Refrigerating machine optimized for carrying out cascade refrigerating cycles

Abstract

 Totally recuperative conditioning system operating two cascade refrigerating cycles with optimized circuit comprising at least an inner unit and an outer unit. The inner unit comprises at least a compressor, three heat exchangers, a throttling valve and a cycle inverting valve and the outer unit comprises at least a compressor, a heat exchanger, a throttling valve, a cycle inverting valve and the heat exchanger shared with said inner unit. The system is able to serve a plurality of users distributing, depending on the requirements, heat or cold for conditioning ambients and hot water for sanitary use, and it is characterized in that it is provided with a simplified water circuit comprising a number of valves not higher than five for the inner unit and five for the outer unit, of which at least an inverting valve for each said unit and in that said heat exchanger functions as evaporator or as condenser for cycles operating in said units depending on the opening state of said valves.

Description

[0001] The present invention relates to a machine for carrying out a vapor compression refrigerating cycle apt to provide heat to the user for heating ambients or for the production of sanitary hot water, or for subtracting heat in order to guarantee the ambients to be cooled, which is particularly efficient to work at considerable temperature differences and possibly at particularly low outer temperatures. Moreover the present invention relates to a method for managing the devices constituting the circuit apt to carry out said cycle.

[0002] In the state of the art, there are known circuits optimized to provide heat and cold to the users and hot water to the sanitary fittings. In the state of the art there are further known various vapor compression refrigerating cycles made up of two "cascade" operated vapor compression cycles. It is in fact known that in a vapor compression refrigerating cycle, when the temperature difference between hot source and cold source increases, the cycle compression ratio increases as well, and that it is convenient, in determined conditions, to manage the temperature difference by operating two cascade refrigerating cycles, in which the heat absorbed by the evaporator of the upper cycle is provided by the condensation of the lower cycle.

[0003] Cascade refrigerating cycles can be used both to provide the heat subtracted to the outer environment to the user as useful effect, and to dispose of the heat subtracted to the user in the environment. Referring to the equipments installed in the buildings, the first is the typical case of heating ambients during winter and of providing heat for sanitary hot water. The second case relates to the air-conditioning of ambients during summer. As it is known, there exists also the possibility that the user requires heat for heating water for sanitary use and subtraction of heat for summer air-conditioning of ambients at the same time.

[0004] The machines known in the state of the art to carry out the cascade refrigerating cycles have some disadvantages which limit their application fields, such for example the need to use many components and the consequent dimensioning difficulties of the same components, which are not often optimized for every functioning condition. For adjusting such devices, in many cases this requires the need of ad hoc programmed microprocessors.

[0005] The object of the present invention is to provide a machine characterized by an optimized circuit able to operate two cascade refrigerating cycles in order to provide and/or subtract heat to the user and to provide sanitary hot water at the same time. According to another aspect of the present invention it is provided a control logic to manage a machine operating two cascade vapor compression refrigerating cycles.

[0006] The invention will be described in the following with reference to the appended drawings. In which:

Figure 1 shows a circuit scheme of the refrigerating machine according to the present invention;

Figure 2 shows the circuit scheme of the machine according to the present invention with reference to the position of the probes used for adjusting the same machine;

Figure 3 shows an example of introducing the machine according to the present invention inside a house distribution equipment.

[0007] As it is shown in figure 1, the circuit operating the refrigerating cycle contained in the machine according to the present invention is made up of two units, an inner unit (1) where it is carried out the cycle allowing the production of water for heating, sanitary hot water and cooling water and an outer one (2) where it is carried out the lower cycle which exchanges heat with the outdoor air. The inner unit (1) comprises at least a compressor (11), at least an exchanger able to exchange heat with the outer unit (12), an exchanger serving the users for heating/cooling (13) and a recuperative heat exchanger for heating sanitary hot water (14), a cycle inverting valve (15), a throttling valve (16) and three valves (17, 18 and 19), besides every necessary element to guarantee the correct functioning of machines operating vapor compression cycles, known according to the state of the art and therefore not described in detail.

[0008] As a way of example and in a not limiting way, when this unit functions with refrigerating gas R134A, it can reach the condensation temperature of 85°C, beginning from evaporation temperatures up to 15°C, with maximum pressures around 30 bar.

[0009] The outer unit (2) comprises at least a compressor (21), a heat exchanger (22) able to give and absorb heat from the outdoor air or other heat source, such for example groundwater, superficial water or ground. Such exchanger can be made up of a battery finned and fanned by means of a fan (28) or a plate-type or a shell and tube exchanger with inverter controlled pump. Moreover, the outer unit comprises a cycle inverting valve (23), a throttling valve (24), three valves (25, 26, 27) and shares the heat exchanger (12) with the inner unit.

