Matters Concerning the Installation of Parallel Units [Part 2]

2025-04-11

III. Connection of the Refrigeration Pipeline:

The parallel compressor units produced in the factory are generally arranged with corresponding refrigeration pipelines, such as the liquid supply and return gas pipelines, according to the enterprise standards or the special requirements of the engineering contractors. Carefully check the numbers of the compressor and the refrigeration pipeline before installation. In addition, for some large systems, the liquid receiver and the unit are placed separately, and on-site connection of the liquid supply pipeline is required.
The pipeline system of the unit has been cleaned and dried before leaving the factory. External sundries may enter the system during on-site pipe connection. Therefore, care must be taken to prevent external sundries from entering the pipeline system during the installation of the pipeline. The installation of all components of the refrigeration system should be carried out in strict accordance with the industry installation specifications, and the construction should be carried out by personnel with relevant qualifications.
In order to prevent different degrees of equipment damage or pipeline rupture caused by strong vibration, collision, extrusion, etc. during equipment installation, it is recommended to pressurize the unit to 10Bar before pipeline connection, and if the pressure remains unchanged after 12-18 hours, the pipeline connection can be started. It should be noted that the angle valve of the suction sensor equipped with the unit has been closed before leaving the factory. Please do not open the angle valve without authorization during pressurization to avoid affecting the use accuracy of the sensor.
During the installation of the refrigeration pipeline, the following requirements should be followed:
4.1 For the suction and liquid supply pipelines, select the appropriate welding rod for welding according to the refrigeration installation specifications. When connecting and welding copper pipes, nitrogen protection welding must be used. Control the usage and dosage of the flux during welding to prevent internal contamination of the welded parts.
4.2 Do not expose the openings of the dried compressor or the drying filter to the atmosphere. Always cover and seal the opening parts to prevent contamination.
4.3 Only refrigeration-grade copper pipes can be used. The return gas pipeline should incline towards the compressor at a very small angle (a slope of 3/1000). The exhaust pipeline should incline towards the condenser at a very small angle (a slope of 2/1000).
4.4 When welding and connecting the pipeline, protect the delicate components (hoses, pressure switches, etc.) near the welding part.
4.5 When welding is required near the connection between the pipeline material and the valve, carefully remove the valve, and pay special attention to the connection between the valve and the pipeline material. If the valve is not convenient to remove, wrap them with a wet cloth.
In terms of the pipeline routing setting:
5.1 When the unit is higher than the evaporator: If the unit is higher than the evaporator (for example, the unit is placed on the second floor and the display cabinet is placed on the first floor), an oil return bend should be set at the joint between the horizontal return gas pipe of the evaporator and the rising vertical pipe according to the regulations. If the unit is much higher than the evaporator, it is necessary to consider setting an oil return bend at every rising suction section of about 6m.
5.2 When the unit is lower than the evaporator: If the unit is lower than the evaporator (such as the unit is placed on the first floor and the display cabinet is placed on the second floor), the return gas pipe should rise to the same level as the upper surface of the evaporator, and then run towards the unit.

5.3 Connection between the unit and the separated condenser: Generally, if the condenser is higher than the unit, for every 6 meters that the condenser is higher than the compressor unit, an additional oil return bend should be added to the rising section of the exhaust pipe. In addition, in the system where no one-way stop valve is installed in the exhaust part, the rising exhaust pipe should rise above the horizontal plane of the coil of the air-cooled condenser and then be connected to the condenser.
Fixing of the refrigeration pipeline: The refrigeration pipeline needs to be fixed and supported to avoid excessive pipeline vibration and noise. The fixing and support of the pipeline are generally completed by means of semi-fixed brackets and hangers. All semi-fixed pipeline clamps should be provided with insulating materials (such as silicone rubber gaskets) to prevent metal-to-metal contact. The straight pipe should be fixed and supported near both ends, and additional supports are required for longer pipelines. The layout of the pipeline brackets and hangers depends on the layout form of the pipeline and the stress situation of the pipeline. The maximum allowable distance of the pipeline brackets and hangers is mainly determined by the vertical load they bear.
Insulation of the refrigeration pipeline:
7.1 For low-temperature units, it is recommended to wrap the return gas pipeline from the evaporator to the parallel unit with a closed-cell insulation material with a thickness of at least 30mm. For medium-temperature units, it is recommended to wrap the return gas pipeline from the evaporator to the parallel unit with an insulation material with a thickness of at least 25mm. A low-temperature resistant adhesive should be applied between the insulation material and the pipeline to make them adhere closely.
7.2 The long liquid pipe exposed to a high-temperature environment should be insulated with an insulation material with a thickness of at least 13mm. The subcooled liquid supply pipe should be wrapped with an insulation material with a thickness of at least 13mm.
7.3 The return gas and liquid pipelines are strictly prohibited from being bundled with straps or welded together.
7.4 All insulation measures must comply with the on-site specifications and requirements.
Requirements for the pressure relief valve: In order to prevent the sudden increase in the pressure of the unit caused by unpredictable reasons such as fire and improve the safety factor of the unit operation, it is recommended to connect a pressure relief pipeline (about 1-1/8 inches) from the pressure relief valve of the unit's liquid receiver and lead the pipeline from the machine room to a safe area that will not cause asphyxiation. When the unit is in operation, it is absolutely not allowed to close the stop valve in front of the pressure relief valve.

IV. Requirements for Electrical Installation:

Most units have provided complete wiring points for power, control, remote alarm, etc. for users before leaving the factory. Refer to the electrical control diagram provided by the manufacturer in detail for electrical connection. In order to ensure the correct operation of the equipment and reduce the refrigeration interruption caused by power supply failures, the following preventive measures must be observed:
a) All electrical work must be completed in accordance with national electrical regulations and existing local regulations.
b) The supplied power should be consistent with the parameters on the unit nameplate.
c) A power supply with sufficient power should be provided.
d) The voltage fluctuation shall not exceed ±7%, and the allowable value of phase unbalance is 2%, and it shall not exceed 4% in a short time.
e) The control power is a single-phase power supply, 50Hz. Refer to the voltage requirements in the unit wiring diagram.
f) Before starting the parallel unit, ensure that all fuses and motor protections are in place and the wiring is firm.
System electrical connection:
2.1 Connect the power supply line of the unit to the wire splitter in the electrical control box.
2.2 Connect the power line of the condenser to the condenser motor contactor in the electrical control box according to the correct number.
2.3 If the condenser fan needs to be equipped with overheating protection, the thermal overload contact of the condenser fan can be connected in series to the control circuit of the condenser.
2.4 If the user needs to provide remote alarm information, each alarm signal (passive contact) of the unit can be led to the upper monitoring system by itself.
The power supply of the unit should meet the following conditions:
a) All control and safety switch circuits must be correctly connected according to the wiring diagram.
b) The phase (unbalance) shall not exceed 4.5%.
c) The normal working voltage of the system is 93%-107% of the nominal power supply voltage.
Without the consent of the manufacturer, it is strictly prohibited to privately modify the wiring in the factory.