by Rich Grimes
Water Solutions Marketing

I have had many projects where lack of combustion/ventilation air has been the issue. It reminds me of how many installations I have seen like this. Surely more than I can remember… Lack of air on a water heater is similar to lack of air on a car or small engine. Poor combustion results in lost efficiency and more hazardous emissions. Symptoms such as sooting and constant flame failures can be indicators of air issues. Imagine a candle snuffer that does not touch the wick of the candle, but it captures all of the heat from the flame. The flame uses up all of the air inside the small candle snuffer and the flame cannot maintain combustion. Soot is produced as the fresh air is used up by the flame. Gradually, the flame is extinguished due to lack of combustion air.

 

In this article we shall discuss combustion and ventilation air requirements for gas-fired appliances. Combustion and Ventilation Air requirements are set forth in the National Fuel Gas Code and typically apply to Atmospheric or Fan-Assisted Combustion. As we discussed in previous articles regarding venting, Category IV appliances typically have a direct air intake from outdoor, negating the need for separate combustion/ventilation air louvers in the wall or door. Separate Air Intake systems for gas-fired appliances are specified by the manufacturer and must be part of the vent system approval.

 

PRINCIPLE

Gas-fired appliances require adequate Intake Air for Combustion and Ventilation. There are two methods for sizing Intake Air. The Standard method is used almost exclusively, requiring a minimum volume of 50 cubic feet per 1,000 BTU/hr. The second is the Known Air Infiltration Rate Method. This method is rarely used and requires calculations based on atmospheric or fan-assisted combustion and air change per hour.

The movement of air between two louvers allows fresh air to enter the mechanical room and be circulated. A larger, single louver can be utilized to allow enough air to enter and circulate. Each particular air intake arrangement has its own sizing based on the total BTU input of all appliances in the room and where the air is communicated from. The sizing of combustion and ventilation air is specified in the National Fuel Gas Code / NFPA54 / ANSI Z223.1 Section 9.3.

 

REQUIREMENTS

The intake air sizing is based on the total BTU input of all appliances and is determined by the following installation parameters:

 

AIR FROM OUTDOORS (TWO PERMANENT OPENINGS)

This method requires two (2) permanent openings. One opening is located within 12 inches of the top of the enclosure and the other is located within 12 inches of the bottom of the enclosure. These openings must communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors:

1) Where communicating directly with the outdoors (LOUVERS) or through VERTICAL DUCTS, EACH opening shall have 1 Square Inch per 4,000 BTU/hr, the total of all appliances.

Example: 200,000 BTU Heater = 200,000 ÷ 4,000 = 50 Square Inches Free Area per opening.

2) When communicating directly with the outdoors through HORIZONTAL DUCTS, EACH opening shall have 1 Square Inch per 2,000 BTU/hr, the total of all appliances.

Example: 200,000 BTU Heater = 200,000 ÷ 2,000 = 100 Square Inches Free Area per opening.

 

 

AIR FROM OUTDOORS (ONE PERMANENT OPENING)

This method requires one (1) permanent opening. This opening is located within 12 inches of the top of the enclosure. This opening must communicate directly, or by Vertical or Horizontal ducts, with the outdoors or spaces that freely communicate with the outdoors:

1) Where communicating directly with the outdoors (Louvers) or through Vertical or Horizontal Ducts, EACH opening shall have 1 Square Inch per 3,000 BTU/hr, the total of all appliances.

Example: 200,000 BTU Heater = 200,000 ÷ 3,000 = 66.67 Square Inches Free Area opening.

2) The minimum free area must be not less than the sum of the areas of all vent connectors in the space.

 

AIR FROM INDOORS (TWO PERMANENT OPENINGS ONLY)

This method requires two (2) permanent openings. One opening is located within 12 inches of the top of the enclosure and the other is located within 12 inches of the bottom of the enclosure. These openings must communicate directly via Louvers, with an indoor space that is adequately ventilated:

1) Where communicating directly with another interior space, ON THE SAME STORY, VIA LOUVERS, EACH opening shall have 1 Square Inch per 1,000 BTU/hr, the total of all appliances.

Example: 200,000 BTU Heater = 200,000 ÷ 1,000 = 200 Square Inches Free Area per opening.

2) Where communicating directly with another interior space, ON A DIFFERENT STORY, VIA LOUVERS, EACH opening shall have 2 Square Inch per 1,000 BTU/hr, the total of all appliances.

Example: 200,000 BTU Heater = 200,000 ÷ 500 = 400 Square Inches Free Area per opening.

