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How to Size a Water
Softener
The following must be considered when sizing a
water softening system:
- Flow rate
(gallons per minute)
- Influent water hardness (grains per
gallons)
- Usage (gallons per day)
- Hours of operation
- Economics
- Physics
Flow
rate
In general, it is best to base the size of
your water softening system on continuous flow rather that peak
flow rates. During peak flow rates the jeopardy of hardness
break through is present. If flow rates are not known, helpful
charts are included to approximate flow rates.
The following information has been prepared
as a guide for estimating maximum flow rates for private and
public buildings. The numbers assigned the various fixtures are
based on a combination of flow rate and probability of use.
1. Count and total the number of each type of
fixture to be serviced by the water softening system.
2. Mulitply the number of each type of
fixture by the UNIT COUNT given in the Fixture Unit able.
Private –
Motels
Apartment Buildings
Trailer Parks
Group Homes
Public - Office Buildings
Hospitals
Country Clubs
Schools
3. Find the total FIXTURE COUNT by adding up
the values found in step 2.
4. Using the correct table below, find the
FIXTURE COUNT closest to the calculated value. The figure given
the right hand column is the approximate maximum GPM required.
EXAMPLE:
Type of Fixture
Qty. Unit Count Total
Water Closet (FV) 8 X 10 =
80
Shower 10 X 4 =
40
Lavatory 15 X 2
= 30
TOTAL FIXTURE
UNIT COUNT = 150
Estimated Flow Rate = 80GPm
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Fixture
Unit Table
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Type
of Fixture
|
Units
-Private-
|
Units
-Public-
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Bar Sink
Bathtub
Bedpan Washer
Bidet
Combination Sink &Tray
Dental Unit or Cuspidor
Dental Laboratory
Drinking Fountain
House Bib or Sill Cock (Std)
House Trailer (each)
Laundry Tub or Washer
Lavatory
Lawn Sprinkler (each head)
Shower
Sink; Service (Janitor’s)
Sink or Dishwasher
Sink (flushing rim, clinic)
Sink (wash up, each set)
Sink (circular spray)
Urinal (wall or stall)
Urinal (flush tank)
Water Closet:
Flushometer Valve
Tank Type
|
1
2
-
2
3
-
1
1
3
6
2
1
1
2
2
2
-
-
-
-
-
6
3
|
2
4
10
4
-
1
2
2
5
6
4
2
1
4
4
4
10
2
4
5
3
10*
5*
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*Double this amount for schools
Water supply outlets fro items not listed
above shall be computed at their maximum demand, but in no
case less than:
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3/8 inch pipe
1/2 inch pipe
3/4 inch pipe
1 inch pipe
|
1
2
3
6
|
2
4
6
10
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OR
You can determine your approximate flow rate by
the size of your plumbing feeding the water softening system.
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COPPER PIPE –
SIZE VS. FLOW RATE
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Size of Pipe
|
GPM through
100’ or type “L” copper tubing
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at 5 pound pressure
drop
|
At 10 pound
pressure drop
|
at 15 pound
pressure drop
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½”
¾”
1”
1-1/4”
1-1/2”
2”
2-1/2”
3”
4”
5”
6”
|
2
6
12
21
33
70
122
195
410
720
1180
|
3
9
18
30
49
100
178
283
595
1050
1720
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4
11
22
38
60
126
222
355
740
1310
2150
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PLASTIC PIPE
– SIZE VS. FLOW RATE
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Size of Pipe
|
GPM through
100’ or type “L” copper tubing
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|
at 5 pound pressure
drop
|
At 10 pound
pressure drop
|
at 15 pound
pressure drop
|
|
½”
¾”
1”
1-1/4”
1-1/2”
2”
2-1/2”
|
2
6
12
21
33
70
122
|
3
9
18
30
49
100
178
|
4
11
22
38
60
126
222
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Water Hardness, Water Quality and Daily Use
Hardness is present in the water supply as
calcium and magnesium bicarbonate, CaCO 3. Other water quality
factors will influence the way the water softening system
works. Dissolved iron, If present, must be taken into account
when sizing the water softening system. Maximum allowable iron
is 2 ppm.
To calculate the required capacity of a water
softening system take a water sample and have it analyzed for
hardness and iron content, or call the local municipal water
treatment facility. Hardness, as CaCO 3, if expressed in parts
per million (ppm) or milligrams per liter (mg/l) is converted
to grains per gallon (gpg) by dividing ppm or mg/l by 17.1. If
iron is present, multiply the amount of dissolved iron (ppm) by
4 and add it to the total grains of hardness. At this point,
your total grains per gallon has been determined.
