English
En [KJ]
STPEN
ENI
ENE
En [KJ]
STPEN
ENI
ENE
En [KJ]
STPEN
ENI
ENE
En [KJ]
STPEN
ENI
ENE
En [KJ]
STPEN
ENI
ENE
En [KJ]
STPEN
ENI
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0%
100%
Economizer
Room
Enthalpy
(kJ/kg)
Enthalpy_STP
Enthalpy_Diff
13
SysAer
3.6.5. ENTHALPY-BASED FREECOOLING AND FREEHEATING CONTROL
Opening the outdoor-air damper will not be a suitable response in either of the conditions illustrated above (1, 2)
since indoor enthalpy is nearer to the enthalpy set point than the outdoor enthalpy.
The enthalpy-based freecooling and freeheating control feature manages external damper opening based
on internal and external enthalpy conditions.
With room temperature and air humidity, the controller calculates the room enthalpy (see the Inputs/Outputs
menu), with external (outdoor) temperature and humidity, the controller calculates the outdoor enthalpy;
and with the temperature and Humidity control set points, it calculates the enthalpy set point. The aim of
the control feature is to keep room enthalpy as near as possible to the Enthalpy set point to save energy.
The following conditions may occur:
Opening the damper will be a suitable response in either of the conditions illustrated above (3, 4) since
external enthalpy is nearer to the enthalpy set point than internal enthalpy.
STPENS
Enthalpy set point [KJ]
ENI
Indoor enthalpy [KJ]
ENE
External enthalpy [KJ]
In case number 5 illustrated above, indoor
enthalpy is nearer to the enthalpy set point than
external enthalpy. However, in this case, opening
the damper is a suitable response because, with
the mixing of the two enthalpies (indoor and
external), indoor enthalpy will however approach
the enthalpy set point.
In case number 6 illustrated above, external
enthalpy is nearer to the enthalpy set point than
indoor enthalpy. Consequently, opening the
damper is a suitable response because, with the
mixing of room air and external air, indoor enthalpy
will however approach the enthalpy set point.
In standard operation:
Enthalpy setpoint = 38 kJ/kg (from
temperature and humidity setpoints),
Enthalpy diff = 5kJ/kg.
1
2
3
4
5
6
Should any of the cases illustrated above (3, 4, 5, 6) occur, damper opening will depend on internal enthalpy
as shown in the figure below:
