McQuay SWP 095

IM708 29
Building pressurization applications
1. Install a tee fitting with a leak-tight removable cap in
each tube near the sensor. This will facilitate connecting
a manometer or pressure gauge if testing is required.
2. Locate the building pressure (HI) tap in the area that
requires the closest control. Typically, this is a ground
level floor that has doors to the outside.
3. Locate the building tap so that it is not influenced by
any source of moving air (velocity pressure). These
sources may include air diffusers or outside doors.
4. Connect the tube to the 1/4 inch HI fitting on sensor
SPS1. Assure that the sensor does not support the
weight of the tubing; use tube clamps or some other
means.
5. Locate the reference pressure (LO) tap on the roof. Keep
it away from the condenser fans, waIls, or anything else
that may cause air turbulence. Mount it high enough
above the roof so that it is not affected by snow. If the
reference tap is not connected to the sensor, unsatisfac-
tory operation will result.
6. Use an outdoor static pressure top (Dwyer A306 or
equivalent) to minimize the adverse effects of wind.
Place some type of screen over the sensor to keep out
insects. Loosely packed cotton works well.
7. Route the outdoor tap tube out of the main control panel
through a small field-cut opening in the edge of the con-
trol wiring raceway cover. Cut this "mouse hole" in the
vertical portion of the edge. Seal the penetration to pre-
vent water from entering. Connect the tube to the 1/4
inch LO fitting on sensor SPS1.
Freezestat
A non-averaging type freezestat (FS1) is available to protect
hydronic coils from subfreezing temperatures. If the unit has
an economizer coil the control is mounted on the entering
face of the economizer coil. If the unit does not have an
economizer coil the control will be mounted on the leaving
face of the hot water coil. Upon sensing a hazardous temper-
ature, the unit will shutdown, open hydronic control valves
and send an alarm indication via the MicroTech II controller.
The freezestat has a field adjustable setpoint range of 35°F to
40°F. The setpoint may be changed by turning the adjust-
ment screw until pointer is opposite the desired cutout point.
The adjustment screw is accessible at the bottom of the con-
trol or at the top when the cover is removed.
Condenser Water Flow Switch
A pressure differential type flow switch (WF1) is available
to verify flow to the unit condensers before compressor oper-
ation is allowed. The flow switch is factory installed in the
unit next to the condenser piping connections. If a loss of
condenser water flow is sensed, the cooling will be locked
out via the MicroTech II controller. When flow is restored,
the unit will automatically reset.
The factory settings for the water flow switch N.O. contacts
are as follows:
Unit Size Close Adj. Open Adj.
Ft. wc Range Ft. wc Range
018D-040D
3.0 +0.0 1.5 +0.5
-0.5 -0.5
045D-105D
4.5 +0.0 3.0 +0.5
-0.5 -0.5
Water Side Economizer
A completely factory installed, piped and controlled water
side economizer system is available on any constant or vari-
able air volume system. Whenever the entering water tem-
perature is more than 3°F (adjustable at the MicroTech II
keypad/display) below the mixed air temperature to the unit,
the control valves modulate to provide cooling directly from
the tower water. The economizer system can be used to pro-
vide 100% of the cooling demand or supplement mechanical
cooling by precooling the return air. The economizer system
consists of a water coil and two, two-way control valves. The
unit's MicroTech II controller will modulate the control
valves to satisfy the cooling demand whenever the entering
water is suitable. When the control valves are in the 90%
open position, the unit's compressors will be allowed to be
staged on to satisfy the cooling load. When the entering
water temperature is no longer suitable, the economizer con-
trol valve will close and the unit will be on 100% mechanical
cooling.
Two valve control arrangements are available from the fac-
tory. The first maintains full flow through the unit condens-
ers at all times. This control arrangement is used for systems
with constant pumping systems. For installations with a vari-
able pumping system, the control valves will be sequenced
such that flow is removed from the unit whenever cooling is
not required. A mechanical clutch is provided on each valve
to manually close or open the valves.
The economizer system is factory piped and the coil takes
advantage of the same drain pan and condensate connection.
Air may be vented from the economizer coil by using the
uppermost clean out plug. The torque requirement for the
cleanout plugs is 10 inch-lb.
CAUTION
Fragile sensor fittings. May damage pressure
sensor.
If tubing must be removed from a pressure sen-
sor fitting, use care. Do not wrench the tubing
back and forth to remove or the fitting may break
off.