Heating / Cooling coil 2-stage heat pump, four binary outputs with internal reversing control and hot gas heating (HCclHpu22)

Required elements and how to configure them:

Function

The figure below shows BACnet objects associated with this application function. Primary signal flow is summarized as follows:

The demand signal(s) are received (HCclHReq / HCclCReq / HCclDhuReq) and processed into binary output signals for heat pump coil stage position (HpuCmdH1St / HpuCmdH2St / HpuCmdC1St / HpuCmdC2St).

Basic function: Accept request signal from associated room controller and pass it through a device mode logic switch; Output the result as a command to the BACnet object that controls the device.

Sequence - heating, cooling and dehumidification control

If heating, cooling or dehumidification is used, the accepted request signal (HCclHReq, HCclCReq, HCclDhuReq) will be converted into binary output signal(s) for heat pump coil position, reversing valve position (when present), source control and hot gas reheat coil.

Note
This AF does not perform loop control; its main purpose is to run commands. Loop control processes (for this AF) are managed in the "room" AF(s) that collaborate with this AF to command the end device.

Device mode: The input signal for device mode is a multistate value. HCclDevMod supports the following states:

• Off
• Control mode
• Fully open, heating
• Fully open, cooling

Availability signals – heating, cooling and dehumidification

Heating availability: When the following conditions are true, the binary output signal for "Heating / cooling coil available for heating" (HCclAvlH) will be Yes (available):

• Device mode = Control mode
• Manual control mode parameter (CtlModMan) = Automatic or Heating
• Present dehumidification request is 0%
• OA temperature not below a configurable limit (optional - see EnLockHTOaLo in Configuration)

When HCclAvlH is Yes, and the heating request signal is greater than the switch-on point, the heating request signal will be accepted.

Cooling availability: When the following conditions are true, the binary output signal for "Heating / cooling coil available for cooling" (HCclAvlC) will be Yes (available):

• Device mode = Control mode
• Manual control mode parameter (CtlModMan) = Automatic or Cooling
• Present dehumidification request is 0%

When HCclAvlC is Yes, and the cooling request signal is greater than the switch-on point, the cooling request signal will be accepted.

Dehumidification availability: When the following conditions are true, the binary output signal for "Heating / cooling coil available for dehumidification" (HCclAvlDhu) will be Yes (available):

• Device mode = Control mode
• Manual control mode parameter (CtlModMan) = Automatic or Cooling

When HCclAvlDhu is Yes, and the dehumidification request signal is greater than the switch-on point, the dehumidification request signal will be accepted.

Heat pump state (HpuSta)

HpuSta is a MCalcVal object that indicates the operating state of the heat pump (Off, Heating, or Cooling). If device mode (HCclDevMod) is off, HpuSta will be off. HpuSta will also be off if the heat pump unit’s internal reversing valve control logic requires the compressor(s) be off during the performance of internal reversing valve switching functions.

Compressor commanding (HpuCmdH1St, ..CmdH2St, ..CmdC1St, ..CmdC2St)

The 0-100% demand signal (heating, cooling or dehumidification) is converted to binary output via two hysteresis switches (stage 1: 33% on, 16% off; stage 2: 83% on, 66% off). And each stage of operation has a minimum on / minimum off time of 3 minutes (3 minutes on, 3 minutes off both configurable).

Note
Loop control objects in the Room AF for cooling, heating, and dehumidification are defined per default as PID controllers. To enable staged control the following properties can be changed for each controller as needed:

• Controller type = Staged controller
• Number of stages = 2

During normal operation an interstage time delay (a property of the loop control objects in the Room AF; default 5 minutes) prevents both compressors from energizing / cycling off at the same time. However, if the room operating mode changes from Comfort or Pre-Comfort to Economy or Protection and no demand is present, then both stages can shut off at the same time.

Equipment protection
The normal runtime priority for compressor commanding is 15 (Auto mode 6). During startup and interlock functions such as airflow status, minimum On/Off timers and source state monitoring, the compressor(s) are commanded at priority 5 (Protection mode 2) to ensure equipment protection.

The system evaluates a set of conditions in sequential order. If (as soon as) one is found to be True the compressor(s) are commanded On or Off at priority 5 and the evaluation sequence stops. See table.

If none of the conditions require protection, the heat pump compressor command at priority 5 is released.

