Heating/Cooling switchover
Heating/Cooling switchover| With
this function block, the system switches between heating and cooling
mode. A moving average of the outside temperature is formed, using the
same method as the "Average time" function block. The set number of
days is the time constant: after this period the average has
followed about two thirds of a temperature change. So it is not an
average over a fixed time window, but a slowly trailing value. If this
average is below the "Limit heating", the heating enable is set; if it
is above the "Limit cooling", the cooling enable is set. The separate
limits create a neutral range in between (neither heating nor cooling).
The average is provided at the output and stored; after a restart of
the controller it continues with the stored value. On the very first start without a stored value, the block uses the first available outside temperature reading as its starting value. Until then, both enables remain off. The "Limit heating" must be lower than the "Limit cooling". If the two values are swapped, an error message is issued and the cooling enable is blocked, so that both enables are never active at the same time. When generating the group addresses, no address is created for the enable input on purpose: an assigned enable starts at 0 and would block the function block. No address is created for the outside temperature either, it comes from the bus and is assigned manually. |
Inputs |
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| FG |
Enable |
Optional enable. If the input is not connected, the block
is enabled. Without enable (input 0) both outputs are set to 0. |
| AT |
Outside temperature* |
Current outside temperature from which the average is
formed. |
| TD |
Days average* |
Time constant of the average in days. The higher the value,
the more slowly the average follows the outside temperature. There is no
upper limit, the smallest value is 1 day. If the input is not assigned,
1 day is used. |
| GH |
Limit heating* |
If the average is below this value, „Enable heating“ is
set (default 16). |
| GK |
Limit cooling* |
If the average is above this value, „Enable cooling“ is
set (default 28). |
Outputs |
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| FH |
Enable heating |
1 if the outside-temperature average is below „Limit
heating“, otherwise 0. |
| FK |
Enable cooling |
1 if the outside-temperature average is above "Limit
cooling", otherwise 0. Stays at 0 if the limits are swapped. |
| DS |
Average |
Calculated moving outside-temperature average. The value is
stored and continues after a restart. |
Parameters |
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| This function block has no parameters of its own; the limits and the number of days are specified via the inputs. | ||