HVAC Economizers 101 Section #5 Typical Economizer .

HVAC Economizers 101Section #5Typical Economizer Controls onRooftop Unitsthat Utilize Honeywell Controls5-1

Section #5-Typical EconomizerControls on Rooftop Units UtilizingHoneywell Controls Dampers ((nott shown)Dh)Damper actuatorMAT/DAT sensorsSolid state controllerOAT/RAT sensorsDry bulbEnthalpyActuator M7414ControllerW7212Temperature SensorC7046CEnthalpy SensorC7400A(Honeywell shown, often basis of OEM RTU brands, out there for20 years)Source: Honeywell Controls5-2

Honeywell W7459 Economizer andAssociated Control Components5-3

Basic Economizer Cycle SequenceTypical for Honeywell with only 1 stg. Cooling(For typical packaged RTU with DX mechanical cooling)On a First Call for Cooling From Commercial Thermostat (Y1) Controller signal is routed to the economizer logic module.IF THE OUTDOOR AIR IS SUITABLE FOR FREE COOLING:COOLING Actuator modulates the outdoor damper open until the room temperatureis cool enough to satisfy the call for cooling and maintain the desired setpoint When the mixed or discharge air is between 50 and 55 Fpoint.F, theactuator will hold the damper position. When the mixed or supply air goesbelow 50 F, the damper is modulated towards closed. When the mixed orpp y air ggoes above 56 F, the damperp is modulated towards open.psupplyIF THE OUTDOOR AIR IS NOT SUITABLE FOR FREE COOLING: The first stage of the cooling compressor is turned on and the dampersare set to minimum for occupancy requirementsrequirements.5-4

Basic Economizer Cycle SequenceTypical for Honeywell with one stage Cooling(For typical packaged RTU with DX mechanical cooling)5-5

Economizer Control Diagram for Oneg CoolinggStage5-6

Basic Economizer Cycle SequenceTypical for Honeywell With TwoStage Cooling with EconomizerOn a Call for Single Stage Cooling Controller signal is routed to the economizer logic module to maintain spacetemperature using outside air for free cooling.On a Call for Second Stage Cooling If the outdoor air is suitable for free cooling and the outside are dampersare open, The economizer logic turns on the first stage of mechanical cooling forthe second stage of cooling required by the commercial thermostat. If the outdoor air is not suitable for free cooling, The dampers are set tominimum for occupancy requirements, the first stage cooling compressor is on,and the logic module turns on the second stage of mechanical cooling if available. NOTENOTE: A commerciali l ththermostatt t withith a minimumi ioff ttwo stagestoff coolingli iisrequired. The first stage must be available for economizing if outside air issuitable.5-7

Basic Operation of HoneywellThermostat and Controls for Two StagegCooling with Outside Air EconomizerSource: Honeywell Controls5-8

Economizer Control Diagram for Twog CoolinggStage5-9

Troubleshooting Factory SchematicsRequiresequ es Identifyingde t y g Sensors,Se so s, Thermostats,e ostats,Controllers, Relays, and ActuatorsControllerSensorActuatorThermostatSource: HoneywellControlsCoolingRelays5-10

ECONOMIZER Checkout Sheet (sample)ECONOMIZER INFORMATION(For completion by Service Technician)SensorWhere PlacedType(EM orSS/DB or, h)*As foundconditions(temp andRH (ifenthalpy))Output(DC Volts, mA,kΩ-- enterexpectedt d anddactual values)Book ActualAdjustedoutputCleaned?R l d?Replaced?Enter C or ROutside AirMixed Air TempDischarge Air TempReturn* EM electromechanical, SS solid state, DB dry bulb, h enthalpy (total energy)Control Logic(check choices & circlesettings. If DIPs,convert to temperature(if known). Fordifferential record asdifferential,asfound changeover POTsetting.Change if not on D.)As Found Changeover ( A, B, C, D, DIP settings, Snap Disk) T if DIPDifferential (outside & return air sensors wired) POTFinalChangeover ( A, B, C, D, DIP settings, Snap Disk) T if DIPDifferential (outside & return air sensors wired) POTSource: PSE5-11

Economizer Checkout Results(Summarize repairs and replacements)Upon your arrival, was economizer fully functional?If not, briefly describe problem(s):Yes NoSensor output was checked (enter values above)Yes NoThe outside air damper moves to full open without catching orbindingYes NoThe outside air damper moves to minimum setting withoutcatching or bindingYes NoType of relief air: barometric damper mechanically powered exhaustnoneController operation was checkedYes NoEconomizer changeover was adjusted to match climateconditions at A, B, C, or D ? If not, explain why not:YesYesNoNoShould demand controlled ventilation (DCV) be added?YesYesNoNoIf (DCV) was added, was min. air set to 5% of system flow?Yes No5-12

