Plural Compressors Application Guidelines
Plural Compressors Application Guidelines 1. Introduction Scroll compressor of Siam Compressor [SCI] with state- of- the-art Frame Compliance Mechanism [so called “FCM Scroll Compressor”] has great ability and flexibility for varieties of applications by parallel assembly. FCM Scroll Compressor is capable of parallel connection of up to three compressors [so called Plural FCM Scroll Compressors]. SCI Plural FCM Scroll Compressor can be combined by either Inverter driven FCM Scroll Compressor or Standard FCM Scroll Compressors or both. This document describes recommendations for Plural application of SCI FCM Scroll Compressors. Test and adjustment in actual system design is necessary to reach an optimum point and get the best performance and highest reliability out of the system.
2. System Composition 2.1 Oil equalization SCI FCM Scroll compressor is a high pressure shell type which the pressure inside shell is discharge gas. Oil equalization is different from what being used in a low pressure shell type compressor. Oil equalization mechanism of SCI Plural FCM Scroll compressor works by balancing oil level from higher oil volume compressor to a lower one. Excess oil amount is forced out from the compressor by high pressure inside the shell to the others. The excess oil is supplied to suction line of compressor which having lower oil to equalize oil level of the total Plural system. Figure 1: Example of Oil equalization Diagram for Plural FCM Scroll Compressor. 1 Oil separator in the system (Turn on oil management function more often than 1 Compressor : 1 Oil separator)
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Figure 2: Example of Oil equalization Diagram for Plural FCM Scroll Compressor. 1 Compressor : 1 Oil separator
2.2 Suction Muffler FCM Scroll Compressor is equipped with suction check valve. There is possibility to create chattering sound at suction valve of the compressor which is stopping while the other compressors are running. Additional Suction Muffler at suction line of each compressor is required if the chattering sound happens in the compressor. For Inverter driven application with Inverter driven FCM Scroll Compressor, it is not necessary to add Suction Muffler as it is recommended that Inverter driven FCM Scroll compressor should be the last to stop.. 2.3 Check Valve Plural FCM Scroll Application requires check valves at Discharge line and Oil pipe of each compressor. Check valve at Discharge line prevents refrigerant flowing into stopping compressor while the other compressors are running. And check valve at Oil pipe protects oil flowing into stopping compressor while the other compressors are running. For the system which composes of an Inverter driven FCM Scroll Compressor, it is not required any discharge check valve at the Inverter FCM Scroll Compressor as it is recommended that the compressor should be the first to start . 2.4 Stop valve
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Oil equalization system is not necessary when only one compressor operates in the system. At the operation, shutting off of stop valve at oil equalization line can be done to increase the system performance. Oil level in the active compressors will be reduced during starting period. Then the stop valve of oil equalization system should be opened at every starting time of any compressor for at least until oil level in all active compressors stable. Time requires for each system to stabilize oil level should be confirmed and identified by actual testing. 2.5 Capillary tube Size of capillary tube in the oil equalization system must be enough for oil flow. It is recommended that the size of capillary tube should have minimum flow coefficient (Cv) at 0.02. If the size of capillary tube has too large Cv, the system efficiency will be dropped. The initial capillary tube size for actual confirmation of oil equalization performance is inner diameter of 1.2 mm. with length 30 cm.. 2.6 Accumulator FCM Scroll Compressor has ability to handle liquid refrigerant in most of transient conditions such as starting, defrosting. A suction accumulator is not required in most systems, especially systems designed with electronic expansion valves or with thermostatic expansion valves. However, having continuously flood back of large liquid refrigerant will dilute the oil. Then lubrication performance at all sliding parts and bearings decreases, abnormal wear may occur. Installation of an additional accumulator at suction line can protect the negative effects to the compressor. The minimum capacity of the accumulator at 80%wt of total refrigerant charge amount is recommended.
