EP3835681B1

EP3835681B1 - Reversible air conditioning unit performing smart defrost operations

Info

Publication number: EP3835681B1
Application number: EP20213592.7A
Authority: EP
Inventors: Carlo Tosca
Original assignee: Mitsubishi Electric Hydronics and IT Cooling Systems SpA
Current assignee: Mitsubishi Electric Hydronics and IT Cooling Systems SpA
Priority date: 2019-12-12
Filing date: 2020-12-11
Publication date: 2022-10-26
Anticipated expiration: 2040-12-11
Also published as: IT201900023745A1; ES2932056T3; EP3835681A1

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102019000023745 filed on 12/12/2019 .

TECHNICAL FIELD

The present invention concerns a reversible air conditioning unit performing smart defrost operations.

BACKGROUND OF THE INVENTION

As it is known, air conditioning units are reversible machines that may operate in summer mode to cool an inner ambient and may also operate in winter mode to warm such an inner ambient.
When an air conditioning unit operates in winter mode, the compressed gas is forced to expand in the external coil and is compressed in the internal coil that gets warm. A fan is used to direct air towards the internal coil to produce a stream of warm air that is used to warm the inner ambient.
For that reason, the external coil gets quite cold and a layer of ice may be formed on the surfaces of the external coil. As it is known, the ice acts as thermal insulant and prevents thermal exchange with air of the outside ambient; therefore the external coil must be periodically defrosted in order to permit the air conditioning unit to operate properly.
For defrosting operations the refrigerant circuit is reversed by modifying the position of the reversing valve and for some time the gas is compressed in the external coil that gets warm and melts the ice and vice versa the gas is forced to expand in the internal coil that gets cold as it happens during normal summer mode. For that reason, during defrosting operation, a flux of rather cold air is provided towards the inner ambient.
Accordingly the defrosting operation implies cooling down the inner ambient in un unwanted manner; people in the inner ambient may feel discomfort for such an unwanted temperature change. Moreover, the cold air exiting in the inner ambient through vent grills, could annoying people if the cold air hits directly people's heads.
It is the scope of the present invention to provide a reversible air conditioning unit that solves the above technical problem by operating in a smart manner.
EP 3.093.572 shows a reversible air condition unit according to the preamble of claim 1. . Other relevant documents are CN 109 520 072 and
CN 110 260 493 .

SUMMARY OF THE INVENTION

The above problem is solved by the present invention as it relates to an air conditioning unit as defined in claim 1.

BRIEF DESCRIPTION OF DRAWINGS

The invention shall be described according to the drawings that represent a preferred not limiting example of the invention wherein:

Figure 1 shows - in a schematized and simplified manner
- a reversible air conditioning unit realized according to the present invention;
Figure 2 shows the reversible air conditioning unit of figure 1 working in a first operative position;
Figure 3 shows the reversible air conditioning unit of figure 1 working in a second operative position; and
Figure 4 is a flow chart detailing the operations of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In figures 1, 2 and 3 numeral 1 indicates, as a whole, a reversible air condition unit comprising a refrigerant circuit 2 (of a known kind and shown schematically) provided with a compressor 3 (a couple of compressors ) of a known kind are shown schematically) designed to compress a refrigerant gas.
The conditioning unit 1 has an external coil 5 that is conveniently placed in an outside ambient 8, more specifically the ambient outside of a building B (one wall is shown schematically) enclosing an inner ambient 6 (for instance a room) whose temperature has to be controlled. Thus the external coil 5 is configured be placed outside of the room 6 and is designed to establish a heat exchange with the air of the outside ambient 8 to provide thermal energy or to receive thermal energy.
The air conditioning unit 1 has an internal coil 9 that is placed in a housing 10 (shown schematically) provided with a first air inlet 11a communicating with the inner ambient 6 (for instance by means of a conduit C1) and configured to suck air (see black arrow) from the inner ambient 6 and a first air outlet 12a configured to provide (for instance by means of a conduit C2) cool or warm air towards the inner ambient 6 (see the arrow).
The container 10 is provided with a second air inlet 11b configured to communicate with the outside ambient 8 and second air outlet 12b configured to communicate with the outside ambient 8.
A respective shutter device 13 is provided to the first and second inlet 11a, 12a and to the first and second outlet 11b, 12b and is movable between an open and closed position under the control of an electronic unit 14 as will be clarified in the following.
An electric fan 15 is placed in the housing 10 (conveniently but not constrained is placed in the middle of the elongated housing 10) and is designed to move air from the inlets 11a/11b towards the outlets 12a/12b.
An air filter 16 (of known type) is contained in the housing 10 and is placed to be interposed between the first and second air inlet 11a/11b and the electric fan 15.
The refrigerant circuit 2 also comprises a reversing valve 20 that is connected with the compressor 3, the external coil 5 and the internal coil 9 according known schema using piping 21 and is designed to be placed in two operative positions, namely:

