Carrier 48/50AJ specifications Indoor Air Quality Control The indoor air quality

RELEVANT ITEMS

The economizer’s commanded output can be found in Outputs→ECON→ECN.C.

The configurable fire speed override for supply fan VFD is in Configuration→SP→SP.FS.

The supply fan relay’s commanded output can be found in Outputs→FANS→S.FAN.

The supply fan VFD’s commanded speed can be found in Outputs→FANS→S.VFD.

Indoor Air Quality Control — The indoor air quality

(IAQ) function will admit fresh air into the space whenever space air quality sensors detect high levels of CO2.

When a space or return air CO2 sensor is connected to the unit control, the unit’s IAQ routine allows a demand-based control for ventilation air quantity, by providing a modulating outside air damper position that is proportional to CO2 level. The ventilation damper position is varied between a minimum ventilation level (based on internal sources of contaminants and CO2 levels other than from the effect of people) and the maximum design ventilation level (determined at maximum populated status in the building). Demand control ventilation (DCV) is also available when the ComfortLink™ unit is con- nected to a CCN system using ComfortID™ terminal controls.

This function also provides alternative control methods for controlling the amount of ventilation air being admitted, including fixed outdoor air ventilation rates (measured as cfm), external discrete sensor switch input and externally generated proportional signal controls.

The IAQ function requires the installation of the factory- option economizer system. The DCV sequences also require the connection of accessory (or field-supplied) space or return air CO2 sensors. Fixed cfm rate control requires the factory- installed outdoor air cfm option. External control of the ventilation position requires supplemental devices, including a 4 to 20 mA signal, a 10 kilo-ohm potentiometer, or a discrete switch input, depending on the method selected. Outside air CO2 levels may also be monitored directly and high CO2 economizer restriction applied when an outdoor air CO2 sensor is connected. (The outdoor CO2 sensor connection requires installation of the CEM.)

The ComfortLink control system has the capability of DCV using an IAQ sensor. The indoor air quality (IAQ) is measured using a CO2 sensor whose measurements are displayed in parts per million (ppm). The IAQ sensor can be field-installed in the return duct. There is also an accessory space IAQ sensor that can be installed directly in the occupied space. The sensor must provide a 4 to 20 mA output signal and must include its own 24-v supply. The sensor connects to terminal TB5-6 and 7. Be sure to leave the 182-ohm resistor in place on terminals 6 and 7.

OPERATION — The unit’s indoor air quality algorithm mod- ulates the position of the economizer damper between two user configurations depending upon the relationship between the IAQ and the outdoor air quality (OAQ). Both of these values can be read at the Inputs→AIR.Q submenu. The lower of these two configurable positions is referred to as the IAQ Demand Vent Min Position (IAQ.M), while the higher is referred to as Economizer Minimum Position (EC.MN). The IAQ.M should be set to an economizer position that brings in enough fresh air to remove contaminants and CO2 generated by sources other than people. The EC.MN value should be set to an economizer position that brings in enough fresh air to remove contaminants and CO2 generated by all sources including people. The EC.MN value is the design value for maximum occupancy.

The logic that is used to control the dampers in response to IAQ conditions is shown in Fig. 12. The ComfortLink™ con- trols will begin to open the damper from the IAQ.M position when the IAQ level begins to exceed the OAQ level by a

configurable amount, which is referred to as Differential Air Quality Low Limit (DAQ.L).

If OAQ is not being measured, OAQ can be manually con- figured. It should be set at around 400 to 450 ppm or measured with a handheld sensor during the commissioning of the unit. The OAQ reference level can be set using the OAQ Reference Set Point (OAQ.U). When the differential between IAQ and OAQ reaches the configurable Diff. Air Quality Hi Limit (DAQ.H), then the economizer position will be EC.MN.

When the IAQ–OAQ differential is between DAQ.L and DAQ.H, the control will modulate the damper between IAQ.M and EC.MN as shown in Fig. 12. The relationship is a linear relationship but other non-linear options can be used. The damper position will never exceed the bounds specified by IAQ.M and EC.MN during IAQ control.

If the building is occupied and the indoor fan is running and the differential between IAQ and OAQ is less than DAQ.L, the economizer will remain at IAQ.M. The economizer will not close completely. The damper position will be 0 when the fan is not running or the building is unoccupied. The damper posi- tion may exceed EC.MN in order to provide free cooling.

The ComfortLink controller is configured for air quality sensors which provide 4 mA at 0 ppm and 20 mA at 2000 ppm. If a sensor has a different range, these bounds must be reconfigured. These pertinent configurations for ranging the air quality sensors are IQ.R.L, IQ.R.H, OQ.R.L and OQ.R.H. The bounds represent the PPM corresponding to 4 mA (low) and 20 mA (high) for IAQ and OAQ, respectively.

If OAQ exceeds the OAQ Lockout Value (OAQ.L), then the economizer will remain at IAQ.M. This is used to limit the use of outside air which outdoor air CO2 levels are above the OAQ.L limit. Normally a linear control of the damper vs. the IAQ control signal can be used, but the control also supports non-linear control. Different curves can be used based on the Diff.AQ Responsiveness Variable (IAQ.R). See Fig. 13.

SETTING UP THE SYSTEM — The IAQ configuration op- tions are under the Local Display Mode Configuration→IAQ. See Table 84.

Economizer Min Position (Configuration→IAQ→DCV.C →EC.MN) — This is the fully occupied minimum economiz- er position.

IAQ Demand Vent Min Pos. (Configuration→IAQ→DCV.C →IAQ.M) — This configuration will be used to set the mini- mum damper position in the occupied period when there is no IAQ demand.

IAQ Analog Sensor Config (Configuration→IAQ→ AQ.CF→IQ.A.C) — This is used to configure the type of IAQ position control. It has the following options:

•IQ.A.C = 0 (No analog input). If there is no other mini- mum position control, the economizer minimum position will be Configuration→IAQ→DCV.C→EC.MN and there will be no IAQ control.

•IQ.A.C = 1 (IAQ analog input). An indoor air (space or return air) CO2 sensor is installed. If an outdoor air CO2 sensor is also installed, or OAQ is broadcast on the CCN, or if a default OAQ value is used, then the unit can per- form IAQ control.

•IQ.A.C = 2 (IAQ analog input with minimum position override) — If the differential between IAQ and OAQ is above Configuration→IAQ→AQ.SP→DAQ.H, the economizer minimum position will be the IAQ override position (Configuration→IAQ→AQ.SP→IQ.O.P).

•IQ.A.C = 3 (4 to 20 mA minimum position) — With a 4 to 20 mA signal connected to TB5-6 and 7, the econo- mizer minimum position will be scaled linearly from 0% (4 mA) to EC.MX (20 mA).

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