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ENG
ir33 universale +030220801 - rel. 2.1 - 21.06.2011
St1=13°C and di erential P1=2.0°C.
For compensation in cooling: c19=2, enabled for outside temperatures,
measured by B2, greater than 28°C, therefore St2=28. The authority,
considering that St1 must be lowered by 3°C in response to a variation in
B2 of 6°C (34-28), will be c4= -0.5. Finally, to prevent the inlet temperature
from falling below 10°C, a minimum limit must be set for St1, with c21=10.
The graph below shows the trend in St1.
St1_comp
13
c21=10
St2=28 34 B2
c4=-0,5
Fig. 6.k
Key:
St2 Activation set point 2
St1_comp E ective set point 1
B2 Outside probe
c4 Authority
c21 Minimum value of set point 1
6.5.4 Compensation in heating (parameter c19=3)
Compensation in heating can increase or decrease the value of St1
depending on whether c4 is negative or positive respectively.
St1 only varied if the temperature B2 is less than St2:
• if B2 is lower than St2 then: e ective St1 = St1 + (B2-St2)*c4
• if B2 is greater than St2: e ective St1 = St1
St2
c4=-2
c4=+0,5
c4=-0,5
B2
c22
St1_comp
c21
St1
c4=2
Fig. 6.l
Key:
St2 Activation set point 2e
St1_comp E ective set point 1
B2 Outside probe
c4 Authority
c21 Minimum value of set point 1
c22 Maximum value of set point 1
Example 4:
The design speci cations are as follows: in order to optimise the e ciency
of a boiler in a home heating system, the operating temperature (St1) can
be set at 70°C for outside temperatures above 15°C. When the outside
temperature drops, the operating temperature of the boiler must increase
proportionally, until reaching ad a maximum temperature of 85°C when
the outside temperature is less than or equal to 0°C.
Solution: use a controller with the main probe B1 on the water circuit,
mode 2 (heating), set point St1=70 and di erential P1=4. In addition,
probe B2 must be installed outside and compensation enabled in
heating (c19=3) with St2=15, so that the function is only activated when
the outside temperature is less than 15°C. To calculate the authority”,
consider that in response to a variation in B2 of -15°C (from +15 to 0°C),
St1 must change by +15°C (from 70°C to 85°C), so c4= -1.
Finally, set the maximum limit for St1, selecting c22=85°C. The following
graph shows how St1 varies as the outside temperature measured by B2
decreases.
St1_comp
c22=85
70
St2=15
0
B2
c4=-1
Fig. 6.m
Key:
St2 Activation set point 2
St1_comp E ective set point 1
B2 Outside probe
c4 Authority
c22 Maximum value of set point 1
6.5.5 Continuous compensation (parameter c19=4)
The compensation of St1 is active for values of B2 other than St2: with
this value of c19, parameter P2 can be used to de ne a dead zone around
St2 in which compensation is not active, that is, when the value read by
B2 is between St2-P2 and St2+P2, compensation is disabled and St1 is
not changed:
if B2 is greater than (St2+P2), e ective St1 = St1+ [B2-(St2+P2)]*c4
if B2 is between (St2-P2) and (St2+P2), e ective St1 =St1
if B2 is less than (St2-P2), e ective St1 = St1+ [B2-(St2-P2)]*c4
Compensation using c19=4 is the combined action of compensation
in cooling and compensation in heating, as described above. The
following diagrams show continuous compensation for positive and
negative values of c4. Neglecting the e ect of P2, if c4 is positive St1
increases when B2>St2 and decreases when B2<St2. Vice-versa, if c4 is
negative St1 decreases when B2 > St2 and increases when B2 is below
St2.
St1_comp
St2
c4>0
c22
c21
B2
P2P2
St2
c4<0
c22
c21
B2
P2P2
Fig. 6.n
Key:
St2 Activation set point 2
St1_comp E ective set point 1
B2 Outside probe
c4 Authority
c22 Maximum value of set point 1
c21 Minimum value of set point 1
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