EP2644768A1

EP2644768A1 - Heat pump for a clothes treatment appliance

Info

Publication number: EP2644768A1
Application number: EP12382127.4A
Authority: EP
Inventors: Jose Gonzalvez Macia; Iñaki OTERO GARCIA; Roberto San Martin Sancho
Original assignee: BSH Electrodomesticos Espana SA
Current assignee: BSH Electrodomesticos Espana SA
Priority date: 2012-03-30
Filing date: 2012-03-30
Publication date: 2013-10-02

Abstract

The heat pump P' for a clothes treatment appliance H comprises a compressor 1, a condenser 2, a restrictor 3, and an evaporator 4, and further comprises a liquid-suction heat interchanger 8. A clothes treatment appliance H comprises the heat pump P'.

Description

The invention relates to a heat pump for a clothes treatment appliance, in particular clothes drying appliance, comprising a compressor, a condenser, a restrictor, and an evaporator. The invention also relates to a clothes treatment appliance comprising such a heat pump.
A laundry dryer comprising a heat pump has improved efficiency (in terms of kWh/kg) as compared to a conventional laundry dryer only employing an electrical heater. Thus, in principle a related operational carbon dioxide emission of the laundry dryer comprising the heat pump is lower than that of the conventional dryer due to its lower electric consumption. However, a refrigerant used in the heat pump must be taken into account with its GWP ('Global Warming Potential'). Nowadays, typical refrigerants used in a heat pump are fluorinated hydrocarbon compounds (HFC) whose GWP is higher than 1500.
Within the air path or process air circuit; process air flows from a drum to the evaporator. At a drum outlet, the air is at a medium temperature and relatively wet. At the evaporator, the air is cooled and dehumidified and then flows to the condenser where it is heated. Hot and dry air is then introduced again in the drum where it can absorb moisture from laundry contained in the drum.
The evaporator and the condenser are typically of a tube-and-fins type. The tubes of the evaporator and the condenser may be separate entities as described in prior art documents WO 2008/004802 A3 , EP 2 261 416 A1 , and EP 1 593 770 B1 , or may be joined in the same core, as described in prior art document WO 2008/004802 A3 .
Another typical construction of the evaporator and the condenser is the so-called aluminium single-tube type (no-frost type) in which an aluminium tube is bended and fins are placed along it without tube expansion.
An outer diameter of the tubes of the evaporator and the condenser used at present in heat pump dryers are as follows: 3/8" (9.525mm) and 7 mm for a tube-and-fins type evaporator and condenser and 8 mm for an aluminium single-tube type evaporator and condenser.
One possibility to reduce TEWI ('Total Equivalent Warming Impact', that includes direct and indirect emission) of these systems is to use hydrocarbon refrigerants that have a low GWP like R-290 (propane) or R-1270 (propylene). The main drawback of these refrigerants is that they are flammable and therefore IEC 60335-2-11 standard limits the maximum charge (150g) in a laundry dryer. It is generally known that an optimum refrigerant charge can be found for a specific system, but the refrigerant limit of 150 g imposed by the IEC 60335-2-11 standard is typically lower than the optimum charge of refrigerant for a heat pump of a laundry dryer.
A clothes drying appliance having a heat pump typically comprises a refrigerant circuit and an air path. The refrigerant flows through the compressor, the condenser, the restrictor and the evaporator, in this order. These elements are connected by refrigerant lines, in particular pipes. The refrigerant releases heat to the process air flowing through the air path by means of the condenser and absorbs heat and humidity from the process air flowing through the air path by means of the evaporator. The compressor absorbs power and compresses the refrigerant in the refrigerant circuit.
A liquid-suction heat interchanger (also called a liquid-to-suction heat exchanger or regenerator) is mainly known in low temperature refrigeration systems using a vapour compression system where there is a long distance between the evaporator and the compressor. The liquid-suction heat interchanger typically comprises two refrigerant lines or channels (e.g. pipes), wherein in one of the refrigerant lines (the 'liquid' line) flows liquid refrigerant and in the other refrigerant line (the 'suction' line) flows refrigerant in its vaporous form. The lines are thermally connected to each other to allow a heat transfer between them and are typically thermally isolated against the environment. The liquid-suction heat interchanger may increase cooling capacity and reduce power input in vapour compression systems for some refrigerants. For refrigeration systems the liquid-suction heat interchanger may work with evaporation temperatures below zero degrees centigrade (corresponding to an evaporator outlet temperature of around -20°C). Therefore, an external superheating (between the refrigerant and an ambient air) is created in the suction line due to a high temperature difference. This external superheating degrades the heat pump's COP (coefficient of performance; cooling capacity divided by power input) because the compressor power consumption is increased with no effect on the cooling capacity. Liquid-suction heat interchangers are only rarely used in air conditioning systems because the liquid-suction heat interchanger introduces a pressure drop that significantly reduces its benefits for an air conditioning system.
