TEC2664Z-3 BACnet® MS/TP Rooftop Controller for Stand-Alone and Networked Zoning Systems
Installation Instructions
13
Sequence of Operation
The sequence of operation of the zones is commanded
from the TEC2664Z-3 Rooftop Controller on a Change
of Value (COV) basis. The rooftop controller transmits
its current sequence mode to the zones, depending on
the highest or highest average PI demand. The
available sequence values at the zones are heating
and cooling. There is a 2-minute delay when toggling
between the heating and cooling modes. This delay
only applies when the system is switching over from
the network demand. The delay is not active when
working with the
Comm Lost
parameter using the
return air temperature sensor or the room air
temperature sensor. If the system mode of the rooftop
controller is set to off, the sequence value at the zone
is cooling by default.
Note:
If no return air sensor is installed and loss of
communication occurs, control of the rooftop unit is
based on the onboard sensor readings of the rooftop
controller.
The user can choose between a single highest
PI demand, an average of the three highest
PI demands, or an average of the five highest
PI demands.
Using the five highest PI demands as an example, five
buffers are required in the BACnet module of the
rooftop controller for the PI heating demand, and five
additional buffers are required for the PI cooling
demand. Each time a new zone sends its PI cooling
demand, the rooftop controller compares it to the
lowest of the five values already stored and buffers it (if
required). The rooftop controller averages these five
values, and the PI heating demand or PI cooling
demand controls the rooftop controller.
See Figure 8 through Figure 18 for sequence of
operation examples.
Figure 8: Rooftop Controller Sequence of Operation for
Two-Stage Heating and Two-Stage Cooling
FI
G
:t
w
_s
tg
_ht
ng
_t
w
_
st
g
_
cl
g
PI Demand (Depends on Control Type Selected)
Increase Heating
Stage 2
Start/Stop
(Approx.)
Stage 1
Start/Stop
(Approx.)
Stage 1
Start/Stop
(Approx.)
100%
PI Demand
PI Demand (Depends on Control Type Selected)
Increase Cooling
Stage
1
Stage
2
Stage
1
Stage
2
Stage 2
Start/Stop
(Approx.)
0%
PI Demand
100%
PI Demand