a first operative position wherein the reversible conditioning unit 1 operates a summer mode and the compressed gas is forced to expand in the internal coil 9 and is compressed in the external coil 5 - a flux of cooled air is supplied to the inner ambient 6; and
a second operative position wherein the reversible conditioning unit 1 operates a winter mode and the compressed gas is compressed in the internal coil 9 and is forced to expand in the external coil 5 - a flux of warmed air is supplied to the inner ambient 6.

The electronic control unit 14 when the air conditioning unit 1 operates in the above summer mode sends commands to the shutter devices 13 so that the first air inlet 11a is opened and the first air outlet 12a is also opened (see figure 2); the second air inlet 11b and the second air outlet 12b are kept closed. Warm air is thus sucked from the air inlet 11a from the inner ambient 6 and is provided to the internal coil 9 that reduces the temperature of the air; cooled air is then pushed by the thrust of the electric fan 15 to the air outlet 12a and returned to the inner ambient 6 that is cooled.
The electronic control unit 14 when the air conditioning unit 1 operates in the above winter mode sends commands to the shutter devices 13 so that the first air inlet 11a is opened and the first air outlet 12a is also opened (figure 2); the second air inlet 11b and the second air outlet 12b are kept closed. Air is thus sucked from the air inlet 11a from the inner ambient 6 and is provided to the internal coil 9 that increases the temperature of the air; warmed air is then pushed by the thrust of the electric fan 15 to the air outlet 12a and returned to the inner ambient 6 that is warmed.
The operation of the reversible air condition unit 1 in the winter mode concurs in the formation of a layer of ice on the external coil 5; when the electronic control unit 14 senses that the external coil has to be defrosted (this part will be dealt in detail by means of the figure 4) performs the following operations ( if operations of forced defrost are performed, these operations will be dealt with greater detail in the following) :

Operates the closure of the first inlet 11a (see figure 3) and of the fist outlet 12a by closing the relative shutter devices 13;
Operates the opening of the second inlet 11b and of the second outlet 12b by opening the relative shutter devices 13; and
Sucks outside air in the container 10 through the second inlet 11b and expels the air from the container 10 through the second outlet 12b ( see dashed white arrow )- during the above operation the temperature of the external coil 5 increases (detail will be given in the following) and the process of melting the ice starts as the refrigerant circuit 2 is inverted.

Accordingly the housing 10 is kept separated by the inner ambient 6 and the flux of cool air that is outputted by the housing 10 is sent outside ambient 8 and thus cannot annoy people in the inner ambient and/or reduce the temperature of the inner ambient 6 in an unwanted manner. This is a smart operation as the defrosting operation do not provide any discomfort to the people in the inner ambient.
When defrosting operation are terminated the positions of the winter mode are resumed and the refrigerant circuit 2 is again inverted.If free defrost operations are performed the first inlet 11a and the first outlet 12a may be kept opened as shown in figure 2 and the second inlet 11b and the second outlet 12b must not be necessarily opened. In this case, even if air is supplied to the room 6 the temperature of the air is not reduced and discomfort is not felt. Also this part will be dealt with grater detail with respect to figure 4.
With reference to figure 4, the electronic unit 14 receives a number of measured parameters (block 100) including:

the measure of the relative humidity UR% of the air of the external ambient 8;
the temperature Text of the air of the external ambient 8;
the value pev of the evaporation pressure; and
the time elapsed τ_nodefrost since the last defrost operation.