 

ALTERNATIVES

There are a few options available such as engineered installations and mechanical air intake fans. Mechanical air intake systems can provide a controlled air intake. These systems employ a Power Air Fan that will force fresh air in at a given CFM. These must be interlocked with ALL appliances to insure that combustion air is being provided and proved prior to burner ignition. There are also many products that can utilize Direct Air Intake through a fan-assisted/power burner combustion process and separate air intake pipe. These heaters and boilers have become very popular because of their multiple vent and air capabilities. High Efficient appliances that utilize PVC and other plastic vent materials are great options when combustion air is limited.

 

CONSIDERATIONS

Many restaurants operate in a negative pressure within the building. This is mainly due to exhaust hoods that extract smoke and fumes from cooking. These exhaust fans are extremely strong and can cause burner operational problems. They will draw up and consume the combustion air needed for proper operation. If you open a door to the outside, air rushes into the building.

Equipment such as atmospheric stoves operate properly because they are located directly beneath the exhaust hood and all available air is drawn by them. A water heater or boiler that is located in another part of the restaurant can experience sooting, leakage of combustion products and flame failures due to this lack of air. The big problem is that leakage of combustion products equals spillage of carbon monoxide in the restaurant. The vent stack for the heater becomes an air intake pipe and air is drawn down from the rooftop. When the heater fires, the combustion exhaust spills out at the draft hood as it cannot be drawn up the vent pipe. It is very common to see atmospheric gas heaters choking in this type of installation. A smoke test at the draft hood of the heater will help indicate if flue products are exhausting properly. The test should be performed with the burner on and off and with the door open and closed. A burner that is starving for air will burn very yellow or orange in color. When the air pressure is relieved by opening a nearby door, the burner flame should be blue in color with slight yellow/orange tips.

These situations can be resolved with heaters that allow for direct air intake. Just because there was an atmospheric heater originally installed, replacement may be better suited to a higher efficient heater that allows or requires direct air intake. Restaurants are not the only buildings that can have negative pressures. The same problem can occur in a small mechanical room where an exhaust fan has been installed. This has the same effect, just in a smaller application. Unventilated closets can produce the same problems.

Louvers should also be checked for free area of square inches. Many louvers can restrict the free area and sometimes a larger size louver is required. Mesh screens should not be placed over louver openings as they will clog up and eventually create an air issue. Double-faced louvers can cut free area by one half, requiring twice as large of a surface area compared to an unrestricted, full flow louver.

 

SUMMARY

All of these are extremely hazardous installations because they put the inhabitants in direct contact with combustion exhaust containing carbon monoxide. Combustion and Ventilation Air is often overlooked and should be investigated and accounted for when installing any gas fired appliance. Combustion and Ventilation Air are crucial to a good, safe installation.

I hope that these articles are helpful to you and we look forward to seeing you in the next issue!

Thanks,

Rich Grimes

by Rob Spence (Mechanical Engineer) and Abigail Cantor (Chemical Engineer)

Introduction

This article is part of a series discussing the growth of microorganisms in plumbing systems.  As previously noted, microorganisms can grow and thrive in a plumbing system when water that enters a system is not used for a long time.   This article looks at sizing pipes and tanks in order to minimize the volume of water stored on-site and the residence time of water in the plumbing system.

Current plumbing and home designers are at odds with this desire to reduce system volume.  New homes and bathroom remodels are incorporating multiple head showers, body sprays, and large whirlpool tubs.  This drives up the plumbing system requirement with larger pipes, water heaters, water softeners, expansion tanks, and filtration units.  Many times the added capacity is only utilized a fraction of the time, which results in very long residence times.

Fixture Units

Residence time can be addressed first in design by considering “fixture units”.  The Plumbing Code assigns a fixture unit to each type of device in the plumbing system so that pipes can be properly sized with adequate flow and pressure to each fixture.  The plumbing designer must tally up all the fixture units serviced by each segment of the piping system (hot, cold, combined, branch, and mains) and size the pipes accordingly.  Therefore, as we add bathrooms, whirlpool tubs and extra shower heads, the pipe sizes must get larger.

Let’s contrast a typical home with 2 ½ baths utilizing single shower heads to a luxury home with 3 full baths and two ½ baths.  One of the luxury baths will have a rain head shower and a hand-held spray plus six body sprays, as well as a 75 gallon soaking tub.

In our example, the luxury house fixture count would require 1¼” supply line and 1” hot and cold mains with a 1” branch just to the master bath.  The shower alone could have a fixture count as high as 15.  In contrast, our standard home would only require a ¾” main.  Note that the 1¼” supply pipe in the luxury house has over six times the volume of water per linear foot than the standard ¾” supply pipe.  The Code doesn’t allow us to reduce the pipe size in these cases, but there are things we can do to reduce the load on the pipe so that the number of fixture units are lowered and the pipe sizes are calculated to be smaller.

