13.63   Test Procedure: NA7.5.4 Air Economizer Controls Acceptance
Use Form NRCA-MCH-05-A

Purpose (Intent) of Test

There are basically two types of economizer controls: 1) stand-alone packages (e.g. Honeywell W7459A, Trane Precedent or Voyager, Carrier Durablade, which are most common); and 2) DDC controls.

The stand-alone packages are most commonly associated with rooftop packaged HVAC equipment and DDC controls are typically associated with built-up or large packaged air handling systems. Test procedures for both economizer control types have been developed and a brief description of each control strategy is provided below.

If the economizer is factory installed and certified by the manufacturer to the California Energy Commission, then Construction Inspection is required, but the Functional Test is not required.

The typical economizer control will have the following components:

•      a controller (stand alone or DDC);

•      an actuator that will drive both outside and return air dampers (sometimes separate actuators in built-up systems);

•      an outdoor air sensor;

•      a return air sensor where differential high-limit controls are used;

•      and a mixed/discharge air temperature sensor to which the economizer is controlled.

The sensor types used to measure outside and return air include dry-bulb temperature sensors, enthalpy sensors, and electronic enthalpy sensors (a combination of dry-bulb and enthalpy).  Standards Section 140.4(e)4E requires that outdoor air, return air, mixed air, and supply air sensors be calibrated to within specific accuracies, as follows:

•      Dry bulb and wet bulb temperatures accurate to ±2°F over the range of 40°F to 80°F.

•      Enthalpy accurate to ±3 Btu/lb over the range of 20 Btu/lb to 36 Btu/lb.

•      Relative humidity (RH) accurate to ±5 percent over the range of 20 percent to 80 percent RH.

In general, a first-stage call for cooling from the zone thermostat will enable the economizer controller, which will either allow the outdoor air damper to open fully if outdoor air conditions are suitable or enable the compressor. When the zone thermostat calls for a second stage of cooling, the compressor is enabled to provide mechanical cooling.

The three strategies available for economizer control are: 1) fixed dry-bulb; 2) fixed enthalpy + fixed dry-bulb; and 3) differential dry-bulb. The fixed dry-bulb and fixed enthalpy + fixed dry-bulb strategies both compare outdoor air conditions to a “fixed” setpoint to determine if the economizer can be enabled.  On the other hand, the differential dry-bulb strategy compares outdoor air and return air conditions to enable the economizer when outdoor air conditions are more favorable.

The economizer is considered integrated if the economizer can operate simultaneously with the compressor or chilled water coil. If the controls disable the economizer when the compressor (or chilled water coil) is on, it is considered non-integrated. Where economizers are required by the Standards, they must have integrated controls.

Construction Inspection

Air Economizer high limit setpoint complies with Standards Table 140.4-B per §140.4(e)3. For DDC control systems, the high limit setpoint should be a control parameter in the sequence of operations that can be verified for compliance. For stand-alone packages, the high limit setpoint is determined by settings on the controller (for example A, B, C, D settings on the Honeywell W7459A controller or dip switches on a Trane control package). Consult with manufacturer’s literature to determine the appropriate A, B, C, D or dip switch settings.

Unit controls must have the mechanical capacity controls interlocked with the economizer controls such that the economizer is at 100 percent open position when mechanical cooling is on, and does not begin to close until the leaving air temperature is less than 45°F.

A snap disk is a temperature sensitive relay with a fixed temperature setpoint, and thus a type of fixed dry-bulb control.  The snap disk closes the economizer circuit when the air temperature is below setpoint and opens the circuit when the air temperature exceeds setpoint. The standards specify if the high-limit control is a fixed dry-bulb, it must have an adjustable setpoint.  Thus, a snap disk is not an acceptable high limit control device because it does not provide an adjustable setpoint.

