13.8. NA7.5.4 Air Economizer Controls Acceptance

NA7.5.4 Air Economizer Controls Acceptance

Use Document NRCA-MCH-05-A

Purpose of the Test

Functionally Testing an air economizer cycle verifies that an HVAC system uses outdoor air to satisfy space-cooling loads. 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. DDC controls are typically associated with built-up or large packaged air handling systems.

Cooling fan systems > 54,000 Btu/hr must have an economizer. Air economizers must be able to provide 100 percent of the design supply air with outside air; water economizers must be able to provide 100 percent of the design cooling load at 50°F dry-bulb and 45°F wet-bulb.

The in-field economizer functional tests do not have to be conducted for units that are factory-installed and certified operational by the manufacturer to the Energy Commission’s economizer quality control requirements. A copy of the manufacturer's certificate must be attached to the NRCA-MCH-05-A. Regardless of whether the economizer is field- or factory-installed, complete the construction inspection, including the compliance with high temperature lockout temperature setpoints.

Instrumentation

Instrumentation to perform the test includes:

Hand-held temperature probe (must be calibrated within the past year).

Device capable of calculating enthalpy (must be calibrated within the past year)

1.2 kOhm resistor (when specified by the manufacturer).

620 Ohm resistor (when specified by the manufacturer).

•Test Conditions

Equipment installation is complete (including HVAC unit, duct work, sensors, control system, thermostats).

Non-DDC DX systems are required to have a two-stage thermostat.

The HVAC system must be ready for system operation, including completion of all start-up procedures per manufacturer’s recommendations.

For those units having DDC controls, it may be necessary to use the building automation system (BAS) to override or temporarily modify the variable(s) to achieve the desired control. BAS programming for the economizer, cooling valve control, and related safeties must be complete.

For built-up systems all interlocks and safeties must be operable − for example, freeze protection, limit switches, static pressure cut-out, and so on.

Document the initial conditions before overrides or manipulation of the settings. All systems must be returned to normal at the end of the test.

Before conducting the test, demand control ventilation systems must be disabled, if applicable.

Estimated Time to Complete

Construction Inspection: 0.5 to 1 hours (depending on familiarity with the controls)

Functional Testing: 0.5 to 2 hours (depending on familiarity with the controls and issues that arise during testing)

Acceptance Criteria

If 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 complies with Energy Standards Table 140.4-B per §140.4(e)3. This table is reproduced in Table 13-6 located below.

Outside sensor location accurately reads true outdoor air temperature and is not affected by exhaust air or other heat sources.

All sensors are located appropriately to achieve the desired control.

During economizer mode, the outdoor air damper modulates open to a maximum position, and the return air damper modulates 100 percent closed.

The outdoor air damper is 100 percent open before mechanical cooling is enabled and remains at 100 percent open while mechanical cooling is enabled (economizer integration when used for compliance with §140.4(e)2B). The economizer is capable of providing partial cooling even when additional mechanical cooling is required to meet the load. For unit controls, the outdoor air damper may not begin to close until the leaving air temperature is below 45°F.

When 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.

If the unit has heating capability, the outdoor air damper remains at minimum position when heating is enabled. When the unit is turned off or otherwise disabled, the outdoor air damper closes.

Potential Issues and Cautions

If conditions are below freezing when test is performed, coil(s) may freeze when operating at 100 percent outdoor air.

Outdoor air and relief dampers should be closed when the system is in unoccupied and warm-up modes, preventing problems with unconditioned air entering the building during unoccupied hours.

If the damper interlocks fail and the outdoor air damper does not open before the return damper closes, damage to the air handling unit or associated duct work may occur.

Air economizers with poor mixing can have excessively stratified air streams that can cause comfort problems or freeze stat trips. Mixing problems are more likely to occur as the VAV system reduces flow, leading to reduced velocities in the mixing box and through the dampers.

Check for exterior doors standing open and other signs of building over pressurization when all units are on full economizer cooling (100 percent OSA).

Newly Constructed and Additions/Alterations: All new equipment with air economizer controls must comply. Units with economizers that are installed at the factory and certified with the Energy Commission do not require functional testing but do require construction inspection.

1. Stand-alone packages (for example, Honeywell W7459A, Trane Precedent or Voyager, Carrier Durablade, which are most common). These are most commonly associated with rooftop packaged HVAC equipment.

2. DDC controls. These 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.

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

• 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). §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.

• 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 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 Energy Standards, they must have integrated controls.

Air economizer high limit setpoint complies with Energy Standards Table 140.4-B (Table 13-6) 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 Energy 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.

1. Check that the 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).

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

• 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:

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

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

Table 13-6: Air Economizer High Limit Shut off Control Requirements

Device Type a	Climate Zones	Required High Limit (Economizer Off When):
Device Type a	Climate Zones	Equation b	Description
Fixed Dry Bulb	1, 3, 5, 11-16	TOA > 75°F	Outdoor air temperature exceeds 75°F
	2, 4, 10	TOA > 73°F	Outdoor air temperature exceeds 73°F
	6, 8, 9	TOA > 71°F	Outdoor air temperature exceeds 71°F
	7	TOA > 69°F	Outdoor air temperature exceeds 69°F
Differential Dry Bulb	1, 3, 5, 11-16	TOA > TRA°F	Outdoor air temperature exceeds return air temperature
	2, 4, 10	TOA > TRA-2°F	Outdoor air temperature exceeds return air temperature minus 2°F
	6, 8, 9	TOA > TRA-4°F	Outdoor air temperature exceeds return air temperature minus 4°F
	7	TOA > TRA-6°F	Outdoor air temperature exceeds return air temperature minus 6°F
Fixed Enthalpyc + Fixed Drybulb	All	hOA > 28 Btu/lb c or TOA > 75°F	Outdoor air enthalpy exceeds 28 Btu/lb of dry air c or Outdoor air temperature exceeds 75°F
a Only the high limit control devices listed are allowed to be used and at the setpoints listed. Others, such as dew point, fixed enthalpy, electronic entha lpy, and differential enthalpy controls, may not be used in any climate zone for compliance with §140.4(e)1 unless approval for use is provided by the Energy Commission Executive Director. b Devices with selectable (rather than adjustable) setpoints shall be capable of being set to within 2°F and 2 Btu/lb of the setpoint listed. c At altitudes substantially different than sea level, the fixed enthalpy limit value shall be set to the enthalpy value at 75°F and 50 percent relative humidity. As an example, at approximately 6,000 foot elevation, the fixed enthalpy limit is about 30.7 Btu/lb.