Consider using diverting valves in shower systems rather than volume controls or separate valves on each device.  This lets the user choose only one of the multiple heads at once rather than the ability to have all functions at the same time.  Some of the pre-assembled shower towers utilize this functionality as well as low flow body sprays, so they only require ½” supply lines.  Contrast that with a luxury shower with individually mounted body sprays, which would require a 1” equalization loop going to all six locations. As you can see by utilizing a shower tower or diverting valve you only have to count one of the devices in the shower, which reduces the pipe sizes in the shower, branch circuit, and even the mains.  This choice reduces piping system volumes as well as labor for installation!

One other plumbing option to consider for reducing pipe volume is a “home run system”.  This is a design where manifold pipelines host connections to groups of fixtures instead of each fixture connection branching off from the main piping all through the building.  This type of system utilizes individual ½” or ¾” lines to each fixture or bath group.  The design will typically increase the overall linear feet of piping, but because it is smaller diameter pipe, the system volume is less.

Hot Water Tank Volume

As with considering fixture units, the Plumbing Designer must also adequately size a hot water heating system to handle all the potential flow. The Code states that the design “must provide adequate hot water for peak load”.  With traditional tank-type systems, our luxury home might need to be designed with several hundred gallons of storage.  We’ve all heard it:  “This is a high end customer and they don’t want to run out of hot water”.  So, the system is designed with multiple large tank-type heaters or a boiler system with several indirect tanks.  All of this hot water is sitting and waiting for one or two days per year when it is really required.  It makes sense to consider tankless water heaters that do not store any hot water.  It is true that in some cases, it will require two or three tankless water heaters.  But, the risk for damaging biofilm growth is greatly reduced.

Educate the home owner of the risks of over-sizing the domestic hot water package.  By utilizing the diverter valves in the shower system, we can get by in our luxury home with only two tankless water heaters.  In addition, the Plumbing Code now gives an alternate method for sizing tankless heaters.  It allows the designer to base the heater size on 65% of the peak fixture load.  Using this method, our typical home only requires one tankless heater.

One other method of reducing water heater tank volume is the use of an indirect water heater mated to a boiler system.  Typically, these systems have higher recovery rates (rates of heating and re-heating water), so many times a smaller hot water storage tank can be used than in direct heating.  For example, a standard 75 gallon gas water heater has a first hour delivery of 120 gallons per hour (GPH) compared to a 30 gallon indirect water heater that is rated at 183 GPH. In this comparison, there is an increased first hour delivery rate for indirect water heaters with a tank volume reduced by 45 gallons.

For water systems with private water sources, utilizing a constant pressure well pump will also decrease system volume.  A typical expansion tank for a standard well pump is 50 to 75 gallons.  However, that drops to 5 or 10 gallons on a constant pressure pump system.

We’ve been talking about decreasing system volume to reduce the risk biofilm growth, which is the primary goal of this article.  However, if it is determined that the system must have large hot water storage tanks, the design temperature of those tanks can be elevated to a much higher temperature (160 to 180 degrees F) to prevent biofilm growth.  This system must be fitted with an anti-scald valve to reduce the temperature to a safe level for the distribution to the house.  Indirect water heaters are a good choice for this type of system since they typically have a much lower energy loss as the water sits in the storage tank.

The Tub Dilemma

The required hot water tank volume also depends on the fill rate of bath tubs.  Large whirlpool tubs typically have tub fillers capable of 12 to15 gallons per minute (gpm).  Most designers would recommend an additional hot water storage tank at least as large as the tub volume, since no tank-type heater will keep up with 15 gpm fill rate.  Again, this requires large piping and major domestic hot water heating equipment that can lead to the growth of biofilms.

However, plumbing designers can educate homeowners about this dilemma.   If a homeowner can accept a slightly lower fill rate for the tub, one or two tankless water heaters can be used instead of a large tank-type heater with hot water storage.  In addition, the tankless heaters will maintain outlet temperature indefinitely so that there will be no drop in temperature as the tub slowly fills.  With a large tank-type water heater and additional large storage tank, a 75 gallon tub could potentially fill in 5 minutes.  With one tank-less water heater, the max fill time would be, at worst, 15 minutes.

There are a few issues that must be considered when applying a tank-less heater.  There is a phenomenon called a “Cold Water Sandwich.” That is, the first gallon or two of water is room temperature because it has been sitting in the room’s piping.  Then, the cold influent water comes in and has not had adequate time for heating, so there is about 3 to 5 seconds of cold water.  Then the properly heated water arrives.  A person can’t jump right into a shower or a bath tub and can’t turn the water on and off repeatedly.  But, a 2 to 5 gallon buffer tank can be used to solve the cold water sandwich problem.

