Demand Ventilation - York MILLENNIUM Y22 Installation Manual

NOTE: As opposed to the PI algorithm used in economizer
control, the PI algorithm used here for economizer
loading function does not need to utilize the High
saturation state for any additional control functions.
Therefore no complications arise when switching
between direct and reverse acting modes.
Economizer loading option in heating:
In heating, this function uses additional outside air (as modu-
lated by the economizer dampers) in order to decrease SAT
when only the first stage of heating is running and keep the
SAT below the programmed "Economizer Loading Setpoint in
Heating". This prevents heating stage from cycling on its
internal temperature limit safety switch (which is typically set
°
about 10 F above the Economizer Loading Setpoint). A need
for economizer loading arises in Communicating Zoning Sys-
tem applications ("VVT" systems) using supply air bypass
when heating load in the zones is low and a large amount of
hot supply air is bypassed back into return and mixed air tem-
perature is very high. Economizer loading may also be
needed when supply air flow across the heat exchanger is
lower than expected (e.g. wrong setting of fan speed,
plugged air filters). A secondary benefit of economizer load-
ing is an improvement in comfort as the supply air tempera-
ture is more stable and cycling of the unit is minimized.
The economizer loading option in heating is not implemented
in VAV applications as these do not use supply air bypass
and (in case of using a zone thermostat) run all heating
stages during heating (economizer loading applies to only the
st
1 heating stage).
The economizer loading minimizes cycling of heating stage
#1 and makes a trade-off between energy and the benefits
described above.
The Economizer Loading in heating option requires a SAT
sensor that can sense SAT in heating mode (a sensor placed
downstream of the heating stages). Such a sensor is pro-
vided only as a field-installed accessory, on units equipped
with heating stages. The SAT sensor that is factory-installed
can be used for cooling mode only. If a field-installed sensor
is added, it will replace the factory-installed one and will then
be usable for both heating and cooling modes.
The loading is done by the similar control algorithm as used
in the normal economizer operation. The algorithm is acti-
vated to do this function in following conditions:
• Heating mode
• The programmable option "Economizer Loading to Con-
trol SAT" is ON
• Only heating stage #1 is running
The PI control algorithm in this case has a capability to auto-
matically change from direct to reverse acting in response to
difference between OAT and RAT. When OAT is less than
RAT the algorithm is direct acting, when OAT is greater than
RAT the algorithm is reverse acting.
90
This way, the "loading" of the heating stage is correctly done
with return, or outdoor air, as appropriate, and there is no
need to activate this "loading" function only in some specific
range of outdoor air temperatures (e.g. OAT > programmed
first heating stage trip point minus 50
NOTE: In this case, the provision for direct vs. reverse act-
ing switching is not essential feature of the control
algorithm and the algorithm could be implemented
as direct acting only in order to simplify implementa-
tion and save code space. The situation when econ-
omizer loading in heating is required while OAT
greater than RAT is unlikely and if it should occur,
the difference between OAT and RAT is negligible in
comparison to the SAT control setpoint. The Econo-
mizer Loading function in heating controls SAT to a
fixed temperature deadband of programmed "Econ-
omizer Loading Setpoint in Heating" and 5
this setpoint (the setpoint is programmable between
° °
100 F - 195 F, default is 160
In units that use hydronic heat, the Economizer Loading func-
tion may be enabled in order to be used for cooling (the on/off
programming choice for this function is common to both cool-
ing and heating). In this case, it is important to ensure that the
programmed value of the "Economizer Loading Setpoint in
Heating" is set higher than the value of "Hydronic Heat First
Stage Setpoint". That, in normal conditions, assures that the
Economizer Loading function in heating is effectively disabled
and the economizer is closed to its minimum position during
heating.
VAV
When is the Economizer operation used? If the rooftop unit is
equipped with an economizer and free cooling is available
then the Economizer Operation as specified in this section is
used in the following operation modes:
VAV cooling (except the programmed Economizer First Stage
Setpoint and Economizer Second Stage Setpoint are
replaced by the programmed VAV Upper Cooling SAT Set-
point and VAV Lower Cooling SAT Setpoint)

DEMAND VENTILATION

Demand Ventilation Operation control mode is self-configur-
ing for the use of an Indoor Air Quality (IAQ) sensor - it will
automatically detect that an IAQ sensor is connected and use
it any time the IAQ sensor input indicates an IAQ level of 200
ppm, or higher.
NOTE: Due to the self-configuration operation, an error due
to IAQ sensor failure can be indicated only in case
the IAQ sensor fails during normal controller opera-
tion. If the IAQ sensor fails, or is removed / discon-
nected during a power-off condition (e.g. during
servicing of the unit while the control is not pow-
ered), the control will, on power up, self configure
without the IAQ sensor and no error indication is
provided.
102777-YIM-E-0206
°
F).
°
F below
°
F).
Unitary Products Group