Return, Relief, and Exhaust

This checklist identifies Key Commissioning Test Requirements and Key Preparations and Cautions for a building's return, relief, and exhaust systems. 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

The following key commissioning test requirements for return, relief, and exhaust systems are similar to the requirements associated with the supply fans and drives. Note that many of the following test requirements pertain to issues that should be addressed and checked during design, construction, or initial start-up and TAB in order to successfully test each system.

• ___ 1. During design review, the following items were addressed to avoid issues during functional testing:
  • a) All fans have good access for control installation, maintenance, and component replacement.
  • b) Variable speed drive installation and operation requirements have been taken into account.
  • c) The VFDs and motors are compatible.
  • d) If necessary, the motor shaft is grounded.
  • e) The drive arrangement is suitable for the application.
  • f) The fan motor cannot run in the wrong direction, or the system can handle and correct it.
  • g) The air handler specification includes desirable options. For example, VFD-compatible motors or factory-installed backdraft dampers are specified.
  • h) Network failures and recovery does not result in unsafe system operating modes.
  • i) Life safety equipment and systems are viable and reliable, including smoke and fire control systems.
  • j) Pressures in open plenum returns (ceiling plenums) have been considered, ensuring that the plenum pressures will be satisfactory in all operating modes to minimize infiltration and prevent unintended movement of ceiling tiles. (Satisfactory pressures may be positive with respect to outside in warm, humid climates, or negative in cold climates, but should not be excessively positive or negative.)
  • k) Low pressure drop designs are used for fire and smoke dampers. (Example)
  • l) The system is designed to handle pressures created by the rapid closing of dampers.
• ___ 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) Any belt drives have been adjusted and aligned.
  • b) Drive settings and adjustments provide for safe and reliable system operation at peak efficiency levels in all operating modes. Verify that the VFD operates near 100% speed at full load (in other words, don’t use the VFD as a throttling device when the fan system is oversized).
  • c) Construction and installation changes from design do not increase the return, relief, and exhaust system pressure drop.
  • d) During construction, ducts are not contaminated with water, construction dust, or debris prior to installation.
• ___ 3. Backdraft dampers need to be tested for proper operation. Non-motorized dampers must open and close freely without binding. Motorized dampers must be connected to the DDC control system and verified that they are commanded open prior to fan operation.
• ___ 4. Fan size and capacity is verified, taking into account the accuracy of in instrumentation and the actual conditions at the time of the test.
• ___ 5. The system designer is familiar with acceptance criteria related to code, OSHA dictated hazard control functions, process cleanliness, or control functions. Compliance criteria are specified in the contract documents.
• ___ 6. Pressure relief doors are installed and operate correctly to protect the ductwork if fire/smoke dampers shut quickly but fans are still slowing down.

The following key commissioning test requirement for return, relief, and exhaust systems are similar to the requirements associated with the supply-side distribution system.

• ___ 7. Return, relief, and exhaust system pressure drops do not exceed design expectations.

Key Preparations and Cautions

• 1. Working with or around hazardous exhaust may require that additional safety precautions be included in the test procedures. Typical exposure hazards may include:
  • a) Viral, microbiological, or radioactive contamination in exhaust systems serving hospital and laboratory systems or pharmaceutical processes
  • b) Acids or caustics in exhaust systems serving scrubbers
  • c) Fine dust and particulates in exhaust systems that serve dust collection systems and dust generating processes
  • d) Explosive atmospheres in exhaust systems conveying explosive gasses or serving perchloric acid hoods
  • e) Non-breathable atmospheres and toxic fumes in process and laboratory exhaust systems
• 2. Consult and coordinate with the system owners, designers, and the Environmental Health and Safety Manager for all testing of potentially hazardous exhaust systems. MSDS sheets should be available onsite for any toxic substances used in the construction process.
• 3. Be aware that differences in static pressure requirements between the return and relief path can introduce instabilities into economizer and return and supply fan volume control loops, making them more difficult to tune.
• 4. Safety and interlock testing, verification of some of the drive settings, and loop tuning efforts will place the system at risk. Appropriate precautions and procedures should be in place to protect the personnel and machinery involved in the test process, including plans for quickly aborting the test.

Page last updated: September 11, 2006