What HVAC control strategies are required (DDC, economizers, demand‑controlled ventilation)?

Grounded in the retrieved California Energy Code — click a citation to read the verbatim passage:

• § 804.3 High relevance — show source text

  (3) Duct leakage on a subset of small single-zone systems depending on the ductwork location (Form MECH-4A).

  (4) Air economizer controls for economizers that are not factory installed and tested (Form MECH-5A).

  (5) Demand-controlled ventilation control systems (Form MECH-6A).

  (6) Supply fan variable flow controls (Form MECH-7A).

  (7) Valve leakage for hydronic variable flow systems and isolation valves on chillers and boilers in plants with more than one chiller or boiler being served by the same primary pumps through a common header (Form MECH8A).

  (8) Supply water temperature reset control strategies programmed into the building automation system for water systems (e.g., chilled, hot, or condenser water) (Form MECH-9A).

  (9) Hydronic variable flow controls on a water system where the pumps are controlled by variable frequency drives (e.g., chilled and hot water systems; water-loop heat pump systems) (Form MECH-10A).

  (10)Automatic demand shed control (Form MECH-11A).

  (11)Fault detection and diagnostic for DX units (Form MECH-12A).

  (12)Automatic fault detection and diagnostic systems (AFDD) (Form MECH-13A).

  (13)Distributed energy storage DEC/DX AC systems (Form MECH-14A).

  (14)Thermal energy storage (TES) systems (Form MECH15A). E 804.3 Acceptance Process. The functional testing process shall comply with Section E 804.3.1 through Section E 804.3.4.

  E 804.3.1 Plan Review. The installing contractor, registered design professional of record, owner’s agent, or the person responsible for certification of the acceptance testing on the certificate of acceptance (responsible person) shall review the plans and specifications to ensure that they are in accordance with the acceptance requirements. This is typically done prior to signing a certificate of compliance. E 804.3.2 Construction Inspection. The installing contractor, registered design professional of record, owner’s agent, or the person responsible for certification of the acceptance testing on the certificate of acceptance (responsible person) shall perform a construction inspection prior to testing to ensure that the equipment that is installed is capable of complying with the requirements of this appendix and is calibrated. The installation of associated systems and equipment necessary for proper system operation is required to be completed prior to the testing.

  2025 CALIFORNIA MECHANICAL CODE 481

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  APPENDIX E

  E 804.3.3 Acceptance Testing. One or more field technicians shall perform the acceptance testing; identify performance deficiencies; ensure that they are corrected; and where necessary, repeat the acceptance procedures until the specified systems and equipment are performing in accordance with the acceptance requirements. The field technician who performs the testing shall sign the certificate of acceptance to certify the information has been provided to document the results of the acceptance procedures is true and correct.

  The responsible person shall review the test results from the acceptance requirement procedures provided by the field technician and sign the certificate of acceptance to certify compliance with the acceptance requirements. The responsible person shall be permitted to perform the field technician’s responsibilities, and shall then sign the field technician declaration on the certificate of acceptance to certify that the information on the form is true and correct.

• § 805.12.1.2 High relevance — show source text

  hardware is installed on equipment by the manufacturer, and that equipment make and model include factory-installed FDD hardware that match the information indicated on copies of the manufacturer’s cut sheets and on the plans and specifications.

  This procedure applies to fault detection and diagnostics (FDD) system for direct-expansion packaged units containing the following features:

  (1) The unit shall include a factory-installed economizer and shall limit the economizer dead band to not more than 2°F (-17°C).

  (2) The unit shall include direct-drive actuators on outside air and return air dampers.

  (3) The unit shall include an integrated economizer with either differential dry-bulb or differential enthalpy control.

  (4) The unit shall include a low temperature lockout on the compressor to prevent coil freeze-up or comfort problems.

  (5) Outside air and return air dampers shall have maximum leakage rates in accordance to this appendix.

  (6) The unit shall have an adjustable expansion control device such as a thermostatic expansion valve (TXV).

  (7) To improve the ability to troubleshoot charge and compressor operation, a high-pressure refrigerant port will be located on the liquid line. A low-pressure refrigerant port will be located on the suction line.

  (8) The following sensors shall be permanently installed to monitor system operation, and the controller shall have the capability of displaying the value of each parameter:

  (a) Refrigerant suction pressure

  (b) Refrigerant suction temperature

  (c) Liquid line pressure

  (d) Liquid line temperature

  (e) Outside air temperature

  (f) Outside air relative humidity

  (g) Return air temperature

  (h) Return air relative humidity

  (i) Supply air temperature

  (j) Supply air relative humidity

  The controller will provide system status by indicating the following conditions:

  (1) Compressor enabled

  (2) Economizer enabled

  (3) Free cooling available

  (4) Mixed air low limit cycle active

  (5) Heating enabled

  488 2025 CALIFORNIA MECHANICAL CODE

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  APPENDIX E

  The unit controller shall have the capability to manually initiate each operating mode so that the operation of compressors, economizers, fans, and heating system can be independently tested and verified.

  E 805.12.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:

  Step 1: Test low airflow condition by replacing the existing filter with a dirty filter or appropriate obstruction.

  Step 2: Verify that the fault detection and diagnostics system reports the fault.

  Step 3: Verify that the system is able to verify the correct refrigerant charge.

