Plural Compressors Application Guidelines
Inverter Development Guideline (For Scroll & Twin Rotary) 1. Define System Requirement 1.1 Minimum and Maximum Capacity Requirement Minimum and maximum capacity can be calculated from SEER concept or SEER standard of each country. Capacity calculation from SEER concept 1. Define a using area of an inverter system.( Using a Temperature map of each country ) 2. Calculate maximum and minimum load of capacity from temperature map. Load of Air to Air or Air to Water system is ambient temperature. Example: Capacity Calculation in France Ambient Temperature in France 1000 STRASBOURG
900
PARIS_ ORLY
Hr/year
800 700
BREST LYON
600
BORDEAUX
500 400 300 200 100 0 -12 -10 -8
-6
-4 -2
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 o
Ambient Temp( C)
Figure 1 Ambient Temperature in France Temperature map of each country is different. To design inverter system, a chart of heat/cool load and using range should be firstly defined.
Figure 2 Minimum and Maximum capacity calculation of Paris in France
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In Paris, heating mode runs at ambient temperature from -6 to 12 oC, Cooling mode runs at ambient temperature from 20 to 33 oC The data can be conversed to maximum and minimum capacity requirement. 1.2 COP or SEER Level Requirement COP or SEER requirement of system for cooling and heating mode should be defined. 1.3 Safety Standard Requirement EN14511, APF, ARI 210/240, EMC, PF, Others 2. Compressor Selection 2.1 Compressor Size The Capacity and COP requirement from No.1 is used for compressor selection. If a selected compressor is too small, the compressor will run at High speed, resulting to a drop in system SEER. If a selected compressor is too big, the compressor will switch. On and Off at low capacity control, resulting to a poorer control over temperature and humidity. To get the highest SEER and highest control quality, maximum capacity should match with compressor speed not more than 100 rps. 2.2Refrigerant (R407C or R410A) SCI compressors for both R407C and R410a have the same wide-range operating area. The difference is only the maximum condensing temperature. Maximum condensing temperature for R407C is 68oC Maximum condensing temperature for R410A is 65oC If a required water temperature is not over than 60oC in Heat Pump, SCI recommends to use R410A as it delivers better efficiency than R407C. 2.3 DC or AC Inverter DC compressor gives better efficiency than AC compressor at low speed(Figure 3). Thanks to a lower loss of DC motor. From this advantage, higher SEER can be achieved from DC Compressor. Device comparison between DC and AC Inverter system 1. Compressor difference DC compressor has a permanent magnet at rotor. 2. Driver difference Driver Hardware is the same. Driver software is different. 3. Controller is the same.
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System COP DC Compressor AC Compressor
Compressor Speed Figure 3 Motor comparison between AC and DC 3. Driver Selection 3.1 Driver Size. Driver size should match with the maximum current of compressor. Maximum current of compressor can be calculated from compressor performance curve at overload condition (ET 12oC, CT 65oC for R410A compressor), at the maximum speed of compressor as set from No.2. 3.2 Driving Method (PWM, PAM, sine wave, square wave) Driving method is affected to system efficiency, system quality control, and compressor reliability and driver price. Some driving method can not drive compressor in some load condition. We recommend using only verified drivers that have been passing SCI quality checking. 3.3 Compressor Protection Driver should have software and hardware protection for compressor as inverter compressor does not have any self protection system. Recommend compressor protections from driver are Reverse phase, phase loss and demagnetize protection (for DC motor). 3.4 Communication Digital signal: RS485 Analog signal: DC 0-10 Volt Driver communication should be matched with your controller communication. 3.5 EMC, Harmonics, Others requirement. All requirements should pass standard level. EMC Directive: 1. For current < 16 amp should pass EN61000-3-2 2. For current >16 and < 75 amp should pass EN61000-3-12 Harmonics: 1. For current > 16 amp per phase should pass EN61000-3-4
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4. Controller design for compressor protection. Inverter compressor is not self – protected. It should be protected by Driver and Controller. 4.1 Compressor operating limit. Customer have to check operating limit for specific model from operating area document (Download from technic.siamcompressor.com or request from marketing department), as shown in Figure 4. And compressor must be running under its operating area at all times. 4.2 Compressor discharge temperature limit. (Refer to General specification No.6-8) SCI Scroll and Rotary compressor is a high pressure shell type. Compressor motor was designed to cool down by discharge gas, therefore, temperature of discharge gas must be controlled not to be higher than the limit So, Discharge temperature have to be controlled within envelope limitation in each area.
