> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/user-guide/2d-building/building/hvac/space-hvac/variable-refrigerant-flow.md).
# Variable Refrigerant Flow
A Variable Refrigerant Flow (VRF) system regulates refrigerant flow to individual indoor units based on the specific cooling or heating demands of different zones. This dynamic control allows for precise temperature management in various spaces, enhancing energy efficiency. VRF systems are known for their flexibility, enabling simultaneous heating and cooling in different building areas.
### Outdoor Air / Person
Specify each zone's outdoor airflow rate in terms of litres per second per person.
### Supply Fan Total Efficiency
Specify the total efficiency of the supply fan. This is the ratio of the power delivered to the air to the electrical input power at maximum flow. This is also the product of the fan motor efficiency and fan (impeller) efficiency. The motor efficiency is the power delivered to the shaft divided by the electrical power input to the motor. The fan efficiency is the power delivered to the air divided by the shaft power. The power delivered to the fluid is the mass flow rate of the air multiplied by the pressure rise divided by the air density.
### Supply Fan Delta Pressure
Specify the pressure rise in pascals at full flow and standard conditions. Standard conditions are considered 20 degrees Celsius at sea level, 101325 Pa.
### Supply Fan Motor Efficiency
Specify the shaft power of the supply fan divided by the electrical power consumed.
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