, a condenser Cond, an expansion device LEV, a liquid separator LS, two valves V1, V2 and a first heat exchanger PHEX and is comprised by an outdoor unit. Refrigerant circulates through the refrigerant circuit. The first heat exchanger PHEX is in thermal connection with a slurry circuit SC. The slurry circuit SC comprises a pump P, a main valve SMV and a bypass valve BPV within a bypass line BL, which are comprised by a hydronic box HB, and further comprises a second heat exchanger HEX2 and a third heat exchanger HEX3 which are comprised by an indoor unit IU. A slurry of a phase change material circulates through the slurry circuit SC.
Figure 2 shows a schematic drawing of an architecture of the controller of an air conditioning system according to the invention. The controller controls the opening degree of the expansion device of the refrigerant circuit to determine the degree of superheat in the refrigerant circuit. Furthermore, the controller controls the speed of the compressor of the refrigerant circuit to determine the cooling capacity of the refrigerant. Moreover, the controller controls the opening degree of the bypass valve of the slurry circuit to determine the cooling capacity of the second and third heat exchanger of the indoor unit. Besides, the controller controls the speed of the pump of the slurry circuit to further determine the cooling capacity of the second and third heat exchanger of the indoor unit. "e(t)" is the control error which equals to the setpoint of controlled variable (CV) minus the measurement of CV. "SH" is the super heat, which is defined as the differential temperature of measured temperate of gas phase and the saturation temperature under same pressure. "ΔT_pcs" is the differential temperature of phase change slurry between inlet and outlet at first heat exchanger PHEX (ΔT_pcs = T_PCS,inlet- T_PCS,outlet). "T_PCs,inlet" is the temperature of the heat transfer medium containing the phase change material at the inlet of the first heat exchanger. "Q_HEX" is the heat transfer rate of the first heat exchanger PHEX (or its cooling capacity).
Figure 3 shows a schematic drawing of an alternative architecture of the controller of an air conditioning system according to the invention. The controller controls the opening degree of the expansion device of the refrigerant circuit to determine the degree of superheat in the refrigerant circuit. Furthermore, the controller controls the speed of the compressor of the refrigerant circuit to determine the cooling capacity of the refrigerant. Moreover, the controller controls the opening degree of the bypass valve of the slurry circuit to determine the cooling capacity of the second and third heat exchanger of the indoor unit. Besides, the controller controls the speed of the pump of the slurry circuit to further determine the cooling capacity of the second and third heat exchanger of the indoor unit. "e(t)" is the control error which equals to the setpoint of controlled variable (CV) minus the measurement of CV. "SH" is the super heat, which is defined as the differential temperature of measured temperate of gas phase and the saturation temperature under same pressure. "ΔT_pcs" is the differential temperature of phase change slurry between inlet and outlet at first heat exchanger PHEX (ΔT_pcs = T_PCS,inlet- T_PCs,outlet). "T_PCS,inlet" is the temperature of the heat transfer medium containing the phase change material at the inlet of the first heat exchanger. ""T_indoor" is the indoor temperature value which be measured by a thermostatic sensor.
Figure 4 shows the pressure loss in dependence of the opening degree of the bypass valve (in %). By adjusting the opening degree of the bypass valve by the controller, it can be ensured the operation temperature of the slurry will span across the phase change temperature of the phase change material, which is related to the concentration of PCM. By doing so, a minimum flow rate for the slurry circuit can be achieved.
Figures 5 to 8 show a control and performance of several actuators of a system according to the invention over time. Figure 5 shows the control and performance of the compressor of the heating and/or cooling part (refrigerant circuit). Figure 6 shows the control and the performance of the expansion device of the heating and/or cooling part (refrigerant circuit). Figure 7 shows the control and performance of the bypass valve of the slurry circuit. Figure 8 shows the control and performance of the pump of the slurry circuit.

