S&P SLIM Series, Manual, Page: 53 / 72

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27. WATER HEATER FROST PROTECTION
In models equipped with hot/reversible water coil (see section "29. INSTALLATION AND CONTROL OF EXTERNAL BA-
TTERIES"), the temperature of the water return is continually supervised by a probe, in order to prevent it from freeze.
Depending on the unit status, the controller will activate 2 different strategies.
Unit stopped:
The controller will automatically go into standby when the operating mode is changed to “Off”.
In this confi guration, in order to give antifreeze protection to the water coil, the controller manage the heating valve
maintaining a constant water temperature (25°C by default).
Unit running:
The analogic output for opening the heating valve increases when the frost protection temperature drops below the
“Frost protection alarm threshold (7°C) + Prop. (5°C)” to reach 100% when the temperature is equal to the
frost protection alarm threshold. In this case the unit is stopped and the isolation dampers (if exist) closed .
Internal signal
100%
0%
Proportional band (5°C)
Alarm threshold
(7°C)
Frost protection sensor
(12°C)
It is possible to complete this strategy of frost protection by adding glycol to the water, to ensure protection in case of
failure in the hot water production system.
28. PROTECTION OF HEAT EXCHANGER
This functionality prevents freezing of the condensates existing inside the heat exchanger (on the side of expulsion of
air to the outside).
In order to protect the heat exchanger, the SLIM controller implemented 4 different strategies:
Function Strategy
Preheater control A preheater is needed as an accessory. See section "30. INSTALLATION AND CONTROL OF AN
ELECTRICAL PREHEATER", for details.
The preheater will be activated when the exhaust air temperature descends
6ºC . The
preheater heats the external air entering in the unit before it reaches the heat exchanger.
Fans unbalancing If the exhaust air temperature descends 4ºC , the unit comes into DEFROST MODE: The supply
air fan is set at 50% of its set point while the extract air fan continues following the same set
point. This function will be active during 30 minutes, when this time expires the exhaust air
temperature is checked again during 1 minute.
By-pass opening This function is active when the exhaust air temperature descends 2ºC . At that moment the
by-pass damper opens sending the outdoor air directly into the building. The extract air is
used to defrost the heat exchanger. This function is active during at least 5 minutes. In this
situation, the alarm
Analogue de-icing is activated.
Supply air
temperature
supervision Regardless of the protection strategies activated, if the supply air temperature falls below
11ºC , after a time delay of 5 minutes the unit will stop and restart again after 1 hour.