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COOLING - - The WSHP O pen c ontroller will operate one or
twostages of compression
tomaintain thedesired cooling s et
point. The compressor
outputs are controlled bythe PI(propor-
tional-integral)
cooling l oop and cooling s tages capacity algo-
rithin. T hey will beused tocalculate thedesired number of
stages needed tosatisfy t he space bycomparing
the space tem-
perature (SPT) tothe appropriate
cooling s et p oint. T he water
side economizer,
if applicable,
willbeused f orfirst s tage c ool-
inginaddition tothecompressor(s).
The following c onditions
must betrue inorder forthe cooling a lgorithin torun:
• Cooling i sset t oEnable.
• Heating modeis not active andthecompressor time
guard h as expired.
• Condensate
overflow inputisnormal.
• If occupied, theSPT isgreater than theoccupied cooling
set p oint.
• Space temperature
reading i svalid.
• If unoccupied, theSPTis greater thantheunoccupied
cooling s etpoint.
• If economizer cooling is available a ndactiveandthe
economizer
alone isinsufficient toprovide e nough c ool-
ing.
• OAT(if available is greater thanthecooling lockout
temperature.
If allthe above c onditions are met, t he compressors
will be
energized
asrequired, otherwise they will bedeenergized.
If
cooling i s active and should t heSAT approach theminimum
SATlimit,thefanwill beindexed tothenext h igher speed.
Should this beinsufficient and if theSAT falls further (equal to
the minhnum SAT lhnit), t he fanwill beindexed tothe maxi-
mum speed. If theSAT continues tofall5cF below the mini-
mum SAT limit, a llcooling s tages willbedisabled.
During Cooling m ode, thereversing valve output will be
held inthecooling p osition (either BorOtype asconfigured)
even a fter t he compressor
isstopped. The valve w ill not s witch
position until t he Heating mode i srequired.
The configuration screens c ontain the minimum SAT
parameter aswell ascooling lockout based o noutdoor-air
temperature
(OAT) Bothcanbeadjusted to meet v arious
specifications.
There i s a5-minute offthne forthecompressor
as well a sa
5-minute t imedelay when staging u pto allowtheSATto
achieve astable t emperature
before e nergizing asecond stage
ofcapacity. Likewise, a45-second
delay isused when s taging
down.
After a compressor
is staged off, it may be restarted
again
after a normal time-guard
period of 5 minutes and if the sup-
ply-air temperature
has increased
above the minimum
supply-
air temperature
limit.
The WSHP Open controller provides
a status input to moni-
tor the compressor
operation.
The stares is monitored
to deter-
mine if the compressor
status matches
the colmnanded
state.
This input is used to determine if a refrigerant
safety switch or
other safety device has tripped and caused the compressor
to
stop operating
normally. If this should occur, an alarm will be
generated to indicate the faulted compressor
condition.
HEATING
-- The WSHP Open controller
will operate one or
two stages of compression
to maintain
the desired heating set
point. The compressor
outputs are controlled
by the heating PI
(proportional-integral)
loop and heating
stages capacity
algo-
rithin. They will be used to calculate
the desired number
of
stages needed to satisfy the space by comparing
the space tem-
perature (SPT) to the appropriate
heating set point. The follow-
ing conditions
must be true in order for the heating algorithin to
run:
•
Heating
is set to Enable.
•
Cooling
mode
is not active
and the compressor
time
guard has expired.
•
Condensate
overflow
input is normal.
•
If occupied,
the SPT is less than the occupied
heating
set
point.
•
Space temperature
reading
is valid.
•
If unoccupied,
the SPT is less than the unoccupied
heat-
mg set point.
•
OAT
(if
available)
is less than
the heating
lockout
temperature.
If all the above conditions
are met, the heating outputs will
be energized as required, otherwise they will be deenergized.
If
the heating is active and should the SAT approach
the maxi-
1hum SAT lhnit, the fan will be indexed
to the next higher
speed. Should this be insufficient,
and the SAT rises further
reaching
the maximum
heating
SAT limit, the fan will be
indexed to the maximum
speed. If the SAT still continues to
rise 5 c F above the maximum
limit, all heating stages will be
disabled.
During Heating
mode, the reversing
valve output will be
held in the heating position (either B or O type as configured)
even after the compressor
is stopped. The valve will not switch
position until the Cooling mode is required.
The
configuration
screens
contain
the maximum
SAT
parameter
as well as heating
lockout
based
on outdoor-air
temperature
(OAT);
both can be adjusted
to meet
various
specifications.
There is a 5-minute offtime
for the compressor
as well as a
5-minute
time delay when
staging
up to allow the SAT to
achieve a stable temperature
before energizing
a second stage
of capacity. Likewise,
a 45-second
delay is used when staging
down.
After a compressor
is staged off, it may be restarted
again
after a normal time-guard
period of 5 minutes
and if the sup-
ply-mr temperature
has fallen below the maximum
supply air
temperature
limit.
The WSHP Open controller provides
a status input to moni-
tor the compressor
operation.
The stares is monitored
to deter-
mine if the compressor
status matches
the colrnnanded
state.
This input is used to determine if a refrigerant
safety switch or
other safety device has tripped and caused the compressor
to
stop operating
normally. If this should occur, an alarm will be
generated to indicate the faulted compressor
condition. Also, if
auxiliary
heat is available (see below), the auxiliary
heat will
operate to replace the reverse cycle heating
and maintain
the
space temperature
as required.
AUXILIARY
HEAT -- The WSHP Open controller can con-
trol a two-position,
modulating
water, or steam valve connect-
ed to a coil on the discharge side of the unit and supplied by a
boiler or a single-stage
ducted electric heater in order to main-
tain the desired heating set point. Should the compressor
capac-
ity be insufficient
or a compressor
failure occurs, the auxiliary
heat will be used. Unless the compressor
fails, the auxiliary
heat will only operate
to supplement
the heat provided
by the
compressor
if the space temperature
falls more than one degree
below
the desired
heating
set point
(the amount
is config-
urable). The heat will be controlled
so the SAT will not exceed
the maximum
heating SAT lhnit.
Auxiliary
Modulating
Hot
Water/Steam
Heating
Reheat
-- The control can modulate
a hot water or steam valve con-
nected to a coil on the discharge side of the unit and supplied
by a boiler in order to maintain the desired heating
set point
should the compressor
capacity be insufficient
or a compressor
failure occurs. Unless a compressor
fault condition
exists, the
valve will only operate to supplement
the heat provided
by the
compressor
if the space temperature
falls more than one degree
below the desired heating
set point. The valve will be con-
trolled so the SAT will not exceed the maximum
heating SAT
limit.
Two-Position
Hot Water/Steam
Heating
Reheat
-- The con-
trol can operate a two-position,
NO or NC, hot water or steam
valve connected
to a coil on the discharge side of the unit and
41
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