How to Create Treating and Recycling Water

Treating and
Recycling Water
In the United States, each person generates almost
75,700 liters (20,000 gallons) of sewage each year.
Fruits, vegetables, grains, milk products, and meats derived
from nutrients in the soil are brought into cities,
to be later flushed out as sewage. Some communities
discharge bacteria-laden sewage into nearby lakes, rivers,
or the ocean. Most cities and towns send the sewage to
treatment plants, where the solid matter (sludge) settles
out. The remaining liquid is chlorinated to kill bacteria
and then dumped into a local waterway.
The sludge is pumped into a treatment tank, where
it ferments anaerobically (without oxygen) for several
weeks. This kills most of the disease-causing bacteria
and precipitates out most minerals. The digested
sludge is then chlorinated and pumped into the local
waterway.

Waterways can’t finish the natural cycle by returning
the nutrients back to the soil, and end up with increasing
amounts of nutrients. This nutrient-rich water
promotes the fast growth of waterweeds and algae. The
water becomes choked with plant growth, and the sun
is unable to penetrate more than a few inches below the
surface. Masses of plants die and decay, consuming
much of the oxygen in the water in the process. Without
oxygen, fish suffocate and die. The waterway itself
begins to die. Over a few decades, it becomes a swamp,
then a meadow. Meanwhile, the farmland is gradually
drained of nutrients. Farm productivity falls, and produce
quality declines. Artificial fertilizers are applied to
replace the wasted natural fertilizers.

Designers can step into this process when they make
decisions about how wastes will be generated and handled
by the buildings they design. Sewage treatment is
expensive for the community, and becomes a critical issue
for building owners where private or on-site sewage
treatment is required. In a geographically isolated community,
like Martha’s Vineyard off the Massachusetts
coast, restaurants have been forced out of business by
the high cost of pumping out their septic tanks. One local
businessman calculates that it costs him about one
dollar per toilet flush, and if his septic tank fills up, he
will have to shut down before it can be pumped. In
1997, Dee’s Harbor Café was closed after its septic system
failed, and the owner lost her life savings. Even in
less remote locations, dependence on a septic tank
often limits the size of a restaurant and prohibits
expansion.
Sewage disposal systems are designed by sanitary
engineers and must be approved and inspected by the
health department before use. The type and size of private
sewage treatment systems depend on the number
of fixtures served and the permeability of the soil as de-

Treating and
Recycling Water

RURAL SEWAGE TREATMENT
In times past, rural wastes ended up in a cesspool, a
porous underground container of stone or brick, which
allowed sewage to seep into the surrounding soil. Cesspools
did not remove disease-causing organisms. Within
a short time, the surrounding soil became clogged with
solids, and the sewage overflowed onto the surface of
the ground and backed up into fixtures inside the
building.

Cesspools have mostly been replaced by septic systems
tank, a distribution box, and a leach field of perforated
drainpipes buried in shallow, gravel-filled trenches.
Septic tanks are nonporous tanks of precast concrete,
steel, fiberglass, or polyethylene that hold sewage for a
period of days while the sewage decomposes anaerobically.
Anaerobic digestion produces methane gas and
odor.

During this time, the sewage separates into a clear,
relatively harmless effluent and a small amount of mineral
matter that settles to the bottom. Soaps and slowto-
degrade fats and oils float to the top of the tank to
form a layer of scum. Inlet and outlet baffles in the tank
prevent the surface scum from flowing out. The liquid
moves through a submerged opening in the middle of
the tank to a second chamber. Here finer solids continue
to sink, and less scum forms. This part of the process
is known as primary treatment.

When the effluent leaves the septic tank, it is about
70 percent purified. The longer sewage stays in the tank,
the less polluted is the effluent. If the building and its
occupants practice water conservation, less water and
wastes flow through the septic tank, the effluent stays
in the tank longer before being flushed out, and it
emerges cleaner. Every few years, the sludge is pumped
out of the septic tank and is hauled away and processed
to a harmless state at a remote plant. The methane gas
and sewage odor stay in the tank.
Each time sewage flows into the tank, an equal volume
of nitrate-rich water flows out and is distributed
into the leach field, which provides secondary treatment.
There the water is absorbed and evaporates. Nitratehungry
microbes in the soil consume the potentially
poisonous nitrates. In the process, plant food is manufactured
in the form of nitrogen.