[0010] As a way of example and in a not limiting way, this unit can work with gas R410A and can work at very low outer air temperatures, up to -20°C, which imply evaporation temperatures around -25°C and condensation temperatures around 30°C. The working pressure field is between 3 and 20 bar.

[0011] The refrigerating machine according to the present invention can provide various kinds of cycles, depending on the user temporary needs, useful to provide heat or cold to the user served by the exchanger (13) and heat for the production of sanitary hot water to the recuperative heat exchanger (14).

[0012] The passage from the one to the other functioning mode described in the following occurs by suitably actuating the two cycle inverting valves (15) and (23) and the valves (17, 18, 19, 25, 26, 27). Depending on the functioning of the inner and outer unit there can be identified the following machine states, the Heat Pump mode functioning being indicated with PdC and the heat recuperation for sanitary hot water being indicated with Rec.

[0013] For describing the functioning mode and the machine control logic, it is referred to an embodiment which comprises the provision of an inverter on the electric motors controlling the compressors (11) and (21) and the fan (28) serving the heat exchanger (22).

State	Machine Mode	Inner unit Mode	outer unit mode
1	Chiller	"water-gas" Chiller	Chiller
2	Pdc	"water-gas" Pdc	Pdc
3	Chiller+Rec	Chiller+Rec	OFF
4	Rec	Sanitary Pdc	Pdc

[0014] In the functioning state 1, with the machine in Chiller mode, the useful effect required by the user is to provide cold to the exchanger (13). In this functioning mode, the exchanger (13) functions as evaporator. The heat exchanger (12) functions as condenser for the upper cycle operated by the inner unit (1) and as evaporator for the lower cycle operated by the outer unit (2), which disposes of the heat in the finned battery (22), or plate-type or shell and tube exchanger which in this functioning mode functions as condenser.

[0015] In this functioning mode, the rotation speed of the compressor of the inner unit (11) is controlled according to the temperature sensed by the probe (31) shown in figure 2, arranged at the output of the exchanger (13) and to the evaporation pressure value of the outer unit (2) sensed by the probe (32), remaining around the value needed for maximizing the efficiency of the two units contemporaneous working. This value is approximately around 11.5 bar.

[0016] The rotation speed of the compressor (11) will be held at its maximum until the set-point for the temperature sensed by the probe (31) at the output of the exchanger (13) will be satisfied, decreased by 25% only in case the evaporation pressure value of the outer unit (2) in the exchanger (12) sensed by the probe (32) excesses the set "set-point" value for such parameter of a 4 bar difference. When the set set-point for the temperature of the compressor (11) is reached, it remains off until the value indicated by the readings of the respective probes is not in a predetermined tolerance interval.

[0017] When the set-point temperature at the output of the exchanger (13) is reached, the compressor (21) of the outer unit (2), which was on with the highest rotation speed, is switched off synchronously with the compressor (11) of the inner unit (1) in order to avoid the problems linked to the pressure differences in conjunction with asynchronous switching offs.

[0018] The two units provide synchronously the response to the alarm for high condensation pressure of the outer unit in the exchanger (22) as well, which can occur at high outer temperatures and which can be sensed by means of a pressure probe (33) which measures inside the exchanger (22). In this case, the rotation speed of the compressor (11) decreases, thus decreasing the thermal power absorbed by the user in order to allow that the heat dissipation at the exchanger (22) lowers again the condensation pressure to acceptable levels.

[0019] In the functioning modes indicated by numbers 2 and 4, the useful effect is to provide heat only to the exchanger (13) for heating ambients or only to the exchanger (14) for the production of sanitary hot water.

[0020] These two functioning modes can be shown together, since the only difference is the active circulation pump; if the demand is for heating ambients, the circulation pump (34) on the exchanger (13) will be activated, if the demand is for production of sanitary hot water the circulation pump (35) on the recuperative heat exchanger (14) will be activated. The rotation speed of the compressor (11) of the inner unit (1) will be adjusted according to the temperature read by the probe (31) or (36) positioned on the exchangers (13) and (14), depending on the user to be satisfied. The rotation speed of the compressor (11) will be set at its maximum until the temperature set-point on the probe (31) or (36) is reached. When the set-point is reached, the compressor (11) is switched off, until the value indicated by the readings on the respective probes remains in the preset tolerance interval. When the reading on the probe (31) or (36) goes out of such interval, the compressor (11) is switched on again with rotation speed proportional to the derivative with respect to the time of the temperature reading, that is to the gradient of the temperature curve in the temperature/time graph. If the value of the temperature derivative with respect to the time tends to zero, the compressor (11) is actuated only if it is out of the tolerance interval, at the minimum speed. If the value of the temperature derivative with respect to the time tends to increase, the compressor (11) is actuated at an initial speed which is a fraction of the highest one (ex. 50%) and such speed is increased at preset time intervals according to the derivative of the temperature with respect to time, sensed at constant time intervals.