Example - Method according to the invention

For controlling the air conditioning system, a bypass line is present in the heat transfer circuit of the system to bypass at least one indoor heat exchanger (second heat exchanger and optionally third heat exchanger).
The flow rate of the medium containing the phase change material (PCM) can be controlled by the controller of the system. The functions of the following parts of the system is highlighted:
The expansion device of the refrigerant circuit mainly ensures the superheat (SH) at the suction line of the compressor has a predetermined value, so the compressor will be running safely. The measured superheat will be compared with a setpoint first, then an error value is calculated and then passed to the controller. For example, if the measurement value is higher than the setpoint, the controller will send a control signal to the expansion device in which openness of the expansion device will increase so that more refrigerant flow will be present in the evaporator then the super heat will reduce.
The compressor of the refrigerant circuit mainly keeps the temperature of the PCS at the inlet of the first heat exchanger slightly higher than the melting (equilibrium) temperature of the PCM. The controller is using the compressor to control the inlet temperature of the medium containing the PCM at the inlet of the first heat exchanger on the side of the heat transfer circuit. The measured medium temperature is compared with a setpoint, an error is calculated and then a value is feed to the controller. The controller will output a signal to the compressor based on the error value. For example, if the measurement is lower than the setpoint, the controller will output an increased frequency value to the compressor in which compressor will operate harder and bring down the evaporation temperature. Then, the inlet temperature of the medium containing PCM will lower towards the setpoint.
The pump of the heat transfer circuit modulates the flow rate of the medium containing PCM to set said medium to a predetermined temperature (preferably essentially the phase change temperature of the heat medium) at an exit of the first heat exchanger, so that the PCM material in the medium has its maximum cooling capacity (melting enthalpy of the PCM material). The cooling capacity is calculated based on the flow rate of the medium containing the PCM and a differential temperature of the medium containing the PCM, the measurement is compared with a setpoint, then an error value is obtained and a value fed to the controller. The controller will output the pump speed signal accordingly. For example, if measured value is lower than the setpoint, the controller will increase pump speed so more medium containing PCM will be pumped to the indoor unit heat exchanger to increase the cooling capacity toward to its setpoint. Alternatively, if the indoor temperature is used as CV the measurement is taken at a constant interval and then compared with the setpoint. An error value is calculated and then fed into the controller. The controller then outputs a control signal to the actuator pump. For example, if the indoor temperature is higher than the setpoint, the controller will increase the pump speed so more medium containing the PCM will be fed into indoor unit to reduce the indoor room temperature.
The bypass valve in the heat transfer circuit tunes the flow rate of medium containing the PCM to ensure that the system will deliver the right cooling capacity to the indoor heat exchanger and maintains a desired indoor room temperature according to a setpoint. The controller is using the bypass valve (e.g. a stepper motorized valve) to control the differential temperature of the medium containing the PCM which flows between the inlet and the outlet of the first heat exchanger. ΔT_PCS is measured by two temperature sensors at the inlet and outlet of the first heat exchanger and then compared with a setpoint so an error value will be calculated and fed to the controller. The controller will output the control signal according to the value to the bypass valve. For example, if the measurement value is lower than the setpoint, the bypass valve will increase its openness so more flow will be pumped in the slurry circuit. Then, the differential temperature will reduce towards the setpoint.

List of reference signs

RC:: refrigerant circuit (heating and/or cooling part);
SC:: slurry circuit (heat transfer circuit);
PHEX:: first heat exchanger;
FP:: first part of first heat exchanger;
SP:: second part of first heat exchanger;
HEX2:: second heat exchanger;
HEX3:: third heat exchanger;
IU:: indoor unit (in indoor space);
OU:: outdoor unit (in outdoor space);
HB:: hydronic box;
P:: Pump;
BL:: bypass line;
BPV:: bypass valve (e.g. a stepper motorized valve);
LEV:: expansion device (e.g. an expansion valve);
Comp:: compressor;
Cond:: condenser;
LS:: liquid separator;
V1, V2:: valves of the refrigerant circuit.