Nothing that can kill bacteria should ever be flushed
down the drain into a septic system. Paints, varnishes,
thinners, waste oil, photographic solutions, and pesti-
cides can disrupt the anaerobic digestion. Coffee grounds,
dental floss, disposable diapers, cat litter, sanitary napkins
and tampons, cigarette butts, condoms, gauze bandages,
paper towels, and fat and grease add to the sludge
layer in the bottom of the tank. Some systems include a
grease trap in the line between the house and the septic
tank, which should be cleaned out twice a year.
Trained professionals must clean the tank at regular
intervals. As the sludge and scum accumulate, there
is less room for the bacteria that do their work, and the
system becomes less effective. If the scum escapes
through the outlet baffle into the leach field, it clogs the
earthen walls of the trenches and decreases the necessary
absorption. Most tanks are cleaned every two to
four years.

Most septic systems eventually fail, usually in the
secondary treatment phase. If the septic tank or the soil
in the leaching field is not porous enough, or if the system
is installed too near a well or body of water, or beside
a steep slope, the system can malfunction and contaminate
water or soil. Most communities have strict
regulations requiring soil testing and construction and
design techniques for installing septic tanks. If the site
can’t support the septic tank, the building can’t be built.
Aerobic (with oxygen) treatment units (ATUs) can
replace septic tanks in troubled systems. By rejuvenating
existing drainfields, they can extend the system’s life.
Air is bubbled through the sewage or the sewage is
stirred, facilitating aerobic digestion. After about one
day, the effluent moves to the settling chamber where
the remaining solids settle and are filtered out. Because
aerobic digestion is faster than anaerobic digestion, the
tank can be smaller. However, the process is energy intensive
and requires more maintenance. The effluent
then moves on to secondary treatment.

Secondary treatment can use a number of different
techniques, with varying impact on the building site.
Disposal fields are relatively inexpensive, and do not require
that the soil be very porous or that the water table
be very deep below the surface. Drainlines of perforated
pipe or agricultural tile separated by small openings are
located in shallow trenches on a bed of gravel and covered
with more gravel. The effluent runs out of these
lines and through the gravel, until it seeps into the earth.
The gravel’s spaces hold the liquid until it is absorbed.
Buried sand filters that use sand, crushed glass, mineral
tailings, or bottom ash are also used for secondary
treatment. They are applied where the groundwater level
is high, or in areas of exposed bedrock or poor soil. A
large site area is required, but the ground surface can
become a lawn or other nonpaved surface. Buried sand
filters can be a remedy for failed disposal fields.
Seepage pits are a form of secondary treatment appropriate
for very porous soil and a low water table only.
Seepage pits can also be used as dry wells to distribute
runoff from pavement gradually.

MUNICIPAL SEWAGE
TREATMENT PLANTS
Larger scale sewage treatment plants continue to improve
the efficiency of their processes, and municipalities
are active in reducing the amount of sewage they
process. Larger plants use aerobic digestion plus chemical
treatment and filtration, and can produce effluent
suitable for drinking. Clean effluent is pumped into the
ground to replenish depleted groundwater. Digested
sludge is dried, bagged, and sold for fertilizer. Some
plants spray processed sewage directly on forests or cropland
for irrigation or fertilizer.

ON-SITE LARGE-SCALE
TREATMENT SYSTEMS
After years of sending sewage to distant treatment plants,
it is becoming more common for groups of buildings
to treat their wastes on site. The advantages include savings
to the community, reusable treated water for landscaping
and other purposes, and even pleasant and
attractive outdoor or indoor environments. In some
campus-type industrial, educational, or military facilities,
septic tanks are installed at each building, and the
outflow is combined for the secondary treatment process.
Use of sand filters for secondary treatment offers
simple maintenance, very low energy use, and greater
available usable land area.

Constructed Wetlands
By constructing an environment that filters and purifies
used water and recycles it for additional use, we can reduce
municipal sewage treatment costs and support local
plant and animal life. Free-surface (open) wetlands
use effluents to nourish vegetation growing in soil. Human
contact with these secondary treatment areas must
be controlled.
The Campus Center for Appropriate Technology at
Humboldt State University in Arcata, California, uses a
graywater treatment marsh that consists of an open

channel of water with a gravel-filled channel planted
with vegetation. A primary treatment tank filters out
large particles such as hair, grease, and food scraps.
Water then penetrates down through the gravel in the
channel. Once it reaches the end of the channel, the
water is removed from the bottom of the marsh by a
perforated pipe. This pipe then conveys water to the next
gravel marsh box, a process that supplies it with oxygen.
After treatment in the graywater marsh, water from
the sinks and shower is reused on the lawns and ornamental
plants. Except for periodic maintenance, very little
energy is used.

Subsurface flow wetlands consist of a basin lined
with large gravel or crushed rock, and a layer of soil with
plants above. Plants encourage the growth of microorganisms,
both anaerobic and aerobic, and bring air
underwater through their roots. The effluent is then filtered
through sand and disinfected. It is then safe to use
for many purposes, including landscape watering. This
secondary treatment option is safer for human contact,
and also attracts birds. The master plan for the Coffee
Creek Center southeast of Chicago features constructed
wetlands for on-site treatment of wastewater from
homes and businesses.

