FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
LOADING AND UNLOADING OF
COMPRESSORS IN COOLING SYSTEMS;
BLUE STAR LIMITED A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS KASTURI BUILDINGS, MOHAN T. ADVANl 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 to cooling systems. More particularly the invention relates to loading and unloading of compressors in the cooling systems.
BACKGROUND OF THE INVENTION
Conventionally, a capacity of the cooling system is adjusted by a PID {Proportional-Integral-Derivative) control scheme or some mathematical calculation. To adjust the capacity of the cooling system, the process of loading or unloading of the compressor is done by a PID controller. Generally, the process of loading and unloading of the compressor includes measuring leaving water temperature (LWT) of evaporator of the cooling system, comparing with the LWT set point and accordingly switch on or off the compressor having fixed capacity or increase/decrease the step or RPM of motor connected to the compressor to minimize the error between the actual LWT and LWT set point. The process of controlling the loading and unloading of compressors based on LWT, generally includes using relays or electrically driven controller. The relay or controller monitoring loading and unloading of compressors, utilize desired set points which are logged into the controllers before installation of the vapor compression system. The controller receives feedback from different elements present within the compressor system. The preferred elements providing feedback to the controller are sensors. Based on the feedback, the controller compares the feedback data with the logged data to determine loading or unloading of the compressor.

Further, the loading and unloading of the compressors of the presently available cooling system works in a fixed manner only. For example: if the chiller system is a tandem chiller having four compressor that is one evaporator will be shared by four compressor, then everyday the chiller starts in morning with the fixed defined pattern of loading/unloading with respect to PID or PI irrespective of capacity demand of the system. Such as if the PID has given the command of starting the compressor one by another, it will start one compressor first, then second and like onwards. These results in time delay to reach at require capacity which is critical if chiller or cooling system is used for process application in the Industry.
Therefore, there is a need for system for efficient loading and unloading of a compressor of the cooler system.
SUMMARY OF THE INVENTION
Accordingly, the present invention in first aspect provides a method of loading and unloading a compressor in a cooling system, the method comprising the steps of providing a controller having a PID operation mode and an auto operation mode, measuring a temperature of water flowing from an outlet of the cooling system, determining an actual capacity based on the temperature, generating first demand corresponding to the PID operation mode, generating second demand corresponding to the auto operation mode, comparing the first and second demand, and selecting the operation modes corresponding to less demand for loading and unloading of the compressor in the cooling system.
In second aspect, the present invention provides cooling system. The system comprises a compressor to compress gaseous refrigerant; a condenser supplied with compressed gas from the compressor to liquefy the compressed gas; an evaporator for chilling liquid, said evaporator having inlet port for receiving liquid refrigerant and outlet port for supplying

vaporized refrigerant, an expansion device connected between the condenser and the evaporator, a temperature sensor at the outlet of the evaporator for detecting a temperature parameter of water flowing, and a temperature sensor at the outlet of the evaporator for detecting a temperature parameter of water flowing, and a controller having PID operation mode and auto operation mode for controlling the system, the controller configured for selecting an operation mode based on comparison of a first demand corresponding to the PID operation mode and a second demand corresponding to the auto operation mode wherein the controller selects the operation mode whose corresponding demand is lower for loading and unloading of the compressor in the cooling system According to preferable embodiment of the invention, the controller generates demand when the cooling system achieves the actual capacity monitoring temperature. The present invention is advantageous in providing a method of loading and unloading of the compressor in cooling system where any type of compressor like screw, centrifugal, scroll, reciprocating etc can be used.
Further, the present invention determines the loading and unloading of the compressor based on actual load condition analysis of the site by utilizing fuzzy logic.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features, and advantages of certain exemplary
embodiments of the present invention will be more apparent from the following description
taken in conjunction with the accompanying drawings in which:
Fig. 1 shows a flowchart of a method of loading and unloading of a compressor in a
cooling system in accordance with one embodiment of the present invention.
Fig. 2 shows a cooling system according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the present invention provide a system and a method of loading and unloading of a compressor in a cooling system.
Referring to Fig. 1 the present invention provides a method 100 of loading and unloading of a compressor in a cooling system. In step S110 of the method at least one temperature parameter of the compressor is detected. In S120 an actual capacity monitoring temperature of the system is determined based on the at least one temperature parameter. In S130 a log data of a log pattern is stored in a controller. In S140 at least two demands (D1 & D2) are generated by the controller wherein a demand D1 is generated for a PID mode and a demand D2 is generated for an auto operation mode. In S150 D1 is compared with D2 for selecting an operating mode for the system. If D1 is lower than D2, in S152 PID mode is selected for operating the system with PID algorithm else in S154 auto operation mode is selected for operating the system based on the log data stored in the controller.
The actual capacity monitoring temperature is determined by adding a capacity monitoring constant to the temperature parameter.
In an embodiment, the operating mode is a PID operating mode.
In the PID mode, a first demand of the at least two demands is generated based on a PID algorithm.
In another embodiment, the operating mode is an auto operation mode.
In the auto operation mode, a second demand of the at least two demand is generated by the controller.

