FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See Section 10; rule 13)
TITLE OF THE INVENTION
“SYSTEM AND METHOD FOR CONTROLLING CONDENSER DISCHARGE PRESSURE FOR VEHICLE ROOF MOUNTED AC SYSTEM”
APPLICANTS
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
SAMBHAJI JAYBHAY, SANGEET HARI KAPOOR,
PRASANNA NAGARHALLI AND PRAJNA HEGDE;
All are Indian Nationals
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in
which it is to be performed.

FIELD OF THE PRESENT INVENTION
The present invention generally relates to Heating Ventilation and Air Conditioning (HVAC) System (100). More particularly, the present invention relates to a system and method for reducing refrigerant discharge pressure for vehicle roof mounted Air conditioning system.
BACKGROUND
The mobile AC roof units used in buses and ambulances have a condenser (heat rejection unit) situated on roof top of the buses and ambulances. Thus, the ram air effect on these condensers is not as much as that in case of passenger cars which have the condenser coil in the front of the vehicle, due to this reason, issues of high discharge pressure are faced on buses. Condensing (discharge) pressure is a critical parameter for ensuring safe operation of an air conditioning system. Maintaining condensing (discharge) pressure within recommended prescribed limits is critical as several problems arise if condensing (discharge) pressure exceeds recommended prescribed limits. More specifically, if the condensing (discharge) pressure exceeds beyond recommended prescribed limits, then high pressure tripping of the AC compressor can occur and as a result AC system may get cutoff, thereby resulting in passenger discomfort.
Maintaining the condensing (discharge) pressure under control is even more critical in case of vehicle roof mounted Air conditioning systems, wherein the condenser mounted on vehicle roof top is directly under solar load. Further, as the condenser is mounted on vehicle roof top, the condenser or heat rejection unit does not get cooling effect of ram air. More specifically, bus AC systems have larger heat exchangers to serve the huge volume of occupant space, hence these system are designed for safe operating high pressure limit of 23~24 bar. During severe ambient operation, particularly after the bus has been soaked in solar load, AC system pressure goes beyond its safe operating limit and AC system cuts off and end up in to customer irritant.
During severe ambient conditions (45°C and solar load 1200 W/m2), the condenser air in
temperature goes to 62~64 °C. Once the AC is started and the engine is kept running at
idle, the discharge (refrigerant) pressure goes to 27~29 bar. Due to this high pressure, the
AC operation stops, till its discharge pressure comes down within the safe limit. Once the
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condenser fan is ON, the condenser air out temperature goes to 73~75 °C and only 10 to 12°C effective delta temperature drop can be achieved across heat rejection coil.
Although some of the prior art documents disclose air conditioning systems having provisions for reducing condensing (discharge) pressure but such provisions are not meant for vehicle roof mounted air conditioning systems and fail to maintain condensing (discharge) pressure within recommended prescribed limits at severe ambient conditions. Further such conventional systems/provisions are ineffective and expensive.
OBJECTS OF THE PRESENT INVENTION
The main object of the present invention is to overcome at least one of the above problem.
Another object of the present invention is to provide a Heating Ventilation and Air Conditioning (HVAC) system (100) or a system (100) to be mounted on roof of a vehicle and method for maintaining condensing (discharge) pressure for vehicle roof mounted Air Conditioning (AC) systems within recommended prescribed limits.
Still another object of the present invention is to provide a system (100) and method for maintaining condensing (discharge) pressure for vehicle roof mounted AC system (100) within recommended limits that ensures safe operation of the AC system even at severe ambient conditions.
Yet another object of the present invention is to provide a system (100) for maintaining condensing (discharge) pressure for vehicle roof mounted AC system (100) within recommended limits that is simple in construction, less expensive and easy packaging thereof in the vehicle is simple and convenient.
Another object of the present invention is to provide a system (100) and method for maintaining condensing (discharge) pressure for vehicle roof mounted AC systems (100) within recommended prescribed limits that enhances the service life and reliability of the air conditioning system.
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Still another object of the present invention is to provide a system (100) and method for maintaining condensing (discharge) pressure for vehicle roof mounted AC system within prescribed limits that is convenient to use.
