Page 35
Operation and Maintenance
Envistar Flex
DSEF191101.05.EN
Continuous product development may give rise to specification changes without notice.
Functional description, defrost and bypass function (ODS) (EXMM-XP/NP)
Under certain operating conditions, frost and ice may build-up on the extract air
side of the plate heat exchanger. In order to optimise heat recovery, there is a
built-in defrost function. This is based on the principle that the defrost function
is engaged when the pressure drop over the extract air side of the counter-flow
exchange exceeds a certain value.
Defrosting takes place through the regulation of dampers on the outdoor air
side of the counter-flow exchanger. The dampers have separate damper motors
that are controlled by a defrost program. Damper control means that there are a
number of different combinations of damper positions, for instance that one of
the dampers can be partly open while another is closed and the third damper is
fully open.
During full heat recovery, the dampers must be fully open and the bypass
damper must be closed.
When the unit is switched off, all dampers must be closed.
When there is a risk of frost, the dampers can be in different positions.
The defrost and bypass function is preset at the factory and any adjustments
must be performed by IV Produkt.
Functional description, frosting function (BYP) (EXMM-NP, EXPP-NO/NP/XP)
Under certain operating conditions, frost and ice may build-up on the extract
air side of the plate heat exchanger. In order to optimise heat recovery, and
avoid freezing, there is a built-in frosting function. The principle is based on the
frosting function starting when the temperature of the exhaust air side’s coldest
surface falls below a certain value.
The freezing process is prevented by reducing heat recovery gradually through
regulating dampers on the heat exchanger’s exhaust air side. The dampers for
the extract air/exhaust air temperature close and the bypass damper opens. In
this way, the exhaust air temperature is increased and freezing is avoided.
During full heat recovery and when the unit is switched off, the dampers should
be fully open (bypass damper closed).
The frosting and bypass functions are preset at the factory and any adjustments
may only be performed by IV Produkt.
