FR2778970A1 - Deicing evaporators of refrigeration equipment and/or heat pumps - Google Patents

Abstract

In refrigerating mode the method includes operating in parallel or otherwise at least two evaporators (3,4). In deicing mode the method has the following stages: diverting all or part of the refrigerating fluid when it is at high pressure and high temperature; and introducing the high pressure/temperature refrigerating fluid into one of the two evaporators (3) downstream of the regulator (7). Simultaneously the other evaporator (4) is maintained in service. The refrigerating equipment and/or the heat pumps have refrigerating liquid circulating circuits. The refrigerating fluid goes through a temperature and a pressure cycle by passing successively from a high pressure and high vapor phase temperature at the output of a compressor (1), to a high pressure/temperature at the output of another condenser (2), and then to a low pressure, low temperature phase at the output of a regulator (7) before entering evaporators (3,4). In refrigerating mode, the two evaporators are operated in parallel or otherwise. In the deicing mode, all or part of the refrigerating fluid is diverted when it is at high pressure and high temperature, the high pressure/temperature refrigerating fluid is introduced into one of the two evaporators (3) downstream of the regulator (7), so as to proceed with the deicing, and simultaneously, the other evaporator is maintained in service. An Independent claim is included for an evaporator deicer.

Description

I Method and device for defrosting by condensation and / or

  refrigerant subcooling.

  The present invention relates to refrigerated display cabinets and / or heat pumps. It relates more particularly to a method and a device for defrosting the fins of evaporators otherwise called air coolers. It is known that the defrosting process involves increases in the temperature of the air circulating on air coolers, as well in all refrigeration applications, cold stores, refrigerated display cabinets (MFV), but also for pumps. heat pumps with an air cooler for evaporation. This interruption of refrigeration production can have harmful consequences for the temperature of the products which must be kept within very precise limits. This is particularly true for MFVs used in commercial refrigeration. Patents and patent applications EP 0768 501A2, FR 2 713 320 Ai, US 4 449 374, US 5

  031 413 propose solutions which try to overcome these drawbacks.

  In the same way for air / air or air / water heat pumps (PAC), the formation of frost on exchangers whose fin pitch is particularly close (for obvious reasons of cost), involves rapid malfunctions and numerous. The present invention aims to maintain the temperature of the supply air at a constant cold temperature for maintaining the temperature of the products or the continuity of the refrigeration production, and to carry out the defrosting while minimizing the energy consumption. The defrosting method according to the invention relates to refrigeration equipment and / or heat pumps which comprise, in a manner known per se, circuits traversed by a refrigerant. These circuits are composed of one or more compressors, condensers and evaporators generally mounted in a battery. The refrigerant undergoes a temperature and pressure cycle passing successively from a high pressure and high temperature vapor phase at the outlet of the compressor, to a high temperature high pressure liquid phase at the outlet of the condenser, then to a phase low pressure and low temperature at the outlet of the regulator, in particular

  thermostatic, before entering the evaporator coil.

  The method according to the invention has the following characteristic features. When the refrigeration equipment and / or the heat pump are operated in refrigeration mode, in this case they are arranged so that two evaporators can operate either in parallel or in alternating operation. In the defrosting phase, the process according to

  the invention comprises the following stages.

  It includes the steps of deriving all or part of the refrigerant when it is at high pressure and at high temperature, then introducing the high pressure and high temperature refrigerant thus derived, into one of said two evaporators, downstream of the regulator, in order to defrost it. During the implementation of these process steps, the other exchanger is kept in service. Thanks to this process, the continuity of refrigeration production is ensured. In particular in the case of refrigeration equipment containing products to be stored, the supply air temperature is maintained at a constant cold temperature. Furthermore, defrosting is carried out in

  minimizing energy consumption.

  The method increases the overall energy efficiency of the refrigeration cycle (including defrosting) by using the heat of sub-cooling (first embodiment) or of condensation (second embodiment) for defrosting. The energy losses are therefore limited to the heating of the air around the defrosted battery, which is in any case very low since experience shows that the

  defrosting is completed for wall temperatures above 10 C (approximately).