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2.7 Oil Separator Oil separator is not required for most of the systems. However it is recommended to install oil separator for system which has high possibility to accumulate large amount of oil in the system especially for multi air condition system. 2.8 Crankcase Heater If the crankcase heater must be used, the crankcase heater must be installed at lower part of compressor shell. The crankcase heater must be energized during off cycles of compressor. When the compressor stopped for long time or at the initial start of the system in the field, the crankcase heater must be energized for at least 6 hours prior to start the compressor. The capacity of a crankcase heater depends on the application of compressor. The minimum capacity of crankcase heater should be 38 watts. Figure 2 is an example of crankcase heater installation.
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3. Piping The recommendation for pipe connection is shown as follows. Suction Pipe and Discharge pipe Horizontal Plane
Vertical Plane
Oil Pipe
Suction muffler
Top
Top
Bottom
Bottom
Example of Assembling Arrangements and Layout
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4. Operating Envelope Figure 7 is an envelope for Scroll Compressor model with R-407C : AE series and BE series
Figure 8 is an envelope for Scroll Compressor (inverter) model with R-407C : AEB series
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Figure 9 is an envelope for Scroll Compressor model with R-410A : AN series and BN series
Figure 10 is an envelope for Scroll Compressor (inverter) model with R-410A : ANB series
Discharge Temperature ≤ 120°C Suction Superheat > 0 K Discharge Superheat > 10 K
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5. Controls It is recommended to start only a compressor at a time. Just in case that there is inverter compressor in the combination, inverter compressor must be started first. And before starting another compressor, it is recommended to wait until the previous operated compressor has discharge superheat at least 10 K or suction superheat more than 0 K. At the start-up process, it is strongly recommended to run compressor at the speed of 50-60 rps for 3 minutes allowing it to reach stable stage of pressure and refrigerant temperature before adjusting to other speed and to create enough different pressure between suction side and discharge side which is enough to make oil supply in compressor and create enough sliding force of 4-ways valve. The minimum pressure difference to make oil supply is 0.4 MPaG for R-410A or 0.25 MPaG for R-407C. This is to ensure enough lubricating oil quantity in the compressors. If the speed is too fast, too much lubricating oil in compressor will be released into the system which can cause the lubricating oil level be lower than minimum limit. On the other hand, if the speed is too slow, the system cannot create pressure difference which causes insufficient oil supply in the compressor and insufficient sliding force of the 4-ways valve. In case of system with many indoor units, the starting speed can be set at more than 60 rps. To determine a proper starting speed in the first 3 minutes, please follow the “Oil Flow Control” chart as below. For combination of all non inverter-driven compressors, any sequence of start or stop compressor is allowed.
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Figure 9 is an example of compressors control with inverter-driven compressor
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6. Evaluate Oil level Actual test for Oil level confirmation in each compressor is recommended. The test shall be done with installation of sight glass compressors in the actual designed system and without oil equalization devices , or with shut off of the stop valve of oil equalization system. The test is to find the condition of oil shortage in the compressor. There are several severe conditions which oil level evaluation is needed. a. Transient condition of Compressor’s starting. The example of starting pattern is as shown in figure 9. There are two conditions for the evaluation. One condition is compressor starting during lowest temperature condition. Another condition is Flood starting; the condition when refrigerant completely condenses into the compressors’ shell at the lowest temperature. b. Continuous running at combination conditions of system’s boundary. The concerned factors with variation of oil level are Minimum/Maximum of operating & setting temperature, Minimum/Maximum of Heating/Cooling Load, Maximum piping length & Piping Height and Maximum refrigerant amount. When the condition of oil shortage has been found, the test should be repeated with oil equalization system to make sure that oil level in the compressor will be sufficient at those conditions. Figure 10 is an example of evaluation table condition of Air-Conditioning system. Conditions
Temperature
Indoor Temperature Outdoor Temperature
Mode
Min. Max. Min. Max.
Cooling Heating
System ’s Capacity Indoor’s Air Flow rate Total piping length Indoor unit above Outdoor unit Outdoor unit above Indoor unit Refrigerant amount
Min. Max. Max. Max. Max. Max. Max.
