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Setting the indoor fan speed too high can bring a risk of any
condensation being sucked off the fins of the indoor coil
and into the supply air duct. Water could then start leaking
from the supply air vents and diffusers and corrosion of
ducting may occur.
Setting the indoor fan speed too high can also bring a risk
of ‘over-condensing’ (when the unit is heating) which in turn
could cause the unit to perform more outdoor coil de-ice
cycles than necessary.
Refer Appendix II Air Handling graphs for min./max.
airflows.
6. OPERATION
6.1 User Operation (RS-SSD)
The tempe/– buttons adjust the room set
temperature. (You can limit the range of user adjustment by
setting the heating and cooling control limits in the Installer
menu of the Viking Controller.)
The Select button toggles the LCD display between current
‘room’ temperature, ‘set’ temperature, inside relative
humidity (RH), outside temperature and outside RH.
The After Hours button starts (or cancels) the after hours
run timer.
The LCD will also provide other information such as whether
there are any faults, and if outside air is being used for
economy cooling, etc.
6.2 Scheduling
The Viking HVAC Controller, in the unit, can be programmed
to operate at different time intervals:
• Always On
• Manual (default)
• 7 Day, 1 Event
• 7 Day, 2 Events
• 365 Day, 1 Event
• 365 Day, 2 Events
• After Hours (2 hours default)
• Daylight Saving Time (DST)
• Holidays
Refer to the Viking User & Installer Manual for more
information and Schedule set-up instructions.
Note: RS-SSD can not be used as an interface to program
the Schedule.
6.3 Safety Timers
The UC8 receives control signals and transfers the signals
to the outputs after enforcing safety timers and other
protection functions. If the compressor is held off, or held
on, by a safety timer then the display shows
message ‘H-O-L-d’.
Normal durations of safety timers are:
• Minimum off time
3 minutes
• Minimum run time 1.5 minutes
• Min. cycle time
6 minutes (up to 10 compressor
starts per hour)
• Min. mode change-over time
10 minutes (cooling to heating or
vice-versa)
6.4 Variable Capacity
The OPA unit is equipped with a single variable capacity
compressor – inverter scroll type. Compressor operating
capacities are 16%–100% using 1.6V–10V control voltages.
At any time, when operating conditions dictate, system
protection functions can restrict unit operating capacity.
When a capacity signal is presented that is lower than the
minimum capacity (for example 0V on input ‘VC’) then the
compressor operates on minimum duty.
If a unit operates on low capacity for extended periods
then the unit may periodically perform oil flush cycles.
Under such operating conditions compressor lubricating oil
may slowly settle in parts of the refrigeration system other
than the compressor. Oil flush cycles help to return the
lubricating oil to the compressor. During an oil flush cycle
compressor speed is increased for a duration of 1 minute.
Variable capacity indoor air fan – Refer Section 5.3
6.5 Economiser / Economy Cycle
The Economy Cycle function has been pre-set. No on-site
Installer setting is required.
The Economiser package fitted consists of two opposed
blade dampers – one for fresh air intake and one for indoor
return air. A 0–10V dc control signal drives the dampers
open and closed. This signal comes from the Viking HVAC
temperature/humidity controller. The return air damper
will close proportionally as the fresh air damper opens
proportionally and vice versa.
The control strategy is by Enthalpy (ie a combination of
dry and wet bulb temperatures) so that free cooling is
used without adding any heat load to the building. This is a
requirement of Australian NCC and NZ Building Code.
The Viking will shut the F/A damper automatically when it
outdoor humidity is too high (ie raining) to prevent moisture
being drawn into the unit
When Economy Cycle is not operating, the maximum
amount of fresh air should not exceed 25% of the unit’s
nominal airflow.
The fresh air damper’s adjustable stop can be set such
that it does not close 100%. Many installations require
a minimum fresh air introduction of 10 – 15% and the
stop may be set on site to facilitate this. Set the Fresh
Air damper motor ‘stop’ to the equivalent negative static
pressure as with F/A damper closed. This is to ensure the
air flow volume remains constant and does not dramatically
increase when introducing fresh air.
Demand Control Ventilation:
Air Quality (CO
2
) sensors can
be used to proportionally control the fresh and return air
dampers (via the Viking control system).
In all situations the UC8 Unit Controller will allow the
compressors to operate with the fresh air damper open
providing the refrigeration system is not compromised.
The compressor(s) could be stopped from operating by
normal protection devices such as low suction temperature/
pressure or indoor coil frost protection and too many trips
of either fault could lead to a lock out of the compressor(s)
operation. Should this occur then a review of the control
settings may be necessary.