Table 13-3 – Standards Table 140.4-B Air Economizer High Limit Shut Off Control Requirements

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Check that air economizer outside (lockout) sensor location is adequate to achieve the desired control and prevent false readings. Outdoor air sensors should be located away from building exhausts and other heat sources like air-cooled condensers and cooling towers; should be open to the air but not exposed to direct sunlight (unless it is provided with a radiation shield); and could be located either directly in the air stream or remote from the unit (for example mounted on a north-facing wall).  

Check that economizer reliability features are present per Section 140.4(e)4.  This includes the following:

Verify the economizer has a 5-year warranty of the assembly.

Provide a product specification sheet proving economizer assembly capability of at least 60,000 actuations.

Provide a product specification sheet proving economizer damper sections are certified by AMCA 511 for a maximum damper leakage rate of 10 cfm/sf at 1.0 in. w.g. (Class 1A, 1, and 2 are acceptable)

If the high limit setpoint is fixed dry-bulb or fixed enthalpy + fixed dry-bulb then the control shall have an adjustable setpoint.

Outdoor air, return air, mixed air, and supply air sensors shall be calibrated as follows:

•      Dry bulb and wet bulb temperatures accurate to ±2°F over the range of 40°F to 80°F

•      Enthalpy accurate to ±3 Btu/lb over the range of 20 Btu/lb to 36 Btu/lb

•      Relative humidity (RH) accurate to ±5% over the range of 20% to 80% RH

Check that the sensor performance curve(s) is provided by the factory with economizer instruction materials, and that sensor output values measured during sensor calibration are plotted on the performance curve(s).

Sensors used for high limit control shall be located to prevent false readings, including but not limited to being properly shielded from direct sunlight.

For unitary systems 65,000 Btu/hr or less, verify that a two-stage thermostat is used, and that the system is wired so that the economizer is the first stage of cooling and the compressor is the second stage.

Check that all systems have some method of relief to prevent over pressurization of the building when in full economizing mode (100 percent outdoor air). Most packaged HVAC units with stand-alone economizer controls will typically have barometric dampers to exhaust the return air when the return dampers are fully closed and the unit is in economizer mode. Built-up and larger packaged air handling units may control return fans, relief dampers, or dedicated relief fans to actively maintain building pressurization when the unit is in economizer mode.

For systems with DDC controls, check that lockout sensor(s) are either factory calibrated or field calibrated. For systems with non-DDC controls, check that manufacturer’s startup and testing procedures have been applied.

Functional Testing

Since the test procedures vary significantly between stand-alone packages and DDC controls, the procedures for each system type are provided. 'In addition, there can be significant differences in test procedures between various stand-alone packages themselves. Contact your equipment supplier to see if they have equipment and test protocols that will allow you to easily field test their economizer to  NA7.5.4 Air Economizer Controls for filling out form NRCA-MCH-05-A. While it would not be feasible to cover every variation, three of the most common stand-alone packages are discussed below. The common feature of these procedures is that they all exercise the economizer function either by enabling an on-board diagnostic function or by “fooling” the control by inserting resistors that simulate mild weather conditions while the system is in cooling mode.

Stand-Alone Package

Trane Voyager and Precedent Series.

Both of these control packages have internal test sequences that can be used to verify proper system operation. Each operating mode is enabled by providing a momentary (2 second) jump across the test terminals.

Step 1. Disable demand control ventilation (DCV) system modes, if applicable for the unit.

Step 2. Use internal test sequences to enable operating modes.

Refer to manufacturer’s literature for detailed description of the procedures, however the basic steps are outlined below:

•      1st jumper – supply fan is enabled

•      2nd jumper – economizer mode is enabled

•      3rd jumper – compressor is enabled

•      4th jumper – heating stage is enabled

Verify and Document

•      The outdoor air damper opens completely and the return damper closes completely during economizer mode (Step 2 on the Acceptance Form NRCA-MCH-05-A). Verify that the outside air damper remains 100% open with the use of mechanical cooling, when the cooling demand cannot be met by outside air alone and when the system is still below the lockout point.

