DAMPER MOVEMENT — Damper movement from full open to full closed (or vice versa) takes 2 1/2 minutes.
THERMOSTATS — The Economizer control works with conven- tional thermostats that have a Y1 (cool stage 1), Y2 (cool stage 2), W1 (heat stage 1), W2 (heat stage 2), and G (fan). The Economizer control does not support space temperature sensors. Connections are made at the thermostat terminal connection board located in the main control box.
OCCUPANCY CONTROL — The factory default configuration for the Economizer control is occupied mode. Occupied status is provided by the black jumper from terminal TR to terminal N. When unoccupied mode is desired, install a field supplied time clock function in place of the jumper between TR and N. See Fig. 44. When the time clock contacts are closed, the Economizer control will be in occupied mode. When the time clock contacts are open (removing the 24-v signal from terminal N), the Economizer will be in unoccupied mode.
DEMAND CONTROLLED VENTILATION (DCV)—When using the Economizer for demand controlled ventilation, there are some equipment selection criteria which should be considered. When selecting the heat capacity and cool capacity of the equipment, the maximum ventilation rate must be evaluated for design conditions. The maximum damper position must be calculated to provide the desired fresh air. Typically the maximum ventilation rate will be about 5 to 10% more than the typical CFM required per person, using normal outside air design criteria. An exponential anticipatory strategy should be taken with the following conditions: a zone with a large area, varied occupancy, and equipment that cannot exceed the required ventilation rate at design conditions. Exceeding the required ventilation rate means the equipment can condition air at a maximum ventilation rate that is greater than the required ventilation rate for maximum occupancy. An exponential-anticipatory strategy will cause the fresh air supplied to increase as the room CO2 level increases even though the CO2set point has not been reached. By the time the CO2 level reaches the set point, the damper will be at maximum ventilation and should maintain the set point. In order to have the CO2 sensor control the economizer damper in this manner, first determine the damper voltage output for minimum or base ventilation. Base ventilation is the ventilation required to remove contaminants during unoccupied periods. The following equation may be used to determine the percent of outside-air entering the building for a given damper position. For best results there should be at least a 10_F (12.2_C) difference in outside and return-air temperatures.
(To x OA/100) + (TR x RA/100) = TM TO = Outdoor-Air Temperature
OA = Percent of Outdoor Air
TR = Return-Air Temperature
RA = Percent of Return Air TM = Mixed-Air Temperature
Once base ventilation has been determined, set the minimum damper position potentiometer to the correct position. The same equation can be used to determine the occupied or maximum ventilation rate to the building. For example, an output of 3.6 volts to the actuator provides a base ventilation rate of 5% and an output of 6.7 volts provides the maximum ventilation rate of 20% (or base plus 15 CFM per person). Use Fig. 42 to determine the maximum setting of the CO2 sensor. For example, a 1100 ppm set point relates to a 15 CFM per person design. Use the 1100 ppm curve on Fig. 42 to find the point when the CO2 sensor output will be 6.7 volts. Line up the point on the graph with the left side of the chart to determine that the range configuration for the CO2 sensor should be 1800 ppm. The Economizer controller will output the 6.7 volts from the CO2 sensor to the actuator when the CO2 concentration in the space is at 1100 ppm.
The DCV set point may be left at 2 volts since the CO2 sensor voltage will be ignored by the Economizer controller until it rises above the 3.6 volt setting of the minimum position potentiometer. Once the fully occupied damper position has been determined, set the maximum damper demand control ventilation potentiometer to this position. Do not set to the maximum position as this can result in over ventilation to the space and potential high-humidity levels.
CO2 SENSOR CONFIGURATION — The CO2 sensor has preset standard voltage settings that can be selected anytime after the sensor is powered up. Use setting 1 or 2 for equipment. See Table 16.
1.Press Clear and Mode buttons. Hold at least 5 seconds until the sensor enters the Edit mode.
2.Press Mode twice. The STDSET Menu will appear.
3.Use the Up/Down button to select the preset number. See Table 16.
4.Press Enter to lock in the selection.
5.Press Mode to exit and resume normal operation.
The custom settings of the CO2 sensor can be changed anytime after the sensor is energized. Follow the steps below to change the nonstandard settings:
1.Press Clear and Mode buttons. Hold at least 5 seconds until the sensor enters the Edit mode.
2.Press Mode twice. The STDSET Menu will appear.
3.Use the Up/Down button to toggle to the NONSTD menu and press Enter.
4.Use the Up/Down button to toggle through each of the nine variables, starting with Altitude, until the desired setting is reached.
5.Press Mode to move through the variables.
6.Press Enter to lock in the selection, then press Mode to continue to the next variable.
DEHUMIDIFICATION OF FRESH AIR WITH DCV CONTROL—Information from ASHRAE indicates that the largest humidity load on any zone is the fresh air introduced. For some applications, an energy recovery unit can be added to reduce the moisture content of the fresh air being brought into the building when the enthalpy is high. In most cases, the normal heating and cooling processes are more than adequate to remove the humidity loads for most commercial applications.
If normal rooftop heating and cooling operation is not adequate for the outdoor humidity level, an energy recovery unit and/or a dehumidification option should be considered.
