Heat Pump Comprising a First Heating Circuit and a Second Heating Circuit

The present invention relates to a heat pump comprising a first heating circuit and a second heating circuit.

A heat pump is capable of transferring thermal energy from a heat source to a heat sink, thereby forcing the thermal energy to flow opposite to its natural flow direction from hot to cold. In this way, heat may be extracted from air (such as ambient air or air of an indoor ventilation system), from water, or from the earth, allowing heat to be extracted from sustainable sources or from waste streams. Such heat pumps may be used to either heat or cool an indoor area or heat a water storage tank that stores water for (domestic) use.

A heating circuit of a basic heat pump comprises an evaporator, a compressor, a condenser, and an expansion valve. In the evaporator, a liquid refrigerant absorbs heat at a first pressure level by evaporation. The compressor increases the pressure of the refrigerant from the first pressure level to a second pressure level, thereby also causing the temperature of the refrigerant to increase significantly. Still at the second pressure level, the refrigerant successively condenses in the condenser, thereby releasing heat. The condenser is a heat exchanger, and the heat released from the refrigerant may be used to act as a heat source for a further heating circuit, e.g. for indoor heating. In the expansion valve, the refrigerant expanses and the pressure drops from the second pressure level to the first pressure level. Due to this pressure drop, the refrigerant cools down, preparing it to absorb heat when it successively evaporates in the evaporator.

Before a heat pump comes into operation, a refrigerant charge is introduced into the heating circuit. The optimal amount of refrigerant charge in the heating circuit is determined based on the expected average operating conditions, and aims to optimize the amount of refrigerant in the condenser and in the evaporator. The efficiency of the heat pump is dependent on the amount of refrigerant in said condenser and evaporator. For example, if there is too much refrigerant in the condenser, the refrigerant takes up too much space in the condenser and may consequently leave too limited space left for optimal condensation purposes, thereby also reducing the efficiency of the condenser. To complicate the situation even further, the density of the refrigerant is temperature dependent. Thus, for a certain fixed amount of refrigerant, the volume it occupies will differ when the operating temperature of the heat pump changes. As the actual operating conditions will most of the time differ from the expected average operating conditions the charge of the refrigerant was based on, the efficiency of a heat pump is almost always suboptimal.

UK Patent Application GB 2 758 391 is considered to define the closest prior art. It discloses a refrigeration apparatus having a condenser that comprises a first sub-condenser and a second sub-condenser. In normal operating conditions, the first sub-condenser and the second sub-condenser are actively arranged in a series connection, and consequently they together define the condenser. However, in case of leakage in any one of the first and the second sub-condenser, said leaking sub-condenser may be temporarily bypassed. The other, i.e. the non-leaking sub-condenser, may however remain active. In this safety mode, the condenser is defined by the one remaining non-leaking sub-condenser. Consequently, even when refrigerant leakage occurs in one of the first sub-condenser and the second-sub-condenser, it is possible to continue operation without stopping the operation of the refrigeration apparatus. Therefore, until the condenser is replaced with a new one, it is possible to temporarily continue the operation of the refrigeration apparatus. Of course, since only one of the sub-condensers is active in such a safety mode, the efficiency of the heat pump of the refrigeration apparatus is suboptimal. Under normal operating conditions, the condenser is defined by the series-connected first sub-condenser and the second sub-condenser. As such, the heat pump of the refrigeration apparatus of GB 2 758 391 is in fact a normal heat pump as described above, facing the same challenges as described above. After all, it will also comprises a certain fixed amount of refrigerant. The optimal amount of refrigerant charge in the heating circuit is determined based on the expected average operating conditions. As described above, the actual operating conditions will most of the time differ from the expected average operating conditions the charge of the refrigerant was based on, and consequently also the efficiency of the heat pump of the refrigeration apparatus disclosed in GB 2 758 391 is almost always suboptimal.

