Carrier 48TC*D08 appendix IAQS = IAQD + OAQ OAQ = 400 ppm if not present

There is also a SAT tempering routine that will act as SAT low limit safety to prevent the SAT from becoming too cold should the economizer fail to close. One stage of heating will be energized if it is not in the Cooling or Free Cooling mode and the OAT is below 55_F and the SAT is below 40_F. It will deenergize when the SAT > (SPT + 10_F).

Indoor Air Quality — If the optional indoor air quality (IAQI) sensor is installed, the PremierLink controller will maintain indoor air quality within the space at the user configured differential setpoint (IAQD) in the CONFIG configuration table. The setpoint is the difference between the IAQI and an optional outdoor air quality sensor (OAQ). If the OAQ is not present then a fixed value of 400 ppm is used. The actual space IAQ setpoint (IAQS) is calculated as follows:

IAQS = IAQD + OAQ (OAQ = 400 ppm if not present)

As air quality within the space changes, the minimum position of the economizer damper will be changed also thus allowing more or less outdoor air into the space depending on the relationship of the IAQI to the IAQS. The IAQ algorithm runs every 30 seconds and calculates IAQ minimum position value using a PID loop on the IAQI deviation from the IAQS. The IAQ minimum position is then compared against the user configured minimum position (MDP) and the greatest value becomes the final minimum damper position (IQMP). If the calculated IAQ minimum position is greater than the IAQ maximum damper position (IAQMAXP) decision in the SERVICE configuration table, then it will be clamped to IAQMAXP value.

If IAQ is configured for low priority, the positioning of the economizer damper can be overridden by comfort requirements. If the SPT > OCSP + 2.5 or the SPT < OHSP - 2.5 then IAQ minimum position becomes 0 and the IQMP = MDP. The IAQ mode will resume when the SPT ≤ OCSP + 1.0 and SPT ≥ OHSP - 1.0.

If IAQ is configured for high priority and the OAT < 55_F and the SAT < (SPT - 10_F), the algorithm will enable the heat stages to maintain the SAT between the SPT and the SPT + 10_F.

IAQ Pre-Occupancy Purge — This function is designed to purge the space of airborne contaminants that may have accumulated 2 hours prior to the beginning of the next occupied period. The maximum damper position that will be used is temperature compensated for cold whether conditions and can be pre-empted by Temperature Compensated Start function. For pre-occupancy to occur, the following conditions must be met:

S IAQ Pre-Occupancy Purge option is enabled in the CONFIG configuration table

S Unit is in the unoccupied state S Current Time is valid

S Next Occupied Time is valid

S Time is within 2 hours of next Occupied period

S Time is within Purge Duration (user-defined 5 to 60 minutes in the CONFIG configuration table)

S OAT Reading is available

If all of the above conditions are met, the economizer damper IQMP is temporarily overridden by the pre-occupancy damper position (PURGEMP). The PURGEMP will be set to one of the following conditions based on atmospheric conditions and the space temperature:

S If the OAT ≥ NTLO (Unoccupied OAT Lockout Temperature) and OAT < 65_F and OAT is less than or equal to OCSP and Enthalpy = Low then PURGEMP = 100%.

S If the OAT < NTLO then PURGEMP = LTMP (Low Temperature Minimum Position - defaults to 10%)

S If the OAT > 65_F or (OAT ≥ NTLO and OAT > OCSP) or Enthalpy = High then PURGEMP = HTMP (High Temperature Minimum Position defaults to 35%).

The LTMP and HTMP are user adjustable values from 0 to 100% in the SETPOINT table. Whenever PURGEMP results in a number greater than 0%, the IAQ pre-occupancy purge mode will be enabled turning on the Indoor Fan Relay and setting the economizer IQMP to the PURGEMP value. When IAQ pre-occupancy mode is not active PURGEMP = 0%.

Unoccupied Free Cooling — Unoccupied free cool function will start the indoor fan during unoccupied times in order to cool the space with outside air. This function is performed to delay the need for mechanical cooling when the system enters the occupied period. Depending on how Unoccupied Free Cooling is configured, unoccupied mode can occur at any time in the unoccupied time period or 2 to 6 hours prior to the next occupied time. Once the space has been sufficiently cooled during this cycle, the fan will be stopped. In order to perform unoccupied free cooling all of the following conditions must be met:

S NTEN option is enabled in the CONFIG configuration table

S Unit is in unoccupied state S Current time of day is valid

S Temperature Compensated Start mode is not active S COOL mode is not active

S HEAT mode is not active S SPT reading is available S OAT reading is available S Enthalpy is low

SOAT > NTLO (with 1_F hysteresis) and < Max Free Cool setpoint

If any of the above conditions are not met, Unoccupied Free Cool mode will be stopped, otherwise, the mode will be controlled as follows:

The NTFC setpoint (NTSP) is determined as NTSP = (OCSP + OHSP) / 2

The Unoccupied Free Cool mode will be started when: SPT > (NTSP + 2_F) and SPT > (OAT + 8_F)

The Unoccupied Free Cool mode will be stopped when: SPT < NTSP or SPT < (OAT + 3_F)

48TC

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