It is an object of the current invention to at least partially overcome at least some of the problems of the art with respect to clothes treatment appliances comprising a heat pump and to particularly provide a heat pump for a clothes treatment appliance that has a reduced GWP and a high efficiency.
The object is achieved by the features of the independent claims. Advantageous embodiments are particularly referred to by the dependent claims.
The object is achieved by a heat pump for a clothes treatment appliance, comprising a compressor, a condenser, a restrictor, and an evaporator, and further comprising a liquid-suction heat interchanger.
The additional use of a liquid-suction heat interchanger in a clothes treatment appliance gives the advantage of a potential increase of the enthalpy in the evaporator (in particular at a refrigerant inlet of the evaporator). A further advantage is that the refrigerant mass flow may be decreased. Therefore a temperature of the refrigerant at the compressor inlet is increased due to extra superheating in the liquid-suction heat interchanger. Thus, a density of the refrigerant at the compressor inlet is lowered which leads to a decrease of a power consumption of the compressor. In particular, if the heat pump comprising the liquid-suction heat interchanger is working in its optimum operation point (showing superheating in the evaporator), the cooling capacity in the evaporator is increased (since the effect of an enthalpy increase is bigger than that of a mass flow decrease) and the power consumption is reduced to achieve the same compression ratio. It follows that a dehumidification rate is increased with a reduction of the power consumption. This means that a drying time and an energy consumption of the drying cycle are reduced. Also, an increase in cooling capacity in the evaporator improves the COP, especially for hydrocarbon refrigerants.
The heat pump of the heat interchanger may use a flammable or non-flammable refrigerant.
It is an advantageous embodiment that one side of the first refrigerant line (suction line) of the heat interchanger is coupled to an outlet of the evaporator and the other side of the first refrigerant line is coupled to an inlet of the compressor; and further one side of the second refrigerant line (liquid line) is coupled to an outlet of the condenser and the other side of the second refrigerant line is coupled to an inlet of the restrictor. In particular this kind of connection allows the heat interchanger to cool down refrigerant from the condenser outlet (giving more subcooling) and to heat up the evaporator outlet (giving more superheat).
The heat interchanger can be of different configurations (e.g. as a double pipe, as a plate heat exchanger and so on).
It is another advantageous embodiment that the second (liquid) refrigerant line is thermally more isolated against the ambient than the first (suction) refrigerant line. This preserves the temperature increase at the compressor inlet. In case of a double pipe design (in which a first pipe surrounds a second pipe) this design may be implemented by using the first pipe as the first (suction) refrigerant line and using the second pipe as the second (liquid) refrigerant pipe. Thus, the vaporous refrigerant flowing in the first pipe experiences a lower temperature difference to the environment while the liquid refrigerant flowing in the second pipe experiences a higher temperature difference since it is thermally shielded against the environment by the first pipe.
It is yet another advantageous embodiment that the compressor exhibits a displacement of 12 cc/rev (cubic centimeters per revolution) or less, in particular 10.5 cc/rev or less. This embodiment reflects the surprising finding that if the compressor displacement is bigger (in particular for typical household appliances), it might be required to increase a heating capacity at the condenser in order to enable a dissipation of energy coming from the compressor. To increase condenser capacity, in turn, necessitates a higher condenser area and volume. Therefore, it would be required to also increase the refrigerant charge in order to enable the condensation of the refrigerant in the condenser. This, however, makes it difficult comply with the charge limit (150g) for flammable refrigerants of the IEC 60335-2-11 standard and might shift an optimum charge for an operating point of the heat pump further away from the (present) 150g limit.
