Economizer and Mixed Air

This checklist identifies Key Commissioning Test Requirements and Key Preparations and Cautions for the economizer and mixing section of an air handler. When writing a test, use this checklist to help ensure that these key areas have been covered. The buttons following the checklist items link to supporting information within the Functional Testing Guide and the Control System Design Guide.

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Test Guidance

Tips

Typical Problems

Design Issues

Control System Design Guide

Key Commissioning Test Requirements

• ___ 1. During design review, the following items were addressed to avoid issues during functional testing:
  • a) The control process provides reliable free cooling when conditions are appropriate under all operating conditions, including automatic and manual control modes.
  • b) Alarms are provided to alert the operating staff to operating conditions that indicate an economizer control failure, which could lead to energy waste and/or a freezestat trip.
  • c) Damper oversizing or high (VAV) flow turn-down ratios do not cause instability.
  • d) Precautions have been taken to avoid nuisance freezestat trips.
  • e) The controls designed to protect coils from freezing function correctly.
• ___ 2. The following "prefunctional" checks were completed and verified prior to performing a functional test (note that this is not a comprehensive list of all prefunctional checks):
  • a) Interlocks return the economizer dampers to safe and efficient positions when the air handling system is shut down.
  • b) Interlocks protect the air handling system and building areas from damage in the event of a failure of the economizer control process or a system component.
  • c) At all damper positions, there is good mixing of the outside air and return air streams, with the flow well-mixed prior to any sensors, coils, or flow branches.
• ___ 3. The economizer cycle is integrated properly with other building processes and systems in both normal and emergency control modes. Building processes and systems include, but are not limited to,building pressurization requirements, zone pressurization requirements, and minimum outdoor air requirements.
  • • Minimum outdoor air
  • • Economizer free cooling
  • • Building pressure control and return air heat recovery
• ___ 4. Building pressurization does not require excessive outside air to compensate for excessive envelope leakage.
• ___ 5. Interlocks disable the economizer cycle when it no longer provides an energy savings benefit.
• ___ 6. Minimum outside air flow rates are appropriate and controlled properly under all operating conditions.

Key Preparations and Cautions

• 1. General cautions as outlined in Section 12: General Precautions and Preparations (in the Functional Testing Basics module of the FT Guide) should be observed.
• 2. Safety interlocks such as the low temperature cut-out and the mixed air plenum low static pressure cut-out and permissive interlock functions must be verified early to protect the system from experiencing problems or catastrophic failures during functional testing.
• 3. If economizer testing occurs in extreme weather, the heating and cooling/dehumidification functions associated with the system should be functional to prevent undesirable air conditions within the space.

Page last updated: September 11, 2006