Carel pCO2 Series Manual

Standard Shelter
Cod. +030221471 – Rel. 2.0 – April 01, 2003
13
9 FREECOOLING
Energy savings can be achieved using outside air as a means of cooling the environment being air-conditioned. This is done using a damper to
let in outside air that is colder than the air inside the environment.
It must be established whether the temperature of the outside air is sufficiently below the ambient temperature so as to enable freecooling. The
difference must be less than or equal to a certain value, defined as the Freecooling offset.
The freecooling function is modulated according to the ambient temperature.
The freecooling option can be set to operate at the same time as the compressors, or alternatively not. If opting for separate operation, when the
compressor starts the freecooling damper closes.
The freecooling request decreases proportionally to the lowering of the air outlet temperature (see OUTLET LIMITATION)
If the freecooling function is not enabled, due to one of the above causes, the damper can still remain minimally open, at a level set by the user.
The freecooling damper is closed completely only in the following cases:
- When the shelter is off
- Outside temperature probe faulty, not connected or not enabled
- Room temperature probe faulty or not connected
- Fire/Smoke alarm
The freecooling function can be controlled in two different ways:
• Using a 0-10V modulating output on the pCO1-pCO2
• Using two digital outputs (not available on pCO1xs)
See TEMPERATURE CONTROL.
In the event of blackouts, the freecooling function continues to operate, thus continuing, if possible, the inlet of air that is colder than the
ambient temperature. During this phase the normal freecooling offset (default value 2.0ºC) is no longer considered, but rather a new fixed offset
of 1.0ºC is used. In this phase the outlet fan also operates at 100% speed.
Even if the compressor/compressors cannot operate due to alarms, the normal freecooling offset (default value 2.0ºC) is no longer considered,
but rather the fixed offset of 1.0ºC is used.
The humidity in the room is also controlled.
9.1 HUMIDITY CONTROL IN FREECOOLING
NB.: All the values in the following graph refer to the default values
If the ambient humidity is too high, the freecooling function will be disabled for a certain time that can be set by the manufacturer. Once this
time has elapsed, if the humidity has fallen below the freecooling re-enabling threshold, the damper will be able to modulate normally again.
During a blackout this function is disabled.
9.2 0-10Volt MODULATING DAMPER
Dampers that use a 0-10Volt modulating signal from the pCO1-pCO2 to vary their degree of opening from 0% to 100%. The 0-10Volt electrical
signal is directly proportional to the proportional temperature band, therefore the degree of opening always corresponds to demand.
9.3 FREECOOLING CONTROLLED BY DIGITAL OUTPUTS
Based on the activation time of the relays, the degree of opening of the damper varies from 0% to 100%, using a travel time called the “running
time” (time required to open or close completely, a rated value for the valves). The degree of opening of the damper is calculated based on the
proportion between the temperature differential and the running time.
9.3.1 REALIGNMENT
As can be imagined, the control of the damper using this system is quite difficult for the program to manage, as there is no feedback on the exact
position of the damper. The following solutions are used to overcome this problem:
• whenever the temperature control functions require the complete opening or closing of the damper, the program increases the
activation time of the opening or closing relays by 25% to ensure the complete closing / opening.
• whenever the board is switched on, the damper is closed completely for the running time, after which modulating operation can begin
based on the actual request.
Ambient
Humidit
y
FREECOOLING ENABLING
Enabled
Disabled
0 70.0

Carel pCO2 Series Specifications

General

Brand	Carel
Model	pCO2 Series
Category	Controller
Language	English