Figure 4 Example of Operating area and Discharge temperature limit
4.3 Compressor oil circulation (Refer to General specification No.5) SCI Scroll compressor uses Pressure difference between Pd and Ps to supply oil, so pressure different have to satisfied oil supply limit for each compressor model. Recommendation for discharge temperature measuring position: 1. at top shell of scroll compressor. 2. at discharge pipe of Scroll and Twin Rotary, not further than 15 cm from compressor shell
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Recommendation for discharge temperature protection control (Figure 5): The compressor should not be stopped too often. To increase the control quality, the controlling point should be set before reaching the compressor stopping limit. Example: Separating the control zone; Normal zone and protection zone.
Figure 5 Discharge temperature control procedure The control concept can be applied to the other compressor’s limits too. It can improve system control quality. Recommendation for discharge temperature control in high compression zone.
High Compression Zone
Figure 6 High compression area
Td Control for High compression zone In general system, superheat control is at suction side. The control value is between 5-10K. But it may have problem of discharge temperature over than compressor limit (115oC & 120oC) by this control method. Then it seems that compressor can not operate in this zone. Recommendation for solving the problem Discharge superheat [DSH] control for this area is recommended. The control value of DSH is between 20-30 K. Suction superheat by this control will be close to zero K or a little wet refrigerant. By this method, expansion valve will open more and discharge temperature will reduce to be lower than the limit. Furthermore, this method can improve system efficiency. Note: DSH control method has no reliability problem from liquid back if DSH is more than following limit. Scroll compressor DSH limit is > 10 K, and Twin rotary compressor DSH limit is > 20 K.
4.3 Liquid back protection (Refer to General specification No.9)
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Compressor can not operate in liquid back condition. It should be protected by; 1. Suction superheat control Suction superheat should be more than 0K. (SSH = Ts – Tssat) Note: Ts = Suction temperature. Tssat = Saturated temperature from suction pressure. 2. Discharge superheat control Discharge superheat should be more than 10K for Scroll compressor and 20K for Twin rotary compressor. (DSH = Td-Tdsat) Note: Td = Discharge temperature. Tdsat = Saturated temperature from discharge pressure. 3. Control % of refrigerant mixed in compressor oil % of oil concentration by weight should be controlled to be more than 50%. The percentage can be measured in 2 ways. 3.1 Direct measurement Take mixing oil & Refrigerant from compressor and measure weight of oil and refrigerant. 3.2 Calculation from oil property chart By measuring of oil pressure (discharge pressure) and oil temperature (at bottom shell of compressor), the calculation of mixing % can be done from oil property chart. (Oil property chart is to be provided from SCI) 4.4 Starting Function Requirement Scroll Compressor should be started at 50-60 rps and kept running at the speed until Pressure difference is satisfied compressor specification and DSH is greater than compressor limit (10 K for scroll or 20 K for rotary). This is to warm up the system and protect oil leaving out from the compressor. 4.5 Compressor stopping control method Normally compressor should be stopped by reducing the speed to the minimum level before stop the compressor. In case of emergency stop, direct cut off of power supply can be done. It does not have any effect to the compressor reliability. 4.6 Acceleration and Deceleration limit Case 1 for normal control: It should not be faster than 2 rps/sec. Case 2 for protection mode: Acceleration and Deceleration should not be faster than 7 rps/sec for Scroll compressor 5 rps/sec for Twin rotary compressor. For emergency stop, it can be stopped suddenly. 4.7 Compressor speed limit for defrost. For Scroll compressor, during changing running mode from heating to cooling or cooling to heating, It is not necessary to stop compressor but compressor speed during changing 4-way valve should be lower than 40 rps (Figure 7).
