SystemAir HHFlex C, Operating Instructions Manual, Page: 33 / 47

33
5.15 Mixing Box management
A mixing box (3-damper arrangement) can be used to modulate the air recirculation from extract to supply duct.
Commands
5.15.1 ON/OFF recirculation
This mode uses the logic defined as recirculation damper.
5.15.2 Modulated recirculation as heating/cooling capacity
In this mode the signal for heat recovery system is split between HR command and mix command:
Then the mixing section is enabled only when primary heat recovery system is fully loaded.
5.15.3 Minimum fresh air threshold
The mix command can be clamped by the minimum fresh air threshold value.
For example, if minfreshair = 20%, then the maximum allowed value for mix command is (100% - 20%) = 80 %.
The primary heat recovery system shall be turned off when the recirculation is 100%.
Output command
Recirculation
(Analog)
Outdoor
(Analog)
Exhaust
(Digital)
INDOOR
OUTDOOR
100% 50% 0%
100%
Mix
command
100%
50%
0%
100%
Mix
command
Recirculation Damper (CD07)
Outdoor Damper (CD11)
Output command
100%
50% 0%
Close
Mix
command
Exhaust Damper (CD15)
Output command
Open
100% 50%
100%
Heat Recovery Demand
HR command
0% 100%
50%
0%
100%
Mix command
Heat Recovery Demand
Minimum fresh air threshold