By multiplying the gallons of usage per day
by grains per gallon will determine the capacity per day. If
daily usage is not known, a helpful chart has been included to
assist you in estimation the daily usage of many types of
facilities.
Water softening systems are typically rated
at 30,000 grains of removal per cubic foot of resin. However,
the systems are typically operated at 20,000 grains of removal
per cubic foot of resin for economy salt dosing.
EXAMPLE:
Hardness
250
ppm
Convert
to grains per gallon divide by
17.1
Hardness
in grains per gallon
14.6
Iron
1
ppm
Convert
to grains per
gallon
4
Iron
in grains per
gallon
4
Total
grains per gallon
18.6
grains
–
add iron + hardness
Daily
Usage
1000
grains
Daily
Capacity – Multiply usage by
total 18,600
grains
per gallon
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Daily Water Usage Estimations
Facility Daily Water Usage Facility Daily
Water Usage
Assembly Halls 2 gals/seat Food Service Operations
Apartment Baildings 150-200 gals/unit Average Restaurant 70
gals/seat
Barber Shops 55 gals/chair 24 Hour Restaurant 100 gals/seat
Beauty Salons 270 gals/station Curb Service 50 gals/car space
Bowling Alleys 75 gal/lane Hotels .256 gal/sq. ft.
Camps Institutions
Day
-(no meals) 15 gals/person Hospitals 250 gals/bed
Resorts
-(day & night 50 gals/person Rest Homes 100 gals/bed
with limited plumbing) Laundries
Tourist-
(with central 35 gals/person Coin Operated 2.17 gals/sq. ft.
Bath & toilet facilities) Commercial .253 gals/sq. ft.
Country Club Motels 100 gals/unit
per resident member 100 gals
Office Building 20 gals/employee
per non- resident member 25 gals
Schools
Dance Halls 2 gals/person Boarding 80 gals/student
Department Store .216 gals/sp. ft. Day (with cafeterias, 25
gals/student
of sales area gym and showers)
Factories Day (with cafeteria only) 20 gals/student
(excluding process water) Day (no
cafeteria or gym) 15 gals/student
without showers 25
gals/person/shift Service Stations 1000 gal-first bay
with shower 500 gal/add’l
bay
Farms or 10 gal/vehicle
Cow, beef 12 gal/head Shopping Center .160 gal/sq.ft.
Cow, dairy 20gal/head Stores 400 gal/toilet room
Goat 2 gal/head Theatres
Hog 12 gal/head Drive-In 5 gals/car space
Horse 12 gal/head Movie 2 gals/seat/movie
Mule 12 gal/head Trailer Parks 100 gals/space
Sheep 2 gals/head
Chickens 10 gals/100
Turkeys 18 gals/100
Hours of Operation
One of the most important factors in
determining the size and configuration of a water softening
system is the hours of service the system will be called upon
to produce soft water. If the system will be required to
produce soft water 24 hours per day and no down time can be
determined, a dual system will be required. If the system is
only required to produce soft water part of the day and down
time can be determined, a single tank water softening system
may be used. However, in certain circumstances when capacity
greatly exceeds flow rate requirements, a dual system can
provide a cost savings.
Economics
Once the minimum size and type of water
softener needed have been determined, you may have several
water softener options. You may only want to spend a minimum
amount of money for the water softener, or you may want a more
expensive meter initiated system in order to spend less money
on salt in the years to come. If the capacity required greatly
exceeds the flow rote requirements, a multiple tank system
could be more economical than a single tank water softener.
Physics
A water softener may be the right type and
may be properly sized for the application it will serve, but
there are other factors to be considered before quoting the
system. The water softener must fit in the space allowed. The
brine tank must fit through the door. A drain must be within
the specified range and must be capable of handling the drain
flow. The temperature of the water must meet specifications.
The drain line should not be susceptible to freezing, etc.
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Water
Softening System Sizing Worksheet
Hardness (ppm) ____________
divide by ________ 17.1
Hardness (gpg) ____________
Iron (ppm) X 4 add ____________
Total grains per gallon ____________
Usage per day (gallons) multiply ____________
Capacity per day (grains) ____________
Required flow rate (gpm) ____________
Peak flow rate (gpm) ____________
Hours of service ____________
Down time ____________
Grains Per
Day vs. Flow Rate
Water softener must meet or exceed both:
--Flow rate specified by the water softening system and
--Total capacity in grains per day specified by the water
softening system
Single-Tank Water Softening System vs Dual Tank
Water Softening System
Down-time of water softening Soft water requirement is for
24 hours or
system is known. exact down time is not known.