  Step 4: Calibrate outside air, return air, and supply air temperature sensors. E 805.12.2 Acceptance Criteria. The system is able to detect a low airflow condition and report the fault. The system is able to detect where refrigerant charge is low or high and the fault is reported. E 805.13 Automatic Fault Detection Diagnostics (FDD) for Air Handling Units (AHU) and Zone Termi- nal Units (Form MECH-13A). The purpose of this test is to verify that the system detects common faults in air handling units and terminal units. FDD systems for air handling units and zone terminal units require DDC controls to the zone level. Successful completion of this test provides a compliance credit where using the performance approach.

• § 805.5 High relevance — show source text

  CERTIFICATE OF ACCEPTANCE MECH-5A	Col2
  Air Economizer Controls Acceptance (Page 2 of 3)	Air Economizer Controls Acceptance (Page 2 of 3)
  Project Name/Address:	Project Name/Address:
  System Name or Identification/Tag:	System Location or Area Served:

  Intent: Verify that airside economizers function properly.

  Construction Inspection

  1. Instrumentation to perform test includes, but not limited to: a. Handheld temperature probes calibration. Date: (must be within last year). b. Multimeter capable of measuring ohms and milliamps.
  2. Test method (check one of the following):  Economizer comes from HVAC system manufacturer installed by and has been factory calibrated and tested. Attach documentation and complete certification statement. No functional testing required.

   Economizer field installed and field tested or factory installed and field tested.

  3. Installation (check all of the following first level boxes).  Economizer lockout setpoint complies with Section E 805.5 through Section E 805.5.2.

   Economizer lockout control sensor is located to prevent false readings.

   System is designed to provide up to 100% 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 have been applied.

  A. Functional Testing.	Col2
  Step 1: Disable demand control ventilation systems (if applicable).	Step 1: Disable demand control ventilation systems (if applicable).
  Step 2: Enable the economizer and simulate a cooling demand large enough to drive the economizer fully open (check and verify the following).	Step 2: Enable the economizer and simulate a cooling demand large enough to drive the economizer fully open (check and verify the following).
   Economizer damper modulates 100% open.	 Economizer damper modulates 100% open.
   Return air damper modulates 100% closed.	 Return air damper modulates 100% closed.
   Where applicable, verify that the economizer remains 100% open when the cooling demand can no longer be met by the economizer alone.	 Where applicable, verify that the economizer remains 100% open when the cooling demand can no longer be met by the economizer alone.
   All applicable fans and dampers operate as intended to maintain building pressure.	 All applicable fans and dampers operate as intended to maintain building pressure.
   The unit heating is disabled.	 The unit heating is disabled.
  Step 3: Simulate a cooling load and disable the economizer (check and verify the following).	**Step 3: Simulate a cooling load and disable the economizer (check and verify the following).

• § 805.5.2 High relevance — show source text

  Step 3: Disable the economizer and simulate a cooling demand. Verify and document the following:

  (1) Economizer damper shall close to its minimum position.

  (2) Applicable fans and dampers shall operate as intended to maintain building pressure.

  (3) 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:

  484 2025 CALIFORNIA MECHANICAL CODE

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  APPENDIX E

  (1) Where the economizer is factory installed and certified, a valid factory certificate is required for acceptance. No additional equipment tests are necessary.

  (2) 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.

  (3) Sensors are located to achieve the desired control.

  (4) During economizer mode, the outdoor air damper shall modulate open to a maximum position and return air damper to 100 percent closed.

  (5) 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).

  (6) 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. E 805.6 Demand-Controlled Ventilation Systems Acceptance (Form MECH-6A). The purpose of this test is to verify that systems required to employ demand-controlled ventilation shall be permitted to vary outside ventilation flow rates based on maintaining interior carbon dioxide (CO 2 ) concentration setpoints. Demand-controlled ventilation refers to an HVAC system’s ability to reduce outdoor air ventilation flow below design values where the space served is at less than design occupancy. Carbon dioxide is a good indicator of occupancy load and is the basis used for modulating ventilation flow rates.

  E 805.6.1 Test Procedure. The procedure for performing a functional test for demand-control ventilation (DVC) systems shall be in accordance with Section E 805.6.1.1 and Section E 805.6.1.2.

  E 805.6.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

  (1) Carbon dioxide control sensor is factory calibrated or field-calibrated in accordance with this appendix.

  (2) The sensor is located in the high-density space between 3 feet (914 mm) and 6 feet (1829 mm) above the floor or at the anticipated level of the occupants’ heads.

  (3) DCV control setpoint is at or below the carbon dioxide concentration permitted by this appendix.

  E 805.6.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:

  Step 1: Disable economizer controls.

• § 805.4.2 High relevance — show source text

  E 805.4.2 Acceptance Criteria. Flexible ducts are not compressed or constricted. Duct connections shall comply with the requirements of this appendix and this code (new ducts only). Joints and seams are properly sealed in accordance with the requirements of this appendix and this code (new ducts only). Duct R-values shall comply with the minimum requirements of this appendix (new ducts only). Insulation is protected from damage and suitable for outdoor usage where applicable (new ducts only). The leakage shall not exceed the rate in accordance with Section E 503.4.7.2.1.

  E 805.5 Air Economizer Controls Acceptance (Form MECH-5A). 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:

  (1) Economizer lockout setpoint is in accordance with this appendix.

  (2) Economizer lockout control sensor is located to prevent false readings.

  (3) System is designed to provide up to 100 percent outside air without over-pressurizing the building.