Another issue is that there is higher pressure drop in tankless water heater units which must be considered in the plumbing design.

Water Treatment Equipment

The water softener and other water treatment equipment are also sites of large residence times.  As plumbing features of a luxury home are added, the peak flow rate increases.  This large flow rate alone given to a water treatment designer may result in very large water softening and treatment system.  However, the homeowner can describe the intent of how the luxury plumbing features will be used.  If the use of multiple luxury features is only going to occur for a short period, say 10 to 15 minutes every few weeks, consider installing a smaller softener and any other required water treatment equipment.  As long as the connections to the softener and other water treatment equipment are sized to handle that flow, the momentary surge will only result in partially softened/treated water going down stream for that short period.  Size the water treatment equipment for every day flow.

Hot Water Recirculation Lines

Hot water recirculation lines are needed in larger buildings so that hot water is immediately available throughout the building instead of having to travel from the hot water tank first.  However, hot water recirculation lines are notorious for biofilm growth because of added residence time of water and because the recirculation serves as a means to spread microbiological colonies to previously unaffected parts of the hot water system.

The “home run” plumbing system discussed in the section about “Fixture Units” can eliminate the need for a hot water recirculation line.

Summary

In summary, it is difficult to lower water residence time and water volumes in modern plumbing systems, but it can be done.

Using diverting valves, shower towers, or home run system design can decrease the number of fixture units in a plumbing design. This will result in smaller piping and decrease the size of heating and water treatment equipment.

Homeowners can be encouraged to choose tank-less water heaters and to accept lower tub fill rates to drastically reduce system volume.   Where tank-type water heaters are used, indirect heaters require less hot water storage than direct heaters.

Water softeners and other water treatment equipment can be sized for typical daily flow if peak flows are minimized by the homeowner.

Volume can be reduced further on systems with private water sources by using constant pressure well pumps.

We can’t expect plumbing designers and consumers to eliminate all the luxuries that we have grown accustom to.   But, as a plumbing community we need to be smart with our designs and educate our customers on the consequences of over-engineering.  With very small concessions, consumers can enjoy substantial energy savings as well as lower risks to health and to pipe integrity.

KEY WATER HEATING CHARTS AND FORMULAS
by Rich Grimes 

It’s 2012 already and in this issue we will try to give you plenty of information and useful charts related to water heating. I don’t receive many requests so I am glad to accommodate on such a pertinent subject. The best part is that you won’t have to read too much from me as these charts and formulas speak for themselves! So here we go…

BTU

A British Thermal Unit (BTU) is a measurement of heat energy. One BTU is the amount of heat energy required to raise one pound of water by 1ºF. Water weighs 8.33 pounds per gallon so we can calculate that one gallon of water requires 8.33 BTU to raise the temperature 1ºF.

BTU CONTENT OF FUELS

ENERGY SOURCE                        BTU PER HOUR

COAL

1 Pound                                         =       10,000 – 15,000

1 Ton                                              =       25 Million (app.)

ELECTRICITY

1 KW                                              =       3,412

OIL

1 Gallon #1 Fuel                            =       136,000

1 Gallon #2 Fuel                            =       138,500

1 Gallon #3 Fuel                            =       141,000

1 Gallon #5 Fuel                            =       148,500

1 Gallon #6 Fuel                            =       152,000

GAS

1 Pound of Butane                         =       21,300

1 Gallon of Butane                         =       102,800

1 Cubic Ft. of Butane                     =       3,280

1 Cubic Ft. of Manufactured Gas    =       530

1 Cubic Ft. of Mixed                        =       850

1 Cubic Ft. of Natural                     =       1,075

1 Cubic Ft. of Propane                   =       2,570

1 Pound of Propane                       =       21,800

1 Gallon of Propane                       =       91,000

HORSEPOWER

1 Boiler Horsepower (BHP)            =       33,475 BTU

1 Boiler Horsepower (BHP)            =       34.5 Pounds of Steam @ 212ºF

1 Boiler Horsepower (BHP)            =       9.81 KW

COOLING

1 Ton of Cooling                             =       12,000

GAS INFORMATION

NATURAL             PROPANE

Specific Gravity                                                          =       0.62                    1.52

Flammability Limits (GAS/AIR Mixture)           =       4%-14%             2.4%-9.6%

Maximum Flame Propagation (GAS/AIR Mixture) =       10%                    5%

Ignition Temperature                                                =       1200ºF                950ºF

1 Pound of Gas (1 PSI)         = 28″ Water Column (w.c.)

1 Pound of Gas (1 PSI)         = 16 Ounces (oz.)

1 Therm = 100,000 BTU

 