Pasveer Oxidation System
The Pasveer oxidation sewage treatment system was used
by the New York Institute of Technology in Old Westbury
on Long Island in New York. Purified effluent returns
to the ground through 48 leaching wells under the
school’s athletic field. The sludge is processed using a
mechanical aerator for aerobic digestion. There is no
compressor, only the noise of splashing water. The process
has a low profile and is screened by trees.

Greenhouse Ecosystems
Greenhouse ecosystems (Fig. 11-2) are secondary sewage
treatment systems that are constructed wetlands moved
indoors. Marine biologist John Todd developed Living
Machines at Ocean Arks International. They consist of a
series of tanks, each with its own particular ecosystem.
The first is a stream, and the second is an indoor marsh
that provides a high degree of tertiary wastewater treatment.
The system costs less to construct and about the
same to maintain as a conventional sewage treatment
system. It uses less energy, depending upon solar energy
for photosynthesis and on gravity flow. There is no need
for a final, environmentally harmful chlorine treatment.
The system produces one-quarter of the sludge of other
systems.
These greenhouse environments are pleasant to
look at and smell like commercial greenhouses. They
are welcome in the neighborhoods they serve, and can
save huge costs in sewer lines that would otherwise run
to distant plants. Greenhouse ecosystems offer an opportunity
to enrich the experience of an interior environment
while solving a serious ecological problem.

Within the greenhouse ecosystems, aerobic bacteria
eat suspended organic matter and convert ammonia to
nitrates, producing nitrites. Algae and duckweed eat the
products of the bacteria. Snails and zooplankton then
eat the algae. The floating duckweed creates shade that
discourages algae growth in the later stages of production.
Finally, fish eat the zooplankton and snails. The
systems support water hyacinth and papyrus, canna
lilies, bald cypress, willows, and eucalyptus, which remove
phosphorus and heavy metals during the lives of
the plants, returning them to the earth when the plants
die. Small fish (shiners) are sold as bait, and dead plants
and fish are composted.
On-site wastewater treatment has a significant impact
on the design of the building’s site. Interiors are
also affected, as the system may use special types of
plumbing fixtures and may include indoor greenhouse
filtration systems.

RECYCLED WATER
Water is categorized by its purity. Potable water has usually
been treated to be safe for drinking. Rainwater offers
a sporadic supply of pure water that can be used for
bathing, laundry, toilet flushing, irrigation, or evaporative
cooling with little or no treatment. Graywater is
wastewater that is not from toilets or urinals. It comes
from sinks, baths, and showers. Blackwater is water with
toilet or urinal waste.
Graywater may contain soap, hair, or human waste
from dirty diapers and other laundry. It can be treated
and recycled for uses like toilet flushing and filtered drip
irrigation. Dark graywater comes from washing machines
with dirty diaper loads, kitchen sinks, and dishwashers,
and is usually prohibited by codes from being
reused. If graywater contains kitchen wastes, grease and
food solids are a problem. Currently, few communities
allow the reuse of graywater; and those that do tend to
restrict its use to underground landscape irrigation for
single-family houses. New York-based architect William
McDonough has used gray and blackwater in designs
for Eurosud-Calvission, a software research and development
facility in southern France.

Future water conservation measures may include
the use of water from bathing for flushing toilets,
which would save 21 gallons per person each day. The
14-gallons per person used daily for laundry can help
with irrigation, preferably through underground distribution
systems that limit contact with people.
The Aquasaver Company in England has developed
a system that diverts and cleans water from lavatories,
baths, and showers for flushing toilets, washing clothes,
washing cars, and irrigation. A low-pressure system installed
behind panels in the bathroom pumps graywater
through a series of filters, removing soaps, detergents,
and other impurities. The water then goes to a storage
tank in the attic or above points of use. The system uses
nonhazardous cleaning agents and a network of carbon
filters.

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How to create Waste Plumbing in Instalation building (HOME)

Waste Plumbing
downhill, and normal atmospheric pressure must be
maintained throughout the system at all times. Cleanouts
are located to facilitate removal of solid wastes
from clogged pipes.

