56
Related operating modes are under Operating Modes
→
MODE.
The first thing the control determines is whether the unit
is in the occupied mode (OCC) or in the temperature compen-
sated start mode (T.C.ST). If the unit is occupied or in tempera-
ture compensated start mode, the occupied heating set point
(OHSP) is used. In all other cases, the unoccupied heating
setpoint (UHSP) is used.
The control will call out a low or high heat mode by
comparing the controlling temperature to the heating set point
and the heating set point offset. The set point offsets are used as
additional help in customizing and tweaking comfort into the
building space.
Demand Level Low Heat on Offset (L.H.ON) — This is the
heating set point offset below the heating set point at which
point Low Heat starts.
Demand Level High Heat on Offset (H.H.ON) — This is the
heating set point offset below [the heating set point minus
L.H.ON] at which point high heat starts.
Demand Level Low Heat Off Offset (L.H.OF) — This is the
heating set point offset above [the heating set point minus
L.H.ON] at which point the Low Heat mode ends.
See Fig. 7 for an example of offsets.
To enter into a LOW HEAT mode, if the controlling temper-
ature falls below [the heating set point minus L.H.ON], then
HVAC mode = LOW HEAT.
To enter into a HIGH HEAT mode, if the controlling tem-
perature falls below [the heating set point minus L.H.ON mi-
nus H.H.ON], then HVAC mode = HIGH HEAT.
To get out of a LOW HEAT mode, the controlling tempera-
ture must rise above [the heating set point minus L.H.ON plus
L.H.OF].
To get out of a HIGH HEAT mode, the controlling tempera-
ture must rise above [the heating set point minus L.H.ON plus
L.H.OF/2].
The Run Status table in the local display allows the user to
see the exact trip points for both the heating and cooling modes
without doing the calculations.
Heat Trend Demand Level (H.T.LV) — This is the change in
demand that must be seen within the time period specified by
H.T.TM in order to hold off a HIGH HEAT mode regardless of
demand. This is not applicable to VAV control types (C.TYP=1
and 2) in the occupied period. This technique has been referred
to as “Comfort Trending.” As long as a LOW HEAT mode is
making progress in warming the space, the control will hold off
on a HIGH HEAT mode. This is relevant for the space sensor
machine control types (C.TYP = 5 and 6) because they may
transition into the occupied mode and see an immediate and
large heating demand when the set points change.
Heat Trend Time (H.T.TM) — This is the time period upon
which the heat trend demand level (H.T.LV) operates and may
work to hold off staging or a HIGH HEAT mode. This is not
applicable to VAV control types (C.TYP=1 and 2) in the
occupied period. See “Heat Trend Demand Level” section for
more details.
HEAT MODE DIAGNOSTIC HELP — To quickly deter-
mine the current trip points for the low and high heat modes,
there is a menu in the local display which lets the user quickly
view the state of the system. This menu also contains the cool
trip points as well. See Table 44 at the local display under Run
Status
→
TRIP.
Table 44 — Mode Trip Helper Table
The controlling temperature is “TEMP” and is in the middle
of the table for easy reference. Also, the “HVAC” mode can be
viewed at the bottom of the table.
TWO-STAGE GAS AND ELECTRIC HEAT CONTROL
(HT.CF = 1,2) — If the HVAC mode is LOW HEAT:
• If electric heat is configured, then the control will request
the supply fan ON
• If gas heat is configured, then the IGC IFO input controls
the supply fan request
• The control will turn on Heat Relay 1 (HS1)
• If evaporator discharge temperature is less than 50 F,
then the control will turn on Heat Relay 2 (HS2)*
If the HVAC mode is HIGH HEAT:
• If electric heat is configured, then the control will request
the supply fan ON
• If gas heat is configured, then the IGC IFO input controls
the supply fan request
• The control will turn on Heat Relay 1 (HS1)
• The control will turn on Heat Relay 2 (HS2)
*The logic for this “low heat” override is that one stage of
heating will not be able to raise the temperature of the supply
airstream sufficient to heat the space.
HYDRONIC HEATING CONTROL (HT.CF = 4) — Hy-
dronic heating in Z Series units refers to a hot water coil con-
trolled by an actuator. This actuator is a Local Equipment Net-
work (LEN) communicating actuator and may be field sup-
plied. When Configuration
→
HEAT
→
HT.CF=4, there is a
thermistor array called Tem p eratures
→
AIR.T
→
CCT, that is
connected to the RCB, that serves as the evaporator discharge
temperature (EDT). The leaving-air temperature (LAT) is as-
signed the thermistor that is normally assigned to EDT and is
located at the supply fan housing (Temperatures
→
AIR.T
→
SAT).
The configurations for hydronic heating are located at
the local displays under Configuration
→
HEAT
→
HH.CF.
See Table 45.
ITEM EXPANSION RANGE CCN POINT
MODE MODES CONTROLLING UNIT
OCC Currently Occupied ON/OFF MODEOCCP
T.C.ST Temp.Compensated Start ON/OFF MODETCST ITEM EXPANSION UNITS CCN POINT
TRIP MODE TRIP HELPER
UN.C.S Unoccup. Cool Mode Start dF UCCLSTRT
UN.C.E Unoccup. Cool Mode End dF UCCL_END
OC.C.S Occupied Cool Mode Start dF OCCLSTRT
OC.C.E Occupied Cool Mode End dF OCCL_END
TEMP Ctl.Temp RAT,SPT or Zone dF CTRLTEMP
OC.H.E Occupied Heat Mode End dF OCHT_END
OC.H.S Occupied Heat Mode Start dF OCHTSTRT
UN.H.E Unoccup. Heat Mode End dF UCHT_END
UN.H.S Unoccup. Heat Mode Start dF UCHTSTRT
HVAC the current HVAC MODE String
H.H.ON
L.H.OF L.H.OF/2
L.H.ON
HEATING SET POINT
66.5 F
67.5 F
66.0 F
68.0 F
Fig. 7 — Heating Offsets
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