Frost protection and optimum start control are under the control of the FP/OS Control Zone (see Controls). If this zone is unspecified (i.e. if it is set to '0') then no frost protection or optimum start will operate.
Frost protection, if selected, applies to periods when the plant would otherwise be off. That is, periods outside the plant operation periods specified under Internal Conditions.
The following parameters are applicable:
Internal Frost Protection Temperature
Frost protection is under the control of an internal sensor situated in the Frost Protection/Optimum Start Control Zone. In this zone, frost protection will attempt (subject to plant availability) to maintain the air temperature at or above the Internal Frost Protection Temperature during hours when the plant would otherwise be off. If frost protection operates in the Frost Protection/Optimum Start Control Zone at any hour, it will also operate in all other zones for which heating is available, attempting to maintain the temperature in those zones at or above the Internal Frost Protection Temperature.
Internal Frost Protection Load Factor
The fraction of heating capacity available for internal frost protection. For example, if only 25% of capacity is to be made available for frost protection, then a load factor of 0.25 is entered. A load factor of '0' will disable Internal Frost Protection.
External Frost Protection Temperature
Subject to the setting of External Frost Protection Load Factor the heating plant is turned on whenever the external temperature falls below the External Frost Protection Temperature.
External Frost Protection Load Factor
The fraction of heating capacity delivered during external frost protection. A value of '0' will disable the external frost protection. A nonzero External Frost Protection Load Factor causes any internal frost protection to be overridden.
Note - The internal frost protection control will be subject to the control band specified under Internal Conditions. If this band is not zero then the zone temperature will be held slightly above the Internal Frost Protection Temperature.
Warning - External frost protection cannot be specified if the Zone
Maximum Load (for heating or cooling) is set to "SIZING" or
"DESIGN SIZING".
Warning - External compensation does not operate during the frost protection period.
Warning - No frost protection will be provided if a load factor of '0' is specified.