User manual
24
Sbrinamento
Intervallo di tempo dI
(impostato) tra gli sbrinamenti
Nuovo intervallo di tempo
(calcolato) tra gli sbrinamenti
Intervallo di tempo dI (impostato)
tra gli sbrinamenti
dI dI
1
dI
2
dI
dI
DdI DdI
tempo
0
dE < dn%
dE < dn%
dE > dn%
Fig. 6.a
ENGLISH
ir33 +030220441 - rel. 2.5 - 16.06.10
6.7 New defrost activation modes
6.7.1 Defrost according to compressor running time
To enable the controller for this operating mode, set a value >0 for parameter d10. This mode a ects the start defrost, that is,
according to the evaporator temperature (parameter d11), the controller checks the compressor running time (parameter d10)
and decides whether to activate the defrost or not. There are two parameters:
• d10: compressor running time, with the evaporation temperature less than the threshold, after which a defrost request is
generated;
• d11: evaporation temperature threshold.
The defrost is generated if the compressor has operated:
• for time d10;
• with an evaporator probe reading less than d11.
If there are two evaporators, two separate timers will be used for each evaporator, and the count of each timer will be activated
whenever the compressor is ON and the corresponding evaporation probe is below the threshold d11. The defrost will start when
at least one of the two timers has expired, that is, when at least one of the evaporators has operated for the time d10 below the
temperature threshold d11.
6.7.2 Defrost at variable intervals (dI)
To enable the controller for this operating mode, set parameter d12=1.
The control algorithm, according to the duration of the previous defrost, increases or decreases the defrost interval (dI) proportio-
nally for the following defrosts.
The following parameters are associated with this function.
• dI: interval between defrosts;
• d12: enable the function;
• dn: nominal duration of the defrost, in proportion to the set defrost timeout (value expressed as a %);
• dP1 and dP2: maximum defrost duration for evaporator 1 and 2;
• dH: control proportional factor.
The algorithm uses the following formulae:
dn1 dP1
100
dn
and
dn2 dP2
100
dn
to calculate the nominal defrost times dn1 and dn2 (in the case of the second evaporator) obtained as percentages dn of dP1 and dP2.
Therefore, if a defrost lasts less than the set time “dn”, the algorithm proportionally lengthens (depending on the value assigned to
parameter dH) the next defrost interval “dIn”.
The parameter ‘dH’ is a proportional factor that ampli es or attenuates the variation of “dI”:
ΔdI
dn
100
dI
dH
50
dE
*
dP
dE* = e ective defrost duration
Δd
I
dI
dI
n
may vary between and
Example:
If, for example, the defrost interval (dI) is set to 8 hours and the maximum defrost duration (dP1 or dP2) is set to 30 minutes,
however usually the defrost is required for 50% less than the time dP1 or dP2, set parameter dn = 50%. The control algorithm
will calculate, using the formula dn/100 x dP1= dn1 or dn/100 x dP2= dn2 (in the case of the second evaporator), the nominal
defrost times “dn1” or “dn2”, which, in the example shown, corresponds to 15 minutes, that is, 50% of dP.
The new interval dI1 for the next defrost is calculated by the algorithm, using the formula:
dI
1
dn
100
dIdI +
dH
50
dE
dP
At this point, if the defrost ends after 10 minutes (dE), replacing the known values in the formula gives:
dI
1
50
100
10
30
88
dH
50
consequently:
dI
1
1.167
8 +
dH
50
.
It is therefore clear how the factor dH increases or decreases the new dI1.
1) If dH= 0 (no in uence) dI1= 8 + 0= dl 8 hours
2) If dH= 25 (low in uence) dI1= 8 + (1.167*0.5) 8 h & 34 min.
3) If dH= 50 (medium in uence) dI1= 8 + (1.167*1) 9 h & 9 min.
4) If dH= 75 (med/high in uence) dI1= 8+(1.167*1.25) 9 h & 27 min.
5) If dH=100 (high in uence) dI1= 8 + (1.167*2) 10 h & 19 min.
In summary, dI1 varies from 8 hours (dI) by setting dH=0 (minimum value), to 10 hours and 19 minutes, by setting dH=100
(maximum value).
d
I
dI
2
2d
I