Specifications

92 Control and Automation Solutions Guide
to condense. The heat generated by
the vapor is often discarded. However,
in some systems the heat generated
is later used to warm water, or used
to reduce the energy required to heat
water for DHW or other uses. In a heat
pump, this heat is used to heat a home.
The liquid refrigerant, still under high
pressure, enters an expansion valve
that allows only a slow ow of liquid
to escape, keeping its inlet side at
high pressure. The outlet side is at
low pressure where the liquid enters
the evaporator and is exposed to
warm surroundings, usually warm
air owing over the evaporator coils
where low pressure and warmth
causes the refrigerant to evaporate.
This evaporation absorbs large
quantities of heat, so the air is cooled
as desired. In a heat pump for a house,
the same cycle is used, but the cold
air is pumped outside while the heat
generated is used to warm the interior.
Absorption Refrigeration Cycle
The absorption refrigeration cycle is a
bit more complex. It uses a refrigerant
that vaporizes at a very low temperature
and, as in the vapor-compression
cycle, this evaporation draws away the
heat. The main dierence is that, in
transforming the vaporized refrigerant
back to a liquid, heat is used and the
process is silent. In this part of the
process, the vaporized refrigerant is
“absorbed” or actually dissolved into
another liquid that has a high anity
for it. This reduces the vapor pressure of
the refrigerant vapor, allowing more to
evaporate. The refrigerant-laden liquid
is then heated by the heat source, which
drives the refrigerant out of the liquid.
It then enters a heat exchanger where
it is cooled to room temperature; due
to the high pressure, it condenses back
into a liquid where it is returned to the
evaporator, completing the cycle.
All these systems on an industrial scale
need sensing, monitoring, and controls
for pump motors, valves, fans, blowers,
etc., as well as safety systems to ensure
proper shutdown under fault conditions.
Controls must obviously respond
to remotely sensed temperatures,
pressures, and ow meters that
are often long distances from the
compressor and related equipment.
Wireless communication is increasingly
common, especially in homes where
distances are relatively short.
Maxim has a variety of temperature
sensors with digital interfaces enabling
precise communication over longer
distances than analog sensors. For
more information on other sensor
types and sensor conditioning
functions, see the Sensors chapter. For
industrial HVAC installations, PLCs or
similar control equipment is used to
communicate over eldbuses. Maxim
has many oerings in this area. See
the Programmable Logic Controllers
(PLCs) chapter for more information.
Lighting Control Systems
Lighting systems for area lighting or
individual room lighting are used to
enhance occupants’ experiences and
to save energy by turning out lights
when rooms are vacated or when
light from outside is sucient to dim
the lights. In addition to responding
to occupancy, area lighting can also
be controlled based on the time
of day, the day of the week, or the
occurrence of a special event. These
lighting types enhance occupants’
experiences when the space is used
for dierent activities. For example, a
restaurant will use dim warm lighting
during dinner but brighter lights during
breakfast and lunch; when it is time
to clean and maintain the restaurant,
very bright lighting may be used.
Expanding use of LEDs for a wide variety
of lighting applications is helping to
put downward pressure on their price.
While their initial cost per lumen is
still signicantly higher than other
lighting technologies (incandescent
and cold-cathode orescent lamps
(CCFLs), for example), their much longer
life and higher ecacy make their
operating-life cost signicantly lower
than the established technologies. As
the technology continues to evolve
we will see higher ecacy (lumens/
watt) and longer lumen maintenance
(% of brightness remaining after
time), which continues to add to the
number of applications for which
their use is justied. This ecient,
environmentally friendly, long life and
rugged lighting technology will continue
to improve our lives in many ways.
Maxim recognizes this important
market by oering many products that
drive all kinds of LEDs. Our products
provide communications capability
to control area lighting remotely and
autonomously. For more information,
refer to our LED Lighting Solutions Guide
at: www.maxim-ic.com/lighting.
Room Automation
Many homeowners are connecting
their audio/video (A/V) systems to their
HAS. In commercial buildings such
as schools, hotels, oce buildings,
lecture halls, conference rooms, board
rooms, museums, and theaters, room
automation systems (RASs) control
the lighting and A/V systems, which
enhance the audience’s experience of
everything from simple presentations
to complex stage productions. The
A/V equipment (video conferencing,
video projectors, lighting systems,
public address systems) falls under a
dierent market segment (consumer
and professional A/V equipment),
but the control systems for this
equipment are within this subset of the
environmental automation segment.
The control equipment involved
includes dedicated computers, lighting
controls, and related controllers to turn
on and o ceiling-mounted projectors
and the teleconferencing equipment.
Because the scope of RASs is a single
room, wireless communication is
very viable. Many systems set up
a wireless hub and with wireless
transceivers placed on each piece of
equipment; they all gain a network
presence and can be controlled from
a single computer. With advanced
applications programs, the sequence