Unit Operation
Possible |
| Heat Pump | |
Fan Modes |
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OFF |
| Fan Off | |
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| Continuous: (Field | |
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| Modified) | |
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| z In occupied mode, the | |
AUTO |
| fan runs continuously. | |
| In unoccupied mode, | ||
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| the fan cycles OFF | |
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| when no heating or | |
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| cooling is required. | |
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| Cycling: (Factory Default) | |
AUTO |
| z The fan cycles ON and | |
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| OFF with compressor | |
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| operation. | |
The ZN510 controller receives the fan mode from either a wired zone sensor or as a communicated valve. When neither a zone sensor nor communicated fan mode are present, the ZN510 controller will default unit operation to AUTO.
Note:
zA building automation system can also generate a fan mode request and communicate this request to the controller.
zIf the ZN510 controller does not receive a hardwired or commu- nicated request for the fan mode, the unit recognizes the fan input as AUTO and the fan operates according to the default configuration.
Fan Off Delay
When the heating output is controlled off, the ZN510 automatically runs the fan ON for an additional 30 seconds to give the fan time to blow off any residual heat.
Leaving Water Temperature ZN510 uses analog input 1 (AI 1) as the leaving water temperature input for use with a thermistor. This input (AI 1) is automatically assigned as a leaving water temperature input. As explained in the binary input section, the leaving water temperature input protects the heat exchanger (circuit 1) from low temperatures. The second heat exchanger, present in units with two compressors is protected with a binary low temperature detection device. Based on the application of the unit, circuit operation is terminated when the leaving water temperature falls below 35 F or
20 F. This is set when the unit is ordered.
The ZN510 controller compares the measured leaving water temperature to the leaving water temperature low limit value to determine a fault condition. When the measured leaving water temperature is less than the leaving water temperature low limit, the controller generates a Low Temp Detect diagnostic. If the Leaving Water Temp Sensor fails to open or close the controller generates a Leaving Water Temp Failure diagnostic. This disables unit operation.
Note:
A low temperature detection failure diagnostic for compressor 1 may require you to manually reset the unit to restore compressor opera- tion.
Similarly, the ZN510 controller uses a binary low temperature detection device (fixed low limit trip point) to
See the Diagnostics section on page 28 for information about the automatic diagnostic reset function.
Filter Maintenance Timer
The controller’s filter maintenance timer is based on the unit fan’s cumulative run hours. The controller compares the fan run time against an adjustable fan run hours limit (maintenance required setpoint time, stored in the controller) and recommends unit maintenance (i.e. changing the filter).
Use Rover or BAS system to edit the maintenance required setpoint time. Once the setpoint limit is exceeded the controller generates a filter maintenance timer diagnostic. When the maintenance required setpoint time is zero, the controller disables the diagnostic feature.
Discharge Air Temperature Analog input 2 (AI 2) is used as the discharge air temperature input for use with a 10,000 ohm thermistor. Typical factory placement of the thermistor is at the discharge area of the unit. The discharge air temperature sensor does not affect unit operation. The measured temperature is for information only to be read by the building automation system or for troubleshooting unit operation with Rover.
Once a valid discharge air temperature signal has been established by the thermistor or communicated and the value is no longer present, the controller generates a discharge air temperature failure diagnostic. This will not disable unit operation. If the sensor returns with a valid temperature, the diagnostic automatically clears
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