  (4) For systems with DDC controls lockout sensor(s) are either factory calibrated or field calibrated.

  (5) 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:

  (1) Economizer damper is 100 percent opened and return air damper is 100 percent closed.

  (2) Where applicable, verify that the economizer remains 100 percent open where the cooling demand can no longer be met by the economizer alone.

  (3) Applicable fans and dampers operate as intended to maintain building pressure.

  (4) The unit heating is disabled.

  Step 3: Disable the economizer and simulate a cooling demand. Verify and document the following:

  (1) Economizer damper shall close to its minimum position.

  (2) Applicable fans and dampers shall operate as intended to maintain building pressure.

  (3) The unit heating is disabled.

• § 0.22 High relevance — show source text

  BRINE, AND REFRIGERANT)4**|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4| |40–55|0.22–0.28|100|0.5|0.5|1.0|1.0|1.0| |Below 40|0.22–0.28|100|0.5|1.0|1.0|1.0|1.5|

  For SI Units: °C= (°F-32)/1.8, 1 British thermal unit inch per hour square foot degree Fahrenheit = [0.1 W/(m•K)], 1 inch = 25 mm

  Notes: 1 For insulation outside the stated conductivity range, the minimum thickness ( T ) shall be determined as follows: T = r {(1 + t/r) [K/k ] – 1}

  Where:

  T = minimum insulation thickness (inches). r = actual outside radius of pipe (inches) (mm). t = insulation thickness listed in this table for applicable fluid temperature and pipe size. K = conductivity of alternate material at mean rating temperature indicated for the applicable fluid temperature [Btu•in/(h•ft [2] - °F)] [W/(m•K)]. k = the upper value of the conductivity range listed in this table for the applicable fluid temperature. 2 These thicknesses are based on energy efficiency considerations only. Additional insulation is sometimes required relative to safety issues/surface temperature. 3 Piping insulation is not required between the control valve and coil on run-outs where the control valve is located within 4 feet (1219 mm) of the coil and the pipe size is 1 inch (25 mm) or less. 4 These thicknesses are based on energy efficiency considerations only. Issues such as water vapor permeability or surface condensation sometimes require vapor retarders, additional insulation or both. 5 For piping exposed to outdoor air, increase insulation thickness by 1 ⁄ 2 of an inch (12.7 mm). The outdoor air is defined as any portion of insulation that is exposed to outdoor air. For example, attic spaces and crawl spaces are considered exposed to outdoor air.

  TABLE E 502.6

  VENTILATION AIR

  [ASHRAE 90.2-2007: TABLE 6.6.1]

  CATEGORY	MINIMUM REQUIREMENT	CONDITIONS
  Mechanical ventilation1	50 ft3/min outdoor air	Where summer design infiltration rate calculated in accordance with reference standard (a) or (b) is less than 0.35 ACH2.
  Kitchen exhaust	100 ft3/min intermittent	All conditions
  Bath exhaust	intermittent	All conditions

  For SI units: 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s

  Notes: 1 Calculate in accordance with Equation E 502.6. 2 Reference standards:

  (a) ACCA Manual J (b) ASHRAE GRP-158

  416 2025 CALIFORNIA MECHANICAL CODE

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  APPENDIX E

• § 805.6 High relevance — show source text

  (6) 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. E 805.6 Demand-Controlled Ventilation Systems Acceptance (Form MECH-6A). The purpose of this test is to verify that systems required to employ demand-controlled ventilation shall be permitted to vary outside ventilation flow rates based on maintaining interior carbon dioxide (CO 2 ) concentration setpoints. Demand-controlled ventilation refers to an HVAC system’s ability to reduce outdoor air ventilation flow below design values where the space served is at less than design occupancy. Carbon dioxide is a good indicator of occupancy load and is the basis used for modulating ventilation flow rates.

  E 805.6.1 Test Procedure. The procedure for performing a functional test for demand-control ventilation (DVC) systems shall be in accordance with Section E 805.6.1.1 and Section E 805.6.1.2.

  E 805.6.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

  (1) Carbon dioxide control sensor is factory calibrated or field-calibrated in accordance with this appendix.

  (2) The sensor is located in the high-density space between 3 feet (914 mm) and 6 feet (1829 mm) above the floor or at the anticipated level of the occupants’ heads.

  (3) DCV control setpoint is at or below the carbon dioxide concentration permitted by this appendix.

  E 805.6.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:

  Step 1: Disable economizer controls.

  Step 2: Simulate a signal at or slightly above the carbon dioxide concentration setpoint required by this appendix. Verify and document the following:

  (1) For single zone units, outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.

  (2) For multiple zone units, either outdoor air damper or zone damper modulate open to satisfy the zone ventilation requirements.

  Step 3: Simulate signal well below the carbon dioxide setpoint. Verify and document the following:

  (1) For single zone units, outdoor air damper modulates to the design minimum value.

  (2) For multiple zone units, either outdoor air damper or zone damper modulate to satisfy the reduced zone ventilation requirements.

  Step 4: Restore economizer controls and remove system overrides initiated during the test.

  Step 5: With controls restored, apply carbon dioxide calibration gas at a concentration slightly above the setpoint to the sensor. Verify that the outdoor air damper modulates open to satisfy the total ventilation air called for in the certificate of compliance.

  E 805.6.2 Acceptance Criteria. Demand-controlled ventilation systems acceptance criteria shall be as follows:

  (1) Each carbon dioxide sensor is factory calibrated (with calibration certificate) or field calibrated.

