Carrier 48AJ, 48EW, 48AW, 48EK Occupied Heat and Morning Warm-Up, Operation and Controlling Factors

Table 40 — Occupied Heat and Morning Warm-Up

Operation and Controlling Factors

	OCCUPIED	MORNING	TEMPERATURE
SOFTWARE	HEAT	WARM-UP	CONDITION
VERSION	ENABLED	MAY START	FOR HEAT
	VIA	DURING	TO START
3.0 and Later		Smart start or
	DIP switch no. 5	within	RAT < OHSP
		10 minutes

LEGEND

OHSP — Occupied Heat Set Point

RAT — Return-Air Temperature

SPACE TEMPERATURE SENSOR CONTROL — If the unit is equipped with a field-supplied space sensor and a remote start/stop switch, constant volume (CV) cooling will operate as follows: Stage 1 cooling begins when there exists a 1.5° F demand and ends when the demand returns back to 0.5° F. Stage 2 cooling begins when there is a 2.0° F demand and will continue until the demand returns 1.0° F. Stage 2 cannot be en- ergized until a minimum of eight minutes of Stage 1 operation or as long as stage 1 is making a reduction in the space temper- ature trend. If the temperature trends stop improving but the demand still exceeds 2.0° F, then Stage 2 cooling will be energized.

When economizer operation is suitable, the control will use economizer, as the first stage of cooling will bring on the com- pressor 1 when Stage 2 demand is called for. If supply-air tem- perature (SAT) remains above supply-air set point (SASP) for 15 minutes after energizing compressor 1, then compressor 2 shall be started. When Stage 2 is satisfied, the last stage of compression shall be dropped. When Stage 1 is satisfied, the control will drop all DX cooling.

If the unit is equipped with a field-supplied space sensor and a remote start/stop switch, CV heating will operate as follows: Stage 1 heating begins when there exists 1.5° F demand and ends when the demand returns back to 0.5° F. Stage 2 heating begins when there is a 2.0° F demand and will continue until the demand returns to 1.0° F. Stage 2 cannot be energized until a minimum of eight minutes of Stage 1 operation or as long as Stage 1 is making an increase in the space temperature trend. If

the temperature trends stop improving but the demand still ex- ceeds 2.0° F, then Stage 2 heating will be energized

SPACE TEMPERATURE RESET SENSOR (VAV Only) — An accessory space temperature sensor (T-55 or T-56 without offset) is required. Space temperature reset is used to reset the supply-air temperature set point of a VAV system higher, as the space temperature falls below the Occupied Cool set point. As the space temperature falls below the Occupied Cool set point, the supply-air temperature will be reset upward as a function of the reset ratio. (Default is 3.) Reset ratio is expressed in degrees change in supply-air temperature per degree of space tempera- ture change. A reset limit will exist which will limit the maxi- mum number of degrees the supply-air temperature may be raised. (Default is 10 F.) Both the reset ratio and the reset limit are user definable. The sequence of operation is as follows:

1.The on/off status of the unit supply fan is determined.

2.If the fan is ‘‘on,’’ the sequence will check if the system is occupied.

3.If the system is in Occupied mode, the sequence will de- termine if the reset option is enabled.

4.If the reset option is enabled, the sequence will read the space temperature and compare it to the Occupied Cool set point. If the temperature is below the Occupied Cool set point, the algorithm will compute the reset value and compare this value against the reset limit. If it is greater than the reset limit, the sequence will use the reset limit as the reset value. See Fig. 61.

NOTE: A computer equipped with Carrier network access software (ComfortWORKS®, Building Supervisor, or Service Tool) or an accessory Remote Enhanced Display is required to enable this function.

Space Temperature Reset Example — The occupied cooling set point is set to 73 F. The Reset Ratio is set to 5. The Reset Limit is set to 20 F. The Reset Ratio determines how many de- grees F the temperature is reset. At 72 F, the supply tempera- ture will be reset 5 degrees higher. At 71 F, the supply tempera- ture will be reset 10 degrees higher. At 70 F, the supply temper- ature will be reset 15 degrees higher. At 69 F, the supply temperature will be reset 20 degrees higher and the Reset Limit will have been reached.

BASE MODULE

CONTROL BOARD

(+) T11		4-20 mA
(-) T12		INPUT
		FIELD
		SUPPLIED
	INPUT DEVICE

LEGEND

T — Terminal

NOTE: The 4 to 20 mA input is a field-supplied non-Carrier EMS (Energy Management System) device.

mA INPUT	DEG. F RESET
4	0.00
5	1.25
6	2.50
7	3.75
8	5.00
9	6.25
10	7.50
11	8.75
12	10.00
13	11.25
14	12.50
15	13.75
16	15.00
17	16.25
18	17.50
19	18.75
20	20.00

Fig. 61 — Space Temperature Reset Wiring

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