Claims

Air conditioning system comprising
a heating and/or cooling part (RC) comprising a first part (FP) of a first heat exchanger (PHEX), wherein the first heat exchanger (PHEX) comprises the first part (FP) and a second part (SP) and is configured to exchange heat between the first part (FP) and second part (SP),
a heat transfer circuit (SC) comprising the second part (SP) of the first heat exchanger (PHEX) and further comprising
a pump (P) configured to circulate a heat transfer medium in the heat transfer circuit (SC),
a second heat exchanger (HEX2) configured to transfer heat between the heat transfer medium and an indoor space (IU), and
a bypass line (BL) bypassing the second heat exchanger (HEX2), wherein the bypass line (BL) comprises a bypass valve (BPV) between a first and a second end of the bypass line (BL), the bypass valve (BPV) being configured to control a flow through the bypass line (BL), wherein the heat transfer circuit (SC) comprises a heat transfer medium, which is configured to be circulated in the heat transfer circuit (SC), wherein the heat transfer medium contains a phase change material; and
a controller which is configured to control an opening degree of the bypass valve (BPV).
Air conditioning system according to the preceding claim, wherein the heating and/or cooling part is a refrigerant circuit comprising a compressor (Comp), a condenser (Cond), an expansion device (LEV), a liquid separator (LS) and a refrigerant.
Air conditioning system according to one of the preceding claims, wherein the bypass line (BL) branches off from a main circuit of the heat transfer circuit (SC) between the pump (P) and the second heat exchanger (HEX2) on its first end and branches of the main circuit between the second part of the first heat exchanger (PHEX) and the second heat exchanger (HEX2) on its second end.
Air conditioning system according to one of the preceding claims, wherein the heat transfer circuit (SC) further comprises
i) a third heat exchanger (HEX3) which is configured to transfer heat between the heat transfer medium and an indoor space; and/or

ii) a storage device for storing the phase change material (PCM).
Air conditioning system according to one of the preceding claims, wherein the phase change material
i) is present in the heat transfer medium in the form of a dispersion of solid phase change material in a liquid, preferably is present in the heat transfer medium in the form of a slurry; and/or

ii) is present in the heat transfer medium in a concentration of 5 to 20 wt.-%, preferably 7 to 15 wt.-%, more preferably 8 to 12, especially 10 wt.-%, relative to the total weight of the heat transfer medium; and/or

iii) has a phase change temperature in the range of -5 °C to 10 °C, preferably -5 °C to 5 °C.
Air conditioning system according to one of the preceding claims, wherein the system comprises
i) in the heat transfer circuit (SC), a temperature sensor (TS1) at a first end of the second part of the first heat exchanger; and/or

ii) in the heat transfer circuit (SC), a temperature sensor (TS2) at a second end of the second part of the first heat exchanger; and/or

iii) in the refrigerant circuit, a temperature sensor (TS3) and a pressure sensor (PS) at the discharge line of a compressor (Comp) of the refrigerant circuit.
Air conditioning system according to one of the preceding claims, wherein the controller is configured to control an opening degree of an expansion device of the heating and/or cooling part based on a degree of superheat determined from a temperature sensor (TS3) and a pressure sensor (PS) at the discharge line of a compressor (Comp) of the refrigerant circuit, preferably such that
i) if the determined degree of superheat is higher than a predetermined value, the opening degree of the expansion device (LEV) is increased; and/or

ii) if the determined degree of superheat is lower than a predetermined value, the opening degree of the expansion device (LEV) is decreased.
Air conditioning system according to one of the preceding claims, wherein the controller is configured to control the speed of a compressor (Comp) of the system based on the temperature of the heat transfer medium, preferably such that
i) the speed of the compressor (Comp) is increased if the temperature of the phase change material is higher than the phase change temperature of the phase change material; and/or

ii) the speed of the compressor (Comp) is decreased if the temperature of the phase change material is lower than the phase change temperature of the phase change material;
wherein the temperature of the phase change material is preferably obtained from a temperature sensor (TS1) at an inlet of the first heat exchanger (PHEX).
Air conditioning system according to one of the preceding claims, wherein the controller is configured to control the opening degree of the bypass valve (BPV) based on a differential temperature of the heat transfer medium between an inlet of the first heat exchanger (PHEX) and an outlet of the first heat exchanger (PHEX), preferably such that
i) the opening degree of the bypass valve (BPV) is increased if the differential temperature is lower than a predetermined set point; and/or