Cast iron is used for waste plumbing in both small
and large buildings. Cast iron was invented in Germany
in 1562 and was first used in the United States in 1813.
It is durable and corrosion resistant. Cast iron is hard
to cut, and was formerly joined at its hub joints using
molten lead. Today, cast-iron pipes use hubless or belland-
spigot joints and fittings or a neoprene (flexible
plastic) sleeve.
Plastic pipes made of ABS or PVC plastic are lightweight
and can be assembled in advance. Copper pipes
have been used since ancient times. Some building
codes also allow galvanized wrought iron or steel pipes.
Engineers size waste plumbing lines according to
their location in the system and the total number and
types of fixtures they serve. Waste piping is laid out as
direct and straight as possible to prevent deposit of
solids and clogging. Bends are minimized in number
and angled gently, without right angles. Horizontal
drains should have a 1 : 100 slope (_ in. per foot) for
pipes up to 76 mm (3 in.) in diameter, and a 1:50 slope
 in. per foot) for pipes larger than 76 mm. These large,
sloping drainpipes can gradually drop from a floor
through the ceiling below and become a problem for
the interior designer.

Cleanouts are distributed throughout the sanitary
system between fixtures and the outside sewer connection.
They are located a maximum of 15 meters (50 ft)
apart in branch lines and building drains up to 10 cm
(4 in.). On larger lines, they are located a maximum of
30.5 meters (100 ft) apart. Cleanouts are also required
at the base of each stack, at every change of direction
greater than 45 degrees, and at the point where the
building drain leaves the building. Wherever a cleanout
is located, there must be access for maintenance and
room to work, which may create problems for the unwary
interior designer.

Fixture drains extend from the trap of a plumbing
fixture to the junction with the waste or soil stack.
Branch drains connect one or more fixtures to soil or
waste stacks. A soil stack is the waste pipe that runs from
toilets and urinals to the building drain or building
sewer. A waste stack is a waste pipe that carries wastes
from plumbing fixtures other than toilets and urinals.
It is important to admit fresh air into the waste plumbing
system, to keep the atmospheric pressure normal
and avoid vacuums that could suck wastes back up into
fixtures. A fresh-air inlet connects to the building drain
and admits fresh air into the drainage system of the
building. The building sewer connects the building
drain to the public sewer or to a private treatment facility
such as a septic tank.

Floor drains are located in areas where floors need
to be washed down after food preparation and cooking.
They allow floors to be washed or wiped up easily in
shower areas, behind bars, and in other places where
water may spill. Interceptors, also known as traps, are intended to
block undesirable materials before they get into the
waste plumbing. Among the 25 types of interceptors are
ones designed to catch hair, grease, plaster, lubricating
oil, glass grindings, and industrial materials. Grease
traps are the most common. Grease rises to the top of
the trap, where it is caught in baffles, preventing it from
congealing in piping and slowing down the digestion
of sewage. Grease traps are often required by code in
restaurant kitchens and other locations.
Sewage ejector pumps are used where fixtures are below
the level of the sewer. Drainage from the below-grade
fixture flows by gravity into a sump pit or other receptacle
and is lifted up into the sewer by the pump. It is
best to avoid locating fixtures below sewer level where
possible, because if the power fails, the equipment shuts
down and the sanitary drains don’t work. Sewage ejector
pumps should be used only as a last resort.

Residential Waste Piping
The waste piping for a residence usually fits into a
15-cm (6-in.) partition. In smaller buildings, 10-cm
(4-in.) soil stacks and building drains are common. It
is common to arrange bathrooms and kitchens back-toback.
The piping assembly can then pick up the drainage
of fixtures on both sides of the wall. Sometimes an extra-
wide wall serves as a vertical plumbing chase, which
is a place between walls for plumbing pipes. Fitting both
the supply and waste plumbing distribution trees into
the space below the floor or between walls is difficult,
as larger waste pipes must slope continually down from
the fixture to the sewer. Some codes require that vertical
vents that penetrate the roof must be a minimum of
10 cm (4 in.) in diameter, to prevent blocking by ice in
freezing weather; such a requirement, of course, adds
another space requirement between walls.

Large Building Waste Piping Systems
In larger buildings, the need for flexibility in space use
and the desire to avoid a random partition layout means
that plumbing fixtures and pipes must be carefully
planned early in the design process. The location of the
building core, with its elevators, stairs, and shafts for
plumbing, mechanical, and electrical equipment, affects
the access of surrounding areas to daylight and views.
When offices need a single lavatory or complete toilet
room away from the central core (as for an executive
toilet), pipes must be run horizontally from the core. In
order to preserve the slope for waste piping, the farther
the toilet room is located from the core, the greater
amount of vertical space is taken up by the plumbing.
Wet columns group plumbing pipes away from
plumbing cores to serve sinks, private toilets, and other
fixtures, and provide an alternative to long horizontal
waste piping runs. Wet columns are usually located at
a structural column, which requires coordination with
the structural design early in the design process. Individual
tenants can tap into these lines without having
to connect to more remote plumbing at the core of the
building.

