terminals9and10onTB2.SeeFig.30.Whenthetimeclock
contactsareclosed,theEconoMiSerIVcontrolwillbeinoccu-
piedmode.Whenfiletimeclockcontactsareopen(removing
the24-vsignalfromterminalN),theEconoMiSerIVwillbein
unoccupiedmode.
Demand Controlled Ventilation (DCV) -- When using the
EconoMiSerlV for demand controlled ventilation, there me
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 dmnper position must be cal-
culated to provide the desired fresh tdl:
Typically file maximum ventilation rate will be about 5 to
10% more than the typical cfm required per peLson, using
normal outside air design criteria.
A proportional anticipatory strategy should be taken with
the following conditions: a zone with a large area, varied occu-
pancy, and equipment that cannot exceed the required ventila-
tion rate tit design conditions. Exceeding the required ventila-
tion rate means the equipment can condition air tit 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
dmnper will be tit maximum ventilation and should maintain
the set point.
In order to have the CO2 sensor control the economizer
dalnper in this manner, first determine the damper voltage out-
put for minimum or base ventilation. Base ventilation is the
ventilation required to remove contaminants during unoccu-
pied 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.
OA RA
(To x l---if6-) + (TR x _ = 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 mini-
mum dmnper position potentiometer to the correct position.
The stone equation can be used to determine the occupied or
maximum ventilation rate to the building. For example, tin out-
put of 3.6 volts to the actuator provides a base ventilation rate
of 5% and an output of 6.7 volts provides the maximum venti-
lation rate of 20% (or base plus 15 cfin per person). Use Fig. 37
to determine the maximum setting of the CO,__sensor For ex-
ample, a 1100 ppm set point relates to a 15 cfln per person de-
sign. Use the 1100 ppm curve on Fig. 37 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
EconoMiSerIV controller will output the 6.7 volts from the
CO,__sensor to the actuator when the CO,_ concentration in the
space is tit 1100 ppm. The DCV set point may be left tit 2 volts
since the CO2 sensor voltage will be ignored by the
EconoMiSerIV controller until it rises above the 3.6 volt setting
of the minimum position potentiometer
Once the fully occupied dmnper position has been deter-
mined, set file maximum dalnper demand control ventilation
potentiometer to this position. Do not set to the maximum posi-
tion as this can result in over-ventilation to the space and poten-
tial high-humidity levels.
CO,_ Sensor Configuration --The CO2 sensor has preset
standard voltage settings that can be selected anytime after the
sensor is powered up. See Table 10.
Use setting 1 or 2 for Carrier equipment. See Table 10.
1. Press Clear and Mode buttons. Hold tit least 5 seconds
until the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appem:
3. Use the Up/Down button to select the preset numbel: See
Table 10.
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 any-
time after the sensor is energized. Follow the steps below to
change the non-stanchrd settings:
1. Press Clear and Mode buttons. Hold tit least 5 seconds
until the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appem:
3. Use the Up/Down button to toggle to the NONSTD menu
and press Entel:
4. Use the Up/Down button to toggle through each of the
nine variables, starting with Altitude, until the desired set-
ting 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 vmiable.
Dehumidification of Fresh Air with DCV Control -- Infor-
mation from ASHRAE indicates that the largest humidity load
on any zone is the fresh air introduced. For some applications,
a field-supplied energy recovery unit can be added to reduce
the moisture content of the fresh tdr being brought into the
building when the enthalpy is high. In most cases, the normal
heating and cooling processes are more than adequate to re-
move the humidity loads for most commercial applications.
If normal rooftop heating and cooling operation is not ade-
quate for the outdoor humidity level, an energy recovery unit
and/or a dehumidification option should be considered.
24
To Next Page
Loading...