Another object of the present invention is to provide a system (100) and method for maintaining condensing (discharge) pressure for vehicle roof mounted AC systems (100) within recommended prescribed limits that is retrofit-able in the vehicles in use.
SUMMARY
The present invention provides a Heating Ventilation and Air Conditioning (HVAC) system (100) and method for maintaining condensing (discharge) pressure for vehicle roof mounted Air Conditioning (AC) system (100) within recommended prescribed limits even at severe ambient conditions. The system and method for maintaining condensing (discharge) pressure for vehicle roof mounted AC system within recommended limits that ensures safe operation of the air conditioning system. The system is simple in construction, less expensive and easy packaging thereof in the vehicle is simple and convenient. The system of present invention enhances the service life and reliability of the AC system. The present invention provides a convenient method for maintaining condensing (discharge) pressure for vehicle roof mounted Air conditioning system within prescribed limits. The system may be retrofitted on any of the existing passenger or commercial vehicles as it utilizes already available sub-systems of the existing passenger or commercial vehicles with minor modifications.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:
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FIG.1 illustrates a circuit diagram for a system for maintaining condensing (discharge) pressure for vehicle roof mounted Air conditioning systems within recommended prescribed limits in accordance with an embodiment of the present invention; and
FIG. 2 illustrates a flow chart depicting control strategy used by a system for maintaining condensing (discharge) pressure for vehicle roof mounted Air conditioning systems within recommended prescribed limits in accordance with an embodiment of the present invention.
DETAIL DESCRIPTION
The foregoing has broadly outlined the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
Accordingly the present invention provides a heating ventilation and air conditioning (HVAC) system (100) for a vehicle and method for operating the same. The said system (100) comprises a roof Air Conditioning (AC) unit (50) mounted on roof of the vehicle comprising a roof control unit (90) coupled with an AC controller (40) and Electronic Control Unit (ECU) (30), a condenser (70) with condenser fan(s) (80) coupled with roof
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control unit (90) and driven by condenser motors, an evaporator with one or more blowers (60) coupled with blower motors controlled through the roof control unit (90), one or more pressure sensors (150, 160), operably coupled with roof control unit (90), connected in refrigerant circuit on low and high pressure side to provide inputs for discharge and/or suction pressure to roof control unit (90); and a compressor (20) coupled with the ECU (30) and engine (10) of the vehicle and at least one ambient temperature sensor (120), wherein a water spray arrangement operably coupled with the roof control unit (90) via ECU (30) being provided to spray water on the condenser (70) for cooling of the condenser on trigger point.
In one aspect of the present invention, the water spray arrangement comprises nozzle arrangement (110) coupled with windscreen washer arrangement (130) via water pump (140).
In one more aspect of the present invention, the nozzle arrangement (110) being provided in vicinity to the condenser (70) to spray water on the condenser (70).
In another one aspect of the present invention, the compressor (20) being mounted near the engine (10) of the vehicle and being driven by the engine (10).
In still another aspect of the present invention, the condenser (70) being sandwiched between the nozzle arrangement (110) and condenser fan(s) (80).
In yet another aspect of the present invention, the one or more pressure sensors (150, 160) are disposed on higher pressure side and lower pressure side of the system (100).
In further aspect of the present invention, the temperature sensor (120) being disposed on the AC unit (50).
In furthermore aspect of the present invention, the roof control unit (90) coupled with the temperature sensor (120) and pressure sensors (150, 160) to receive signals and sends the received signals to ECU (30).
