Specifications

61
The following inputs will be used by this routine:
Y1 — Thermostat Cooling Stage 1 input. Status can be
checked in the INPUT-STAT submenu using the Y1 variable.
Y2 — Thermostat Cooling Stage 2 input. Status can be
checked in the INPUT-STAT submenu using the Y2 variable.
W1 — Thermostat Heating Stage 1 input — Status can be
check in the INPUT-STAT, submenu using the W1 variable.
W2 — Thermostat Heating Stage 2 input — Status can be
checkedintheINPUT-STATsubmenuusingtheW2variable.
HVACSPT2 ROUTINE — The HVACSPT2 routine is a de-
mand driven routine. The routine compares space temperature
to either the occupied cooling or heating set point if in occupied
mode, or to either the unoccupied cooling or heating set point
if in unoccupied mode to determine a demand level. The
demand levels and timings will be used to determine low cool,
high cool, low heat and high heat HVAC modes. The routine
can use a proportional space sensor (T55, T56, or T58) or a re-
turn air temperature sensor. It can also be used with a conven-
tional 2-stage thermostat with a Y1 and Y2 output. The Y1 will
be used as a low cool demand the Y2 as a high cool demand.
The routine will then provide multiple stage control for a
2-stage thermostat.
For the HVACSPT2 and HVAC_VAV routines, the follow-
ing set points and inputs will be used:
• Space Sensor Temperature (SPT) — This is the temperature
measured by the T55, T56, or T58 sensor. Status of the input
can be found in the TEMPERATURE-UNIT submenu.
• Occupied Cool Set point (OCSP) — This is the desired
space cooling temperature to be used in the Occupied Cool-
ing mode. It can be configured using the SETPOINTS-
COOL submenu.
• Occupied Heat Set point (OHSP) — This is the desired
space temperature to be used during the Occupied Heating
mode. It can be configured using the SETPOINTS-HEAT
submenu.
• Unoccupied Cool Set point (UCSP) — This is the desired
space cooling temperature to be used in the Unoccupied
Cooling mode. It can be configured using the SETPOINTS-
COOL submenu.
• Unoccupied Heat Set point (UHSP) — This is the desired
space temperature to be used during the Unoccupied Heat-
ing mode. It can be configure using the SETPOINTS-
HEAT submenu.
• Space Temperature Offset (SPTO) — This is used to config-
ure the amount of offset that can be used to adjust the space
temperature on a T56. The SPTO offset value can be read in
the TEMPERATURE-UNIT submenu. To use this option,
configure the Space Temp Offset (STO.S) variable in the
CONFIGURATION-OPTS submenu and then set the range
using the space temperature offset range (±) (STO.R), also
located in the CONFIGURATION-OPTS submenu.
• Heat Cool Set Point Gap (GAP) — This the minimum dif-
ference that must be maintained between the heating and
cooling set points as required by many building codes.
(ASHRAE 90-1 requires a 5° F minimum deadband). It is
configured in the SETPOINTS-GAP submenu.
• DMD Level Lo Cool On (LC.ON) — This is the low cool-
ing differential demand enable set point temperature. It is
the space temperature differential above the cooling set
point which will enable low cooling demand. It is config-
ured in CONFIGURATION-CMF.D submenu.
• DMD Level (–) Lo Cool Off (LC.OF) — This is the low
cooling differential demand disable set point temperature. It
is the space temperature differential above the cooling set
point which will turn off low cooling demand. It is config-
ured in CONFIGURATION-CMF.D submenu.
• DMD Level (+) Hi Cool On (HC.ON) — This is the incre-
mental differential temperature at which high cooling will
be enabled. It is configured in CONFIGURATION-CMF.D
submenu.
• DMD Level Lo Heat On (LH.ON) — This is the low heat-
ing differential demand enable set point temperature. It is
the space temperature differential below the heating set
point which will enable low heating demand. It is config-
ured in CONFIGURATION-CMF.D submenu.
• DMD Level (–) Low Heat Off (LH.OF) — This is the low
heating differential demand disable set point temperature. It
is the space temperature differential below the heating set
point which will turn off low heating demand. It is config-
ured in CONFIGURATION-CMF.D submenu.
• DMD Level (+) High Heat On (HH.ON) — This is the
incremental differential temperature at which high heating
will be enabled. It is configured in CONFIGURATION-
CMF.D submenu.
The algorithm compares space temperature to either the
occupied cooling or heating set point if occupied or to either
the unoccupied cooling or heating set point if unoccupied to
determine a demand level. The demand level and timing are
used to determine the low cool, high cool, low heat, high heat
demands. The high and low heating demands will then be
used to determine the amount of heating (number of stages),
free cooling (economizer position), and mechanical cooling
(compressor stages).
For units with heating and cooling, there are three modes of
temperature control: heating, ventilation, and cooling. The
selected heating and cooling logic will determine the mode.
The control logic is shown in Fig. 23. The values are
configurable and can be found in the CONFIGURATION
Menu under CMF.D and in the SETPOINTS Menu under
COOL and HEAT submenus.
The following are some examples of the logic with default
values.
COOLING MODES EXAMPLE
LC.ON = 1.5 F
LC.OF = 0.5 F
HC.ON = 2.0
OCSP = 75 F
• CoolingDemand=SpaceTemp(SPT)–(setpoint).
• Low Cool begins when a 1.5 F demand exists (SPT = 76.5
[75.0 + 1.5]).
• Low Cool ends when the demand returns to 0.5 F (SPT =
76 F [76.5-0.5]).
• High Cool begins when the demand exceeds 2.0 F (SPT =
78.5 [76.5 + 2.0]).
• High Cool ends when the demand returns to LC.OF/2 below
low demand on point (SPT = 76.25 [76.5-0.5/2]).
B=HC.ON
A=LL.ON
Cooling
(Econo/
Comp’s)
D=C/2
C=LC.OF
Vent
Mode
Heating
(Gas or
Electric)
D= C/2
C=LH.OF
A=LH.ON
Cooling Setpoint
(OC.SP)
Heating Setpoint
(OH.SP)
B= HH.ON
LEGEND
Fig. 23 — Demand Drive Control Logic
A—1st Stage Relative To Set Point
B—2nd Stage Relative To Set Point
C—1st Stage Off Relative to A
D—2nd Stage Off Relative to A (C/2)