TEMPERATURE DRIVEN HEAT MODE EVALUATION — This section discusses the control method for selecting a heat- ing mode based on temperature. Regardless of whether the unit is configured for return air or space temperature, the logic is ex- actly the same. For the rest of this discussion, the temperature in question will be referred to as the “controlling temperature.”
First, the occupied and unoccupied heating set points under Setpoints must be configured.
ITEM | EXPANSION | RANGE | UNITS | CCN | DEFAULT | |
POINT | ||||||
OHSP | Occupied Heat | dF | OHSP | 68 | ||
| Setpoint |
|
|
|
| |
UHSP | Unoccupied | dF | UHSP | 55 | ||
Heat Setpoint | ||||||
|
|
|
|
|
Then, the heat/cool set point offsets under Configuration→ D.LV.T should be set. See Table 66.
Related operating modes are under Operating Modes→ MODE.
ITEM | EXPANSION |
| RANGE |
| CCN POINT |
MODE | MODES CONTROLLING UNIT |
|
| ||
OCC | Currently Occupied |
| ON/OFF |
| MODEOCCP |
|
| ||||
T.C.ST | Temp.Compensated Start |
| ON/OFF |
| MODETCST |
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. 9 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 minus 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 method of operation has been referred to as “Comfort Trending.” As long as a LOW HEAT mode is making progress in warming the space, the con- trol will hold off on a HIGH HEAT mode. This is relevant for the space sensor machine control types (C.TYP = 5 and 6) be- cause 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 67 at the local display under Run Status→TRIP.
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.
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 indoor fan 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)*
the "Heating Setpoint"
L.H.ON
L.H.OF | L.H.OF/2 |
|
H.H.ON
Fig. 9 — Heating Offsets
Table 66 — Heat/Cool Set Point Offsets
ITEM |
| EXPANSION |
|
| RANGE |
| UNITS |
| CCN POINT |
| DEFAULT |
D.LV.T | COOL/HEAT SETPT. OFFSETS |
|
|
|
|
|
|
|
|
| |
L.H.ON | Dmd Level | Lo Heat On |
|
| ^F |
| DMDLHON |
| 1.5 | ||
|
|
|
| ||||||||
H.H.ON | Dmd Level(+) Hi Heat On |
| 0.5 | - 20.0 |
| ^F |
| DMDHHON |
| 0.5 | |
L.H.OF | Dmd |
| 0.5 - 2 |
| ^F |
| DMDLHOFF |
| 1 | ||
L.C.ON | Dmd Level | Lo Cool On |
|
| ^F |
| DMDLCON |
| 1.5 | ||
H.C.ON | Dmd Level(+) Hi Cool On |
| 0.5 - 20.0 |
| ^F |
| DMDHCON |
| 0.5 | ||
L.C.OF | Dmd |
| 0.5 - 2 |
| ^F |
| DMDLCOFF |
| 1 | ||
C.T.LV | Cool Trend Demand Level |
| 0.1 - 5 |
| ^F |
| CTRENDLV |
| 0.1 | ||
H.T.LV | Heat Trend Demand Level |
| 0.1 - 5 |
| ^F |
| HTRENDLV |
| 0.1 | ||
C.T.TM | Cool Trend Time |
| 30 - 600 |
| sec |
| CTRENDTM |
| 120 | ||
H.T.TM | Heat Trend Time |
| 30 - 600 |
| sec |
| HTRENDTM |
| 120 | ||
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