Ten Taboos in VRF Multi-Split Central Air Conditioning Installation
VRF (Variable Refrigerant Flow) central air conditioning installation is indeed said to be "30% product, 70% installation," as the installation process directly determines the later cooling effect, energy consumption, and service life. Based on publicly available information, the "ten forbidden zones" commonly emphasized in VRF installation projects mainly focus on the following key aspects.
I. On-site material storage
Materials should be stacked neatly and orderly, with both ends sealed to ensure cleanliness. Copper pipes should be placed on shelves that are well-ventilated, dry, and at least 300mm above the ground.
II. Outdoor Unit Installation
1. Selection of outdoor unit installation location
The outdoor unit of the air conditioner must be at least one meter away from the wall to ensure heat dissipation and provide sufficient space for maintenance.
2. Basic Construction
The foundation must be constructed according to the installation dimensions of the equipment and have sufficient load-bearing capacity. The foundation must be level.
3. Outdoor unit in place
When hoisting the outdoor unit, keep the machine level and add soft padding to the contact area between the machine body and the hoisting rope to prevent wear or scratches on the machine.
Place shock-absorbing pads at the mounting holes and stress points where the outdoor unit contacts the foundation, and secure them with nuts.
III. Indoor Unit Installation
1. Hanging bracket manufacturing and selection
After determining the length of the suspension rod based on the indoor unit's installation height and the floor height, the material is cut.
2. Indoor unit installation
Use an infrared locator to determine the installation position of the indoor unit's hanging rod, mark it, and then drill holes with an electric drill.
The indoor unit should be installed in a location that allows for the drainage of condensate, and the ductwork should be easy to install and ensure smooth airflow.
A fully threaded hanger rod must be used, and the indoor unit must be secured with double nuts to ensure that the machine is firmly suspended.
After the indoor unit is installed, it must be leveled.
Throttling components must be installed vertically upwards and horizontally; tilting or inversion is prohibited, and attention must be paid to the connection direction during connection.
The indoor unit is covered with a dust cover to prevent a large amount of dust from entering the machine and affecting its operation.
Ensure sufficient installation and maintenance space around the indoor unit, and organize the supply and return airflow reasonably.
IV. Refrigerant Piping Installation
1. Bracket Installation
The distance between the brackets should not be too large, and the installed brackets must be arranged neatly.
2. Refrigerant piping installation
Cut copper pipes to the appropriate length using a cutter.
Clean the burrs at the port and the copper pipe debris inside the pipe.
3. Refrigerant pipe protection
If piping cannot be connected to the indoor or outdoor unit in a timely manner, it must be sealed to prevent dust, moisture, etc. from entering; when piping passes through the wall, sleeves must be added and sealed in a timely manner for protection.
4. Branch pipe installation
Branch pipes cannot be replaced by tees; they can only be installed horizontally or vertically. The horizontal straight pipe section between the copper pipe bend and the adjacent branch pipe must be ≥1M; the horizontal straight pipe section distance between two adjacent branch pipes must be ≥1M; the horizontal straight pipe section distance connecting the indoor unit after the branch pipe must be ≥0.5M.
5. Expansion tube connection
For copper refrigerant pipe connections, expansion fitting must be used; flaring fitting is prohibited.
6. Expand the flared mouth
When flaring the pipe opening with a flaring tool, the opening should be smooth and free of burrs, and the flared opening should be free of deformation and cracks. For nut connections, two adjustable wrenches must be used.
7. Nitrogen-filled welding of refrigerant pipes
To ensure construction safety, the nitrogen cylinder must be connected to a pressure reducing valve, and the nitrogen pressure should be controlled at 0.2-0.3 kcal/cm² during welding. Determine the nitrogen path, insert the nitrogen pipe into the inlet of the refrigerant pipe to be welded and seal it, open the nitrogen cylinder valve, adjust the nitrogen flow rate using the pressure reducing valve, and finally carry out the welding.
8. Refrigerant pipe airtightness test
Connect the gas and liquid lines together, extend a pressure gauge through the connection, and seal the connection. For R22, use 28 kg/cm² nitrogen for pressure testing (40 kg/cm² for R410A systems). Note the pressure correction before and after the test; each +1°C will result in a +0.1 kg/cm² pressure change. Record both the test temperature and the confirmed temperature.