U.S. Pat. No. 6,941,770 B1 discloses a hybrid reheat system with performance enhancement. It describes how refrigerant may be forced via a so-called economizer cycle, via a reheat coil, or via both the economizer cycle and the reheat coil. In the economizer cycle, a portion of the refrigerant flowing from the condenser is tapped and passed through an economizer expansion device and then to an economizer heat exchanger. This tapped refrigerant subcools a main refrigerant flow that also passes through the economizer heat exchanger. The tapped refrigerant leaves the economizer heat exchanger usually in a vapor state and is injected back into the compressor at an intermediate compression point. The economizer cycle lowers the temperature of the refrigerant in the main line by subcooling it in the economizer heat exchanger by the tapped refrigerant, which is expanded to lower pressure and temperature in the economizer expansion device. Alternatively, a reheat coil may be used, at least a portion of the refrigerant upstream of the expansion device is passed through a reheat heat exchanger and then is returned back to the main circuit. At least a portion of a conditioned air, having passed over the evaporator, is then passed over this reheat heat exchanger to be reheated to a desired temperature. In U.S. Pat. No. 6,941,770 B1, refrigerant may on the one hand pass via the reheat coil for obtaining dedicated humidity control, while refrigerant may on the other hand pass via an economizer circuit if the sensible cooling load demand is relatively high. Combinations are also possible if cooling and dehumidification are both desired, predominantly for hot and humid environments. In U.S. Pat. No. 6,941,770 B1, the optimal amount of refrigerant charge in the heating circuit is determined based on the expected average operating conditions, and it may be selectively flow via one or both of the economizer loop and the reheat coil.

An objective of the present invention is to provide a heat pump, that is improved relative to the prior art and wherein at least one of the above stated problems is obviated or alleviated.

Said objective is achieved with the heat pump according to claim, that according to the present invention comprises a first heating circuit and a second heating circuit, said heat pump comprising:

The skilled person will acknowledge that heat pumps may be reversible if a reversing valve is applied, allowing the heat pump to work in either direction and thereby use it for heating or cooling. In order to prevent unnecessary repetition, the invention is described with reference to the heat pump having a first “heating” circuit and a second “heating” circuit, simply because the heating mode will be the most used mode for such a system. In such a heating mode, the common line passes through the evaporator, while this evaporator may temporarily function as a condenser in a reverse operating condition, e.g. for defrosting the evaporator. It is also emphasized that whether a cycle may be interpreted as a heating cycle or a cooling cycle is also dependent on the position of the observer. After all, indoor heating may be interpreted as outdoor cooling, wherein heat is withdrawn from the environment.

The heat pump proposed by the present invention comprises a first heating circuit and a second heating circuit, that share a common line passing through the evaporator and the compressor. For some embodiments the common line may optionally also pass through the expansion valve, although this may be different for embodiments wherein the first and the second heating circuit each comprise a dedicated expansion valve, as will be explained in more detail below.

During normal operation, only one of the first heating circuit and the second heating circuit is involved in an active heating cycle, and the distributor allows refrigerant charge to be moved from the first heating circuit to the second heating circuit, or vice versa. In this way, the refrigerant charge of the active heating circuit may be optimized, wherein it is even possible to adjust the refrigerant charge during operation, thereby increasing the efficiency of the heat pump. For example, when the active heating circuit is used for heating a water storage tank, the average water temperature in said water storage tank may increase from e.g. 30° C. starting temperature to 50° C. or even higher. Instead of setting a fixed predetermined refrigerant charge for the expected mean temperature of 40° C., the distributor allows the refrigerant charge to be adjusted during the heating. In this way, it is possible to gradually adjust the refrigerant charge to take the differing operation conditions into account and thereby optimize the efficiency of the heat pump. This efficiency may be selectively set to correspond to one of: the optimum coefficient of performance, and thus the minimum energy use on the one hand, and the maximum heating capacity obtainable on the other hand. In this way, it is possible to selectively choose for energy efficiency most of the time, while having the ability to temporarily prioritize for setting the heat pump to obtain maximum heating capacity.

