Carrier 33ZCSECTRM Especificaciones descargar pdf (Pagina 19)

The zone controller temperature control loop determines the

airflow set point that is required to maintain space temperature

at the heating set point. Each zone controller modulates be-

tween the minimum heating cfm and the maximum heating

cfm during central heating. This CFM should be limited to a

configured range of values that allows the air source to operate

properly in the heating mode.

In a system with an air source controlled by CCN device,

the zone controller will notify the corresponding linkage mas-

ter zone controller that the unit is heat mode or in morning

warm up.

In the case of a non-CCN controlled air source, the zone

controller should be set up as the linkage master for that air

source. The zone controller will determine if the primary air

temperature is greater than the weighted average space temper-

ature, and if higher, then declares the central air source in

heating.

VAV Central Heating with Ducted Zone

Heat —

When heating is available at the zone (ducted), and

central heating is also available, the zone heat will work in par-

allel to provide heating to the space. This heating function pro-

vides the required volume of heated air from the central appa-

ratus. This volume is determined by a PID airflow control, the

space temperature, and the desired set point. In addition, the

temperature of the air can be supplemented by the local heat

source, if the current air temperature cannot meet zone require-

ments. Each zone controller configured for heat (ducted or non

ducted) will operate its heating control loop when ever the

space temperature is below the heating set point to determine a

desired supply air discharge temperature that is necessary to

maintain space temperature at the heating set point.

NOTE: Central heat with ducted zone heat requires a supply

air sensor.

Morning Warm-Up —

The zone controller performs

Morning Warm-Up when its air source is in the Morning

Warm-Up mode. During Morning Warm-Up mode, the zone

controller operates the same as it does during heating. The zone

controller uses its occupied heating set point during Morning

Warm-Up, regardless of the current status of Occupancy. For

series fan terminal applications, the zone controller turns on the

air terminal’s fan during Morning Warm-Up operation.

If the zone controller is configured to perform supplemental

heating, it operates as defined for ducted or non-ducted heating

as applicable.

Damper Override —

Damper Override mode is initiat-

ed by the air source in response to input from a field-supplied

smoke control panel. When the air source enters an override

mode the linkage coordinator signals the zone controllers to

take corresponding action. The override can take either of two

forms: pressurization or evacuation. In Pressurization mode,

the zone controller commands the air terminal’s supply air

damper to maximum cool cfm. In Evacuation mode, it com-

mands the damper completely closed.

Damper Override supersedes the cfm setting the zone con-

troller would otherwise maintain based on space temperature.

The smoke control panel that commands the override mode

must be in accordance with local codes, as must its installation.

Nighttime Free Cooling —

Nighttime Free Cooling

(NTFC) is an air handler cooling function that can be em-

ployed during unoccupied periods when conditions permit. If

outside air is acceptable, based on temperature and enthalpy,

during unoccupied early morning hours, the air handler will de-

liver the cool outside air to the air terminals. When the air

source indicates that NTFC is operating, the zone controller at

each air terminal controls to midway between the occupied

heating and occupied cooling set points, rather than to the high-

er unoccupied cooling set point that would otherwise be in ef-

fect at that time.

For series fan terminal applications, the zone controller

turns on the air terminal’s fan during NTFC operation.

NOTE: This feature is only available to CCN systems where

fully compatible linkage air source controls are used.

Single Duct Terminal Applications —

When ap-

plying the 33ZCVAVTRM zone controller, ducted heat can

only be used when the air source is on, since the air source is

providing the only means of airflow into the zone.

Either model zone controller can support the Reheat func-

tion for single duct terminals.

With a single duct terminal application, if the central air

source is on and in cooling mode and the terminal is equipped

with heat, then the heat will be used to reheat the supply air to

prevent over cooling of the space. Reheat will occur when the

space temperature drops below the heating set point. The zone

controller will enable the heating control algorithm. At this

point the zone controller will provide primary airflow equiva-

lent to the larger of either the minimum cooling CFM require-

ment (to satisfy the minimum air flow for the air source) or the

reheat CFM requirement (to provide minimum airflow for the

heating coil).

COOLING — The primary control function of zone controller

is to provide cooling to the space by modulating the amount of

supply airflow through its primary damper.

The Zone Controller uses pressure independent operation to

control the amount of cool air entering the space. The control

variable is terminal airflow (CFM). A PID temperature control

loop determines the airflow set point needed to maintain space

temperature at the cooling set point.

The airflow set point is limited to a configured range of val-

ues that allow the air source to operate properly in the cooling

mode. These configured limits are listed in the Installation In-

structions for the zone controller. The minimum limit ensures

that the sum of all air terminal minimum requirements fall

within the minimum cooling operating range of the air source.

The maximum limit ensures that airflow will not increase

above the maximum design value and that the noise level gen-

erated at this maximum airflow will be acceptable to the occu-

pants of the zone.

When using VAV Heating, it is the system designer’s

responsibility that the central apparatus is protected during

heating to provide proper airflow over the central heating

device. Ensure that there will be a minimum system air-

flow that will allow the air source to operate safely in the

heating mode. The zone controller will allow for the option

of disabling the VAV central heating function in a given

zone. This means that a central air source may provide

heating for the entire system, or possibly only provide it for

those terminals without heat at the zone level.

The minimum airflow required by the heat at each terminal

must be configured properly to protect and ensure proper

heat transfer for the heating coil. If the minimum cooling

cfm limit is below the terminal’s recommended minimum

value, use the reheat cfm limit for this configuration. The

minimum heat cfm limit should also be set to this value.

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