VEX3300T Bypass de-icing
The VEX300T is designed with de-icing bypass. If there is a risk of icing, then a certain amount of outdoor air will bypass the heat exchanger and go directly to the after heating coil. This increases the demands on the after heating coil’s output. However, it avoids a costly preheating coil. The drawing below is an example of a de-icing situation, where 20% of outdoor air is directed through the bypass damper.
Heating coil and de-icing function:
The de-icing situation is shown above, a heating coil is included here. A coil is absolutely necessary, in order for the de-icing function to work correctly. Without the heating coil, the de-icing process will cause the temperature of the supply air to fall and sooner or later the VEX unit will stop because of icing.
The heat exchanger has two forms of frost protection: temperature-controlled or pressure-controlled. The actual de-icing can take place in several ways, depending on whether an after heating coil has been fitted. An after heating coil is always recommended to maintain continuous ventilation.
Which method is used when?
Temperature-controlled
Standard on VEX310T-330T |
Temperature is below the set value,
e.g. tice < 0 °C |
Residences, changing rooms, and
rooms with variable humidity in the winter. |
Pressure-controlled
Standard on VEX340-350T |
Pressure across the heat exchanger exceeds the set value, e.g. + 45 % |
Offices, schools, after-school club facilities,
and rooms with low humidity in winter. |
Temperature-controlled frost protection Tice
The control system has temperature-controlled frost protection as standard. It is an inexpensive solution and provides sufficient frost-protection in some situations.
A temperature sensor is fitted inside the heat exchanger and if the temperature falls to a pre-set value, de-icing begins. This temperature level is factory set to 0 °C but it can also be changed to a new value via the control system.
Temperature-controlled frost protection triggers the de-icing process even if there is no ice in the heat exchanger.
Pressure-controlled frost protection (requires accessories AFC (airflow measurement) and DEP (frost protection - pressure))
The control system monitors the actual airflow and also the pressure drop across the heat exchanger. If ice forms in the heat exchanger, the pressure drop across the heat exchanger will increase and when it exceeds a pre-set value, de-icing begins.
Pressure-controlled frost protection only starts de-icing when ice has actually formed, regardless of whether there are sub-zero temperatures.
