Access has 3 independent freeze protection controllers for the water heaters. The water return temperature is measured by the freeze protection temperature sensor. At low temperatures, the controller forces up output of the sequence (the heating valve opens and the hot water flow increases). The flow increase is inversely proportional to temperature of the return water.

At the default settings, the controller will take over regulating of sequence output (heating valve) if freeze protection temperature falls below [12] oC.

Activation of the freeze protection controller triggers freeze protection warning (AL-64). By default AL-64 is for notification but can be reconfigured for actions if necessary.

The controller attempts to increase the freeze protection temperature above warning level by gradually increasing output of the sequence. The responsiveness of the controller is defined by its own PID settings.

Control over the sequence is handed back to the supply controller once safe temperature is reached.

If, however, the temperature falls below the critical level [7.0] oC - the freeze protection alarm is triggered. There is a severe risk of freezing and the default action is to fast stop of the AHU.

The same algorithm is used if the water heater is controlled by thepreheater function. In this case freeze protection has supremacy over the preheater controller.

Zone control function include 3 more independent freeze protection controllers.


In all cases, the method of freeze protection is chosen at a particular sequence, preheater or zone configuration.

Default settings of the freeze protection controller


Available options & Selection


PID Settings

Configuration > PID controllers > Freeze protection 1


100 oC

PID settings for the freeze protection controller. PID active only during standby mode


100 s


0 s

Freeze protection settings

Data & Settings > Temperature control > Heating > Freeze protection 1

Freeze protection


Actual temperature of freeze protection sensor

Alarm limit running mode

7.0 oC

AL-96 Freeze protection alarm 1 if the temperature is

< 7 oC

P-band running mode

5.0 oC

AL-64 Warning freeze protection if the temperature is

< 12 oC

(7 oC + 5 oC : "Alarm limit" + "P-band")

Setpoint standby mode

25.0 oC

If frost protection is activated - freeze protection controller will control the heating output to maintain a constant temperature at the frost protection sensor

Access also supports the use of 1 capillary thermostat instead of, or in addition to, water temperature monitoring.