  Preferably, in the case of the first alternative embodiment, the process according to the invention is such that all of the high pressure and high temperature refrigerant introduced into the first evaporator to be defrosted is derived in the liquid phase at the outlet. of said condenser. The liquid refrigerant comes out in the sub-cooled state of

  the evaporator during defrosting.

  In the case of this first alternative embodiment, the method further comprises the step of recycling the subcooled liquid refrigerant coming from the evaporator during defrosting, upstream of the expansion valve of the second evaporator. The second

  evaporator operates in refrigeration mode.

  Preferably, in the case of the second variant embodiment, the method according to the invention is such that all or part of the refrigerant at high pressure and at high temperature, introduced into the first evaporator to be defrosted, is derived in the vapor phase at the outlet of said compressor. The evaporator is defrosted by the heat of condensation of the refrigerant. In the case of this second variant embodiment, the method further comprises the step of recycling the refrigerant leaving the liquid state of the first evaporator during defrosting, upstream of the pressure reducer of the

  second evaporator. The second evaporator operates in refrigeration mode.

  Advantageously, the evaporator during defrosting is isolated from the circulating air.

  in refrigeration or heat pump equipment.

  The present invention also relates to a defrosting device for the evaporators of refrigeration equipment and / or heat pumps comprising circuits traversed by a refrigerant. The refrigerant undergoes a temperature and pressure cycle passing successively from a high pressure and high temperature vapor phase at the outlet of the compressor, to a high temperature high pressure liquid phase at the outlet of the condenser, then to a phase low pressure and low temperature at the outlet of the regulator before entering the evaporators. The device according to the invention comprises: - at least two evaporators (or two evaporator batteries) mounted in parallel by means of an input T and an output T, - circuits and valves (or solenoid valves) enabling the

  device according to two operating modes.

  a) Refrigeration mode. In this case, the refrigerant leaving in the liquid state, at high pressure and at high temperature is introduced through the pressure reducer either in the two evaporators in the option parallel operation of the evaporators, or in only one for the option alternate operation. The refrigerant in the vapor state at the outlet of the evaporators is compressed by the compressor before entering the condenser, The production of cold results from the expansion and evaporation of the fluid

  refrigerant in the said evaporators.

  b) Defrost mode. In this case, said circuits include bypass means, in particular bypass circuits and valves, make it possible to bypass the circulation of the refrigerant at the outlet of said compressor or at the outlet of said condenser. At the outlet of the compressor, as at the outlet of the condenser, the fluid

  refrigerant is at high pressure and high temperature.

  The bypass means also make it possible - to introduce the high pressure and high temperature refrigerant thus derived, into one of said two evaporators, downstream of the regulator, in order to defrost it, and - to simultaneously maintain circulation refrigerant in the other

  exchanger, by introducing it upstream of the regulator.

  Thanks to this combination of means, it is possible to ensure: - the continuity of refrigeration production and

  - defrost while minimizing energy consumption.

  Thus, in particular in the case of refrigeration equipment containing products to be preserved, the supply air temperature is maintained at a temperature

constant cold.

  Preferably, according to a first embodiment, the bypass means, in particular the bypass circuits and the associated valves, of the defrosting device are such that, in defrosting mode, the circulation of all of the refrigerant at high pressure and at high temperature is derived in liquid phase at the outlet of the condenser, before being introduced downstream of the regulator, in the first evaporator to be defrosted. The liquid refrigerant leaves in the sub-cooled state from the evaporator during defrosting. In the case of this first alternative embodiment, the bypass means, in particular the bypass circuits and the associated valves are also such that, in defrosting mode, all of the subcooled liquid refrigerant coming from the evaporator being defrost, is introduced upstream of the regulator

  from the second evaporator. The second evaporator operates in refrigeration mode.

  Preferably, according to a second alternative embodiment, the bypass means, in particular the bypass circuits and the associated valves, are such that, in defrosting mode, all or part of the high pressure and high temperature refrigerant is bypassed in the vapor phase at the outlet of said compressor, before being introduced downstream of the regulator, in the first evaporator to be defrosted. So the

  defrosting of the evaporator is ensured by the heat of condensation of the refrigerant.