Furthermore, being able to control migration of refrigerant charge has the advantage that a maldistribution of refrigerant charge can be avoided. Such a maldistribution could for example arise in heat pumps with two or more condensers without controlled migration, especially when the condensers are not equal in size and/or when the condensers are operating at different temperatures.

Due to the distributor being able to redistribute a refrigerant charge from the first heating circuit to the second heating circuit or vice versa, the amount of total refrigerant charge in the heat pump, i.e. in all heating circuits thereof, may be minimized, because the refrigerant charge in the “inactive” circuit may be minimized and temporarily redistributed to the “active” heating circuit.

Conversely, and according to a preferred embodiment, excess refrigerant charge that is not needed for optimizing the refrigerant charge in the “active” heating circuit may be temporarily stored in the “inactive” circuit, thereby making a refrigerant accumulator and an additional expansion valve redundant. The controlled migration of refrigerant charge between heating circuits enables operation of the heat pump with an optimum refrigerant charge at each operating condition without the need for an additional refrigerant accumulator and an additional expansion valve, which would otherwise be needed to achieve an optimum refrigerant charge in the circuits at all operating conditions. Being able to refrain from applying a refrigerant accumulator and an additional expansion valve related to the refrigerant accumulator, the heat pump can operate with a minimum total charge of refrigerant, and the heat pump is simplified, and especially the absence of a refrigerant accumulator saves precious space.

The ability to adjust the refrigerant charge in the active circuit enables operation at a preset optimum level of subcooling for each operating condition. This ability cannot be achieved in a reversible heat pump with one condenser and one evaporator, without adding an additional refrigerant accumulator and an additional expansion valve related to the refrigerant accumulator.

Further advantages that may be obtained, are that firstly, a heat pump for space heating and water heating with two condensers can operate at a lower condensing temperature than a heat pump for space heating and water heating with one refrigerant to water condenser, a three way valve and a water to water heat exchanger, due to the absence of the temperature drop in the water-to-water heat exchanger. Thus, for the same hot water storage temperature, a lower condensing temperature is required. Secondly, the lower condensing temperature as described here above leads to a better coefficient of performance, and thus to a lower energy consumption.

According to a further preferred embodiment, the controller is configured to redistribute the refrigerant charge from the first heating circuit to the second heating circuit or vice versa, in dependency of the actual operating conditions that are defined by a level of subcooling of the refrigerant in at least one of the first heating circuit and the second heating circuit. The level of subcooling is directly related to the volume of liquid refrigerant present in the condenser, and is as such a reliable parameter in determining the actual operating conditions. For example, if the condenser is filled for 50% with liquid refrigerant, its active capacity is also 50%, but the level of subcooling increases. Instead of the level of subcooling, also the level of superheating in the evaporator may be used, but this is more complex because the flow rate of the expansion valve also influences the level of superheating.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, and in particular the aspects and features described in the attached dependent claims, may be an invention in its own right that is related to a different problem relative to the prior art.

The prior art reversible heat pumpshown incomprises an evaporator, a compressor, a condenser, and an expansion valve. A controllermay control the setting of a four-way reversing valveto allow the flow direction of a refrigerant inside the heating circuit to be reversed between a heating mode () and a cooling mode (), as well as other components, such as the compressor.

In the heating mode of, the evaporatoris capable of extracting heat from air (such as ambient air or air of an indoor ventilation system) or from the earth. The temperature of the refrigerant may be increased by the compressorcompressing the refrigerant, after which this heat may be extracted from the refrigerant in the condenser, where it may be used for e.g. indoor heating.

In the cooling mode of, the flow direction of the refrigerant is reversed relative to the flow direction of. The heat exchanging element that functioned as the evaporatorinnow acts as the condenser, and the heat exchanging element that functioned as the condenserinnow acts as the evaporator.

