Carrier 48/50AJ specifications

HVAC mode = “Tempering LoCool” HVAC mode = “Tempering HiCool”

The decision making/selection process for the tempering trip set point is as follows:

•If an HVAC cool mode is in effect, then the vent trip point is T.CL.

•If in a pre-occupied purge mode (Operating Modes→ MODE→IAQ.P=ON), then the trip point is T.PRG.

•If in an occupied mode (Operating Modes→MODE →IAQ.P=ON), then the trip point is T.V.OC.

•For all other cases, the trip point is T.V.UN.

NOTE: The unoccupied economizer free cooling mode does not qualify as a HVAC cool mode as it is an energy saving feature and has its own OAT lockout already. The unoccupied free cooling mode (HVAC mode = Unocc. Free Cool) will override any unoccupied vent mode from triggering a temper- ing mode.

If OAT is above the chosen tempering set point, tempering will not be allowed. Additionally, tempering mode is locked out if any stages of mechanical cooling are present.

A minimum amount of time must pass before calling out any tempering mode. In effect, the EDT must fall below the trip point value –1° F continuously for a minimum of 2 minutes. Also, at the end of a mechanical cooling cycle, there must be a minimum 10 minutes of delay allowed before con- sidering tempering during vent mode in order to allow any residual cooling to dissipate from the evaporator coil.

If the above conditions are met, the algorithm is free to select the tempering mode (MODETEMP). If a tempering mode becomes active, the modulating heat source (staged gas) will attempt to maintain leaving-air temperature (LAT) at the tempering set point used to trigger the tempering mode. The technique for modulation of set point for staged gas and hydronic heat is the same as in a heat mode. More information regarding the operation of heating can be referenced in the Heating Control section.

Recovery from a tempering mode (MODETEMP) will occur when the EDT rises above the trip point. On any change in HVACMODE, the tempering routine will re-assess the tempering set point which may cause the control to continue or exit tempering mode.

Static Pressure Control — Variable air volume (VAV) air-conditioning systems must provide varying amounts of air to the conditioned space. As air terminals downstream of the unit modulate their flows, the unit must maintain control over the duct static pressure in order to accommodate the needs of the terminals and meet the varying combined airflow require- ment.

A 48/50AK,AY,A3,A5 unit equipped with a duct pressure control system is provided with a variable frequency drive (VFD) for the supply fan. The speed of the fan can be con- trolled directly by the ComfortLink™ controls. A transducer is used to measure duct static pressure. The signal from the trans- ducer is received by the ECB-2 board and is then used in a PID control routine that outputs a 4 to 20 mA signal to the VFD.

Generally, only VAV systems utilize static pressure control. It is required because as the system VAV terminals modulate closed when less air is required, there must be a means of controlling airflow from the unit, thereby effectively prevent- ing overpressurization and its accompanying problems.

The three most fundamental configurations for most appli- cations are Configuration→SP→SP.CF, which is the static pressure control type, Configuration→SP→SP.S, used to enable the static pressure sensor, and Configuration→SP →SP.SP, the static pressure set point to be maintained.

OPERATION — On units equipped with a VFD and a proper static pressure sensor, when SP.CF, SP.S and SP.SP are config- ured, a PID routine periodically measures the duct static

pressure and calculates the error from set point. This error is simply the duct static pressure set point minus the measured duct static pressure. The error becomes the basis for the propor- tional term of the PID. The routine also calculates the integral of the error over time, and the derivative (rate of change) of the error. A value is calculated as a result of this PID routine, and this value is then used to create an output signal used to adjust the VFD to maintain the static pressure set point.

Static pressure reset is the ability to force a lowering of the static pressure set point through an external control signal. The unit controls support this in two separate ways, through a 4 to 20 mA signal input wired to the unit’s isolator board input terminals (third party control) or via CCN.

When employing the CCN, this feature uses the communi- cations capabilities of VAV systems with ComfortID™ termi- nals under linkage. The system dynamically determines and maintains an optimal duct static pressure set point based on the actual load conditions in the space. This can result in a significant reduction in required fan energy by lowering the set point to only the level required to maintain adequate airflow throughout the system.

SETTING UP THE SYSTEM — The options for static pressure control are found under the Local Display Mode Configuration→SP. See Table 75.

CAUTION

Failure to correctly configure SP.CF and SP.FN when operating in VFD Bypass mode will result in the indoor fan motor running continuously. Damage to unit could result.

Static Pressure Configuration (SP.CF) — This variable is used to configure the use of ComfortLink™ controls for static pressure control. There are the following options:

0 (None) — There will be no static pressure control by Com- fortLink controls. This setting would be used for a constant volume (CV) application when static pressure control is not re- quired or for a VAV application if there will be third-party con- trol of the VFD. In this latter case, a suitable means of control must be field installed.

Additionally, SP.CF must be set to 0 (None) when a unit is equipped with optional VFD bypass and is operating in Bypass mode. Failure to change this configuration in Bypass mode will result in the indoor fan motor running continuously.

1 (VFD Control) — This will enable the use of ComfortLink controls for static pressure control via a supply fan VFD.

Static Pressure Fan Control? (SP.FN) — This is automatical- ly set to Yes when SP.CF = 1. When the user would like the 4 to 20 mA output to energize the VFD, as opposed to the fan re- lay, SP.FN may be set to Yes when SP.CF = 0. When the con- trol turns the fan ON, the control will send the SP.MX value of the 4 to 20 mA signal to the third party VFD control.

Additionally, SP.FN must be set to NO when the unit is equipped with optional VFD bypass and is operating in Bypass mode. Failure to change this configuration in bypass mode will result in the indoor fan motor running continuously.

Static Pressure Sensor (SP.S) — This variable enables the use of a supply duct static pressure sensor. This must be enabled to use ComfortLink controls for static pressure control. If using a third-party control for the VFD, this should be disabled.

Static Pressure Low Range (SP.LO) — This is the minimum static pressure that the sensor will measure. For most sensors this will be 0 in. wg. The ComfortLink controls will map this value to a 4 mA sensor input.

Static Pressure High Range (SP.HI) — This is the maximum static pressure that the sensor will measure. Commonly this will be 5 in. wg. The ComfortLink controls will map this value to a 20 mA sensor input.

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