Honeywell W7459 Checkout andp ProceduresSetup Verify all sensors are reading correctly. (See next3 slides for more details on sensor checkout.) Generate a call for cooling. Adjust A-B-C-D setting to “D” (Humid Climates)– For changeover controlcontrol, economizer should be disabledand outside air damper at minimum if outside airconditions are greater than 55 F (dry bulb) or between 20and 22 Btu/lb (enthalpy). Adjust A-B-C-D setting to “A” (Dry Climates)– For changeover control, economizer should be enabledand outside air damper modulate full open if outside airconditionsditiare lless ththan 85 F (dry(d bulb)b lb) or bbetweent23and 32 Btu/lb (enthalpy). For differential control strategy, economizer willonly be enabled when outside air temperature isless than return temperature.5-13

Honeywell W7459 Sensor Signal andCheckout Analog temperature sensors typically:– Produce a milliamp or resistance signal; check with a DMM in mAor Ω (ohms).( h ) SSee nextt slide.lid– Measure sensor output and current temperature and compareeach value with manufacturer’s published data; checked with aDMM in Ω (ohms) at a known temperature. Thermostats simply change state at specific temperatures– Compare existing temperature to point when thermostat changesstate; checked with a DMM in continuity mode, as a switchclosure. SnapSDiDiscs changehstatet t onlyl– They cannot be adjusted or verified with any degree of accuracy.– They typically change state between 60 F60 F and 65 F65 F, which is afixed setting at the factory; checked with a DMM in continuitymode, as a switch closure at design temperatures.5-14

Honeywell C7150 and C7046 AnalogTemperaturepSensor Checkout Chart (ohms/ F)()5-15

Honeywell Temperature Sensor C7650Checkout Chart (mA/(mA/ F)F)5-16

The W7459 is used in conjunction with a Honeywellactuator (M7415) and sensors to control outdoor andreturn air dampers free cooling using outside air. It isdesigned to be installed directly on the actuator.5-17

Honeywell W7459 Economizer Control5-18

W7459 Enthalpy Economizer Controlg A,B,C,, , , or DSettings5-19

Adjusting Minimum Damper PositionyW7459Afor Honeywell Note: The W7459A uses inputs from mixed or discharge air temperaturesensors. Minimum Position Adjustment - Minimum position potentiometer keepsoutdoor air damper from closing completely during system operation toprovide ventilation.1. Disconnect mixed air sensor from terminals T and T1.2. Make sure either factory-installed jumper is in place acrossp ppositioner is required,qthat it isterminals P and P1 or if remote damperwired according to Honeywell instructions and turned fully clockwise.See Figure on next slide.3. Connect 24 Vac across terminals TR and TR1.4. Adjust potentiometer on face of W7459A with screwdriver todesired minimum position.5. Note: Check actual percentage of OSA by utilizing % charts orformulas, discussed later.5-20

Honeywell W7459A5-21

Honeywell W7459A5-22

Adjusting Minimum Damper PositionyW7459Bfor Honeywell Note: The W7459B is designed for use with a W7401 Logic Panelor a HoneywellyLegacyg y direct digitalgcontroller.1. Make sure either the factory-installed jumper is in place acrossterminals P and P1 or if remote damper positioner is required, itis wired according to Honeywell instructions, and turned fullyclockwise. See figure on next page.2. Connect jumper across terminals M1 and M3.3. IMPORTANT: Do not contact or connect jumper to M2. If M2 isjumpered to M1, the motor will not respond to the controller.4. Connect 24 Vac across terminals TR and TR1.5. Adjust potentiometer on face of W7459B with screwdriver todesired minimum position.5-23

Honeywell W7459B5-24

Checkout and Troubleshooting W74595-25

Exercise #5((Provide Answers below on notes ppage)g )1. T or FWhen wired properly, the 1st stage of cooling mustgo through the economizer controller circuit prior toenergizing the compressor.2. T or FWhen differential enthalpy is utilized, one sensor isin the outside air and one sensor is in the mixedair.3. T or FWhen the enthalpy sensor is set at “D”, the unit issett tot theth minimumi ilevelll forf humidh id climates.li t4. T or FTo simulate high and low enthalpy settings, tworesistors are needed: a 62O Ω and 1.2 kΩ.5. T or FA milliamp reading of 3 to 25 mA is the expectedreading to check the differential enthalpy sensor.5-26

Basic Economizer Cycle Sequence Typical for Honeywell with only 1 stg. Cooling (For typical packaged RTU with DX mechanical cooling) On a First Call for Cooling From Commercial Thermostat (Y1) Controller signal is routed to the economizer logic module. IF THE OUTDOOR AIR IS SUITABLE FO