A first preferred embodiment of the invention is shown in, wherein the heat pumpcomprises a first heating circuit Cand a second heating circuit C. The heat pumpcomprises an evaporator, an expansion valvethat is arranged upstream of the evaporator, and a compressoris arranged downstream of the evaporator. A first condenseris arranged in the first heating circuit Cand a second condenseris arranged in the second heating circuit C, wherein the first heating circuit Cand the second heating circuit Cshare a common linepassing through the evaporatorand the compressor. In this first preferred embodiment, the common linealso passes through the expansion valve, but this is not essential, as will be elucidated with reference to the fourth preferred embodiment shown in. The heat pumpfurther comprises a distributorcomprising at least two valves V, wherein the distributor is configured to redistribute a refrigerant charge from the first heating circuit Cto the second heating circuit Cor vice versa by controlling the at least two valves V. In the first preferred embodiment, the two valves V comprise two three-way valves Tand T. It is remarked that the distributorcomprises the controllerand the valves V. For clarity, only the control lines between the controllerand the valves V that belong to the distributorare shown with dashed lines. In addition, the controllermay comprise further (not shown) control lines to other components, such as the compressorand the optional four-way reversing valve.

The four-way reversing valveis optional and only necessary to make the heat pumpreversible, also allowing a cooling mode as shown in.may be considered a defrost mode, wherein the evaporatoris defrosted.

The first condenseris arranged in the first heating circuit C, which inis connected to a space heating circuitthat is configured to provide a continuous heated water flow for indoor heating when it is active. The active state of the first heating circuit Cis represented by the thick lines in.

The second condenseris arranged in the second heating circuit C, which inis connected to a water tankof a domestic water heating circuit. The second condensermay be used to heat up the water in the water tank. The active state of the second heating circuit Cis represented by the thick lines in.

Heat pumpcomprises a branchthat is arranged downstream of the compressorand configured to branch the common lineoff into a first line Lassociated with the first heating circuit Cand a second line Lassociated with the second heating circuit C.

Heat pumpfurther comprises a combinerthat is arranged upstream of the evaporatorand configured to re-combine the line Lof the first heating circuit Cand the line Lof the second heating circuit Cinto the common line. For this first preferred embodiment, as well as for the second preferred embodiment () and the third preferred embodiment (), the combineris also arranged upstream of the expansion valve. This is however not essential, as becomes apparent from the fourth preferred embodiment that is shown in.

In the first preferred embodiment shown in, the distributorcomprises a three-way valve Tthat defines the combiner, and a further three-way valve Tthat defines the branch. By selectively setting the two three-way valves Tand T, the controllermay activate the first heating circuit Cor the second heating circuit C, but also control the distributorto redistribute the refrigerant charge from the first heating circuit Cto the second heating circuit Cor vice versa. In order to cause this redistribution of refrigerant charge, the first heating circuit Cand the second heating circuit Care temporarily connected to each other. How this works, will be discussed in more detail when discussing the next, even more preferred, second embodiment.

A second and even more preferred embodiment of the invention is shown in. This second preferred embodiment is closely related to the first embodiment, except that the distributor now comprises at least two shut-off valves S, S.

Also for this second preferred embodiment, the heat pumpcomprises a first heating circuit Cand a second heating circuit C. The heat pumpcomprises an evaporator, an expansion valvethat is arranged upstream of the evaporator, and a compressoris arranged downstream of the evaporator. A first condenseris arranged in the first heating circuit Cand a second condenseris arranged in the second heating circuit C, wherein the first heating circuit Cand the second heating circuit Cshare a common linepassing through the evaporatorand the compressor. In this embodiment, the common linealso passes through the expansion valve. The heat pumpfurther comprises a distributorcomprising at least two valves V, wherein the distributoris configured to redistribute a refrigerant charge from the first heating circuit Cto the second heating circuit Cor vice versa by controlling the at least two valves V.