  In the case of this second alternative embodiment, the bypass means, in particular the bypass circuits and the associated valves are also such that, in defrosting mode, the refrigerants coming in the liquid state from the first evaporator during defrosting and / or the condenser, are introduced upstream of the regulator of the

  second evaporator; The second evaporator operates in refrigeration mode.

  Advantageously, the evaporator during defrosting is isolated from the air circulating in the refrigerating equipment or in the heat pump by means of one or two movable flaps, tilting or sliding. These shutters make it possible to close the air passage section during defrosting and to isolate the defrosting battery from that which is then in

refrigeration operation.

  The invention also relates to refrigeration equipment (refrigerated cabinet, refrigerated display cabinet) implementing any of the methods of

  defrosting and / or defrosting devices defined above.

  The invention also relates to a heat pump implementing any of the defrosting methods and / or defrosting devices defined above. Other characteristics and advantages of the invention will appear on reading the

  description of alternative embodiments of the invention, given by way of indicative example and

  nonlimiting, and of: - Figure 1 which shows the diagram of the refrigeration circuit and the defrosting circuit in the case where defrosting is obtained by cooling the refrigerant alone; - Figure 2 which shows the diagram of the refrigeration circuit and the defrosting circuit in the case where defrosting is obtained by bypassing all of the hot gases and reintegration of the condensate upstream of the regulator; - Figure 3 which shows the diagram of the refrigeration circuit and the defrosting circuit in the case where defrosting is obtained by bypassing all of the hot gases and reintegration of the condensate upstream of the condenser; - Figure 4 which shows the diagram of the refrigeration circuit and the defrosting circuit in the case where defrosting is obtained by bypassing part of the hot gases and reintegrating the condensate upstream of the regulator; - Figure 5 which shows a side sectional view of an alternative embodiment of two evaporators alternately isolable from the air stream by tilting flaps. In FIGS. 1 to 4, the main elements constituting a refrigeration equipment (in particular a refrigerated sales cabinet or a refrigerated cabinet) or a heat pump are recognized; the compressor (s) 1; the water or air condenser (s) 2; A group of at least two refrigeration batteries 3, 4 otherwise called evaporators. The number of pairs of batteries can be twenty. Two flaps 5 and 6 (see Figure 7) tilting or sliding to close the air passage section during defrosting. Two solenoid valves 8a, 8b and 9a, 9b arranged at the inputs of the T-pipes 10a, 10b at the inlet of each evaporator 3, 4. Two solenoid valves 1a, 12a, and 1 lb, 12b arranged

  at the outputs of the T-pipes 13a, 13b at the outlet of each evaporator 3, 4.

  The elementary pattern (cf. Figures 1, 2, 3 and 4) is therefore composed of 2 air-cooling batteries (or evaporators) and this pattern can be reproduced indefinitely. It comprises a supply branch comprising a branch solenoid valve 14, a branch regulator 7 which can be thermostatic or electronic. The arrows f (in Figures 1 to 4) indicate the direction of flow of the refrigerant in the circuits. We will deduct the

  valves or solenoid valves that are open.

  The table below indicates the open or closed position of the different solenoid valves. Operation is only explained for evaporator 3. The logic is

identical for evaporator 4.

  Solenoid valves 14 8a 8b 9a 9b lia 12a l1b 12b Cold production O F F O O F O F O Defrost F O F F O O F F O (F: Closed; O: Open) In cold production, for the option where the evaporators operate in parallel, the solenoid valve 12b is open. In cold production for option o the evaporators operate alternately, depending on whether the evaporator 3 or 4 is in refrigeration production, the solenoid valve 9a is open and the solenoid valve 9b is closed or vice versa. For the supply of defrosting heat by the high pressure refrigerant, two options exist: supply by high pressure steam by bypass at the outlet of the compressor or supply by high pressure liquid by bypass at the outlet of the condenser. The choice between the two options depends essentially on the ratio

  between the available heating power and the amount of frost to melt.

  Option 1 - Defrosting by sub-cooling of the refrigerant only.

  We will now describe FIG. 1 which explains the operating principle of this option by referring to the evaporator 3. The reverse operation is deduced therefrom for the other evaporator 4. It suffices thereafter to extend the reasoning for as much

branches as needed.