It is yet another advantageous embodiment that an outer diameter of the condenser pipes (i.e. pipes used with a condenser) and/or an outer diameter of the evaporator pipes (i.e. pipes used with n evaporator) measures less than 7 mm. This reduces a refrigerant circuit volume and allows to effectively cool the refrigerant even at a low charge (in particular of less than 150g) while by virtue of the liquid-suction heat interchanger an efficiency of the heat pump remains high. In particular, the use of the outer diameter being smaller than 7 mm is advantageous in order to enable the condensation of the refrigerant in the condenser (using a smaller refrigerant charge in the condenser). Thus, two positive effects can be achieved at the same time: the increase of subcooling in the condenser and the proper efficiency of liquid-to-suction heat exchanger (additional subcooling on the high pressure side and additional superheating on the low pressure side).
In practice, lines (and pipes in particular) are measured and characterized by their outer diameter which correlates to its inner diameter and thus to the volume available for the refrigerant.
It is a particular embodiment that an outer diameter of the condenser pipes measures less than 7 mm while an outer diameter of the evaporator pipes measures 7 mm or more, e.g. 3/8" (9.525mm) or 7 mm for a tube-and-fins type evaporator and 8 mm for an aluminium single-tube type evaporator. This embodiment makes use of the fact that the refrigerant line of the condenser (also called condenser coil) is the part of the refrigerant circuit which has the highest inner volume and consequently the highest amount of refrigerant (i.e. a higher volume and a higher density of the refrigerant). With the use of the outer diameter smaller than 7 mm, the inner volume is decreased, so for the same mass of refrigerant a higher density is obtained. This in turn means that a larger percentage of liquid refrigerant in liquid-vapour phase is obtained which in turn allows a sooner condensation of the refrigerant in the condenser. Thus, a higher subcooling is achieved with the consequent benefit for the cooling capacity.
It is an especially advantageous embodiment that an outer diameter of the condenser pipes and/or an outer diameter of the evaporator pipes is about 6 mm or less, in particular 5 mm or less. An outer diameter of about 5 mm has been found to be a particularly good compromise between a small charge of the refrigerant and a high efficiency.
As a concrete example a comparison between a conventional 7 mm condenser (i.e. a condenser with a refrigerant pipe having an outer diameter of 7 mm) and a 5 mm condenser of a household tumble dryer using 150g of propane / R290 is considered. The 5 mm condenser has a 12% lower volume of the refrigerant than the 7 mm condenser. The 5 mm condenser achieves a drying time reduction of 13% and an energy consumption reduction of 11 %. In order to achieve a similar dryer performance using the 7 mm condenser and employing the same drying time and a 4% higher energy consumption, 210g of R290 is needed.
Furthermore, the combination of a 5 mm condenser and a 5 mm evaporator may bring an additional improvement as compared to the reference case of a 7 mm condenser (and 7 mm evaporator). The use of the 5 mm condenser and the 5 mm evaporator brings a drying time reduction of 16% and an energy consumption reduction of 14%.
It is even another advantageous embodiment that a refrigerant of the heat pump is a flammable refrigerant. This embodiment is made practical by enabling a charge of the refrigerant of 150g or less. Flammable refrigerant often has a lower GWP than non-flammable refrigerant.
It is an advantageous embodiment thereof that the refrigerant comprises a hydrocarbon refrigerant / hydrocarbon refrigerants. Hydrocarbon refrigerants show a low to negligible GWP. Hydrocarbon refrigerants are particularly useful to be used in the liquid-suction heat interchanger to improve system COP.
It is one embodiment thereof that the refrigerant comprises propane (R290). Propane has the advantage to have a relatively low GWP (of 3.3 times the GWP of carbon dioxide), does not destroy the ozone layer, may be used as an alternative to R-12, R-22, R-134a and other hydrochlorofluorocarbons, and is readily available.
It is another embodiment thereof that the refrigerant comprises propylene (R1270).
It is another embodiment that the refrigerant comprises HFO-1234yf or 2,3,3,3-Tetrafluoropropene. HFO-1234yf has almost no environmental impact, acquiring a GWP rating 335 times less than that of the conventional R-134a and an atmospheric lifetime of about 400 times shorter. Furthermore, HFO-1234yf is only mildly flammable.
The object is also achieved by a clothes treatment appliance comprising a heat pump, wherein the heat pump is a heat pump as described above.
It is an advantageous embodiment that the clothes treatment appliance is a clothes drying appliance, e.g. a stand-alone clothes dryer or a washer-dryer.
It is another advantageous embodiment that the clothes treatment appliance is a household appliance.
In the Figures of the attached drawing, the invention is schematically shown by means of an exemplary embodiment. In particular,

