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supplied byaboiler i norder t omaintain the desired heating set
point s hould t hecompressor
capacity beinsufficient oracom-
pressor failure o ccurs. Unless acompressor
fault c ondition ex-
ists, t he valve willonlyopen tosupplement
theheat p rovided
bythe compressor
if the space temperature
falls more than one
degree below thedesired heating s et p oint. T he valve will be
controlled sotheSAT will notexceed themaximum h eating
SATlhnit. T heheat s tage w ill also besubject to a2-minute
minimum OFF time toprevent excessive
valve cycling.
Single Stage Electric
Auxiliary_ Heat -- The control can op-
erate a field-installed
single stage of electric heat installed on
the discharge side of the unit in order to maintain
the desired
heating set point should the compressor
capacity be insufficient
or a compressor
failure occurs. Unless a compressor
fault con-
dition exists, the heat stage 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
heat stage will be controlled
so the SAT will not exceed the
maximum
heating SAT limit. The heat stage will also be sub-
ject to a 2-minute
minimum
OFF thne to prevent
excessive
cycling.
INDOOR
AIR QUALITY
(IAQ)
AND
DEMAND
CON-
TROLLED
VENTILATION
(DCV) -- If the
optional
in-
door air quality sensor is installed, the WSHP Open controller
can maintain
indoor air quality via a modulating
OA damper
providing
demand controlled
ventilation.
The control operates
the modulating
OA damper during occupied periods. The con-
trol monitors
the CO2 level and compares it to the configured
set points, adjusting the ventilation rate as required. The control
provides
proportional
ventilation
to meet the requirements
of
ASHRAE
(American
Society of Heating,
Refrigerating
and
Air Conditioning
Engineers)
specifications
by providing
a base
ventilation rate and then increasing the rate as the CO2 level in-
creases. The control will begin to proportionally
increase venti-
lation when the CO 2 level rises above the start ventilation
set
point and will reach the full ventilation
rate when the CO 2 level
is at or above the maximum
set point. A user-configurable
min-
imum damper position ensures that proper base ventilation
is
delivered when occupants
are not present. The IAQ configura-
tions can be accessed
through the configuration
screen.
The
following conditions
must be true in order for this algoritlnn to
ran:
•
Damper
control is configured
for DCV.
•
The unit is in an occupied
mode.
•
The IAQ
sensor
reading
is greater
than the DCV
start
control set point.
The control has four user adjustable
set points: DCV start
control set point, DCV maximum
control set point, minimum
damper position, and DCV maximum
damper position.
Two-Position
OA Damper
-- The control can be configured
to operate
a ventilation
damper in a two-position
ventilation
mode to provide the minimum
ventilation requirements
during
occupied periods.
DEHUMIDIFCATION-
The WSHP
Open controller
will
provide
occupied
and unoccupied
dehumidification
only on
units that are equipped
with the modulating
hot water reheat
(HWR) option. This function requires an accessory
space rela-
tive humidity
sensor. When using a relative humidity
sensor to
control dehumidification
during occupied or unoccupied
thnes,
the dehumidification
set points are used accordingly.
When the
indoor relative humidity
becomes greater than the dehumidifi-
cation set point, a dehumidification
demand will be acknowl-
edged. Once acknowledged,
the dehumidification
output will
be energized,
bringing on the supply fan (medium speed), me-
chanical
cooling, and the integral
hot water reheat
coil. The
controls will engage Cooling mode and waste heat from the
compressor
cooling cycle will be returned to the reheat coil si-
multaneously,
meaning
that the reversing
valve is causing the
compressor
to operate in the Cooling mode. During Cooling
mode, the unit cools, dehumidifies,
and disables the HWR coil;
however, once the call for cooling has been satisfied and there
is still a call for dehumidification,
the unit will continue to op-
erate using the reheat mode and HWR coil.
WATERSIDE
ECONOMIZER
-- The WSHP Open control-
ler has the capability
of providing
modulating
or two-position
water economizer
operation
(for a field-installed
economizer
coil mounted to the entering air side of the unit and connected
to the condenser
water loop) in order to provide
free cooling
(or preheating)
when water conditions
are optimal. Water econ-
omizer settings can be accessed
through the equipment
status
screen. The following
conditions
must be true for economizer
operation:
•
SAT reading
is available.
•
LWT reading
is available.
•
If occupied,
the SPT is greater than the occupied
cooling
set point or less than the occupied
heating
set point
and
the condenser
water is suitable.
•
Space temperature
reading
is valid.
•
If unoccupied,
the SPT is greater
than the unoccupied
cooling
set point or less than the unoccupied
heating
set
point and the condenser
water is suitable.
Modulating
Water Economizer
Control
--
The control has
the capability
to modulate
a water valve to control condenser
water flowing through a coil on the entering air side of the unit.
(_oli_g
-- The purpose
is to provide
an economizer
cooling
function by using the water loop when the entering water loop
c
temperature
is suitable (at least 5 F below space temperature).
If the water loop conditions
are suitable, then the valve will
modulate open as required to maintain a supply-air temperature
that meets the load conditions.
Should the economizer
coil ca-
pacity alone be insufficient
for a period greater than 5 minutes,
or should a high humidity condition occur, then the compressor
will also be started
to satisfy the load. Should the SAT ap-
proach the lninimum
cooling SAT lhnit, the economizer
valve
will modulate closed during compressor
operation.
Heating
-- Additionally,
the control will modulate
the water
valve should the entering water loop temperature
be suitable
for heating (at least 5 c F above space temperature)
and heat is
required. The valve will be controlled
in a shnilar manner ex-
cept to satisfy the heating requirement.
Should the economizer
coil capacity alone be insufficient
to satisfy the space load con-
ditions for more than 5 minutes,
then the compressor
will be
started to satisfy the load. Should the SAT approach the maxi-
mum heating
SAT limit, the economizer
valve will modulate
closed during compressor
operation.
Two-Position
Water Economizer
Control
-- The control has
the capability
to control a NO or NC, two-position
water valve
to control condenser
water flow through a coil on the entering
air side of the unit.
(_oling-
The purpose is to provide a cooling economizer
function directly from the condenser water loop when the en-
tering water loop temperature is suitable (at least 5c F below
space temperature). If the optional coil is provided and the wa-
ter loop conditions are suitable, then the valve will open to pro-
vide cooling to the space when required. Should the capacity
be insufficient for a period greater than 5 minutes, or should a
high humidity condition occur, then the compressor will be
started to satisfy the load. Should the SAT reach the minimum
cooling SAT limit, the economizer valve will close during
compressor operation.
Healing -- Additionally, the economizer control will open the
water valve should the entering water loop temperature be suit-
able for heating (at least 5c F above space temperature) and
heat is required. The valve will be controlled in a shnilar man-
her except to satisfy the heating requirement. Should the coil
capacity be insufficient to satisfy the space load for more than
5 minutes, then the compressor will be started to satisfy the
load. Should the SAT reach the maximum heating SAT limit,
the economizer valve will close during compressor operation.
42
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