WattMaster VAVBOX - Manual (Page 16)

Technical Guide
VAVBOX Controller 16
Sequence Of Operations
Space Heating Mode
Occupied Space Heating mode is initiated by the temperature in the
space falling to within 0.5 ºF of the Occupied Heating Setpoint.
If the HVAC unit is in the Supply Air Cooling mode and another
VAVBOX controller has a heating demand, the damper/airflow for the
VAVBOX controller requiring heating will position itself to provide the
Cooling Minimum amount of air into the space. No modulation open
will occur because the space does not want the cold air currently being
supplied by the air handler.
When the HVAC unit is in the Occupied Supply Air Heating mode, the
damper will be held at the Heating Minimum position until the space
temperature falls to within 0.5 ºF of the Occupied Heating Setpoint.
As the space temperature falls below the heating setpoint, the damper/
airflow calculation causes the air valve to open proportionally until the
maximum setpoint is achieved at 3.5 ºF below the setpoint. This is a 4
ºF proportional window starting 0.5 ºF above the heating setpoint to 3.5
ºF below the heating setpoint.
Two different configurations are available for the Occupied Space Heat-
ing mode. If the box is configured to allow reheat during Supply Air
Heating mode, the reheat relays can be activated even when the HVAC
unit is in the Supply Air Heating mode. If the box is configured not to
allow reheat when the HVAC unit is in Supply Air Heating mode, the
box heat relays will be de-energized when the HVAC unit is in Supply
Air Heating mode. In either configuration, when the HVAC unit is in
the Supply Air Heating mode, the damper will modulate open propor-
tionally to the space demand. The proportional window for the space
temperature is 0.5 ºF above to 3.5 ºF below the heating setpoint. This
allows the space to take advantage of the warm supply air in the duct.
See Table 2: Relay Staging - Occupied Mode for a complete layout of
the various fan and heat relay staging points.
Series Flow Fan Terminals
If the VAVBOX Controller has been configured as a Series Fan Pow-
ered terminal unit, the series fan relay will activate and run the series
box fan continuously anytime the HVAC unit fan is running.
In all cases, before the series box fan can be activated, the air damper is
driven fully closed and held that way for 30 seconds to make sure the
series box fan hasn’t inadvertently started to spin backwards. Once the
series box fan starts, it waits an additional 10 seconds to allow the fan
to spin up before it starts to open the damper and introduce airflow from
the HVAC unit fan.
Parallel Flow Fan Terminals
On parallel fan powered terminal units, the fan will run whenever Space
Heating mode is active. At all other times, the fan will only activate if
the damper/airflow is below a user defined low limit setting. This causes
it to be used as a make-up air source. When the damper/airflow rises
15% above the low limit setpoint, the fan will be deactivated if there are
no heating stages active, and no space demand exists.
The check for main fan status setting has no effect on the Parallel Fan
box when in the occupied mode. The Parallel Fan will only be ener-
gized when in the Space Heating mode.
B o x F a n R e la y & R e h e a t R e la y S ta g in g
O c c u p ie d M o d e
R e la y s S ta g e
O n A t
S e rie s
F a n
P a ra lle l
F a n
H e a t
S ta g e
1
H e a t
S ta g e
2
H e a t
S ta g e
3
+ 0 .5 ºF
A b o v e B o x
H e a t
S e tp o in t
O N
W ith
H V A C
F a n
X
A t B o x H e a t
S e tp o in t
X
-1 .0 ºF
B e lo w B o x
H e a t
S e tp o in t
X
-2 .0 ºF
B e lo w B o x
H e a t
S e tp o in t
X
R e la y s S ta g e
O ff A t
S e rie s
F a n
P a ra lle l
F a n
H e a t
S ta g e
1
H e a t
S ta g e
2
H e a t
S ta g e
3
+ 1 .0 ºF
A b o v e B o x
H e a t
S e tp o in t
O F F
W ith
H V A C
F a n
X
+ 1 .0 ºF
A b o v e B o x
H e a t
S e tp o in t
X
A t B o x H e a t
S e tp o in t
X
-1 .0 ºF
B e lo w B o x
H e a t
S e tp o in t
X
Table 2: Relay Staging - Occupied Mode
Unoccupied Mode Sequences
Space Vent Mode
This mode only applies to the Occupied Mode of operation. If the equip-
ment is in the Unoccupied Mode, then a lack of heating or cooling
demand would generate the Off Mode.
Off Mode
This mode only applies to the Unoccupied Mode of operation. If the
equipment is in the Unoccupied Mode, then a lack of heating or cooling
demand would generate this mode. The VAVBOX controller will put
the damper into the Night/Reheat minimum position if check main fan
status has been selected. If check main fan status has not been selected
the damper will be in the fully closed position.
Space Cooling Mode
During unoccupied mode the HVAC unit is normally off. Unoccupied
Space Cooling mode is initiated by the temperature in the space rising
to within 0.5 ºF of the Unoccupied Cooling Setpoint.