FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A HOT - GAS DEFROST SYSTEM FOR
ENSURING LOW NOISE AND LOW
VIBRATION OPERATION DURING
DEFROST CONDITION AND METHOD THEREOF;
BLUE STAR LIMITED A COMPANY
INCORPORATED UNDER THE
COMPANIES ACT, 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVANI CHOWK, JAMSHETJI TATA ROAD, MUMBAI - 400 020, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF INVENTION
The present invention relates in general relates to a refrigeration circuits and in particular to a hot gas defrost system for a refrigeration circuit including air conditioning apparatus comprising a heat pump.
BACKGROUND OF INVENTION
In a typical hot gas defrost system, a portion of the superheated gaseous heat transfer fluid is conducted through a heat exchanger to melt accumulated ice from the heat exchanger thereby causing the heat transfer fluid passing within the heat exchanger to condense. The condensed heat transfer fluid is passed through a suction line to an accumulator into which a portion of the superheated gaseous heat transfer fluid is conducted. The gaseous superheated refrigerant acts to vaporize the condensed heat transfer fluid contained within the accumulator to provide a supply of gaseous refrigerant to the compressor inlet.
Heat pumps, for example, function to transfer heat between an indoor heat exchanger and an outdoor heat exchanger through the use of a heat-exchange fluid which is selectively vaporized and condensed in accordance with the desired mode of operation. During warm weather, warm air indoors is circulated about an indoor heat exchanger so that the heat from the indoor air is absorbed by the heat-exchange fluid, or refrigerant, which is then carried outdoors to the outdoor heat exchanger releasing the heat to the surrounding air. In cold weather the cycle is reversed. Heat, which has already been produced outdoors by the sun and stored in the earth and air, is transferred to the heat-exchange fluid by the outdoor heat exchanger and discharged from the heat-exchange fluid indoors.

One of the frequently encountered and well known problems associated with such heat pump equipment is that during heating operations the outdoor heat exchanger, which is functioning as an evaporator, tends to accumulate frost or ice when the appropriate weather conditions occur. The accumulation of frost on the outdoor heat exchanger reduces the ability of the heat exchanger to transfer heat from the ambient air in contact with the heat exchanger surfaces to the refrigerant. In order to remove the accumulated frost and ice from the surfaces of the outdoor heat exchanger, various automatic defrosting systems have been devised. These systems include heating the heat exchanger from an external heat source, and reversing the operation of the system to pass hot refrigerant gas through the outdoor heat exchanger.
In such hot gas reverse defrost systems, the gas conducted to the outdoor heat exchanger melts the ice formed thereon and thereby changes state from a gas to a liquid within the outdoor heat exchanger. The condensed heat-exchange fluid, or liquid refrigerant, is then flashed to a gas in an evaporator and any remaining liquid refrigerant is collected in an accumulator which separates and retains liquid refrigerant to prevent the liquid from being conveyed into and damaging the compressor.
In the present hot gas defrost system, superheated defrosting gas is by-passed around the expansion valve and discharged from the compressor outlet directly into the inlet of the outdoor heat exchanger wherein the hot gas is condensed melting the ice and liquid refrigerant or a mixture of gaseous and liquid refrigerant is discharged from the outdoor heat exchanger outlet. The outlet from the outdoor heat exchanger is coupled to a component which serves as an accumulator to prevent the liquid refrigerant from being introduced into the compressor and as a re-evaporator to vaporize the liquid refrigerant received from the compressor. A portion of the superheated hot gas by-passes the indoor heat exchanger and expansion valve and is introduced directly into the liquid refrigerant contained in the accumulator to vaporize the liquid refrigerant. The vaporized liquid refrigerant is thereby returned for use by the system compressor providing a more efficient system to control defrost operation. The heat energy of this defrost system may be constantly monitored to determine when defrost has been effected. The accumulator serves as a receiver for storing liquid refrigerant during heat transfer operation and as a direct contact heat exchanger during defrost operations.

