Specifications

88 Control and Automation Solutions Guide
systems. On the evaporator, the heat
exchanger transfers the coldness into
the water to be piped throughout the
building for cooling in the AHUs and
related equipment. On the condenser,
the heat exchanger warms water that
is carried away, often to cooling towers
on the outside of the building that are
designed to discard this heat. After
being cooled by the tower, this water
returns to the condenser heat exchanger,
coming full circle. More ecient
installations may use this “waste” heat
for pre-warming water that is ultimately
used for steam heat or DHW use.
The need for many types of sensors and
controls is evident on a chiller system.
The usual sensors such as temperature,
pressure, and ow rate are needed
in several areas. Controls are needed
for valves and for motor speed. There
are several opportunities for energy
savings. Savings can result through
exible responses to varying loads on
the system, which are inuenced by
outside temperatures and occupancy
usage rates. For example, under a light
usage load, instead of pumping water
at full capacity through the system, the
rate of water ow can be reduced.
Control Panels
On all the systems discussed so far
and on those to be discussed, there
is always some kind of control panel
with input devices and indicators, even
if the equipment will be completely
controlled by its network interface to
an HAS or BAS. There will be at least
emergency stop buttons, usually manual
start/stop buttons, and potentially
several other controls from simple
pushbuttons and dials to touch screens
on the complex machines. Indicators
can range from only a few LEDs to full
graphic displays on complex machines.
Touch screens, which use graphic
displays, are becoming common.
For most industrial applications,
resistive touch-screen controllers like
the MA X1180 0 are simple to implement,
and they prevent responses to multiple
simultaneous touches. For pushbutton
interfaces, the MAX16054, a ±15kV
ESD-protected switch debouncer,
makes it easy to avoid any failures or
false inputs at this interface. LEDs, due
to their robustness and long life, have
completely replaced incandescent bulb
indicators. To drive several LEDs for
indicators or backlighting, the MAX6979
oers LED fault detection and watchdog
features to provide assurance that
LED indicators are working properly.
Chiller room for a building cold water system.
Control panel with a variety of input and output types.