Vsd Frequently Asked Questions - York VSD 270 Operation Manual

FORM 160.00-O4
ISSUE DATE: 12/19/2017

VSD FREQUENTLY ASKED QUESTIONS

Why doesn't the measured input amps of the OSCD
agree with the rated FLA?
The input current to the OSCD may be considerably
lower, compared to the output current. This is due to
the power factor at the input to the OSCD being greater
than .95, and nearly unity when the Harmonic Filter
option is included. Chiller FLA must be measured at
the motor terminals, where the power factor is the nor-
mal motor power factor. Use a true RMS reading meter
to make these measurements.
Is a Condenser Water Strainer used with the shell
and tube heat exchanger?
Since the shell and tube heat exchanger can be cleaned
with a rifle brush, no extra precautions are needed to
keep the heat exchanger cleaned. No strainer is pro-
vided with this OSCD. The intent is to have the heat
exchanger cleaned annually. Gaskets are available (re-
fer to the service parts list).
What is the timing of the Anti-Recycle when an
OSCD is applied?
The anti-recycle time is much quicker with an OSCD
than with a starter. The reason is the elimination of
inrush current on start-up. The OptiSpeed compres-
sor drive slowly accelerates the compressor motor so
that the motor does not consume more than 100% of
the motor's nameplate full load amps. The anti-recy-
cle time is five (5) starts in succession, followed by a
ten minute wait. After ten minutes, the OSCD can be
started five more successive starts. This is permitted
on OSCD units only, due to the low current draw and
reduced motor heating during startup.
Should the customer install isolation between the
Power Conduits and the OptiSpeed Compressor
Drive?
We no longer require a section of non-metallic conduit
at the entrance and exit of the OSCD as we did on pre-
vious products. If any customer or installer wishes to
continue to follow this practice, we have no objections
as long as the OSCD is properly grounded.
32
When is a Booster Pump required on a Retrofit Op-
tiSpeed Compressor Drive?
Detailed information is supplied in Form 160.05-N4. In
general, the OSCD requires 8 ft of head for proper wa-
ter flow to the OSCD heat exchanger. If this amount of
head is not available, then a booster pump is required.
Can I apply an OptiSpeed Compressor Drive to a
generator?
Yes, the OSCD can be applied to a generator. No modi-
fications are required for a generator application. We
have several OSCD installations running on generator
power without difficulty. It is necessary that the gen-
erator's output voltage and frequency be maintained
within the specified range for that particular OSCD.
This is usually not a problem for most generators, since
motor current at startup is limited to less than 1X the
Full Load Amps (FLA).
My chiller will not slow down, why?
The OSCD will not reduce the motor speed until the
leaving chilled water temperature is below 0.5 degree
from setpoint. Once in this window, the speed still can-
not be reduced until the operation is deemed to be sta-
ble, based upon the vanes are not continually moving
open and closed to maintain temperature. This hunting
effect is normally due to one of the following:
• Chilled water and Condenser water flows are not
at design GPMs. The rate of change in flow maybe
too fast for the chiller to be determined as stable.
• Return water temperature is varying due to 3-way
valves or other system configuration, and the
chiller is simply following changes in load.
• Vane stroke is too large. Remove the sensitivity
jumper in the Micro Computer Control Center, or
program a lower sensitivity on the OptiView Con-
trol Center. Also, check the vane motor to see that
the fullest possible stroke is being utilized. Mov-
ing the vane motor arm pivot point closer to cen-
ter, and extending the degrees of travel by adjust-
ing the internal end stops, will reduce the amount
of vane action for the same period of operation.
JOHNSON CONTROLS