Fig.1: shows a schematic drawing of a household tumble dryer using a heat pump;
Fig.2: shows a schematic drawing of a heat pump of the tumble dryer; and
Fig.3: shows a sectional side view of a liquid-suction heat interchanger of the heat pump.

Fig.1 shows a clothes treatment appliance in form of a household tumble dryer H. The tumble dryer H comprises a heat pump P having at least a compressor 1, a condenser 2 of a tube-and-fins type, a restrictor 3, and an evaporator 4 of a tube-and-fins type as elements. The elements 1 to 4 are serially connected in the shown order by refrigerant pipes 5 to form a refrigerant circuit or path.
The tumble dryer H also comprises a process air circuit or path 6 wherein process air A flows. The air circuit 6 comprises a rotatable drum 7 for holding to be processed clothes. The air A leaves the drum 7 at a medium temperature and wet. The air A then flows to the evaporator 4 that is placed in the air circuit A downstream the drum 7 and works as a heat exchanger. At the evaporator 4 the air A is cooled down and condenses. The resultant condensate is collected in a water tank W. At the evaporator 4, the air A also cools down and transfers part of its thermal energy upon the evaporator 4 and thus onto the refrigerant R within the evaporator 4. This enables the evaporator 4 to transform the refrigerant R from a liquid state into a vaporous state.
Further downstream the air circuit 6 the now dry and cool air A passes through the condenser 2 where a heat transfer from the condenser 2 and the refrigerant R within to the air A is effected to heat up the air A and cool down the refrigerant R to its liquid state. The then warm and dehumidified / dry air A is subsequently reintroduced into the drum 7 to warm up the clothes and to pick up moisture.
The refrigerant R is moved within the refrigerant circuit 1 to 5 by the compressor 1.
The working of such a tumble dryer H with its heat pump P (comprising the refrigerant circuit 1 to 5) and its air circuit 6 is well known and does not need to be explained in greater detail.
Fig.2 shows a schematic drawing of a heat pump P'. The heat pump P' may be used in the tumble dryer H instead of the heat pump P. The heat pump P' differs from heat pump P in that it comprises a liquid-suction heat interchanger 8.
As shown in Fig.3, the heat interchanger 8 is of a double pipe design and comprises a first refrigerant line in form of a tubular (suction) pipe 9 having a suction pipe inlet 9i for inputting low pressure refrigerant R and a suction pipe outlet 9o for outputting the vaporous refrigerant R. Centrically through the tubular suction pipe 9 leads a second refrigerant line in form of a tubular (liquid) pipe 10 having a liquid pipe inlet 10i for inputting high pressure refrigerant R and a liquid pipe outlet 10o for outputting the liquid refrigerant R at a respective end. The suction pipe 9 and the liquid pipe 10 are highly thermally connected, e.g. by a common metal wall. The suction pipe 9 may or may not be thermally isolated against its environment.
Back to Fig.2, the suction pipe inlet 9i is coupled to an outlet 4o of the evaporator 4 via a refrigerant pipe 5, and the suction pipe outlet 9o is coupled to an inlet 1i of the compressor 1 via another refrigerant pipe 5. The liquid pipe inlet 10i of the liquid pipe 10 is coupled to an outlet 2o of the condenser 2 and the liquid pipe outlet 10o is coupled to an inlet 3i of the restrictor 3. This kind of connection allows the heat interchanger 8 to cool down refrigerant R from the condenser outlet 2o (giving a stronger subcooling) and to heat up the evaporator outlet 4o (giving a stronger superheating).
The compressor 1 of the heat pump P' exhibits a displacement lower than 10.5 cc/rev. The outer diameter of the tube or pipe of the tube-and-fins type condenser 2 is 5 mm. The outer diameter of the tube or pipe of the evaporator 4 may also be 5 mm.
The refrigerant R comprises propane, propylene and/or HFO-1234yf.
Of course, the invention is not restricted to the shown embodiment(s).