ELECTRICAL INFORMATION

1 Kilowatt (kW)   =       3412 BTU Per Hour

1 Kilowatt (kW)   =       1000 Watts Per Hour

1 Kilowatt Hour (kWH) will evaporate 3.5 pounds of water from and at 212ºF

 

Amperage – Single Phase (1 Ø)      =       KW x 1000                   or      WATTAGE
                                                                         VOLTAGE                               VOLTAGE

 

Amperage – Three Phase (3 Ø)      =       KW x 1000                   or      WATTAGE
                                                                      VOLTAGE x 1.732                  VOLTAGE x 1.732

 

WATER HEATING FORMULAS

 

BTU Per Hour Requirement

BTU OUTPUT        =       GPM x Temperature Rise x 8.33 Lbs/Gallon x 60 Minutes

 

BTU INPUT           =       (GPM x Temperature Rise x 8.33 Lbs/Gallon x 60 Minutes)

% Efficiency

 

Heat Transfer Efficiency

% EFFICIENCY    =       (GPH x Temperature Rise x 8.33 Lbs/Gallon)
BTU/Hr INPUT

 

Heat-Up Time

Time in Hours      =       (GPH x Temperature Rise x 8.33 Lbs/Gallon)
                                               (BTU/Hr INPUT x % Efficiency)

 

Temperature Rise

Temp. Rise (∆T)   =           (BTU/Hr INPUT x % Efficiency)   

(GPM x 60 Minutes x 8.33 Lbs/Gallon)

 

GPH Recovery

Electric                =       (kW INPUT x 3412 BTU/kW x % Efficiency)

(Temperature Rise x 8.33 Lbs/Gallon)

 

Gas                     =                (BTU/Hr INPUT x % Efficiency)       

(Temperature Rise x 8.33 Lbs/Gallon)

 

MIXED WATER FORMULA

% of Hot Water Required      =       (Mixed Water ºF – Cold Water ºF)

(Hot Water ºF – Cold Water ºF)

 

WATER INFORMATION

1 Gallon     =       8.33 Pounds

1 Gallon     =       231 Cubic Inches

1 Cubic Ft   =       7.48 Gallons

1 Cubic Ft   =       62.428 Pounds (at 39.2ºF – maximum density)

1 Cubic Ft   =       59.83 Pounds (at 212ºF – boiling point)

1 Ft of Water Column (w.c.) = .4333 PSI

 

Water expands 4.34% when heated from 40ºF to 212ºF

Water expands 8% when frozen solid

 

OPEN VESSEL

BOILING POINT @ 0 PSI      ALTITUDE

212ºF                                    0 Feet (Sea Level)

210ºF                                    1000 Feet

208ºF                                    2000 Feet

207ºF                                    3000 Feet

205ºF                                    4000 Feet

203ºF                                    5000 Feet

201ºF                                    6000 Feet

199ºF                                    7000 Feet

 

CLOSED VESSEL BOILING POINT @ PSI @ Sea Level

BOILING POINT             GAUGE PRESSURE

212ºF                                    0 PSI

240ºF                                    10 PSI

259ºF                                    20 PSI

274ºF                                    30 PSI

287ºF                                    40 PSI

298ºF                                    50 PSI

316ºF                                    70 PSI

331ºF                                    90 PSI

ONLINE RESOURCES

There are an unlimited number of online tools and calculators for every mathematical formula. The internet is full of helpful resources to get the job done quicker. Here are a few links to some useful websites:

 

WEBSITE/PROGRAM                                         WEB ADDRESS

Amtrol Expansion Tank Sizing                                   http://amtrol.com/support/sizing.html

Engineering Toolbox Calculators                      http://www.engineeringtoolbox.com/

State Water Heater Sizing (Online)                          http://www.statewaterheatersizing.com/

AO Smith Water Heater Sizing (Online)            http://www.hotwatersizing.com/

Lochinvar Water Heater Sizing (Download)     http://www.lochinvar.com/sizingguide.aspx

 

Cylinder Calculator (Storage Tanks) / Other Math Calculators http://www.calculatorfreeonline.com/calculators/geometry-solids/cylinder.php

Electrical/Mechanical/Industrial/Civil/Chemical/Aeronautical Calculators http://www.ifigure.com/engineer/electric/electric.htm

B&G System Syzer (Piping/Pressure Drop Tool Download) http://completewatersystems.com/brand/bell-gossett/selection-sizing-tools/system-syzer/

B&G Selection and Sizing Tools (Pumps, Regulators, Steam and Condensate) http://completewatersystems.com/brand/bell-gossett/selection-sizing-tools/

Taco Pump Selection Wizard (Online Pump Selector)                                        http://www.taco-hvac.com/en/wizard_pumps.html

Lawler Mixing Valve Sizing (Online – account setup) http://www.lawlervalve.com/index.php?p=page&page_id=Sizing_Program

DSIRE Database of State/Federal Renewable Energy Rebates      http://www.dsireusa.org/

ASCO Valve Online Product Selector (Valves – solenoid, pilot, pneumatic, etc.) http://www.ascovalve.com/Applications/ProductSearch/ProductSearch.aspx?ascowiz=yes

 

SUMMARY

There is a lot of other information that we could add such as Steam. It is a viable heating source and there are several factors that must be considered such as operating pressure, steam trap and condensate line sizing and so on. We will have to do a separate article on Steam in a future issue.

