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Access 4.x |
Plate exchanger defrosting with pressure monitoring |
The differential pressure transmitter is used to measure the drop in the air pressure over the exchanger's extract and exhaust sides. The defrosting function is activated if the differential pressure exceeds calculated limit. Options of Bypass and Stop defrosting can be used individually or in combination:
Bypass: defrosting of the exchanger is achieved by 100% bypassing the cold Outdoor - Supply airflow.
Warm Extract - Exhaust air is the only air flow that is allowed through the exchanger, to defrost it to the operational level.
Defrosting the exchanger doesn't add to heating and therefore has to be compensated by other sources (e.g. heating, pre-heater, extra sequence).
Stop defrosting: defrosting of the exchanger is achieved by temporarily stopping the supply air fan.
The exchanger is defrosted with the only warm airflow of Extract - Exhaust left.
The drawback is that under-pressure in the room is created, which might be unacceptable.
A configuration example for the combined use of Bypass and Stop defrosting
Variable |
Available options & Selection |
Note |
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Sequence selection |
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Configuration > Functions > Function activation > Heating/Cooling sequence setup |
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Sequence for exchanger |
...| SEQ-B Exchanger |… |
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Sequence settings |
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Configuration > Functions > Function activation > Heating/Cooling sequence setup > Exchanger |
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Type of sequence |
... | Exchanger | … |
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Type of exchanger |
| Rotary | Plate | Liquid | |
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Type of defrosting |
...| Pressure monitoring | ... |
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Defrosting configuration |
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Configuration > Functions > Temperature control > Defrosting pressure monitoring |
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Bypass |
| Off | On | |
Defrosting by bypassing cold air |
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Stop defrosting |
| Off | On | |
Defrosting by stopping supply air fan |
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Fan speed when defrosting |
|Auto | Low | Normal | High | |
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Allocate analog inputs |
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Configuration > I/O allocation settings > Analog inputs |
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Flow extract air |
Any available I/O |
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Pressure exchanger extract air |
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Defrost operational settings |
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Data & Settings > Temperature control > Exchanger > Defrosting pressure monitoring |
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Exchanger outdoor temperature to allow defrosting (Tavf) |
[0] oC |
Defrosting is enabled (not activated yet) if air entering the heat exchanger is colder than 0oC |
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Exchanger outdoor temperature for stop of supply air fan (Tsavf) |
[-10] oC |
Bypass defrosting is disabled, Supply air fan stop defrosting is enabled if air entering the heat exchanger is colder than -10oC |
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Max deviation exchanger pressure to start defrosting (Spavf) |
[50] % |
Defrosting is active if pressure drop over the heat exchanger is more than 50% higher (compared to the calibrated value) longer than delay time |
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Hysteresis to end defrosting (SPhys) |
[60] % |
Defrosting is deactivated then at least 60% of initial exchanger's air permeability is restored longer than delay time |
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Delay for pressure limits |
[10] s |
Delay time for activation and deactivation of the defrosting |
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Reduction of supply air fan (Nred) |
[5] % |
Fixed reduction of supply air fan output during bypass defrosting (valid with manual fan control type) |
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Max reduction supply- and extract air fan setpoints (Nafr) |
[20] % |
The bypass defrosting function will linearly decrease fan setpoint to the MAX reduction when supply temperature is lower than supply temp setpoint. It reaches max setpoint reduction when supply temperature is 4°K lower than setpoint. If supply temperature drops lower than -4°K from setpoint the bypass defrosting will stop. |
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Max time in bypass defrosting |
[15] min |
Delay for switching to stop defrosting or AL-66 Defrosting alarm (if stop defrosting in not allowed) |
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Max time in stop defrosting |
[20] min |
AL-66 Defrosting alarm is triggered if SAF stop defrosting is active longer than 20 minutes |
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Actual pressure exchanger extract |
___ Pa |
Actual and critical pressure drop (at current airflow through the heat exchanger) |
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Actual setpoint start defrosting |
___ Pa |
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