The PID operating mode is selected when the first demand is lower than the second demand whereas the auto operation mode is selected when the second demand is lower than the first demand.
In an embodiment, the second demand of the controller is generated depending upon a log data of a load pattern stored in the controller.
In an embodiment, the method of the present invention further comprises closing a compressor intake valve and a compressor output valve when the compressor is turned off.
In an embodiment, the method of the present invention further comprises opening a compressor intake valve and a compressor output valve when the compressor is turned on.
In an embodiment, the present invention provides a cooling system 200 as shown in Fig. 2. The system comprises a condenser 210, a compressor 220, an evaporator 230, a temperature sensor for providing an indication of a temperature, a compressor intake valve coupled to an input of the compressor 220, a compressor output valve coupled to an output of the compressor 220, and a controller 240 coupled to the compressor 220, the temperature sensor, the compressor intake valve, and the compressor output valve, the controller 240 configured for selecting an operating mode based on comparison of at least two demands generated by the controller wherein the operating mode is selected when the system achieves the actual capacity monitoring temperature.
The system 200 also includes an electric motor for compressor and an electronic expansion valve.

In an embodiment, the evaporator 230 is shell and tube type evaporator with flooded type of system where, the refrigerant is on shell side and water is on tube side in evaporator. The evaporator is heat exchanging medium and is utilized for cooling load which may be the flow of water to and from the Shell/Tube depending on the type of evaporator. A suction line connects the evaporator flooded type (as shown fig. 2) to the compressor and passes vaporized refrigerant from the evaporator to the compressor where the vapour is then compress and discharge to condenser via a discharge line with V1 valve and non return valve too.
A chilling liquid, water to be chilled is pumped into the cooling system via inlet line through the tubes where temperature sensor T1 is located to measure the temperature of inlet fluid and discharge from the cooling system via outlet line in which other temperature sensor T2 is located .As the water flows through the tube, heat transfer from chilled water to the liquid refrigerant, causing the refrigerant to boil and vaporize and pass to the compressor. This heat transfer causes the temperature of the chilling liquid flowing out of the cooling system to be lower than the temperature of the chilling liquid flowing into the cooling system.
The condenser which is shell and tube type heat exchanger type which condenses the compressed refrigerant vapour usually in shell received from compressor. The heat of condensation is rejected to condensing water which enters the condenser through the line where the temperature sensor T3 is located, circulates through the tube contained in the shell and exist the condenser via line were temperature sensor T4 is located. One more line from condenser to compressor with valve V3 & drier is for compressor cooling purpose. After condenser the condense refrigerant passed through the drier & V3 valve which absorb moisture in refrigerant.

The refrigerant enters the EXV inlet as a high-pressure liquid. The refrigerant flow is restricted by a metered orifice through which it must pass. As the refrigerant passes through this orifice, it changes from a high-pressure liquid to a low-pressure liquid. An interface is connected to various input like T1 ,T2,T3,T4,DP,SP,ST,DT,ETC. compressor onboard controller. The controller received input information from sensors as mention above like Suction Pressure & temperature, discharge pressure & temperature etc. The control system consist of a processor board which contains a microprocessor that receives and store information sent it from other component from the system. The controller also include output such as compressor motor control output which allows the controller to turn on or off any of the compressor .Other compressor output include such as load solenoid valve (SV2) & Unload solenoid valve (SV1) for screw compressor system as well as CMOvolt, 0-5volt, 4-20 milli-ampere analogue output which signal to reduced speed of motor in case of variable frequency mounted compressor. The speed will be varying proportionally from minimum to maximum corresponding to the type of analogue output used.
The controller is connected to analogue input like evaporator water flow rate to measure water flow rate, power analyzer to know the power consuming, the differential transmitter (DP) to calculate water flow rate.
The loading, unloading or cycling of single or multiple compressor is controlled by drop in LWT and desired set-point mention in controller memory. The temperature of the heat transfer fluid leaving the evaporator is sensed to determine the temperature drop in heat exchanger. The drop is an indication of how much is the LWT is change when capacity stage is added or subtracted.