Based on the above measured parameters, and knowing the type of exchange surface of the external coil 5, the electronic unit 14 calculates (block 105) the estimate of the value mm_frost of a mass of ice that should have been formed on the surfaces of the external coil 5 after the last defrosting operation. This operation may be performed using a formula or by using a table containing experimental parameters.
Block 105 is followed by block 110 that checks if the calculated value mm_frost is over a limit value mm_frost_max; in the negative (mm_frost< mm_frost_max) block 110 goes back to block 100 and in the affirmative (mm_frost> = mm_frost_max) block 110 goes to block 120 that enables the defrosting operations. The value of mm_frost_max has been determined with experimental tests .
Block 120 is followed by two blocks 130 and 140 that perform parallel operations.
Block 130 calculates τ_fd, i.e. the time needed to perform a defrost operation without reversing the refrigerant circuit 2 from winter mode to summer mode and with stopped compressor 3.
Conveniently, τ_fd is calculated based on:

the estimate of the value mm_frost of a mass of ice;
the temperature Text of the air of the external ambient 8; and
the relative humidity UR% of the air of the external ambient.

Block 140 calculates an overall time limit τ_lim for defrost operation, based on a number of parameters namely:

the temperature Troom of the inner ambient 6;
the percentage of compressor load %CMP;
the coefficient of thermal dispersion; and
indoor loads.

Blocks 130 and 140 are followed by block 150 that compares τ_fd with τ_lim and if the calculated time τ_fd is below the limit τ_lim the electronic unit 14 is designed to perform free defrosting operations (see block 170).
Accordingly, the electronic control unit 14 performs the following operations of free defrost:

the first inlet 11a and of the fist outlet 12a are kept opened (see figure 2);
the second inlet 11b and of the second outlet 12b are kept closed (see figure 2);
Switches off the compressor 3 and set fan 15 running to recirculate air;
An axial fan 30 coupled with the external coil 5 is driven at maximum speed.

Accordingly air is drawn from inner space 6 and is resent to the inner space 6, i.e. is recirculated by using fan 15. During the above operation ice present on external coil 5 melts due to the temperature of the refrigerant that is over 0 C° - (normally is between +3 / +4 C°) and due to the mechanical action of fan 30.
The above operation continue for the time τ_fd as set by a timer 155 and when the time τ_fd is elapsed a full winter mode is resumed (block 180). Block 180 is followed by block 100.
If block 150 checks that τ_fd is greater then τ_lim block 150 is followed by a block 160 that calculates τ_crd, i.e. the time needed to perform a defrost operation by reversing the refrigerant circuit 2 from winter mode to summer mode and with running compressor 3.
Conveniently τ_crd is calculated based on the estimate of the value of a mass of ice mm_frost.
Accordingly, the electronic control unit 14 performs the following operations of forced defrost (block 190):

Fan 30 is completely stopped; Operates the closure of the first inlet 11a and of the fist outlet 12a by closing the relative shutter devices 13 (figure 3);
Operates the opening of the second inlet 11b and of the second outlet 12b by opening the relative shutter devices 13 (figure 3);
Keeps the compressor running 3 and changes the position of the reversing valve 20;
Sucks outside air in the container 10 through the second inlet 11b and expels the air from the container 10 through the second outlet 12b - during the above operation the temperature of the external coil 5 increases as gas is compressed in the external coil and the process of melting the ice starts.
Fan 15 runs at maximum speed.

The above operation continue for the time τ_crd as set by a timer 156 and when the time τ_crd is elapsed a full winter mode is resumed (block 180). Block 180 is followed by block 100.