9. Refrigerant pipe purging
In principle, top-down or horizontal blowing should be used for decontamination, with a blowing pressure of 5 kg/cm², to ensure that there are no impurities in the system. The following blowing method should be used:
A. Hold a suitable sealing material against the main air pipe opening on the indoor unit's air side;
B. Gradually pressurize the tube with nitrogen gas. When the pressure increases to an unbearable level, suddenly release the pressure from the tube opening.
Repeat steps A and B to perform repeated purging.
10. Refrigerant pipe insulation repair
Cut the insulation material to the required gap using a utility knife. Apply glue to the ends of the insulation pipe. Pull the two ends apart, insert the insulation material, and glue the joints together.
V. Condensate pipe installation
1. Condensate pipes should be installed with a slope of 1/100.
2. When installing a vent, two elbows must be added so that the vent faces downwards to prevent dust and other contaminants from falling into the pipe and clogging it.
3. Horizontal drain pipes must avoid backflow to prevent poor drainage.
4. For models equipped with a booster pump, the height of the booster pipe must not exceed the maximum value specified by the equipment, and no vents may be installed in the booster section.
5. The spacing between horizontal pipe supports is generally 0.8~1.2M, and should not be too large, otherwise it will cause deflection and form air pockets.
6. For indoor units with high negative pressure at the drain outlet of the water collection pan, a water trap must be installed in the drain pipe. After installation, a full water flow test must be performed.
VI. Installation of Insulation for Piping Systems
1. The insulation material for refrigerant pipes should be closed-cell foam insulation material, flame-retardant B1 grade, and heat-resistant exceeding 120°C. When the outer diameter of the copper pipe D ≤ 12.7 mm, the insulation layer thickness should be ≥ 15 mm; when the outer diameter of the copper pipe D ≥ 15.88 mm, the insulation layer thickness should be ≥ 20 mm.
2. Condensate pipes should be insulated with flame-retardant B1-grade rubber and plastic insulation cylinders, with an insulation layer thickness of 10mm.
3. Pipes must be sleeved when passing through walls.
VII. Signal cable installation
1. A dedicated power supply line must be installed, and the allowable voltage fluctuation range is ±10% of the rated voltage; the power supply capacity must be sufficient, the cable diameter must meet the requirements, and there must be a corresponding circuit breaker protection device; the grounding system must be reliable, and if the air conditioner outdoor unit is installed at the highest point of the building, attention should be paid to lightning protection.
2. The signal cable must be a three-core shielded cable, and the shielding layer of the signal cable must be connected to the grounding of the electrical control box sheet metal.
8. Vacuum drying
Vacuum must be drawn simultaneously from both the gas and liquid sides; the ultimate vacuum of the vacuum pump must reach -756 mmHg or below, and its discharge capacity must reach 4 liters/second or above; the vacuum pump used for the R410A system must be equipped with a check valve, or a vacuum pump with a check valve must be used.
9. Add refrigerant
Calculate the refrigerant addition amount based on the actual liquid pipe size and length using the formula, and record the added refrigerant amount in the outdoor unit refrigerant addition table; never estimate the refrigerant amount by measuring operating current, pressure, etc.
10. Debugging
Confirm that the number of indoor units connected matches the number displayed on the outdoor unit's digital display; turn on the unit and check if the drainage is unobstructed, if there are any faults in the indoor unit's electrical control board, and if the unit's operating current and inlet/outlet air temperatures are within the allowable range.
Finally, here are ten prohibitions for installing multi-split air conditioning systems:
1. It is prohibited for indoor units of a unified system to not be powered by a unified power supply.
2. Carbon tetrachloride must not be used to clean pipelines.
3. Welding of pipelines without nitrogen protection is prohibited.
4. Do not install the indoor and outdoor unit branch pipes horizontally.
5. It is prohibited to use "copper-aluminum connecting pipes" instead of copper pipes for air conditioning system installation.
6. It is forbidden to insulate gas and liquid two-phase pipelines together.
7. Outdoor units must not be installed in locations with poor air supply and return.
8. It is prohibited to install multi-split air conditioners in computer rooms or similar locations.
9. It is forbidden to bundle control lines (communication lines) and power lines (high voltage) together.
10. It is prohibited to select cables that do not meet the wire diameter requirements in the technical manual.