In another aspect of the present invention a method for maintaining condenser discharge pressure for a Heating Ventilation and Air Conditioning (HVAC) system (100) for a vehicle
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mounted on roof of the vehicle comprises step of running engine on idle speed (speed 3), turning on Air Conditioning (AC) system in the vehicle; receiving ambient temperature (Tamb) from temperature sensor (120) and discharge pressure (Pd) from pressure sensor (150) by roof control unit (90), sending the signals to Electronic Control Unit (ECU) (30), comparing the ambient temperature (Tamb) with predetermined temperature (T1) and discharge pressure (Pd) with predetermined discharge pressure (Pd1) by the ECU; actuating the water spray arrangement by ECU if Tamb and Pd are greater than the T1 and Pd1 respectively for spraying water on condenser for predetermined time period; and turning on condenser fan (80) at high speed (speed 1); or operating/starting compressor (20) if ambient temperature Tamb and discharge pressure Pd are less than the T1 and Pd1 respectively; receiving discharge pressure (Pd) from pressure sensor (150) and suction pressure from pressure sensor (160) by roof control unit (90), sending the signals to the ECU, comparing the discharge pressure (Pd) with second predetermined discharge pressure (Pd2) and suction pressure (Ps) with predetermined suction pressure (Ps1) by the ECU; operating the condenser fan (80) continue at high speed (speed 1) as of above step if Pd is greater than Pd2 and Ps is less than the Ps1; or increasing the engine speed to a predetermine speed (speed 4) if Pd is less than the Pd2 and Ps is less than the Ps1; receiving discharge pressure (Pd) from pressure sensor (150) by roof control unit (90), sending the signals to the ECU, comparing the discharge pressure (Pd) with third predetermined discharge pressure (Pd3) by the ECU; running of the condenser fan continues at high speed (speed 1) if Pd is greater than the Pd3; or operating the condenser fan at a speed (speed 2) if the Pd is less than the Pd3.
In still another aspect of the present invention, the roof control unit (90) gives command to ECU (30) to actuate the water spray arrangement for spraying water on condenser.
In yet another aspect of the present invention, the roof control unit (90) coupled with condenser fan(s) to operate and regulate the condenser fan(s) speed.
In further aspect of the present invention, the ECU (30) gives command for increasing the speed of the engine (10).
In furthermore aspect of the present invention, roof control unit (90) is coupled with temperature sensor (120), pressure sensors (150, 160) to receive signals and sends the signals to ECU (30).
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In another aspect of the present invention, the roof control unit (90) coupled with ECU (30)
controls fast idle control device (FICD) to regulate compressor speed.
In still another aspect of the present invention, the compressor is driven by engine of the
vehicle.
The present invention provides a Heating Ventilation and Air Conditioning (HVAC) system (100) and method for maintaining condensing (discharge) pressure for vehicle roof mounted Air Conditioning (AC) systems (100) within recommended prescribed limits by reducing the high discharge pressure at severe ambient conditions. The system and method for maintaining condensing (discharge) pressure for vehicle roof mounted AC systems of present invention may utilize already available sub-systems of the existing passenger or commercial vehicles with minor modifications and accordingly the system can be retrofitted on any of the existing passenger or commercial vehicles. It may contemplated that the phrases “Heating Ventilation and Air Conditioning (HVAC) system (100)”, “Air Conditioning (AC) system (100)” or system (100) may interchanged hereinafter and shall represents the Heating Ventilation and Air Conditioning (HVAC) system (100) of the present invention.
Referring to Fig.1, a circuit diagram for a system (100) for maintaining condensing (discharge) pressure for vehicle with roof mounted air conditioning systems (100) within recommended prescribed limits in accordance with an embodiment of the present invention. The system (100) comprises a roof AC unit (50) mounted on the roof of the vehicle coupled with an Electronic Control Unit (ECU) (30) having fast idle control device (FICD) to regulate AC compressor speed. The ECU (30) is coupled with engine of the vehicle. The roof AC unit (50) comprises condenser (70) with condenser fans (80) for heat rejection to atmosphere, evaporator with twin blowers (60) for cabin cooling and ventilation, discharge pressure sensor (150) and suction pressure sensor (160) for refrigerant circuit safety, the temperature sensor (120) to sense the ambient temperature and an AC controller (40) to control AC functions like blower speed and cabin set temperature. An AC compressor (20) is mounted on vehicle engine (10) or vehicle chassis and driven by the vehicle engine (10). The inlet and outlet of AC compressor (20) are
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connected to the roof AC unit (50). The AC compressors (20) is controlled by engine ECU (30) after getting input from AC controller (40) and AC roof unit controller (90). The system (100) further includes water spray arrangement comprising nozzle arrangement (110) coupled with windscreen washer bottle (130) via a water pump (140) according to an embodiment of the present invention. The discharge pressure sensor (150) is disposed in high pressure side of refrigerant circuit to measure refrigerant pressure while the suction pressure sensor (160) is disposed in low pressure side of the refrigerant circuit to measure low pressure as shown in Fig. 1. It may apparent to the person skilled in the art that the high pressure side in refrigerant circuit is from AC compressor to thermostatic expansion valve before evaporator while the low pressure side is from evaporator to AC compressor. The roof control unit (90) is coupled with the temperature sensor (120) and pressure sensors (150, 160) to receive signals. The roof control unit is also coupled with condenser fan(s) (80). The roof control unit is further coupled with the ECU (30) to send the received signals.
