CN203286825U - Defrosting device of air source heat pump - Google Patents

Abstract

The utility model discloses an air source heat pump defrosting device, which comprises a compressor, a four-way valve, a gas-liquid separator, a heat exchanger, a liquid storage device, a filter, a first fin tube heat exchanger, a second fin tube Fin-tube heat exchanger, the first electric damper set at the air inlet of the first fin-tube heat exchanger, the second electric damper set at the air inlet of the second fin-tube heat exchanger, and the second electric damper set at the air inlet of the two fin-tube heat exchangers The fan at the air outlet of the heater, and the first solenoid valve, the second solenoid valve, the first one-way valve, the second one-way valve, the third one-way valve, the fourth one-way valve, the fifth one-way valve arranged on the pipeline One-way valve, sixth one-way valve, electronic expansion valve and third solenoid valve. The temperature fluctuation of the device of the utility model is very small, the comfort of the air conditioning system is improved, the total time of the defrosting process of the system is shortened, and the heat supply rate per unit time of the heat pump system is improved.

Description

Air source heat pump defrosting device

technical field

The utility model belongs to the technical field of design and manufacture of refrigeration and air-conditioning systems, and relates to a defrosting method for an air source heat pump system and a device for realizing the method.

Background technique

Air source heat pumps have the advantages of energy saving, cooling and heating, flexible use, convenience, low initial investment, and small space occupation, and have been widely used in most areas of our country. However, the biggest problem encountered by air source heat pumps during heating operation in winter is the frosting on the surface of the evaporator. Due to the formation and growth of the frost layer, the heat transfer resistance between the surface of the evaporator and the air is increased, and the flow of air is increased. The flow resistance of the evaporator makes the air flow through the evaporator decrease, and the heat exchange efficiency is significantly reduced, resulting in a decrease in the heat exchange between the air and the evaporator, the deterioration of the working condition of the heat pump unit, the decline in performance, and even malfunction. Therefore, when the air source heat pump is operating under frosting conditions, it must be defrosted in time.

At present, the defrosting method commonly used for air source heat pumps is realized through the reverse cycle of the system (running the refrigeration cycle), that is, the evaporator that absorbs heat and exchanges heat with the air during heating becomes a condenser during defrosting, and the original condensation The device becomes an evaporator. This traditional reverse defrosting method has a series of disadvantages: when defrosting, due to the reversing of the four-way valve, the original high and low pressure parts of the refrigeration system are switched, which causes the compressor of the refrigeration system to "run oil" and reduces the reliability of the compressor. performance and service life; when defrosting, the refrigerant needs to absorb heat from the heating system for defrosting, causing sharp fluctuations in the temperature of the heating system, thus affecting the comfort of the air conditioning system; at the same time, from the beginning of defrosting to the end of defrosting, four The through valve needs to be operated twice, and the high and low pressure parts of the system (evaporator and condenser) need to be switched twice to re-establish the pressure and temperature balance, which not only causes a large amount of energy loss but also prolongs the total time of the system defrosting process.

Utility model content

Technical problem: The purpose of this utility model is to solve the many disadvantages brought by the existing reverse defrosting method to the refrigeration system, to provide a high reliability, shorten the defrosting time, improve the defrosting effect, and improve the heating efficiency of the heat pump unit. Air source heat pump defrosting device for comfort and air conditioning system.

Technical solution: The air source heat pump defrosting device of the present utility model includes a compressor, a four-way valve, a gas-liquid separator, a heat exchanger, a liquid storage device, a filter, a first fin tube heat exchanger, a second fin tube Fin-tube heat exchanger, the first electric damper set at the air inlet of the first fin-tube heat exchanger, the second electric damper set at the air inlet of the second fin-tube heat exchanger, and the second electric damper set at the air inlet of the two fin-tube heat exchangers The fan at the air outlet of the heater, and the first solenoid valve, the second solenoid valve, the first one-way valve, the second one-way valve, the third one-way valve, the fourth one-way valve, the fifth one-way valve arranged on the pipeline One-way valve, sixth one-way valve, electronic expansion valve and third solenoid valve.

