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OPERATION
Frost protection
All ventilation units with a counterflow heat exchanger will ice
up if the outdoor temperature is below freezing for a
prolonged period.
The extracted air condenses when it is cooled down during heat
recovery. The high temperature efficiency will slowly turn the
condensate to ice, which will block up the counterflow heat
exchanger unless action is taken to remedy this.
Consideration must be given to whether the unit's operation
can be protected during a lengthy period of frost or whether it
is acceptable to decrease its operation.
In homes which are occupied at night, it would be advisable
to protect the unit against frost when the outdoor tempera-
ture is coldest by using a pre-heating element. On the other
hand, if the ventilation is for an office, it may be acceptable to
decrease the operating level at night.
Normal operation
Normal operation secured
until outdoor temp. < -12 °C
When outdoor temp. < -12 °C
reduced air volume
The example below shows the energy used to frost protect versus defrosting.
Air volume
Frost protection when outside temperature is
Hours during the year
Energy used to frost protection via pre-heating
Loss of energy when icing
Loss of energy when deicing
Energy savings by using frost protection
Average calculation by Danish dry weather data.
ɳt[%]
Operation Ice building
The energy used for the preheating is not wasted, as it ensures
a constant high temperature efficiency
Frost protection
No
Outdoor temperature
< -3 °C
Yes
Pre-heater
installed
Yes
126 m
/h
216 m
/h
3
3
-2 °C
-2 °C
676
676
107 kWh/a
183 kWh/a
105 kWh/a
180 kWh/a
200 kWh/a
343 kWh/a
198 kWh/a
340 kWh/a
14
Defrost
Ice building
After 30 min.
No
Defrost function
starts when:
Outdoor temp < 1 °C (T8)
Discharge air < 3 °C in 5 min.
1. Bypass damper opens
2. The intake motor switches off
3. Warm extracted air will flow
through the heat exchanger
4. The ice is melting
Defrosting stops when:
Discharge air > 7°C (T4)
With pre-heater
t
> -3°C
Außen
t
< -3°C
Außen
Defrost function
Defrost
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