Instead of the two three-way valves T, Tof the first preferred embodiment, the at least two valves V of the distributornow comprises at least two shut-off valves S, S, wherein a first shut-off valve Sis arranged downstream of the second condenserand upstream of the combiner, and a second shut-off valve Sis arranged downstream of the first condenserand upstream of the combiner. The two shut-off valves Sand Sare a preferred advantageous alternative for a three-way valve at the combiner. The first and second shutoff-valves S, Smay be solenoid operated valves, that allow for easy control by the controller.

The distributorshown incomprises at least two further shut-off valves S, S, wherein a third shut-off valve Sis arranged downstream of the branchand upstream of the first condenser, and a fourth shut-off valve Sis arranged downstream of the branchand upstream of the second condenser. The two shut-off valves S, Sare a preferred advantageous alternative for the three-way valve Tat the branchof the first embodiment. The third and fourth shutoff-valves S, Sare preferably solenoid operated valves, that allow for easy control by the controller.

The distributoris configured to selectively activate one of the first heating circuit C(as shown in) and the second heating circuit C. The first heating circuit Cis activated by opening the third shut-off valve Sand the second shut-off valve Sand closing the fourth shut-off valve Sand the first shut-off valve S. The second heating circuit Cis activated by opening the fourth shut-off valve Sand the first shut-off valve Sand closing the third shut-off valve Sand the second shut-off valve S.

The arrangement of the first heating circuit Cand the second heating circuit Cwith the distributorcomprising at least two valves V allows the distributorto selectively redistribute the refrigerant charge from the first heating circuit Cto the second heating circuit Cor vice versa. For example, refrigerant may be distributed from the first heating circuit Cto the second heating circuit Cby opening the second shut-off valve Sand the fourth shut-off valve Swhile the first shut-off valve Sand the third shut-off valve Sare closed (). Alternatively, refrigerant may be distributed from the second heating circuit Cto the first heating circuit Cby opening the first shut-off valve Sand the third shut-off valve Swhile the second shut-off valve Sand the fourth shut-off valve Sare closed (). By redistributing refrigerant charge between the first heating circuit Cand the second heating circuit C, the amount of refrigerant charge may be continuously adapted, thereby improving the efficiency of the heat pump. The skilled person will understand that applying three-way valves T, Taccording to the first preferred embodiment also allows the distributorto redistribute refrigerant charge. Nevertheless, the second embodiment having a plurality of shut-off valves S, S, S, Sis preferred. Firstly, shut-off valves are less susceptible to leaking than three-way valves. Secondly, shut-off valves may be easily controllable, especially when they are embodied as solenoid valves. Thirdly, it provides the option to combine more than two lines, as will be elucidated in more detail in the third preferred embodiment shown in.

In the first, second and third embodiment according to the invention, the distributorpreferably comprises a controllerthat is configured to redistribute the refrigerant charge from the first heating circuit Cto the second heating circuit Cor vice versa, in dependency of a level of subcooling of the refrigerant in at least one of the first heating circuit Cand the second heating circuit C. In this context, subcooling is defined as a temperature difference between the condensing temperature and a temperature of the refrigerant.

The controllermay be configured to adjust the refrigerant charge in the active heating circuit at a preset optimum level of subcooling. This optimum subcooling may be selectively set to correspond to one of: the optimum coefficient of performance, and thus the minimum energy use on the one hand, and the maximum heating capacity obtainable on the other hand.

Preferably, the subcooling of at least the most critical heating circuit, which is typically the heating circuit comprising the condenser with the lowest volume, is taken into account by the controller. After all, the skilled person will acknowledge that the volume of refrigerant is far more critical in a relatively small heat exchanger, relative to a larger heat exchanger. For example, referring to a situation as shown in, the condensermay be part of a small plate heat exchanger, whereas the condensermay be defined by a large coil arranged in or wrapped around a heated water tank. When wrapped around the heated water tank, the length may be multiple tens of meters.

