49
Operation
(Reference)
System Settings
Menu Item
Description
FC Change
Over
(2)
Free Cooling
For free cooling, the controller automatically controls the ventilation equipment. In this
case the HRV unit is set at the bypass mode and/or an outside air damper is opened to
intake outside air.
This sequence facilitates Free Cooling which happens when the outside air temperature
is lower than the room temperature. To avoid over cooling, the controller stops intake of
outside air when the room temperature reaches the minimum free cooling setpoint which
is the intermediate temperature between the preset cooling and heating setpoints.
The following two charts illustrate this process. The numbered arrows on the charts
correspond to the numbered boxes providing explanations for the two graphs.
1) Outside air temperature should be lower than the room temperature
The outside air temperature must be 4
°
C lower than the room temperature to allow the
free cooling operation. Hereafter, when the outside air temperature reaches the indoor
temperature, free cooling will be suspended.
2) Room temperature should be higher than the minimum free cooling temperature
Free cooling is permitted while the room temperature is above the minimum free cooling
target temperature which is the intermediate temperature between the preset cooling and
heating setpoints.
See page
84
88
to
1
2
Temperature
Room temperature
(Return air temperature of the
representative indoor unit)
Outdoor temperature
Free
Cooling
permitted
Free
Cooling
permitted
Free
Cooling
prohibited
4
°
C
Free cooling is prohibited when the outside air temperature rises above the
room temperature.
1
When the outdoor temperature decreases to 4
°
C below the room temperature,
Free cooling is permitted. The 4
°
C temperature difference prevents frequent
cycling of the free cooling operating sequence.
2
When the room
temperature decreases to
the minimum free cooling
temperature, Free cooling
is prohibited.
1
When the room
temperature increases to
1
°
C above the minimum
free cooling temperature,
Free cooling is permitted.
2
1
2
Room
temperature
Minimum free
cooling target
temperature
Free Cooling
permitted
Free Cooling
permitted
1
°
C
