Carel k.Air, User Manual, Page: 70 / 192

70
Functions
k.air +030220981 rel. 1.2 - 01.12.2020
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+
+
H%
T
T
H%
EXH AUST
FRESH
AI 0
AI 2 AI 3
DO 0
AO 2
AO 4
AI 9
Key
AI0 Supply temperature
AI2 Return temperature
AI3 Return humidity
AI9 Exhaust humidity
AO2/DO0 Bypass damper signals
AO4 Fresh air damper signal
AO16/DO58 IEC signal
Fig. 9.z
IEC stage activation
The activation logic determines in advance whether the humidity conditions of the exhaust air are suffi cient to start the indirect
cooling process. This is done by measuring the return humidity, which must be lower than the “activation threshold” set on scre-
en I005. A diff erential is provided to prevent rapid transients. If the activation condition is verifi ed, the IEC stage is available as part
of sequential temperature control, and is bypassed by acting directly on the subsequent stage. Another condition required for
activation is that the heat recovery unit is not bypassed (this condition is only true when the damper is fi tted).
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OFF
Thr
ON
RetH
IEC activation
diff
Fig. 9.aa
IEC stage control
Following verifi cation of the conditions for activation of the IEC stage, the humidity request from the sequential temperature
control stage is sent via the analogue, digital or serial output. See chapters “PID controllers” and “Temperature control”. The PI
parameters used to manage IEC need to be set on screen I001.
On/off humidifi ers are switched on and off when the PI request reaches 100% and 0% respectively.
IEC stage limitation
The IEC limit function is necessary to reduce wasted water when the exhaust air reaches saturation. The power supplied to the
IEC humidifi er is used to increase the amount of moisture introduced into the saturated air, which then precipitates, meaning
water is wasted as it does not serve to lower the exhaust air temperature. Therefore, two possible functions are available to
improve IEC effi
ciency:
• Air saturation limit, using the exhaust humidity probe measurement (appropriately enabled). On screen I010, a threshold
can be set beyond which a PI limit controller gradually begins to reduce the request sent to the IEC humidifi er. If necessary,
fi ne-tine the values of parameters kp and ti. For on/off IEC humidifi ers used with an exhaust humidity probe, the limit will still
be used, however instability may arise in the system due to the lack of modulation, and therefore it is recommended to set
the limit threshold at 100%, thus disabling the limit.
• IEC limit based on exhaust air quantity. If no saturation probe is installed, or in any case as an additional preventive function,
the IEC request can be reduced proportionally based on the closure of the fresh air damper. This is because it is assumed
that a reduction in the amount of fresh air introduced corresponds to a reduction in the amount of exhaust air discharged,
meaning a lower quantity of air to be handled by the IEC. This function only has one parameter, available on screen I015,
which determines the maximum proportional reduction value calculated based on the total travel of the fresh air damper.
For example, if set to 30%, it means when the fresh air damper is fully closed, IEC is limited by 30%. By default the parameter
is set to 0%, i.e. the limit is disabled.