Specifications

85Environmental Automation
Water Supply Systems
Because water is needed in any
residential or commercial building,
water supply systems are critical to
the design. It is often assumed that a
building will have a reliable, clean supply
of water, but the water supply from a city
system may not meet the water purity
standards of some establishments or
even for some home use. “Domestic”
water for hotels and other commercial
establishments is sometimes supplied
for use only after being treated in
a variety of ways, which include
ltering, softening, and disinfection.
Water Pressure
Very tall buildings create a water
pressure problem. In a static column of
water, the pressure drops 1 decibar for
every meter of height or 4.33lb/sq in for
every 10ft. In multiple-story buildings,
oors are separated by approximately
10ft, so in a 100-story skyscraper the
pressure drop is 43psi. This is enough of
a drop so that xtures do not operate
properly. To remedy this, pumps are
needed to create pressure for the upper
oors, and pressure-reducing valves
are needed to keep pressures within
acceptable ranges for the xtures.
Noninstrumented systems may seem
adequate when everything is working
properly, but when leaks occur or pipes
break, water damage can quickly mount.
Pressure sensors (see the Pressure Sensors
and Weigh Scales (Force Sensing) section
in the Sensors chapter) and electronically
controlled shuto valves strategically
located throughout the system can
quickly isolate a region around the
failure and alert the BAS of the problem
and its location. With proper plumbing
design, large areas of the building
remain unaected while repairs are
made. By implementing pumps driven
by motors with variable-speed drives
(see the Motor Control chapter), pressure
surges are limited, thereby reducing
“water hammer” and the strain it places
on the plumbing. Power consumption
is also reduced to match the amount
that is adequate for the usage rate.
Tall buildings always have several
oors below ground level, so pumps
are needed to push waste water back
up to surface drainage levels. Sump
pumps, water level detection, ltration,
and additional treatment equipment
can be used with monitoring and
control systems tied into the BAS.
Water Filters and Softeners
In developed countries, “city” water is
generally good enough for washing
and most other uses, but the use of
home ltration systems ensure that
water is contaminant-free and actually
tastes good. Soft water reduces scale
buildup and extends the eectiveness
of soaps and detergents. Home
lters and softeners are usually not
(yet) connected to an HAS; they just
incorporate local controls and indicators,
but eventually incorporating these types
of devices will provide the benet of
automated notications for malfunctions
and the need for maintenance.
In commercial buildings, incoming
water also may not meet standards
of cleanliness the facility needs, so
lters and softening systems are often
employed. But lters need to be changed
periodically, and softening systems
need a salt supply and other periodic
maintenance. If a lter system has
no sensor, relying on the calendar to
predict when to change the lter may
be inadequate because both water-
usage rates and sediment levels can vary
over time and season. By monitoring
the ow rates and measuring the total
volume owing through the lter,
a better estimate is achieved. But if
sediment levels are unpredictable, this
tracking method can also fall short of
indicating the best time to change the
lter. The best method is to monitor the
pressure drop across the lter element
when the ow rate is at some nominal
level. Pressure vs. ow-rate charts can
be generated for new vs. clogged
lters. Pressure sensors on both sides
of the lter and a ow-rate sensor are
needed. Additionally, a temperature
sensor is needed since the water
temperature usually aects the readings
of pressure sensors (see the Sensors
chapter). Data from these sensors can
then be gathered, communicated to a
monitoring system, and processed. The
result indicates when it is time to change
the lter (see the Programmable Logic
Controllers (PLCs) chapter). Additionally,
detection of pressures that are too low
across the lter may also be needed if
a lter blowout failure is possible. With
instrumentation to detect pressure,
maintenance levels are reduced, lter
life is maximized, water pressure drop
is kept within reasonable levels, and
failures are detected immediately,
assuring high water quality.
For softeners, similar pressure and
temperature sensing is needed
on large systems including saline
concentration, salt supply, and
potentially other parameters. There
are various types of softeners, so other
chemical-sensing systems are possible.
Automatic salt-feeding systems can
be incorporated when regeneration
is needed and their proper operation
may need to be monitored.
Water Heaters and Boilers
In residential buildings, water heaters
are usually small and simple since
they supply individual residences with
domestic hot water (DHW), and they
are typically not (yet) tied into any
HAS. But in larger residential buildings
and commercial buildings, the water
heating systems are large capacity
and instrumented. Water heaters are
quite straightforward. Inlet and outlet
temperatures as well as ow rate can
be monitored and used to predict the
heating rate needed, as opposed to
simply watching the output temperature
and responding when it changes. This
improved instrumentation and the
use of the computational power of the
BAS results in more consistent output
temperatures under varying inlet water
temperatures, ambient temperatures,
and ow rates. This instrumentation
provides energy savings. If the
controller is given predictions of
Elements of Environmental Automation Systems