  For the evaporator 3, on an inlet T 10Oa, two solenoid valves 8a and 9a are arranged, and on an outlet T 13a, two solenoid valves 11a and 12a placed symmetrically. In refrigeration operation, the solenoid valve 8a is closed and therefore the refrigerant coming from the branch regulator 7 passes through the piping where the solenoid valve 9a is located in the open position. In this case the refrigerant evaporates (for example 4bar, -10 C, but also lbar 40 C) leaves in the vapor phase of the exchanger. At the outlet, the solenoid valve 1a is closed, the solenoid valve 12a is open, and the steam from

  refrigerant joins the general suction pipe.

  In defrosting operation, the solenoid valve 14 is closed, the solenoid valve 8a is open and the liquid refrigerant (for example, 15bar, 20 C, but also 24 bar, 45 C) leaving the condenser enters the evaporator which then operates as a subcooling exchanger. The refrigerant leaves this air cooler with a sub

greater cooling.

  The solenoid valve 12a is then closed, the solenoid valve 1a is open and the highly sub-cooled refrigerant returns downstream of the solenoid valve 14 and enters the

  regulator 7 to supply the evaporator 4.

  Defrosting is typically carried out over a period of 7 to 8 minutes, since it is

  it is possible to avoid the increase in frost formation unduly.

  Refrigeration systems or heat pumps work with pressure control systems (pressure switch or electronic pressure gauges) to stop or start the system from pressure thresholds. The formation of frost on the coil implies a clear decrease in the air flow which is hampered in its passage by the frost formed on the fins. This lowering of the external flow rate results in a lowering of the internal temperature of evaporation of the refrigerant and therefore of the evaporation pressure since a greater temperature difference between the refrigerant and the average air temperature is required to exchange the same quantity. of energy. Therefore the low pressure or pressure switch, connected to an electronic card, is adjusted with a differential threshold which allows the defrost to be triggered by closing the solenoid valve 14 and

  the solenoid valve 12a and the opening of the solenoid valve 8a and of the solenoid valve 11a.

  The defrost stop criterion is provided by a temperature sensor placed on the coldest part of the exchanger (generally at its inlet) which stops the

  defrost when this temperature is above 10 C.

  This simple logic allows sufficiently sensitive control of the formation of the

  frost and is reproduced as many times as necessary.

  This defrosting option by sub-cooling the liquid is particularly suitable for refrigeration systems or heat pumps with few evaporators. Option 2 - Defrosting by hot gases It is interesting to use the same principle but, instead of defrosting by sub-cooling the liquid, defrosting is done by partial or total condensation of the refrigerant vapors which are then taken off upstream of the condenser (for example bar, 60 or 90'C). This technique requires either an additional solenoid valve, the solenoid valve 20 (Figures 2, 3 and 4) or two solenoid valves plus an adjustment valve

  (solenoid valve 20, solenoid valve 21 and valve 22) for partial removal.

  Option 2.1 - Defrosting by total or partial removal of hot gases (see Figures 2 and 4) and reintegration of the condensate upstream of the regulator The needs for defrosting on one or more evaporators are such that it is possible to bypass the flow total vapor upstream of the condenser so that these vapors condense fully in the evaporator (s). Condensed flow is reinstated

  fully upstream of the regulator.

  This diagram is shown in Figure 2 where we recognize the same basic pattern, the only difference is therefore the additional solenoid valve 20 which is open in cycle

  normal refrigerator and which is closed during defrosting.

  For the option with partial reintegration (see Figure 4), the sampling device is more complicated. Two adjustment valves 24 and 22 are required. The valve 24 allows the flow rate to be adjusted and the valve 22 creates a pressure drop so that the pressure on the sampling branch is slightly higher than the pressure of the fluid leaving the condenser to ensure the reintegration of the liquid formed in the branch of

liquid leaving the condenser 4.

  Otherwise the circulation of the refrigerant in the two air-cooling batteries is identical to

the one described for option 1.

