1. A non-stop defrosting method is used for defrosting control of a cooling and heating variable frequency air conditioner and is characterized by comprising the following steps:

in the heating process, when the defrosting condition is met, firstly reducing the frequency of the compressor, when the switching frequency FrqDefPre is reached, FrqDefPre is more than 0, controlling the four-way valve to change the direction, converting the air conditioner from the heating mode to the cooling mode, then increasing the frequency of the compressor to the defrosting frequency FrqDefRun and running for a period of time until defrosting is finished.

2. The frost non-stop method according to claim 1, wherein the switching frequency FrqDefPre is between 30Hz and 40Hz, and the defrosting frequency FrqDefRun is between 80Hz and 90 Hz.

3. The frost method without stopping defrosting of claim 1, wherein after defrosting is completed, the frequency is reduced to the switching frequency FrqDefPre again, and the four-way valve is controlled to reverse again to return to the heating mode, thereby completing a complete defrosting cycle.

4. The non-stop defrosting method according to claim 3, wherein the defrosting condition involves parameters including compressor operationTime T, outer unit condenser coil or condenser outlet temperature T_CAnd an outdoor ambient temperature Ta, which are required to satisfy simultaneously: t is greater than or equal to t_{Set value}、Tc≤Tc_{Set value}、Tc-Ta≥T_{Temperature difference set value}When the frost is dissolved, the defrosting is started.

5. The non-stop defrosting method according to claim 4, wherein the threshold value in the defrosting condition is set as follows:

t_{set value}＝30min；Tc_{Set value}＝1℃；T_{Temperature difference set value}＝2℃。

6. The method of claim 4, wherein the defrosting is stopped by monitoring the temperature T of the condenser coil or the condenser outlet of the outdoor unit_CJudging whether defrosting is finished or not, wherein the specific conditions are as follows: when Tc rises to 15 ℃, the defrosting is withdrawn.

Background

Fig. 1 is a schematic diagram of a cooling and heating variable frequency air conditioner. The arrow 1 indicates a refrigerant circulation path in the cooling mode, the arrow 2 indicates a refrigerant circulation path in the heating mode, and switching between the heating mode and the cooling mode is realized by controlling the four-way valve to change over.

In the cooling mode, when the compressor starts operating, a low-temperature and low-pressure refrigerant is sucked into the compressor, compressed into a high-temperature and high-pressure superheated gas in the compressor cylinder, and discharged to the condenser. The high-temperature and high-pressure refrigerant gas is radiated by the condenser, the temperature is continuously reduced, and the refrigerant gas is gradually cooled to be saturated vapor with normal temperature and high pressure and further cooled to be saturated liquid. After the condensed refrigerant saturated liquid is throttled and depressurized, the refrigerant begins to absorb heat and vaporize in the evaporator, so that the temperature of the evaporator and the surrounding area of the evaporator is reduced, and the refrigerant is changed into low-temperature and low-pressure gas.

In heating mode, the functions of the condenser and evaporator are reversed. In the heating mode, the condenser coil is easy to frost, even ice is formed to cover the surface of the coil, heat exchange of a heat exchanger (a general name of a condenser and an evaporator) is influenced, heat exchange efficiency is reduced, even the coil is frozen, product performance is influenced, and use comfort of the product is reduced.

In order to solve the above problems, there are two main methods for defrosting:

firstly, defrosting without stopping by adopting a bypass branch. The disadvantages are as follows: the circuit structure needs to be added, the air conditioner cost is increased, and the scheme weakens the cost competitive advantage of the air conditioner under the background that the price of raw materials of the current bulk commodity rises.

And secondly, stopping the machine for defrosting. The defrosting operation is carried out by switching the flow direction of the refrigerant through the four-way valve, switching the heating mode into the cooling mode, and delivering the high-temperature and high-pressure refrigerant output by the compressor into the frosted heat exchanger of the outdoor unit so as to melt the frost layer on the outdoor unit. Because of the reversing operation of the four-way valve, the conventional means in the industry is to shut down the compressor first, which is also the source of the term "shutdown" in shutdown defrost schemes. The disadvantages of this solution are: the running frequency of the air conditioner is firstly reduced to 0Hz, the air conditioner starts to rise from 0Hz after the four-way valve finishes switching, and the lower the frequency is, the lower the refrigerating/heating quantity is, and the poorer the defrosting effect is. Therefore, the defrosting time Of the shutdown defrosting scheme is longer, and the Coefficient Of heating Performance COP (Coefficient Of Performance) is smaller.

