Viconics VWZS Application Guide - Manual (Page 26)

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3I) Indoor Air Quality Control & Operation
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. Here
are the control sequences available:
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.