When running pipes vertically, a hole in the floor
for each pipe is preferred over a slot or shaft, as it interferes
less with the floor construction. Where waste
piping drops through the floor and crosses below the
floor slab to join the branch soil and waste stack, it can
be shielded from view by a hung ceiling. An alternative
method involves laying the piping above the structural
slab and casting a lightweight concrete fill over it. This
raises the floor 127 to 152 mm (5–6 in.). Raising the
floor only in the toilet room creates access problems, so
the whole floor is usually raised. This creates space for
electrical conduit and to serve as an open plenum
for heating, ventilating, and air-conditioning (HVAC)
equipment as well.

WASTE COMPONENTS OF
PLUMBING FIXTURES
Originally, the pipe that carried wastewater from a
plumbing fixture ran directly to the sewer. Foul-smelling
gases from the anaerobic (without oxygen) digestion in
the sewer could travel back up the pipe and create a
health threat indoors.
The trap (Fig. 10-2) was invented to block the waste
pipe near the fixture so that gas couldn’t pass back up
into the building. The trap is a U-shaped or S-shaped
section of drainpipe that holds wastewater. The trap
forms a seal to prevent the passage of sewer gas while
allowing wastewater or sewage to flow through it. Traps
are made of steel, cast iron, copper, plastic, or brass. On
water closets and urinals, they are an integral part of the
vitreous china fixture, with wall outlets for wall-hung
units and floor outlets for other types.
Drum traps are sometimes found on bathtubs in
older homes. A drum trap is a cylindrical trap made
from iron, brass, or lead, with a screw top or bottom.
Water from the tub enters near the bottom and exits
near the top, so the wastewater fills the trap and creates
a water plug before flowing out. Sometimes the screwoff
top, called a cleanout, is plated with chrome or brass
and left exposed in the floor so it can be opened for
cleaning. Drum traps can cause drainage problems because
debris settles and collects in the trap. If not
cleaned out regularly, these traps eventually get com-
Figure 10-2 Trap.
pletely clogged up. Drum traps should be replaced during
remodeling.

Every fixture must have a trap, and every trap must
have a vent. Each time the filled trap is emptied, the
wastewater scours the inside of the trap and washes debris
away. Some fixtures have traps as an integral part
of their design, including toilets and double kitchen
sinks. There are a few exceptions to the rule that each
fixture should have its own trap. Two laundry trays and
a kitchen sink, or three laundry trays, may share a single
trap. Three lavatories are permitted on one trap.
Traps should be within 0.61 meters (2 ft) of a fixture
and be accessible for cleaning. If the fixture isn’t
used often, the water may evaporate and break the seal
of the trap. This sometimes happens in unoccupied
buildings and with rarely used floor drains.

VENT PIPING
The invention of the trap helped to keep sewer gases out
of buildings. However, traps were not foolproof. When
water moving farther downstream in the system pushes
along water in front of it at higher pressures, negative
pressures are left behind. The higher pressures could
force sewer water through the water in some traps, and
lower pressures could siphon (suck) water from other
traps, allowing sewer gases to get through (Fig. 10-3).

Vent pipes (Fig. 10-4) are added to the waste piping
a short distance downstream from each trap to prevent
the pressures that would allow dirty water and
sewer gases to get through the traps. Vent pipes run upward,
join together, and eventually poke through the
roof. Because the roof may be several floors up and the
pipes may have to pass through other tenants’ spaces,
adding vent pipes in new locations can be difficult. The
vent pipe allows air to enter the waste pipe and break
the siphoning action. Vent pipes also release the gases
of decomposition, including methane and hydrogen
sulfide, to the atmosphere. By introducing fresh air
through the drain and sewer lines, air vents help reduce
corrosion and slime growth.

The vent pipes connect an individual plumbing fixture
to two treelike configurations of piping. The waste
piping collects sewage and leads down to the sewer. The
vent piping connects upward with the open air, allowing
gases from the waste piping to escape and keeping
the air pressure in the system even. This keeps pressure
on foul gases so that they can’t bubble through the trap
water, and gives them a local means of escape to the
outdoors.

The vent must run vertically to a point above the
spillover line on a sink before running horizontally
so that debris won’t collect in the vent if the drain
clogs. Once the vent rises above the spillover line, it
can run horizontally and then join up with other vents
to form the vent stack, eventually exiting through
the roof.
When all fixtures are on nearly the same level, a separate
vertical vent stack standing next to the soil stack
is not required. In one-story buildings, the upper extension
of the soil stack above the highest horizontal
drain connected to the stack becomes a vent called the
stack vent. It must extend 31 cm (12 in.) above the roof
surface, and should be kept away from vertical surfaces,
operable skylights, and roof windows.