In general, the existing defrosting scheme needs additional components to increase the air conditioning cost, or has long defrosting time and smaller COP.

Disclosure of Invention

The invention aims to provide a defrosting method without shutdown, which can shorten defrosting time and improve COP (coefficient of performance) without increasing the hardware cost of an air conditioner.

The invention achieves the aim through the following technical scheme: a non-stop defrosting method is used for defrosting control of a cooling and heating variable frequency air conditioner and comprises the following steps:

in the heating process, when the defrosting condition is met, firstly reducing the frequency of the compressor, when the switching frequency FrqDefPre is reached, FrqDefPre is more than 0, controlling the four-way valve to change the direction, converting the air conditioner from the heating mode to the cooling mode, then increasing the frequency of the compressor to the defrosting frequency FrqDefRun and running for a period of time until defrosting is finished.

According to the invention, through adjusting the control logic, when the frequency of the compressor is reduced to a certain value FrqDefPred and does not reach 0Hz, the four-way valve is operated to complete the switching from the heating mode to the refrigerating mode. In the process of switching to the refrigeration mode, the processes of FrqDefPre → 0Hz and 0Hz → FrqDefPre are not carried out, and the compressor not only continuously operates in the whole process, but also always operates in a higher frequency section more than FrqDefPre, so that the defrosting time ratio ((defrosting time/compressor heating operation time) × 100%) can be effectively shortened, and COP is improved.

The scheme has the advantages that: the heating coefficient of performance COP containing defrosting period is improved on the basis of not increasing the cost of a prototype; the disadvantages are that: the switching frequency FrqDefPre is designed and verified for a relatively long time. In comparison, the switching frequency FrqDefPre is lower to facilitate the reversing of the four-way valve, and the defrosting frequency FrqDefRun is higher to ensure that the condenser is defrosted cleanly during defrosting. Generally, the FrqDefPred value is between 30Hz and 40Hz, and the FrqDefrun value is between 80Hz and 90 Hz.

When the refrigeration mode is switched back to the heating mode, the invention preferably adopts the following scheme to further shorten the defrosting time ratio and improve the COP:

after defrosting is finished, the frequency is reduced to the switching frequency FrqDefPref again, the four-way valve is controlled to change the direction again, the heating mode is returned, and a complete defrosting period is completed.

The parameters related to the defrosting condition of the invention comprise the running time T of the compressor and the temperature T of the coil pipe of the condenser or the outlet of the condenser of the external unit_CAnd an outdoor ambient temperature Ta, which are required to satisfy simultaneously: t is greater than or equal to t_{Set value}、Tc≤Tc_{Set value}、Tc-Ta≥T_{Temperature difference set value}。

And the defrosting procedure is started when the three conditions are met. t is used for judging whether the running time is reasonable or not so as to avoid frequent defrosting; tc and Tc-Ta were used to determine whether the condenser surface frosting was severe.

The threshold suggested settings in the defrosting conditions of the present invention are as follows:

t_{set value}＝30min；Tc_{Set value}＝1℃；T_{Temperature difference set value}＝2℃。

In addition, the invention recommends monitoring the temperature T of the coil pipe or the outlet of the condenser of the outdoor unit_CJudging whether defrosting is finished or not, wherein the specific conditions are as follows: when Tc rises to 15 ℃, the defrosting is withdrawn.

Has the advantages that:

the mode switching is carried out when the frequency of the air conditioner is reduced to FrqDefPres and is not yet in contact with 0Hz only by optimizing the control logic, so that the process that the frequency of the air conditioner is FrqDefPres → 0Hz and 0Hz → FrqDefPres when the heating mode is switched to the refrigerating mode is omitted, and the heating coefficient of performance (COP) containing the defrosting period is improved on the basis of not increasing the cost of a prototype;

when the refrigeration mode is switched back to the heating mode, the air conditioner is controlled to be switched before the frequency is reduced to OHz, the defrosting time ratio of the air conditioner is further shortened, and the COP is further improved.

Drawings

FIG. 1 is a schematic diagram of a cooling-heating variable frequency air conditioner;

FIG. 2 is a control flow diagram of a non-stop defrosting method according to an embodiment of the present invention;

fig. 3 shows the variation of the frequency of the non-stop defrosting and the stop defrosting.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the accompanying drawings and specific embodiments.