[0021] The outer unit (2) in this functioning mode is adjusted so that the evaporation pressure in the inner unit (1) in the exchanger (12), measured by means of the probe (37), is maintained constant. The adjustment occurs at the rotation speeds of the compressor (21) and of the fans (28) initially at the maximum value. In case the system in place of the finned battery is provided with a plate-type or shell and tube exchanger, the adjustment occurs in the same way as by means of the circulation pump. According to the evaporation pressure at the exchanger (12), it is firstly reduced the rotation speed of the compressor (21) up to the lower limit of the adjustment field, and subsequently the rotation speed of the fan (28) possibly up to its complete switching off. Also in this case the modulation, after reaching the set value of evaporation pressure, is carried out in differential mode. When the evaporation pressure goes out or under the low limit of the tolerance interval, the fan (28) first and then the compressor (21) are re-activated at constant speed increments but always more frequent. The adjustment occurs according to the derivative with respect to the time of the evaporation pressure at the exchanger (12) sensed at regular time intervals by the probe (37).

[0022] The functioning mode 3 is activated when the demand on cold at the exchanger (13) for the summer air-conditioning of ambients and on heat at the exchanger (14) for the production of sanitary hot water occurs at the same time.

[0023] In this particular, intermediate cycle between the heat pump and the chiller, the outer unit (2) remains off and the inner unit (1) works in water/water mode. The exchanger (13) functions as evaporator, and the exchanger (12) is not interested by this cycle, since the inner unit (1) condenses on the recuperative heat exchanger (14) and the outer unit (2) is off.

[0024] The rotation speed of the compressor (11) of the inner unit (1) is managed in the same way as for the functioning mode 2. The rotation speed is adjusted in fact according to the set set-point for the temperature read by the probe (31), at reaching thereof the compressor (11) being stopped. After the deviation from the set-point value, the compressor (11) is re-activated at speed which varies proportionally to the derivative with respect to the time of the temperature sensed by the probe (31), as stated above.

[0025] It is convenient to note that when the machine works in the above described chiller mode plus recuperation, if the heat demand profiles of the two users, the hot one and the cold one, cannot be superimposed, the machine can pass to the chiller mode or heat pump mode.

[0026] As above described, depending on the cycle the inner unit (1) is carrying out, the outer machine can change the functioning cycle as well, thus allowing the exchanger (12) to function alternatively as condenser or evaporator for the inner unit (1), with the clear advantage of carrying out with the same machine a series of different cycles with the lowest number of heat exchangers, valves and other components.

[0027] The machine according to the present invention allows also to optimize the choice of coolants, thus allowing a control of the working pressures. For example, the choice of the coolant R410A in the first cycle allows also for very low temperatures of outdoor air, approximately up to -25°C, not to go under pressures lower than 1 bar, since the highest condensation temperatures the first cycle has to reach, do not exceed 30°C.

[0028] According to an embodiment shown in figure 3, the machine according to the present invention can be realized with the functional units, the inner one and outer one, separated. Such embodiment is particularly indicated for applications in places where the outer temperatures can be particularly low, for example lower than -10°C. In fact, in this configuration, the components constituting the inner unit (1), and comprising every exchanger where the available thermo-vector fluids are treated, are protected against the outer low temperatures and against the fluid freezing danger in the pipes. In figure 3, it is shown by way of example and in a not limiting way, a possible introduction inside the equipment of a building of a machine according to the present invention, with the heat exchanger (13) serving a radiant panels heating device (41) supplied by the accumulation tank (42) and the heat exchanger (14) serving the water distributing equipment for sanitary use supplied by the tank (43) in which it is also stored the heat collected by the solar panels (44). According to another embodiment, the machine according to the present invention can be realized with the functional units, the inner one and the outer one, enclosed in a sole equipment to be mounted outside, thus reducing at minimum the inner room of the building needed for installation. This embodiment is clearly advantageous in places where the temperatures can be considered constantly higher then -10°C.

