Controlling The Cooling Capacity; General; Operating Principle - Siemens PolyCool CPS 40 Manuel D'installation Et D'utilisation

SMX
Exemple
Building Technologies
HVAC Products
6 Controlling the cooling
capacity

6.1 General

The cooling capacity of the refrigeration unit drops as the
superheat of the suction gas increases. This effect can be
utilized by PolyCool Superheat for controlling the cooling
capacity.

6.2 Operating principle

The capacity controller continuously varies with the setpoint
of superheat within a certain range. The assignment is made
proportionally to a DC 0...10 V signal, or to the manipulated
variable of the capacity controller. DC 0 V / 4 mA corre-
sponds to the setpoint of superheat (∆T SP), and DC 10 V /
20 mA corresponds to the sum of (∆T SP+SMX) based on
the configuration of. Both parameters can be entered in the
parameter mode. The greater SMX, the more the cooling
capacity can be reduced. But as the capacity drops, the
evaporation pressure will also drop, and thus the evaporation
temperature. The average drop for each additional K super-
heat is as follows:
• The evaporation temperature by 1 °C
• The cooling capacity Q
Required is a reduction in cooling capacity of 50 %,
i.e. 50 % / 3.1 ≅ 16 K for SMX
To ensure lubrication and cooling of the compressor at all
times, superheat cannot be increased beyond certain limits.
For the minimum permissible suction pressure, refer to the
compressor's specification sheet.
If the cooling capacity is reduced too much, excessive icing
can occur on the evaporator (air coolers). The drop in
evaporator temperature should also be observed for chillers
without frost protection.
CPS40
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22.09.2006