List of Reference Numerals

1: compressor
1i: inlet of the compressor
2: condenser
2o: outlet of the condenser
3: restrictor
3i: inlet of the restrictor
4: evaporator
4o: evaporator outlet
5: refrigerant pipe
6: air circuit
7: rotatable drum
8: liquid-suction heat interchanger
9: suction pipe
9i: suction pipe inlet
9o: suction pipe outlet
10: liquid pipe
10i: liquid pipe inlet
10o: liquid pipe outlet
A: process air
H: household tumble dryer
P: heat pump
P': heat pump
R: refrigerant
W: water tank

Claims

Heat pump (P') for a clothes treatment appliance (H),
- comprising a compressor (1), a condenser (2), a restrictor (3), and an evaporator (4),

- and further comprising a liquid-suction heat interchanger (8).
Heat pump (P') according to claim 1, wherein
- the liquid-suction heat interchanger (8) comprises a first refrigerant line (9) and a second refrigerant line (10) that are thermally coupled to each other;

- one side (9i) of the first refrigerant line (9) of the heat interchanger (8) is coupled to an outlet (4o) of the evaporator (4) and the other side (9o) of the first refrigerant line (9) is coupled to an inlet (1i) of the compressor (1); and

- one side (10i) of the second refrigerant line (10) is coupled to an outlet (2o) of the condenser (2) and the other side (100) of the second refrigerant line (10) is coupled to an inlet (3i) of the restrictor (3).
Heat pump (P') according to claim 2, wherein the first refrigerant line (9) is thermally less isolated against an environment of the heat interchanger (8) than the second refrigerant line (10).
Heat pump (P') according to any of the preceding claims, wherein the compressor (1) exhibits a displacement of 10.5 cc/rev or less.
Heat pump (P') according to any of the preceding claims, wherein an outer diameter of at least one pipe of the condenser (2) and/or an outer diameter of at least one pipe of the evaporator (4) is less than 7 mm.
Heat pump (P') according to claim 5, wherein an outer diameter of at least one pipe of the condenser (2) and/or an outer diameter at least one pipe of the evaporator (4) is about 5 mm or less.
Heat pump (P') according to any of the preceding claims, wherein a refrigerant (R) of the heat pump (P') is a flammable refrigerant (R).
Heat pump (P') according to claim 7, wherein the refrigerant (R) comprises propane or propylene.
Heat pump (P') according to any of claims 7 or 8, wherein the refrigerant (R) comprises HFO-1234yf.
Clothes treatment appliance (H) comprising a heat pump, wherein the heat pump is a heat pump (P') according to any of the preceding claims.
Clothes treatment appliance (H) according to claim 10, wherein the clothes treatment appliance (H) is a clothes drying appliance.