When a sink is located in an island, as in some
kitchen designs, there is no place for the vent line to go
up. Instead, a waste line is run to a sump at another location,
which is then provided with a trap and vent. A
fresh-air vent, also called a fresh air inlet, is a short air
pipe connected to the main building drain just before
it leaves the building, with a screen over the outdoor
end to keep out debris and critters.

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Hot Water System and Review

Domestic hot water (DHW) is hot water that is used for
bathing, clothes washing, washing dishes, and many
other things, but not for heating building spaces. Domestic
hot water is sometimes called building service
hot water in nonresidential uses. Sometimes, when a
well-insulated building uses very little water for space
heating but uses a lot of hot water for other purposes,
a single large hot water heater supplies both.

HOT  WATER TEMPERATURES
Excessively hot water temperatures can result in scalding.
People generally take showers at 41°C to 49°C
(105°F–120°F), often by blending hot water at 60°C
(140°F) with cold water with a mixing valve in the
shower. Most people experience temperatures above
43°C (110°F) as uncomfortably hot.
Some commercial uses require higher temperatures.
The minimum for a sanitizing rinse for a commercial
dishwasher or laundry is 82°C (180°F). Generalpurpose
cleaning and food preparation requires 60°C
(140°F) water. Temperatures above 60°C can cause serious
burns, and promote scaling if the water is hard.
However, high temperatures limit the growth of the
harmful bacterium Legionella pneumophila, which causes
Legionnaire’s disease. Water heaters for high temperature
uses have larger heating units, but the tanks can
be smaller because less cold water has to be mixed in.
Some appliances, such as dishwashers, heat water at the
point of use. Codes may regulate or limit high water
temperatures.
Lower temperatures are less likely to cause burns,
but may be inadequate for sanitation. Lower temperature
water loses less heat in storage and in pipes, saving
energy. Smaller heating units are adequate, but larger
storage tanks are needed. Solar or waste heat recovery
sources work better with lower temperature water
heaters. For energy conservation, use the lowest possible
temperatures.

WATER HEATERS
Water heating accounts for over 20 percent of the average
family’s annual heating bill. Hot water is commonly
heated using natural gas or electricity. It is also possible
to use heat that would be wasted from other systems,
or heat from steam, cogeneration, or wood-burning
systems.

Hot Water

Solar Water Heaters
Solar energy is often used for the hot water needs of
families in sunny climates. In temperate climates with
little winter sun, solar water heaters can serve as preheating
systems, with backup from a standard system.
The solar water heater raises the temperature of the
water before it enters the standard water-heating tank,
so that the electric element or gas burner consumes less
fuel. Solar water heaters can cut the average family’s
water-heating bill by 40 to 60 percent annually, even in
a cold climate. Heavy water users will benefit the most.
Although initial costs of solar water heaters may be
higher than for conventional systems, they offer longterm
savings. A complete system costing under $3000
can provide two-thirds of a family’s hot water needs even
in New England. This is competitive with the still less
expensive gas water heater. Some states offer income tax
credits, and some electric utilities give rebates for solar
water heaters. Solar water heaters are required on new
construction in some parts of the United States.
Solar water heating isn’t always the best choice.
When considering a decision to go solar, the existing
water heater should first be made as efficient as possible.
A careful analysis of the building site will determine
if there is adequate sun for solar collectors, which will
need to face within 40 degrees of true south. Trees,
buildings, or other obstructions should not shade the
collectors between 9 a.m. and 3 p.m.

Solar water heaters use either direct or indirect systems.
In a direct system, the water circulates through a
solar collector (Fig. 9-1). Direct systems are simple, efficient,
and have no piping or heat exchanger complications.
In an indirect system, a fluid circulates in a
closed loop through the collector and storage tank. With
an indirect system, the fluid is not mixed with the hot
water, but heat is passed between fluids by a heat exchanger.
This allows for the use of nonfreezing solutions
in the collector loop.

Solar water heater systems are categorized as either
active or passive. In passive systems, gravity circulates
water down from a storage tank above the collector. The
heavy tanks may require special structural support.
These systems tend to have relatively low initial installation
and operating cost and to be very reliable mechanically.
Active systems use pumps to force fluid to
the collector. This leaves them susceptible to mechanical
breakdown and increases maintenance and energy
costs. Active systems are more common in the United
States.

Solar energy can heat outdoor swimming pools during
the months with most sun. Solar pool heating extends
the swimming season by several weeks and pays
for itself within two years. The pool’s existing filtration
system pumps water through solar collectors, where
water is heated and pumped back to the pool. More
complex systems are available for heating indoor pools,
hot tubs, and spas in colder climates.