Claims

Reversible air conditioning
unit (1) comprising a refrigerant circuit (2) wherein an external coil (5) is designed to be placed in an outside ambient and is designed to establish a heat exchange with the air of the outside ambient (8); the refrigerant circuit also comprise an internal coil (9) placed in a housing (10) with a first air inlet (11a) designed to communicate with an inner ambient (6) and configured to suck air from the inner ambient (6) and a first air outlet (12a) designed to communicate with the inner ambient (6) and configured to provide respectively cool or warm air to the inner ambient (6) if the reversible air conditioning unit is operation in summer mode or winter mode,

the air conditioning unit (1) providing, during winter mode, a defrosting operation wherein the refrigerant circuit (2) is reversed to warm the external coil (5) and remove the ice that is formed on the external coil (5),

wherein the housing (10) is provided with a second air inlet (11b) configured to communicate with the outside ambient (8) and second air outlet configured to communicate with the outside ambient (8); shutter means (13) being provided to the first inlet (11a) and to first outlet (12a) and to the second inlet (11b) and to the second outlet (12b) and being controlled by an electronic unit (14) that is configured, during forced defrosting operations in which said refrigerant circuit is inversed, to close said first inlet (11a) and said first outlet (12a) and to open said second inlet (11b) and said second outlet (12b) to provide a flux of air toward the external ambient thus preventing that the flux of air that comes from the housing is provided to the inner ambient (6);

characterized in that

the electronic unit (14) comprises first calculating means (130) designed to calculate the time τ_fd needed to perform a free defrost operation without reversing the refrigerant circuit (2) from winter mode to summer mode and with stopped compressor; the electronic unit (14) comprises second calculating means (140) designed to calculate a time limit τ_lim for defrost operation, based on a number of parameters; and second comparing means checking if τ_fd is smaller than τ_lim to perform a free defrosting operation;

said air conditioning unit (1) is configured to execute free defrost operation in case the result of said second comparing means (140) is positive.
Air conditioning unit as defined in claim 1, wherein the electronic unit (14) comprises estimating means (100,105) for calculating the estimate of the value mm_frost of a mass of ice that should have been formed on the surfaces of the external coil (5) after the last defrosting operation; the electronic unit (14) further comprises comparing means (110) for comparing the estimate of the value mm_frost with a limit threshold mm_frost_max; said comparing means (110) enabling said defrosting operation if the estimate of the value mm_frost is greater than said limit threshold mm_frost_max.
Air conditioning unit as defined in claim 2, wherein said estimating means (100,105) are designed to calculate said value of a mass of ice mm_frost based on a number of parameters including one or more of the following:
the measure UR% of the relative humidity of the air of the external ambient (8);

the temperature Text of the air of the external ambient (8) ;

the value of the evaporation pressure pev; and

the time elapsed τ_nodefrost since the last defrost operation.
Air conditioning as defined in claim 1, wherein the electronic unit (14) is designed to perform the following free defrosting operations:
• keeps the first inlet (11a) and of the fist outlet (12a) open;

• keeps the second inlet (11b) and of the second outlet (12b) closed;

• drives a fan (30) coupled with the external coil (5) to run at its maximum speed; and

• switches off the compressor (3).
Air conditioning as defined in claim 4, wherein the electronic unit (14) is designed to perform the following defrosting operations:
• Operates the closure of the first inlet (11a) and of the fist outlet (12a) by closing the relative shutter devices (13);

• Operates the opening of the second inlet (11b) and of the second outlet (12b) by opening the relative shutter devices (13);

• Keeps the compressor running (3) and changes the position of the reversing valve (20);

• Controls a fan (15) placed in a housing (10) to run at maximum speed;

• Sucks outside air in the container (10) through the second inlet (11b) and expels the air from the container (10) through the second outlet (12b); during the above operation the temperature of the external coil (5) increases as gas is compressed in the external coil and the process of melting the ice starts.