Scroll Compressor Speed Limit for Defrost
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Figure 7 Compressor control for Defrost 4.8 Piping resonance control Inverter compressor can vary its speed widely, so some running speeds, can be the same as a natural frequency of piping. It may be affected to piping crack. Therefore, a controller must be designed to have a skip frequency function. 4.9 Crankcase heater and Accumulator Crankcase heater and Accumulator need to install in case of refrigerant charge amount more than the limit. 4.9.1 Limit for Scroll A-Series = 4.5 kg. (for R407C,R410A) 4.9.2 Limit for Scroll B-Series = 5.2 kg. (for R407C,R410A) 4.9.3 Limit for Twin rotary S-Series = 1.4 kg. (for R410A) 4.9.4 Limit for Twin rotary T-Series = 3.5 kg. (for R410A) 4.10 Crankcase heater control Crankcase heater should open after shell temperature lower than 5 oC (for R410a) and o 15 C (for R407C)
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5. Testing 5.1 Performance (COP, SEER, APF) 5.1.1 Refrigerant charge amount selection Inverter compressor can deliver wide range of capacity. The best refrigerant charge amount should be set from the best COP at maximum using hour per year. This selection method gives the best SEER of the system. 5.2.2 After getting the best refrigerant charge amount, performance testing in accordance with each country standard should be done If the standard doesn’t exist, the test can be done as per the following SEER concept. Recommendation of SEER concept: 1. Measure system COP at High load and low load. 2. Measure system COP at least 3 speeds of compressor (Minimum, rated and maximum speed) 3. Calculate SEER by temperature map of each country. 5.2 Operating limit and compressor protection. Check compressor protection by all severe conditions of the system. All protection from software and hardware should be able to control the compressor to work in operating area at all cases. Recommended running condition for checking 5.2.1 Maximum Piping Length. 5.2.2 Maximum and Minimum load condition. (Highest and Lowest ambient temperature or Highest and Lowest water temperature) 5.2.3 Maximum refrigerant and minimum refrigerant charge amount. 5.2.4 Defrost mode. 5.3 Minimum oil level checking At all running conditions of the system, the oil amount in the compressor should be higher than minimum limit of compressor in each series. Example For A series scroll compressor, the minimum oil level in the compressor is 300 cc. For B series scroll compressor, the minimum oil level in the compressor is 450cc. For S series Twin rotary compressor, the minimum oil level in the compressor is 180cc. For T series Twin rotary compressor, the minimum oil level in the compressor is 320cc. The minimum oil amount can be checked by using a sight glass compressor. (The sight glass compressor can be provided from SCI upon request), If the oil amount is lower than minimum level during testing, oil separator is recommended to install. Recommended condition for checking 1. Start up condition: Start compressor at lowest ambient temperature. 2. Defrost condition. 3. Stable condition: Lowest Evaporating Temp, Highest Condensing Temp and Highest discharge temp. Keep running about 3-4 Hr.
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Recommendation for oil separator: It should be used in case of 1. Multi Indoor unit 2. Long piping application. (Evaporator and condenser is a split type and piping length is over than 5 m)
450 CC
300 CC
Scroll A-Series
Scroll B-Series
200 cc
SNB Compressor
320 cc
TNB Compressor
5.4 Noise and Vibration Testing The compressor should be tested at all speed range; minimum to maximum speed, increase step by step at 1rps interval) to find abnormal piping vibration. The compressor should be controlled to skip running at some particular speed which creates the same frequency at the piping natural frequency to prevent piping crack. Recommendation for Insulating Compressor 1. SCI compressor is high pressure shell type. To improve system efficiency, Insulating compressor is recommended. 2. To reduce high frequency noise from motor driving, Insulating compressor is recommended.