The four-way valve is provided with a first input end of the four-way valve, a first output end of the four-way valve, a second input end of the four-way valve and a second output end of the four-way valve, and the heat exchanger is provided with an input end of the heat exchanger and The output end of the heat exchanger, the first finned tube heat exchanger is provided with the input end of the first finned tube heat exchanger and the output end of the first finned tube heat exchanger, and the second finned tube heat exchanger is provided with The input end of the second finned tube heat exchanger and the output end of the second finned tube heat exchanger. The output end of the compressor is connected to the first input end of the four-way valve, and the second input end of the four-way valve is connected to the input end of the heat exchanger through the first electromagnetic valve, and is also connected to the second finned tube heat exchanger through the second electromagnetic valve. The input end is connected, the first output end of the four-way valve is divided into two circuits, one is connected to the input end of the first finned tube heat exchanger, and the other is connected to the input end of the second finned tube heat exchanger through the third solenoid valve, The second output end of the four-way valve is connected to the input end of the gas-liquid separator, and the output end of the gas-liquid separator is connected to the input end of the compressor;

The output end of the heat exchanger is connected to the inlet of the first one-way valve and the outlet of the second one-way valve at the same time. The valve is connected to the output end of the second finned tube heat exchanger, the other one is connected to the output end of the first finned tube heat exchanger through the fourth one-way valve, and the output end of the liquid reservoir is connected to the input port of the electronic expansion valve through a filter The output end of the electronic expansion valve is divided into three paths, one path is connected to the input end of the second check valve, one path is connected to the output end of the second finned tube heat exchanger through the fifth one-way valve, and the other path is connected through the sixth The one-way valve is connected with the output end of the first finned tube heat exchanger.

In the device of the utility model, the compressor is a variable frequency compressor or a compressor capable of energy regulation.

In the device of the utility model, when the first finned tube heat exchanger is defrosted, the first electric damper is closed and the second electric damper is opened; when the second finned tube heat exchanger is defrosted, the first electric damper is opened, The second electric damper is closed.

In the device of the present invention, when the first finned tube heat exchanger is defrosted, the second finned tube heat exchanger acts as an evaporator to absorb heat from the air; when the second finned tube heat exchanger is defrosted, the second finned tube heat exchanger The fin-and-tube heat exchanger acts as an evaporator to absorb heat from the air.

When the air source heat pump is running in summer cooling mode: the low-temperature and low-pressure refrigerant gas is sucked by the compressor from the gas-liquid separator, compressed and becomes high-temperature and high-pressure superheated vapor, and then discharged, and then comes out from the first output port of the four-way valve after passing through the four-way valve After that, it is divided into two paths, respectively entering the first finned tube heat exchanger and entering the second finned tube heat exchanger through the third electromagnetic valve. At this time, the second electromagnetic valve is closed. In the two-finned tube heat exchanger, the refrigerant exchanges heat with the air, releases heat and condenses into a liquid, and then passes through the fourth unit after coming out of the first finned tube heat exchanger and the second finned tube heat exchanger respectively. After the one-way valve and the third one-way valve, they merge into the liquid reservoir, and then pass through the filter and the electronic expansion valve in turn to become a low-temperature and low-pressure gas-liquid two-phase, and then enter the heat exchanger after passing through the second one-way valve. The heat is absorbed and evaporated in the heat exchanger, and the cooling capacity is released. After the refrigerant is completely evaporated, it becomes a superheated gas. After coming out of the heat exchanger, it enters the gas-liquid separator through the first solenoid valve and the four-way valve, and then is sucked into the compressor again. Thereby, the refrigeration cycle is completed, and now the first electric damper and the second electric damper are all opened, and the blower fan works.

When the air source heat pump is running in winter heating mode: the low-temperature and low-pressure refrigerant gas in the gas-liquid separator is sucked by the compressor, compressed, and then discharged into the four-way valve. Heat exchanger, at this time the second solenoid valve is closed, the refrigerant releases heat in the heat exchanger, condenses into a liquid and then flows out, and enters the liquid receiver through the first one-way valve, and the refrigerant passes through the filter after coming out of the liquid receiver 1. After the electronic expansion valve is throttled into gas-liquid two-phase, it is divided into two paths, one path enters the second finned tube heat exchanger through the fifth one-way valve, and the other path enters the first finned tube heat exchanger through the sixth one-way valve In the heat exchanger, the refrigerant exchanges heat with the air in the two heat exchangers, and becomes superheated steam after absorbing heat. The refrigerant comes out of the first finned tube heat exchanger and comes out of the second finned tube heat exchanger The refrigerant that passes through the third electromagnetic valve merges and enters the four-way valve, comes out of the second output end of the four-way valve, enters the gas-liquid separator, and is sucked into the compressor again to complete the cycle. At this time, the first electric damper, The second electric dampers are all opened, and the fan works.