  (2) Each carbon dioxide sensor is wired correctly to the controls to ensure proper control of the outdoor air damper.

  (3) Each carbon dioxide sensor is located correctly within the space 1 foot (305 mm) to 6 feet (1829 mm) above the floor.

  (4) Interior carbon dioxide concentration setpoint is not more than 600 parts per million (ppm) plus outdoor air carbon dioxide value where dynamically measured or not more than 1000 ppm where no OSA sensor is provided.

• § 803.2.1.3 High relevance — show source text

  The responsible person shall perform the field testing and verification work, and where this is the case, the responsible person shall complete and sign both the field technician’s signature block and the responsible person’s signature block on the certificate of acceptance form. The responsible person assumes responsibility for the acceptance testing work performed by the field technician agent or employee. E 803.2.1.3 Certificate of Acceptance. The certificate of acceptance shall be submitted to the Authority Having Jurisdiction in order to receive the final certificate of occupancy. The Authority Having Jurisdiction shall not release a final certificate of occupancy unless the submitted certificate of acceptance demonstrates that the specified systems and equipment have been shown to be performing in accordance with the applicable acceptance requirements. The Authority Having Jurisdiction has the authority to require the field technician and responsible person to demonstrate competence, to its satisfaction. Certificate of acceptance forms are located in Section E 806.0.

  E 804.0 Commissioning Tests. E 804.1 General. Functional tests shall be performed on new equipment and systems installed in either new construction or retrofit applications in accordance with this section. The appropriate certificate of acceptance form along with each specific test shall be completed and submitted to the Authority Having Jurisdiction before a final occupancy permit can be granted.

  E 804.2 Tests. Functional testing shall be performed on the devices and systems listed in this section. The functional test results are documented using the applicable certificate of acceptance forms shown in parenthesis and located in Section E 806.0. The functional tests shall be performed in accordance with Section E 805.0 using the following forms:

  (1) Minimum ventilation controls for constant and variable air volume systems (Form MECH-2A).

  (2) Zone temperature and scheduling controls for constant volume, single-zone, unitary air conditioner and heat pump systems (Form MECH-3A).

  (3) Duct leakage on a subset of small single-zone systems depending on the ductwork location (Form MECH-4A).

  (4) Air economizer controls for economizers that are not factory installed and tested (Form MECH-5A).

  (5) Demand-controlled ventilation control systems (Form MECH-6A).

  (6) Supply fan variable flow controls (Form MECH-7A).

  (7) Valve leakage for hydronic variable flow systems and isolation valves on chillers and boilers in plants with more than one chiller or boiler being served by the same primary pumps through a common header (Form MECH8A).

  (8) Supply water temperature reset control strategies programmed into the building automation system for water systems (e.g., chilled, hot, or condenser water) (Form MECH-9A).

  (9) Hydronic variable flow controls on a water system where the pumps are controlled by variable frequency drives (e.g., chilled and hot water systems; water-loop heat pump systems) (Form MECH-10A).

  (10)Automatic demand shed control (Form MECH-11A).

  (11)Fault detection and diagnostic for DX units (Form MECH-12A).

  (12)Automatic fault detection and diagnostic systems (AFDD) (Form MECH-13A).

  (13)Distributed energy storage DEC/DX AC systems (Form MECH-14A).

  (14)Thermal energy storage (TES) systems (Form MECH15A). E 804.3 Acceptance Process. The functional testing process shall comply with Section E 804.3.1 through Section E 804.3.4.

• § 801.0 High relevance — show source text

  • I am a licensed contractor or registered design professional who is eligible per the requirements of the Authority Having Jurisdiction to take responsibility for the scope of work specified on this document and attest to the declarations in this statement (responsible person).

  • I certify that the information provided on this form substantiates that the construction/installation identified on this form complies with the acceptance requirements indicated in the plans and specifications approved by the enforcement agency, and conforms to the applicable acceptance requirements and procedures specified in Section E 801.0 through Section E 806.0.

  • I have confirmed that the Installation Certificate(s) for the construction/installation identified on this form has been completed and is posted or made available with the permit(s) issued for the building.

  • I will ensure that a completed, signed copy of this Certificate of Acceptance shall be posted, or made available with the building permit(s) issued for the building, and made available to the enforcement agency for all applicable inspections. I understand that a signed copy of this Certificate of Acceptance is required to be included with the documentation the builder

  provides to the building owner at occupancy.	Col2	Col3	Col4
  Company Name:	Company Name:	Company Name:	Phone:
  Responsible Person’s Name:	Responsible Person’s Name:	Responsible Person’s Signature:	Responsible Person’s Signature:
  License:	Date Signed:	Position With Company (Title):	Position With Company (Title):

  502 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  APPENDIX E

  CERTIFICATE OF ACCEPTANCE MECH-5A	Col2
  Air Economizer Controls Acceptance (Page 2 of 3)	Air Economizer Controls Acceptance (Page 2 of 3)
  Project Name/Address:	Project Name/Address:
  System Name or Identification/Tag:	System Location or Area Served:

  Intent: Verify that airside economizers function properly.

  Construction Inspection

  1. Instrumentation to perform test includes, but not limited to: a. Handheld temperature probes calibration. Date: (must be within last year). b. Multimeter capable of measuring ohms and milliamps.
  2. Test method (check one of the following):  Economizer comes from HVAC system manufacturer installed by and has been factory calibrated and tested. Attach documentation and complete certification statement. No functional testing required.