  Option 2.2 - Defrosting by total removal of hot gases (see fig. 3) and reintegration of the condensate upstream of the condenser When it is necessary to defrost hot gas but it is likely that the refrigerant vapors will not be fully condensed, the two-phase mixture leaving from the defrosting evaporator (s) is fully reintegrated upstream of the condenser as shown in figure 3. The condenser completes the condensation of the refrigerant which normally circulates towards the branch evaporator of the solenoid valve 7 and

  which expands in the evaporator which is in refrigeration production.

  Minimization of energy losses for the different options Let us consider that the formation of frost tolerated on the surface of the fins is 1 mmn. For a battery size, a given operation will lead to the formation of

x kg of frost.

  To melt this frost, it is necessary: - to bring the mass of the evaporator up to a temperature greater than 0, typically up to + 3 C. For this it is necessary to provide an elementary theoretical power Q1, to raise the temperature of the frost up to its melting temperature and therefore supply a quantity of heat QG 1, - supply the heat of fusion which is typically for ice of 330 kJ / kg, ie QG2 =

330 x.

  - partially dry the battery by reassembling all of the metal and the residual water

  up to a temperature of around 10 C, this is a quantity of heat Q4.

  The terms Q1, QG1 and QG2 do not cause thermal loss in the aeraulic system when this is isolated from the air flow which usually sweeps the battery of the air cooler. This isolation of the air flow is obtained by shutters 5 and 6. On the other hand, Q1, QG1, QG2 and Q4 require energy. This energy is supplied according to the invention, either by condensation or better by sub-cooling. Subcooling consists in cooling the condensate, under the condensing pressure, which constitutes an energy gain. In this defrosting phase, there is therefore, either absence of loss

  (condensation), or energy gain (sub-cooling).

  On the other hand, the quantity of heat Q4 constitutes a calorific contribution which will have to be compensated but experience shows that this quantity represents 20 to 25% of the quantity

total energy exchanged.

  The device which is the subject of the invention therefore clearly implies a very significant minimization of energy consumption, all the more so as the conventional devices or those used in the aforementioned patents use electrical resistors which imply additional energy consumption and above all an operating time. many

  longer since the exchange is much less efficient than by internal defrosting.

  For a reversible heat pump, the system works in air conditioning in summer. The water condenser (inside the building) is then an evaporator and

  conversely the air evaporator (outside the building) becomes a condenser.

  In winter operation, the evaporator located outside frost as soon as the

  air temperature is typically less than 7 C.

  The application of the principle of defrosting by condensation and subcooling as developed previously implies that the evaporator is double, which makes it possible to carry out defrosting as explained above. Under normal operating conditions, it is not even necessary to have flaps to separate the evaporator in defrosting from the air flow, because, unlike refrigerated display cabinets, the warming of atmospheric air due to the defrosting has no effect on the operation of the other evaporator. The score is

  advantageously performed vertically to facilitate the flow of defrost water.

12 2778970

Claims (11)