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 among various stand-alone packages. 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 document 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.

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.

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

• Verify the outdoor air damper opens completely and the return damper closes completely during economizer mode (Step 2 on the acceptance document NRCA-MCH-05-A).

• Verify that the outside air damper remains 100 percent open while using mechanical cooling when the demand cannot be met by outside air alone and 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 document 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 document NRCA-MCH-05-A).

• Outdoor air damper is at minimum position when heating is enabled and economizing is enabled (Step 4 on the acceptance document 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.

• Turn the unit off at the disconnect. This is Step 5 on the acceptance document NRCA-MCH-05-A.

After restoring power, the unit returns to normal operation. This is Step 6 on the acceptance document NRCA-MCH-05-A.

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

There are many Honeywell controllers available. The most common controller is the W7459A series with checkout, which may be used on other models. (Always refer to manufacturer’s literature for additional information.) All Honeywell controllers have 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. The controllers typically come from the factory with the adjustment pot at the “D” setting. This setting does not mean the use of a differential control strategy. The easiest way to verify a differential changeover strategy is to look at the SR and + terminals on the controller. When standard sensor wires are connected to the terminals, the controller uses a differential control strategy. When there is a 620 Ohm resistor jumpered across these terminals, then the controller uses a fixed control strategy.

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

Install a 1.2 kOhm resistor across the SO and + terminals on the controller. (This is the outdoor air temperature sensor.)

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

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 percent open at this point.

Leave the 1.2 kOhm resistor across the SO and + terminals and 620 Ohm resistor across the SR and + terminals in place.

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.

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

• Leave the 1.2 kOhm 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.

Final economizer changeover setting (A, B, C, D) complies with Energy 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 and enthalpy control strategies. The controller must be set on “D” for all differential control strategies.

Most Carrier HVAC units use 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 uses 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.

Disconnect the wire from the Y2 terminal at the unit terminal strip. (This will prevent the second stage of cooling from being enabled during the test.)

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.

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

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

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

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

• 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.

Step 1: Disable demand controlled ventilation (DCV) system modes, if applicable.

For DDC systems, this may include overriding the readings from the CO₂ sensor(s) or temporarily disabling the sensor(s).

• Commanding the discharge air temperature set point to be lower than current discharge conditions.

• For a fixed dry-bulb or enthalpy control strategy, raising the economizer lockout set point to be above current outdoor air conditions (if this is not the case already) to enable the economizer.

• For a differential dry-bulb control strategy, raise the return air conditions to be above current outdoor air conditions (if this is not the case already) to enable the economizer.

• Verify return air damper modulates closed and is 100 percent closed when the outdoor air dampers are 100 percent open. Return dampers should close tight to minimize leakage.

• Verify outdoor air damper is 100 percent open before mechanical cooling is enabled, which implies that cooling coil valves in chilled water systems should not modulate or compressors in DX systems should not start until the unit is in 100 percent economizer mode. Depending on the speed of the PID loop, mechanical cooling could be commanded on before the outdoor air dampers actually stroke fully open. When this situation occurs, the system has not failed the test. One remedy is to watch the output of the PID loop and verify that the command sent to the outdoor air damper reaches 100 percent before a command is sent to the mechanical cooling devices.

• Although space pressurization requirements are not part of the current Energy Standards, most systems employ some form of control strategy to maintain space pressure during economizer mode. Control strategies can include, but are not limited to, 1) return fan speed control, 2) dedicated relief fans, or 3) relief damper controls. Observe that the space served by the air handling unit being tested does not appear to experience any pressurization problems (in other words, perimeter doors pushed open or excessive airflow between zones served by different units).

• Keep the discharge air temperature setpoint lower than current discharge conditions.

• For a fixed dry-bulb or enthalpy control strategy, lower the economizer lockout setpoint to be below current outdoor air conditions (if this is not the case already) to disable the economizer.

• For a differential dry-bulb or enthalpy control strategy; lower the return air conditions to be below current outdoor air conditions (if this is not the case already) to disable the economizer.

• Return air damper opens to normal operating position when the system is not in economizer mode.

• Mechanical cooling remains enabled to satisfy discharge air temperature setpoint.

Step 4: If the system has heating, simulate a heating demand and enable the economizer.

• Command the discharge air temperature setpoint to be higher than current discharge conditions.

• For a fixed dry-bulb or enthalpy control strategy, raise the economizer lockout setpoint to be above current outdoor air conditions (if this is not the case already) to keep the economizer enabled.

• For a differential dry-bulb control strategy, raise the return air conditions to be above current outdoor air conditions (if this is not the case already) to keep the economizer enabled.

• Ensure all schedules, setpoints, operating conditions, and control parameters are placed back at their initial conditions.