To begin the defrost cycle, a solenoid valve of the condenser is closed and a solenoid valve provided on a bypass line which leads directly from upstream of the condenser to upstream of the evaporator is opened. These solenoid valves normally open and close rapidly. When the bypass line has some liquid in it in addition to the hot gas from the compressor (as is frequently the case) a "slug" of liquid or a liquid-gas mixture rapidly passes through the second solenoid valve and strikes downstream system components, including the evaporator. What is known as "hydraulic shock" occurs and, particularly where the system is operating at low temperatures, severe damage to the system can result. Further, the high pressure gas is directly injected into the evaporator. This gives rise to heavy noise along with huge vibration in refrigerant piping. Moreover, vibrations are generated in the liquid piping and thus refrigerant pipes may break/leak.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a hot gas defrost system and method thereof that substantially obviates one or more problems due to limitations and disadvantages of the related art.
In one embodiment, the present invention provides the hot - gas defrost system for ensuring low noise and low vibration operation during defrost condition, said hot - gas defrost system comprising a refrigerant circuit having atleast one compressor for compressing refrigerant, an indoor heat exchanger atleast functioning as a condenser, an expansion valve for reducing the pressure of the refrigerant, an outdoor heat exchanger atleast functioning as an evaporator, which are connected in series to one another for circulating the refrigerant in the refrigerant circuit, a hot-gas defrost pipe adapted on the refrigerant circuit for bypassing hot gas from the compressor to the outdoor heat exchanger, a hot gas defrost valve disposed on said hot gas defrost pipe and a controller configured for initiating defrost operation. According to the present invention the controller on sensing a defrost condition, switch-off the compressor for a predetermined time and simultaneously full opens the expansion valve for equalizing the pressure between the high pressure discharge line and low pressure inlet line in the refrigerant circuit. Further the controller opens the hot defrost valve after equalizing

pressure in the refrigerant circuit and switch-on the compressor for carrying out defrosting heat exchanger of the evaporator thereby ensuring low noise and iow vibration during defrost condition.
In another embodiment, the present invention provides a method for ensuring low noise and low vibration operation in a hot gas defrost system. The said method comprises the steps of: switching-OFF compressor for a predetermined time upon sensing a defrost condition and subsequently, full-opening the expansion valve over the system for equalizing pressure between high pressure discharge line and low pressure inlet line in the system, opening hot gas defrost valve after equalizing the pressure in the system; and restarting, the compressor for carrying defrosting, of outdoor heat exchanger thereby ensuring low vibration and noise operation.
According to another embodiment of the present invention, the controller switches off the fan of evaporator along with the compressor for the predetermined time.
According to the present invention, the predetermined time is 2 minutes.
According to further embodiment of the present invention, the controller delays switch-on of the compressor after opening the hot defrost valve. Advantageously, the controller delays starting of the compressor by 10 seconds.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Fig. 1 shows a hot gas defrost system embodied in a refrigeration circuit according to the present invention; and
Fig. 2 illustrates graphical representation of method of the hot gas defrost system of the present invention.

DESCRIPTION OF THE INVENTION
Disclosed herein is a method for ensuring low noise and low vibration operation in a hot gas defrost system.
The present invention provides a hot gas defrost system and method for system for ensuring low noise and low vibration operation during defrost condition. According to the present invention, the compressors are switch off on sensing the defrost condition and the refrigerant pressure is equalized within the system by wide opening the expansion valve which is followed by opening of hot gas defrost valve and delayed switching ON of the compressors to carry out defrost operation. This ensures low noise and vibration in the refrigeration system during the defrost operation.
Referring now to the Figure 1, there is shown a hot gas defrost system embodied in a refrigeration circuit including air conditioning apparatus comprising a heat pump according to the present invention. The heat pump system comprises an expansion valve (110), an outdoor heat exchanger (120), an accumulator (130), a compressor (140), an indoor heat exchanger (150), and a four-way valve (160) are connected in a closed fluidic circuit for effecting the transfer of heat between the outdoor heat exchanger (150) and the indoor heat exchanger (160). The compressor (140) is in fluid communication with the indoor heat exchanger (150) through a four-way valve (160) for discharging superheated gaseous refrigerant thereinto for effecting heating of an enclosure during operation of the refrigeration system.
In the heating mode of operation as the heat exchange fluid is passed from compressor (140) to the four-way valve (160) and through the indoor heat exchanger (150). An indoor fan (155) energizes to direct a stream of air through the indoor heat exchanger (150) effecting heat transfer between the heat exchange fluid and the enclosure whereby the gaseous refrigerant is condensed to a liquid. The indoor heat exchanger (150) is coupled by a line (30) to the expansion valve (110) through which the refrigerant passes and enters in the outdoor heat exchanger (120). An outdoor fan (125) energizes to effect heat transfer between outdoor air and the heat exchange fluid passing through the inlet heat exchanger (120) such that the liquid refrigerant is vaporized to a gaseous refrigerant. After heat transfer has been effected through the

