Overview

This procedure provides detailed guidance on how to commission a 100% fresh air unit (OAU) connected to a VRF system.
It covers all required inspection, testing, and operational checks to ensure proper refrigerant performance, airflow balance, and noise control.

1. General Commissioning Overview

There is no difference in outdoor unit control whether an Outdoor Air Unit (OAU) is installed or not in a refrigerant cycle — however, specific commissioning checks are required for the OAU itself.
Key checkpoints include:

  • Airflow volume and velocity (static pressure verification)

  • Cooling and heating test runs (superheat and subcooling values)

  • Solenoid valve operation

  • Drainage, noise, and vibration assessment

2. Airflow and Static Pressure Check

  • Confirm required airflow (Q) using either:

    • Rectangular outlet: Q=W×H×vQ = W × H × vQ=W×H×v

    • Circular outlet: Q=πR2×vQ = πR^2 × vQ=πR2×v

  • Target outlet velocity: < 5 m/s (for office applications).

  • If resistance at exhaust outlets is high, airflow volume decreases even if the static pressure setting is the same.

  • Adjust static pressure as needed to achieve design airflow.

3. Cooling Test Run Operation

Reference conditions: Outdoor 27°C / Setpoint 14°C

  • Superheat (ΔTshe = TH24 – TH22): 2°C ≤ ΔTshe ≤ 10°C

  • Discharge air temperature (TH25): ≥ Setpoint − 5°C

  • EEV pulse range: 45–1400 (45 = closed)

Deviations indicate:

  • Improper refrigerant charge or piping

  • Temperature sensor malfunction (TH21–TH25)

  • Incorrect external static pressure

4. Heating Test Run Operation

Reference conditions: Outdoor 7°C / Setpoint 28°C

  • Subcooling (ΔTsc = HPS Saturation Temp − TH22): 4°C ≤ ΔTsc ≤ 50°C

  • EEV pulse range: 45–1400

  • TH25: Warm air discharge must be confirmed

Issues may point to:

  • Poor refrigerant circulation

  • Incorrect charge

  • Static pressure imbalance or thermistor error

5. Solenoid Valve (SV21) Verification

During heating operation:

  • If other indoor units are in heating mode and the OAU is in thermostat-off condition, SV21 opens, allowing refrigerant flow.

  • When SV21 is open: TH21 ≈ TH22 ≈ TH25, and EEV closes (45 pulses).

  • When all indoor units stop, SV21 closes.
    Confirm correct open/close timing during operation.

6. Drainage, Noise, and Vibration

  • Water Check: No water should drip from the OAU during cooling.

  • Noise Check: There must be no hitting or vibration noise during any operating condition.

7. Verification and Documentation

Use the Commissioning Check Sheet to document results:

  • Record refrigerant circuit name and OAU address.

  • Log subcooling, superheat, discharge pressures (HPS/LPS), discharge air temperatures, and airflow.

  • Confirm no abnormal noise or water leakage.

  • Verify velocity < 5 m/s and that total airflow matches design requirements.

8. Reference – Refrigerant Pressure vs. Temperature

Page 11 provides a reference chart for R410A, indicating that at 2.58 MPa, the saturated liquid temperature is approximately 44°C.
This is essential for verifying refrigerant conditions during subcooling and superheat calculations.

Summary

To commission a 100% fresh air OAU:

  1. Verify airflow and static pressure meet design.

  2. Conduct both cooling and heating test runs, checking superheat and subcooling.

  3. Confirm proper SV21 and EEV operation.

  4. Ensure no abnormal noise, vibration, or drainage issues.

  5. Record all measurements on the commissioning sheet for compliance.