   Economizer field installed and field tested or factory installed and field tested.

  3. Installation (check all of the following first level boxes).  Economizer lockout setpoint complies with Section E 805.5 through Section E 805.5.2.

   Economizer lockout control sensor is located to prevent false readings.

   System is designed to provide up to 100% 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 have been applied.

  A. Functional Testing.	Col2
  Step 1: Disable demand control ventilation systems (if applicable).	**Step 1: Disable demand control ventilation systems (if applicable).

• § 805.12 High relevance — show source text

  
  Outside air and return air dampers shall have maximum leakage rates conforming to Section E 805.12
  through Section E 805.12.2.|Y / N
  | |
  
  g.
  The unit shall have an adjustable expansion control device such as a thermostatic expansion valve
  (TXV).|Y / N
  | |
  
  h.
  To improve the ability to troubleshoot charge and compressor operation, a high-pressure refrigerant
  port will be located on the liquid line. A low-pressure refrigerant port will be located on the suction line.
  
  |Y / N
  | |
  
  i.
  The following sensors should be permanently installed to monitor system operation and the controller
  |
  Y / N| |
  
  
  
  should have the capability of displaying the value of each parameter:
   Refrigerant suction pressure
   Supply air relative humidity
   Return air temp
   Supply air relative
   Refrigerant suction temp
   Outside air relative humidity  Supply air temp
  humidity
   Liquid line pressure
   Return air relative humidity
   Outside air temp
  |
  
  
  
  should have the capability of displaying the value of each parameter:
   Refrigerant suction pressure
   Supply air relative humidity
   Return air temp
   Supply air relative
   Refrigerant suction temp
   Outside air relative humidity  Supply air temp
  humidity
   Liquid line pressure
   Return air relative humidity
   Outside air temp
  | |
  
  
  j.
  The controller will provide system status by indicating the following conditions:
   Compressor enabled
   Economizer enabled
   Free cooling available
   Heating enabled
   Mixed air low limit cycle active
  
  
  Y / N|Y / N| |
  k.
  The unit controller shall have the capability to manually initiate each operating mode so that the operation
  of compressors, economizers, fans, and heating system can be independently tested and verified.|Y / N|

  For SI units: °C = (°F-32)/1.8

  520 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  APPENDIX E

  CERTIFICATE OF ACCEPTANCE MECH-12A	Col2
  Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units (Page 3 of 3)	Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion Units (Page 3 of 3)
  Project Name/Address:	Project Name/Address:
  System Name or Identification/Tag:	System Location or Area Served:

  B. Functional Testing.	Col2	Results
  **Step 1: Low airflow test.

• CMC § 2025 High relevance — show source text

  | |Step 3: Simulate a cooling load and disable the economizer (check and verify the following).|Step 3: Simulate a cooling load and disable the economizer (check and verify the following).| |
  Economizer damper closes to its minimum position.|
  Economizer damper closes to its minimum position.| |
  All applicable fans and dampers operate as intended to maintain building pressure.|
  All applicable fans and dampers operate as intended to maintain building pressure.| |
  The unit heating is disabled.|
  The unit heating is disabled.| |Step 4: Simulate a heating demand and enable the economizer (check and verify the following).|Step 4: Simulate a heating demand and enable the economizer (check and verify the following).| |
  Economizer damper closes to its minimum position.|
  Economizer damper closes to its minimum position.| |Step 5: System returned to initial operating conditions.|Y/N|

  B. Testing Results.	PASS / FAIL	Col3
  Step 1: Simulate cooling load and enable the economizer (all check boxes are complete).
  Step 2: Simulate cooling load and disable the economizer (all check boxes are complete).
  Step 3: Simulate heating demand and enable the economizer (all check boxes are complete).

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  APPENDIX E

  CERTIFICATE OF ACCEPTANCE MECH-5A	Col2
  Air Economizer Controls Acceptance (Page 3 of 3)	Air Economizer Controls Acceptance (Page 3 of 3)
  Project Name/Address:	Project Name/Address:
  System Name or Identification/Tag:	System Location or Area Served:

  C.	PASS/FAIL Evaluation (check one):
  	PASS: AllConstruction Inspection responses are complete andTesting Results responses are “Pass.”
  	FAIL: AnyConstruction Inspection responses are incomplete_OR_ there is one or more “Fail” responses inTesting Results section. Provide explanation below. Use and attach additional pages if necessary.

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  APPENDIX E

• § 805.4.1 High relevance — show source text

  (1) Outdoors.

  (2) In a space directly under a roof where the U-factor of the roof is greater than the U-factor of the ceiling.

  (3) In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces.

  (4) In an unconditioned crawl space.

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  APPENDIX E

  (5) In other unconditioned spaces.

  This test applies to both new duct systems and to existing duct systems being extended or the space conditioning system is altered by the installation or replacement of space conditioning equipment, including: replacement of the air handler; outdoor condensing unit of a split system air conditioner or heat pump; cooling or heating coil; or the furnace heat exchanger. Existing duct systems do not have to be tested where they are insulated or sealed with asbestos. E 805.4.1 Test Procedure. The procedure for performing a functional test for air distribution systems shall be in accordance with Section E 805.4.1.1 and Section E

  805.4.1.2.

  E 805.4.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

  (1) Duct connections shall comply with the requirements of this appendix and this code.