Hot gas reheat coil commanding (EnHpuReHcl)

EnHpuReHcl will be set to True at Automatic mode 6 (Prio 15) when the following are true:

• Device mode is Control mode
• Room AF indicates heating sequence is active (HCDmd = Heating)
• Present dehumidification request (PrDhuReq) is greater than the switch-on point

Source commanding

When the present demand (heating, cooling or dehumidification) exceeds the switch-on point, a delay-off timer (DlyOffEnSrc) is activated to prevent compressor cycling and then the enable source command (EnHpuSrc) and source demand (HpuSrcDmd) will both be True.

Source available for monitoring

The source available indicates that media is available and heat pump coils can be activated. Source available indication can be from a central group function (Prio 15) or from a local BI sensor input (Prio14). If source available monitoring function is enabled (EnMonSrcAvl is Yes) and source is unavailable, device mode is set to off at Prio4 and each temperature/dehumidifier PID controller is turned off.

Source state monitoring

The source state indicates that media is flowing and heat pump coils can be activated.

The type of source state is configured to identify the location of the source (SrcStaMon). SrcStaMon is a multistate configuration parameter:

• None – The off command at equipment safety priority to device mode is disabled.
• Monitor enable source - When the source is commanded On, after a delay (DlyOnSrcSta) the compressor will be released; otherwise the compressor is set to off at equipment safety priority.
• Monitor source state - The source state (SrcSta) can come from a local BI sensor in the automation station. When there is no media flow the compressor is set to off at equipment safety priority.

Interlocks

Air volume flow status: When the switch indicates no airflow, the component sets compressors off at equipment safety priority (Prio 5, Protection mode 2). When the switch indicates airflow, the safety command to the compressors is released.

Air volume flow requests (heating, cooling, dehumidification)

Airflow heating request: When the present heating request signal is greater than the switch-on point or the device mode is "Fully open, heating" and the manual control mode is Automatic or Heating, then after a delay the Air volume flow heating request will be True.

Airflow cooling request: When the present cooling request signal is greater than the switch-on point or the device mode is "Fully open, cooling" and the manual control mode is Automatic or Cooling, then after a delay the Air volume flow cooling request will be True.

Airflow dehumidification request: When the present dehumidification request signal is greater than the switch-on point, then after a delay the Air volume flow dehumidification request will be True.

Airflow hold requests (heating, cooling)

Airflow hold for heating: When the present demand signal is greater than the switch-on point, the Air volume flow hold for heating will be True. When the present demand signal is less than the switch-on point minus a hysteresis, then after a delay the Air volume flow hold for heating will be False.

Airflow hold for cooling: When the present demand signal is greater than the switch-on point, the Air volume flow hold for cooling will be True. When the present demand signal is less than the switch-on point minus a hysteresis, then after a delay the Air volume flow hold for cooling will be False.

Signals in table are internal signals, not BACnet objects. For this reason they are not visible in the tool, but the parameters associated with them are. See comment column for hints on parameters that affect interlock functionality.

Equipment output limits

To avoid ice and refrigerant problems, specifications may call for logic that turns off the heat pump when the outside air is very cold. The following heat pump lock out feature is not active by default. To enable it, EnLockHpuTOaLo must be set to 1:Yes.

When the measured OA temperature value is below a configured cut out temperature, device mode (HcclDevMod) is set to Off at equipment safety priority (Prio 4). When the OA temperature rises above the cut out temperature plus a configured deadband, HcclDevMod is released from priority 4 and returns to normal control.

Fault inputs

Several Heat pump safety switches can be connected to shut off the equipment, including:

• Low suction pressure
• High compressor pressure
• High refrigerant pressure
• Low refrigerant pressure

Note
See the Hvac17 room segment AF for how to configure a condensate level monitor. Hvac17

Optional binary input object(s) pick up any Heat pump equipment alarm switch. When the switch indicates a fault, the component sets device mode to off at equipment safety priority (Prio 4). The "Available" signals for cooling and dehumidification also turn off. When the switch indicates no fault, the command to the device mode is disabled.

Heat pump compressor power

The nominal electric power usage of the compressor is provided for energy monitoring and coordination with other devices. When one stage of the heat pump coil is on, the compressor electric power (HpuElPwr) is equal to half nominal power (NomElPwr). NomElPwr can be obtained from the heat pump name plate (from heat pump manufacturer). When both stages of the heat pump coil are on, the compressor electric power is equal to NomElPwr. When the Heat pump coil is off, HpuElPwr equals zero.

Configuration

Parameters