Menu Item Description
8 RTHC-SVD01B-EN
Unlike other UCP2 applications, for RTHC, the Restart Inhibit Timer is
not automatically set at 30 seconds following either a software or hard-
ware reset. It is instead recalculated from the Background Timer's
value which was saved nonvolatile with the previous removal or loss of
power and recovered upon power restoration. This is necessary due to
the lack of any winding temperature sensor to confirm that the motor is
not too hot to start again.
Comment: This method would normally permit two starts in rapid suc-
cession and a third start 9 minutes after the second (Assuming 1
minute Run Times and a 5 minute motor heating constant). After the
third start the motor would be permitted to cool. This method:
• Approximates current practice in the field (e.g. can do three starts
in a row and wait after that)
• Models a fixed amount of energy put into the motor and starter
each time it starts with increasingly greater cooldown periods after
successive starts.
• Usually Permits rapid restart after a Momentary Power Loss, but
only if Background Timer was less than 8 min. 30 seconds when
power was lost. The Background Timer does not continue to count
down while power is lost to UCP2.
Example of this Method using the following settings
Motor Heating Constant = 5 minutes
Max. RI time = 20 Minutes
See Figure 2-1
The restart inhibit timer is used as short cycling protection. This feature
in UCP2 uses a different logic than the UCP1 controllers used on the
RTHA units. UCP2 uses a background timer (BT) as well as the motor
winding temperatures to determine how quickly the compressor can be
cycled back on.
2-3. Soft Loading
When soft loading is enabled, it slows the rate of loading at start-up.
Soft loading is factory set as disabled.When disabled, the compressor
will load up as fast as needed to allow the chiller to reach setpoint. In
situations where frequent cycling is an issue, soft loading can be
enabled to slow the pull down process.
The items that can be set in UCP2 are:
Located in Service Settings, Field Start-up Group (++--++)
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