outdoor heat exchanger (120), the heat exchange fluid passes from the outdoor heat exchanger through four-way valve (160), into the accumulator (130). The gaseous refrigerant separated in the accumulator (130) is then passed to the compressor (140) to repeat the cycle as is known to those skilled in the art. It is also known that the system has a high pressure discharge line (20) and a low pressure inlet line (40) partitioned by the expansion valve (110). In the cooling mode of operation of air conditioner, the four way valve acts to reverse the flow of refrigerant such that the outdoor heat exchanger becomes the condenser and the indoor heat exchanger becomes the evaporator.
After the heat pump system has been in operation in the heating mode, frost or ice may form on the outdoor heat exchanger (120). The amount of frost and rate of accumulation are dependent upon the ambient environmental conditions. When ice accumulates on the outdoor heat exchanger (120), the heat transfer efficiency of the refrigeration system decreases and, therefore, the accumulation of ice must be removed to maintain efficiency within the system. Upon the accumulation of a sufficient amount of ice on the outdoor heat exchanger (120), the ice is melted from the outdoor heat exchanger (120) by circulating hot refrigerant through the outdoor heat exchanger (120).
On detection of the predetermined amount of ice accumulation, the controller (170) initiate the defrost cycle according to the present invention. According to the present invention, the controller (170) switch-OFF the compressor (140) for a predetermined time and simultaneously swing open the expansion valve (110) in order to equalize the pressure between high pressure discharge line (20) and low. pressure inlet line (40). Advantageously the controller switches off the outdoor fan (125) along with compressor (140) for the said predetermined time. According to the present inventors, about 2 minutes are required to equalize the pressure between the high pressure discharge line and the low pressure inlet line. Therefore, the compressors are kept off for this period, hence, the predetermined time is 2 minutes. After, equalization of pressure, the controjler opens the hot defrost valve (180) which bypasses hot compressed refrigerant leaving the compressor (140) to the outdoor heat exchanger (120). Upon opening the hot defrost valve (180), a portion of superheated discharged gas from the outlet of the

compressor (120) passes into the outdoor heat exchanger (120). According to the present invention as shown in Figure 2, the compressor (140) is switched on after opening the hot gas defrost valve (180).
According to one embodiment of the present invention, the starting of the compressor (140) is delayed after the opening of the hot defrost valve (180). The delay in switch on of the compressor is for further equalization of the refrigerant pressure in the system. Figure 2 shows the delay in starting the compressor (140). According to the present invention the delay is 10 second.
Figure 2 shows method steps according to the present invention. It shows when a accumulation of the ice takes place, the defrost cycle turns from OFF to ON and compressor is turned OFF. Accordingly the expansion valve of the is opened fully and simultaneously outdoor fan is turned OFF. But, Indoor Fan is kept running, liquid line valve is also kept open in order to equalize the refrigerant pressure within the system and defrost valve is kept OFF for predetermined time which is 2 minutes. After two minutes, first defrost valve is opened followed by turn-ON of the compressor after 10 seconds for carrying out defrosting of the outdoor heat exchanger.
Due to the equalization of the pressure in the system, the pressure difference between the compressed refrigerant and the refrigerant in the system decreases resulting in the substantial elimination of sudden shock/vibration to piping. Further, the pressures are equalized at the time of opening of the hot gas defrost valve, the heavy sound of gas flow is substantially eliminated as the pressure difference at the inlet and outlet of the hot defrost valve is substantially less.
While the present invention is in the initiation of defrost cycle which eliminates noise and vibrations, such defrost cycle may be initiated periodically by means of a timer, or other suitable systems for the detection of an amount of ice on the heat exchanger. The defrost cycle is then carried out in a known way.
The invention has been described herein to allows a portion of the superheated refrigerant to pass through the indoor heat exchangers thereby provides heating operation at the indoor without interruption during defrosting cycle unlike conventional

