Air Balance Multizone, How to air balance a multizone air system

Air Balance Multizone speaks to how to air balance a multizone air system serving a building.

Multizone systems are used primarily in schools, small office buildings and additions to existing buildings. These are normally low pressure systems although high pressure systems are used in special situations.

Procedure to air balance multizone air system:

Check and note the following items on the supply and return fans.

  • Correct fan rotation.
  • Filter condition.
  • Cooling coil condition. Set the system up to operate with maximum return air and minimum outside air. Set all thermostats to full cooling and verify that the mixing dampers go to full cool position.
  • Balance Multizone Fans

    The following preliminary data should be obtained at the supply and return fans to air balance multizone system.

  • Fan and motor RPM.
  • Motor current and voltage.
  • Fan, coil and filter static pressures.
  • Nameplate data on the fans and motors.
  • Motor sheave, fan pulley and belt sizes.

    Traverse all supply zones and the return system.

    Adjust the supply and return fan deliveries to approximately 5% above the design CFM. If the supply system zones are greater than 20% out of balance, they should be proportionally balance before changing the supply fan.

    Adjust each zone CFM delivery to design conditions.

    Make preliminary outlet readings and adjust each outlet CFM delivery conditions. No adjustments should be made during the final set of readings.

    Balance the return system.

    The following final data should be obtained at the supply and return fans.

    Check the following controls.

  • Economizer section - function, calibration and dampers.
  • Face and bypass dampers - function and calibration.
  • High temperature limit shutoff - function and calibration.
  • Low temperature limit shutoff - function and calibration. Adjust the hot and cold decks to design settings. Measure the hot and cold deck temperatures. Measure the temperature in each zone at the traverse point or the first outlet. Any zone which a temperature more than 3 degrees above the cold deck temperature should have its mixing dampers inspected and corrected for excess leakage. To air balance multizone system set all zone thermostats to full heating one at a time. Verify that each thermostat controls the proper mixing dampers and that the dampers go to the full heat position. Read one outlet on each zone. Any zone that has a change of more than 10% should have all outlets read and this fact noted in the report. To air balance multizone system measure and adjust the hot and cold deck temperatures. Measure the temperature in each zone at the traverse point or the first outlet. Any zone which has a temperature less than 3 degrees below the hot deck temperature should have it's mixing dampers inspected and corrected for excess leakage. Set the zone thermostats to 73 degrees and allow the system time to reach a modulated state where all spaces are satisfied. Read one outlet on each zone. Any zone that has a change of more than 10% should have all outlets read and this fact noted in the report. Record the zone thermostat set point and thermometer readings. Thermostats which indicate a difference of more than 3 degrees between these readings should be calibrated using an accurate thermometer. Set all controls to their normal set points.
  • Professional Air Balance

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