Capacity requirement greatly exceeds flow rate requirement
(i.e., softener needed tosatisfy capacity requirement is much
larger than the softener required to satisfy the flow rate)
Daily usage requirements fluctuate or
actual daily usage cannot be determined.
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PRINCIPLES OF REVERSE OSMOSIS
Reverse osmosis is a process for
removing dissolved mineral salts, organic molecules, and
certain other impurities from water by permitting water under
increased pressure to pass through a semi-permeable membrane.
It is called reverse osmosis as it is the reverse of the
natural osmotic process in which fluids with a low
concentration of suspended and dissolved solids pass through a
membrane into an area of higher concentration. With reverse
osmosis water treatment, water is make to pass from a state of
high dissolved solids concentration to a state of low
concentration.
Since reverse osmosis does not occur
naturally, it must be created by applying higher pressure to
the high dissolved solids water in order to force it through
the membranes. Membranes must be strong and resistant enough to
withstand the high pressures of the RO operation… from
200 to 400 psi in most applications: 1000, or even 1200psi for
sea water desalination. The pressure applied to the feed side
of the RP membrane must be higher than the natural osmotic
pressure of the water in order for the osmotic process to be
reversed. High pressure pumps are used to created the needed
pressure.
Reverse Osmosis Membranes – Several types of
membranes have been developed for RO applications. Three types are
widely used.
Thin
Film Composite
The first
type of commonly available membrane capable of high salt
rejection is the composite membrane, usually called a thin film
composite (TFC) membrane. TFC membranes are three layers of
material; a thin (0.25um) barrier coating on the surface of a
micro-porous layer of polymers, such as polyamines, polyimines,
or polyethers.
TFC membranes have high salt rejection
rates, usually operate at lower pressures that CA or HF, and
have exhibited good performance under wide ranging pH and
temperature conditions. They are not degradable by
microorganisms and hold their flux rates over long periods of
time. Like hollow fiber membranes, they do not withstand
chlorine well, so chlorine removal is needed as a pretreatment
step. Most TFC membranes are produced in a spiral wound module
configuration.
Cellulose
Acetate
Another
commonly used membrane is made of cellulose acetate (CA). These
membranes are asymmetric. This means they consist of a thin
dense salt barrier attached to a thicker micro-porous layer
manufactured in one step so it is essentially one layer.
Polyaramid
Hollow Fiber
A
third membrane used in the past and used occasionally is the
hollow fiber (HF) membrane. These membranes have been developed
in the form of bundles of thousands of tiny hollow filaments.
These hollow fibers are approximately the diameter of a human
hair in the form of a tiny tube that can take the high pressure
of RO operations. Like CA membranes, they are asymmetric. A
dense skin on the outside serves as the salt barrier to reject
mineral salts, and a porous inner layer allows the water to
pass through to service.
Polyaramid membranes normally operate at
higher flow volumes, have good temperature and pH stability,
good corrosion resistance and are not degradable by
microorganisms. Due to the tiny sixe, they are more prone to
turbidity fouling than spiral wound types. Hollow fiber
membranes have low resistance to chlorine. Pretreatment of the
water to remove chlorine is required for successful application.
All
three membranes perform essentially the same task…they
allow purified product water to pass through the membrane while
stopping the passage of dissolved and suspended matter. RO
membranes also have excellent rejection of organic matter, colloids
and turbidity (although, turbidity can foul them). The percent
rejection of each impurity varies somewhat according to the
type of impurity and the membrane. Rejection tables are
available for each membrane.
Design
Considerations – Ro units do not deliver
to service all of the water that is fed to them. During
operation, some of the incoming water is used to wash down the
membrane and only part becomes finished product water. Product
water is referred to as permeate, and waste water is referred
to as concentrate. The percent of water delivered as permeate
is called the recovery and depends on the membrane and total RO
unit design considerations.
Ro membranes are volume rated at 77 º F (25 º
C) incoming water temperature. Conversions must be made if the
incoming water temperature varies. For optimum RO unit
performance, mixing valves or heaters are often used to
maintain deed water at the rated temperature.