The charts and information above are all essential to water heating. They are proven mathematical formulas of algebra and geometry. If you input the accurate information then the results will be correct. It is also good to use the online tools and calculators. They are true time savers.

Thanks and we’ll see you in the next article!

 

Microorganisms: The effects of on-site water treatment
by Abigail Cantor, P.E.

This article is part of a series discussing the growth of microorganisms in plumbing systems.  As previously noted, many types of on-site water treatment equipment create conditions for microorganisms to grow and thrive by increasing the residence time of the water in the plumbing system with extra water storage volume, providing additional surface area for microorganisms to form biofilms on, and removing or using up any available disinfection to fight microorganisms.

The best practice in plumbing design is to provide on-site water treatment only when it is absolutely necessary to do so.  It is also important to select the appropriate treatment system, to determine a proper location for the equipment in the plumbing system, and to size the equipment so that volume and surface area are minimized.  Finally, automatic clean-in-place systems or manual cleaning protocols must be utilized to keep the equipment free of biofilms.

Determining Necessary Water Treatment

The first step in plumbing design is to determine specifically what contaminants, if any, are of concern in a building’s water source.  To do this, one must consider that there are numerous chemical compounds and types of microorganisms that can potentially contaminate drinking water.  Contaminants are identified and regulated in the United States with separate standards for municipal water systems, private water systems, and bottled water.  See Table 1.

If the building is connected to a public water system, the water has already been rigorously tested for the list of contaminants listed in Tables 2 and 3.  The results of those tests are public record, available at the regulatory agency that governs the state or territory where the building is located.  The results are also sent to each water utility customer annually in the Consumer Confidence Report.  There might be local issues to be concerned about, such as increasing concentrations of an industrial chemical in a public well.  In that case, the property owner should keep track of water utility plans to resolve the problem and attend water commission meetings, read the water utility website, or call the water quality manager.  If a building owner is not comfortable with the utility’s approach to removing the contaminant threat, then an on-site water treatment device should be used for removal.  It would be a rare and special case to need such a device.

It is possible for building plumbing systems to receive debris from municipal water distribution system piping.   Debris occurs in the distribution system when particles, like sand, settle out and when dissolved chemicals in the water, like manganese, iron, or aluminum, chemically precipitate out.  The possibility varies with the nature of the water and the water utility’s pipe cleaning and replacement program.  Debris can temporarily be entrained in the water during utility or road construction; it can happen seasonally due to water main flushing and other routine maintenance activities.  If a property owner experiences discolored water at an intolerable frequency, then on-site removal of the debris may be desired.

There is also the possibility that a building’s plumbing system leaches contaminants into the water.  Lead, copper, and iron are known to transfer from piping materials into water to varying degrees depending on characteristics of the individual water system.

If the property owner owns the water source, such as a private well, they must take the responsibilities of a water utility manager.  After complying with any state regulations on water quality for private water sources, the property owner must decide what other contaminants they might want to test for and, if significant, remove.  See Tables 2 and 3.  A common issue for private wells is high iron concentrations which can precipitate out and stain sinks and laundry.

For both private water sources and municipal water, the hardness of the water can be an issue.  Water hardness is mostly a measure of calcium and magnesium concentrations in the water.  Depending on other characteristics of the water, including temperature, the calcium and magnesium can precipitate out of the water as solid compounds.  The solids can cover heating surfaces in hot water heating systems, which in turn, will require more energy to heat the water; the buildup of solids will also reduce the life of the hot water heating tank.  For this reason, it is more economical to remove hardness from water where hardness is greater than about 120 mg/L as calcium carbonate (7 grains of hardness). Many people argue that hard water for cold domestic use should be softened; they state that hard water will clog pipes, create spots on glass shower doors, and react with soap so that it will not lather.  These are debatable arguments.  Even in locations with very high hardness (300 to 500 mg/L as calcium carbonate or 17.5 to 30 grains), cold un-softened water does not typically cause these severe problems.  Older residences in those locations only use softened water for the hot water system.  It is only recently, with modern plumbing practices, that cold water is also softened.

