Lochinvar HERALD HCB116CE, Руководство по установке, Страница: 82 / 92

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21.9.5 C
ASCADE
D
IFFERENTIAL
This parameter determines how much the temperature must go below the turn off temperature (Set point + Offset)
before the lead boiler turns on. This parameter can be adjusted by the installer by accessing the Cascade Differential
parameter. The temperature range of this parameter is 0°C to 33°C The default value is 11°C.
21.9.6 C
ASCADE
T
YPE
(L/L / EFF)
There are two (2) options for the way a Cascade divides the load between its heaters. The first is Lead/Lag,
designated as L/L in the menu. This method is used when it is desired to have the least amount of total flow through
the boilers. This method will modulate the last two (2) boilers that are firing. This provides for smooth transitions
when a boiler turns on or off. When the last boiler reaches 100% and the calculated load is still increasing, it will start
the next boiler at 20% and reduce the previous boiler to 80%, thus eliminating the sudden jump in total output of the
Cascade. When the calculated load is decreasing and the last boiler gets down to 20% fire, it will hold it there and
start lowering the firing rate on the next-to-last boiler. When the next-to-last boiler reaches 20%, it will turn the last
boiler off and raise the rate of the next-to-last boiler to 40%, thus eliminating the sudden drop in total output of the
Cascade.
The other Cascade divider method is Efficiency Optimisation, designated as EFF in the menu. This method is used,
as the name implies, when it is desired to have the most efficient system. When the first boiler reaches 100% rate, it
lowers its rate to 50% and turns on the next boiler at 50%. The two (2) boilers then modulate at the same rate. As the
calculated load increases further and both boilers ramp up to 100%, it lowers the rate of the first two (2) boilers to
67% and brings the next boiler on at 67%. The three (3) boilers then modulate together. As the calculated load
decreases, the boilers will reach 20%, at which time the last boiler (the third in our example) will turn off and the
Cascade will increase the rates of the remaining boilers to provide the equivalent total output as before ((3 x 20%) / 2
= 30% in our example).
Efficiency optimisation is automatically selected when boilers of different sizes are programmed into the Leader
control (see Boiler Size on page 27).
21.9.7 M
INIMUM
O
N
/O
FF
T
IME
In order to prevent units in a Cascade from short cycling, this parameter defines the minimum ON and OFF time for
each unit. The installer can adjust this time by accessing the Minimum On/Off Time parameter. The minimum
setting is 0 seconds and the maximum setting is 10 minutes. The default is 30 seconds.
21.9.8 M
INIMUM
N
EXT ON
T
IME
In order to reduce the risk of temperature overshoot with a Cascade, this parameter defines the minimum time delay
from starting one unit until the next unit may be started. The installer can adjust this time delay by accessing the
Minimum Next On Time parameter. The minimum setting is 0 minutes and the maximum setting is 10 minutes. The
default is 60 seconds.
21.9.9 M
INIMUM
N
UMBER OF
P
UMPS
O
N
When the boiler is a Cascade Leader, it can force a minimum number of boiler pump outputs to be on continuously,
regardless of how many boilers are firing. This is normally used when the boilers are piped in a full-flow configuration,
and the boiler pump outputs are controlling isolation valves. The Leader will force the boiler pump output on the
highest priority boiler to turn on first, then the boiler pump output on the second highest priority boiler, and so forth,
until the minimum number of pump outputs are turned on. The range of this parameter is 0 to 8. The default value is
0.