1
2
3
4
5
6
7
8
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O O O O
O O O O
O O O O
O
O
O O
O
O O
O
O O
O O O
O O
O O
O
O O O
O O O O
O
O
9
10
11
12
13
14
15
16
O O
O O
O O
O O
O
O
O
O
O O
O
O
O O
O
O
O O
O
O O
O O
O
O O
O O O
O O
O O
O O O
O O O O
O
O
TDCS08J001 / Rev. 2 / Sep, 2016
O O
O O
O O O
O O
O O
O O O
O O O O
O
O
O O
O O O
O O
O O
11
2. System Composition 2.1 Oil equalization SCI FCM Scroll compressor is a high pressure shell type which the pressure inside shell is discharge gas. Oil equalization is different from what being used in a low pressure shell type compressor. Oil equalization mechanism of SCI Plural FCM Scroll compressor works by balancing oil level from higher oil volume compressor to a lower one. Excess oil amount is forced out from the compressor by high pressure inside the shell to the others. The excess oil is supplied to suction line of compressor which having lower oil to equalize oil level of the total Plural system. Figure 1: Example of Oil equalization Diagram for Plural FCM Scroll Compressor. 1 Oil separator in the system (Turn on oil management function more often than 1 Compressor : 1 Oil separator)
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Figure 2: Example of Oil equalization Diagram for Plural FCM Scroll Compressor. 1 Compressor : 1 Oil separator
2.2 Suction Muffler FCM Scroll Compressor is equipped with suction check valve. There is possibility to create chattering sound at suction valve of the compressor which is stopping while the other compressors are running. Additional Suction Muffler at suction line of each compressor is required if the chattering sound happens in the compressor. For Inverter driven application with Inverter driven FCM Scroll Compressor, it is not necessary to add Suction Muffler as it is recommended that Inverter driven FCM Scroll compressor should be the last to stop.. 2.3 Check Valve Plural FCM Scroll Application requires check valves at Discharge line and Oil pipe of each compressor. Check valve at Discharge line prevents refrigerant flowing into stopping compressor while the other compressors are running. And check valve at Oil pipe protects oil flowing into stopping compressor while the other compressors are running. For the system which composes of an Inverter driven FCM Scroll Compressor, it is not required any discharge check valve at the Inverter FCM Scroll Compressor as it is recommended that the compressor should be the first to start . 2.4 Stop valve
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Oil equalization system is not necessary when only one compressor operates in the system. At the operation, shutting off of stop valve at oil equalization line can be done to increase the system performance. Oil level in the active compressors will be reduced during starting period. Then the stop valve of oil equalization system should be opened at every starting time of any compressor for at least until oil level in all active compressors stable. Time requires for each system to stabilize oil level should be confirmed and identified by actual testing. 2.5 Capillary tube Size of capillary tube in the oil equalization system must be enough for oil flow. It is recommended that the size of capillary tube should have minimum flow coefficient (Cv) at 0.02. If the size of capillary tube has too large Cv, the system efficiency will be dropped. The initial capillary tube size for actual confirmation of oil equalization performance is inner diameter of 1.2 mm. with length 30 cm.. 2.6 Accumulator FCM Scroll Compressor has ability to handle liquid refrigerant in most of transient conditions such as starting, defrosting. A suction accumulator is not required in most systems, especially systems designed with electronic expansion valves or with thermostatic expansion valves. However, having continuously flood back of large liquid refrigerant will dilute the oil. Then lubrication performance at all sliding parts and bearings decreases, abnormal wear may occur. Installation of an additional accumulator at suction line can protect the negative effects to the compressor. The minimum capacity of the accumulator at 80%wt of total refrigerant charge amount is recommended.
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2.7 Oil Separator Oil separator is not required for most of the systems. However it is recommended to install oil separator for system which has high possibility to accumulate large amount of oil in the system especially for multi air condition system. 2.8 Crankcase Heater If the crankcase heater must be used, the crankcase heater must be installed at lower part of compressor shell. The crankcase heater must be energized during off cycles of compressor. When the compressor stopped for long time or at the initial start of the system in the field, the crankcase heater must be energized for at least 6 hours prior to start the compressor. The capacity of a crankcase heater depends on the application of compressor. The minimum capacity of crankcase heater should be 38 watts. Figure 2 is an example of crankcase heater installation.
