Minimum Position Control
There is a minimum damper position potentiometer on the EconoMi$er IV controller. See Fig. 28. The minimum damper position maintains the minimum airflow into the building during the occupied period.
When using demand ventilation, the minimum damper position represents the minimum ventilation position for VOC (volatile organic compounds) ventilation requirements. The maximum demand ventilation position is used for fully occupied ventilation.
When demand ventilation control is not being used, the min- imum position potentiometer should be used to set the occu- pied ventilation position. The maximum demand ventilation position should be turned fully clockwise.
Adjust the minimum position potentiometer to allow the minimum amount of outdoor air, as required by local codes, to enter the building. Make minimum position adjustments with at least 10° F temperature difference between the out- door and return-air temperatures. To determine the mini- mum position setting, perform the following procedure:
1.Calculate the appropriate mixed-air temperature using the following formula:
(TO x | OA | ) + (TR x | RA | ) = TM |
100 | 100 |
TO = Outdoor-Air Temperature OA = Percent of Outdoor Air TR = Return-Air Temperature RA = Percent of Return Air TM = Mixed-Air Temperature
As an example, if local codes require 10% outdoor air during occupied conditions, outdoor-air temperature is 60 F, and return-air temperature is 75 F.
(60 x .10) + (75 x .90) = 73.5 F
2.Disconnect the supply-air sensor from terminals T and T1.
3.Ensure that the factory-installed jumper is in place across terminals P and P1. If remote damper posi- tioning is being used, make sure that the terminals are wired according to Fig. 26 and that the minimum position potentiometer is turned fully clockwise.
4.Connect 24 vac across terminals TR and TR1.
5.Carefully adjust the minimum position potentiometer until the measured mixed-air temperature matches the calculated value.
6.Reconnect the supply-air sensor to terminals T and T1.
Remote control of the EconoMi$er IV damper is desirable when requiring additional temporary ventilation. If a field-supplied remote potentiometer (Honeywell part num- ber S963B1128) is wired to the EconoMi$er IV controller, the minimum position of the damper can be controlled from a remote location.
To control the minimum damper position remotely, remove the factory-installed jumper on the P and P1 terminals on the EconoMi$er IV controller. Wire the field-supplied poten- tiometer to the P and P1 terminals on the EconoMi$er IV controller. See Fig. 26.
Damper Movement
Damper movement from full open to full closed (or vice versa) takes up to 21/2 minutes.
Thermostats
The EconoMi$er IV control works with conventional thermo- stats that have a Y1 (cool stage 1), Y2 (cool stage 2), W1 (heat stage 1), W2 (heat stage 2), and G (fan). The EconoMi$er IV control does not support space temperature sensors like the T55 or T56. Connections are made at the thermostat terminal connection board located in the main control box.
Occupancy Control
The factory default configuration for the EconoMi$er IV con- trol is occupied mode. Occupied status is provided by the black jumper from terminal TR to terminal N. When unoccu- pied mode is desired, install a field-supplied timeclock func- tion in place of the jumper between TR and N. See Fig. 26. When the timeclock contacts are closed, the EconoMi$er IV control will be in occupied mode. When the timeclock con- tacts are open (removing the 24-v signal from terminal N), the EconoMi$er IV will be in unoccupied mode.
Demand Control Ventilation
When using the EconoMi$er IV for demand control ventila- tion, 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.
A proportional 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. A proportional- anticipatory strategy will cause the fresh air supplied to increase as the room CO2 level increases even though the CO2 set 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 degree difference in outside and return-air temperatures.
(TO x | OA | ) + (TR x | RA | ) = TM |
100 | 100 |
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 mini- mum damper position potentiometer to the correct position.