When the heat pump needs defrosting after heating for a period of time, the heat pump switches to the defrosting mode. The system adopts alternate defrosting methods for the first finned tube heat exchanger and the second finned tube heat exchanger. When the heating mode is switched to the defrosting mode, the second finned tube heat exchanger is defrosted first: at this time, the refrigerant in the gas-liquid separator is sucked and compressed by the compressor, and then discharged into the four-way valve. At this time, compared with the heating mode, there is no action. The refrigerant flows out from the second input end of the four-way valve and enters the second finned tube heat exchanger through the second solenoid valve. At this time, the first solenoid valve and the third solenoid valve Closed, the high-temperature and high-pressure refrigerant releases heat in the second finned tube heat exchanger and melts the frost layer on the surface of the heat exchanger. After the refrigerant condenses into liquid, it flows out from the second finned tube heat exchanger and passes through the third one-way After the valve, it enters the liquid receiver, and then passes through the filter and the electronic expansion valve to be throttled into gas-liquid two-phase, and then enters the first finned tube heat exchanger through the sixth one-way valve, and the refrigerant is exchanged in the first finned tube The heat absorbed in the heater evaporates, and after complete evaporation, it flows out of the first finned tube heat exchanger, enters the four-way valve, flows out from the second output end of the four-way valve, and is sucked by the compressor again through the gas-liquid separator to complete the second The defrosting cycle of the finned tube heat exchanger, at this time, the first electric damper is opened, the second electric damper is closed, and the fan works.

When the second finned tube heat exchanger finishes defrosting, switch the four-way valve, and the refrigerant sucked, compressed and discharged by the compressor from the gas-liquid separator passes through the four-way valve and flows from the first output end of the four-way valve After flowing out, it enters the first finned tube heat exchanger. At this time, the third electromagnetic valve is closed, and the refrigerant releases heat in the first finned tube heat exchanger to melt the frost layer. After the refrigerant condenses into liquid, it flows from the first finned tube heat exchanger. The outflow of the tube heat exchanger enters the liquid storage through the fourth one-way valve, and then passes through the filter and the electronic expansion valve in turn to form a gas-liquid two-phase flow, and then enters the second finned tube heat exchanger through the fifth one-way valve. The refrigerant exchanges heat with the air in it, absorbs heat and evaporates completely, flows out of the second finned tube heat exchanger, and enters the four-way valve through the second solenoid valve (the first solenoid valve is closed at this time), and the refrigerant flows from the four-way valve to the first four-way valve. After the second output flows out, it passes through the gas-liquid separator and is sucked into the compressor again to complete the cycle of defrosting the first finned tube heat exchanger. At this time, the first electric damper is closed, the second electric damper is opened, and the fan works. When the first finned tube heat exchanger finishes defrosting, the four-way valve moves in reverse, the first electric damper and the second electric damper are both opened, the fan keeps working, and the system restarts the heat pump heating cycle. 

Beneficial effect: compared with the prior art, the utility model has the following advantages:

During defrosting, the refrigerant does not absorb heat from the heating system for defrosting, so that the temperature fluctuation of the heating system is small and the comfort of the air conditioning system is improved; from the beginning of defrosting to the end of defrosting, although the four-way valve operates twice times, but the pressure balance and temperature balance in the heat exchanger are not destroyed, which avoids a large amount of energy loss (there is such a loss in conventional reverse cycle defrosting), and at the same time shortens the total time of the system defrosting process and improves The heating rate per unit time of the heat pump system. ``

Description of drawings

Fig. 1 is a schematic diagram of a new air source heat pump defrosting device of the present invention.