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3. Piping The recommendation for pipe connection is shown as follows. Suction Pipe and Discharge pipe Horizontal Plane
Vertical Plane
Oil Pipe
Suction muffler
Top
Top
Bottom
Bottom
Example of Assembling Arrangements and Layout
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4. Operating Envelope Figure 7 is an envelope for Scroll Compressor model with R-407C : AE series and BE series
Figure 8 is an envelope for Scroll Compressor (inverter) model with R-407C : AEB series
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Figure 9 is an envelope for Scroll Compressor model with R-410A : AN series and BN series
Figure 10 is an envelope for Scroll Compressor (inverter) model with R-410A : ANB series
Discharge Temperature ≤ 120°C Suction Superheat > 0 K Discharge Superheat > 10 K
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5. Controls It is recommended to start only a compressor at a time. Just in case that there is inverter compressor in the combination, inverter compressor must be started first. And before starting another compressor, it is recommended to wait until the previous operated compressor has discharge superheat at least 10 K or suction superheat more than 0 K. At the start-up process, it is strongly recommended to run compressor at the speed of 50-60 rps for 3 minutes allowing it to reach stable stage of pressure and refrigerant temperature before adjusting to other speed and to create enough different pressure between suction side and discharge side which is enough to make oil supply in compressor and create enough sliding force of 4-ways valve. The minimum pressure difference to make oil supply is 0.4 MPaG for R-410A or 0.25 MPaG for R-407C. This is to ensure enough lubricating oil quantity in the compressors. If the speed is too fast, too much lubricating oil in compressor will be released into the system which can cause the lubricating oil level be lower than minimum limit. On the other hand, if the speed is too slow, the system cannot create pressure difference which causes insufficient oil supply in the compressor and insufficient sliding force of the 4-ways valve. In case of system with many indoor units, the starting speed can be set at more than 60 rps. To determine a proper starting speed in the first 3 minutes, please follow the “Oil Flow Control” chart as below. For combination of all non inverter-driven compressors, any sequence of start or stop compressor is allowed.
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Figure 9 is an example of compressors control with inverter-driven compressor
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6. Evaluate Oil level Actual test for Oil level confirmation in each compressor is recommended. The test shall be done with installation of sight glass compressors in the actual designed system and without oil equalization devices , or with shut off of the stop valve of oil equalization system. The test is to find the condition of oil shortage in the compressor. There are several severe conditions which oil level evaluation is needed. a. Transient condition of Compressor’s starting. The example of starting pattern is as shown in figure 9. There are two conditions for the evaluation. One condition is compressor starting during lowest temperature condition. Another condition is Flood starting; the condition when refrigerant completely condenses into the compressors’ shell at the lowest temperature. b. Continuous running at combination conditions of system’s boundary. The concerned factors with variation of oil level are Minimum/Maximum of operating & setting temperature, Minimum/Maximum of Heating/Cooling Load, Maximum piping length & Piping Height and Maximum refrigerant amount. When the condition of oil shortage has been found, the test should be repeated with oil equalization system to make sure that oil level in the compressor will be sufficient at those conditions. Figure 10 is an example of evaluation table condition of Air-Conditioning system. Conditions
Temperature
Indoor Temperature Outdoor Temperature
Mode
Min. Max. Min. Max.
Cooling Heating
System ’s Capacity Indoor’s Air Flow rate Total piping length Indoor unit above Outdoor unit Outdoor unit above Indoor unit Refrigerant amount
Min. Max. Max. Max. Max. Max. Max.
1
2
3
4
5
6
7
8
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O O O O
O O O O
O O O O
O
O
O O
O
O O
O
O O
O O O
O O
O O
O
O O O
O O O O
O
O
9
10
11
12
13
14
15
16
O O
O O
O O
O O
O
O
O
O
O O
O
O
O O
O
O
O O
O
O O
O O
O
O O
O O O
O O
O O
O O O
O O O O
O
O
TDCS08J001 / Rev. 2 / Sep, 2016
O O
O O
O O O
O O
O O
O O O
O O O O
O
O
O O
O O O
O O
O O
11