The nozzle arrangement (110) for water spray is provided in vicinity to the condenser (70). The nozzle arrangement (110) is connected with a water pump (140). The water pump (140) is also connected with windscreen washer arrangement/bottle (130) of the vehicle. More specifically, the nozzle arrangement (110) utilizes the water from windscreen washer arrangement (130) for spraying the water according to an embodiment of the present invention. The water spray arrangement of the present invention is being used for supplying water for cooling of the condenser (70) on the vehicle roof. In accordance with an embodiment, the windscreen washer arrangement (130) may be a windscreen washer bottle. Further, one or more nozzles are provided in nozzle arrangement (110) which are connected to water pipe of the windscreen washer arrangement (130). The said nozzle arrangement sprays water below the condenser (70) on the vehicle roof for a predetermined set time period 1, before the AC starts. Such spraying of the cooling water below the condenser (70), locally cools the area near the heat rejection coil (condenser), thereby reducing the discharge pressure (Pd). The water spray arrangement is controlled by the roof control unit (90) according to an embodiment of the present invention.
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The method of present invention involves running the condenser fans at high speed prior to engagement of the compressor (20), to dissipate the heat according to an embodiment of the present invention. The method further involves, spraying water on the condenser (70) for providing additional cooling effect through the process of evaporative cooling according to another embodiment of the present invention. The condenser fan’s (80) speed is controlled to result in better initial cooling, reduce discharge pressure and save electric consumption. The method still further involves delaying Fast Idling Control Device (FICD) operation to control discharge pressure. Delaying FICD operation for the initial few minutes, and preferably 2-3 minutes, reduces refrigerant pumping speed. With such steps, the condenser (70) temperature and ultimately discharge pressure reduces and high pressure tripping of the compressor (20) may be avoided. Accordingly service life and reliability of the condenser (20) and hence the AC system as a whole is enhanced. All these three steps effectively reduce the discharge pressure (Pd) without hampering the cool down performance of the roof AC system.
Referring to FIG. 2, a flow chart depicting control strategy used by the system (100) for maintaining condensing (discharge) pressure for vehicle roof mounted Air Conditioning (AC) systems (100) within recommended prescribed limits. The flow chart is described in detail here below:
Once the vehicle ignition is turned “ON” and the engine is cranked. The engine runs at idle speed, set speed 3. In an exemplary embodiment the set speed 3 may be in the range of 700-800 RPM.
Stage 1: Once the AC is turned ON, the ambient temperature (Tamb) and discharge pressure (Pd) are checked by AC roof control unit (90). If the ambient temperature (Tamb) is greater than predetermined temperature (T1) and Pd is greater than predetermined first discharge pressure (Pd1), then the roof control unit (90) gives command to ECU (30) to actuate the water spray arrangement for spraying water on the condenser for predetermined time period. The water spray will take place for a predetermined set of time period, for 10 to 20 seconds as an exemplary embodiment of the present invention, after
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which the condenser fan (80) will turn ON at high speed (set speed 1). The high speed operation of the condenser fans (80) help to reduce condenser air temperature. According to an exemplary embodiment of the present invention, at this stage, the temperature may fall from 62-64°C to 50~52°C which in-turn reduce discharge pressure (Pd). Next, the ambient temperature (Tamb) and discharge pressure (Pd) will be checked once again and the same procedure is repeated until the ambient temperature (Tamb) and discharge pressure (Pd) falls below the predetermined temperature (T1) and predetermined first discharge pressure (Pd1). It may be contemplated that in the description of the present invention hereinafter the terms/phrase predetermined first discharge pressure, first discharge pressure (Pd1) or Pd1 may be used while referring to predetermined first discharge pressure (Pd1). Similarly, the predetermined temperature (T1) or T1 may be used while referring to predetermined temperature (T1). In an exemplary embodiment of the present invention the predetermined temperature (T1) may be up to 42o C and Pd1 may be up to 10 Bar.
