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E 805.5 Air Economizer Controls Acceptance (Form MECH-5A)
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The purpose of functionally testing an air economizer cycle is to verify that an HVAC system uses outdoor air to satisfy space cooling loads where outdoor air conditions are acceptable. There are two types of economizer controls; stand-alone packages and DDC controls. The stand-alone packages are commonly associated with small unitary rooftop HVAC equipment, and DDC controls are typically associated with built-up or large packaged air handling systems. Test procedures for both economizer control types are provided.
For units with economizers that are factory installed and certified operational by the manufacturer to economizer quality control requirements, the in-field economizer functional tests do not have to be conducted. A copy of the manufacturer's certificate shall be attached to the Form MECH-5A. However, the construction inspection, including compliance with high-temperature lockout temperature setpoint, shall be completed regardless of whether the economizer is field or factory installed.
E 805.5.1 Test Procedure
The procedure for performing a functional test for air economizer controls shall comply with Section E 805.5.1.1 and Section E 805.5.1.2.
E 805.5.1.1 Construction Inspection
Prior to functional testing, verify and document the following:
- Economizer lockout setpoint is in accordance with this appendix.
- Economizer lockout control sensor is located to prevent false readings.
- System is designed to provide up to 100 percent outside air without over-pressurizing the building.
- For systems with DDC controls lockout sensor(s) are either factory calibrated or field calibrated.
- For systems with non-DDC controls, manufacturer's startup and testing procedures are applied.
E 805.5.1.2 Functional Testing
The functional testing shall be in accordance with the following steps:
Step 1: Disable demand control ventilation systems (where applicable).
Step 2: Enable the economizer, and simulate a cooling demand large enough to drive the economizer fully open. Verify and document the following:
- Economizer damper is 100 percent opened and return air damper is 100 percent closed.
- Where applicable, verify that the economizer remains 100 percent open where the cooling demand can no longer be met by the economizer alone.
- Applicable fans and dampers operate as intended to maintain building pressure.
- The unit heating is disabled.
Step 3: Disable the economizer and simulate a cooling demand. Verify and document the following:
- Economizer damper shall close to its minimum position.
- Applicable fans and dampers shall operate as intended to maintain building pressure.
- The unit heating is disabled.
Step 4: Simulate a heating demand, and set the economizer so that it is capable of operating (e.g., actual outdoor air conditions are below lockout setpoint). Verify the economizer is at minimum position.
Step 5: Restore demand control ventilation systems (where applicable) and remove system overrides initiated during the test.
E 805.5.2 Acceptance Criteria
Air economizer controls acceptance criteria shall be as follows:
- Where the economizer is factory installed and certified, a valid factory certificate is required for acceptance. No additional equipment tests are necessary.
- Air economizer lockout setpoint is in accordance with this appendix. Outside sensor location accurately reads true outdoor air temperature and is not affected by exhaust air or other heat sources.
- Sensors are located to achieve the desired control.
- During economizer mode, the outdoor air damper shall modulate open to a maximum position and return air damper to 100 percent closed.
- The outdoor air damper is 100 percent open before mechanical cooling is enabled and for units 75 000 Btu/h (22 kw) and larger remains at 100 percent open while mechanical cooling is enabled (economizer integration where used for compliance).
- Where the economizer is disabled, the outdoor air damper closes to a minimum position; the return damper modulates 100 percent open, and mechanical cooling remains enabled.
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