The capacity stage addition or subtraction is increasing or decreasing the speed in case of VFD based machine or increase or decrease capacity stage like screw type of compressor as mention in fig (B) & (C)
The present invention will be work on actual site condition too with respect to LWT only. When the cooling system is commissioned on site, controller will start the collect data required for the "Auto Operation Mode". The auto operation mode is the mode which is other than conventional ways of calculating the required demand in system with respect to LWT.
When the "Auto Operation Mode" is enabled from compressor, the cooling system controller will start to log data for load pattern. The cooling system actual tonnage is calculated by controller either with direct input from water flow meter and temperature different across evaporator using the formula as mention below or either directly with fuzzy logic in-line with water pressure drop values by utilizing the controller logic.
Cooling system Capacity (Ton) = (T2-T1)* evaporator flow rate (USGPM)/24 When the mode is active, the controller will start to store the data in the format table 1.0 as shown below:
Load Monitoring chart

Sr.No % Load (Tr) Time (Hours)
1 50 1
2 55 2
3 60 3
4 75 4
5 100 5
6 100 6
7 72 7
8 69 8
9 85 9
10 77 10
11 62 11

12 95 12
The controller starts to collect the data for the cooling system once the "Auto Operation Mode" is active as shown above. The data is recorded for 24 hours after the mode is active. The table 1.0 above shows sample load pattern for 12 hour of cooling system operation. The table 1.0 shows that for 1st hour the average load is 50 Tr, for first hour of running like 9am to 10 am whereas it is 55 Ton for 10am to 11am etc.
The design specification of cooling system is available in controller memory. The capacity monitoring is displayed on the controller screen when the "T2" temperature of cooler reaches to predetermine value of "Actual Capacity Monitoring temperature". This is constantly displayed and modified on controller screen.
To explain the process in detail, by way of example, consider: When the running "T2" value (Assume 44 F, set point/constant for leaving cooler water temperature) & "Actual Capacity Monitoring temperature "(constant value assume as 5) are two values available in controller
The Actual Capacity monitoring temperature in F=T2+ Actual Capacity Monitoring Constant
= 44+5=49
The data show in table 1.0 above is the average value of Tonnage recorded by the cooling system after 49.0 Deg F and the below temperature is achieved by LWT. The average is

calculated by collecting the sample of reading for every second and calculated the average for complete hour as shown in the table 1.0.
Average of the hour=(X1+X2+X3 Xn) /Number of sample collected
Where X1, X2 is the sample collected every second.
When the cooling system operates and achieve the Actual Capacity monitoring temperature, there will be two demand generated in the controller as below:-
1. The first demand is the Primary demand (D1) generated either by PID algorithm or any other user define algorithm
2. Whereas the second demand (D2) is generate due to enabling the "Auto Mode Operation"
After achieving the Actual Capacity monitored temperature, these two demands are
generated by the controller.
When the cooling system comes in the zone of "Auto Operation Mode", the cooling system
starts to check both the demand D1 & D2. Whenever the demand D1 is lower than
demand D2, the cooling system follows D1 whereas when D2 is lower than D1, the cooling
system followed the following sequence of operation.
Sequence of operation in "Auto Operation Mode" when Actual Capacity temperature is
reached :-
1. The cooling system shows two demand as D1 & D2.
2. When D2 is lower than D1, cooling system will start to follow the D2 as command as behaves accordingly.

3. D2 is generated by the average of previous day operation as mention above
4. If D2 is lower than D1, cooling system will start to follow D2.But sometime due to operating conditions, environmental condition, load variation there will be always some variation between demand generated by D2 & D1.
5. These above factors will make it mandatory to monitor D1 too to meet the site condition
6. D2 will start to adjust itself if there is variation with D1
7. The below example make it more clear
In an embodiment, considering as example, if D2 is showing demand as 60% (as shown in table 1.0, with average of 3rd operating hour) whereas D1 which is based on current LWT and with PID or user define algorithm showing 75%, then in this case the cooling system will start to maintain load as 60 % initially based on best efficiency metrics in case of multiple compressor as shown in the table 1.0. The controller will calculate the variation between D1 & D2 as below
Demand Variation=D1-D2
In above example it is 15 % If Demand Variation is positive value then the controller will start to look at "Rate of heat Transfer" called as RHT by collecting RHT sample as mention in set point" RHT interval" The RHT interval is the constant, indicating the number of samples required to be collected to calculate RHT.
If "RHT interval" value is 90 in controller, then for every second the LWT running value is stored in controller till next 90 seconds. So after every 90 second, the new value is stored and old removed. This is continuous process once "Auto Operation Mode" is active. The RHT is calculated by following formula by controller: RHT= First reading of RHT interval - Last reading of RHT interval Further, if LWT is 48.0 F & 47.0 F is recorded as first & last reading of the RHT interval.