Determining Type of Water Treatment System

When specific contaminants have been identified in the water, then the proper contaminant removal technique can be selected.  The proper technique is the one that removes all contaminants of concern at the highest efficiency for the lowest financial and environmental costs.  Below are descriptions of common on-site treatment techniques.

Activated carbon filters

Activated carbon is carbon, typically from charcoal, that has been processed to make it very porous.  The more pores in the carbon, the higher the surface area.  The higher the surface area, the more specific contaminants can be pulled from the water to adhere to the carbon, a process called “adsorption”.

Different chemicals have different attractions to the carbon.  For example, heavier compounds have a greater attraction than lighter compounds.   This means carbon filters will not remove every type of contaminant.  In addition, the carbon can become saturated with contaminants and stop removing them.  Most importantly, just before the saturation point, the concentration of contaminants in the water flowing out of the filter begins increasing at a rapid rate.   Therefore, a carbon filter must be removed before the “breakpoint” of the least adsorptive contaminant or else the consumer will be drinking high levels of the contaminant that they intended to remove.  Filter manufacturers make assumptions as to what contaminants might typically be in water and set a common time when filters should be changed.   This may or may not be applicable in individual water systems.

Some carbon filters, such as certain ones that attach to sink faucets, are manufactured so that they combine treatment techniques within a small block of carbon.  Like other activated carbon filters, they have their limitations as to what contaminants can be treated and for how long.  In addition, the filters, themselves, can add contaminants to the water, based on compounds in the manufactured filter material.   There are research projects looking into this phenomenon.

Reverse osmosis and other membrane technologies

Reverse osmosis is a treatment technique that places a membrane barrier in the water.  The membrane is made of synthetic organic materials that do not have straight-through pores like a filter.  Instead, the pores are like a microscopic maze that can prevent many dissolved contaminants from passing through.  High pressure on the upstream side pushes the water, minus many of the contaminants, through the membrane.

There are other membrane technologies where the pores are straighter but very small.  Those technologies remove specific contaminants at lower pressures than reverse osmosis.

Membrane technologies prevent a percentage of the incoming water from going through the membrane, and instead, the water is sent down the drain to waste with the rejected contaminants.  The technique is not practical when it is too expensive to waste a percentage of the available water.  In addition, the synthetic organic membranes can dissolve in contact with some chemicals that might be in the water.  Chlorine used for disinfection is one of the chemicals and it is typically removed in a carbon filter upstream of the membrane.

Physical filters

Physical filters provide a physical barrier that can remove particles from water.  The filters can be made of sand or flossy material that will not allow particles of a certain size to pass through.

Ion exchange/water softeners

Ion exchange is a treatment process where one ion is taken out of the water and others are put into the water in its place.  An ion is an atom or molecule with either additional electrons or missing electrons; this gives the atom or molecule a negative or positive electric charge.   Water softeners are an example of an ion exchange process.  Here, calcium and magnesium, dissolved in the water as positively-charged ions, are “stuck to” negatively-charged ions.  When in contact with the ion exchange material, they are attracted and adhere to the material.  In exchange, the material releases two sodium ions for every calcium or magnesium ion; the sodium ions, then, form a union with the negatively-charged ions that were left behind in the water.  In the case of softening, the sodium concentration increases in the water.

At certain intervals, the ion exchange material must be cleaned to knock off the exchanged ions and replenish the original type of ions on the material.  In the case of water softeners, a solution of sodium chloride (brine) is used to flush out the ion exchange material.  This regeneration process creates a waste stream of chloride-laden water that is sent down the drain and out to the wastewater treatment plant.

Iron and manganese removal

Dissolved iron and manganese in the water eventually react with an oxidant like oxygen or chlorine in the water and precipitate out as a solid on pipe walls, sinks, and laundry.  To remove dissolved iron and manganese before it drops out elsewhere, an oxidant is pumped or bubbled into the water.  After a certain contact time, the iron and manganese are oxidized to a solid form and the particles are filtered out in a sand filter.

The filter must be backwashed periodically to clean the solids out and send them in a waste stream down the drain.

Sequestering

Sequestering is used to hold metals like iron and manganese in the water and prevent them from precipitating out as solids.  Traditionally, polyphosphate chemical products have been used in water systems to hold the metals in the water.  This is especially done when a small water utility or private property owner cannot afford a treatment process to remove iron and manganese.

It is now known that the use of polyphosphates carries negative side effects.  The polyphosphates not only can hold iron and manganese in the water but can also pull lead, copper, and iron from pipes and hold those metals in solution as well.  The consumer drinks any concentration of the metals being held in the water.  Polyphosphates also provide an essential nutrient, phosphorus, for the growth of microorganisms and in doing so, can aid in biofilm formation.  Finally, as the phosphorus from the polyphosphates eventually flows to waste, the wastewater treatment plants struggle with meeting stringent phosphorus discharge limits.