In the figure there are: compressor 1, four-way valve 2, first input end 2a of four-way valve, first output end 2b of four-way valve, second input end 2c of four-way valve, second output end 2d of four-way valve, second A solenoid valve 3, a second solenoid valve 4, a heat exchanger 5, a heat exchanger input port 5a, a heat exchanger output port 5b, a first one-way valve 6, a second one-way valve 7, and a third one-way valve 8 , the fourth one-way valve 9, the fifth one-way valve 13, the sixth one-way valve 14, the reservoir 10, the filter 11, the electronic expansion valve 12, the first finned tube heat exchanger 15, the first fin The input end 15a of the tube heat exchanger, the output end 15b of the first finned tube heat exchanger, the first electric damper 16, the second finned tube heat exchanger 17, the input end 17a of the second finned tube heat exchanger, the second The output end 17b of the finned tube heat exchanger, the second electric damper 18 , the fan 19 , the third electromagnetic valve 20 , and the gas-liquid separator 21 .

Detailed ways

Further illustrate the utility model below in conjunction with accompanying drawing and embodiment.

The specific connection method of the utility model is that the output end of the compressor 1 is connected to the first input end 2a of the four-way valve, and the second input end 2c of the four-way valve is connected to the input end 5a of the heat exchanger through the first electromagnetic valve 3, and also through the first electromagnetic valve 3. The second solenoid valve 4 is connected to the input end 17a of the second finned tube heat exchanger, and the output end 5b of the heat exchanger is connected to the inlet of the first one-way valve 6. The outlet of the first one-way valve 6 is divided into three paths, and one path is connected to the liquid reservoir. The input end of 10, one way is connected to the output end 17b of the second finned tube heat exchanger through the third one-way valve 8, and the other way is connected to the output end 15b of the first finned tube heat exchanger through the fourth one-way valve 9, and the liquid storage The output end of the device 10 is connected to the input end of the electronic expansion valve 12 through the filter 11, and the output end of the electronic expansion valve 12 is divided into three paths, one path is connected to the output end 5b of the heat exchanger through the second one-way valve 7, and the other path is connected to the output end 5b of the heat exchanger through the fifth one-way valve. The direction valve 13 is connected to the output end 17b of the second finned tube heat exchanger, and the other way is connected to the output end 15b of the first finned tube heat exchanger through the sixth one-way valve 14, and the input end 15a of the first finned tube heat exchanger is connected to The first output end 2b of the four-way valve, and the input end 17a of the second finned tube heat exchanger is also connected to the first output end 2b of the four-way valve through the third solenoid valve 20, and the second output end 2d of the four-way valve is connected to the gas-liquid separation The input end of the device 21, the output end of the gas-liquid separator 21 is connected to the input end of the compressor 1, and the first electric damper 16 is installed at the air inlet of the first finned tube heat exchanger 15, and the first electric damper 16 is installed at the air inlet of the second finned tube heat exchanger. The air inlet of the heat exchanger 17 is equipped with a second electric damper 18, and a fan 19 is installed at the air outlets of the first finned tube heat exchanger 15 and the second finned tube heat exchanger 17.

When the air source heat pump is running in summer cooling mode: the low-temperature and low-pressure refrigerant gas is sucked by the compressor 1 from the gas-liquid separator 21, compressed and becomes a high-temperature and high-pressure superheated vapor, and then discharged from the four-way valve 1 after passing through the four-way valve 2. After the output end 2b comes out, it is divided into two paths, respectively entering the first finned tube heat exchanger 15 and entering the second finned tube heat exchanger 17 through the third electromagnetic valve 20. At this time, the second electromagnetic valve 4 is closed, and the first In the finned tube heat exchanger 15 and the second finned tube heat exchanger 17, the refrigerant exchanges heat with the air, releases heat and condenses into a liquid, and then flows from the first finned tube heat exchanger 15 and the second finned tube heat exchanger 15 and the second finned tube heat exchanger respectively. After the heat exchanger 17 comes out, it passes through the fourth one-way valve 9 and the third one-way valve 8 respectively, and then merges into the liquid reservoir 10, and then passes through the filter 11 and the electronic expansion valve 12 in turn to become a low-temperature and low-pressure gas-liquid two-way system. Phase, and then enter the heat exchanger 5 after passing through the second one-way valve 7, the refrigerant absorbs heat and evaporates in the heat exchanger 5, and releases cooling capacity. The first electromagnetic valve 3 and the four-way valve 2 enter the gas-liquid separator 21, and then are sucked into the compressor 1 again to complete the refrigeration cycle. At this time, the first electric damper 16 and the second electric damper 18 are opened, and the fan 19 works.