•      Outdoor air damper is at minimum position when the supply fan is enabled (Step 3 on the Acceptance Form NCRA-MCH-05-A).

•      Outdoor air damper is at minimum position when the compressor is enabled and economizing is disabled (Step 3 on the Acceptance Form NRCA-MCH-05-A).

•      Outdoor air damper is at minimum position when heating is enabled and economizing is enabled (Step 4 on the Acceptance Form NRCA-MCH-05-A).

•      Verify the mixed/discharge cut-out sensor wire is landed on the SA terminal on the OEM board. If the sensor wire is not landed on the SA terminal, the economizer will not operate.

Step 3. Turn off the unit.

•      Turn the unit OFF at the disconnect. This is step 5 on the Acceptance Form NRCA-MCH-05-A.

Verify and Document

•      Economizer dampers close completely.

•      Return air damper opens.

Step 4. Return system to normal operation.

The unit will return to normal operation when power is restored. This is Step 6 on the Acceptance Form NRCA-MCH-05-A.

Verify and Document

•      Final economizer changeover dip-switch settings comply with Standards Table 140.4-B per §140.4(e)3.

Honeywell Controllers

There are many Honeywell controllers available, but the most common is the W7459A series and most of the procedures used to check out this controller can be used on the others as well (always refer to manufacturer’s literature for additional information). All Honeywell controllers have an Install a 620 Ohm resistor across the SR and + terminals on the adjustment pot with “A, B, C, D” settings. For a fixed changeover strategy, the position of the adjustment pot with respect to the A, B, C, D settings will determine the economizer lockout setpoint. For a differential changeover strategy, the controller should be on the “D” setting. Note that the controllers typically come from the factory with the adjustment pot at the “D” setting, but this does not mean a differential control strategy is being used. The easiest way to verify a differential changeover strategy is to look at the SR and + terminals on the controller. If standard sensor wires are connected to the terminals, then it is a differential control strategy. If there is a 620 Ohm resistor jumpered across these terminals, then a fixed control strategy is being used.

Step 1. Disable demand controlled ventilation (DCV) system modes, if applicable for the unit.

Step 2. Simulate a cooling load and enable the economizer.

The simplest way to determine if the controller is functioning is to:

•      Turn the unit OFF at the disconnect.

•      Install a 1.2K Ohm resistor across the S_O and + terminals on the controller (this is the outdoor air temperature sensor).

•      Install a 620 Ohm resistor across the S_R and + terminals on the controller (this resistor is already installed for a fixed control strategy and must only be installed if there is a return air sensor).

•      Turn the economizer set point adjustment pot all the way to the “A” setting.

•      Install a jumper across the R and Y1 terminals at the unit terminal strip.

•      Turn the unit back ON at the disconnect.

Verify and Document

•      Outdoor air dampers open fully. Adjust linkages, if necessary, to ensure dampers are at the desired position.

•      Return air dampers close completely. Adjust linkages, if necessary, to ensure dampers are at the desired position.

•      Compressor runs when cooling load becomes too high for economizing to meet alone. The outdoor air dampers should remain 100% open at this point.

Step 3. Simulate a cooling load and disable the economizer.

Continuing from above:

•      Turn the unit OFF at the disconnect.

•      Leave the 1.2K Ohm resistor across the S_O and + terminals and 620 Ohm resistor across the S_R and + terminals in place.

•      Turn the economizer setpoint adjustment pot all the way to the “D” setting.

•      Leave jumper across the R and Y1 terminals at the unit terminal strip.

•      Turn the unit back ON at the disconnect.

Verify and Document

•      Outdoor air dampers close to minimum position. Adjust linkages, if necessary, to ensure dampers are at the desired position.

•      Return air dampers open completely. Adjust linkages, if necessary, to ensure dampers are at the desired position.

•      Compressor operates.

Step 4. If the unit is equipped with heating, simulate a heating load with the economizer enabled.

Continuing from above:

•      Turn the unit OFF at the disconnect.

