Product data

55
to satisfy the space load conditions for more than 5 min-
utes, then the compressor will be started to satisfy the load.
Should the SAT approach the maximum heating SAT limit,
the economizer valve will modulate closed during compres-
sor 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.
Cooling — The purpose is to provide a cooling economiz-
er function directly from the condenser water loop when
the entering water loop temperature is suitable (at least
5° F below space temperature). If the optional coil is pro-
vided and the water loop conditions are suitable, then the
valve will open to provide cooling to the space when re-
quired. Should the capacity be insufficient for a period
greater than 5 minutes, or should a high humidity condi-
tion 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.
Heating — Additionally, the economizer control will open
the water valve should the entering water loop temperature
be suitable for heating (at least 5° F above space tempera-
ture) and heat is required. The valve will be controlled in a
similar manner 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 maxi-
mum heating SAT limit, the economizer valve will close
during compressor operation.
Demand limit — The WSHP Open controller has the
ability to accept three levels of demand limit from the net-
work. In response to a demand limit, the unit will decrease
its heating set point and increase its cooling set point to
widen the range in order to immediately lower the electri-
cal demand. The amount of temperature adjustment in re-
sponse is user adjustable for both heating and cooling and
for each demand level. The response to a particular de-
mand level may also be set to zero.
Condenser water linkage — The control provides opti-
mized water loop operation using an universal controller
(UC) open loop controller. Loop pump operation is auto-
matically controlled by WSHP equipment occupancy
schedules, unoccupied demand and tenant override condi-
tions. Positive pump status feedback prevents nuisance
fault trips. The condenser water linkage operates when a
request for condenser water pump operation is sent from
each WSHP to the loop controller. This request is generat-
ed whenever any WSHP is scheduled to be occupied, is
starting during optimal start (for warm-up or pull down pri-
or to occupancy), there is an unoccupied heating or cool-
ing demand, or a tenant pushbutton override. At each
WSHP, the water loop temperature and the loop pump
status is given. The WSHP will NOT start a compressor un-
til the loop pumps are running or will shutdown the com-
pressors should the pumps stop. This prevents the WSHP
from operating without water flow and thus tripping out on
refrigerant pressure, causing a lockout condition. The
WSHP Open controller will prevent this from occurring.
Also, the loop controller can be configured to start the
pumps only after a configurable number of WSHPs are re-
questing operation (from 1-"N"). This can be used to pre-
vent starting the entire loop operation for only one WSHP.
Meanwhile, the WSHPs will not operate if the loop pump
status is off and therefore the WSHP compressor will not
run.