Once the values of the ambient temperature (Tamb) and discharge pressure (Pd) fall below to the predetermine T1 and Pd1, the AC compressor (20) clutch get engaged and the AC compressor is in “ON” stage now.
Stage 2: When the AC compressor (20) is “ON”, the discharge pressure (Pd) and suction
pressure (Ps) are checked/compared with predetermined second discharge pressure (Pd2)
and predetermined suction pressure (Ps1) respectively. If the discharge pressure (Pd) is
higher than the predetermined second discharge pressure Pd2 and the suction pressure (Ps)
is lower than the predetermined suction pressure Ps1, the condenser fans (80) continue to
run at high speed, set speed 1. In an exemplary embodiment of the present invention the
set speed 1 may be in the range of 2400-3600 RPM. The compressor (20) operates without
the FICD (FICD is not be activated) to keep refrigerant pumping low, FICD operates once
the discharge pressure (Pd) value comes below predetermined second discharge pressure
Pd2. With such steps the condensing (discharge) pressure is reduced and the electrical
power consumption is reduced. The system (100) utilizes discharge pressure and ambient
temperature readings from discharge pressure sensor (150) and ambient temperature
sensor (120) respectively for logical decision making without measuring solar load.
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Further, the discharge pressure (Pd) and suction pressure (Ps) will be checked once again and the same procedure is repeated until the discharge pressure (Pd) falls below the predetermined second discharge pressure Pd2 and the suction pressure (Ps) rises greater than the predetermined suction pressure Ps1. The condenser fan (80) continues to run till the discharge pressure (Pd) comes down to the predetermined second discharge pressure Pd2 and the suction pressure (Ps) comes greater than the predetermined suction pressure Ps1 according to embodiment of the present invention. Once the discharge pressure (Pd) and suction pressure (Ps) are within the desired limit, the engine starts operating at the set rpm, set speed 4, with FICD logic functional. In an exemplary embodiment of the present invention the set speed 4 may be in the range of 900-1000 RPM. In still another exemplary embodiment of the present invention the predetermined second discharge pressure Pd2 may be up to 21 Bar and the predetermined suction pressure Ps1 may be 5 Bar.
Stage 3: When the engine starts operating at set speed 4, the discharge pressure (Pd) at this stage is continuously monitored. The discharge pressure (Pd) is compared with predetermined third discharge pressure (Pd3). If the discharge pressure (Pd) is found greater than the third discharge pressure (Pd3), the condenser fans (80) operate at high speed (set speed 1). This procedure may be repeated until the discharge pressure (Pd) falls below than the predetermined third discharge pressure Pd3. Subsequently, when the discharge pressure (Pd) is found lesser than the predetermined third discharge pressure Pd3, the condenser fans (80) operate at set speed 2. In an exemplary embodiment of the present invention the set speed 2 may be in the range of 1200-1800 RPM. In yet another exemplary embodiment of the present invention the Pd3 may be up to 17 Bar.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
Referral Numerals:

Reference Number Description
10 Engine
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20 Compressor
30 Electronic Control Unit or ECU
40 AC controller
50 Roof AC unit
60 Twin blowers
70 Condenser
80 Condenser fans
90 Roof control unit
100 Heating Ventilation and Air Conditioning (HVAC) system or system
110 Nozzle arrangement for water spray
120 Ambient temperature sensor
130 Windscreen washer bottle
140 Water Pump
150 Discharge pressure sensor
160 Suction pressure sensor
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WE CLAIM
1. A Heating Ventilation and Air Conditioning (HVAC) system (100) for a vehicle comprises:
a roof Air Conditioning (AC) unit (50) mounted on roof of the vehicle comprising
a roof control unit (90) coupled with an AC controller (40) and Electronic
Control Unit (ECU) (30),
a condenser (70) with condenser fan(s) (80) coupled with roof control
unit (90) and driven by condenser motors,
an evaporator with one or more blowers (60) coupled with blower motors
controlled through the roof control unit (90), one or more pressure sensors (150, 160), operably coupled with roof control unit (90), connected in refrigerant circuit on low and high pressure side to provide inputs for discharge and/or suction pressure to roof control unit (90); and a compressor (20) coupled with the ECU (30) and engine (10) of the vehicle and at least one ambient temperature sensor (120),
wherein a water spray arrangement operably coupled with the roof control unit (90) via ECU (30) being provided to spray water on the condenser (70) for cooling of the condenser on trigger point.
