York ZB Series Installation Manual

5808009-YIM-A-0320Johnson Controls Ducted Systems 43If the SAT drops to less than the operating VAV SAT setpoint -1.8°F, the staged percent command begins to decrease.If the staged percent command remains at 0% for 5 consecutiveminutes, the economizer modulates to control to the upper SATsetpoint +/-0.5°F.VAV unit sensor option BWhen free cooling available and the SAT is greater than theoperating VAV SAT setpoint, the dampers modulate to controlthe operating VAV SAT setpoint +/-0.5°F.If the economizer position remains at 100% for 10 consecutiveminutes and the SAT is greater than the operating VAV SATsetpoint +5°F, the first compressor output energizes. If theeconomizer position remains at 100% for another 5 minutesand the SAT is greater than the operating VAV SAT setpoint+5°F, the second compressor output energizes. If theeconomizer position remains at 100%, the process repeatsevery 5 minutes until all the compressors energize.If the economizer position drops below 100% and does notreach the minimum position then returns to 100%, remains at100% for 5 minutes, and the SAT is greater than the operatingVAV SAT setpoint +5°F, the next available compressorenergizes. If the economizer position remains at 100%, theprocess repeats every 5 minutes until all the compressorsenergize.Any time the economizer remains at the minimum position for 5consecutive minutes or the SAT is lower than the operatingVAV SAT setpoint -5°F, the last energized compressor turnsoff. If it remains at the minimum position or the SAT remainslower than the operating VAV SAT setpoint -5°F, thecompressors de-energize every 5 minutes until all thecompressors are off.If all compressor outputs de-engerize, the economizermodulates to control to operating VAV SAT Setpoint +/-0.5°F.When the cooling demand ends the compressors de-energizeimmediately and the dampers return to operating minimumposition.Economizer loadingThe economizer loading function only works when only onecompressor is operating.If the SAT is less than the SAT low limit setpoint and theoperating OAT is greater than 60°F, the economizer outputincreases to control the SAT to the operating SAT setpoint +/-0.5°F.Power exhaustSetpoints• Economizer enable ON• Power exhaust enable ON• Modulating power exhaust OFF• Exhaust VFD installed OFF• Building pressure sensor enabled OFF• Econo damper position for exh fan ON Percent• Econo damper position for exh fan OFF PercentInputsNo inputs are present for non-modulating power exhaust.Outputs• 2-10 VDC from ECON on the economizer expansionmodule• 24 VAC from EX-FAN to energize the exhaust fan on theeconomizer expansion moduleOperationOperation details include the following items:a. Compares the economizer output to the economizerdamper position for exhaust fan on and offb. Energizes the exhaust fan when the economizer outputis above the economizer damper position for exhaust fanonc. De-energizes the exhaust fan when the economizeroutput is below the economizer damper position forexhaust fan off