Pretreatment
– Pretreatment of water prior to the RO
process is almost always required. Chlorine has been mentioned,
but high hardness minerals should also be controlled by a
softener or other suitable methods. For example, hard water
scale build-up causes membrane hydrolysis and impairs RO unit
performances. Turbidity, iron and other impurities must be
controlled for optimum RO performance.
System
Engineering – RO units are often used to
provide low dissolved solids feed water to deionizers. This
extends the deionizer service cycle and lowers regeneration
frequency. Considerable costs can be saved through reduction of
regenerant chemicals. Systems engineering of water treatment
problems takes on added significance as RO and DI processes are
put into use together.
CA
membranes are usually fabricated in spiral wound module configurations
with a fabric support to provide a great deal of membrane
surface area in a small space. As water is forced against the
barrier layer, the dissolved salts are rejected and low
dissolved solids product water passes through to an inner
cylinder or tube and then to service.
Cellulose triacetate (CTA) is also used in RO
applications. It has a higher rejection of salt than regular
cellulose acetate, is more resistant to chlorine and can
operate at higher pH values (up to 8.5). Blends of cellulose
diacetate and cellulose triacetate are also used. This blend
has good resistance and salt rejection, but with higher flux
than cellulose acetate. Flux is the rate at which water is
transported through the membrane.
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Temperature Correction Factors
|
TEMPERATURE
|
CORRECTION FACTOR
|
|
º C
|
º F
|
FILMTEC
|
FLUID SYSTEMS TFCL
|
DESAL
C.A.
|
DESAL
N.F.
|
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
|
33.8
35.6
37.4
39.2
41.0
42.8
44.6
46.4
48.2
50.0
51.8
53.6
55.4
57.2
59.0
60.8
62.6
64.4
66.2
68.0
69.8
71.6
73.4
75.2
77.0
78.8
80.6
82.4
84.2
86.0
87.8
89.6
91.4
93.2
95.0
96.8
98.6
100.4
102.2
104.0
105.8
107.6
109.4
111.2
113.0
114.8
116.6
118.4
120.2
122.0
|
2.43
2.34
2.25
2.16
2.08
2.00
1.92
1.85
1.77
1.71
1.63
1.58
1.53
1.48
1.42
1.37
1.33
1.28
1.24
1.19
1.14
1.11
1.07
1.03
1.00
0.97
0.94
0.91
0.89
0.86
|
2.15
2.07
2.04
1.94
1.87
1.81
1.75
1.70
1.64
1.59
1.54
1.49
1.44
1.40
1.35
1.31
1.27
1.23
1.20
1.16
1.13
1.09
1.06
1.03
1.00
0.97
0.94
0.92
0.89
0.87
0.84
0.82
0.80
0.77
0.75
0.73
0.71
0.69
0.68
0.66
0.64
0.62
0.61
0.59
0.58
0.56
0.55
0.54
0.52
0.51
|
1.98
1.93
1.87
1.82
1.77
1.72
1.67
1.62
1.57
1.52
1.48
1.44
1.41
1.37
1.34
1.30
1.26
1.22
1.19
1.15
1.11
1.08
1.06
1.03
1.00
098
0.96
0.94
0.91
0.88
0.86
0.83
|
2.27
2.21
2.14
2.08
2.01
1.94
1.87
1.80
1.74
1.67
1.62
1.55
1.48
1.41
1.34
1.37
1.32
1.28
1.23
1.18
1.14
1.10
1.07
1.03
1.00
0.93
0.94
0.91
0.88
0.85
0.82
0.79
|
|
|
Conductivity Conversions
|
CONDUCTIVITY
(micro-mhos-cm)
|
RESISTIVITY
(ohms)
|
TOTAL DISSOLVED
SOLIDS
(ppm or mg/l)
|
|
0.056
0.059
0.063
0.067
0.072
0.077
0.084
0.091
0.100
0.111
0.125
0.143
0.167
0.200
0.250
0.333
0.500
1.000
1.110
1.250
1.430
1.670
2.000
2.500
3.330
5.000
10.00
11.10
12.50
14.30
16.70
20.00
25.00
33.30
50.0
100.0
111.0
125.0
143.0
|
18,000,000
17,000,000
16,000,000
15,000,000
14,000,000
13,000,000
12,000,000
11,000,000
10,000,000
9,000,000
8,000,000
7,000,000
6,000,000
5,000,000
4,000,000
3,000,000
2,000,000
1,000,000
900,000
800,000
700,000
600,000
500,000
400,000
300,000
200,000
100,000
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
9,000
8,000
7,000
|
0.0277
0.0294
0.0313
0.0333
0.0357
0.0384
0.0417
0.0455
0.0500
0.0556
0.0625
0.0714
0.0833
0.1000
0.1250
0.1670
0.2500
0.5000
0.5560
0.6250
0.7140
0.8330
1.0000
1.2500
1.6700
2.5000
5.0000
5.5600
6.2500
7.1400
8.3300
10.000
12.500
16.700
25.000
50.000
55.600
62.500
71.400
|
|
|
Ultraviolet Technology &
Applications
What
is Ultraviolet Light?