[0029] As above described, the device object of the present invention allows to operate efficiently and with a reduced number of components, which are possibly integrated in a sole unit, every refrigerating cycle needed by the summer and winter air-conditioning of ambients and for the production of sanitary hot water. Further it is provided a managing logic of the device object of the present invention which allows to manage simply the two units, which constitute the device, in the various functioning conditions.

Claims

1. Totally recuperative conditioning system operating two cascade refrigerating cycles with optimized circuit comprising at least an inner unit (1) and an outer unit (2), said inner unit (1) comprising at least a compressor (11), three heat exchangers (12, 13, 14), a throttling valve (16) and a cycle inverting valve (15) and said outer unit (2) comprising at least a compressor (21), a heat exchanger (22), a throttling valve (24), a cycle inverting valve (23) and the heat exchanger (12) shared with said inner unit (1), able to serve a plurality of users distributing by means of said heat exchangers (13, 14) of said inner unit (1), depending on the requirements, heat or cold for conditioning ambients and hot water for sanitary use, characterized in that it is provided with a simplified water circuit comprising a number of valves not higher than five for the inner unit (1) and five for the outer unit (2), of which at least an inverting valve for each said unit and in that said heat exchanger (12) functions as evaporator or as condenser for cycles operating in said units (1, 2) depending on the opening state of said valves.

2. Method for adjusting a refrigerating machine according to claim 1 functioning so that heat is subtracted to the user served by said heat exchanger (13), comprising the following steps:

- setting at the highest possible value the rotation speed of said compressor (11) serving said inner unit (1) and of said compressor (21) serving said outer unit (2);

- maintaining said rotation speed of said compressor (11) constant until reaching the programmed value for the thermo-vector fluid temperature in output from said heat exchanger (13) sensed by a suitable temperature probe (31), and decreasing it only in case of increments considered excessive of the evaporation pressure of said outer unit (2) measured by a pressure probe (32);

- switching off said compressor (11) when it is reached said programmed value for the thermo-vector fluid temperature in output from the heat exchanger (13) and switching off said compressor (21) serving said outer unit (2) at the same time;

- maintaining said compressors (11, 21) switched off until said temperature sensed by said probe (31) remains in a prefixed tolerance interval.

3. Method for adjusting a refrigerating machine according to claim 1 functioning so that heat is provided to the user served by said heat exchanger (13) or by said heat exchanger (14), comprising the following steps:

- setting at the highest possible value the rotation speed of said compressor (11) serving said inner unit (1), of said compressor (21) serving said outer unit (2) and of said fan (28) serving said heat exchanger (22);

- maintaining said rotation speed constant until reaching the programmed value for the thermo-vector fluid temperature in output from said heat exchanger (13) sensed by a suitable temperature probe (31), or the programmed value for the thermo-vector fluid temperature in output from said heat exchanger (14) sensed by a suitable temperature probe (36);

- switching off said compressor (11) when it is reached said temperature programmed value sensed by one of said temperature probes (31, 36) and maintaining it off until said temperature is in the defined tolerance interval;

- switching on again said compressor (11) at initial speed equal to a fraction of the highest one and increasing said speed proportionally to the derivative with respect to the time of said temperature sensed at regular time intervals by said probe (31 or 36);

- maintaining the rotation speed of said compressor (21) serving said outer unit (2) constant until reaching a preset value for the evaporation pressure of the inner unit (1) in the heat exchanger (12), sensed by means of suitable pressure probe (37);

- maintaining said evaporation pressure of the inner unit (1) in the heat exchanger (12) constant, reducing firstly the rotation speed of said compressor (21) up to the lower limit of its adjustment field and after of said fan (28) until the possible switching off to lower said evaporation pressure, and increasing said rotation speed in inverted order to increase said evaporation pressure.

4. Method for adjusting a refrigerating machine according to claim 1 functioning so that heat is subtracted to the user served by said heat exchanger (13) and to provide heat to the user served by said heat exchanger (14), comprising the following steps:

- setting at the highest possible value the rotation speed of said compressor (11) serving said inner unit (1), and setting at zero the rotation speed of said compressor (21) serving said outer unit (2) and of said fan (28) serving said heat exchanger (22);

- maintaining said rotation speed of said compressor (11) constant until reaching the programmed value for the thermo-vector fluid temperature in output from said heat exchanger (13) sensed by a suitable temperature probe (31);

- switching off said compressor (11) when it is reached said temperature programmed value sensed by said temperature probe (31) and maintaining it off until said temperature is in the defined tolerance interval;

- switching on again said compressor (11) at initial speed equal to a fraction of the highest one and increasing said speed proportionally to the derivative with respect to the time of said temperature sensed at regular time intervals by said probe (31).

Drawing