When the air source heat pump is running in winter heating mode: the low-temperature and low-pressure refrigerant gas in the gas-liquid separator 21 is sucked by the compressor 1, compressed, and then discharged into the four-way valve 2. After coming out of the second input port 2c of the four-way valve, it passes through the second A solenoid valve 3 enters the heat exchanger 5, at this time the second solenoid valve 4 is closed, the refrigerant releases heat in the heat exchanger 5, condenses into a liquid and then flows out, and enters the liquid receiver 10 through the first one-way valve 6 for refrigeration. After the agent comes out of the liquid reservoir 10, it passes through the filter 11 and the electronic expansion valve 12 and is throttled into gas-liquid two-phase. The other way passes through the sixth one-way valve 14 and enters the first finned tube heat exchanger 15. The refrigerant exchanges heat with the air in the two heat exchangers respectively, and becomes superheated steam after absorbing heat, and is exchanged from the first finned tube The superheated steam flowing out of the heater 15 merges with the superheated steam flowing out of the second finned tube heat exchanger 17 and passing through the third electromagnetic valve 20, then enters the four-way valve 2, and enters the gas flow after coming out from the second output port 2d of the four-way valve. The liquid separator 21 is then sucked into the compressor 1 again to complete the cycle. At this time, the first electric damper 16 and the second electric damper 18 are all opened, and the blower fan 19 works.

When the heat pump needs defrosting after heating for a period of time, the heat pump switches to the defrosting mode. The system adopts an alternate defrosting method for the first finned tube heat exchanger 15 and the second finned tube heat exchanger 17 . When the heating mode is switched to the defrosting mode, the second finned tube heat exchanger 17 is defrosted first: at this time, the refrigerant in the gas-liquid separator 21 is sucked and compressed by the compressor 1, and then discharged into the four-way valve 2 At this time, the four-way valve 2 does not act compared to the heating mode, and the second solenoid valve 4 is opened. The refrigerant flows out from the second input port 2c of the four-way valve and enters the second finned tube through the second solenoid valve 4. Heater 17, at this time the first solenoid valve 3 and the third solenoid valve 20 are closed, and the high-temperature and high-pressure refrigerant releases heat in the second finned tube heat exchanger 17, melting the frost layer on the surface of the finned tube heat exchanger, and cooling After the solvent is condensed into liquid, it flows out from the second finned tube heat exchanger 17, passes through the third one-way valve 8, enters the liquid reservoir 10, and then passes through the filter 11 and the electronic expansion valve 12 to be throttled into gas-liquid two-phase Then enter the first finned tube heat exchanger 15 through the sixth one-way valve 14, the refrigerant absorbs heat and evaporates in the first finned tube heat exchanger 15, and flows out of the first finned tube heat exchanger 15 after completely evaporating. Enter the four-way valve 2, flow out from the second output end 2d of the four-way valve, and then pass through the gas-liquid separator 21 and be sucked by the compressor 1 again to complete the cycle of defrosting the second finned tube heat exchanger 17. At this time, the first The electric damper 16 is opened, the second electric damper 18 is closed, and the blower fan 19 works.

When the second finned tube heat exchanger 17 completes the defrosting, switch the four-way valve 2, the refrigerant in the gas-liquid separator 21 is sucked, compressed and discharged by the compressor 1, and after passing through the four-way valve 2, the refrigerant from the four-way After the first output port 2b of the valve flows out, it enters the first finned tube heat exchanger 15. At this time, the third electromagnetic valve 20 is closed, and the refrigerant releases heat in the first finned tube heat exchanger 15, melting the frost layer, and the refrigerant After being condensed into a liquid, it flows out from the first finned tube heat exchanger 15, passes through the fourth one-way valve 9, enters the liquid reservoir 10, and then passes through the filter 11 and the electronic expansion valve 12 in sequence to form gas-liquid two-phase, and then passes through the fifth The one-way valve 13 enters the second finned tube heat exchanger 17, where the refrigerant exchanges heat with the air, absorbs heat and evaporates completely, flows out of the second finned tube heat exchanger 17, and enters the four-way through the second solenoid valve 4. Valve 2 (the first solenoid valve 3 is closed at this time), the refrigerant flows out from the second output end 2d of the four-way valve, passes through the gas-liquid separator 21, and is sucked by the compressor 1 again, completing the cooling of the first finned tube heat exchanger 15 cycles of defrosting, at this time the first electric damper 16 is closed, and the second electric damper 18 is opened. After the defrosting of the first finned tube heat exchanger 15 is completed, the four-way valve 2 moves in reverse, the first electric damper 16 and the second electric damper 18 are opened, the fan 19 keeps working, and the system restarts the heat pump heating cycle.

