Viconics VBZS Engineering Guide Specifications - Manual (Page 11)

Sequence for economizer on VZ7656E1000B only:
The fresh air damper can be controlled through more than one sequence to achieve different control
strategies such as free cooling (economizer mode), minimum fresh air control and CO
2
level control.
Note: For the sequences mentioned below, the following conditions must be met in order for the
sequences to be performed as stated:
- Max Pos parameter value must be greater than Min Pos Parameter value.
- Mac CO
2
parameter value must be greater than Min CO
2
Parameter value.
- Max FA parameter value must be greater than Min FA Parameter value.
Economizer Control Mode Only
If the fresh air damper is to be used only for free cooling purposes (economizer mode, without fresh air
measurement station or CO
2
control), only the Min Pos parameter and the free cooling sequence will be
active.
- The FA Range parameter should be set to 0 CFM. (Default Value = 0 CFM)
- Set the Chngstpt parameter to desired value which free cooling is enabled. (Default Value =
55°F)
If the outside air temperature is greater than the changeover setpoint, then normal mechanical cooling will
be used. If the outside air temperature is less than or equal to the changeover setpoint, then free cooling
will be enabled and mechanical cooling stages will be locked out.
Economizer Mode and Fresh Air Measurement Station
If the fresh air damper is to be used for both free cooling and minimum fresh air volume control
(economizer mode and fresh air measurement station, but without CO
2
level control), only the Min FA
parameter and the free cooling sequence will be active.
- The FA Range parameter should be set to a value higher than 0 CFM (0 CFM disables the fresh
air control).
- Min FA (minimum fresh air) parameter should be set to the desired level.
The FA Range parameter value should be set to the maximum capacity of the fresh air measurement
station. Therefore the relationship between air volumes and input signals can be established. For
example, if the fresh air station capacity is 10000 CFM, set FA Range to 10000.
This will set the relationship of 0 VDC = 0 CFM and 10VDC = 10000 CFM.