What should be considered before installing a VRF air conditioning system?
Things to confirm before installing a VRF multi-split air conditioner :
I. Load and System Selection (First)
Calculate the heating and cooling load for each room : Do not estimate based on area alone; focus on orientation, floor-to-ceiling windows, western exposure, rooftop, personnel and equipment heat dissipation, and external wall insulation. The load for shops and computer rooms should be increased.
System type determined : ordinary heat pump VRF (same mode), heat recovery VRF (partial room cooling, partial heating, suitable for large commercial use).
Capacity connection rate (over-sizing rate) : 50%~130% is the standard. For offices and residences with low simultaneous usage, 110%~130% can be used. For places with high simultaneous usage (restaurants, conference rooms), it is recommended to be ≤100%. Excessive over-sizing can easily lead to high temperature protection and insufficient heating.
Operating condition correction : The cooling capacity reduction caused by local extreme summer high temperature, winter low temperature, defrosting attenuation, and pipeline length and elevation difference is checked and corrected using the manufacturer's selection software.
II. Refrigerant Piping Limitations (VRF's Core Constraint)
All values are based on the selected brand sample and vary greatly between different brands .
to the equivalent pipe length from the outdoor unit to the furthest indoor unit , the total system pipe length, the length limit from the first branch pipe to the furthest indoor unit , and the height difference between the indoor and outdoor units : the limits differ depending on whether the outdoor unit is on top or bottom; the longer the pipe and the greater the height difference between indoor units in the same system, the more significant the reduction in cooling capacity. If necessary, outdoor units should be installed in sections (placed on refuge floors). The branch pipe model must be matched and installed horizontally; the copper pipe wall thickness and pipe diameter must strictly follow the manufacturer's table, and the oil return scheme cannot be changed arbitrarily: if the riser exceeds a certain height, an oil return bend must be added to ensure oil return to the compressor and prevent burn-out .
III. Site Space and Building Conditions
Indoor side
Ceiling height: The indoor unit of the air duct generally needs 270~300mm, with a maintenance port reserved (for electrical control and motor positions). Airflow organization: Avoid direct blowing and short circuits, and avoid obstruction by light troughs and beams; the indoor unit should not be placed close to the wall. Condensate drainage: Gravity drainage is preferred (slope ≥1%); if gravity drainage is not possible, a condensate lift pump + overflow alarm must be installed . Direct discharge into rainwater pipes and sewage pipes is prohibited, and water traps should be added if necessary to prevent odors and insects .
Outdoor unit location (of utmost importance)
Heat dissipation space: Allow sufficient space for air intake and exhaust around the perimeter to prevent hot air short-circuiting (atriums and narrow recesses are the most common sources of problems). Load-bearing capacity: Verify the load-bearing capacity of the roof and floor foundations, and install vibration damping pads/dampers. Maintenance space: Allow sufficient space in front for maintenance and core-extraction heat exchangers. Environment: Avoid oil fumes, corrosive gases, and dust; ensure organized drainage during winter defrosting to prevent freezing; keep away from bedrooms and offices, and conduct noise assessments and sound insulation measures .
IV. Electrical Conditions
The outdoor unit has an independent dedicated circuit and is not shared with other high-power equipment; the voltage, wire diameter, circuit breaker, and grounding are selected according to the maximum current in the sample, and a voltage drop margin is reserved. Communication signal lines (F1/F2) and high-voltage lines are laid separately, not parallel to each other in the same conduit, and not tangled, to avoid interference. Control schemes include wired control, remote control, centralized controller, building automation system (BAS), and gateway intelligent control, with pipeline and network cable positions reserved in advance .
V. Fresh air system, exhaust system and other supporting facilities
VRF only controls temperature and does not provide its own fresh air supply .
Calculate the fresh air load separately. Fresh air can be supplied by fresh air handling units or total heat exchangers. Fresh air should not be blown directly onto the return air vent of the indoor unit. Bathroom and kitchen exhaust should be independent, and negative pressure should not affect the airflow of the air conditioner .
VI. Noise, Vibration, Compliance and Safety
The noise from the outdoor unit affects sensitive rooms in the surrounding area; nighttime limits apply. For the indoor unit, choose a low static pressure, quiet model. Refrigerant safety: R410A/R32 and other refrigerants are recommended. R32 is a flammable refrigerant, so refrigerant concentration, ventilation, and leak alarm standards must be met. Fire safety: fireproof sealing of ducts and refrigerant pipes passing through fire compartments, fire dampers, and approval documents are required .
VII. Pre-construction, commissioning and after-sales confirmation
The construction contractor must have the brand's certification. VRF has extremely high requirements for welding, nitrogen protection, and vacuuming: the entire welding process must be purged with nitrogen, pressure tested for leaks, and vacuumed for a long time. It cannot be handled as simply as a split-type air conditioner. The refrigerant addition plan must be calculated based on the actual pipe length and diameter, and cannot be added based on guesswork. The drawings must be confirmed with the structure in advance regarding the pipe routing, branch pipe location, elevation, and beam penetration location, avoiding the main reinforcement. After-sales service: local maintenance, parts supply, and warranty terms .