ii) the opening degree of the bypass valve (BPV) is decreased if the differential temperature is higher than a predetermined set point; and/or
wherein the differential temperature is preferably calculated from a temperature obtained from a temperature sensor (TS1) at an inlet of the first heat exchanger (PHEX) and from a temperature obtained from a temperature sensor (TS2) at an outlet of the first heat exchanger (PHEX).
Air conditioning system according to one of the preceding claims, wherein the controller is configured to control the conveying speed of the pump (P) based on a cooling capacity determined from the current flow rate of the heat transfer medium and determined from a differential temperature of the heat transfer medium between an inlet of the first heat exchanger (PHEX) and an outlet of the first heat exchanger (PHEX), preferably such that
i) the conveying speed of the pump (P) is increased if the cooling capacity is lower than a predetermined set point; and/or

ii) the conveying speed of the pump (P) is decreased if the cooling capacity is higher than a predetermined set point;
wherein the current flow of the heat transfer medium is preferably obtained from the pump (P) and the differential temperature is preferably calculated from a temperature obtained from a temperature sensor (TS1) at an inlet of the first heat exchanger (PHEX) and from a temperature obtained from a temperature sensor (TS2) at an outlet of the first heat exchanger (PHEX).
Method for controlling an air conditioning system according to one of the preceding claims, wherein the method comprises a step of controlling an opening degree of the bypass valve (BPV) based on a differential temperature of the heat transfer medium between an inlet of the first heat exchanger (PHEX) and an outlet of the first heat exchanger (PHEX).
Method according to claim 11, wherein an opening degree of an expansion device of the heating and/or cooling part is controlled based on a degree of superheat determined from a temperature sensor (TS3) and a pressure sensor (PS) at the discharge line of a compressor (Comp) of the refrigerant circuit, preferably such that
i) if the determined degree of superheat is higher than a predetermined value, the opening degree of the expansion device is increased; and/or

ii) if the determined degree of superheat is lower than a predetermined value, the opening degree of the expansion device is decreased.
Method according to one of claims 11 and 12, wherein the speed of a compressor (Comp) of the system is controlled based on the temperature of the heat transfer medium, preferably such that
i) the speed of the compressor (Comp) is increased if the temperature of the phase change material is higher than the phase change temperature of the phase change material; and/or

ii) the speed of the compressor (Comp) is decreased if the temperature of the phase change material is lower than the phase change temperature of the phase change material;
wherein the temperature of the phase change material is preferably obtained from a temperature sensor (TS1) at an inlet of the first heat exchanger (PHEX).
Method according to one of claims 11 to 13, wherein the opening degree of the bypass valve (BPV) is controlled based on a differential temperature of the heat transfer medium between an inlet of the first heat exchanger (PHEX) and an outlet of the first heat exchanger (PHEX), preferably such that
i) the opening degree of the bypass valve (BPV) is increased if the differential temperature is lower than a predetermined set point; and/or

ii) the opening degree of the bypass valve (BPV) is decreased if the differential temperature is higher than a predetermined set point;
wherein the differential temperature is preferably calculated from a temperature obtained from a temperature sensor (TS1) at an inlet of the first heat exchanger (PHEX) and from a temperature obtained from a temperature sensor (TS2) at an outlet of the first heat exchanger (PHEX).
Method according to one of claims 11 to 14, wherein a conveying speed of the pump (P) is controlled based on a cooling capacity determined from the current flow rate of the heat transfer medium and determined from a differential temperature of the heat transfer medium between an inlet of the first heat exchanger (PHEX) and an outlet of the first heat exchanger (PHEX), preferably such that
i) the conveying speed of the pump (P) is increased if the cooling capacity is lower than a predetermined set point; and/or

ii) the conveying speed of the pump (P) is decreased if the cooling capacity is higher than a predetermined set point;
wherein the current flow of the heat transfer medium is preferably obtained from the pump (P) and the differential temperature is preferably calculated from a temperature obtained from a temperature sensor (TS1) at an inlet of the first heat exchanger (PHEX) and from a temperature obtained from a temperature sensor (TS2) at an outlet of the first heat exchanger (PHEX).