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5.5 Field Test Field test of the system should last at least 1 season (Cooling mode and Heating Mode). This is to make sure that the system does not have any problem in actual operating condition. Recommendation 1. Pressure and temperature data should be recorded carefully as it will be useful for reviewing if problems happen. 1.1 Discharge & suction pressure 1.2 Discharge & suction temperature 1.3 Ambient temperature
TDCS10J001 / Rev. 3 / Apr 08, 2016
10
900
PARIS_ ORLY
Hr/year
800 700
BREST LYON
600
BORDEAUX
500 400 300 200 100 0 -12 -10 -8
-6
-4 -2
0
2
4
6
8
10 12 14 16 18 20 22 24 26 28 30 32 34 36 o
Ambient Temp( C)
Figure 1 Ambient Temperature in France Temperature map of each country is different. To design inverter system, a chart of heat/cool load and using range should be firstly defined.
Figure 2 Minimum and Maximum capacity calculation of Paris in France
TDCS10J001 / Rev. 3 / Apr 08, 2016
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In Paris, heating mode runs at ambient temperature from -6 to 12 oC, Cooling mode runs at ambient temperature from 20 to 33 oC The data can be conversed to maximum and minimum capacity requirement. 1.2 COP or SEER Level Requirement COP or SEER requirement of system for cooling and heating mode should be defined. 1.3 Safety Standard Requirement EN14511, APF, ARI 210/240, EMC, PF, Others 2. Compressor Selection 2.1 Compressor Size The Capacity and COP requirement from No.1 is used for compressor selection. If a selected compressor is too small, the compressor will run at High speed, resulting to a drop in system SEER. If a selected compressor is too big, the compressor will switch. On and Off at low capacity control, resulting to a poorer control over temperature and humidity. To get the highest SEER and highest control quality, maximum capacity should match with compressor speed not more than 100 rps. 2.2Refrigerant (R407C or R410A) SCI compressors for both R407C and R410a have the same wide-range operating area. The difference is only the maximum condensing temperature. Maximum condensing temperature for R407C is 68oC Maximum condensing temperature for R410A is 65oC If a required water temperature is not over than 60oC in Heat Pump, SCI recommends to use R410A as it delivers better efficiency than R407C. 2.3 DC or AC Inverter DC compressor gives better efficiency than AC compressor at low speed(Figure 3). Thanks to a lower loss of DC motor. From this advantage, higher SEER can be achieved from DC Compressor. Device comparison between DC and AC Inverter system 1. Compressor difference DC compressor has a permanent magnet at rotor. 2. Driver difference Driver Hardware is the same. Driver software is different. 3. Controller is the same.
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System COP DC Compressor AC Compressor
Compressor Speed Figure 3 Motor comparison between AC and DC 3. Driver Selection 3.1 Driver Size. Driver size should match with the maximum current of compressor. Maximum current of compressor can be calculated from compressor performance curve at overload condition (ET 12oC, CT 65oC for R410A compressor), at the maximum speed of compressor as set from No.2. 3.2 Driving Method (PWM, PAM, sine wave, square wave) Driving method is affected to system efficiency, system quality control, and compressor reliability and driver price. Some driving method can not drive compressor in some load condition. We recommend using only verified drivers that have been passing SCI quality checking. 3.3 Compressor Protection Driver should have software and hardware protection for compressor as inverter compressor does not have any self protection system. Recommend compressor protections from driver are Reverse phase, phase loss and demagnetize protection (for DC motor). 3.4 Communication Digital signal: RS485 Analog signal: DC 0-10 Volt Driver communication should be matched with your controller communication. 3.5 EMC, Harmonics, Others requirement. All requirements should pass standard level. EMC Directive: 1. For current < 16 amp should pass EN61000-3-2 2. For current >16 and < 75 amp should pass EN61000-3-12 Harmonics: 1. For current > 16 amp per phase should pass EN61000-3-4
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4. Controller design for compressor protection. Inverter compressor is not self – protected. It should be protected by Driver and Controller. 4.1 Compressor operating limit. Customer have to check operating limit for specific model from operating area document (Download from technic.siamcompressor.com or request from marketing department), as shown in Figure 4. And compressor must be running under its operating area at all times. 4.2 Compressor discharge temperature limit. (Refer to General specification No.6-8) SCI Scroll and Rotary compressor is a high pressure shell type. Compressor motor was designed to cool down by discharge gas, therefore, temperature of discharge gas must be controlled not to be higher than the limit So, Discharge temperature have to be controlled within envelope limitation in each area.
