Trane Symbio 700 - Evaporator Defrost Control

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compressor operation. The defrost cycle is terminated based on the defrost termination
temperature calculation using the outdoor temperature (ODT) +47°F. The defrost termination
temperature (DTT) will be limited between 57° F and 72° F.
Evaporator Defrost Control
To prevent frost build-up on the indoor coil during low ambient conditions, compressor
operation is monitored and controlled accordingly, relative to outdoor air temperature.
Evaporator Defrost Control can be initiated through two means, based on configuration.
• If configured for Evaporator Defrost Control Enabled:
– When the unit is operating in a “Cool” mode with a valid Outdoor Air Temperature, the
EDC function will keep track of the amount of time that at least one compressor in the unit
is commanded ON and the Outdoor Air Temperature Active is less than the low ambient
temperature defined in table 3. If the Accumulated Compressor On Time reaches 10
minutes, the EDC function will cause the Compressor Output(s) to de-energize for three
minutes. The supply fan continues to operate during this three-minute interval at 100%
capacity. After the three-minute EDC timer has expired, the EDC function is ended and
compressors are allowed to operate as requested by the algorithm.
– Low Ambient Temperature Sepoints:
• Single Compressor Systems: 55° F
• Multi-Compressor Systems: 40° F
• If configured for FroStat Installed:
– A FroStat input can also be used to directly request the Evaporator Defrost Control
function
– When the unit is running in an effective “Cool” mode, the FroStat input will directly
control the FroStat diagnostic. If the FroStat input CLOSES, the diagnostic will be
annunciated.
– When the unit is running in an effective “Heat” mode, and the Refrigeration System ==
Heat Pump, the FroStat diagnostic will be controlled “Inactive” until the following are
true:
• FroStat input is CLOSED
• One or More Compressors have been active for Heat Pump Heating for more than 30
seconds.
Once the above two conditions are met, the FroStat Diagnostic will become Active.
– The FroStat diagnostic is an Auto-Reset diagnostic such that it will be reset when the
FroStat input is OPEN in either effecting unit mode.
– If the FroStat diagnostic becomes active, the Compressor Output(s) will de-energize until
the FroStat diagnostic is cleared. The supply fan continues to operate during the FroStat
diagnostic, so long as it is still requested by a heating or cooling function.
FroStat and Evaporator Defrost Control can both be configured on a unit, although in most cases,
only one should be necessary.
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