A frost non-stop method suitable for a cooling and heating variable frequency air conditioner is disclosed, the control flow chart of which is shown in figure 2, and the method comprises the following steps:

1) when the air conditioner is operated in the heating mode, the continuous operation time t of the compressor, the outlet temperature Tc of a condenser coil or a condenser and the outdoor environment temperature difference are monitored.

2) Entering a defrosting period when the defrosting condition is met

Three defrosting conditions are set in the embodiment:

condition 1: the continuous running time t of the compressor is more than or equal to 30 min;

condition 2: the Tc at the outlet of the condenser is less than or equal to 1 ℃;

condition 3: the difference between the outdoor environment temperature Ta and the condenser outlet temperature Tc is more than or equal to 2 ℃;

defrosting is carried out when the conditions 1, 2 and 3 are met; during defrosting, when Tc rises to 15 ℃, the defrosting is exited and the next cycle is entered.

t is used for judging whether the running time is reasonable or not so as to avoid frequent defrosting; tc and Tc-Ta were used to determine whether the condenser surface frosting was severe.

3) After entering a defrosting period, firstly reducing the frequency of the compressor, when the frequency is reduced to a switching frequency FrqDefPred, controlling the four-way valve to change the direction, so that the air conditioner is switched from a heating mode to a cooling mode, the condenser starts defrosting, then increasing the frequency of the compressor to a defrosting frequency FrqDefRun and running for a period of time, and ending defrosting when the outlet temperature Tc of the condenser reaches a set value, such as being equal to or more than 15 ℃.

The above steps are based on the case that the operation frequency of the air conditioner is greater than the switching frequency FrqDefPre under the normal condition. The FrqDefPre is more than 0, namely the air conditioner is switched to the refrigeration mode, the compressor is continuously operated in the whole process and is always operated in a higher frequency section which is larger than the FrqDefPre, the FrqDefPre → 0Hz and 0Hz → FrqDefPre are not performed, the defrosting time ratio can be effectively shortened, and the COP is improved.

The switching frequency FrqDefPre is determined by presetting and verification. The lower the switching frequency FrqDefPre is, the more the four-way valve is favorable for reversing, the higher the switching frequency FrqDefPre is, the more the switching frequency FrqDefPre is favorable for shortening the defrosting time ratio, and the COP is improved. Under the actual condition, a higher value is more recommended to be selected on the premise of ensuring that the four-way valve can be successfully switched. The defrosting frequency FrqDefRun is higher compared to the switching frequency FrqDefPre to ensure that the condenser is defrosted cleanly during defrosting. Generally, the FrqDefPred value is between 30Hz and 40Hz, and the FrqDefrun value is between 80Hz and 90 Hz.

4) And after the defrosting is stopped, reducing the frequency of the compressor to the switching frequency FrqDefPred again, controlling the four-way valve to reverse again, returning to the heating mode, and finishing a complete defrosting period.

The step is the same as the step 3), the four-way valves are switched in modes when the frequency is reduced to FrqDefPres and does not reach 0Hz, the processes of FrqDefPres → 0Hz and 0Hz → FrqDefPres are omitted, the defrosting time ratio can be further shortened, and COP is improved.

Fig. 3 shows the variation of the frequency of the non-stop defrosting and the stop defrosting, and it can be clearly seen that the FrqDefPre → 0Hz and 0Hz → FrqDefPre processes are not performed when the defrosting is not stopped. The y-coordinate in the figure, when converted to frequency, is divided by 60 s.

Table 1 is a comparison table of operation data of non-stop defrosting and stop defrosting of an air conditioner of the type ASW-H12D 4. Data of prototype 1 and prototype 2 are shown as # 1 and # 2, respectively.

TABLE 1

From the above table, it can be seen that: defrosting is not stopped, defrosting time is shortened by about 52 percent, the defrosting time ratio is reduced by about 22 percent (12.1-9.9)/9.9 x 100 percent), and COP is improved by about 1 percent.

In the COP experiment containing defrosting period, after the COP is adjusted and determined, the COP is difficult to be improved by 1 percent, and the COP is generally realized by increasing the cost and enlarging the heat exchanger. The COP is measured power/measured power, and as can be seen from table 1, although the power of the defrosting scheme without shutdown is increased, the increase of the measured power is more obvious, and reaches more than 4.2%, and under the action of the COP, the COP is finally improved obviously.