Close to a century ago, scientists
first identified that part of the electromagnetic spectrum
responsible for the bacterial effect of sunlight. The most
biologically disruptive frequencies causing this well-known
effect are the shorter wavelengths within ultraviolet (UV)
light known as the UV – C spectrum. This form of light
ranges from 200nm to 300nm, where a nanometer (nm) is one
billionth of a meter. Such energy can now be produced
commercially by electrical discharge devices. UV technology is
harnessed for a range of applications from disinfection to
oxidizing organics.
How is
UV Light Generated?
The UV lamp, a quartz tube similar to a
standard fluorescent bulb with electrodes at each end, is
filled with an inert gas and a minute amount of mercury. Electrical
energy, applied across the electrodes, provides the initial
discharge and means of exciting the gases present. With
relatively small amounts of energy input, a “Low
Pressure” glow is created which produces UV emissions at
185nm and 254nm. As the electrical input energy is increased
the lamp heats up rapidly; causing the internal pressure to
increase, producing the characteristic “Medium
Pressure” spectrum shown. The high output of the medium
pressure lamp is as a result of a complex combination of atomic
spectral, continuum and absorption lines characteristic of
mercury vapor.
How
Does UV Destroy Microorganisms?
High-energy
ultraviolet light will pass easily through cell walls,
cytoplasm, and nuclear membranes. Here, the photons are readily
absorbed by the cellular DNA (the reproductive material). This
UV energy causes permanent, irreparable, inactivation of the microorganism
by fusing together and forming dimmers within portions of the
DNA strands prohibiting replication. The microorganism becomes
unable to maintain metabolism or reproduce itself and
subsequently perishes. All cells, when subjected to germicidal
UV, undergo similar processes:
- Ultraviolet light penetrates the cell
wall.
- UV photons are absorbed by cellular
DNA.
- DNA is permanently altered ceasing any
capability for reproduction.
- Organisms, unable to metabolize or
reproduce, perish and become unable to cause disease or
spoilage.
OZONE
REMOVAL
Ultraviolet systems are highly effective for
destroying ozone in process water. Ozone is commonly used as a
disinfection chemical and also as an oxidant for organic
compounds. Residual ozone can cause harm to process equipment,
affect the final product, or cause health hazards. As chemicals
or heat are unwanted processes in most high purity water
treatment processes, UV is the method of choice to break down
the ozone in a simple flow-through physical process. Aquionics
medium pressure UV technology offers many advantages in
imparting the high UV doses needed to disassociate the ozone
molecules in water in a simple and compact UV chamber design.
There if often a synergistic affect in using
UV in ozonated water which accelerates the destruction of more
difficult to remove organic compounds as an advanced oxidation
process.
CHLORINE
AND CHLORAMINE REMOVAL
Chlorine
and chloramines are commonly used to provide residual
disinfection in water. Chorine will damage RO membranes and
other process equipment and can otherwise affect a product or
process. UV provides a reliable, cost-effective alternative to
activated carbon or bi-sulphite injection. These chlorine
removal process can cause microbiological problems and high
maintenance costs. UV installed before RO to remove free
chlorine will also allow the membranes operate more efficiently
by reduced biofouling and have longer runs between cleaning
cycles.
Chloramination, a more common practice used
by municipalities instead of liquid or gaseous chlorine when
organic levels in the water source are high, can cause problems
with carbon filters. Chloramines will break-through the
activated carbon at a much faster rate and must be steamed and
replaced more frequently. UV dechloramination prior to carbon
filters has been shown to extend carbon life.
These applications normally require very high
doses of UV and require UV wavelengths that are not generated
by conventional low-pressure UV lamps. Aquionics' technology
using high- intensity, broad spectrum UV has been shown to be
most effective in the removal of chlorine and combined in these
applications.
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