Heat Pump Water Heaters
A heat pump water heater takes excess heat from the air
in a hot place, like a restaurant kitchen or hot outdoor
air, and uses it to heat water. In the process, the heat
pump cools and dehumidifies the space it serves. Because
the heat pump water heater moves the heat from
one location to another rather than heating the water
directly, it uses only one-half to one-third of the amount
of energy a standard water heater needs. Heat pump
water heaters can run on the heat given off by refrigeration
units such as ice-making machines, grocery refrigeration
display units, and walk-in freezers.
Because a heat pump water heater uses refrigerant
fluid and a compressor to transfer heat to an insulated

Solar water heater.
storage tank, they are more expensive than other types
of water heaters to purchase and maintain. Some units
come with built-in water tanks, while others are added
onto existing hot water tanks. The heat pump takes up
a small amount of space in addition to the storage tank,
and there is some noise from the compressor and fan.

Storage Tank Water Heaters
Residential and small commercial buildings usually use
centrally located storage tank water heaters. Some buildings
combine a central tank with additional tanks near
the end use to help reduce heat lost in pipes. Circulating
storage water heaters heat the water first by a coil,
and then circulate it through the storage tank.
Storage-type water heaters are rated by tank capacity
in gallons, and by recovery time, which is the time
required for the tank to reach a desired temperature
when filled with cold water. This shows up as the time
it takes to get a hot shower after someone takes a long
shower and empties the tank. Storage water heaters usually
have 20- to 80-gallon capacities, and use electricity,
natural gas, propane, or oil for fuel. The water enters at
the bottom of the tank, where it is heated, and leaves
at the top. The heat loss through the sides of the tank
continues even when no hot water is being used, so storage
water heaters keep using energy to maintain water
temperature. The tanks usually are insulated to retain
heat, but some older models may need more insulation.
Local utilities will sometimes insulate hot water tanks
for free. High-efficiency water heaters are better insulated
and use less energy.

Tankless Water Heaters
Small wall-mounted tankless water heaters (Fig. 9-2) are
located next to plumbing fixtures that occasionally need
hot water, like isolated bathrooms and laundry rooms.
They can be easily installed in cabinets, vanities, or closets
near the point of use. Although they use a great
amount of heat for a short time to heat a very limited
amount of water, these tankless heaters can reduce energy
consumption by limiting the heat lost from water
storage tanks and long piping runs. Because they may
demand a lot of heat at peak times, electric heaters are
usually not economical over time where electric utilities
charge customers based on demand.
These small tankless water heaters (also called instantaneous
or demand heaters) raise the water temperature
very quickly within a heating coil, from which
it is immediately sent to the point of use. A gas burner
or electrical element heats the water as needed. They
have no storage tank, and consequently do not lose heat.
With modulating temperature controls, demand water
heaters will keep water temperatures the same at different
rates of flow.

Without a storage tank, the number of gallons of
hot water available per minute is limited. The largest
gas-fired demand water heaters can heat only 3 gallons
of water per minute (gpm), so they are not very useful
for commercial applications, but may be acceptable for
a residence with a low-flow shower and limited demand.
Gas heaters must be vented.
The largest electric models heat only 2 gpm, and are
used as supplementary heaters in home additions or remote
locations, or as boosters under sinks. Electric
heaters require 240V wiring.
Instant hot water taps use electric resistance heaters
to supply hot water up to 88°C (190°F) at kitchen and
bar sinks. They are expensive and waste energy. Instant
hot water dispensers require a 120V fused, grounded
outlet within 102 cm (40 in.) from the hot water dispenser
tank, plus a water supply.

Some tankless coil water heaters take their heat from
an older oil- or gas-fired boiler used for the home heating
system. The hot water circulates through a heat exchanger
in the boiler. The boiler must be run for hot
water even in the summer when space heating isn’t
needed, so the boiler cycles on and off frequently just
to heat water. These inefficient systems consume 3 Btus
of heat energy from fuel for each Btu of hot water they
produce.
Point-of-use water heater.

Indirect Water Heaters
Indirect water heaters also use a boiler or furnace as the
heat source, but are designed to be one of the least expensive
ways to provide hot water when used with a
new high-efficiency boiler. Hot water from the boiler is
circulated through a heat exchanger in a separate insulated
tank. Less commonly, water in a heat exchanger
coil circulates through a furnace, then through a water
storage tank. These indirect water heaters are purchased
as part of a boiler or furnace system, or as a separate
component. They may be operated with gas, oil, or
propane.

Integrated Water Heating
and Space Heating
Some advanced heating systems combine water heating
with warm air space heating in the same appliance. A
powerful water heater provides hot water for domestic
use and to supplement a fan-coil unit (FCU) that heats
air for space heating. The warmed air is then distributed
through ducts. Integrated gas heaters are inexpensive to
purchase and install. They take up less space and are more
efficient at heating water than conventional systems.