In the defrosting mode, when the first finned tube heat exchanger and the second finned tube heat exchanger are operated respectively, the corresponding first electric damper and the second electric damper are closed, which can reduce the corresponding finned tube heat exchanger. When the heat exchanger defrosts, the heat exchanged with the air loses heat. At the same time, it can increase the air volume of the non-defrosted finned tube heat exchanger and improve the defrosting effect of the system. In the process of alternate defrosting, the operating frequency of the compressor can be adjusted or the energy of the compressor can be adjusted to ensure the best operation of the system during defrosting.

Claims (4)

1. air source heat pump defrosting device, it is characterized in that this device comprises compressor (1), cross valve (2), gas-liquid separator (21), heat exchanger (5), reservoir (10), filter (11), the first finned tube exchanger (15), the second finned tube exchanger (17), be arranged on first MOD (16) of described the first finned tube exchanger (15) air intlet, be arranged on second MOD (18) of described the second finned tube exchanger (17) air intlet, be arranged on the blower fan (19) at two finned tube exchanger air outlet slit places, and be arranged on the first magnetic valve (3) on pipeline, the second magnetic valve (4), the first check valve (6), the second check valve (7), the 3rd check valve (8), the 4th check valve (9), the 5th check valve (13), the 6th check valve (14), electric expansion valve (12) and the 3rd magnetic valve (20),

be provided with cross valve first input end (2a) on described cross valve (2), cross valve the first output (2b), cross valve the second input (2c) and cross valve the second output (2d), be provided with heat exchanger input (5a) and heat exchanger output (5b) on described heat exchanger (5), be provided with the first finned tube exchanger input (15a) and the first finned tube exchanger output (15b) on described the first finned tube exchanger (15), be provided with the second finned tube exchanger input (17a) and the second finned tube exchanger output (17b) on described the second finned tube exchanger (17), the output termination cross valve first input end (2a) of described compressor (1), cross valve the second input (2c) is connected with heat exchanger input (5a) by the first magnetic valve (3), also by the second magnetic valve (4), with the second finned tube exchanger input (17a), be connected simultaneously, cross valve the first output (2b) is divided into two-way, one tunnel is connected with the first finned tube exchanger input (15a), another road is connected with the second finned tube exchanger input (17a) by the 3rd magnetic valve (20), cross valve the second output (2d) is connected with the input of gas-liquid separator (21), the output of gas-liquid separator (21) is connected with the input of compressor (1),

heat exchanger output (5b) simultaneously with the entrance of the first check valve (6) be connected the outlet of check valve (7) and be connected, the outlet of the first check valve (6) is divided into three tunnels, one tunnel connects the input of reservoir (10), the 3rd check valve (8) of leading up to is connected with the second finned tube exchanger output (17b), the 4th check valve (9) of leading up in addition is connected with the first finned tube exchanger output (15b), the output of reservoir (10) is connected with the input of electric expansion valve (12) by filter (11), the output of electric expansion valve (12) is divided into three tunnels, one tunnel is connected with the input of the second check valve (7), the 5th check valve (13) of leading up to is connected with the second finned tube exchanger output (17b), the 6th check valve (14) of leading up in addition is connected with the first finned tube exchanger output (15b).

2. air source heat pump defrosting device according to claim 1, is characterized in that, described compressor (1) maybe can be realized the compressor of energy adjustment for frequency-changeable compressor.

3. air source heat pump defrosting device according to claim 1, is characterized in that, when described the first finned tube exchanger (15) defrosted, the first MOD (16) was closed, and the second MOD (18) is opened; When described the second finned tube exchanger (17) defrosted, the first MOD (16) was opened, and the second MOD (18) is closed.

4. air source heat pump defrosting device according to claim 1, is characterized in that, during described the first finned tube exchanger (15) defrosting, the second finned tube exchanger (17) absorbs heat from air as evaporimeter; During described the second finned tube exchanger (17) defrosting, the second finned tube exchanger (15) absorbs heat from air as evaporimeter.