Figure 4 Example of Operating area and Discharge temperature limit
4.3 Compressor oil circulation (Refer to General specification No.5) SCI Scroll compressor uses Pressure difference between Pd and Ps to supply oil, so pressure different have to satisfied oil supply limit for each compressor model. Recommendation for discharge temperature measuring position: 1. at top shell of scroll compressor. 2. at discharge pipe of Scroll and Twin Rotary, not further than 15 cm from compressor shell
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Recommendation for discharge temperature protection control (Figure 5): The compressor should not be stopped too often. To increase the control quality, the controlling point should be set before reaching the compressor stopping limit. Example: Separating the control zone; Normal zone and protection zone.
Figure 5 Discharge temperature control procedure The control concept can be applied to the other compressor’s limits too. It can improve system control quality. Recommendation for discharge temperature control in high compression zone.
High Compression Zone
Figure 6 High compression area
Td Control for High compression zone In general system, superheat control is at suction side. The control value is between 5-10K. But it may have problem of discharge temperature over than compressor limit (115oC & 120oC) by this control method. Then it seems that compressor can not operate in this zone. Recommendation for solving the problem Discharge superheat [DSH] control for this area is recommended. The control value of DSH is between 20-30 K. Suction superheat by this control will be close to zero K or a little wet refrigerant. By this method, expansion valve will open more and discharge temperature will reduce to be lower than the limit. Furthermore, this method can improve system efficiency. Note: DSH control method has no reliability problem from liquid back if DSH is more than following limit. Scroll compressor DSH limit is > 10 K, and Twin rotary compressor DSH limit is > 20 K.
4.3 Liquid back protection (Refer to General specification No.9)
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Compressor can not operate in liquid back condition. It should be protected by; 1. Suction superheat control Suction superheat should be more than 0K. (SSH = Ts – Tssat) Note: Ts = Suction temperature. Tssat = Saturated temperature from suction pressure. 2. Discharge superheat control Discharge superheat should be more than 10K for Scroll compressor and 20K for Twin rotary compressor. (DSH = Td-Tdsat) Note: Td = Discharge temperature. Tdsat = Saturated temperature from discharge pressure. 3. Control % of refrigerant mixed in compressor oil % of oil concentration by weight should be controlled to be more than 50%. The percentage can be measured in 2 ways. 3.1 Direct measurement Take mixing oil & Refrigerant from compressor and measure weight of oil and refrigerant. 3.2 Calculation from oil property chart By measuring of oil pressure (discharge pressure) and oil temperature (at bottom shell of compressor), the calculation of mixing % can be done from oil property chart. (Oil property chart is to be provided from SCI) 4.4 Starting Function Requirement Scroll Compressor should be started at 50-60 rps and kept running at the speed until Pressure difference is satisfied compressor specification and DSH is greater than compressor limit (10 K for scroll or 20 K for rotary). This is to warm up the system and protect oil leaving out from the compressor. 4.5 Compressor stopping control method Normally compressor should be stopped by reducing the speed to the minimum level before stop the compressor. In case of emergency stop, direct cut off of power supply can be done. It does not have any effect to the compressor reliability. 4.6 Acceleration and Deceleration limit Case 1 for normal control: It should not be faster than 2 rps/sec. Case 2 for protection mode: Acceleration and Deceleration should not be faster than 7 rps/sec for Scroll compressor 5 rps/sec for Twin rotary compressor. For emergency stop, it can be stopped suddenly. 4.7 Compressor speed limit for defrost. For Scroll compressor, during changing running mode from heating to cooling or cooling to heating, It is not necessary to stop compressor but compressor speed during changing 4-way valve should be lower than 40 rps (Figure 7).