Claims   1. Method for defrosting evaporators (3. 4) of refrigeration equipment and / or heat pumps said refrigeration equipment and / or said heat pumps comprising circuits traversed by a refrigerant; said refrigerant undergoing a temperature and pressure cycle passing successively from a high pressure and high temperature vapor phase to the outlet of a compressor (1). to a high pressure high pressure liquid phase at the outlet of a condenser (2). then at a low pressure and low temperature phase at the outlet of a pressure reducer (7) before entering said evaporators (3, 4): said process comprising. in refrigeration mode. the step - operating at least two evaporators (3, 4) in parallel or alternately; said method comprising. during the defrosting phase, the steps to derive (8a, 8b. 9a, 9b. lla. llb, 12a. 12b, 14) all or part of the   refrigerant when at high pressure and high temperature.   - introduce the high pressure and high temperature refrigerant thus derived. in one of said two evaporators (3). downstream of the regulator (7). in order to defrost it and   - keep the other evaporator (4) in service simultaneously.   2. Method according to claim 1 such that - all of the high pressure and high temperature refrigerant, introduced into the first evaporator (3) to be defrosted, is derived in the liquid phase at the outlet of said condenser (2), said process further comprising the step of recycling the sub-cooled liquid refrigerant coming from the evaporator (3) during defrosting, upstream of the pressure reducer (7) of the   second evaporator (4) operating in refrigeration mode. 13 2778970   3. Method according to claim 1 such that - all or part of the high pressure and high temperature refrigerant, introduced into the first evaporator (4) to be defrosted, is derived in vapor phase at the outlet of said compressor (1) said method further comprising the step: - of recycling the refrigerant leaving the first evaporator (4) during defrosting, upstream of the pressure reducer (7) of the second evaporator   (3) operating in refrigeration mode.   4. Method according to claim 1 such that - all or part of the refrigerant at high pressure and at   high temperature, introduced into the first evaporator (4) to be defrosted.   is derived in vapor phase at the outlet of said compressor (1) said process further comprising the step: - of recycling the refrigerant leaving the first evaporator (4)   during defrost. upstream of the condenser (2).   5. Method according to any one of claims 1 to 4 such as   - the evaporator (4) being defrosted is isolated (5, 6) from the air   circulating in refrigeration equipment.   6. Device for defrosting evaporators (3, 4) of refrigeration equipment and / or heat pumps; said refrigeration equipment and / or said heat pumps comprising circuits traversed by a refrigerant said refrigerant undergoing a temperature and pressure cycle passing successively from a vapor phase of high pressure and high temperature to the outlet of a compressor (1), at a high pressure high pressure liquid phase at the outlet of a condenser (2), then at a low pressure and low temperature phase at the outlet of a pressure reducer (7) before entering said evaporators (3, 4): said device comprising: - at least two evaporators (3. 4) mounted in parallel by means of an inlet T (10a, lob) and an outlet T (13a, 13b), - circuits and valves (or solenoid valves) (8a, 8b. 9a, 9b, la, llb, 12a. 12b, 14) allowing the device to be implemented according to two operating modes: a) a refrigeration mode, in which case the fluid refrigerant leaving in liquid state, at high pressure and at high temperature is introduced through the pressure reducer (7) in the two evaporators (3, 4) or in one of the two; the refrigerant in the vapor state at the outlet of the evaporator (3 or 4) or of the evaporators (3 and 4) is compressed by the compressor (1) before to enter the condenser (2).   b) a defrosting mode, in which case said circuits comprising bypass means, in particular bypass circuits and valves, make it possible - to bypass the circulation of the refrigerant, at the outlet of said compressor (1) or the outlet of said condenser (2 ). when at high   pressure and high temperature and.   - Introducing the high pressure and high temperature refrigerant thus derived, into one of said two evaporators (3) downstream of the   regulator (7), in order to defrost it and.   - to simultaneously maintain the circulation of the refrigerant in   the other evaporator (4), by introducing it upstream of the regulator (7).   7. Defrosting device according to claim 6, the means of   bypass, including bypass circuits and associated valves.   being such that, in defrost mode.   - the circulation of all the refrigerant at high pressure and at high temperature is derived in the liquid phase at the outlet of said condenser (2), before being introduced downstream of the expansion valve (7), into the first evaporator (3) to be defrosted, the bypass means, in particular the bypass circuits and the associated valves also being such that. in defrosting mode, - all of the subcooled liquid refrigerant coming from the evaporator (3) during defrosting, is introduced upstream of the pressure reducer (7) of the second evaporator (4). 8. Defrosting device according to claim 6. the bypass means, in particular the bypass circuits and the associated valves, being such that. in defrosting mode, - all or part of the high pressure and high temperature refrigerant is derived in vapor phase at the outlet of said compressor (1). before being introduced downstream of the regulator (7). in the   first evaporator (4) to defrost.   the means of derivation. in particular the branch circuits and the associated valves also being such that. in defrosting mode, - the refrigerant coming in the liquid state from the first evaporator (4) during defrosting and / or from the condenser, is introduced   upstream of the regulator (7) of the second evaporator (3).   9. Defrosting device according to any one of claims 6 to 8   such that - the evaporator (4) being defrosted is isolated from the circulating air   in refrigeration equipment by means of at least one movable flap (5, 6).   10. Refrigeration equipment using any of   defrosting processes forming the subject of claims 1 to 5 and putting   any of the defrosting devices covered by the claims 6 to 9.   11. Heat pump implementing any of the methods of   defrosting which is the subject of claims 1 to 5 and implementing one   any of the deicing devices which are the subject of the claims 6 to 9.