The controlleris preferably configured to determine at least one of:

The skilled person will acknowledge that the condensing temperature at one of the first condenseror the second condensermay be determined directly or indirectly. On the one hand, a direct measurement may be provided by a first temperature sensor,,arranged near an entrance in or shortly upstream of the condenser,, and a second temperature sensor,,arranged near an output in or shortly downstream of the condenser,. On the other hand, in a direct measurement, said condensing temperature may be derived from a condensing pressure, that may be determined by a pressure sensor in a vapour line leading to said condenser, or even via a temperature obtained in a further heating circuit that is heated by the condenser.

The controllermay be configured to at least one of:

The temperature difference between the lower threshold temperature difference and the upper threshold temperature difference may, for a heat pump for domestic use having a subcooling of about 5K, be in the range of 0.2-3° C., preferably in the range of 0.5-2° C., and more preferably in the range of 1-1.5° C. The lower threshold temperature difference is in the range of 0.5-1.2° C., and/or the upper threshold temperature difference is in the range of 0.3-1.2° C. The skilled person will acknowledge that industrial heat pump may have a significantly larger subcooling than 5 K, e.g. a subcooling of 10 K and above, and consequently the temperature ranges may differ.

The heat pumpmay, according to a third preferred embodiment, comprise one or more than one further condenserarranged in a further heating circuit C, wherein the first heating circuit C, the second heating circuit Cand the one or more than one further heating circuit Cshare the common linepassing through the evaporatorand the compressor. In, the common linealso passes through the expansion valve. The distributoris configured to redistribute a refrigerant charge from at least one of the first heating circuit C, the second heating circuit Cand the one or more than one further heating circuit Cto at least one other of the first heating circuit C, the second heating circuit Cand the one or more than one further heating circuit C. In, only one further heating circuit, i.e. a third heating circuit C, is shown, but the skilled person will understand that applying shut-off valves S, S, S, etc., instead of three-way valves T, Tprovides the opportunity to apply multiple further heating circuits in addition to the first heating circuit Cand the second heating circuit C.

shows a schematic view of a heat pumpaccording to a fourth preferred embodiment of the invention. This fourth embodiment is closely related to the second preferred embodiment shown inbut differs relative to this second preferred embodiment in that the first heating circuit Cand the second heating circuit Cnow each comprise a dedicated expansion valve,.

The first shut-off valve Sis defined by a second expansion valveof the one or more than one expansion valve, wherein this second expansion valveis arranged downstream of the second condenserand upstream of the combiner.

The second shut-off valve Sis defined by a first expansion valveof the one or more than one expansion valve, wherein this first expansion valveis arranged downstream of the first condenserand upstream of the combiner.

The common linethat extends between the combinerand the branchnow lacks an expansion valveas applied in the second preferred embodiment. Instead, the common linenow comprises the evaporatorand the compressor. A four-way reversing valveis optionally also arranged in the common line. Replacing the single expansion valvein the common lineof the second preferred embodiment for dedicated expansion valves,in the first heating circuit Cand the second heating circuit C, respectively, allows the expansion valves,to also fulfil the functionality of the shutoff-valve S, Sin said respective heating circuit C, C. In other words, the expansion valve,may also serve as valves V that are controllable by the controllerof the distributorto thereby redistribute refrigerant charge between heating circuits of the heat pump.

Although they show preferred embodiments of the invention, the above-described embodiments are intended only to illustrate the invention and not to limit in any way the scope of the invention. Accordingly, it should be understood that where features mentioned in the appended claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims. Furthermore, it is particularly noted that the skilled person can combine technical measures of the different embodiments. For example, the fourth embodiment ofhaving three heating circuits C, Cand Cmay alternatively apply three (not shown) dedicated expansion valves,and. After all, the skilled person will acknowledge that applying dedicated expansion valves,in each of the heating circuits is not limited to two heating circuits. The scope of protection is defined solely by the following claims.