27
Special conditions:
•
The economiser shall be kept closed when the unit is
stopped or in unoccupied mode.
•
The economiser shall be held at its minimum position of
30% (this value may be configured by Carrier Service)
when:
-
the unit is in heating mode,
-
room temperature is below room control point,
-
the difference between room temperature and out-
door temperature is less than the economiser utilisa-
tion threshold (i.e. a value of 7 K which may be
configured by Carrier Service),
-
blower temperature is below 10
°
C,
-
the unit is fitted with an outside air enthalpy sensor and
this is indicating a high enthalpy which is incompatible
with feeding in air from outside,
•
The economiser shall be kept fully open when purge mode
is active.
•
The minimum position of the economiser shall be altered
in order to meet air quality requirements (see section 5.18).
•
The minimum position of the economiser shall not exceed
25% if the outdoor temperature is below 6
°
C.
•
If the outdoor temperature is below 15
°
C, all compressors
shall be stopped and only free cooling shall be authorised.
If the unit is fitted with a power exhaust louvre, this shall be
open if the position of the economiser is in excess of 50% (this
threshold may be modified by Carrier Service).
5.17 - Purge
This function can only be used if the unit is fitted with an econo-
miser. When the unit switches from unoccupied to occupied
mode, the economiser is kept fully open for two minutes pro-
vided the outdoor temperature is between 10
°
C and 21
°
C. A
purge will not be activated if the occupied period is intended to
last less than two hours. This function must be validated by the
user in the Configuration menu. It is also possible to alter the
length of the purge and the limiting outdoor temperatures in the
Setpoint menu.
5.18 - Controlling air quality
This function is used if the unit is fitted with an air quality sen-
sor and an economiser. With the aid of a PI function, it enables
the position of the economiser to be continually adjusted in
order as far as possible to maintain air quality at its setpoint
whilst preventing the room temperature from drifting too
greatly (in view of the fact that the heating or cooling stages are
not authorised to operate at this point). On the other hand if the
error in the heating or cooling room setpoint being maintained
exceeds 2.2
°
C, this function is disabled and the economiser
returns to its minimum configured position (30%), and the
heating or cooling stages are authorised to operate again. Air
quality control cannot then be authorised for another hour. This
function is not active in unoccupied mode.
5.19 - Controlling humidity
The reading from the relative humidity sensor is compared with
the humidity setpoint to check whether a humidification cycle is
needed. The humidity setpoint together with the occupied and
unoccupied period dead bands may be altered in the Setpoint menu.
The unit switches over to humidification mode if humidity is
below [humidity setpoint less humidity dead band divided by
two]. Humidification mode stays active as long as humidity is
below humidity setpoint. The humidifier output is activated
whilst the humidification function is active. A humidifier must
be provided locally.
5.20 - Master/slave assembly
Up to 6 units can take part in a master/slave assembly. This
group then constitutes a zone in which conflicting states of
cooling/heating are not allowed between units. The master unit
determines the cooling or heating mode for the zone. If one of
the slave units is in a different cooling/heating mode from the
master unit, the unit concerned is switched to ventilation mode
without producing heat or cooling. This function is not active
in anti-freezing mode. The function operates under all
operating types. It requires the use of a communication bus
between the units concerned and must be configured by Carrier
Service.
5.21 - Fire protection
When the normally closed smoke detection contact is open, the
unit is shut down and either the fire damper is closed or the
economiser damper is opened.