  (2) Flexible ducts are not compressed.

  (3) Ducts are fully accessible for testing.

  (4) Joints and seams are properly sealed in accordance with the requirements of this appendix.

  (5) Insulation R-Values shall comply with the minimum requirements of this appendix. E 805.4.1.2 Functional Testing. Perform duct leakage test in accordance with Section E 503.4.7.2.1.

  E 805.4.2 Acceptance Criteria. Flexible ducts are not compressed or constricted. Duct connections shall comply with the requirements of this appendix and this code (new ducts only). Joints and seams are properly sealed in accordance with the requirements of this appendix and this code (new ducts only). Duct R-values shall comply with the minimum requirements of this appendix (new ducts only). Insulation is protected from damage and suitable for outdoor usage where applicable (new ducts only). The leakage shall not exceed the rate in accordance with Section E 503.4.7.2.1.

  E 805.5 Air Economizer Controls Acceptance (Form MECH-5A). 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.

• § 805.5.1.1 High relevance — show source text

  E 805.5.1.1 Construction Inspection. Prior to functional testing, verify and document the following:

  (1) Economizer lockout setpoint is in accordance with this appendix.

  (2) Economizer lockout control sensor is located to prevent false readings.

  (3) System is designed to provide up to 100 percent outside air without over-pressurizing the building.

  (4) For systems with DDC controls lockout sensor(s) are either factory calibrated or field calibrated.

  (5) 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:

  (1) Economizer damper is 100 percent opened and return air damper is 100 percent closed.

  (2) Where applicable, verify that the economizer remains 100 percent open where the cooling demand can no longer be met by the economizer alone.

  (3) Applicable fans and dampers operate as intended to maintain building pressure.

  (4) The unit heating is disabled.

  Step 3: Disable the economizer and simulate a cooling demand. Verify and document the following:

  (1) Economizer damper shall close to its minimum position.

  (2) Applicable fans and dampers shall operate as intended to maintain building pressure.

  (3) 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:

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  APPENDIX E

  (1) Where the economizer is factory installed and certified, a valid factory certificate is required for acceptance. No additional equipment tests are necessary.

  (2) 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.

  (3) Sensors are located to achieve the desired control.

  (4) During economizer mode, the outdoor air damper shall modulate open to a maximum position and return air damper to 100 percent closed.

  (5) 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).

• § 110.12 High relevance — show source text

  ** See Section 110.12 for requirements for automatic demand shed controls. H. Economizer fault detection and diagnostics (FDD). All newly installed air handlers with a mechanical cooling capacity over 33,000 Btu/hr and an installed air economizer shall include a stand-alone or integrated fault detection and diagnostics (FDD) system in accordance with Subsections 160.3(a)2Hi through 160.3(a)2Hviii. i. The following temperature sensors shall be permanently installed to monitor system operation: outside air, supply air and, when required for differential economizer operation, a return air sensor; and ii. Temperature sensors shall have an accuracy of ±2°F over the range of 40°F to 80°F; and iii. The controller shall have the capability of displaying the value of each sensor; and iv. The controller shall provide system status by indicating the following conditions: a. Free cooling available; b. Economizer enabled;

  c. Compressor enabled; d. Heating enabled, if the system is capable of heating; and e. Mixed air low limit cycle active. v. The unit controller shall allow manual initiation of each operating mode so that the operation of cooling systems, economizers, fans and heating systems can be independently tested and verified; and vi. Faults shall be reported in one of the following ways: a. Reported to an energy management control system regularly monitored by facility personnel. b. Annunciated locally on one or more zone thermostats, or a device within 5 feet of zone thermostat(s), clearly visible, at eye level and meeting the following requirements:

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  MULTIFAMILY BUILDINGS—MANDATORY REQUIREMENTS

  I. On the thermostat, the device or an adjacent written sign, display instructions to contact appropriate building personnel or an HVAC technician; and II. In buildings with multiple tenants, the annunciation shall either be within property management offices or in a common space accessible by the property or building manager. c. Reported to a fault management application that automatically provides notification of the fault to remote HVAC service provider. vii. The FDD system shall detect the following faults: a. Air temperature sensor failure/fault; b. Not economizing when it should; c. Economizing when it should not; d. Damper not modulating; and

  e. Excess outdoor air.

  viii. The FDD system shall be certified to the Energy Commission as meeting the requirements of Sections 160.3(a)2Hi through 160.3(a)2Hvii in accordance with Section 110.0 and JA6.3. Exception to Section 160.3(a)2Hviii: FDD algorithms based in direct digital control systems are not required to be certified to the Energy Commission. I. Direct digital controls (DDC). Direct digital controls to the zone shall be provided as specified by Table 160.3-C. i. The provided DDC system shall meet the control logic requirements of Sections 160.3(a)2E and 160.3(a)2G, and be capable of the following: ii. Monitoring zone and system demand for fan pressure, pump pressure, heating and cooling; iii. Transferring zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers; iv. Automatically detecting the zones and systems that may be excessively driving the reset logic and generate an alarm or other indication to the system operator; v. Readily allow operator removal of zone(s) from the reset algorithm; vi.

• § 62.1 High relevance — show source text

  (c) Any higher rate that can be demonstrated, to the satisfaction of the Authority Having Jurisdiction, to reduce overall system annual energy use by offsetting reheat/recool energy losses through a reduction in outdoor air intake for the system.

  (d) The airflow rate required to be in accordance with applicable codes or accreditation standards, such as pressure relationships or minimum air change rates.

  (2) Zones with DDC that comply with the following:

  (a) The airflow rate in dead band between heating and cooling does not exceed the larger of the following:

  (i) The minimum primary airflow rate required to meet the Simplified Procedure ventilation requirements of Chapter 4 or ASHRAE 62.1 for the zone, permitted to be the average airflow rate as allowed by Chapter 4 or ASHRAE 62.1.

  (ii) A higher rate that can be demonstrated, to the satisfaction of the Authority Having Jurisdiction, to reduce overall system annual energy use by offsetting reheat/recool energy losses through a reduction in outdoor air intake.

  (iii) The airflow rate required with applicable codes or accreditation standards, such as pressure relationships or minimum air change rates.

  (b) The airflow rate that is reheated, recooled, or mixed shall be less than 50 percent of the zone design peak supply rate.

  (c) The first stage of heating consists of modulating the zone supply air temperature set

  TABLE E 503.5.3

  DX COOLING STAGE REQUIREMENTS FOR

  MODULATING AIRFLOW UNITS

  [ASHRAE 90.1: TABLE 6.5.1.3]

  RATING CAPACITY, Btu/h	MINIMUM NUMBER OF MECHANICAL COOLING STAGES	MINIMUM COMPRESSOR DISPLACEMENT*
  ≥65 000 and <240 000	3	≤35% of full load
  ≥240 000	4	≤25% full load

  For SI units: 1000 British thermal units = 0.293 kW

  • For mechanical cooling stage control that does not use variable compressor displacement the percent displacement shall be equivalent to the mechanical cooling capacity reduction evaluated at the full load rating conditions for the compressor.

  E 503.5.4 Economizer Heating System Impact. HVAC system design and economizer controls shall be such that economizer operation does not increase the building heating energy use during normal operation.

  Exception: Economizers on variable air valve (VAV) systems that cause zone level heating to increase due to a reduction in supply air temperature. [ASHRAE 90.1:6.5.1.4] E 503.5.4.1 Economizer Humidification Sys- tem Impact. Systems with hydronic cooling and humidification systems designed to maintain inside humidity at a dew-point temperature more than 35°F (2°C) shall use a fluid economizer where an economizer is required in accordance with Section E 503.5 through Section E 503.5.4.1. [ASHRAE 90.1:6.5.1.5] E 503.5.5 Simultaneous Heating and Cooling Limitation, Zone Controls. Zone thermostatic controls shall prevent the following:

  (1) Reheating.

  (2) Recooling.

  (3) Mixing or simultaneously supplying air that has been previously mechanically heated and air that has

• § 120.2 High relevance — show source text

  Exception to Section 120.2(g): Zones designed to be conditioned continuously.

  (h) Automatic demand shed controls. See Section 110.12 for requirements for automatic demand shed controls.

  (i) Economizer fault detection and diagnostics (FDD). All newly installed air handlers with a mechanical cooling capacity over 33,000 Btu/hr and an installed air economizer shall include a stand-alone or integrated Fault Detection and Diagnostics (FDD) system in accordance with Subsections 120.2(i)1 through 120.2(i)8.

  1. The following temperature sensors shall be permanently installed to monitor system operation: outside air, supply air, and when required for differential economizer operation a return air sensor, and
  2. Temperature sensors shall have an accuracy of ±2°F over the range of 40°F to 80°F; and
  3. The controller shall have the capability of displaying the value of each sensor; and
  4. The controller shall provide system status by indicating the following conditions: A. Free cooling available; B. Economizer enabled;

  C. Compressor enabled; D. Heating enabled, if the system is capable of heating; and E. Mixed-air low limit cycle active. 5. The unit controller shall allow manual initiation of each operating mode so that the operation of cooling systems, economizers, fans and heating system can be independently tested and verified; and 6. Faults shall be reported in one of the following ways: A. Reported to an Energy Management Control System regularly monitored by facility personnel. B. Annunciated locally on one or more zone thermostats, or a device within five (5) feet of zone thermostat(s), clearly visible, at eye level, and meeting the following requirements: i. On the thermostat, device, or an adjacent written sign, display instructions to contact appropriate building personnel or an HVAC technician; and ii. In buildings with multiple tenants, the annunciation shall either be within property management offices or in a common space accessible by the property or building manager. C. Reported to a fault management application which automatically provides notification of the fault to a remote HVAC service provider. 7. The FDD system shall detect the following faults: A. Air temperature sensor failure/fault; B. Not economizing when it should; C. Economizing when it should not; D. Damper not modulating; and

  E. Excess outdoor air.

  8. The FDD System shall be certified to the Energy Commission as meeting requirements of Subsections 120.2(i)1 through 120.2(i)7 in accordance with Section 110.0 and JA6.3. Exception to Section 120.2(i)8: FDD algorithms based in direct digital control systems are not required to be certified to the Energy Commission.

