Comprehensive! Piping and Installation of VRF (Variable Refrigerant Flow) System

2025-03-04

01 Permissible Length and Drop of Piping
Maximum Length, Maximum Drop between the Outdoor and Indoor Units, Drop between Indoor Units, Length from the First Diverter to the Farthest End
02 Selection of Connection Pipes between Indoor and Outdoor Units
Selection of Refrigerant Pipe Sizes, Sizes of Diverter Pipes
03 Three Principles for Refrigerant Piping Construction: Cleanliness, Dryness, and Air Tightness
04 Materials Required for Installation
Standard Copper Pipes

Use degreased and dephosphorized seamless red copper pipes.
The material and specifications should meet the requirements of the current national standards GB/T 1527 "Drawn Tubes of Copper and Copper Alloys" and GB/T 17791 "Seamless Copper Tubes for Air Conditioning and Refrigeration".
The wall thickness and hardness of the piping must meet the requirements in the table.
It should have a factory certificate of conformity and a quality certificate.
Thermal Insulation
It must comply with the national standards and should have a factory certificate of conformity and a quality certificate. Use foam rubber and plastic thermal insulation products with a fire protection rating of Class B1.
05 Tools Required for Installation
Professional installation tools can ensure the air tightness of the copper pipe system, avoiding refrigerant leakage of the equipment caused by poor construction in the future, which may affect the daily use of the air conditioner.
06 Installation Requirements and Methods of Diverters
It should be installed horizontally, and there should be a straight pipe of more than 500mm in front of and behind the diverter before turning.
The distance between two diverters should be more than 1000mm.
Requirements for Pipe Processing Technology
It is necessary to use a flaring tool for flaring. Using a screwdriver is strictly prohibited! Be sure to install the nut before starting flaring! After completion, check whether the surface of the flare is of uniform color, round, and confirm that there is no "halo", no "sharp edge", and no cracks. Otherwise, start the rework from cutting the pipe!
Copper pipes need to be expanded, welded, and provided with oil traps.
The height of the oil return trap is 10CM or 3-5 times the outer diameter of the copper pipe.
Method of Replacing Nitrogen for Welding Copper Pipes
Nitrogen shielded welding must be used;
The gauge pressure should be between 0.02MPa and 0.05MPa;
Continue to fill with nitrogen for protection after welding until it cools down to room temperature;
At the same time, the length from the welding joint of the piping to the bent part should not be less than the outer diameter of the pipe and not less than 100mm.
Support Requirements for Piping
The piping must be well supported and fixed, and the support distance is 1.0-2.0m.

Piping Flushing
After the piping welding is completed, before connecting to the indoor and outdoor units, carry out piping flushing;
Use dry nitrogen to blow out the impurities and moisture in the pipeline;
When the pipeline is relatively long, it should be flushed in sections;
Use nitrogen at 0.5MPa, block the pipe opening with insulating material. If it cannot withstand the pressure during the pressure increase, release it quickly.
Use white paper to check whether the flushing is clean when the nitrogen is ejected. Otherwise, repeat the flushing.
Air Tightness Test
Positions Prone to Leakage
When installing the refrigerant piping, at the connection ports with the indoor and outdoor units
Each welding part in the pipeline
Damage caused during the placement and transportation of refrigerant pipes
Inspection Steps (Nitrogen pressure test. To prevent equipment damage, the pressure holding time should not be too long)
Pressurize to 3kg/cm2 and maintain for 3 minutes.
Pressurize to 15kg/cm2 and maintain for 3 minutes.
Pressurize to 4.0Mpa (when not connected to the outdoor unit) and maintain for 24 hours (Pay attention to the influence of the ambient temperature. The empirical value of the nitrogen pressure change caused by the ambient temperature change: the pressure drops by 1.46Kg when the temperature drops by 10℃; the pressure rises by 1.46Kg when the temperature rises by 10℃).
07 Thermal Insulation of Refrigerant Piping
Prevent condensation and dripping, scalding, and reduce heat loss;
The thermal insulation material should have the characteristics of heat insulation, flame retardancy, and high temperature resistance;
All refrigerant piping of the indoor and outdoor units needs thermal insulation (diverter pipes, joints, elbows, etc.), and all gaps must be pasted well;
The gas pipe and the liquid pipe must be thermally insulated separately, and at the same time, pay attention not to press the thermal insulation cotton tightly;
The thermal insulation material should meet the requirements: the thermal conductivity λ ≤ 0.
040W/(m·K) at 20℃, and the moisture resistance factor ≥ 80.
The thickness of the thermal insulation cotton: when the outer diameter D of the copper pipe ≤ 12.7mm, the thickness ≥ 15mm; when the outer diameter D of the copper pipe > 12.7mm, the thickness ≥ 20mm.
08 Fabrication of Condensate Water Pipeline
The thickness of the anti-condensation material should be more than 10mm, and the flame retardant grade should reach Class B1 or above;
A vent hole should be set at the highest point of the drain pipe. At the same time, it should be noted that for the drainage branch pipe with an auxiliary lifting drainage pump, setting an exhaust hole is strictly prohibited.
To prevent the drain pipe from sagging downward, it should be assisted and fixed with hangers and other devices every 1 to 1.5m;
For those that are not insulated as a whole pipe, be sure to re-adhere the cut parts with glue.
09 Condensate Water Flow Test
Test of the natural drainage unit;
Test of the water pump drainage;
Test each indoor unit separately;
Block the drainage port and fill the condensate water pipeline with water.
10 Requirements for Communication Cable Wiring
a. All materials must pass the national CCC certification before they are allowed to be used.
b. When the total distance of the communication cable is within 100 meters, use a 2×0.75mm2 shielded twisted pair.

c. When the total distance of the communication cable is between 100 and 500 meters, use a 2×1.0mm2 shielded twisted pair.
d. When the total distance of the communication cable is greater than 500 meters, consult the factory according to the actual situation.
e. Shielded twisted communication cables must be used.
Key Points for Wiring
The wiring and piping should be numbered and connected correspondingly to prevent cross-connection errors.
11 Vacuum Drying
First Step: Run the vacuum pump for more than 2 hours. If the vacuum degree does not reach below -755mmHg (-100.7kPa) after running for 2 hours, it indicates that there is still moisture or a leak in the pipeline system. At this time, it should be run for another 1 hour. If the vacuum degree still does not reach below -755mmHg (-100.7kPa) after running for 3 hours, check whether there is an air leakage port.
Second Step: When the vacuum degree reaches -755mmHg (-100.7kPa), close the on-off valve, stop the vacuum pump from running, and leave the system for 1 hour. If the vacuum degree does not rise after 1 hour, it is considered qualified. Otherwise, it indicates that there is moisture or an air leakage port in the pipeline.
Precautions (Be sure to measure the vacuum degree with a vacuum gauge):
a: The vacuum pumping operation should be carried out simultaneously from the gas pipe and the liquid pipe. When pumping vacuum, the vacuum pump should not lose power, otherwise the lubricating oil in the vacuum pump may be sucked into the system. To prevent the lubricating oil in the vacuum pump from flowing back, an electronic check valve should be installed...
b: The exhaust volume of the vacuum pump should not be less than 40L/min. Before starting the operation, the vacuum gauge must be checked to ensure that its range can reach below -755mmHg (-100.7kPa).
c: After pumping vacuum and before adding refrigerant, the connection valve should not be replaced to prevent air from entering the system.
12 Refrigerant Addition