Carrier PTV, 50PTH specifications •Cooling is set to Enable

ured maximum heating SAT limit (110 F default). As the SAT approaches this value, the control will increase the fan speed as required to ensure the SAT will remain within the limit. This feature provides the most quiet and efficient operation by oper- ating the fan at the lowest speed possible.

Fan Speed Control (During Cooling) — Whenever mechani- cal cooling is required and active, the control continuously monitors the supply-air temperature to verify it does not fall be- low the configured minimum cooling SAT limit (50 F default). As the SAT approaches this value, the control will increase the fan speed as required to ensure the SAT will remain within the limit. The fan will operate at lowest speed to maximize latent capacity during cooling.

COOLING — The WSHP Open controller will operate one or two stages of compression to maintain the desired cooling set point. The compressor outputs are controlled by the PI (propor- tional-integral) cooling loop and cooling stages capacity algo- rithm. They will be used to calculate the desired number of stages needed to satisfy the space by comparing the space tem- perature (SPT) to the appropriate cooling set point. The water side economizer, if applicable, will be used for first stage cool- ing in addition to the compressor(s). The following conditions must be true in order for the cooling algorithm to run:

•Cooling is set to Enable.

•Heating mode is not active and the compressor time guard has expired.

•Condensate overflow input is normal.

•If occupied, the SPT is greater than the occupied cooling set point.

•Space temperature reading is valid.

•If unoccupied, the SPT is greater than the unoccupied cooling set point.

•If economizer cooling is available and active and the economizer alone is insufficient to provide enough cool- ing.

•OAT (if available) is greater than the cooling lockout temperature.

If all the above conditions are met, the compressors will be energized as required, otherwise they will be deenergized. If cooling is active and should the SAT approach the minimum SAT limit, the fan will be indexed to the next higher speed. Should this be insufficient and if the SAT falls further (equal to the minimum SAT limit), the fan will be indexed to the maxi- mum speed. If the SAT continues to fall 5° F below the mini- mum SAT limit, all cooling stages will be disabled.

During Cooling mode, the reversing valve output will be held in the cooling position (either B or O type as configured) even after the compressor is stopped. The valve will not switch position until the Heating mode is required.

The configuration screens contain the minimum SAT parameter as well as cooling lockout based on outdoor-air temperature (OAT) Both can be adjusted to meet various specifications.

There is a 5-minute off time for the compressor as well as a 5-minute time delay when staging up to allow the SAT to achieve a stable temperature before energizing a second stage of capacity. Likewise, a 45-second delay is used when staging down.

After a compressor is staged off, it may be restarted again after a normal time-guard period of 5 minutes and if the sup- ply-air temperature has increased above the minimum supply- air temperature limit.

The WSHP Open controller provides a status input to moni- tor the compressor operation. The status is monitored to deter- mine if the compressor status matches the commanded state. This input is used to determine if a refrigerant safety switch or other safety device has tripped and caused the compressor to stop operating normally. If this should occur, an alarm will be generated to indicate the faulted compressor condition.

HEATING — The WSHP Open controller will operate one or two stages of compression to maintain the desired heating set point. The compressor outputs are controlled by the heating PI (proportional-integral) loop and heating stages capacity algo- rithm. They will be used to calculate the desired number of stages needed to satisfy the space by comparing the space tem- perature (SPT) to the appropriate heating set point. The follow- ing conditions must be true in order for the heating algorithm to run:

•Heating is set to Enable.

•Cooling mode is not active and the compressor time guard has expired.

•Condensate overflow input is normal.

•If occupied, the SPT is less than the occupied heating set point.

•Space temperature reading is valid.

•If unoccupied, the SPT is less than the unoccupied heat- ing set point.

•OAT (if available) is less than the heating lockout temperature.

If all the above conditions are met, the heating outputs will be energized as required, otherwise they will be deenergized. If the heating is active and should the SAT approach the maxi- mum SAT limit, the fan will be indexed to the next higher speed. Should this be insufficient, and the SAT rises further reaching the maximum heating SAT limit, the fan will be indexed to the maximum speed. If the SAT still continues to rise 5° F above the maximum limit, all heating stages will be disabled.

During Heating mode, the reversing valve output will be held in the heating position (either B or O type as configured) even after the compressor is stopped. The valve will not switch position until the Cooling mode is required.

The configuration screens contain the maximum SAT parameter as well as heating lockout based on outdoor-air temperature (OAT); both can be adjusted to meet various specifications.

There is a 5-minute off time for the compressor as well as a 5-minute time delay when staging up to allow the SAT to achieve a stable temperature before energizing a second stage of capacity. Likewise, a 45-second delay is used when staging down.

After a compressor is staged off, it may be restarted again after a normal time-guard period of 5 minutes and if the sup- ply-air temperature has fallen below the maximum supply air temperature limit.

The WSHP Open controller provides a status input to moni- tor the compressor operation. The status is monitored to deter- mine if the compressor status matches the commanded state. This input is used to determine if a refrigerant safety switch or other safety device has tripped and caused the compressor to stop operating normally. If this should occur, an alarm will be generated to indicate the faulted compressor condition. Also, if auxiliary heat is available (see below), the auxiliary heat will operate to replace the reverse cycle heating and maintain the space temperature as required.

AUXILIARY HEAT — The WSHP Open controller can con- trol a two-position, modulating water, or steam valve connect- ed to a coil on the discharge side of the unit and supplied by a boiler or a single-stage ducted electric heater in order to main- tain the desired heating set point. Should the compressor capac- ity be insufficient or a compressor failure occurs, the auxiliary heat will be used. Unless the compressor fails, the auxiliary heat will only operate to supplement the heat provided by the compressor if the space temperature falls more than one degree below the desired heating set point (the amount is configu- rable). The heat will be controlled so the SAT will not exceed the maximum heating SAT limit.

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