reverse cycle defrost. In other word the air conditioning system provides an uninterrupted heating at the indoors.
The invention has been described herein in reference hot gas defrost system for a heat pump system designed to transfer heat between an outdoor heat exchanger and an indoor heat exchanger. It is to be understood that this invention has like applicability to other forms of refrigeration systems including air conditioning equipment for supplying only cooling to an enclosure as well as air conditioning equipment for supplying both heating and cooling to an enclosure or heating only.
Further, the present system can be used for multi-air conditioner system comprising plurality of indoor heat exchanges and one or more outdoor units having one or more compressors. According to the present Invention, all compressors of the multi air conditioning system are switched-off along with the fans of the outdoor units for the predetermined time before starting defrosting cycle.
As the present invention reduces noise and vibration in the system, the reliability of the system increases.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims.

We Claim
1. A hot - gas defrost system for ensuring low noise and low vibration operation
during defrost condition, said hot- gas defrost system comprising:
a refrigerant circuit having atleast one compressor for compressing refrigerant, an
indoor heat exchanger atleast functioning as a condenser with a fan, an expansion
valve for reducing the pressure of the refrigerant, an outdoor heat exchanger
atleast functioning as an evaporator with a fan, which are connected in series to
one another for circulating the refrigerant in the refrigerant circuit;
a hot-gas defrost pipe adapted on the refrigerant circuit for bypassing hot gas from
the compressor to the outdoor heat exchanger;
a hot gas defrost valve disposed on said hot gas defrost pipe; and
a controller for initiating defrost operation, wherein said controller, on sensing a
defrost condition, is configured to:
a) switch-off the compressor for a predetermined time and simultaneously full opens the expansion valve for equalizing the pressure between the high pressure discharge line and low pressure inlet line in the refrigerant circuit;
b) open the hot defrost valve after equalizing pressure in the refrigerant circuit and
c) switch-on the compressor for carrying out defrosting heat exchanger of the evaporator thereby ensuring low noise and low vibration operation during defrost condition.

2. The hot gas defrost system as claimed in claim 1, wherein the controller switch off the fan of evaporator along with the compressor for the predetermined time.
3. The hot - gas defrost system as claimed in claim 1 or 2 wherein the predetermined time is 2 minutes.
4. The hot - gas defrost system as claimed in claim 1 wherein the controller delays switch-on of the compressor after opening the hot defrost valve by 10 seconds.

5. A method for ensuring low noise and low vibration operation in a hot gas defrost
system as claimed in claim 1, the method comprising the steps of:
switching-OFF the compressor for a predetermined time upon sensing a defrost
condition and subsequently, full-opening the expansion valve over the system for
equalizing pressure between high pressure discharge line and low pressure inlet
line in the system;
opening hot gas defrost valve after equalizing the pressure in the system; and restarting the compressor for carrying defrosting of outdoor heat exchanger thereby ensuring low vibration and noise operation.
6. The method as in claim 5, wherein the method includes switching off the fan of the evaporator along with the compressor for the predetermined time.
7. The method as in claim 5 or 6, wherein the predetermined time is 2 minutes.
8. The method as in claim 5, wherein delaying switch-on of the compressor after opening the hot defrost valve.
9. The method as in claim 8, wherein the delay is of 10 seconds.