Scroll Compressor Speed Limit for Defrost
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Figure 7 Compressor control for Defrost 4.8 Piping resonance control Inverter compressor can vary its speed widely, so some running speeds, can be the same as a natural frequency of piping. It may be affected to piping crack. Therefore, a controller must be designed to have a skip frequency function. 4.9 Crankcase heater and Accumulator Crankcase heater and Accumulator need to install in case of refrigerant charge amount more than the limit. 4.9.1 Limit for Scroll A-Series = 4.5 kg. (for R407C,R410A) 4.9.2 Limit for Scroll B-Series = 5.2 kg. (for R407C,R410A) 4.9.3 Limit for Twin rotary S-Series = 1.4 kg. (for R410A) 4.9.4 Limit for Twin rotary T-Series = 3.5 kg. (for R410A) 4.10 Crankcase heater control Crankcase heater should open after shell temperature lower than 5 oC (for R410a) and o 15 C (for R407C)
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5. Testing 5.1 Performance (COP, SEER, APF) 5.1.1 Refrigerant charge amount selection Inverter compressor can deliver wide range of capacity. The best refrigerant charge amount should be set from the best COP at maximum using hour per year. This selection method gives the best SEER of the system. 5.2.2 After getting the best refrigerant charge amount, performance testing in accordance with each country standard should be done If the standard doesn’t exist, the test can be done as per the following SEER concept. Recommendation of SEER concept: 1. Measure system COP at High load and low load. 2. Measure system COP at least 3 speeds of compressor (Minimum, rated and maximum speed) 3. Calculate SEER by temperature map of each country. 5.2 Operating limit and compressor protection. Check compressor protection by all severe conditions of the system. All protection from software and hardware should be able to control the compressor to work in operating area at all cases. Recommended running condition for checking 5.2.1 Maximum Piping Length. 5.2.2 Maximum and Minimum load condition. (Highest and Lowest ambient temperature or Highest and Lowest water temperature) 5.2.3 Maximum refrigerant and minimum refrigerant charge amount. 5.2.4 Defrost mode. 5.3 Minimum oil level checking At all running conditions of the system, the oil amount in the compressor should be higher than minimum limit of compressor in each series. Example For A series scroll compressor, the minimum oil level in the compressor is 300 cc. For B series scroll compressor, the minimum oil level in the compressor is 450cc. For S series Twin rotary compressor, the minimum oil level in the compressor is 180cc. For T series Twin rotary compressor, the minimum oil level in the compressor is 320cc. The minimum oil amount can be checked by using a sight glass compressor. (The sight glass compressor can be provided from SCI upon request), If the oil amount is lower than minimum level during testing, oil separator is recommended to install. Recommended condition for checking 1. Start up condition: Start compressor at lowest ambient temperature. 2. Defrost condition. 3. Stable condition: Lowest Evaporating Temp, Highest Condensing Temp and Highest discharge temp. Keep running about 3-4 Hr.
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Recommendation for oil separator: It should be used in case of 1. Multi Indoor unit 2. Long piping application. (Evaporator and condenser is a split type and piping length is over than 5 m)
450 CC
300 CC
Scroll A-Series
Scroll B-Series
200 cc
SNB Compressor
320 cc
TNB Compressor
5.4 Noise and Vibration Testing The compressor should be tested at all speed range; minimum to maximum speed, increase step by step at 1rps interval) to find abnormal piping vibration. The compressor should be controlled to skip running at some particular speed which creates the same frequency at the piping natural frequency to prevent piping crack. Recommendation for Insulating Compressor 1. SCI compressor is high pressure shell type. To improve system efficiency, Insulating compressor is recommended. 2. To reduce high frequency noise from motor driving, Insulating compressor is recommended.
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5.5 Field Test Field test of the system should last at least 1 season (Cooling mode and Heating Mode). This is to make sure that the system does not have any problem in actual operating condition. Recommendation 1. Pressure and temperature data should be recorded carefully as it will be useful for reviewing if problems happen. 1.1 Discharge & suction pressure 1.2 Discharge & suction temperature 1.3 Ambient temperature
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