•      Leave the 1.2K Ohm resistor across the S_O and + terminals and 620 Ohm resistor across the S_R and + terminals in place.

•      Turn the economizer setpoint adjustment pot all the way to the “A” setting.

•      Remove the jumper across the R and Y1 terminals at the unit terminal strip, and place the jumper across the R and W1 terminals at the unit terminal strip.

•      Turn the unit back ON at the disconnect.

Verify and Document

•      Outdoor air dampers remain at minimum position.

•      Heating is enabled.

•      Compressor does not operate.

Step 5. Turn off unit.

•      Turn the unit OFF at the disconnect.

Verify and Document

•      Economizer dampers close completely.

•      Return air damper opens.

Step 6: Return system back to normal operating condition.

•      Remove all jumpers and reconnect all wires.

•      Turn the unit ON at the disconnect.

Verify and Document

•      Final economizer changeover setting (A, B, C, D) complies with Standards Table 140.4-B per §140.4(e)3. Consult with manufacturer’s literature to determine the appropriate A, B, C, D setting for both fixed dry-bulb or enthalpy control strategies. The controller must be set on “D” for all differential control strategies.

Carrier Durablade.

Most Carrier HVAC units utilize the “Durablade” economizer control package, which uses a single damper “blade” that slides on a worm gear across both the outside and return air streams. Blade position is determined by end-switches that will cut power to the drive-motor when desired damper position is reached. Typically the economizer will be controlled by either a fixed dry-bulb or fixed enthalpy control strategy. Enthalpy control typically utilizes a customized Honeywell controller and the checkout procedures outlined above can be used to determine economizer functionality. The following test procedures should be followed for a fixed dry-bulb strategy.

Step 1. Disable demand controlled ventilation (DCV) system modes, if applicable to the unit.

Step 2. Simulate a cooling load and enable the economizer.

The simplest way to determine if the economizer is functioning is to:

•      Turn the unit OFF at the disconnect.

•      Install a jumper across the outdoor air temperature thermostat.

•      Install a jumper across the R and Y1 terminals at the unit terminal strip.

•      Disconnect the wire from the Y2 terminal at the unit terminal strip (this will prevent the 2nd stage of cooling from being enabled during the test).

•      Turn the unit back ON at the disconnect.

Verify and Document

•      Damper blade slides completely across the return air duct and mixed air plenum is open to the outdoor air intake. Adjust end-switches as necessary to achieve the desired position.

•      Compressor does not run.

Step 3. Simulate a cooling load and disable the economizer.

Continuing from above:

•      Turn the unit OFF at the disconnect

•      Remove the jumper and disconnect the outdoor air sensor completely from the circuit

•      Leave Y2 disconnected

•      Turn the unit back ON at the disconnect

Verify and Document

•      Damper blade returns to minimum outdoor air position. Adjust end switches as necessary to achieve the desired position

•      Compressor operates

Step 4. If the unit is equipped with heating, simulate a heating load with the economizer disabled.

Continuing from above:

•      Turn the unit OFF at the disconnect.

•      Leave the 1.2K Ohm resistor across the S_O and + terminals and 620 Ohm resistor across the S_R and + terminals in place.

•      Leave the economizer setpoint adjustment pot at the “D” setting.

•      Remove the jumper across the R and Y1 terminals at the unit terminal strip, and place the jumper across the R and W1 terminals at the unit terminal strip.

•    Turn the unit back ON at the disconnect.

Verify and Document

•      Economizer dampers close completely.

•      Return air damper opens.

Step 5. Turn off unit.

•      Turn the unit OFF at the disconnect.

Verify and Document

•      Economizer dampers close completely.

•      Heating and cooling do not operate.

Step 6: Return system back to normal operating condition.

•    Remove all jumpers and reconnect all wires

•    Turn the unit back ON at the disconnect

Verify and Document

•      Final economizer changeover setting complies with Standards Table 140.4-B per §140.4(e)3