Water Heater Safety
and Energy Efficiency
Either sealed combustion or a power-vented system will
assure safety and energy efficiency in a water heater. In
a sealed combustion system, outside air is fed directly
to the water heater and the combustion gases are vented
directly to the outside. Power-vented equipment can
use house air for combustion, with flue gases vented
by a fan. This is not a safe solution in a tightly sealed
building.
In 1987, the National Appliance Energy Conservation
Act set minimum requirements for water heating
equipment in the United States. Equipment is labeled
with energy conservation information. The U.S. Department
of Energy (DOE) developed standardized energy
factors (EF) as a measure of annual overall efficiency.
Standard gas-fired storage tank water heaters may
receive an EF of 0.60 to 0.64. Gas-fired tankless water
heaters rate up to 0.69 with continuous pilots, and up
to 0.93 with electronic ignition. The 2001 DOE standards
for water heaters will increase efficiency criteria,
and should result in significant utility savings over the
life of gas-fired water heaters and electric water heaters.
Water heaters lose less heat if they are located
in a relatively warm area, so avoid putting the water
heater in an unheated basement. By locating the
water heater centrally, you can cut down on heat lost in
long piping runs to kitchens and bathrooms.

Existing water heaters can be upgraded for improved
efficiency. By installing heat traps on both hot and cold
water lines at a cost of about $30 each, you will save
about $15 to $30 per year in lost heat. The cold water
pipe should be insulated between the tank and the heat
trap. If heat traps are not installed, both hot and cold
pipes should be insulated for several feet near the water
heater.
Low-flow showerheads and faucet aerators save
both heat and water. United States government standards
require that showerheads and faucets use less than
2.5 gpm. Low-flow showerheads come in shower massage
styles. Faucets with aerators are available that use
 to 1 gpm. By lowering water temperatures to around
49°C (120°F), you save energy and reduce the risk of
burns.
A relatively inexpensive counterflow heat exchanger
can save up to 50 percent of the energy a home uses to
heat water. It consists of a coil of copper tubing that’s
tightly wrapped around a 76- to 102-mm (3–4-in.) diameter
copper pipe, and installed vertically in the
plumbing system. As waste water flows down through
the vertical pipe section, more than half the water’s heat
energy is transferred through the copper pipe and tubing
to the incoming cold water. There is no pump, no
storage tank, and no electricity used. The counterflow
heat exchanger only works when the drain and supply
lines are being used simultaneously, as when someone
is taking a shower.

Spas and hot tubs must be kept tightly covered and
insulated around the bottom and sides. Waterbeds are
found in up to 20 percent of homes in the United States,
and are sometimes the largest electrical use in the home.
Most waterbeds are heated with electric coils underneath
the bed. Your clients can conserve energy by keeping
a comforter on top, insulating the sides, and putting
the heater on a timer
.
HOT WATER DISTRIBUTION
Hot water is carried through the building by pipes
arranged in distribution trees. When hot water flows
through a single hot water distribution tree, it will cool
off as it gets farther from the hot water heater. To get
hot water at the end of the run, you have to waste the

cooled-off water already in the pipes. With a looped hot
water distribution tree, the water circulates constantly.
There is still some heat loss in the pipes, but less water
has to be run at the fixture before it gets hot. Hot water
is always available at each tap in one to two seconds.
Hot water is circulated by use of the thermosiphon
principle. This is the phenomenon where water expands
and becomes lighter as it is heated. The warmed water
rises to where it is used, then cools and drops back down
to the water heater, leaving no cold water standing in
pipes. Thermosiphon circulation works better the higher
the system goes.

Forced circulation is used in long buildings that are
too low for thermosiphon circulation, and where friction
from long pipe runs slows down the flow. The water
heater and a pump are turned on as needed to keep
water at the desired temperature. It takes five to ten seconds
for water to reach full temperature at the fixture.
Forced circulation is common in large one-story residential,
school, and factory buildings.

Computer controls can save energy in hotels, motels,
apartment houses, and larger commercial buildings.
The computer provides the hottest water temperatures
at the busiest hours. When usage is lower, the
supply temperature is lowered and more hot water is
mixed with less cold water at showers, lavatories, and
sinks. Distributing cooler water to the fixture results in
less heat lost along the pipes. The computer stores and
adjusts a memory of the building’s typical daily use
patterns. Hot water pipes expand. Expansion bends are installed
in long piping runs to accommodate the expansion
of the pipes due to heat.

Where the pipes branch out to a fixture, capped
lengths of vertical pipe about 0.6 meters (2 ft) long provide
expansion chambers to dampen the shock of hot
water expansion. Rechargeable air chambers on branch
lines adjacent to groups of fixtures are designed to deal
with the shock of water expansion. They require service
access to be refilled with air.

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