Disinfection

This series of articles on the growth of microorganisms and the formation of biofilms in piping systems has emphasized that disinfection of water is a main weapon against microorganisms.  With a clean piping system, it typically only takes a low dose of disinfection (0.3 to 0.5 mg/L free chlorine) to fight off intruding microorganisms and keep the piping system clean.

When on-site water treatment systems remove or use up disinfection in the incoming water, a dosing system should be added to replenish the disinfection in the water.  For owners of private water sources, continuous disinfection of the water before and after any treatment should be considered.

Some people complain about the taste of chlorine in their water.  If that is in issue, then drinking water can be left in a big pot open to the air or with cheesecloth covering it to allow the chlorine to transfer from the water into the air.  Alternatively, chlorine can be removed by a carbon filter at the drinking water faucet.  (Refer to the carbon filter discussion above.)

A more serious negative effect of disinfection is the possible formation of carcinogenic disinfection by-products.  This can occur when the water has high naturally-occurring organic carbon compounds that react with the chlorine.  If water is received from a municipal water system, disinfection by-products are tracked and minimized by regulation (Table 2); the property owner should re-chlorinate water within the concentration boundaries of the municipal utility.  For private water sources, the owner should become familiar with the disinfection by-product forming potential in the water and chlorinate accordingly.

Determining the Location of the Water Treatment System

Treatment systems located at the point in the plumbing where the water enters the building is called a point-of-entry water system.  Treatment systems located at the drinking water faucet are called point-of-use systems. The location of on-site water treatment in a building’s plumbing system is a critical design decision.

Point-of-entry systems treat the complete water flow to the building and are subsequently larger in size than point-of-use systems.  This creates a greater possibility of biofilm formation in the treatment equipment from increased surface area and retention of water.  It also increases the volume of water needed to clean and maintain the treatment system.  Many point-of-entry systems remove or use up incoming disinfection and so all of the piping downstream of the treatment system is not protected from the growth of microorganisms unless a disinfection dosing system is added.

Although smaller with little or no waste streams, point-of-use treatment systems must be installed for every drinking water faucet, while point-of-entry systems are installed at one location only.

Water treatment equipment for specific needs, such as water softeners for hot water, should be located as close to the specific need as possible.  Water softeners are typically located in a mechanical room adjacent to the water heating system.

Sizing Water Treatment Equipment

The goal of proper modern plumbing design should be to minimize volume of water retained and surface area of the treatment equipment.  The larger the size of the water treatment equipment, the more volume of water is retained on-site and the more surface area is available for biofilm formation.    As already discussed, one way to minimize volume is to eliminate treatment equipment unless absolutely necessary.  In addition, the volume of water to be treated should be carefully considered.  Divide the estimated total water use into: water for drinking/cooking, water for cleaning, and water for any significant purpose such as filling large bathtubs.  Design separate pipelines and treatment strategies for each purpose.

Cleaning Water Treatment Equipment

Various types of water treatment systems have cleaning cycles.  Sand filters must be backwashed to remove trapped solids.  Ion exchange material must be backwashed to remove solids and must be regenerated to replace ions.  Water treatment of this type has automatic clean-in-place cycles.  The cleaning water can be chlorinated to disinfect and fight developing biofilms routinely.  It is critical to work with the equipment manufacturer in setting up a cleaning water disinfection system; chlorine in too high a dose can destroy the treatment material.

Filters that require replacement of filter cartridges should be changed before or at the time recommended by the manufacturer to prevent breakthrough of contaminants and the development of biofilms.

Summary

This article continues the series warning against the growth of microorganisms and the formation of biofilms in plumbing systems.  On-site water treatment systems can contribute to the growth of microorganisms by increasing  the retention time of water, increasing the surface area where biofilms can form, and by removing or using up disinfection in the water.

The first step in plumbing system design is to determine which contaminants in the water are essential to remove on-site.  In many buildings that receive municipal water, additional water treatment is not necessary.  There is a greater need for on-site water treatment when the building is served by a private water source where the property owner must manage their own personal water utility.  There are also special needs for water treatment such as the need to soften hard water before it enters a hot water heating system.

After it is determined what contaminants must be removed, the best removal system must be selected.  Every treatment system has advantages and disadvantages and has specific removal efficiencies for each individual contaminant.   The sizing of the water treatment equipment and its location in the plumbing system are also critical design choices affecting the growth of microorganisms.

Finally, all water treatment equipment must be cleaned and disinfected or filter cartridges replaced routinely to clean out and prevent the formation of biofilms.

Maintaining a high water quality, including the elimination of microbiological growth, is a very delicate balancing act that should be given the highest priority when designing a plumbing system.