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  NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS

  (j) Direct Digital Controls (DDC) . Direct Digital Controls to the zone shall be provided as specified by Table 120.2-A. The provided DDC system shall meet the control logic requirements of Sections 120.1(d), 110.12(a) and 110.12(b), and be capable of the following:

  The provided DDC system shall meet the control logic requirements of Sections 110.12(a), 110.12(b) and 120.1(d) and be capable of the following:

  1. Monitoring zone and system demand for fan pressure, pump pressure, heating and cooling;
• § 503.3. High relevance — show source text

  Exception : DDC is not required for systems using the simplified approach to compliance in accordance with Section E 503.3. [ASHRAE 90.1:6.4.3.10.1]

  E 503.4.6.12.2 DDC Controls. Where DDC is required by Section E 503.4.6.12.1, the DDC

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  APPENDIX E

  system shall be capable of and configured with all of the following, as required, to provide the control logic required in Section E 503.5:

  (1) Monitoring zone and system demand for fan pressure, pump pressure, heating, and cooling.

  (2) Transferring zone and system demand information from zones to air distribution system controllers and from air distribution systems to heating and cooling plant controllers.

  (3) Automatically detecting those zones and systems that are capable of excessively driving the reset logic and generate an alarm or other indication to the system operator.

  (4) Readily allowing operator removal of zone(s) from the reset algorithm. [ASHRAE 90.1:6.4.3.10.2]

  E 503.4.6.12.3 DDC Display. Where DDC is required in accordance with Section E 503.4.6.12.1 for new buildings, the DDC system shall be capable of trending and graphically displaying input and output points. [ASHRAE 90.1:6.4.3.10.3]

  E 503.4.6.13 Economizer Fault Detection and Diagnostics (FDD). Air-cooled direct-expansion cooling units listed in Tables E 503.7.1(1) and E 503.7.1(2), where an air economizer is installed in accordance with Section E 503.5, shall include a fault detection and diagnostics (FDD) system complying with the following:

  (1) The following temperature sensors shall be permanently installed to monitor system operation:

  (a) Outdoor air

  (b) Supply air

  (c) Return air, where required for economizer control

  (2) The system shall have the capability of displaying the value of each sensor.

  (3) The FDD system or unit controls shall be capable of and configured to provide system status by indicating the following:

  (a) Free cooling available

  (b) Economizer enabled

  (c) Compressor enabled

  (d) Heating enabled

  (e) Mixed-air low-limit cycle active

  (4) The FDD system or unit controls shall have provisions to manually initiate each operating mode so that the operation of compressors, economizers, fans, and the heating system can be independently tested and verified.

  (5) The FDD system shall be capable of and configured to detect the following faults:

  (a) Air temperature sensor failure/fault

  (b) Not economizing when the unit should be economizing

  (c) Economizing when the unit should not be economizing

  (d) Damper not modulating

  (e) Excess outdoor air

  (6) The FDD system shall be capable of and configured to report faults to a fault management appli

  TABLE E 503.4.6.12.1

  DDC APPLICATIONS AND QUALIFICATIONS

  [ASHRAE 90.1:6.4.3.10.1]

• § 503.7 High relevance — show source text

  (4) Section E 503.7, “Minimum Equipment Efficiency Tables.” [ASHRAE 90.1:6.2.1]

  E 503.2.2 Additional Requirements. Mechanical equipment and systems shall comply with one of the following:

  (1) Section E 503.3, “Simplified Approach Building Compliance Path for HVAC Systems”

  Exception: When compliance is shown using Section E 503.2.2(1), compliance with Section E 503.4 is not required.

  (2) Section E 503.5, “Prescriptive Compliance Path”

  Exception: HVAC systems only serving the heating, cooling, or ventilating needs of a computer room with IT equipment load greater than 10 kW (34 000 Btu/h) shall be permitted to comply with Section E 503.4, “Equipment Efficiencies, Verification, and Labeling Requirements” and Section E

  503.8, “Alternative Compliance Path, Computer Room Systems.” [ASHRAE 90.1:6.2.2] E 503.3 Simplified Approach Building Compliance Path for HVAC Systems. The simplified approach shall be an optional path for compliance where the following conditions are met:

  (1) The building is not more than two stories in height. (2) Gross floor area is less than 25 000 square feet (2322.6 m [2] ).

  (3) The HVAC system in the building is in accordance with the requirements listed in Section E 503.3.1. [ASHRAE 90.1:6.3.1] E 503.3.1 Criteria. The HVAC system shall comply with all of the following criteria:

  (1) The system serves a single HVAC zone.

  (2) The equipment shall comply with the variable flow requirements of Section E 503.5.6.2.

  (3) Cooling (where any) shall be provided by a unitary packaged or split-system air conditioner that is either air-cooled or evaporatively cooled, with efficiency that is in accordance with the requirements shown in Table E 503.7.1(1) for air conditioners, Table E 503.7.1(2) for heat pumps, or Table E 503.7.1(4) for packaged terminal and room air conditioners and heat pumps for the applicable equipment category.

  (4) The system shall have an air economizer in accordance with Section E 503.5 and Section E 503.4.6.13.

  (5) Heating (where any) shall be provided by a unitary packaged or split-system heat pump that is in accordance with the applicable efficiency requirements shown in Table E 503.7.1(2) for heat pumps or Table E 503.7.1(4) for packaged terminal and room air conditioners and heat pumps, a fuel-fired furnace that is in accordance with the applicable efficiency requirements shown in Table E 503.7.1(5) for furnaces, duct furnaces, and unit heaters, an electric resistance heater, or a baseboard system connected to a boiler that is in accordance with the applicable efficiency requirements shown in Table E 503.7.1(6) for boilers.

  (6) The system shall comply with the exhaust air energy recovery requirements in accordance with Section E 503.5.10.1.2.

  (7) The system shall be controlled by a manual changeover or dual setpoint thermostat.