RHT=48-47=1
So, the calculated RHT is 1.There is two more set point/constant which decides the next course of action. This is RHT positive which value is assume 1 in this case. This is the constant which is to compared the RHT value. In this value is equal or above the RHT positive value, then there will not be any change is capacity stage. In short we have found demand variation of 15% in above case. But calculated RHT is 1 which is equal to RHT positive value, indicating temperature drop of 1 Deg F in every 90 second. So no need to adjust D2 with D1 as the required temperature will be achieved.
Take the other example where LWT is 48 .0 F & 48.0 F is recorded as first & last reading of the RHT interval. RHT =48-48=0
Calculated RHT is 0 which is lower than RHT positive value, indicating temperature drop of 0 Deg F in every 90 second. So there is a need to adjust D2 with D1 to achieve desired set-point. Now the capacity will change as per "Capacity Adjustment factor" called as set-point or constant. Now in this case, we need to increase the capacity till RHT will get equal to set-point value of 1 .This increase in capacity will be done by "Capacity Adjustment factor" which is 5%. In short the capacity adjustment of 5% will be done as per Set-point "Capacity Adjustment Time" which is 2 minute. So as RHT is lower than set-point mention value of 1, the capacity will get increase by 5% every 2 minute till RHT is equal or more than RHT set-point value 1.
The controller will now increase demand from 60% to 65 % every 2 minute till RHT calculated value is equal or more than 1 as mention above.
The same procedure is followed during every loading & unloading once Actual Capacity monitoring temperature is reach.

Now during next day operation, controller will keep the adjustment he has done for every hour. Let take the above example where there is the variation of 15 % in D1 & D2. In above example D1 is earlier 60 and later increase to 65% and found RHT is equal to RHT set-point 1.So on next day , for this average slot, the controller will modify the value from 60 to 65 % to minimize the error cause due to any reason.
Accordingly the table 1.0 will be modified everyday based on running feedback and observation by controller.
When the cooling system with multiple compressors will stop after achieving the LWT temperature and if cooling system is in Actual Capacity monitoring temperature zone, during start up the controller will look for the tonnage required and start both compressor together considering best efficiency metrics shown in table 1.1. Due to this, both compressor will start together and maintain the condition faster and stable which is critical for process application.
Table 1.1 shows the efficiency metrics to select best combination of the compressor to be run by the controller.

Sr.No Total Demand (%) % Share in Demand by System 1 % Share in Demand by • System 2
1 100 50 50
2 75 37.5 37.5
3 50 25 25
4 25 12.5 12.5
5 <25 25* 0
If the load is 25% of total load, the controller will run both the compressor at 12.5% whereas if it is below 25%, the one compressor will get off and other will, be at 25 % as mention in table 1.1

Due to above logic cycling will get come down as the cooling system operation is adjusting itself after studying the load profile on site.
In the foregoing detailed description of embodiments of the invention, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description of embodiments of the invention, with each claim standing on its own as a separate embodiment.

WE CLAIM:
1. A method of loading and unloading a compressor in a cooling system, the method
comprising the steps of:
providing a controller having a PID operation mode and an auto operation mode;
measuring a temperature of water flowing from an outlet of the cooling system;
determining an actual capacity based on the temperature;
generating first demand corresponding to the PID operation mode;
generating second demand corresponding to the auto operation mode;
comparing the first and second demand; and
selecting the operation modes corresponding to less demand for loading and unloading of the compressor in the cooling system.
2. The method as claimed in claim 1 wherein the controller generates demand when the cooling system achieves the actual capacity monitoring temperature.
3. The method as claimed in claim 1, wherein the actual capacity monitoring temperature is determined by adding a capacity monitoring constant to the temperature parameter.
4. The method as claimed in claim 1, wherein the second demand is generated depending upon a log data of a load pattern stored in the controller.
5. A cooling system, comprising: a compressor; a compressor intake valve coupled to an input of the compressor; a compressor output valve coupled to an output of the compressor; and a controller coupled to the compressor, the temperature sensor, the compressor intake valve, and the compressor output valve, a temperature sensor at

the output valve for detecting a temperature parameter of water flowing; the controller configured for selecting an operation mode based on comparison of a first demand corresponding to a PID operation mode and a second demand corresponding to an auto operation mode wherein the controller selects the operation mode whose corresponding demand is lower for loading and unloading of the compressor in the cooling system.
6. The system as claimed in claim 5 wherein the controller generates demand when the cooling system achieves the actual capacity monitoring temperature.