2. The system (100) as claimed in claim 1, wherein the water spray arrangement comprises nozzle arrangement (110) coupled with windscreen washer arrangement (130) via water pump (140).
3. The system (100) as claimed in claim 1, wherein the nozzle arrangement (110) being provided in vicinity to the condenser (70) to spray water on the condenser (70).
4. The system (100) as claimed in claim 1, wherein the compressor (20) being mounted near the engine (10) of the vehicle and being driven by the engine (10).
5. The system (100) as claimed in claim1, wherein the condenser (70) being sandwiched between the nozzle arrangement (110) and condenser fan(s) (80).
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6. The system (100) as claimed in claim 1, wherein the one or more pressure sensors (150, 160) are disposed on higher pressure side and lower pressure side of the system (100).
7. The system (100) as claimed in claim 1, wherein the temperature sensor (120) being disposed on the AC unit (50).
8. The system (100) as claimed in claim 1, wherein the roof control unit (90) coupled with the temperature sensor (120) and pressure sensors (150, 160) to receive signals and sends the received signals to ECU (30).
9. A method for maintaining condenser discharge pressure for a Heating Ventilation and Air Conditioning (HVAC) system (100) for a vehicle mounted on roof of the vehicle comprises step of running engine on idle speed (speed 3), turning on Air Conditioning (AC) system in the vehicle;
(a) receiving ambient temperature (Tamb) from temperature sensor (120) and discharge
pressure (Pd) from pressure sensor (150) by roof control unit (90), sending the
signals to Electronic Control Unit (ECU) (30), comparing the ambient temperature
(Tamb) with predetermined temperature (T1) and discharge pressure (Pd) with
predetermined discharge pressure (Pd1) by the ECU;
(i) actuating the water spray arrangement by ECU if Tamb and Pd are greater than the T1 and Pd1 respectively for spraying water on condenser for predetermined time period; and turning on condenser fan (80) at high speed (speed 1); or
(ii) operating/starting compressor (20) if ambient temperature Tamb and discharge pressure Pd are less than the T1 and Pd1 respectively;
(b) receiving discharge pressure (Pd) from pressure sensor (150) and suction pressure
from pressure sensor (160) by roof control unit (90), sending the signals to the ECU,
comparing the discharge pressure (Pd) with second predetermined discharge pressure
(Pd2) and suction pressure (Ps) with predetermined suction pressure (Ps1) by the
ECU;
(i) operating the condenser fan (80) continue at high speed (speed 1) as of above step if Pd is greater than Pd2 and Ps is less than the Ps1; or
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(ii) increasing the engine speed to a predetermine speed (speed 4) if Pd is less than the Pd2 and Ps is less than the Ps1; (c) receiving discharge pressure (Pd) from pressure sensor (150) by roof control unit (90), sending the signals to the ECU, comparing the discharge pressure (Pd) with third predetermined discharge pressure (Pd3) by the ECU;
(i) running of the condenser fan continues at high speed (speed 1) if Pd is
greater than the Pd3; or (ii) operating the condenser fan at a speed (speed 2) if the Pd is less than the Pd3.
10. The method as claimed in claim 9, wherein the roof control unit (90) gives command to ECU (30) to actuate the water spray arrangement for spraying water on condenser.
11. The system (100) as claimed in claim 9, wherein the roof control unit (90) coupled with condenser fan(s) to operate and regulate the condenser fan(s) speed.
12. The method as claimed in claim 9, wherein the ECU (30) gives command for increasing the speed of the engine (10).
13. The method as claimed in claim 9, wherein roof control unit (90) is coupled with temperature sensor (120), pressure sensors (150, 160) to receive signals and sends the signals to ECU (30).
14. The system (100) as claimed in claim 9, wherein the roof control unit (90) coupled with ECU (30) controls fast idle control device (FICD) to regulate compressor speed.
15. The system (100) as claimed in claim 9, wherein the compressor is driven by engine of the vehicle.