VTS Medical Systems VENTUS COMPACT HP VVS021c Instructions For Use Manual page 14

2.1.2 FAILURE PROTECTION SYSTEM
The field control function is integrated into the internal control system. This prevents exceeding
the safe conditions for any of the components. Signals from the high and low pressure
transducers provide information to ensure maximum performance without exceeding the set
value. This prevents interruption of cooling or heating by the high and low pressure switches.
The control system ensures maximum recovery capacity at set airflows and outdoor air and
exhaust air temperatures.
Compressor operation protection is implemented by:
•
controls algorithm,
•
low pressure prestostat (limiter),
•
high pressure presotate (limiter),
•
safety valve.
!
! The occurrence of an alarm condition is signalled on both the main panel controller and the heat
pump controller.
! In the event of an emergency stop of the air handling unit, the heat pump does not receive a start
signal. Signalling and resetting of the heat pump alarms is carried out from the control panel of
the air handling unit.
! The control system is equipped with functions to protect the heat pump from damage in the event
of a power outage and in the event of a long standstill of the heat pump with the unit running.
!
In the event of a power failure of the heat pump or in the event of a long standstill, the expansion
valve is opened, which causes the liquid refrigerant to accumulate at the coolest point of the entire
system. On first start-up, after such an event, the heat pump starts up in cooling mode for a time
set by the control system.
During shutdown, the heat pump is protected by the safety valve as a pressure element
independent of the control system. When the heat pump is in operation, the first safety function
is the heat pump control system which, by regulating the compressor speed and the degree of
opening of the expansion valve, keeps the compressor in its field (envelope) of operation.
When operating the compressor outside of its proper field of operation, another safety feature
is the high and low pressure limiters. The low pressure limiter is fitted upstream of the
compressor on the suction side (normally open contact). When the pressure drops to 3.3 bar(g),
the safety contacts of the compressor speed controller are disconnected. On pressure increase
to 4.8 bar(g), there is an automatic switching of contacts
The high-pressure limiter is fitted after the compressor on the discharge side (normally closed
contact). When the pressure rises to 38 bar(g), the safety contacts of the compressor speed
controller are disconnected. When the pressure drops to 28 bar(g) there is an automatic contact
switching.
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